JP6953220B2 - Method for manufacturing polylactic acid-based stretched sheet, method for manufacturing polylactic acid-based stretched sheet, and secondary molded product - Google Patents

Description

The present invention relates to a method for producing a polylactic acid-based stretched sheet, a method for producing a polylactic acid-based stretched sheet, and a method for producing a secondary molded product.

In recent years, it has been recognized by general consumers that the use of plastic products containing various biodegradable polymers is preferable from the viewpoint of environmental protection and the use of plant-derived raw materials from the viewpoint of saving petroleum resources. As a result, attempts to use biodegradable polymers and plant-derived polymers as raw materials have been widely made in industrial products.

In particular, polylactic acid is a polymer derived from a plant and having biodegradability, and polylactic acid, which is a crystalline polymer, can be imparted with heat resistance by stretch-oriented crystallization. For example, Patent Documents 1 to 3 and the like propose a polylactic acid-based stretched sheet, a method for producing the same, and a molded product obtained by molding the polylactic acid-based stretched sheet.

In Patent Document 1, the surface orientation of the polylactic acid-based stretched sheet is adjusted to a specific range in order to obtain a secondary processed product having excellent impact resistance, transparency and moisture heat resistance from the polylactic acid-based stretched sheet. Further, a technique for adjusting the relationship between the calorific value of crystal melting ΔHm and the calorific value of crystallization ΔHc of the polylactic acid-based stretched sheet so as to be a specific relationship, that is, the relative crystallization degree to 70% or more is disclosed.

Patent Document 2 describes a polylactic resin unstretched film in order to obtain a polylactic resin film having less thickness unevenness, excellent flatness, and less variation in mechanical characteristics and optical characteristics in the longitudinal and lateral directions. In the method for producing a biaxially stretched polylactic acid resin film by in this order leading to a longitudinal stretching step, a transverse stretching step, a heat treatment step, and a relaxation treatment step, a cooling step between the transverse stretching step and the heat treatment step, a heat treatment step, A technique for adjusting temperature conditions such as a relaxation treatment step to a specific range is disclosed.

Further, in Patent Document 3, in order to obtain a polylactic acid-based stretched sheet having a good balance of practical impact resistance and moldability and also having good heat resistance and transparency, and a molded product obtained by molding the polylactic acid-based stretched sheet. In addition, the average values of the plane orientation (ΔP) and the orientation relaxation stress (ORS) in the longitudinal direction and the width direction of the polylactic acid-based stretched sheet containing the methacrylate-based resin in the polylactic acid-based resin are adjusted to a specific range. The technology is disclosed.

Japanese Unexamined Patent Publication No. 09-025345 Japanese Unexamined Patent Publication No. 2013-305263 Japanese Unexamined Patent Publication No. 2010-270183

However, good secondary molded products cannot be obtained from the polylactic acid-based stretched sheets obtained under the conditions disclosed in Patent Documents 1 to 3 and the like, or the obtained secondary molded products are not available. A polylactic acid-based stretched sheet, which is inferior in transparency and heat resistance and has excellent secondary moldability, has not been developed.

In view of the above circumstances, the subject of the present invention is a method for producing a polylactic acid-based stretched sheet capable of molding a secondary molded product having excellent transparency and heat resistance, a polylactic acid-based stretched sheet obtained from the manufacturing method, and a polylactic acid-based stretched sheet obtained from the manufacturing method. It provides a method for manufacturing a secondary molded product.

As a result of diligent studies to solve the above problems, the present inventors have melt-extruded the polylactic acid-based resin into a sheet, and then stretched the polylactic acid-based resin in a specific direction in the flow direction (MD) and the direction perpendicular to the flow direction (TD). We have found that it is possible to provide a method for producing a polylactic acid-based stretched sheet that can solve the above problems by stretching under magnification and temperature conditions and performing crystallization heat treatment, and have completed the present invention.
That is, the present invention is as follows.

[1] After melt-extruding a polylactic acid-based resin into a sheet, the sheet is stretched in a flow direction (MD) and a direction (TD) orthogonal to the flow direction (MD), and further heat-treated to crystallize. a method of manufacturing a polylactic acid stretched sheet, the stretch ratio in the perpendicular direction _{(TD) (X} TD) is, the draw ratio _{(X MD)} greater than the flow direction (MD), said flow direction (MD) the stretching temperature for stretching in the _{(T MD)} is that 60 to 120 ° C., the stretching temperature for stretching in the orthogonal direction _{(TD) (T} TD) is the stretching temperature _{(T MD)} lower than the draw ratio _{(X TD} ), using the draw ratio _{(X MD), (X MD} +0. 8) times _~ (X MD +1. 4) times ranging der is, the flow direction (MD) and the perpendicular direction (TD) after stretched, further, heat-treated at a temperature in the range of 80 ° C. to 120 ° C. Ru is crystallized polylactic acid production method of the stretched sheet.

[2] The stretching ratio (X _MD ) in the flow direction (MD) is 1.5 to 3.5 times, and the stretching ratio (X _TD ) in the orthogonal direction (TD) is 2. The method for producing a polylactic acid-based stretched sheet according to the above [1], which is 3 to 4.5 times.
[3] The method for producing a polylactic acid-based stretched sheet according to the above [1] or [2], wherein the polylactic acid-based stretched sheet is stretched in the flow direction (MD) and then in the orthogonal direction (TD).

[4] The draw ratio _{(X TD)} is, by using the draw ratio _{(X MD), (X MD} +1.0) times _~ (X MD +1.4) area by der times, the [1] The method for producing a polylactic acid-based stretched sheet according to any one of [3].

[5] The average value of birefringence of in-plane orientation measured at a plurality of points in the orthogonal direction (TD) of the polylactic acid-based stretched sheet is 1.0 × ^10-2 or less. 4] The method for producing a polylactic acid-based stretched sheet according to any one of the items.
[6] When the amount of heat of crystal melting ΔHm when the temperature of the polylactic acid-based stretched sheet is raised and the amount of heat of crystallization ΔHc generated by crystallization during the temperature rise are defined as {(ΔHm−ΔHc) / ΔHm × 100} The method for producing a polylactic acid-based stretched sheet according to any one of [1] to [5] above, wherein the relative crystallization degree Wc calculated in 1) is 90% or more.
[7] The method for producing a polylactic acid-based stretched sheet according to any one of [1] to [6] above, wherein the polylactic acid-based resin has an optical purity of 90 mol% or more of L-form polylactic acid.

[8] A polylactic acid-based stretched sheet obtained from the production method according to any one of the above [1] to [7].
[9] A method for producing a secondary molded product, wherein the polylactic acid-based stretched sheet according to the above [8] is secondary molded at 100 to 120 ° C.

By the method for producing a polylactic acid-based stretched sheet of the present invention, a polylactic acid-based stretched sheet capable of molding a secondary molded product having excellent transparency and heat resistance can be obtained. To manufacture secondary molded products of various general-purpose packages such as lids, trays, food packs, blister packs, other various packs, and cases of containers such as food packaging containers by the method for producing secondary molded products of the present invention. Can be done.

Hereinafter, the present invention will be described in detail.

In the present invention, a polylactic acid-based resin is melt-extruded into a sheet, then stretched in a sheet flow direction (MD) and in a direction perpendicular to the flow direction (MD) (TD), and further heat-treated to crystallize. This is a method for producing a polylactic acid-based stretched sheet.

The polylactic acid-based resin used in the present invention is a polymer containing 85% by mass or more of lactic acid monomer unit, and may contain 95% by mass or more of lactic acid monomer unit, and may contain 95% by mass or more of lactic acid monomer unit. May be contained in an amount of 98% by mass or more. The polylactic acid-based resin contains polylactic acid, a copolymer of lactic acid and other hydroxycarboxylic acids, aliphatic ring esters, dicarboxylic acids, diols, or a lactic acid monomer unit in an amount of 85% by mass or more. It may be a composition of a polymer. Polylactic acid-based resins are hydrolyzed by water in the environment to reduce their molecular weight, and can be finally decomposed into carbon dioxide and water by microorganisms and the like.

In the polylactic acid-based resin used in the present invention, lactic acid can be used by mixing L-form lactic acid and D-form lactic acid, but from the viewpoint of excellent heat resistance of the obtained stretched sheet, L-form lactic acid and L-form lactic acid can be used. It is preferably composed of one of the isomers of D-form lactic acid, and specifically, the D-form content (the molar ratio of D-form lactic acid to the total mass of lactic acid used as a raw material) is 10 mol% or less. Alternatively, 90 mol% or more is preferable, and 5.0 mol% or less or 95 mol% or more is more preferable. The optical purity of the L-form polylactic acid is more preferably 90 mol% or more, and particularly preferably 95 mol% or more.

The method for producing the polylactic acid-based resin used in the present invention is not particularly limited, and various polymerization methods, for example, a direct polymerization method from lactic acid, a ring-opening polymerization method via lactide, and the like can be used. .. Moreover, a commercially available polylactic acid resin can be used. Further, for the purpose of adjusting various physical properties of the obtained sheet and molded product, organic and / or inorganic particles, plasticizers, colorants, pigments and the like may be added in advance to the polylactic acid-based resin and then sheeted by the method described below. good.

After melt-extruding the polylactic acid resin into a sheet, the unstretched sheet is biaxially stretched. This stretching can be performed by existing stretching sheet manufacturing methods such as an inflation method, a simultaneous biaxial stretching method, and a sequential biaxial stretching method, but simultaneous biaxial stretching is possible in that processing with excellent thickness accuracy is possible. The method or the sequential biaxial stretching method is preferable. The simultaneous biaxial stretching method is excellent in that the orientation balance in the sheet surface can be easily controlled and the birefringence can be reduced, but in the present invention, it is easy to control the orientation state of the sheet having both moldability and heat resistance. In addition, the sequential biaxial stretching method is preferable because the film forming speed can be increased and the productivity is excellent. When the sequential biaxial stretching method is performed, the sheet extruded from the T-die is electrostatically applied onto a metal cooling roll to bring it into close contact with the metal cooling roll to obtain an unstretched sheet, and the flow direction of the sheet (MD) is obtained by using the peripheral speed difference of the heating roll. ), Then the sheet is gripped with a clip and stretched in the direction orthogonal to the flow direction (MD) (TD) in the tenter, and the heat treatment is performed with the clip gripped in the width direction. The sequential biaxial stretching method is preferably used.

After melt-extruding the polylactic acid resin into a sheet, the sheet stretched in the flow direction (MD) of the sheet and in the direction orthogonal to the flow direction (MD) (TD) is not sufficiently crystallized. be. Since the uncrystallized sheet has poor heat resistance and is inferior in practicality, the sheet stretched in the flow direction (MD) and the orthogonal direction (TD) is further heat-treated to crystallize. By heat-treating and crystallizing after stretching, a polylactic acid-based stretched sheet having excellent mechanical strength and heat resistance can be obtained.

The polylactic acid stretched sheet production method of the present invention, the stretching ratio of the perpendicular direction (TD) is, the greater than the stretch ratio in the flow direction (MD) (X _MD), extending in the flow direction (MD) stretching temperature _{(T MD)} is that 60 to 120 ° C., lower than the stretching temperature _{(T TD)} is the stretching temperature for stretching in the orthogonal direction _{(TD) (T MD).}

In order to be more excellent secondary formability of polylactic acid stretched sheet, the stretch ratio in the perpendicular direction _(TD) (X TD) using the stretching ratio in the flow direction _{(MD) (X MD),} ( X _MD +0.3) times _~ (X MD +1.8) in the range of _times, more preferably in the range of times (X MD +0.6) times _{~ (X MD +1.6), (} X MD It is particularly preferable that the range is +0.8) times to (X _{MD +1.4) times.}

In a stretched sheet using a crystalline polymer, heat resistance is imparted by stretching the sheet in the flow direction (MD) and / or the orthogonal direction (TD) and then heat-treating it to crystallize it. At this time, crystallization occurs. By doing so, the phase difference may be amplified and the phase difference value (birefringence value) may increase. The polylactic acid stretched sheet production method of the present invention, by setting lower than the stretching temperature for stretching (T _MD) in the stretching temperature for stretching in the orthogonal direction _(TD) (T TD) the flow direction (MD), It was found that the value of the phase difference (birefringence) can be controlled low even if it is crystallized.

The stretching temperature for stretching in the flow direction _{(MD) (T} MD) is more preferably 65 to 110 ° C., particularly preferably 70 to 100 ° C..

Stretch ratio in the stretching ratio in the flow direction _(MD) (X MD) and the perpendicular direction _(TD) (X TD) is those satisfying the above conditions, the crystallization of subsequent heat treatment and sufficient, excellent mechanical strength, in order to better polylactic acid stretched sheet to the secondary formability, in particular, from the viewpoint of preventing whitening of the sheet by the crystallization, the draw ratio in the flow direction _(MD) (X MD) is It is preferably 1.5 times to 3.5 times, more preferably 1.6 times to 3.4 times, particularly preferably 1.7 times to 3.3 times, and the orthogonal direction ( The draw ratio ( _{XTD) of TD} ) is preferably 1.8 to 5.3 times, more preferably 2.0 to 4.8 times, and 2.2 to 4.3 times. Is particularly preferable.

The heat treatment after stretching in the flow direction (MD) and the orthogonal direction (TD) is not limited as long as the necessary crystallization proceeds. In order to ensure sufficient crystallization, the heat treatment temperature for crystallization is preferably in the range of the glass transition point (Tg) + 10 ° C. or higher and the melting point (Tm) or less of the polylactic acid-based resin, and the glass transition. The point (Tg) may be + 20 ° C. or higher, the glass transition point (Tg) may be + 30 ° C. or higher, the glass transition point (Tg) may be + 40 ° C. or higher, and the melting point (Tm) -10 ° C. It may be less than or equal to, and may be in the range of melting point (Tm) −20 ° or less.

In the method for producing a polylactic acid-based stretched sheet of the present invention, the sheet is stretched in the flow direction (MD) of the sheet, then stretched in the direction orthogonal to the flow direction (MD) of the sheet (TD), and then for crystallization. When heat treatment is performed at a relatively high temperature, which is optimal for crystallization, heat may flow from the crystallization heat treatment zone into the stretching treatment zone, and the sheet thickness may be disturbed, resulting in crystallization. _{The stretching temperature (TTD} ) for stretching in the orthogonal direction (TD) immediately before the heat treatment _{is lower than the stretching temperature (TMD} ), and it may be difficult to set it stably. Therefore, from the viewpoint of quality stability of the polylactic acid-based stretched sheet, the heat treatment temperature for crystallization is preferably set lower than the optimum temperature for crystallization, and is used for specific crystallization. The heat treatment temperature is preferably 70 ° C. to 130 ° C., more preferably 80 ° C. to 120 ° C., and particularly preferably 90 ° C. to 110 ° C.

The birefringence of the in-plane orientation of the polylactic acid-based stretched sheet obtained by the production method of the present invention can be reduced even though the polylactic acid-based stretched sheet is sufficiently crystallized, and can be reduced in the orthogonal direction ( The average value of the birefringence of the in-plane orientation measured at a plurality of points in TD) ^{can be 1.0 × 10-2} or less. Here, the "average value of birefringence of in-plane orientation measured at a plurality of points in the orthogonal direction (TD)" is the direction perpendicular to the sheet flow direction (MD) (TD), excluding the clip portions at both ends. When a plurality of measurement points are set evenly and light is incident on those measurement points perpendicularly to the sheet surface to measure the birefringence of the in-plane orientation, the average value of the birefringence of the multiple in-plane orientations is measured. To say. The birefringence of the in-plane orientation of the stretched sheet is relatively homogeneous in the sheet flow direction (MD), whereas the birefringence of the in-plane orientation perpendicular to the sheet flow direction (MD) (TD). Since the distribution of refraction is a value of birefringence such that the central part is recessed and draws an arc, it is necessary to make such a definition.

When the heat of crystal melting ΔHm when the temperature of the polylactic acid-based stretched sheet obtained by the production method of the present invention is raised and the amount of heat of crystallization ΔHc generated by crystallization during the temperature rise are defined as {(ΔHm−ΔHc) / The relative crystallinity Wc calculated by ΔHm × 100} is preferably 90% or more, more preferably 95% or more, and particularly preferably 98% or more.

The thickness of the polylactic acid-based stretched sheet obtained by the production method of the present invention is not particularly limited, but is easy to handle when the molded product is secondarily processed, and the strength and transparency of the molded product. From the viewpoint of the above, it is preferable that the range is in the range of 70 to 500 μm, and more preferably 100 to 300 μm.

The polylactic acid-based stretched sheet obtained by the production method of the present invention can be secondarily molded at 100 to 120 ° C., and the birefringence of the in-plane orientation of the polylactic acid-based stretched sheet is small. By being stretched evenly, high-quality secondary molding is possible, and a molded product having excellent appearance and transparency can be obtained without contact marks on the hot plate.

Further, when the surface of the polylactic acid-based stretched sheet obtained by the production method of the present invention is coated with a surfactant or the like in order to impart antistatic properties, anti-fog properties, etc., at least the polylactic acid-based stretched sheet is used. An aqueous solution of a surfactant or the like adjusted to an appropriate concentration is applied to one surface by various methods such as a squeeze roll coater, an air knife coater, a knife coater, a spray coater, a gravure roll coater, and a bar coater, and then applied. Dry the aqueous solution. Further, from the viewpoint of improving the uniformity of the coating film, it is preferable to apply a surfactant or the like by the above method after corona-treating the sheet surface. The strength of the corona treatment is preferably adjusted so that the contact angle of the sheet with water is 80 to 30 °, and more preferably 70 to 35 °. The preferable upper limit of the contact angle between the surface of the sheet and water is a value for improving the uniformity of the coating film, and the lower limit of the preferable contact angle is a value for preventing blocking when the sheet is rolled into a roll. Is.

The polylactic acid-based stretched sheet obtained by the production method of the present invention can be formed into a molded product by thermoforming. As the thermoforming method, a hot plate contact heat forming method, a vacuum forming method, a vacuum compressed air forming method, a plug assist forming method and the like are preferably used. The hot plate contact heat molding method is particularly preferable from the viewpoint of the uniformity of the thickness of the molded body and the production efficiency of the molded body, but when transparency is particularly important, the vacuum forming method by indirect heating or the vacuum pressure air forming method is used. Further, when performing deep drawing molding, it is also possible to adopt a plug assist molding method.

Hereinafter, the present invention will be described in more detail with reference to Examples. The present invention should not be limited to the scope of these examples.

For polylactic acid-based stretched sheets, tensile strength, tensile elongation, elastic modulus, glass transition point (Tg), melting point (Tm), calorific value of crystallization (ΔHc), calorific value of crystal melting (ΔHm), relative crystallinity, in-plane The average value of the double refraction of the orientation was measured by the following method.

(1) Tensile test Tensile strength: Measurement was performed using Shimadzu Autograph "AG-IS MS type" manufactured by Shimadzu Corporation in an atmosphere of 23 ° C. and 50% Rh. According to JIS K 7127, the sample was cut into a length of 175 mm and a width of 10 mm (test piece type 1B) in the measurement direction and measured at a tensile speed of 10 mm / min.
Tensile elongation: Measurement was performed using a Shimadzu autograph "AG-IS MS type" manufactured by Shimadzu Corporation in an atmosphere of 23 ° C. and 50% Rh. According to JIS K 7127, the sample was cut into a length of 175 mm and a width of 10 mm (test piece type 1B) in the measurement direction and measured at a tensile speed of 10 mm / min.
Elastic modulus: Measurement was performed using a Shimadzu autograph "AG-IS MS type" manufactured by Shimadzu Corporation in an atmosphere of 23 ° C. and 50% Rh. The sample was cut out to a length of 200 mm and a width of 10 mm (test piece type 2) in the measurement direction according to JIS K 7127, and the measurement was performed at a tensile speed of 10 mm / min.

(2) Transition temperature measurement According to JIS-K7121, a differential scanning calorimeter (DSC-60 manufactured by Shimadzu Corporation) is used to measure about 10 mg of a sample from 30 ° C to 200 ° C, a temperature rise rate of 10 ° C / min, and nitrogen. The temperature was raised under the condition of a gas flow rate of 50 ml / min. The glass transition point (Tg) [° C.] was determined from the DSC curve drawn thereby, and the melting point (Tm) [° C.] was determined from the crystal melting endothermic peak.

(3) Measurement of transition heat According to JIS-K7122, a differential scanning calorimeter (DSC-60 manufactured by Shimadzu Corporation) is used to measure about 10 mg of a sample from 30 ° C to 200 ° C at a heating rate of 10 ° C / min and nitrogen. The temperature was raised under the condition of a gas flow rate of 50 ml / min. The crystallization heat quantity (ΔHc) [J / g] is obtained from the crystallization heat generation peak area at the time of temperature rise in the DSC curve drawn thereby, and the crystal melting heat quantity (ΔHm) [J / g] is obtained from the crystal melting heat absorption peak area. The relative crystallinity was calculated from the following formula (5).
Relative crystallinity = (ΔHm−ΔHc) × 100 / ΔHm [%] ・ ・ ・ (5)

(4) Birefringence Polylactic acid-based stretched sheets of Examples 1 to 9 and Comparative Examples 1 to 6 (in Example 1, the width in the direction orthogonal to the sheet flow direction (MD) (TD) is 560 mm (clip portion). (Including))), the remaining width (500 mm in Example 1) excluding the clip portions at both ends was cut out in a plurality of evaluation samples having a width of 35 mm and a length of 35 mm continuously in the orthogonal direction (TD). , Oji Measuring Instruments Co., Ltd. "KOBRA-21D type" is used to inject light perpendicularly to the sheet surface to measure the birefringence of the in-plane orientation of each evaluation sample, and in the orthogonal direction (TD). The average value of 3 different points, 4 points in the orthogonal direction (TD), and a total of 3 × 4 points = 12 points was obtained as the “average value of birefringence of in-plane orientation”.

<Preparation of polylactic acid-based stretched sheet>
[Example 1]
A polylactic acid-based resin (PLA polymer manufactured by Nature Works, 4032D, D-form content of about 1.5%) was extruded into a sheet from a T-die at 210 ° C. using a single-screw extruder having a diameter of φ50 mm. The extruded sheet was rapidly cooled with a cooling roll at about 60 ° C. to obtain an unstretched sheet. The unstretched sheet had a thickness of 1.2 mm and a width of 300 mm.

The obtained unstretched sheet was reheated to a sheet temperature of 80 ° C. (actual temperature) by using a temperature control roll of about 60 ° C. and an infrared heater in combination, and then the sheet was formed by the difference in peripheral speed between the rolls. It was stretched 2.0 times in the flow direction (MD). Next, the sheet was stretched 3.0 times at a sheet temperature of 70 ° C. in a direction orthogonal to the sheet flow direction (MD) with a tenter, and then heat-treated at 110 ° C. for 38 seconds to obtain a poly sheet having a sheet thickness of 200 μm. A lactic acid-based stretched sheet (Example 1) was obtained. After stretching 2.0 times in the flow direction (MD), the thickness of the sheet was 0.6 mm and the width was about 175 mm. After stretching 3.0 times in the orthogonal direction (TD), the thickness of the sheet was 0.2 mm, and the width was about 560 mm including the clip portion.

[Example 2]
A polylactic acid-based stretched sheet (Example 2) was obtained in the same manner as in Example 1 except that the stretching ratio in the orthogonal direction (TD) was changed to 2.5 times.

[Example 3]
A polylactic acid-based stretched sheet (Example 3) was obtained in the same manner as in Example 1 except that the stretching ratio in the orthogonal direction (TD) was changed to 3.2 times.

[Example 4]
A polylactic acid-based stretched sheet (Example 4) was obtained in the same manner as in Example 1 except that the stretching ratio in the orthogonal direction (TD) was changed to 3.5 times.

[Example 5]
Polylactic acid-based stretch sheet (Example 5) in the same manner as in Example 1 except that the stretch ratio in the flow direction (MD) was changed to 3.0 times and the stretch ratio in the orthogonal direction (TD) was changed to 4.0 times. Got

Table 1 shows the production conditions, the average value of birefringence of in-plane orientation, and the evaluation results of the sheet physical characteristics of the polylactic acid-based stretched sheets of Examples 1 to 5.

[Example 6]
The polylactic acid-based stretched sheet (Example 6) was the same as in Example 1 except that the polylactic acid-based resin used was changed to a PLA polymer manufactured by Nature Works (2003D, D-form content of about 4.5%). Got

[Example 7]
A polylactic acid-based stretched sheet (Example 7) was obtained in the same manner as in Example 1 except that the polylactic acid-based resin used was changed to a PLA polymer (2500 HP, D-form content of 1% or less) manufactured by Nature Works. rice field.

[Comparative Example 1]
Polylactic acid-based stretched sheet (Comparative Example 1) in the same manner as in Example 1 except that the stretching ratio in the flow direction (MD) was changed to 2.5 times and the stretching ratio in the orthogonal direction (TD) was changed to 2.5 times. Got

[Comparative Example 2]
Polylactic acid-based stretched sheet (Comparative Example 2) in the same manner as in Example 6 except that the stretching ratio in the flow direction (MD) was changed to 2.5 times and the stretching ratio in the orthogonal direction (TD) was changed to 2.5 times. Got

[Comparative Example 3]
Polylactic acid-based stretched sheet (Comparative Example 3) in the same manner as in Example 7 except that the stretching ratio in the flow direction (MD) was changed to 2.5 times and the stretching ratio in the orthogonal direction (TD) was changed to 2.5 times. Got

Table 2 shows the production conditions, the average value of birefringence of in-plane orientation, and the evaluation results of the sheet physical characteristics of the polylactic acid-based stretched sheets of Examples 6 to 7 and Comparative Examples 1 to 3.

[Example 8]
A polylactic acid-based stretched sheet (Example 8) was obtained in the same manner as in Example 1 except that the sheet temperature during stretching in the flow direction (MD) was changed to 90 ° C.

[Example 9]
A polylactic acid-based stretched sheet (Example 9) was obtained in the same manner as in Example 1 except that the sheet temperature during stretching in the flow direction (MD) was changed to 120 ° C.

[Comparative Example 4]
A polylactic acid-based stretched sheet (Comparative Example 4) was obtained in the same manner as in Example 1 except that the sheet temperature during stretching in the flow direction (MD) was changed to 60 ° C.

[Comparative Example 5]
A polylactic acid-based stretched sheet (Comparative Example 5) was obtained in the same manner as in Example 1 except that the sheet temperature during stretching in the flow direction (MD) was changed to 130 ° C.

[Comparative Example 6]
After stretching in the flow direction (MD) and the orthogonal direction (TD), the heat treatment at 110 ° C. for 38 seconds was changed to the heat treatment at 70 ° C. for 38 seconds in the same manner as in Example 1, and the polylactic acid-based stretched sheet was obtained. (Comparative Example 6) was obtained.

Table 3 shows the production conditions, the average value of birefringence of in-plane orientation, and the evaluation results of the sheet physical characteristics of the polylactic acid-based stretched sheets of Examples 8 to 9 and Comparative Examples 4 to 6.

The polylactic acid-based stretched sheets of Examples 1 to 9 have a small average value of birefringence of in-plane orientation, whereas the polylactic acid-based stretched sheets of Comparative Examples 1 to 5 have an average value of birefringence of in-plane orientation. It was big.

The polylactic acid-based stretched sheets of Examples 1 to 9 have small anisotropy of tensile strength, tensile elongation and elastic modulus in the flow direction (MD) and the orthogonal direction (TD), whereas the polylactic acid-based stretched sheets are comparative examples. The polylactic acid-based stretched sheets 1 to 5 had large anisotropy of tensile strength, tensile elongation and elastic modulus in the flow direction (MD) and the orthogonal direction (TD).

The relative crystallinity of the polylactic acid-based stretched sheets of Examples 1, 6 to 7 and Comparative Examples 1 to 3 was 100%, whereas the relative crystallization of the polylactic acid-based stretched sheet of Comparative Example 6 was performed. The degree was 32.4%.

The melting points (Tm) of the polylactic acid-based stretched sheets of Comparative Examples 1 to 3 of Examples 1 and 6 to 7 were all in the range of 148.3 ° C. to 177.6 ° C. The glass transition points (Tg) of the polylactic acid-based stretched sheets of Comparative Examples 1 to 3 of Examples 1 and 6 to 7 were all in the range of 66.6 ° C. to 78.6 ° C.

<Manufacturing secondary molded products>
[Examples 10 to 18, Comparative Examples 7 to 12]
(Evaluation of secondary moldability)
The polylactic acid-based stretched sheet obtained in Examples 1 to 9 was heated and softened to a sheet temperature of 110 ° C., a vacuum was created between the mold and the sheet, and the sheet was brought into close contact with the mold by compressed air pressure to a depth of 40 mm. Secondary molding was performed in a container (strawberry pack) having an opening of 150 mm × 100 mm (Examples 10 to 18).

From the polylactic acid-based stretched sheets having a sheet thickness of 200 μm in Examples 1 to 4 and 6 to 9, a strawberry pack having a thickness of about 150 μm could be secondarily formed at the bottom portion. From the polylactic acid-based stretched sheet having a sheet thickness of 120 μm in Example 5, a strawberry pack having a thickness of about 90 μm could be secondarily formed at the bottom portion.

From the polylactic acid-based stretched sheets of Examples 1 and 5 to 8, the sheet was not torn due to compressed air, the sheet stretched uniformly, and a molded product having a uniform thickness was produced, and the mold reproducibility was good (◯).
The strawberry pack made of the polylactic acid-based stretched sheet of Example 3 did not tear the sheet due to compressed air, but the uniformity of the elongation of the sheet decreased, and the mold reproducibility of the corner portion was slightly poor (○ △).
The strawberry pack made of the polylactic acid-based stretched sheets of Examples 2, 4 and 9 did not tear the sheet due to compressed air, but the sheet was slightly unevenly stretched and the thickness of the molded product was slightly uneven (Δ). ).

From the polylactic acid-based stretched sheets of Comparative Examples 1 to 5, the elongation of the sheet became non-uniform, the sheet was torn due to compressed air during the secondary molding, and the strawberry pack could not be secondary molded (×: comparison). Examples 7-11).

In the polylactic acid-based stretched sheet of Comparative Example 6 which did not undergo the crystallization heat treatment step, the evaluation of the secondary moldability was good (◯), but whitening occurred and the transparency was difficult (Comparative Example). 12).

Similarly, using the polylactic acid-based stretched sheet obtained in Examples 1 to 9, a container having a depth of 30 m, an opening of 100 mm × 100 mm, and a drawing ratio of 0.3 was secondarily molded.

Similar to the strawberry pack, secondary molding could not be performed from the polylactic acid-based stretched sheets of Comparative Examples 1 to 5.

The polylactic acid-based stretched sheet of Comparative Example 6 could be secondarily molded in the same manner as the strawberry pack, but whitening occurred and transparency was difficult.

The secondary moldability was evaluated according to the following evaluation criteria, and the results are shown in Tables 1 to 3.

● Results of secondary moldability ○: There is no sheet tearing due to compressed air during secondary molding, the sheet stretches uniformly, a molded product with uniform thickness can be produced, and mold reproducibility is good.
○ △: There is no sheet tear due to compressed air during secondary molding, but the uniformity of sheet elongation is reduced and the mold reproducibility at the corners is slightly poor.
Δ: The sheet is not torn due to compressed air during secondary molding, but the elongation of the sheet is non-uniform and the thickness of the molded product is slightly poor.
X: The elongation of the sheet becomes non-uniform, and the sheet is torn due to compressed air during secondary molding, so that molding cannot be performed.

(Evaluation of heat resistance of secondary molded products)
Deformation of the secondary molded products (strawberry packs) obtained in Examples 10 to 18 and Comparative Example 12 from the polylactic acid-based stretched sheets of Examples 1 to 9 and Comparative Example 6 when left at 60 ° C. for 1 hour. The degree was evaluated according to the following evaluation criteria, and the results are shown in Tables 1 to 3.

● About heat resistance evaluation ◎: There is almost no deformation.
×: Deformed and does not retain its original shape.
XX: Cannot be evaluated because the sheet was torn and could not be molded.

The strawberry packs secondarily molded using the polylactic acid-based stretched sheets obtained in Examples 1 to 9 showed almost no deformation even when left at 60 ° C. for 1 hour (⊚), but the poly obtained in Comparative Example 6 was obtained. The strawberry pack that was secondarily molded using the lactic acid-based stretched sheet was deformed to the extent that it did not retain its original shape (x).

Claims (9)

After melt-extruding a polylactic acid resin into a sheet, the polylactic acid resin is stretched in the flow direction (MD) of the sheet and in the direction orthogonal to the flow direction (MD) (TD), and further heat-treated to crystallize. A method for manufacturing a stretched sheet.
The stretching ratio (X _TD ) in the orthogonal direction (TD) is larger than the stretching ratio (X _{MD) in the flow direction (MD).}
The stretching temperature for stretching in the flow direction _{(MD) (T} MD) is that 60 to 120 ° C., the stretching temperature for stretching in the orthogonal direction _{(TD) (T} TD) is the stretching temperature _{(T MD)} lower than,
The draw ratio _{(X TD)} is, by using the draw ratio _{(X MD), (X MD} +0. 8) times _~ (X MD +1. 4) times ranging der is,
Wherein after stretching in the flow direction (MD) and the perpendicular direction (TD), further, heat-treated at a temperature in the range of 80 ° C. to 120 ° C. Ru is crystallized polylactic acid production method of the stretched sheet. The stretching ratio (X _MD ) in the flow direction (MD) is 1.5 to 3.5 times, and the stretching ratio (X _TD ) in the orthogonal direction (TD) is 2. The method for producing a polylactic acid-based stretched sheet according to claim 1, which is 3 to 4.5 times. The method for producing a polylactic acid-based stretched sheet according to claim 1 or 2, wherein the polylactic acid-based stretched sheet is stretched in the flow direction (MD) and then in the orthogonal direction (TD). The draw ratio _{(X TD)} is, by using the draw ratio _{(X MD), (X MD} +1.0) times _~ (X MD +1.4) area by der times, more of claims 1 to 3 The method for producing a polylactic acid-based stretched sheet according to item 1. Any one of claims 1 to 4, wherein the average value of the birefringence of the in-plane orientation measured at a plurality of points in the orthogonal direction (TD) of the polylactic acid-based stretched sheet is 1.0 × ^{10-2 or less.} The method for producing a polylactic acid-based stretched sheet according to the section. When the heat of crystal melting ΔHm when the temperature of the polylactic acid-based stretched sheet is raised and the amount of heat of crystallization ΔHc generated by crystallization during the temperature rise are taken, it is calculated as {(ΔHm−ΔHc) / ΔHm × 100}. The method for producing a polylactic acid-based stretched sheet according to any one of claims 1 to 5, wherein the relative crystallization degree Wc is 90% or more. The method for producing a polylactic acid-based stretched sheet according to any one of claims 1 to 6, wherein the polylactic acid-based resin has an optical purity of 90 mol% or more of L-form polylactic acid. A polylactic acid-based stretched sheet obtained from the production method according to any one of claims 1 to 7. A method for producing a secondary molded product, wherein the polylactic acid-based stretched sheet according to claim 8 is secondary molded at 100 to 120 ° C.