JP2013241504A - Polylactic resin composition and sheet composed of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polylactic resin composition which has excellent crystal performance, can be sufficiently crystallized at a high crystallization rate, even when it is molded into a sheet and a molded product is formed using the sheet, and thus can provide a molded product excellent in heat resistance and transparency; and a sheet composed of the polylactic resin composition.SOLUTION: A polylactic resin composition contains: a polylactic acid resin (A) having a D-body content of 1.0 mol% or less or 99.0 mol% or more; an adipate-based plasticizer (B); and a hydroxylic amide-based crystal nucleating agent (C). The content of the polylactic acid (A) in the resin composition is 85-99.4 mass%, the content of the adipate-based plasticizer (B) is 0.5-10 mass%, and the content of the hydroxylic amide-based crystal nucleating agent (C) is 0.1-5 mass%.

Description

  The main component of the present invention is a polylactic acid resin having a D-form content of 1.0 mol% or less, or 99.0 mol% or more, an adipic ester plasticizer, and an amide crystal nucleating agent having a hydroxyl group. And a sheet obtained from the polylactic acid resin composition.

  In recent years, biodegradable polymers that are decomposed by microorganisms and the like have attracted attention with increasing social demands for environmental protection. Specific examples of biodegradable polymers include aliphatic polyesters such as polybutylene succinate, polycaprolactone and polylactic acid, and aliphatic polyesters such as terephthalic acid / 1,4-butanediol / adipic acid copolymer and aromatic compounds. Examples include polyesters that can be injection-molded or extruded, such as polyesters obtained by copolymerization of group polyesters.

  Among the polyesters that can be injection molded or extruded as described above, the polylactic acid resin can be applied to a wide range of uses because it has excellent crystal performance and heat resistance is improved. Furthermore, since the polylactic acid resin is available at a relatively low cost, it is expected to be applied in a wide range as a biodegradable resin.

  However, when the polylactic acid resin is used alone, the crystal performance is insufficient. When using such polylactic acid resin with insufficient crystal performance, producing a sheet by subjecting it to extrusion molding, and thermoforming the sheet to obtain a molded body, the sheet can be obtained by extrusion molding. In the process of thermoforming the sheet, there is a problem that the crystallization of the polylactic acid resin does not proceed sufficiently. As a result, the obtained molded body is not sufficiently crystallized, and when it becomes 57 ° C. or higher, which is the glass transition temperature of the polylactic acid resin, it is thermally deformed and has poor heat resistance.

Therefore, there is a demand for a polylactic acid resin that can obtain a molded article having excellent heat resistance even when a molded body is obtained using the sheet after the sheet is molded as described above.
For example, a resin composition is obtained by adding a transparent nucleating agent such as an aliphatic carboxylic acid amide, an aliphatic carboxylate, an aliphatic alcohol, or an aliphatic carboxylic acid ester to an aliphatic polyester, and is obtained from this resin composition. There has been proposed a method in which a sheet is heat-treated during or after molding (Cited document 1).

  However, in this case, although the sheet before molding is highly transparent, the transparency may decrease due to crystallization after molding. In addition, the crystallization rate at the time of temperature rise is not sufficient, and the heat treatment time required for crystallization becomes long, so that there is a problem that the practicality is inferior.

  Further, a method is known in which a polylactic acid copolymer is added to a polylactic acid resin and crystallized by heating for a molding cycle time to produce a sheet having excellent transparency and heat resistance (Patent Document 2). Also, a method for producing a sheet having excellent transparency and heat resistance by adding a crystallization accelerator or an organic crystal nucleating agent to a polylactic acid-based polymer and controlling the size of the crystal to cause crystallization by heat treatment. Is known (Patent Document 3). However, in these cases, although the transparency is excellent, the crystallization rate is not sufficient, and therefore, there is a problem that the heat treatment is not sufficient for short time heat treatment and the heat resistance is poor.

  Furthermore, a polylactic acid resin composition having improved crystal performance by blending an adipic acid ester plasticizer and an amide crystal nucleating agent having a hydroxyl group into the polylactic acid resin has also been proposed (Patent Document 4). This resin composition has improved crystal performance, and after producing a sheet, it is possible to obtain a molded body having good moldability, excellent heat resistance and transparency even when a molded body is obtained using the sheet. Met.

  However, in recent years, there has been a demand for a polylactic acid-based resin composition that further shortens the molding cycle and improves the heat resistance of the resulting molded body, that is, has improved crystal performance.

JP 09-278991 A International Publication No. 2007/142106 Pamphlet International Publication No. 2006/121056 Pamphlet JP 2011-241347 A

  The present invention solves the above-mentioned problems, has excellent crystal performance, and after forming a sheet, even when a molded body is obtained using the sheet, the crystallization rate is sufficiently high. It is an object of the present invention to provide a polylactic acid resin composition that can be crystallized to obtain a molded article having excellent heat resistance and transparency. Furthermore, it aims at providing the sheet | seat which consists of this polylactic acid-type resin composition.

The inventors of the present invention have arrived at the present invention as a result of studies to solve the above problems.
That is, the present invention has a polylactic acid resin (A) having a D-form content of 1.0 mol% or less, or 99.0 mol% or more, an adipate ester plasticizer (B), and a hydroxyl group. A resin composition comprising an amide crystal nucleating agent (C), wherein the content of the polylactic acid resin (A) in the resin composition is 85 to 99.4% by mass, and an adipate ester plasticizer The polylactic acid resin composition, wherein the content of (B) is 0.5 to 10% by mass, and the content of the amide-based crystal nucleating agent (C) having a hydroxyl group is 0.1 to 5% by mass. Is a summary.

According to the present invention, since a polylactic acid resin having a D-form content in a specific range is used, the stereoregularity is improved and the crystal performance is excellent. And the polylactic acid-type resin composition of this invention further contains the adipic acid ester plasticizer (B) and the amide type crystal nucleating agent (C) which has a hydroxyl group in such a polylactic acid resin, Crystal performance is improved, and it becomes possible to obtain a molded article having good moldability, excellent heat resistance and transparency. In the present invention, as the polylactic acid resin, the resin composition of the present invention is further improved in crystal performance, heat resistance and moldability by using a polylactic acid resin whose residual lactide amount is 700 ppm or less by performing an acetone treatment. Will be improved.
The polylactic acid resin composition of the present invention can greatly expand the range of use of polylactic acid resin, which is a low environmental load material, and contribute to the saving of exhausted resources such as petroleum. Extremely expensive.

Hereinafter, the present invention will be described in detail.
The polylactic acid resin composition of the present invention (hereinafter sometimes simply referred to as “resin composition”) includes a polylactic acid resin (A), an adipate ester plasticizer (B), and an amide crystal nucleus having a hydroxyl group. Contains the agent (C).
First, the polylactic acid resin (A) will be described. The polylactic acid resin (A) in the present invention is required to have a D-form content of 1.0 mol% or less or a D-form content of 99.0 mol% or more. 0.1 to 0.6 mol%, or 99.4 to 99.9 mol% is preferable. When the D-form content is within this range, the crystal performance is excellent, so that the moldability is excellent (the molding cycle is shortened), and the obtained molded article has improved heat resistance.

  The D-form content of the polylactic acid resin (A) is, as will be described later in the examples, by converting all of the L lactic acid and D lactic acid obtained by decomposing the polylactic acid resin (A) to methyl ester, and the methyl ester of L lactic acid. And a methyl ester of D-lactic acid are calculated by a method of analyzing with a gas chromatography analyzer.

  As polylactic acid resin (A) used for this invention, polylactic acid of the range which D body content prescribes | regulates by this invention among various commercially available polylactic acid resins can be used. In addition, among lactides, which are cyclic dimers of lactic acid, L-lactide having a sufficiently low D-form content or D-lactide having a sufficiently low L-form content is used as a raw material, and a known melt polymerization method is used. Alternatively, those produced by further using a solid phase polymerization method can be used.

  The weight average molecular weight of the polylactic acid resin (A) used in the present invention is preferably 50,000 to 300,000, and the weight average molecular weight is preferably 100,000 to 300,000, more preferably 120,000 to 200,000. . When the weight average molecular weight is less than 50,000, it is difficult to obtain practical strength and durability. On the other hand, if the weight average molecular weight exceeds 300,000, fluidity is poor and melt extrusion may be difficult. When producing a film or the like, the pressurization of an extruder becomes a problem. The weight average molecular weight of the polylactic acid resin is calculated by a method of analysis by gel permeation chromatography (GPC) described later.

  And it is preferable that the polylactic acid resin (A) in this invention is acetone-treated and the amount of residual lactide is 700 ppm or less. Acetone treatment is to wash the polylactic acid resin with acetone, and the following method is preferred as the washing method with acetone. The mass ratio of the polylactic acid resin and acetone is 1: 1 to 1: 3, and stirring is performed for 30 minutes or more with a stirring blade or the like. In addition, the temperature at the time of stirring has the preferable range of 0 degreeC-60 degreeC, Especially, it is 10 degreeC-40 degreeC, More preferably, it is 20 degreeC-30 degreeC. When temperature exceeds 60 degreeC, since the boiling point of acetone is exceeded, volatilization of acetone becomes large. If the temperature is lower than 0 ° C., acetone must be cooled, which is disadvantageous in terms of cost. The stirring speed of the stirring blade is preferably 50 to 1000 rpm, more preferably 100 to 500 rpm, and more preferably 150 to 300 rpm. When it exceeds 1000 rpm, the stirring speed is too high, and the generation of dust increases due to the violent collision of the resins. When it is less than 50 rpm, the amount of lactide extracted into acetone decreases, and the treatment time becomes long.

  In general, other solvents such as methanol can be used to extract unreacted lactide in the polylactic acid resin, but in the present invention, acetone is used as a solvent to simultaneously extract unreacted lactide. It is also possible to improve the crystallization speed of the polylactic acid resin.

  Acetone is a relatively inexpensive solvent and is advantageous in terms of cost, and it is possible to extract not only lactide but also low molecular oligomers in polylactic acid resin. In addition, since lactic acid is not detected from the residue after the treatment, the extract is stable without being decomposed to become lactic acid, which is advantageous in terms of cost when considering the reuse of lactide. From these, it is presumed that the effect of improving the crystallization speed of the polylactic acid resin as described above occurs.

  When other solvent such as methanol is used instead of acetone, a large amount of lactic acid is detected from the residue. For this reason, when lactic acid remains in the resin, problems such as molecular weight reduction may occur during processing and storage, and such polylactic acid resin does not improve the crystallization rate.

  Further, as a method for removing unreacted lactide in the polylactic acid resin, a method of removing lactide by a single screw extruder, a twin screw extruder or the like is also common. However, even when lactide is removed by these methods, low molecular weight oligomers remain in the polylactic acid resin, and the resulting polylactic acid resin does not have a further improved crystallization rate.

  The polylactic acid resin (A) in the present invention is preferably subjected to the acetone treatment as described above so that the amount of residual lactide in the resin is preferably 700 ppm or less, particularly 500 ppm or less, more preferably 400 ppm or less. Is preferred. If the amount of residual lactide exceeds 700 ppm, the effect of improving the crystallization rate is small, and molecular weight reduction or coloring may occur during melt processing. Furthermore, when forming into a sheet | seat using a polylactic acid-type resin composition, since a lactide adheres to a cast roll and operativity may worsen, it is unpreferable.

  The amount of residual lactide of the polylactic acid resin (A) is measured and calculated as follows. First, 9 ml of methylene chloride and 1 ml of an internal standard solution (5000 ppm solution of 2,6-dimethyl-γ-pyrone) are added to 0.1 g of a sample to dissolve the polymer. 40 ml of cyclohexane is added to the polymer solution to precipitate the polymer. After filtration through an HPLC disk filter (pore size 0.45 μm), GC measurement is performed with a 7890A GC System manufactured by Agilent Technologies, and the lactide content is calculated.

  The content of the polylactic acid resin (A) in the polylactic acid resin composition of the present invention needs to be 85 to 99.4% by mass, and preferably 90 to 98% by mass. When the content of the polylactic acid resin (A) is less than 85% by mass, the content of the plasticizer and the crystal nucleating agent is excessively increased and the transparency, heat resistance, moldability and the like are deteriorated. On the other hand, if it exceeds 99.4% by mass, the plasticizer and crystal nucleating agent content decreases, so that the crystal performance is not improved and it takes time to crystallize, resulting in poor productivity. Sheets and molded articles obtained are inferior in heat resistance.

  In the present invention, the adipate ester plasticizer (B) is added for the purpose of increasing the crystallization rate of the polylactic acid resin (A) and maintaining transparency when the polylactic acid resin (A) is crystallized. To do. The adipic acid ester plasticizer (B) is a plasticizer excellent in compatibility with the polylactic acid resin (A). For this reason, when the adipic acid ester plasticizer (B) is used, the crystallization speed is faster than when other plasticizers are used, and the resulting molded article has excellent transparency. There is an advantage of becoming something.

  Examples of the adipate ester plasticizer (B) include bis [2- (2-methoxyethoxy) ethyl] adipate, bis (butyldiglycol) adipate, benzyl [2- (2-methoxyethoxy) ethyl] adipate, di- Examples include n-butyl adipate, dioctyl adipate, methyl diglycol butyl diglycol adipate, benzyl methyl glycol adipate, benzyl butyl diglycol adipate, and the like. Of these, bis [2- (2-methoxyethoxy) ethyl] adipate, bis (butyldiglycol) adipate, benzyl [2- (2-methoxyethoxy) ethyl] adipate are preferred from the viewpoint of compatibility with polylactic acid resin. Can be suitably used. These adipate ester plasticizers may be used alone or in combination.

  The content of the adipic acid ester plasticizer (B) in the polylactic acid-based resin composition needs to be 0.5 to 10% by mass, preferably 0.5 to 5% by mass, More preferably, it is 0.5-3 mass%. If the content is less than 0.5% by mass, the effect of promoting crystallization is poor. On the other hand, when the content exceeds 10% by mass, the adipic acid ester plasticizer (B) bleeds out on the surface of a molded article such as a sheet to be obtained. To do. Moreover, a viscosity may fall and it may become difficult to obtain a sheet | seat and a molded object.

  Furthermore, in the present invention, for the purpose of increasing the crystallization speed of the polylactic acid resin (A) and maintaining transparency when the polylactic acid resin is crystallized, an amide-based crystal nucleating agent (C) having a hydroxyl group is used. (Hereinafter, it may be simply referred to as “amide-based crystal nucleating agent (C)”) is required to be used together with the adipate-based plasticizer (B). The amide-based crystal nucleating agent (C) is a crystal nucleating agent having excellent compatibility with the polylactic acid resin (A). For this reason, when the amide-based crystal nucleating agent (C) is used, there is an advantage that transparency is higher than when other nucleating agents are used.

  Specific examples of the amide crystal nucleating agent (C) include the following compounds. N, N′-ethylene-bis-12-hydroxystearylamide, ricinoleic acid amide, ricinostearolic acid amide, hydroxystearic acid amide, N-hydroxyethyl-ricinoleic acid amide, N-hydroxyethyl-12-hydroxystearylamide N, N′-ethylene-bis-ricinoleic acid amide, N, N′-hexamethylene-bis-ricinoleic acid amide, N, N′-hexamethylene-bis-12-hydroxystearylamide, N, N′-xylylene -Bis-12-hydroxystearylamide and the like. Among these, N, N′-ethylene-bis-12-hydroxystearylamide, N, N′-hexamethylene-bis-ricinoleic acid amide, N, N′-hexa from the viewpoint of crystallization speed and transparency. Methylene-bis-12-hydroxystearylamide and N, N′-xylylene-bis-12-hydroxystearylamide can be suitably used. These amide crystal nucleating agents may be used alone or in combination of two or more.

  The content of the amide crystal nucleating agent (C) in the polylactic acid resin composition needs to be 0.1 to 5% by mass, preferably 0.5 to 3% by mass, More preferably, it is 5-2 mass%. If it is less than 0.1% by mass, the effect of promoting crystallization is poor. On the other hand, if it exceeds 5% by mass, the transparency is lowered and the cost is disadvantageous.

  In the present invention, the above-mentioned adipic acid ester plasticizer (B) is added to the polylactic acid resin (A) having a D-form content of 1.0 mol% or less or 99.0 mol% or more. By using the amide-based crystal nucleating agent (C) in combination, the crystal performance of the polylactic acid resin (A) can be remarkably improved, and a molded product excellent in heat resistance and transparency can be obtained. An effect is produced. As the combination of the adipic acid ester plasticizer (B) and the amide crystal nucleating agent (C), the adipic acid ester plasticizer (B) and the aliphatic amide compound (C) having a hydroxyl group are particularly preferable. The combination of-(2-methoxyethoxy) ethyl] adipate and N, N'-ethylene-bis-12-hydroxystearylamide is most preferred. The reason why this combination is preferable is that the compatibility of both the polylactic acid resins (A) is particularly good, and the polylactic acid resin (A) is plasticized with the adipic acid ester plasticizer (B). This is presumably because the amide-based crystal nucleating agent (C) acts effectively in the resin.

  In order to further promote the crystal performance of the polylactic acid resin, the polylactic acid resin composition of the present invention includes a crystal nucleating agent other than the amide-based crystal nucleating agent (C) as long as the effects of the present invention are not impaired. It is also possible to blend. Examples of such crystal nucleating agents include organic crystal nucleating agents and inorganic crystal nucleating agents. Organic crystal nucleating agents include erucic acid amide, stearic acid amide, oleic acid amide, ethylene bis stearic acid amide, ethylene bis oleic acid amide, ethylene bis lauric acid amide and the like; tricyclohexyl trimesic acid amide, tricyclo Examples thereof include aromatic amides such as hexyl trimellitic acid amide, tricyclohexyl hemimeric acid amide, merophanic acid amide, prenitric acid amide, and pyromellitic acid amide. Examples of the inorganic crystal nucleating agent include layered silicates such as talc, smectite, mica, vermiculite, and swellable fluorine mica.

  In the present invention, in order to further accelerate the crystallization rate of the polylactic acid resin (A), a crosslinking agent may be used in combination as necessary to crosslink the polylactic acid resin (A).

  Examples of the crosslinking agent include (meth) acrylic acid ester compounds, silane compounds, polyhydric anhydrides, epoxy compounds, isocyanate compounds, organic peroxides, metal complexes, and the like. These crosslinking agents can be used alone or in combination of two or more.

  Organic peroxides include n-butyl-4,4-bis-t-butylperoxyvalerate, dicumyl peroxide, di-t-butyl peroxide, di-t-hexyl peroxide, 2,5- Examples include dimethyl-2,5-di (t-butylperoxy) hexane and t-butylperoxy-2-ethylhexyl monocarbonate. In addition, since an organic peroxide decomposes | disassembles and is consumed at the time of mixing with resin, it may not remain | survive in the obtained polylactic acid-type resin composition. Examples of the metal complex include lithium formate, sodium methoxide, potassium propionate, and magnesium ethoxide.

  The content of the crosslinking agent is preferably 0.01 to 1.0% by mass in the polylactic acid resin composition from the viewpoint of transparency and processability to a sheet, and 0.01 to 0 More preferably, it is 1% by mass.

  From the viewpoint of improving durability, the polylactic acid resin composition of the present invention may contain at least one terminal blocker selected from the group consisting of a carbodiimide compound, an epoxy compound and an oxazoline compound. The blending amount of the end-capping agent in the polylactic acid-based resin composition is preferably in the range of 0.01 to 10% by mass, in the range of 0.1 to 5% by mass in order not to inhibit the crystallization rate. More preferably.

  In addition, the thermoplastic resin composition of the present invention, within a range that does not greatly impair the properties, pigments, heat stabilizers, antioxidants, weathering agents, light resistance agents, flame retardants, plasticizers, lubricants, mold release agents, Antistatic agents, fillers and the like can be added. Examples of heat stabilizers and antioxidants include hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, alkali metal halides, and vitamin E. As the flame retardant, a halogen-based flame retardant, a phosphorus-based flame retardant, and an inorganic flame retardant can be used. However, in consideration of the environment, it is desirable to use a non-halogen flame retardant. Non-halogen flame retardants include phosphorus flame retardants, hydrated metal compounds (aluminum hydroxide and magnesium hydroxide), N-containing compounds (melamine and guanidine), and inorganic compounds (borate and Mo compounds). It is done. Inorganic fillers include talc, calcium carbonate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, calcium aluminate, sodium aluminosilicate, magnesium silicate, glass balloon, carbon black, Examples thereof include zinc oxide, antimony trioxide, zeolite, hydrotalcite, metal fiber, metal whisker, ceramic whisker, potassium titanate, boron nitride, graphite, and carbon fiber. Examples of the organic filler include naturally occurring polymers such as starch, cellulose fine particles, wood flour, okara, fir shell, bran, and modified products thereof. In addition, the method of mixing these with the resin composition of this invention is not specifically limited.

The polylactic acid-based resin composition of the present invention containing the components as described above is excellent in crystal performance. Among them, after being melted to a melting point or higher by a differential scanning calorimeter, the temperature drop is 500 ° C./min. was cooled to 0 ℃ at a rate, after cooling, it is heated to 75 ° C. at a heating rate of 500 ° C. / min, the time t _max to exothermic peak of isothermal crystallization curve when holding the 75 ° C. exhibits a peak-top It is preferable that 75 is 2 minutes or less. In the resin composition of the present invention, when t _max 75 exceeds 2 minutes, the crystallization rate is too slow, so that the practicality of the molding process tends to be inferior.
Among these, t _max 75 is more preferably 1.6 minutes or less, and most preferably 1.0 minute or less.

The method for measuring t _max 75 in the present invention will be described in more detail. A differential scanning calorimeter (manufactured by Perkin Elmer, DSC device “DSC7”) is used, and 7 mg of a polylactic acid resin composition is heated from 20 ° C. to 250 ° C. at a temperature rising rate of 500 ° C./min. After holding at 5 ° C. for 5 minutes, the temperature is lowered from 250 ° C. to 0 ° C. at a rate of temperature reduction of 500 ° C./min to 0 ° C. and held for 5 minutes. Furthermore, it heats from 0 degreeC to 75 degreeC with the temperature increase rate of 500 degreeC / min, Time _tmax75 until the exothermic peak of an isothermal crystallization curve when it hold | maintains at 75 degreeC shows a peak top is measured.

  As a method for obtaining the polylactic acid resin composition of the present invention, a polylactic acid resin (A), an adipic acid ester plasticizer (B), and an amide crystal nucleating agent (C) are obtained by a known method such as melt kneading. ) Is kneaded. In melt kneading, a general kneader such as a single screw extruder, a twin screw extruder, a roll kneader, or a Brabender can be used, but in order to improve the dispersibility of each component with respect to the polylactic acid resin, It is preferable to use a twin screw extruder.

  As described above, in the method of obtaining a polylactic acid resin composition by melt-kneading, the polylactic acid resin (A) and the amide crystal nucleating agent (C) may be dry blended and charged from a hopper, The amide crystal nucleating agent (C) may be supplied from the middle of the extruder using a feeder or the like. In addition, since the adipic acid ester plasticizer (B) is liquid at room temperature, a method of supplying it from the middle of kneading using a heating quantitative liquid feeding device or the like is more preferable. Thereafter, the obtained polylactic acid-based resin composition is taken up in a strand shape and cooled, and then cut into a pellet shape to obtain a pellet of the polylactic acid-based resin composition.

  And the sheet | seat of this invention is formed with the polylactic acid-type resin composition of this invention. For example, it can be obtained by extruding the polylactic acid resin composition obtained as described above into a sheet shape.

  The manufacturing method of the sheet | seat of this invention is not specifically limited, For example, a T-die method, an inflation method, a calendar method etc. are mentioned. Among these, from the viewpoint of versatility, a T-die method in which a material is melt-kneaded and extruded using a T-die is preferable.

  When the sheet of the present invention is produced by the T-die method, a resin composition is prepared by kneading a polylactic acid resin, an adipic acid ester plasticizer, and an amide crystal nucleating agent in advance by a known method such as melt kneading. It is preferable to obtain a product and supply the pelletized product of the resin composition to a molding machine. Moreover, you may produce a sheet | seat using the masterbatch pellet which contains an adipic ester plasticizer and an amide type crystal nucleating agent beforehand in large quantities.

  An example of the manufacturing method of the sheet | seat of this invention is shown below. For example, the resin composition (pellet) of the present invention is supplied to a hopper of a single screw extruder or a twin screw extruder, and the twin screw extruder has, for example, a cylinder temperature of 180 to 230 ° C and a T die temperature of 200 to 230 ° C. , The resin composition is melt-kneaded, extruded, and cooled with a cast roll to obtain a sheet. The temperature of the cast roll when cooling the sheet is preferably in the temperature range of 20 to 70 ° C, and more preferably 30 to 50 ° C. When the cast roll temperature is lower than 20 ° C., the polylactic acid monomer adheres to the cast roll and becomes a stain on the sheet, which is not preferable. Further, when the cast roll temperature exceeds 70 ° C., the temperature becomes equal to or higher than the glass transition temperature of polylactic acid, so that cooling is insufficient and a stable sheet cannot be obtained.

  The thickness of the sheet is not particularly limited, and may be set as appropriate depending on the application and required performance. Generally, a thickness of about 80 to 500 μm is appropriate.

  The sheet of the present invention can be formed into various molded products by further molding. For example, it can be used for various containers and trays such as sterilization containers, containers that pour hot water, retort containers, containers that can be used in microwave ovens, lunch boxes, etc. In addition, container lids, blister packs, clear cases, etc. that require further transparency are included.

  The method for forming the sheet of the present invention is not particularly limited, but from the viewpoint of versatility, any one of vacuum forming, pressure forming, vacuum pressure forming, and press forming is preferable. is there. Prior to the forming process, the sheet is preferably heated with a hot plate or hot air. In the hot plate method, since the sheet and the hot plate are in direct contact, the surface state of the hot plate may be transferred to the sheet and impair the transparency of the molded product. preferable.

  A specific example of the method for heating the sheet will be described below. First, in a range of (glass transition temperature of polylactic acid resin composition + 20) ° C. to (glass transition temperature of polylactic acid resin composition + 60) ° C., the sheet is heated with a hot plate or hot air for 10 to 60 seconds, The sheet is softened and additionally partly crystallized. Then, it shape | molds by the method of a vacuum or a compressed air. At this time, if the heating temperature is too low or the heating time is too short, softening is insufficient and shaping cannot be performed. On the other hand, if the heating temperature is too high or the heating time is too long, the crystallization of the sheet proceeds too much, and the formability deteriorates.

  The mold temperature during the molding process may be set below the glass transition temperature of the polylactic acid resin composition and released immediately after molding, but the mold temperature is substantially reduced to the polylactic acid resin. It is preferable to crystallize in the mold within the range of 80 to 130 ° C., which is the temperature at which the composition is most easily crystallized, and more preferable to crystallize at 90 to 120 ° C. When the mold temperature exceeds 130 ° C., the crystallization speed of the polylactic acid resin becomes extremely slow, and the crystal may melt because it approaches the melting point of the polylactic acid resin. It may take time to obtain the rigidity required for delay and mold release. On the other hand, when the mold temperature is less than 80 ° C., crystallization is slow, an uncrystallized portion remains, and heat resistance may be insufficient.

  The time required for molding (molding cycle) is preferably 5 to 60 seconds. In order to improve the molding efficiency, it is practical to use a shorter molding cycle. However, if the molding cycle is less than 5 seconds, crystallization may be incomplete and heat resistance may be poor. On the other hand, when the molding cycle exceeds 60 seconds, the time is too long, which is disadvantageous in terms of cost.

Hereinafter, the present invention will be described more specifically with reference to examples.
<material>
Polylactic acid resin (A)
(A-1) Toyota Motor Corporation S-6 D-form content = 0.2 mol% Residual lactide content = 1100 ppm Weight average molecular weight = 150,000
(A-2) (A-1) was subjected to acetone treatment as follows to obtain (A-2). Measurement was performed so that the mass ratio of (A-1) to acetone was 1: 2, acetone was added to (A-1), and the mixture was stirred at 150 rpm for 1 hour under room temperature conditions. Thereafter, the mixture was filtered and vacuum-dried at 70 ° C. for 24 hours (using Yamato Vacuum dry DP61) to remove acetone, thereby obtaining a polylactic acid resin (A-2). The amount of residual lactide of the obtained (A-2) was 400 ppm.
(A-3) Toyota Motor Co., Ltd. A-1 D body content = 0.6 mol% Residual lactide content = 1020 ppm Weight average molecular weight = 170000
(A-4) The same acetone treatment as when (A-2) was obtained for (A-3) was performed to obtain a polylactic acid resin (A-4). The amount of residual lactide of the obtained (A-4) was 280 ppm.
(A-5) Nature Works 4032D D-form content = 1.2 mol% Residual lactide content = 2000 ppm Weight average molecular weight = 16000

Adipic acid ester plasticizer (B)
(B-1) DAIFATTY-101 (benzyl [2- (2-methoxyethoxy) ethyl] adipate manufactured by Daihachi Chemical Co., Ltd.)
(B-2) BXA (bis (butyldiglycol) adipate) manufactured by Daihachi Chemical Co., Ltd.
Other plasticizers (B-3) Rikenmar PL-019 (glycerin diacetomonocaprylate) manufactured by Riken Vitamin
(B-4) ATBC (tributyl acetylcitrate) manufactured by Taoka Chemical Co., Ltd.

Amide crystal nucleating agent having a hydroxyl group (C)
(C-1) ASA T-530SF (N, N′-ethylene-bis-12-hydroxystearylamide) manufactured by Ito Oil Co., Ltd.
(C-2) ITOHWAX J-630 (N, N′-hexamethylene-bis-12-hydroxystearylamide) manufactured by Ito Oil Co., Ltd.
Other crystal nucleating agents (C-3) Nippon Kasei Co., Ltd. SLIPAX L (Ethylenebislauric acid amide)
(C-4) Alfro H50S (ethylenebisstearic acid amide) manufactured by NOF Corporation

<Characteristic value and evaluation method>
-Residual lactide amount of polylactic acid resin (A) It measured by the said method.
-Mass average molecular weight (Mw) of polylactic acid resin (A)
Using a gel permeation chromatography device (manufactured by Shimadzu Corporation) equipped with a differential refractive index detector (manufactured by Shimadzu Corporation, trade name “RID-10A”), tetrahydrofuran (THF) as an eluent and a flow rate of 1.0 ml / min. , Measured at 40 ° C. As columns, SHODEX KF-805L and KF-804L (manufactured by Showa Denko KK) were used. The sample was dissolved in 0.5 ml of chloroform after dissolving 10 mg of the resin composition, diluted with 5 ml of THF, filtered through a 0.45 μm filter, and then used for measurement. The molecular weight was converted using polystyrene (manufactured by Waters) as a standard sample.

-D-form content of polylactic acid resin (A) Polylactic acid resin is added to 6 mL of 1N potassium hydroxide / methanol solution, and after sufficiently stirring at 65 ° C, 450 μL of sulfuric acid is added and stirred at 65 ° C. Polylactic acid was decomposed. 5 mL of this sample, 3 mL of pure water, and 13 mL of methylene chloride were mixed and shaken. After stationary separation, about 1.5 mL of the lower organic layer was collected, filtered through an HPLC disk filter having a pore size of 0.45 μm, and then subjected to GC measurement using HP-6890 Series GC system manufactured by Hewlett Packard. The ratio (%) of the peak area of D-lactic acid methyl ester in the total peak area of lactate methyl ester was calculated, and this was used as the D-form content (%).
-T _max 75 of polylactic acid resin composition
It was measured and calculated by the method described above.

-Sheet forming processability The forming processability was evaluated according to the following criteria for the presence or absence of deformation at the time of mold release when obtaining a molded article and the shape of the obtained molded article.
○: The shape of the mold was clearly transferred to the molded body, and was not deformed during release.
Δ: The shape of the mold is not clearly transferred to the molded body.
X: The shape of the mold was not clearly transferred to the molded body, and there was deformation at the time of mold release.
・ Molded body crystallization index X
A part of the obtained molded body (container) is cut out to obtain a sample. Then, using a differential scanning calorimeter (DSC device “DSC7”, manufactured by Perkin Elmer Co., Ltd.), 7 mg of the molded product was heated from 20 ° C. to 200 ° C. at a rate of temperature increase of 20 ° C./min. The amount of heat (ΔHc) and the amount of heat of crystal melting (ΔHm) are measured, and the crystallization index X is calculated by the following formula.
Crystallization index X = | ΔHm | − | ΔHc | (J / g)

-Molded body heat resistance 50 ml of water was put into the obtained molded body (container), the surface was sealed with a wrapping film for food packaging, and heated in a 500 W microwave oven for 2 minutes. The container was filled with water before and after heating the molded body (container), the volume of the water was measured, and the volume change rate before and after heating was calculated as follows.
Volume change rate (%) = [(Volume before heat treatment−Volume after heat treatment) / Volume before heat treatment] × 100
And it evaluated in four steps as follows with the volume change rate.
A: Volume change rate is less than 3%.
○: Volume change rate is 3% or more and less than 7%.
Δ: Volume change rate is 7% or more and less than 15%.
X: Volume change rate 15% or more.

-Transparency The haze value (%) was measured for the obtained sheet and the obtained molded body (bottom center part) with a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., model number: NDH2000). And transparency was evaluated in the following four steps by haze value.
A: Haze value is less than 10%.
○: Haze value is 10% or more and less than 15%.
Δ: Haze value is 15% or more and less than 25%.
X: Haze value is 25% or more.

Example 1
Using a twin-screw extruder (TEM37BS type manufactured by Toshiba Machine Co., Ltd.), the polylactic acid resin (A-1) and the amide-based crystal nucleating agent (C-1) having a hydroxyl group are extruded so as to have the ratio shown in Table 1. From the root supply port. Since the adipate plasticizer (B-1) is a liquid, it is supplied from the root supply port of the extruder to the ratio shown in Table 1 using a liquid injection pump, barrel temperature 200 ° C., screw rotation speed 200 rpm. The mixture was melt-kneaded under a discharge rate of 15 kg / h. The molten resin discharged from the tip of the extruder is drawn in a strand shape, passed through a vat filled with cooling water, cooled and solidified, and then cut into a pellet shape to obtain a polylactic acid resin composition (pellet-shaped one). Obtained.
Thereafter, the obtained polylactic acid-based resin composition was vacuum-dried at 60 ° C. for 40 hours, and from a T-die at an extrusion temperature of 215 ° C. using a single screw extruder (manufactured by Nippon Steel Co., Ltd., “P50-22A”). It was melt-extruded and adhered to a cast roll set at 30 ° C. to obtain a sheet having a thickness of 300 μm.
The obtained sheet was supplied to a continuous vacuum / pressure forming machine (FLPD-141-W type manufactured by Asano Laboratory), preheating temperature 250 ° C., preheating time 10 seconds, mold temperature 110 ° C., mold holding time 30 seconds. Molding was performed to obtain a food bowl type container (opening inner diameter = 150 mm, bottom inner diameter = 60 mm, container drawing ratio (L / D) = 0.5).

Examples 2-34
A sheet was obtained in the same manner as in Example 1 except that the types and contents of the polylactic acid resin, the adipic acid ester plasticizer, and the amide crystal nucleating agent having a hydroxyl group were changed as shown in Table 1. And the molded object was obtained from the sheet | seat obtained like Example 1. FIG.

Examples 35, 37, 39
A sheet was obtained using the polylactic acid resin composition of Example 3 in the same manner as in Example 3. And the molded object was obtained like Example 3 except having changed the metal mold | die holding time at the time of shaping | molding the obtained sheet | seat into 5 seconds, 10 seconds, and 15 seconds.

Examples 36, 38, 40
Using the polylactic acid resin composition of Example 20, a sheet was obtained in the same manner as in Example 20. And the molded object was obtained like Example 20 except having changed the metal mold | die holding time at the time of shaping | molding the obtained sheet | seat into 5 seconds, 10 seconds, and 15 seconds.

Comparative Examples 1-26
A sheet was obtained in the same manner as in Example 1 except that the types and contents of the polylactic acid resin, the plasticizer, and the crystal nucleating agent were changed as shown in Table 3. And the molded object was obtained from the sheet | seat obtained like Example 1. FIG.

  The characteristic value and evaluation result of the polylactic acid-type resin composition, sheet | seat, and molded object which were obtained in Examples 1-40 and Comparative Examples 1-26 are shown to Tables 1-3.

As is clear from Table 1, the resin compositions obtained in Examples 1 to 40 were excellent in crystallinity, and therefore t _max 75 was 2 minutes or less, and the crystallization rate was high. Further, the obtained sheet was excellent in transparency. And it was excellent in the moldability at the time of obtaining a molded object from a sheet | seat, the value of the crystallization index | exponent X was high, fully crystallized, and the molded object excellent in both heat resistance and transparency was able to be obtained. Among them, the resin composition obtained by using acetone treatment and using a polylactic acid resin (A-2 or A-4) having a residual lactide amount of 400 ppm or less has improved crystallinity, so that it is crystallized. It was possible to obtain a sheet and a molded body having a higher speed and superior heat resistance.
Further, as is apparent from Table 2, in Examples 35 to 40, the resin composition of Example 3 or Example 20 was used and the mold holding time when the container was molded was shortened. The molding processability, transparency and heat resistance of the product were excellent.

  On the other hand, as is clear from Table 3, since the resin compositions obtained in Comparative Examples 1 to 6 were those using a polylactic acid resin having a D-form content of 1.2 mol%, adipic acid ester series Even when a plasticizer and an amide crystal nucleating agent having a hydroxyl group were added, the crystal performance was inferior (crystallization rate was slow). For this reason, the obtained molded object was not fully crystallized and was inferior in heat resistance.

  The resin compositions obtained in Comparative Examples 7 to 12 were those using a polylactic acid resin having a D-form content of 0.2 mol%, but adipic ester plasticizers and amide crystals having hydroxyl groups. Since neither or one of the nucleating agents was blended, the crystal performance was inferior (the crystallization rate was slow). For this reason, the obtained molded object was not fully crystallized and was inferior in heat resistance.

  The resin composition obtained in Comparative Example 13 had a small amount of adipic ester plasticizer, and the resin composition obtained in Comparative Example 15 had a small amount of amide crystal nucleating agent. Both were inferior in crystal performance (slow crystallization rate). For this reason, the obtained molded object was not fully crystallized and was inferior in heat resistance.

  In the resin composition obtained in Comparative Example 14, the amount of adipic acid ester plasticizer was too large, so that the viscosity was lowered and the sheet was drawn down when producing a sheet, and a satisfactory sheet could be obtained. There wasn't. For this reason, no evaluation was performed.

  The resin composition obtained in Comparative Example 16 was excellent in crystallinity because the compounding amount of the amide crystal nucleating agent was too large, but both the obtained sheet and molded product were inferior in transparency. .

In the resin compositions obtained in Comparative Examples 17 to 26, the combination of the plasticizer and the crystal nucleating agent was not the combination of the adipic acid ester plasticizer and the amide crystal nucleating agent having a hydroxyl group defined in the present invention. The crystal performance was inferior (crystallization speed was slow) or the transparency was lowered. For this reason, the obtained sheet | seat and molded object were inferior to transparency and heat resistance.

Claims (3)

A polylactic acid resin (A) having a D-form content of 1.0 mol% or less, or 99.0 mol% or more, an adipic ester plasticizer (B), and an amide crystal nucleating agent having a hydroxyl group ( C), wherein the content of the polylactic acid resin (A) in the resin composition is 85 to 99.4% by mass, and the content of the adipic ester plasticizer (B) Is 0.5 to 10% by mass, and the content of the amide-based crystal nucleating agent (C) having a hydroxyl group is 0.1 to 5% by mass. The polylactic acid resin composition according to claim 1, wherein the polylactic acid resin (A) has been subjected to an acetone treatment, and the amount of residual lactide is 700 ppm or less. A sheet formed of the polylactic acid resin composition according to claim 1.