JP2011162713A - White biaxially oriented polylactic acid film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a white biaxially oriented polylactic acid film having high heat resistance, good dimensional stability during heating, excellent mechanical properties, and excellent printability. <P>SOLUTION: The white biaxially oriented polylactic acid film includes a resin composition containing a polylactic acid comprising a poly L-lactic acid component and a poly D-lactic acid component, and has a crystal melting peak in a specific temperature range and a specific stereocomplex crystallinity. The L value and apparent specific gravity of the film are each in a specific numerical value range. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a white biaxially stretched polylactic acid film. More specifically, the present invention relates to a white biaxially stretched polylactic acid film that is suitably used for packaging, labeling, and the like.

  In recent years, non-petroleum resins have been developed from the viewpoint of global environmental conservation and concerns about oil depletion. Among them, polylactic acid can be melt-molded and can be produced economically by fermentation using biomass as a raw material and using microorganisms, and is expected to be used as industrial materials such as packaging materials.

However, when conventional polylactic acid (poly L-lactic acid or poly D-lactic acid) is used, the heat resistance is low and the heat shrinkage rate is large. (For example, Patent Documents 1 and 2). In addition, conventional polylactic acid has low mechanical properties, which is also presumed to be a cause of the generation of wrinkles and curls.
From these problems, there has been a demand for a white polylactic acid film that is excellent in heat resistance, thermal dimensional stability, mechanical properties, and printability in order to be suitably used as a packaging material, for example.

JP-A-9-208817 JP 2001-49004 A

  An object of the present invention is to provide a white biaxially stretched polylactic acid film having high heat resistance, good dimensional stability during heating, excellent mechanical properties, and excellent printability.

  The present inventors comprise a resin composition containing polylactic acid composed of a poly L-lactic acid component and a poly D-lactic acid component, having a crystal melting peak in a specific temperature range, and having a specific stereocomplex crystallinity. It was a white biaxially stretched polylactic acid film having (S), and found that the above problems were achieved by setting the L value and the apparent specific gravity in a specific numerical range, and the present invention was achieved.

That is, the present invention
(1) It consists of a resin composition containing polylactic acid (component A) consisting of a poly L-lactic acid component and a poly D-lactic acid component, and has a crystal melting peak at 190 ° C. or higher by differential scanning calorimetry (DSC) measurement. And a white biaxially stretched polylactic acid film having a stereocomplex crystallinity (S) defined by the following formula (i) of 90% or more,
L value calculated | required with a color difference meter is 85 or more,
It is a white biaxially stretched polylactic acid film having an apparent specific gravity exceeding 1.30 g / cm ³ .
S (%) = [ΔHms / (ΔHmh + ΔHms)] × 100 (i)
(However, ΔHms represents the crystal melting enthalpy (J / g) of the stereocomplex phase polylactic acid. ΔHmh represents the crystal melting enthalpy (J / g) of the homophase polylactic acid.)

Furthermore, the present invention provides
(2) The heat shrinkage in the vertical and horizontal directions when treated at 100 ° C. for 1 hour is 3% or less,
(3) containing a stereogenic accelerator and / or a block forming agent,
(4) The stereogenic accelerator is a metal phosphate, and the block forming agent is at least one group selected from the group consisting of an epoxy group, an oxazoline group, an oxazine group, an isocyanate group, a ketene group, and a carbodiimide group. A compound having at least one in the molecule;
(5) containing 3% by mass or more and 45% by mass or less of particles having an average particle size of 0.1 μm or more and 5 μm or less,
(6) The specific gravity of the particles is 2 or more,
(7) The refractive index of the particles is 1.5 or more. (8) The average of the longitudinal breaking strength and the transverse breaking strength is 100 MPa or more, and the longitudinal breaking strength and the transverse breaking strength are The difference is 50 MPa or less,
Of these, by providing at least one of the embodiments, a more excellent white biaxially stretched polylactic acid film can be provided.
The present invention also provides
(9) The mode used for packaging is included.

  According to the present invention, a white biaxially stretched polylactic acid film having a stereocomplex structure composed of a resin composition containing polylactic acid (A component) composed of a poly L-lactic acid component and a poly D-lactic acid component is used. It is possible to provide a white biaxially stretched polylactic acid film having high properties, good dimensional stability during heating, excellent mechanical properties, and excellent printability. Such a white biaxially stretched polylactic acid film can be suitably used for packaging, labeling and the like.

  The present invention will be specifically described below. In the present invention, the machine axis direction in which the film is formed may be referred to as a longitudinal direction, a longitudinal direction, or MD. In addition, a direction perpendicular to the vertical direction may be referred to as a horizontal direction, a width direction, or TD.

  The white biaxially stretched polylactic acid film of the present invention is obtained by molding using a resin composition containing, as an essential component, polylactic acid (component A) composed of poly L-lactic acid and poly D-lactic acid. . The white biaxially stretched polylactic acid film of the present invention has a crystal melting peak at 190 ° C. or higher as determined by differential scanning calorimetry (DSC). The crystal melting peak appearing at 190 ° C. or higher is a crystal melting peak of a stereocomplex phase (hereinafter sometimes abbreviated as a complex phase) polylactic acid.

<Polylactic acid (component A)>
Polylactic acid (component A) includes stereocomplex polylactic acid formed from poly L-lactic acid and poly D-lactic acid. Poly L-lactic acid and poly D-lactic acid are substantially composed of L-lactic acid units or D-lactic acid units represented by the following formula (1).

  “Substantially” means that the component preferably accounts for 75 mol% or more, more preferably 90 mol% or more, and still more preferably 95 mol% or more based on the total components.

  The content of L-lactic acid units in the poly L-lactic acid is preferably 90 to 100 mol%, more preferably 95 to 100 mol%, still more preferably 97.5 to 100 mol%. In order to realize a high melting point, it is 99 to 100 mol%. Examples of other units include D-lactic acid units and units other than lactic acid. The content of other units is preferably 0 to 10 mol%, more preferably 0 to 5 mol%, still more preferably 0 to 2 mol%.

  The content of D-lactic acid units in the poly-D-lactic acid is preferably 90 to 100 mol%, more preferably 95 to 100 mol%, still more preferably 97.5 to 100 mol%. In order to realize a high melting point, it is 99 to 100 mol%. Examples of other units include L-lactic acid units and units other than lactic acid. The content of other units is preferably 0 to 10 mol%, more preferably 0 to 5 mol%, still more preferably 0 to 2 mol%.

  As units other than lactic acid, units derived from dicarboxylic acids, polyhydric alcohols, hydroxycarboxylic acids, lactones and the like having functional groups capable of forming two or more ester bonds, and various polyesters, various polyethers composed of these various components, Examples are derived from various polycarbonates and the like.

  Examples of the dicarboxylic acid include succinic acid, adipic acid, azelaic acid, sebacic acid, terephthalic acid, and isophthalic acid. Examples of the polyhydric alcohol include aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, octanediol, glycerin, sorbitan, neopentyl glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and polypropylene glycol. Alternatively, aromatic polyhydric alcohols such as bisphenol and those obtained by adding ethylene oxide to these can be used. Examples of the hydroxycarboxylic acid include glycolic acid, hydroxybutyric acid, p-oxybenzoic acid and the like. Examples of the lactone include glycolide, ε-caprolactone, β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone, pivalolactone, and δ-valerolactone.

  The weight average molecular weight (Mw) of poly L-lactic acid and poly D-lactic acid is preferably 100,000 to 500,000, more preferably 110,000 to 350,000, and more preferably in order to make the mechanical properties and moldability of the resin composition compatible. Preferably it is the range of 120,000-250,000.

  Poly L-lactic acid and poly D-lactic acid can be produced by a conventionally known method. For example, L- or D-lactide can be heated in the presence of a metal-containing catalyst and produced by ring-opening polymerization. In addition, after crystallizing a low molecular weight polylactic acid containing a metal-containing catalyst, it is heated under reduced pressure or pressure, in the presence or absence of an inert gas stream. It can also be produced by solid phase polymerization. Further, it can be produced by a direct polymerization method in which lactic acid is subjected to dehydration condensation in the presence / absence of an organic solvent.

  The polymerization reaction can be carried out in a conventionally known reaction vessel. For example, a vertical reactor or a horizontal reactor equipped with a stirring blade for high viscosity, such as a helical ribbon blade, can be used alone or in parallel. Moreover, any of a batch type, a continuous type, a semibatch type may be sufficient, and these may be combined.

  Alcohol may be used as a polymerization initiator. Such alcohol is preferably non-volatile without inhibiting the polymerization of polylactic acid. For example, decanol, dodecanol, tetradecanol, hexadecanol, octadecanol and the like can be suitably used.

  In the solid phase polymerization method, polylactic acid having a relatively low molecular weight (approximately 15 to 203) obtained by the above-described ring-opening polymerization method or direct polymerization method of lactic acid is used as a prepolymer. The prepolymer is preferably crystallized in advance in the temperature range of the glass transition temperature or higher and lower than the melting point from the viewpoint of preventing resin pellet fusion. The crystallized prepolymer is filled in a fixed vertical or horizontal reaction vessel, or a reaction vessel (such as a rotary kiln) in which the vessel itself rotates like a tumbler or kiln, and is above the glass transition temperature of the prepolymer and below the melting point. Is heated to a temperature range of. There is no problem even if the polymerization temperature is raised stepwise as the polymerization proceeds. In addition, for the purpose of efficiently removing water generated during solid phase polymerization, a method of reducing the pressure inside the reaction vessels or circulating a heated inert gas stream is also preferably used.

The metal-containing catalyst used in the polymerization of polylactic acid is deactivated with a conventionally known deactivator prior to use, thereby improving the stability of polylactic acid (component A) and resin composition against heat and moisture. This is preferable because it is possible.
Examples of such a deactivator include an organic ligand having a group of chelate ligands having an imino group and capable of coordinating with a polymerized metal catalyst.

  Further, dihydridooxoline (I) acid, dihydridotetraoxodiphosphorus (II, II) acid, hydridotrioxoline (III) acid, dihydridopentaoxodiphosphoric acid (III), hydridopentaoxodi (II, IV) ) Acid, dodecaoxohexaphosphoric acid (III), hydridooctaoxotriphosphoric acid (III, IV, IV) acid, octaoxotriphosphoric acid (IV, III, IV) acid, hydridohexaoxodiphosphoric acid (III, V) acid, hexaoxo Low oxidation number phosphoric acid having an acid number of 5 or less, such as diphosphorus (IV) acid, decaoxotetraphosphoric (IV) acid, hendecaoxotetraphosphoric (IV) acid, and eneoxooxophosphorus (V, IV, IV) acid .

Further, orthophosphoric acid represented by the formula xH ₂ O · yP ₂ O ₅ , x / y = 3, 2> x / y> 1, and diphosphoric acid, triphosphoric acid, tetraphosphoric acid, five Examples thereof include polyphosphoric acid called phosphoric acid and a mixture thereof.

  Further, metaphosphoric acid represented by x / y = 1, in particular, trimetaphosphoric acid, tetrametaphosphoric acid, 1> x / y> 0, and ultralin having a network structure in which a part of the phosphorus pentoxide structure is left. Acid (these may be collectively referred to as metaphosphoric acid compounds). Moreover, acidic salts of these acids, monovalent and polyhydric alcohols, partial esters of polyalkylene glycols, complete esters, phosphono-substituted lower aliphatic carboxylic acid derivatives and the like can be mentioned.

From the viewpoint of catalyst deactivation ability, orthophosphoric acid represented by the formula xH ₂ O · yP ₂ O ₅ and x / y = 3 is preferred. Moreover, 2> x / y> 1, and polyphosphoric acid referred to as diphosphoric acid, triphosphoric acid, tetraphosphoric acid, pentaphosphoric acid and the like, and a mixture thereof are preferable from the degree of condensation. Further, metaphosphoric acid represented by x / y = 1, particularly trimetaphosphoric acid and tetrametaphosphoric acid are preferable. Ultraphosphoric acid represented by 1> x / y> 0 and having a network structure in which a part of the phosphorus pentoxide structure is left (these may be collectively referred to as a metaphosphoric acid compound) is preferable. In addition, acidic salts of these acids, monovalent and polyhydric alcohols, partial ester phosphorooxo acids of polyalkylene glycols, acidic esters thereof, and phosphono-substituted lower aliphatic carboxylic acid derivatives are preferably used.

  Metaphosphoric acid compounds include cyclic metaphosphoric acid condensed with about 3 to 200 phosphoric acid units, ultra-regional metaphosphoric acid having a three-dimensional network structure, or their (alkal metal salt, alkaline earth metal salt, onium salt). Include. Of these, cyclic sodium metaphosphate, ultra-region sodium metaphosphate, phosphono-substituted lower aliphatic carboxylic acid derivative dihexylphosphonoethyl acetate (hereinafter sometimes abbreviated as DHPA) and the like are preferably used.

  The mixing ratio (mass ratio) of poly L-lactic acid and poly D-lactic acid in polylactic acid (component A) is 90:10 to 10:90. In order to improve the stereocomplex crystallinity (S) of polylactic acid (component A) and increase the crystal melting temperature of the complex phase polylactic acid, the mass ratio is preferably 75:25 to 25:75, more preferably. Is in the range of 60:40 to 40:60, and a range as close to 50:50 as possible is preferably selected.

(Weight average molecular weight (Mw))
The weight average molecular weight (Mw) of polylactic acid (component A) is preferably selected in the range of 100,000 to 500,000 from the viewpoint of achieving both moldability and physical properties of the resin composition. The range of 100,000 to 300,000, more preferably 110,000 to 250,000 is more preferably selected. The weight average molecular weight (Mw) is a weight average molecular weight value in terms of standard polystyrene as measured by gel permeation chromatography (GPC) using chloroform as an eluent.

(Stereo Complex Crystallinity (S))
Furthermore, the polylactic acid (component A) used in the present invention preferably has a stereocomplex crystallinity (S) defined by the following formula (i) of 90% or more from the crystal melting peak intensity in DSC measurement. That is, the polylactic acid (component A) preferably has a highly formed stereocomplex phase.
S (%) = [ΔHms / (ΔHmh + ΔHms)] × 100 (i)
In the formula, ΔHms represents the crystal melting enthalpy (J / g) of the stereocomplex phase polylactic acid. ΔHmh represents the crystal melting enthalpy (J / g) of homophase polylactic acid. The crystal melting peak appearing at 190 ° C. or higher in DSC measurement is the crystal melting peak attributed to the melting of the stereocomplex phase polylactic acid, and the crystal melting peak appearing below 190 ° C. is attributed to the melting of the homophase polylactic acid. It is a crystal melting peak. The stereocomplex crystallinity (S) is a parameter indicating the ratio of stereocomplex polylactic acid crystals that are finally produced in the heat treatment process.

  When the polylactic acid (component A) has such a range of stereocomplex crystallinity (S), it becomes easy to achieve the stereocomplex crystallinity (S) of the film defined by the present invention.

(Crystal melting peak)
Polylactic acid (component A) preferably has a crystal melting peak in the range of 190 to 250 ° C. Here, it means that the peak of the crystal melting peak is preferably in the range of 190 to 250 ° C. In addition, the temperature at the top of the crystal melting peak may be referred to as the crystal melting temperature. Such a crystal melting peak is a crystal melting peak attributed to melting of the stereocomplex phase polylactic acid. More preferably, it is an embodiment having a crystal melting peak in the range of 200 to 220 ° C. When the crystal melting peak is in the above numerical range, the heat resistance is excellent. The crystal melting enthalpy is preferably 20 J / g or more, more preferably 30 J / g or more.

(Carboxyl group concentration)
The carboxyl group concentration of polylactic acid (component A) is preferably 10 eq / ton or less, more preferably 2 eq / ton or less, and even more preferably 1 eq / ton or less. When the carboxyl group concentration is within this range, the polylactic acid (component A) and the resin composition can have good physical properties such as melt stability and moist heat resistance. In order to reduce the carboxyl group concentration of polylactic acid (component A) to 10 eq / ton or less, a known method for reducing the carboxyl end group concentration in the polyester composition can be suitably applied. Specifically, a method of adding a terminal blocking agent such as a moist heat resistance improving agent or a method of esterifying or amidating with an alcohol or an amine without adding a terminal blocking agent can be employed.

  As the wet heat resistance improver, a carboxyl group-capping agent having a specific functional group described later can be suitably applied. Among them, a carbodiimide compound whose specific functional group is a carbodiimide group can effectively seal a carboxyl group, and is preferably selected from the viewpoints of polylactic acid, the hue of the resin composition of the present invention, the formation of a complex phase, and moisture and heat resistance. Is done.

(Lactide content)
The lactide content of polylactic acid (component A) is preferably in the range of 0 to 1000 ppm, more preferably 0 to 500 ppm, still more preferably 0 to 200 ppm, and particularly preferably 0 to 100 ppm. When the lactide content is within this range, it is possible to suppress the generation of causal substances such as equipment contamination in the film-forming process and surface defects of the film.

  In order to reduce the lactide content to such a range, a conventionally known lactide reduction treatment method is used alone at any stage from the polymerization of poly L-lactic acid and poly D-lactic acid to the end of production of polylactic acid (component A). It is possible to achieve this by implementing in combination with these.

(Manufacture of polylactic acid (component A))
Polylactic acid (component A) can be produced by coexisting and contacting poly L-lactic acid and poly D-lactic acid at a predetermined mass ratio.
Contacting can be carried out in the presence of a solvent. The solvent is not particularly limited as long as it dissolves poly L-lactic acid and poly D-lactic acid. For example, chloroform, methylene chloride, dichloroethane, tetrachloroethane, phenol, tetrahydrofuran, N-methylpyrrolidone, N, N-dimethylformamide, butyrolactone, trioxane, hexafluoroisopropanol or the like alone or in combination of two or more are preferred.

  Moreover, the said contact can be performed in absence of a solvent. That is, a method of melting and kneading after mixing a predetermined amount of poly L-lactic acid and poly D-lactic acid, a method of adding and kneading one of them after melting one of them can be employed. In the present invention, it is preferable to obtain polylactic acid (component A) by such melt kneading from the viewpoint that polylactic acid (component A) can be obtained efficiently.

  The melt kneading temperature is preferably 230 to 300 ° C., more preferably 240 to 280 ° C., and still more preferably 245 to 275 ° C., from the viewpoint of improving the stability at the time of melting polylactic acid and the stereocomplex crystallinity (S). Range is selected.

  The stereocomplex crystallinity (S) of polylactic acid (component A) is increased to 80% or more by melt kneading within the above-mentioned mixing ratio of poly L-lactic acid and poly D-lactic acid and in the above melt kneading temperature range. It becomes easy.

  Alternatively, the contact can be made by chemical bonding. For example, a block polymer polylactic acid in which a poly L-lactic acid segment and a poly D-lactic acid segment are bonded can easily form a complex phase, and such stereoblock polylactic acid can also be suitably used in the present invention.

  Such block polymers include, for example, a method of producing by sequential ring-opening polymerization, a method of polymerizing poly (L-lactic acid) and poly (D-lactic acid), and then binding them with a chain exchange reaction or a chain extender, A block copolymer having the above-mentioned basic constitution such as a method of polymerizing L-lactic acid and poly-D-lactic acid, blending and then solid-phase polymerizing to chain extension, a method of producing from racemic lactide using a stereoselective ring-opening polymerization catalyst, etc. Any polymer can be used regardless of the production method, but a high-melting stereoblock polymer obtained by sequential ring-opening polymerization or a polymer obtained by a solid-phase polymerization method can be used because of ease of production. More preferred.

  In the polylactic acid (component A) used in the present invention, it is preferable to add a specific additive in order to stably and highly advance the formation of a complex phase within a range not departing from the spirit of the present invention. By adding such an additive, the temperature for stereo-ization can be lowered, that is, the melt kneading temperature and the melt extrusion temperature can be lowered.

(I) For example, a method of adding a phosphoric acid metal salt represented by the following formula (2) or (3) as a stereogenic accelerator is mentioned.

In formula (2), R ₁₁ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ₁₂ and R ₁₃ each independently represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, M ₁ represents an alkali metal atom, an alkaline earth metal atom, a zinc atom or an aluminum atom, p represents 1 or 2, and q represents 0 when M ₁ is an alkali metal atom, an alkaline earth metal atom or a zinc atom. Represents an aluminum atom, 1 or 2.

In formula (3), R ₁₄ , R ₁₅ and R ₁₆ each independently represent a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and M ₂ represents an alkali metal atom, an alkaline earth metal atom, a zinc atom or aluminum. P represents 1 or 2, q represents 0 when M ₂ is an alkali metal atom, alkaline earth metal atom, or zinc atom, and 1 or 2 when M ₂ is an aluminum atom.

M ₁ and M ₂ of the phosphoric acid metal salt represented by the formula (2) or (3) are preferably Na, K, Al, Mg, Ca, Li, and in particular, K, Na, Al, Li, Li and Al can be most preferably used.

(II) In addition, at least one group selected from the group consisting of an epoxy group, an oxazoline group, an oxazine group, an isocyanate group, a ketene group, and a carbodiimide group (hereinafter sometimes referred to as a specific functional group) in the molecule. The method of adding the compound which has at least 1 as a block formation agent is mentioned.

  The content of the metal phosphate is preferably 10 ppm to 2% by mass, more preferably 50 ppm to 0.5% by mass, and still more preferably 100 ppm to 0.3% by mass with respect to polylactic acid (component A). . When the amount is too small, the effect of improving the stereocomplex crystallinity (S) is small, and when the amount is too large, the resin itself is deteriorated.

  Furthermore, if desired, a crystallization nucleating agent can be used in combination so as to enhance the action of the metal phosphate within the scope not departing from the gist of the present invention. As the crystallization nucleating agent, calcium silicate, talc, kaolinite, and montmorillonite are preferable. The content of the crystallization nucleating agent that strengthens the action of the metal phosphate is preferably 0.05 to 5 parts by mass, more preferably 0.06 to 2 parts by mass, per 100 parts by mass of polylactic acid (component A). More preferably, it is the range of 0.06-1 mass part.

  In the present invention, the block forming agent reacts with the molecular end of polylactic acid (component A) to partially link the poly L-lactic acid unit and the poly D-lactic acid unit to form a blocked polylactic acid. Promotes the formation of a stereocomplex phase. What is known as a carboxyl group sealing agent for polyester can be used as the block forming agent. Of these, a carbodiimide compound is preferred because of its influence on the color tone, thermal decomposability, hydrolysis resistance and the like of polylactic acid and the resin composition of the present invention. The amount of the block forming agent used is preferably 0.001 to 5 parts by mass, more preferably 0.01 to 3 parts by mass per 100 parts by mass of polylactic acid (component A). If it is applied in a large amount exceeding this range, the resulting resin hue is undesirably increased, or the concern of plasticization increases. If the amount is less than 0.001 part by mass, the effect is hardly recognized and the industrial significance is small.

  Although the above methods (I) and (II) can be applied alone, a method of applying them in combination is preferable because the formation of a complex phase of polylactic acid (component A) can be more effectively promoted.

  In the present invention, the polylactic acid (component A) preferably contains a compound having a specific functional group serving both as a block forming agent and a heat-and-moisture resistance improver. A carbodiimide compound is preferable as such a compound. The amount of the carbodiimide compound is preferably in the range of 0.001 to 5 parts by mass per 100 parts by mass of polylactic acid (component A). When the amount is less than 0.001 part by mass, it is unsatisfactory to exhibit its function as a block forming agent and a carboxyl group sealing agent. Moreover, if it is applied in a large amount beyond this range, it is not preferable because there is a greater concern that the resin hue will deteriorate or plasticize due to undesirable side reactions such as decomposition of the agent.

  In the present invention, a carbodiimide compound is selected as the main component as the compound having a specific functional group, and other compounds are preferably selected in order to complement and enhance the action of the carbodiimide compound.

  Examples of the compound having a specific functional group applicable in the present invention include compounds such as the following carbodiimide compounds, epoxy compounds, oxazoline compounds, oxazine compounds, and isocyanate compounds. Examples of the carbodiimide compounds include dicyclohexylcarbodiimide and diisopropylcarbodiimide. , Diisobutylcarbodiimide, dioctylcarbodiimide, octyldecylcarbodiimide, di-t-butylcarbodiimide, dibenzylcarbodiimide, diphenylcarbodiimide, N-octadecyl-N′-phenylcarbodiimide, N-benzyl-N′-phenylcarbodiimide, N-benzyl-N '-Tolylcarbodiimide, di-o-toluylcarbodiimide, di-p-toluylcarbodiimide, bis (p-aminopheny ) Carbodiimide, bis (p-chlorophenyl) carbodiimide, bis (o-chlorophenyl) carbodiimide, bis (o-ethylphenyl) carbodiimide, bis (p-ethylphenyl) carbodiimidebis (o-isopropylphenyl) carbodiimide, bis (p-isopropyl) Phenyl) carbodiimide, bis (o-isobutylphenyl) carbodiimide, bis (p-isobutylphenyl) carbodiimide, bis (2,5-dichlorophenyl) carbodiimide, bis (2,6-dimethylphenyl) carbodiimide, bis (2,6-diethyl) Phenyl) carbodiimide, bis (2-ethyl-6-isopropylphenyl) carbodiimide, bis (2-butyl-6-isopropylphenyl) carbodiimide, bis (2,6-diisopropylphenol) Nyl) carbodiimide, bis (2,6-di-t-butylphenyl) carbodiimide, bis (2,4,6-trimethylphenyl) carbodiimide, bis (2,4,6-triisopropylphenyl) carbodiimide, bis (2, 4,6-tributylphenyl) carbodiimide, di-β-naphthylcarbosiimide, N-tolyl-N′-cyclohexylcarbosiimide, N-tolyl-N′-phenylcarbosiimide, p-phenylenebis (o-toluylcarbodiimide) , P-phenylene bis (cyclohexyl carbodiimide, p-phenylene bis (p-chlorophenyl carbodiimide), hexamethylene bis (cyclohexyl carbodiimide), ethylene bis (phenyl carbodiimide), ethylene bis (cyclohexyl carbodiimide), etc. Or a polycarbodiimide compound is illustrated. Of these, dicyclohexylcarbodiimide and bis (2,6-diisopropylphenyl) carbodiimide can be preferably used from the viewpoints of reactivity, stability, and industrial availability.

  Further, a commercially available polycarbodiimide compound as the above polycarbodiimide compound can be suitably used without the need to synthesize, and as such a commercially available polycarbodiimide compound, for example, “Carbodilite (registered trademark)” commercially available from Nisshinbo Co., Ltd. "Carbodilite (registered trademark)" LA-1, or HMV-8CA sold under the trade name "."

  As the epoxy compound that can be used in the present invention, a glycidyl ether compound, a glycidyl ester compound, a glycidyl amine compound, a glycidyl imide compound, a glycidyl amide compound, and an alicyclic epoxy compound can be preferably used. By blending such an agent, a polylactic acid resin composition and a molded product excellent in mechanical properties, moldability, heat resistance, and durability can be obtained.

  Examples of glycidyl ether compounds include, for example, stearyl glycidyl ether, phenyl glycidyl ether, ethylene oxide lauryl alcohol glycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentylene glycol diglycidyl ether, Bisphenol A obtained by condensation reaction of bisphenols such as polytetramethylene glycol diglycidyl ether, glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether and other bis (4-hydroxyphenyl) methane with epichlorohydrin Diglycidyl ether type epoxy resin, etc. Can be mentioned, among others bisphenol A diglycidyl ether type epoxy resin is preferable.

  Examples of glycidyl ester compounds include glycidyl benzoate, glycidyl stearate, persic acid glycidyl ester, terephthalic acid diglycidyl ester, phthalic acid diglycidyl ester, cyclohexanedicarboxylic acid diglycidyl ester, adipic acid diglycidyl ester, and succinic acid. Examples include acid diglycidyl ester, dodecanedioic acid diglycidyl ester, pyromellitic acid tetraglycidyl ester, and the like. Among them, benzoic acid glycidyl ester and versatic acid glycidyl ester are preferable.

  Examples of the glycidylamine compound include tetraglycidylamine diphenylmethane, triglycidyl-p-aminophenol, diglycidylaniline, diglycidyltoluidine, tetraglycidylmetaxylenediamine, triglycidyl isocyanurate, and the like.

  As glycidyl imide and glycidyl amide compounds, N-glycidyl phthalimide, N-glycidyl-4,5-dimethyl phthalimide, N-glycidyl-3,6-dimethyl phthalimide, N-glycidyl succinimide, N-glycidyl-1,2,3 , 4-tetrahydrophthalimide, N-glycidyl maleimide, N-glycidyl benzamide, N-glycidyl stearyl amide and the like. Of these, N-glycidylphthalimide is preferable.

  Examples of the alicyclic epoxy compound include 3,4-epoxycyclohexyl-3,4-cyclohexylcarboxylate, bis (3,4-epoxycyclohexylmethyl) adipate, vinylcyclohexene diepoxide, N-methyl-4,5-epoxycyclohexane. -1,2-dicarboxylic imide, N-phenyl-4,5-epoxycyclohexane-1,2-dicarboxylic imide and the like.

  As other epoxy compounds, epoxy-modified fatty acid glycerides such as epoxidized soybean oil, epoxidized linseed oil, and epoxidized whale oil, phenol novolac type epoxy resins, cresol novolac type epoxy resins and the like can be used.

  Examples of the oxazoline compound that can be used as a carboxyl group blocking agent used in the present invention include 2-methoxy-2-oxazoline, 2-butoxy-2-oxazoline, 2-stearyloxy-2-oxazoline, 2-cyclohexyloxy-2- Oxazoline, 2-allyloxy-2-oxazoline, 2-benzyloxy-2-oxazoline, 2-p-phenylphenoxy-2-oxazoline, 2-methyl-2-oxazoline, 2-cyclohexyl-2-oxazoline, 2-methallyl- 2-oxazoline, 2-crotyl-2-oxazoline, 2-phenyl-2-oxazoline, 2-o-ethylphenyl-2-oxazoline, 2-o-propylphenyl-2-oxazoline, 2-p-phenylphenyl-2 -Oxazoline, 2,2'-bis (2 Oxazoline), 2,2'-bis (4-methyl-2-oxazoline) 2,2'-bis (4-butyl-2-oxazoline), 2,2'-m-phenylenebis (2-oxazoline), 2 , 2′-p-phenylenebis (4-methyl-2-oxazoline), 2,2′-p-phenylenebis (4,4′-methyl-2-oxazoline), 2,2′-ethylenebis (2- Oxazoline), 2,2′-tetramethylenebis (2-oxazoline), 2,2′-hexamethylenebis (2-oxazoline), 2,2′-ethylenebis (4-methyl-2-oxazoline), 2, 2'-tetramethylenebis (4,4'-dimethyl-2-oxazoline), 2,2'-cyclohexylenebis (2-oxazoline), 2,2'-diphenylenebis (4-methyl-2-oxazo) Down), and the like. Furthermore, the polyoxazoline compound etc. which contain the said compound as a monomer unit are mentioned.

  Examples of oxazine compounds that can be used in the present invention include 2-methoxy-5,6-dihydro-4H-1,3-oxazine, 2-hexyloxy-5,6-dihydro-4H-1,3-oxazine, 2- Decyloxy-5,6-dihydro-4H-1,3-oxazine, 2-cyclohexyloxy-5,6-dihydro-4H-1,3-oxazine, 2-allyloxy-5,6-dihydro-4H-1,3 -Oxazine, 2-crotyloxy-5,6-dihydro-4H-1,3-oxazine and the like.

  Further, 2,2′-bis (5,6-dihydro-4H-1,3-oxazine), 2,2′-methylenebis (5,6-dihydro-4H-1,3-oxazine), 2,2′- Ethylenebis (5,6-dihydro-4H-1,3-oxazine), 2,2′-hexamethylenebis (5,6-dihydro-4H-1,3-oxazine), 2,2′-p-phenylene Bis (5,6-dihydro-4H-1,3-oxazine), 2,2′-P, P′-diphenylenebis (5,6-dihydro-4H-1,3-oxazine) and the like can be mentioned. Furthermore, the polyoxazine compound etc. which contain the above-mentioned compound as a monomer unit are mentioned.

  Among the oxazoline compounds and oxazine compounds, 2,2′-m-phenylenebis (2-oxazoline) and 2,2′-p-phenylenebis (2-oxazoline) are preferable.

Examples of isocyanate compounds that can be used in the present invention include aromatic, aliphatic, and alicyclic isocyanate compounds, and mixtures thereof.
Examples of the monoisocyanate compound include phenyl isocyanate, tolyl isocyanate, dimethylphenyl isocyanate, cyclohexyl isocyanate, butyl isocyanate, and naphthyl isocyanate.

As the diisocyanate, 4,4′-diphenylmethane diisocyanate, 4,4′-diphenyldimethylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate Isocyanate, (2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate) mixture, cyclohexane-4,4′-diisocyanate, xylylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, methylcyclohexane Examples thereof include diisocyanate, tetramethylxylylene diisocyanate, and 2,6-diisopropylphenyl-1,4-diisocyanate.
Among these isocyanate compounds, aromatic isocyanates such as 4,4′-diphenylmethane diisocyanate and phenyl isocyanate are preferable.

  Examples of ketene compounds that can be used in the present invention include aromatic, aliphatic, and alicyclic ketene compounds, and mixtures thereof. Specific examples include diphenyl ketene, bis (2,6-di-t-butylphenyl) ketene, bis (2,6-di-isopropylphenyl) ketene, dicyclohexyl ketene, and the like. Among these ketene compounds, aromatic ketenes such as diphenyl ketene, bis (2,6-di-t-butylphenyl) ketene, and bis (2,6-di-isopropylphenyl) ketene are preferable.

  As the block forming agent and the heat-and-moisture resistance improver, one or more compounds can be appropriately selected and used. One of preferred embodiments is to promote the formation of a block structure with a heat-and-moisture resistance improver and to seal a carboxyl group terminal and a part of an acidic low molecular weight compound.

<Resin composition>
The resin composition in the present invention contains polylactic acid (component A). Such a resin composition preferably consists essentially of polylactic acid (component A). Note that “substantially” means that the component occupies preferably 75% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more based on all components.

  The resin composition preferably has a stereocomplex crystallinity (S) determined by the formula (i) of 90% or more. When the stereocomplex crystallinity (S) is 90% or more, the thermal shrinkage rate of the film at 90 ° C. can be reduced. The stereocomplex crystallinity (S) of the resin composition is more preferably 93% or more, still more preferably 97% or more, and particularly preferably the stereocomplex crystallinity (S) is 100%.

  By adding a hydrolysis inhibitor, the resin composition can suppress a decrease in molecular weight due to hydrolysis of polylactic acid (component A). For example, a decrease in strength can be suppressed. As the hydrolysis inhibitor, a compound having reactivity with a carboxylic acid and a hydroxyl group, which are terminal functional groups of polylactic acid, for example, a compound having the above-mentioned specific functional group is preferably applied, and among these, a carbodiimide compound is preferably selected. Is done.

  At this time, it is preferable that 0.001-5 mass% of carbodiimide compounds are contained on the basis of the mass of polylactic acid (A component). This is because when the amount of the carbodiimide compound satisfies such a range, the stability of the resin composition with respect to moisture and the hydrolysis resistance can be suitably increased.

  From this viewpoint, the content ratio of the carbodiimide compound is more preferably 0.01 to 5% by mass, and still more preferably 0.1 to 4% by mass. If the amount is less than this range, the effect of applying the carbodiimide compound is not effectively recognized. Moreover, if it is applied in a large amount beyond this range, further improvement in hydrolysis resistance is not expected, and there is a concern that an undesirable phenomenon such as deterioration of the hue of the resin composition may occur.

  Moreover, the resin composition can contain other polymers other than polylactic acid (component A) as long as the object of the present invention is not impaired. Other polymers include polyolefins such as polyethylene and polypropylene, styrene resins such as polystyrene and styrene acrylonitrile copolymers, polyamides, polyphenylene sulfide resins, polyether ether ketone resins, polyesters, polysulfones, polyphenylene oxides, polyimides, polyetherimides And thermoplastic resins such as polyacetal, thermosetting resins such as phenol resin, melamine resin, silicone resin, and epoxy resin. These can contain 1 or more types.

  Furthermore, arbitrary additives can be mix | blended with a resin composition according to various objectives within the range which does not impair the effect of this invention remarkably. The type of additive is not particularly limited as long as it is generally used for blending resins and rubber-like polymers. Examples of the additive include inorganic fillers and pigments such as iron oxide. Moreover, lubricants and mold release agents such as stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, ethylene bisstearamide and the like can be mentioned. Moreover, softening agents and plasticizers such as paraffinic process oil, naphthenic process oil, aromatic process oil, paraffin, organic polysiloxane, and mineral oil can be used. Examples include antioxidants such as hindered phenolic antioxidants and phosphorus heat stabilizers, hindered amine light stabilizers, ultraviolet absorbers (for example, benzotriazole ultraviolet absorbers), flame retardants, and antistatic agents. Moreover, reinforcing agents, such as organic fiber, glass fiber, carbon fiber, and metal whisker, a coloring agent, and an electrostatic adhesion improving agent are mentioned. Moreover, these mixtures are mentioned.

  Examples of the ultraviolet absorber include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like, but benzotriazole is less colored. System compounds are preferred. Further, from the viewpoint of preventing deterioration of the polarizer and the liquid crystal, those excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less and having little absorption of visible light having a wavelength of 400 nm or more are preferable from the viewpoint of liquid crystal display properties.

  Specific examples of useful benzotriazole ultraviolet absorbers include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl). ) Benzotriazole, 2- (2′-hydroxy-3′-tert-butyl-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl)- 5-chlorobenzotriazole, 2- (2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″, 6 ″ -tetrahydrophthalimidomethyl) -5′-methylphenyl) benzotriazole, 2, 2-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2 ′ Hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol Octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy A mixture with -5- (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate can be mentioned, but is not limited thereto. As commercially available products, TINUVIN 109, TINUVIN 171, TINUVIN 326, and TINUVIN 328 (all manufactured by Ciba Specialty Chemicals) can be preferably used.

  The resin composition can be produced by a known method. For example, using a melt kneader such as a single screw extruder, twin screw extruder, Banbury mixer, Brabender, various kneaders, etc., polylactic acid (component A), hydrolysis inhibitor and other components as necessary It can be added and melt kneaded to produce a resin composition.

<Particle>
In order to make the film white in the present invention, a method of adding an additive for forming voids to the polylactic acid film to make it white, a white layer on the polylactic acid film, a coextrusion method, a laminating method, a coating method However, the method of adding an additive for forming a void can obtain a white biaxially stretched polylactic acid film having a uniform L value and whiteness in the plane. preferable. As such an additive, particles are preferred.

Such particles may be either organic particles or inorganic particles. Examples of the inorganic particles include titanium oxide (TiO ₂ ), barium sulfate, zinc oxide, magnesium carbonate, calcium carbonate, aluminum oxide, silicon oxide (SiO ₂ ), talc, and kaolin. Examples of the organic particles include polystyrene particles and silicone particles. Moreover, these secondary aggregates may be sufficient. In the present invention, one kind or two or more kinds of these particles can be used. In addition, the particle | grains in this invention are inactive with respect to the component contained in a resin composition, such as polylactic acid (A component).

  In the present invention, inorganic particles are preferred because they can be whitened efficiently. Moreover, when it is an inorganic particle, it becomes easy to make the apparent specific gravity of a white biaxially stretched polylactic acid film into the numerical value range prescribed | regulated by this invention.

  The particles in the present invention preferably have a large specific gravity. When the specific gravity of the particles is large, the apparent specific gravity of the white biaxially stretched polylactic acid film can be increased. Thereby, the heat resistance (dimensional stability), whiteness, and printability can be improved. From such a viewpoint, the specific gravity of the particles is preferably 2 or more, more preferably 3 or more, further preferably 3.5 or more, and particularly preferably 4 or more.

  Further, the refractive index of the particles in the present invention is preferably 1.5 or more. When the refractive index is in the above numerical range, light is easily reflected, moderate glossiness is obtained, and the appearance is excellent. From such a viewpoint, the refractive index is more preferably 1.8 or more, further preferably 2.2 or more, and particularly preferably 2.5 or more.

  From the viewpoint that the specific gravity and refractive index as described above can be satisfied at the same time, inorganic particles are preferable, and specifically, calcium carbonate, barium sulfate, and titanium oxide are preferable. Of these, titanium oxide and barium sulfate are preferable. As the titanium oxide, rutile titanium oxide is preferable. As the barium sulfate, precipitated barium sulfate is preferable. By using these particles, it is easy to obtain preferable L value, whiteness, and apparent specific gravity in the present invention. In the present invention, rutile type titanium oxide is particularly preferable.

  The average particle diameter of the above particles is preferably 0.1 μm or more and 5 μm or less, more preferably 0.15 μm or more, further preferably 0.2 μm or more, more preferably 3 μm or less, and further preferably 1.4 μm or less. . If the average particle size is too small, it is difficult to obtain a white film. On the other hand, if the average particle size is too large, tearing is likely to occur during film formation, and particles are likely to fall off during processing, etc., resulting in process contamination. Etc. tend to be prone to occur.

Further, the content of the particles is preferably 3% by mass or more and 45% by mass or less based on the mass of the white biaxially stretched polylactic acid film. More preferably, it is 5 mass% or more and 20 mass% or less. When the content is in the above numerical range, it is easy to simultaneously achieve the L value, whiteness, and apparent density in the present invention. If the content is too small, it becomes difficult to obtain a white film. On the other hand, if the content is too large, tearing tends to occur in the stretching process, and the lip of the die tends to become dirty in the melt extrusion process. Trouble tends to occur, and production efficiency tends to deteriorate.
The above particles are preferably contained in the resin composition and contained in the white biaxially stretched film.

<Manufacture of film>
(Extrusion)
In order to form a film of the obtained resin composition, a molding technique such as extrusion molding or cast molding can be used. For example, the film can be formed using an extruder equipped with a T die, a circular die, or the like. Of these, extrusion molding is preferred.

  When an unstretched film is obtained by extrusion molding, other components such as polylactic acid (component A) and a hydrolysis inhibitor that may be optionally added, additives that may be optionally added, etc. A melt-kneaded material can be used, or a melt-kneaded material can be formed during extrusion molding. An unstretched film can be produced by extruding a molten film onto a cooling drum, and then bringing the film into close contact with a rotating cooling drum and cooling. At this time, an electrostatic adhesive such as a sulfonic acid quaternary phosphonium salt is blended in the molten film, and an electric charge is applied in a non-contact manner from the electrode to the film melting surface, thereby bringing the film into close contact with the rotating cooling drum. An unstretched film with few surface defects can also be obtained.

  When extruding an unstretched film using a material that has been previously melt-kneaded, the melt extrusion temperature is preferably 230 to 250 ° C. When the melt extrusion temperature is in the above numerical range, the unmelted portion can be reduced. In addition, thermal decomposition and thermal deterioration are unlikely to occur, and foreign substances due to decomposition products and deterioration products can be reduced. When the melt extrusion temperature is too low, the unmelted portion tends to increase. On the other hand, when the melt extrusion temperature is too high, foreign matters due to decomposed products and deteriorated products tend to increase. From such a viewpoint, the melt extrusion temperature is more preferably 230 to 245 ° C, and particularly preferably 230 to 240 ° C. Furthermore, from the viewpoint of further promoting threo formation, the melt extrusion temperature is preferably 240 to 280 ° C, and more preferably 245 to 275 ° C. A higher melt extrusion temperature tends to promote stereo-ization.

  When an unstretched film is extruded through melt kneading at the time of extrusion molding, the melt extrusion temperature (that is, such temperature becomes the melt kneading temperature) is 230 to 300 ° C. By making melt extrusion temperature into the said numerical range, the stereocomplex crystallinity (S) of the film obtained can be made into the range which this invention prescribes | regulates. The higher the melt extrusion temperature, the more likely to become stereo. However, when the melt extrusion temperature is too high, there is a tendency that foreign matters due to decomposition products and degradation products increase. On the other hand, if it is too low, a predetermined degree of stereocomplexity (S) cannot be obtained. From such a viewpoint, the melt extrusion temperature is preferably 240 to 280 ° C, more preferably 245 to 275 ° C.

  At that time, the ratio of the lip opening of the extrusion die to the thickness of the sheet extruded on the cooling drum (the draft ratio, the lip opening of the extrusion die, the sheet extruded on the cooling drum (unstretched film)) The ratio obtained by dividing by the thickness is preferably 2 or more and 80 or less.

  When the draft ratio is small, the take-off speed from the extrusion die lip becomes too slow, and the polymer separation speed from the die lip is too slow, and disadvantages such as die lip stripe defects increase, which is not preferable. From such a viewpoint, the lower limit of the draft ratio is preferably 3 or more, more preferably 4 or more, further preferably 6 or more, and particularly preferably 10 or more. On the other hand, if the draft ratio is too large, the deformation when the polymer leaves the die lip is too large, or the flow becomes unstable and the thickness fluctuation (thickness unevenness) becomes worse. From such a viewpoint, the upper limit of the draft ratio is preferably 50 or less, more preferably 25 or less, and particularly preferably 15 or less.

  In addition, a polylactic acid (component A) solvent such as chloroform, methylene dichloride, etc. is used to dissolve polylactic acid (component A), etc., and then cast and solidify by casting to solidify the unstretched film. Can do.

(Stretching)
The white biaxially stretched polylactic acid film of the present invention is subjected to biaxial stretching in order to obtain desired mechanical properties such as practically sufficient film strength and heat resistance.
When the unstretched film is biaxially stretched, it can be stretched by a sequential biaxial stretching method of roll stretching and tenter stretching, a simultaneous biaxial stretching method by tenter stretching, a biaxial stretching method by tubular stretching, or the like.

  As for the draw ratio of biaxial stretching, the lower limit of the area draw ratio (longitudinal draw ratio x transverse draw ratio) is 4.0 times or more, preferably 8.0 times or more, more preferably 10.0 times or more. Especially preferably, it is 11.0 times or more. On the other hand, the upper limit is not particularly limited, but is preferably 25 times or less, more preferably 18 times or less, and further preferably 13 times or less. By setting the area stretch ratio within the above numerical range, excellent mechanical properties and heat resistance can be obtained.

  Regarding the draw ratio in the machine direction and the transverse direction, the draw ratio in the machine direction is preferably 2.0 times or more, more preferably 2.5 times or more, in order to obtain good mechanical properties and heat resistance. More than double is more preferable. Moreover, in order to reduce the fracture at the time of film formation, 5.0 times or less is preferable, 4.0 times or less is more preferable, and 3.7 times or less is more preferable. In order to obtain good mechanical properties and heat resistance, the transverse draw ratio is preferably 2.0 times or more, more preferably 2.8 times or more, and even more preferably 3.3 times or more. Moreover, in order to reduce the fracture | rupture at the time of film forming, 5.0 times or less are preferable, 4.2 times or less are more preferable, and 3.8 times or less are further more preferable.

  The difference between the draw ratio in the machine direction and the draw ratio in the transverse direction is not particularly limited, but the absolute value of the difference in the draw ratio is preferably 2.0 or less, more preferably 1.0 or less, and still more preferably 0.00. 6 or less, particularly preferably 0.4 or less. By making the absolute value of the difference in draw ratio within the above numerical range, the balance of mechanical properties and other physical properties can be improved.

  The stretching temperature is suitably selected in the range from the glass transition temperature (Tg, unit: ° C) to the crystallization temperature (Tc, unit: ° C) of the resin composition. Among these, a temperature range as close to Tc as possible, that is, a temperature range in which crystallization of polylactic acid (component A) is difficult to proceed is more preferably employed.

Since the molecular chain is fixed at a temperature lower than Tg, it tends to be difficult to suitably proceed the stretching operation.
Accordingly, the lower limit of the stretching temperature is more preferably Tg + 5 ° C. or more, and further preferably Tg + 10 ° C. or more. On the other hand, the upper limit is more preferably Tc-5 ° C or lower, and further preferably Tc-10 ° C or lower.

  In the present invention, the stretching temperature is preferably set from the above temperature range from the viewpoint of coexistence of film physical properties and stretching process stabilization. The upper limit of the stretching temperature should be set as appropriate in consideration of the apparatus characteristics because the film properties and the stabilization of the stretching process are in conflict.

  Further, in the stretching step, an embodiment in which the temperature at the stretching end portion is higher by 1 ° C. or more than the temperature at the stretching start portion is preferable, which is desirable because the thickness unevenness of the film becomes good. Further, the higher the temperature at the end of stretching than the temperature at the start of stretching, the voids around the particles are less likely to be formed, or the apparent specific gravity tends to increase, and the apparent specific gravity is a numerical range defined by the present invention. It becomes easy to do. From such a viewpoint, the temperature at the end of stretching is more preferably 2 ° C. or higher, more preferably 3 ° C. or higher, and particularly preferably 4 ° C. or higher than the temperature of the stretching start portion. On the other hand, if the temperature at the end of stretching is too higher than the temperature at the beginning of stretching, a difference in physical properties in the film width direction tends to appear. From such a viewpoint, the temperature difference between the stretch end portion and the stretch start portion is preferably 30 ° C. or less, more preferably 20 ° C. or less, further preferably 15 ° C. or less, and particularly preferably 10 ° C. or less.

  In addition, the slower the stretching speed, the more likely that voids are not formed around the particles, or the apparent specific gravity tends to increase, and the apparent specific gravity can be easily set within the numerical range defined by the present invention. From such a viewpoint, the upper limit of the stretching speed during transverse stretching is preferably 10,000% / min or less, more preferably 6000% / min or less, and further preferably 2000% / min or less. On the other hand, if the lateral stretching speed is too slow, the heating time becomes too long, or the thickness unevenness deteriorates. From such a viewpoint, the lower limit of the stretching speed during transverse stretching is preferably 100% / min or more, more preferably 200% / min or more, and still more preferably 400% / min or more.

(Heat treatment)
The unstretched film, uniaxially stretched film, and biaxially stretched film are preferably heat-treated at 110 ° C. or higher and 200 ° C. or lower. Such heat treatment corresponds to a so-called heat setting treatment. By this heat treatment, crystallization of the complex phase polylactic acid can be promoted, and the thermal contraction rate of the resulting white biaxially stretched polylactic acid film can be suitably reduced. From such a viewpoint, the lower limit of the heat treatment temperature is more preferably 150 ° C. or higher, further preferably 170 ° C. or higher, and particularly preferably 190 ° C. or higher. On the other hand, if the heat treatment temperature is too high and too close to the melting temperature of the resin composition, mechanical properties such as the breaking strength of the polylactic acid film tend to be low, and thickness unevenness tends to be poor. From such a viewpoint, the upper limit of the heat treatment temperature is more preferably 200 ° C. or less, further preferably 195 ° C. or less, and particularly preferably 190 ° C. or less.

  The heat treatment time is preferably in the range of 1 second to 30 minutes. In order to increase the effect of improving the thermal dimensional stability, a relatively short heat treatment is required when the heat treatment temperature is high, and a relatively long heat treatment is required when the heat treatment temperature is low. For example, a resin composition having a Tc of 140 ° C. requires a heat treatment of at least 30 seconds at a heat treatment temperature of 140 ° C., but at a heat treatment temperature of 150 ° C., the heat treatment at a temperature of 90 ° C. The heat shrinkage rate can be 4% or less.

In the above-described range of the draw ratio, adopting the above aspect as the heat treatment is one of the preferable means for setting the mechanical characteristics, heat resistance, and heat shrinkage rate within the numerical ranges defined by the present invention.
Moreover, the film obtained by performing this heat treatment becomes excellent in mechanical properties and heat resistance. Specifically, the heat shrinkage rate when treated at 100 ° C. for 1 hour and the heat shrinkage rate when treated at 150 ° C. for 30 minutes can be reduced.

The film thus obtained can be subjected to surface activation treatment such as plasma treatment, amine treatment or corona treatment by a conventionally known method if desired.
In addition, the obtained white biaxially stretched polylactic acid film can be subjected to surface functionalization treatment such as transparent conductive treatment, electromagnetic wave shielding treatment, gas barrier treatment, and antifouling treatment, if necessary.

<Characteristics of film>
(Apparent specific gravity)
The apparent specific gravity of the white biaxially stretched polylactic acid film in the present invention needs to exceed 1.30 g / cm ³ . Preferably 1.33 g / cm ³ or more, more preferably 1.345 g / cm ³ or more, more preferably 1.36 g / cm ³ or more, and particularly preferably 1.375 g / cm ³ or more. When the apparent specific gravity is in the above numerical range, the printability, whiteness, and dimensional stability are excellent. Moreover, it can be set as a moderate glossiness. If the apparent specific gravity is small, the whiteness and the glossiness tend to be low. If the apparent specific gravity is too small, the whiteness, the glossiness, and the printability tend to be inferior, and the apparent specific gravity is 1.30 g / cm ³ or less. It becomes particularly noticeable. Moreover, it is inferior to dimensional stability. These are presumed that when the apparent specific gravity is lowered, the voids around the particles are excessively increased or the particles are easily dropped off. On the other hand, if the apparent specific gravity is large, the whiteness, printability, and dimensional stability tend to be excellent, but if it is too large, the stretchability at the time of film formation tends to be poor and breakage tends to occur. Therefore, it is preferable to set an appropriate upper limit that does not cause such a problem.

  The method for setting the apparent specific gravity as described above is not particularly limited. For example, a method of applying a paint on the surface, a method of containing inert particles such as inorganic particles and / or organic particles in the film, and the like. Can be mentioned. For example, in order to increase the apparent specific gravity, the specific gravity of the particles to be added is increased, the amount of particles added is increased, and in film formation, the temperature at the stretching end portion is set higher than the temperature at the stretching start portion in the stretching step. There are means such as increasing the speed and decreasing the stretching speed, and these may be used alone or in combination. As for the stretching speed, it is important to slow the stretching speed in the transverse direction.

  In the present invention, in particular, by having the specific stereocomplex crystallinity (S) and the apparent specific gravity as described above, the heat resistance is improved, and a printing process equivalent to that applied to a general-purpose PET film. Secondary processing such as property and vapor deposition workability becomes possible.

(L value)
The white biaxially stretched polylactic acid film of the present invention has an L value determined by a color difference meter of 85 or more. When the L value is in the above numerical range, the whiteness and hiding properties are excellent. Moreover, it is excellent in printability. If the L value is less than 85, the printability and the sharpness of writing tend to be inferior. From such a viewpoint, the L value is preferably 90 or more, more preferably 93 or more.

  Such L value is achieved by appropriately adjusting the refractive index, particle diameter, specific gravity, and addition amount of the particles. For example, when particles having a high refractive index are used or the amount of particles added is increased, the L value tends to increase. Moreover, it is achieved by appropriately adjusting the stretching ratio, stretching temperature, and stretching speed during film formation. For example, when the stretching temperature is lowered, the L value tends to increase. Further, setting the apparent specific gravity within the numerical range defined by the present invention is also an effective means for achieving the L value.

(Whiteness)
The white biaxially stretched polylactic acid film of the present invention has a whiteness (unit:%) determined by the following formula from the viewpoint of improving the appearance, preferably 83 to 100%, more preferably 87 to 99%, More preferably, it is 91-99. In particular, when the whiteness is in the above numerical range, it is particularly suitably used for packaging applications.
Whiteness (%) = 100 − ((100−L) ² + a ² + b ² ) ^1/2
Here, L, a, and b are numerical values obtained by a color difference meter.

  Such whiteness is achieved by appropriately adjusting the refractive index, particle diameter, specific gravity, and addition amount of the particles. For example, if the specific gravity of the particles used is increased, the refractive index is increased, or the amount added is increased, the whiteness tends to increase. Moreover, it is achieved by appropriately adjusting the stretching ratio, stretching temperature, and stretching speed during film formation. For example, the whiteness tends to increase by increasing the stretching speed. Further, setting the apparent specific gravity within the numerical range defined by the present invention is also an effective means for achieving whiteness.

(Glossiness)
The white biaxially stretched polylactic acid film of the present invention has a glossiness of preferably 10 to 70, more preferably 30 to 70, and still more preferably 30 to 60, from the viewpoint of improving the appearance. In particular, when the glossiness is in the above numerical range, it is particularly suitably used for packaging applications.

  The glossiness is achieved by appropriately adjusting the specific gravity, refractive index, particle diameter, and refractive index of the particles used. For example, if the specific gravity of the particles used is increased or the amount added is increased, the glossiness tends to decrease. Moreover, it is achieved by appropriately adjusting the stretching temperature, the temperature gradient, and the stretching speed during film formation. For example, if the stretching temperature is lowered or the stretching speed is increased, the glossiness tends to be lowered. Moreover, setting the apparent specific gravity within the numerical range defined by the present invention is also an effective means for achieving glossiness.

(Breaking strength)
The white biaxially stretched polylactic acid film of the present invention preferably has an average of the longitudinal breaking strength and the transverse breaking strength of 100 MPa or more, and there is a difference between the longitudinal breaking strength and the transverse breaking strength. It is preferable that it is 50 MPa or less. When the average of the breaking strength is increased, the mechanical properties are improved and the transportability during film processing is improved. On the other hand, if the breaking strength is too high, the production efficiency tends to deteriorate, for example, the breaking tends to occur during film formation. In addition, when the difference between the breaking strength in the vertical direction and the breaking strength in the horizontal direction increases, curling tends to occur, and workability and transportability tend to deteriorate, such as poor insertion into a processing apparatus. is there. From such a viewpoint, the average of the breaking strength in the longitudinal direction and the transverse direction is more preferably 110 MPa or more, further preferably 120 MPa or more, and particularly preferably 130 MPa or more. Further, the difference between the breaking strengths in the longitudinal direction and the transverse direction is more preferably 40 MPa or less, further preferably 30 MPa or less, and particularly preferably 20 MPa or more. Further, an aspect in which the breaking strength in the vertical direction is larger than the breaking strength in the horizontal direction is preferable. In order to obtain such mechanical characteristics, it is only necessary to increase the draw ratio, adjust the vertical and horizontal balance of the draw ratio, or increase the stereocomplex crystallinity (S).

(Thickness)
The thickness of the white biaxially stretched polylactic acid film of the present invention is preferably 1 to 300 μm. The thickness is preferably thicker from the viewpoint of ease of wrinkling during handling (wrinkle prevention), more preferably 10 μm or more, still more preferably 20 μm or more, and particularly preferably 30 μm or more. On the other hand, when it is too thick, workability and handling tend to be deteriorated. From this viewpoint, it is more preferably 250 μm or less, further preferably 190 μm or less, and particularly preferably 100 μm or less.

  The white biaxially stretched polylactic acid film of the present invention may be a laminated film having two layers or three or more layers. In the case of three or more layers, the content of the surface layer particles is preferably higher than the content of the inner layer particles. By setting it as such an aspect, L value, whiteness, and concealment property can be made higher, maintaining film forming property.

(Stereo Complex Crystallinity (S))
The white biaxially stretched polylactic acid film of the present invention has a stereocomplex crystallinity (S) defined by the following formula (i) of 90% or more from the crystal melting peak intensity measured by DSC. The stereocomplex crystallinity (S) is more preferably 97 to 100%, particularly preferably 100%. That is, the white biaxially stretched polylactic acid film of the present invention preferably has a highly formed stereocomplex phase. With this embodiment, the heat resistance is excellent.
S (%) = [ΔHms / (ΔHmh + ΔHms)] × 100 (i)
ΔHms represents the crystal melting enthalpy (J / g) of the stereocomplex phase polylactic acid. ΔHmh represents the crystal melting enthalpy (J / g) of homophase polylactic acid. The stereocomplex crystallinity (S) is a parameter indicating the ratio of stereocomplex polylactic acid crystals that are finally produced in the heat treatment process.

  In the present invention, the crystal melting peak appearing at 190 ° C. or higher in the DSC measurement is a crystal melting peak attributed to the melting of the stereocomplex phase polylactic acid, and the crystal melting peak appearing below 190 ° C. is the melting of the homophase polylactic acid. Is a crystal melting peak attributed to.

(Crystal melting peak)
The white biaxially stretched polylactic acid film of the present invention has a crystal melting peak at 190 ° C. or higher as measured by a differential scanning calorimeter (DSC). Here, it means that the peak of the crystal melting peak is preferably in the range of 190 to 250 ° C. In addition, the temperature at the top of the crystal melting peak may be referred to as the crystal melting temperature. Such a crystal melting peak is a crystal melting peak attributed to melting of the stereocomplex phase polylactic acid. In this invention, the aspect which has a crystal melting peak in the range of 190-250 degreeC is preferable, and the aspect which has a crystal melting peak in the range of 200-220 degreeC is more preferable. When the crystal melting peak is in the above numerical range, the heat resistance is excellent.

(Heat shrinkage)
The white biaxially stretched polylactic acid film of the present invention preferably has a heat shrinkage of 3% or less in the machine direction (MD) and the transverse direction (TD) when treated at a temperature of 100 ° C. for 1 hour. The thermal shrinkage rate is more preferably 2.5% or less for both, more preferably 2% or less for both, and particularly preferably 1% or less for both. When the heat shrinkage rate at 100 ° C. is in the above numerical range, the flatness of the film is maintained even when heat is applied during processing or the like, curling is unlikely to occur, and transportability is excellent. Moreover, it is excellent in printability.

  The white biaxially stretched polylactic acid film of the present invention preferably has a thermal shrinkage rate of 5% or less in both the machine direction (MD) and the transverse direction (TD) when treated at a temperature of 150 ° C. for 30 minutes. . The thermal shrinkage rate is more preferably 4% or less for both, and further preferably 3% or less for both. When the heat shrinkage rate at 150 ° C. is in the above numerical range, even when heat is applied during processing or the like, heat shrinkage spots hardly occur and whiteness spots hardly occur. Moreover, it is excellent in printability.

In the present invention, if either the heat shrinkage rate of 100 ° C. or the heat shrinkage rate of 150 ° C. is the above embodiment, the effect of improving the printability can be enhanced, but these heat shrinkage rates are satisfied simultaneously. As a result, the effect of improving printability can be further enhanced.
The heat shrinkage can be achieved by setting the stretching conditions and the heat treatment conditions to the above-described preferred embodiments of the present invention, and it is particularly important to perform the heat treatment.

<Other layers>
The white biaxially stretched polylactic acid film of the present invention can be used in combination with a hard coat layer, a gas barrier layer, a sliding layer, an antistatic layer, an undercoat layer, a protective layer, etc. for the purpose of further improving the function. .

  Hereinafter, the present invention will be described more specifically with reference to examples. (I) Evaluation method and (II) Raw materials will be described.

(I) Evaluation Method Evaluation methods used in the present invention and examples will be described.
(1) Molecular weight The weight average molecular weight (Mw) and the number average molecular weight (Mn) were measured by gel permeation chromatography (GPC) and converted to standard polystyrene.
GPC measurement equipment
Detector; Shimadzu Corporation differential refractometer RID-6A
Column: Toso-Co., Ltd. TSKgelG3000HXL, TSKgelG4000HXL, TSKgelG5000HXL and TSKguardcocumumHXL-L connected in series, or Toso-Co., Ltd.
Chloroform was used as an eluent, 10 μl of a sample having a concentration of 1 mg / ml (chloroform containing 1% hexafluoroisopropanol) was injected at a temperature of 40 ° C. and a flow rate of 1.0 ml / min.

(2) Lactide content The sample was dissolved in hexafluoroisopropanol and quantified by ¹³ C-NMR method.

(3) Carbodiimide compound content The content was measured by comparison between resin characteristic absorption and carbodiimide characteristic absorption with a MAGJA-750 Fourier transform infrared spectrophotometer manufactured by Nicole Corporation.

(4) Carboxyl group concentration The sample was dissolved in purified o-cresol, dissolved in a nitrogen stream, and titrated with an ethanol solution of 0.05 N potassium hydroxide using bromocresol blue as an indicator.

(5) Stereocomplex crystallinity (S), crystal melting temperature, crystal melting peak Stereocomplex crystallinity (S), crystal melting temperature, and crystal melting peak use DSC (TA-2920 manufactured by TA Instruments). The crystal melting peak crystal melting temperature (unit: ° C.) and crystal melting enthalpy (unit: J / g) were measured, and the stereocomplex crystallinity (S) was determined from the crystal melting enthalpy according to the following formula (i). . In addition, the sample amount in DSC measurement was 10 mg in the case of resin before forming into a film, 20 mg in the case of a film, a measurement temperature range of 25 ° C. to 290 ° C., and a temperature increase rate of 20 ° C./min.
S (%) = [ΔHms / (ΔHmh + ΔHms)] × 100 (i)
(However, ΔHms represents the crystal melting enthalpy (unit: J / g) of the complex phase, and ΔHmh represents the crystal melting enthalpy (unit: J / g) of the homophase polylactic acid.)

(6) Film heat shrinkage rate According to ASTM D1204, after treatment at a temperature of 100 ° C. for 1 hour or after heat treatment at 150 ° C. for 30 minutes, the temperature was returned to room temperature (25 ° C.), and the heat shrinkage rate was determined from the change in length. .

(7) L value, whiteness Using a spectroscopic color difference meter SZ-Σ90 manufactured by Nippon Denshoku Co., Ltd., L, a, b values are obtained, and L value and whiteness are obtained in accordance with JIS L1015C method. It was.
In addition, whiteness (unit:%) was calculated | required using the following formula.
Whiteness (%) = 100 − ((100−L) ² + a ² + b ² ) ^1/2

(8) Glass transition temperature It calculated | required using DSC (TA-2920 by TA instrument company). The amount of the sample was 10 mg in the case of the resin before forming into a film, 20 mg in the case of the film, a measurement temperature range of 25 ° C. to 290 ° C., and a temperature increase rate of 20 ° C./min.

(9) Specific gravity (apparent specific gravity, density)
The density was measured by a floatation method at 25 ° C. in a density gradient tube using an aqueous calcium nitrate solution as a solvent.

(10) Thickness unevenness The thickness of the film is measured 0.5 m with an electronic micrometer in the transverse direction (TD, the direction perpendicular to the mechanical flow direction), and the maximum thickness (unit: μm) and the minimum thickness (unit: unit: [mu] m) and the ratio (percentage) between the average thickness (unit: [mu] m) and the thickness variation (unit:%), and evaluated according to the following.
◎: Thickness unevenness is 2% or less ○: Thickness unevenness exceeds 2% and 4% or less △: Thickness unevenness exceeds 4% and 6% or less ×: Thickness unevenness exceeds 6% Thickness unevenness is preferably lower and larger Too much is not preferable because there are problems such as variations in mechanical properties. If the thickness unevenness exceeds 6%, it cannot be put into practical use.

(11) Average particle diameter of the particles The powder of the particles is scattered on the sample stage so that the individual particles do not overlap as much as possible, and a gold thin film deposition layer is formed on the surface with a thickness of 200 to 300 angstroms by a gold sputtering device. , Observed with a scanning electron microscope at a magnification of 10,000 to 3 times, and with a Luzex 500 manufactured by Japan Regulator Co., Ltd., at least 110 particles, a major axis (Dli), minor axis (Dsi), and area circle The equivalent diameter (Di) was determined.
The number n of particles was used, and the value obtained above was used in the following formula, and the number average value of the area equivalent particle diameter (Di) was defined as the average particle diameter (D).

(12) Breaking strength and breaking elongation The breaking strength and breaking elongation were measured using a tensile tester (trade name “Tensilon” manufactured by Toyo Baldwin). Samples each having a length of 200 mm and a width of 10 mm were taken from the sample film in the longitudinal direction (MD) and the transverse direction (TD), and fixed by being sandwiched between chucks set at an interval of 100 mm. Pulling was performed at a speed of 100 mm / min, and the load was measured with a load cell attached to the testing machine. The load at the time of rupture of the unloading curve was read and divided by the cross-sectional area of the sample before tension to determine the rupture strength (unit: MPa). The breaking elongation was calculated from the initial chuck interval (L ₀ ) and the chuck interval at the time of breaking (L ₁ ) using the following formula, and was defined as the breaking elongation (unit:%).
Elongation at break (%) = (L ₁ −L ₀ ) / L ₀ × 100

(13) Glossiness Using a gloss meter manufactured by Nippon Denshoku Industries Co., Ltd., 60 degree glossiness according to JIS K7105 (specular glossiness, which is the ratio of specular reflection light on the surface to light incident at an angle of 60 degrees) ) Was measured. Measurement was carried out at any 10 locations on the sample surface, and the average value thereof was taken as the measured value.

(14) Printability The red color of Nealex 70 manufactured by Nippon Processing Paint Co., Ltd. was applied to a thickness of 2 μm, dried at 120 ° C., and evaluated by looking at the appearance. The case where the ink layer was significantly contracted was evaluated as x, the case where the shrinkage was small was evaluated as ◯, and the intermediate one was evaluated as Δ.

(II) Raw material Polylactic acid (component A) was prepared in the following production examples.
[Production Example 1-1] Production of poly-L-lactic acid (PLLA1) 0.005 parts by mass of tin octylate is added to 100 parts by mass of L-lactide (manufactured by Musashino Chemical Laboratory, Inc., optical purity 100%). The reaction was carried out at 180 ° C. for 2 hours in a reactor equipped with a stirring blade under a nitrogen atmosphere, and 1.2 times equivalent of phosphoric acid was added to tin octylate, and then the remaining lactide was reduced in pressure at 13.3 Pa. After removing and chipping, poly L-lactic acid (PLLA1) was obtained.
The obtained poly L-lactic acid (PLLA1) has a weight average molecular weight (Mw) of 152,000, a glass transition temperature (Tg) of 55 ° C., a melting point of 175 ° C., a carboxyl group concentration of 14 eq / ton, and a lactide content. Was 350 ppm.

[Production Example 1-2] Production of poly-D-lactic acid (PDLA1) The L-lactide of Production Example 1-1 was changed to D-lactide (manufactured by Musashino Chemical Laboratory, Inc., optical purity 100%). Polymerization was performed under the same conditions to obtain poly-D-lactic acid (PDLA1).
The resulting poly-D-lactic acid (PDLA1) has a weight average molecular weight (Mw) of 151,000, a glass transition temperature (Tg) of 55 ° C., a melting point of 175 ° C., a carboxyl group concentration of 15 eq / ton, and a lactide content. Was 450 ppm. The results are summarized in Table 1.

[Production Example 2-1] Production of polylactic acid A1 Poly L-lactic acid (PLLA1) obtained in Production Example 1-1 and poly D-lactic acid (PDLA1) obtained in Production Example 1-2. 50 parts by mass of each and 0.03 part by mass of metal phosphate (“ADEKA STAB” NA-71 manufactured by ADEKA Corporation) were supplied from the first supply port of the biaxial kneader and melt-kneaded at a cylinder temperature of 245 ° C. . Furthermore, “Carbodilite” LA-1 manufactured by Nisshinbo Co., Ltd. is supplied from the second supply port at 0.3 parts by mass per 100 parts by mass of the total amount of poly-L-lactic acid and poly-D-lactic acid, and the vent pressure is 13.3 Pa. And kneaded while being evacuated. Next, it was extruded, cooled and pelletized to obtain polylactic acid A1.
In addition, titanium oxide (Ishihara Sangyo Co., Ltd. CR-63) was oxidized in the same manner as above except that it was supplied from the first supply port of the biaxial kneader so that its concentration was 60% by mass and mixed. Titanium-containing polylactic acid A1W was obtained. The characteristics of the obtained polylactic acid A1W were the same as that of polylactic acid A1 except that it contained titanium oxide.

[Production Example 2-2] Production of polylactic acid A2 Polylactic acid was obtained in the same manner as in Production Example 2-1 except that NA-71 and LA-1 were not added, and was designated as polylactic acid A2.
Table 2 summarizes the weight average molecular weight (Mw), carboxyl group concentration, lactide content, stereocomplex crystallinity (S), glass transition temperature (Tg), and crystal melting temperature of the obtained polylactic acid A2.
In addition, titanium oxide (Ishihara Sangyo Co., Ltd. CR-63) was oxidized in the same manner as above except that it was supplied from the first supply port of the biaxial kneader so that its concentration was 60% by mass and mixed. Titanium-containing polylactic acid A2W was obtained. The characteristics of the obtained polylactic acid A2W were the same as that of polylactic acid A2 except that it contained titanium oxide.

[Production Example 2-3] Production of polylactic acid A3 Poly-L-lactic acid (PLLA1) obtained in Production Example 1-1 was used as polylactic acid A3.
Moreover, in the said manufacture example 1-1, titanium oxide (Ishihara Sangyo Co., Ltd. CR-63) was supplied so that the density | concentration might be 60 mass%, and polylactic acid A3W containing titanium oxide was obtained. The characteristics of the obtained polylactic acid A3W were the same as that of polylactic acid A3 except that it contained titanium oxide.

[Examples 1 to 4]
Polylactic acid A1W in which titanium oxide (Ishihara Sangyo Co., Ltd. CR-63) as shown in Table 3 was mixed with polylactic acid A1 obtained by the operation of Production Example 2-1 was mixed as shown in Table 3. After being blended so as to have a titanium oxide concentration of 5% and dried at 110 ° C. for 5 hours, it was melt kneaded with an extruder at the melt extrusion temperature shown in Table 3, and a die having a lip opening degree shown in Table 3 Was melt-extruded into a film at a die temperature of 230 ° C., adhered to the surface of the cooling drum and solidified to obtain an unstretched film. The purity of titanium oxide was 97%, the specific gravity was 4.2, and the refractive index was 2.7.
Subsequently, the obtained unstretched film was stretched and heat-treated (100 seconds) under the film forming conditions shown in Table 3 to obtain a polylactic acid film. Table 3 shows the physical properties of the obtained polylactic acid film.

[Example 5]
A polylactic acid film was obtained in the same manner as in Example 1 using anatase type titanium oxide (Fuji Titanium Industry Co., Ltd. TA-200) instead of rutile type titanium oxide. Table 3 shows the physical properties of the obtained polylactic acid film. The average particle size of the anatase-type titanium oxide was 0.39 μm, the specific gravity was 3.9, and the refractive index was 2.52.

[Comparative Example 1]
A polylactic acid film was obtained in the same manner as in Example 1 except that silica (Nippon Catalyst, Seahoster KE-E30) was mixed instead of titanium oxide. In addition, the average particle diameter of the silica was 0.27 μm, the specific gravity was 2.1, and the refractive index was 1.45. Table 3 shows the physical properties of the obtained polylactic acid film.
The polylactic acid film obtained in Comparative Example 1 has a small apparent specific gravity, a low L value and whiteness, and a glossiness that is too high, which is insufficient as a white film for packaging and labels. It was.

[Comparative Examples 2 and 3]
Instead of polylactic acid A1 and A1W in Example 1, in Comparative Example 2, polylactic acid A3 and A3W obtained by the operation of Production Example 3 were used, and in Comparative Example 3, obtained by the operation of Production Example 2 above. A polylactic acid film was obtained in the same manner as in Example 1 except that polylactic acid A2 and A2W were used and the extrusion conditions and film forming conditions were as shown in Table 3. Table 3 shows the physical properties of the obtained polylactic acid film.
In Comparative Example 2, the film was melted and fractured at a heat setting temperature of 190 ° C., so that the film was formed at a heat setting temperature of 140 ° C.
In the polylactic acid film obtained in Comparative Example 2, the film was partially melted or greatly deformed by wrinkles, so that the 150 ° C. heat shrinkage rate could not be measured, and the thermal dimensional stability was low. there were. Moreover, it was inferior to printability.
The polylactic acid film obtained in Comparative Example 3 had a low stereocomplex crystallinity (S) and was inferior in thermal dimensional stability. Moreover, it was inferior to printability.

Claims (9)

It consists of a resin composition containing polylactic acid (component A) composed of a poly L-lactic acid component and a poly D-lactic acid component, and has a crystal melting peak at 190 ° C. or higher by differential scanning calorimetry (DSC) measurement. A white biaxially stretched polylactic acid film having a stereocomplex crystallinity (S) defined by the formula (i) of 90% or more,
L value calculated | required with a color difference meter is 85 or more,
A white biaxially stretched polylactic acid film having an apparent specific gravity exceeding 1.30 g / cm ³ .
S (%) = [ΔHms / (ΔHmh + ΔHms)] × 100 (i)
(However, ΔHms represents the crystal melting enthalpy (J / g) of the stereocomplex phase polylactic acid. ΔHmh represents the crystal melting enthalpy (J / g) of the homophase polylactic acid.)   2. The white biaxially stretched polylactic acid film according to claim 1, wherein the heat shrinkage in the longitudinal direction and the transverse direction when treated at 100 ° C. for 1 hour is 3% or less.   The white biaxially stretched polylactic acid film according to claim 1 or 2, comprising a stereogenic accelerator and / or a block forming agent.   The stereogenic accelerator is a metal phosphate, and the block former is at least one group selected from the group consisting of an epoxy group, an oxazoline group, an oxazine group, an isocyanate group, a ketene group and a carbodiimide group in the molecule. The white biaxially stretched polylactic acid film according to claim 3, which is a compound having at least one.   The white biaxially stretched polylactic acid film according to any one of claims 1 to 4, comprising particles having an average particle size of 0.1 µm to 5 µm in an amount of 3% by mass to 45% by mass.   The white biaxially stretched polylactic acid film according to claim 5, wherein the specific gravity of the particles is 2 or more.   The white biaxially stretched polylactic acid film according to claim 5 or 6, wherein the refractive index of the particles is 1.5 or more.   The average of the breaking strength in the longitudinal direction and the breaking strength in the transverse direction is 100 MPa or more, and the difference between the breaking strength in the longitudinal direction and the breaking strength in the transverse direction is 50 MPa or less. The white biaxially stretched polylactic acid film described.   The white biaxially stretched polylactic acid film according to any one of claims 1 to 8, which is used for packaging.