JP2001162676A - Polylactic acid molding and its molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a biodegradable molding excellent in heat resistance and impact resistance. SOLUTION: A polylactic acid molding is molded by a method in which a polylactic acid sheet having a degree of surface orientation (ΔP) of 3.0×10-3 to 30×10-3 is heated in advance to a temperature between the glass transition temperature (Tg) of the polymer and Tg+50 deg.C and then is molded and heat- treated at a temperature between the crystallization temperature (Tc) of the polymer -20 deg.C and the melting point (Tm) of the polymer -20 deg.C while being kept in contact with a heating mold and cooled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a biodegradable container and a molded article having excellent heat resistance and a method for molding the same.

[0002]

2. Description of the Related Art Containers containing various foods such as blister products and natto, which are used for display packaging of various products, etc., are made of a material having excellent transparency so that the products inside can be seen through for display purposes. In addition, a material having excellent heat resistance that does not deform due to the environment during transportation or storage is required.
Therefore, as a material for a blister product, a sheet of polyvinyl chloride, polyethylene terephthalate, polystyrene, polypropylene, polycarbonate, or the like has been used according to the intended use. However, since these sheets are chemically stable and have no biodegradability, when left in a natural environment, they remain and accumulate without being substantially decomposed. Therefore, they not only scatter in the natural environment and pollute the living environment of animals and plants,
There is a problem that even if buried as garbage, it is hardly decomposed and remains in the ground, immediately saturating the capacity of the garbage disposal site. Therefore, a biodegradable material that does not cause such a problem is required, and much research and development has been performed. Polylactic acid is known as one of the biodegradable materials. Japanese Patent Application Laid-Open No. 6-122148 discloses that L which is excellent in transparency and moldability by vacuum suction, pressurized air or vacuum pressurized air using a transparent L-lactic acid-based polymer sheet having an L-lactic acid-based polymer content of 75% or more. -A method for obtaining a lactic acid-based polymer molded article is disclosed. However, a molded article made of a conventional polylactic acid-based polymer has insufficient strength and impact resistance, and has problems such as holes during handling. In addition, the moisture and heat resistance is insufficient, and the transportation, storage,
When placed in a high-temperature, high-humidity environment at the time of use, a so-called whitening occurs in which the molded product is deformed or the transparent molded product is whitened. JP-A-9-25345 discloses that the degree of plane orientation (ΔP) is 3.0 × 10 ⁻³ to 30 × 10 ⁻³ ,
The difference (ΔHm−ΔHc) between the heat of crystal fusion (ΔHm) when the sheet is heated and the heat of crystallization (ΔHc) generated by crystallization during the temperature rise is 20 J / g or more; (△ H
Molded articles having excellent impact resistance and transparency obtained by thermoforming an oriented polylactic acid-based sheet having m- {Hc) / {Hm} of 0.75 or more are disclosed. It was not yet satisfactory in terms of gender.

[0003]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above problems, and is a biodegradable molded article excellent in impact resistance and heat resistance, particularly a container for a blister pack and a container for foods. The purpose is to obtain.

[0004]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems, and as a result, completed the present invention. That is, in one embodiment of the method for molding a polylactic acid-based polymer of the present invention, the degree of plane orientation (ΔP) is 3.0 × 10 ^{−3 to} 3 × 3.
A sheet of a polylactic acid-based polymer having a ^particle size of 0 × 10 ⁻³ and a glass transition temperature (Tg) of the polylactic acid-based polymer equal to or higher than (Tg)
+ 50 ° C.) or less, and then kept in contact with a heating mold {the crystallization temperature (Tc) of the polylactic acid-based polymer −20 ° C.) or more, {the polylactic acid-based polymer The molding and the heat treatment are performed at a temperature in the range of not more than the melting point (Tm) of −20 ° C., and thereafter, cooling is performed.
In another embodiment of the method for molding a polylactic acid polymer of the present invention, a sheet of a polylactic acid polymer having a degree of plane orientation (ΔP) of 3.0 × 10 ⁻³ to 30 × 10 ⁻³ is used. After preheating the polylactic acid-based polymer to a temperature in the range of not less than the glass transition temperature (Tg) and not more than (Tg + 50 ° C.), it is molded along a heating mold by pressurized air, and the obtained molded article is heated. Crystallization temperature of the polylactic acid-based polymer (Tc)
−20 ° C. or higher, melting point (Tm) of the polylactic acid-based polymer
After performing heat treatment at a temperature in the range of −20 ° C. or less, and then fitting the cooling mold having a shape substantially corresponding to the heating mold,
It is characterized in that the molded article is transferred to the cooling mold by blowing compressed air from the heating mold side and cooled while contacting the cooling mold. The molded article of the polylactic acid-based polymer of the present invention has an impact resistance of 80 kgf · mm or more and a heat resistance of 5% in volume shrinkage when dried in a hot air drier at 80 ° C. for 20 minutes. It is characterized by the following. A molded article of the polylactic acid-based polymer of the present invention is produced by using the above-mentioned molding method. Here, the molded article of the polylactic acid-based polymer can be used as a food container of the polylactic acid-based polymer.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. In the molding method of the present invention, the sheet of the polylactic acid-based polymer is preheated to a predetermined temperature, and then heated (for example, female).
The sheet is brought into contact with, for example, compressed air, subjected to heat molding and heat treatment, and then cooled and molded. The cooling method is not particularly limited. For example, after heat molding and heat treatment, a corresponding cooling mold (for example, a male mold) is fitted to the heating mold via the sheet, and then the sheet is transferred to the cooling mold. It can be cooled and molded along.

The polylactic acid-based polymer used in the present invention is:
It is a polylactic acid or a copolymer of lactic acid and another hydroxycarboxylic acid, or a mixture of these polymers, and may be mixed with other polymer materials as long as the effects of the present invention are not impaired. In addition, additives such as plasticizers, lubricants, inorganic fillers, ultraviolet absorbers and the like, modifiers and the like can be added for the purpose of adjusting the moldability and the physical properties of sheets and molded articles. Lactic acid includes L-lactic acid, D-lactic acid or a mixture thereof, and other hydroxycarboxylic acids include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, and 4-hydroxyvaleric acid. Representative examples include folic acid and 6-hydroxycaproic acid.

As these polymerization methods, any known methods such as a condensation polymerization method and a ring-opening polymerization method can be employed, and a small amount of a chain extender such as diisocyanate is used for the purpose of increasing the molecular weight. Chain extenders such as compounds, epoxy compounds and acid anhydrides can be used.
The weight average molecular weight (Mw) of the polylactic acid-based polymer is 50,
The range of 000 to 1,000,000 is preferred. When the weight average molecular weight is 50,000 or more, practically usable physical properties can be exhibited.
If it is not more than 000, no problems such as the sheet strength being unable to be maintained during thermoforming will not occur, and the melt viscosity will not be too high and the molding processability will not be inferior.

The polylactic acid-based polymer sheet used in the present invention is obtained by drying the polylactic acid-based polymer sufficiently to remove water, and then subjecting the sheet to general melt molding such as extrusion, calendering, and pressing. It is obtained by forming into a sheet by the method and then quenching. Practically, it is preferable that the polymer melt-extruded into a sheet is rapidly cooled by contact with a rotating casting drum (cooling drum).
The temperature of the casting drum is suitably 60 ° C. or less. If the temperature of the casting drum is higher than 60 ° C., the polylactic acid-based polymer sheet sticks to the casting drum, making it difficult to wind up the sheet, and promotes crystallization to develop spherulites and reduce transparency. At the same time, thermoforming becomes difficult. Accordingly, it is preferable that the sheet is rapidly cooled by being brought into contact with a casting drum at a temperature of 60 ° C. or lower, so that a substantially amorphous sheet is obtained.

In the present invention, in order to greatly improve the inherent brittleness of the polylactic acid-based polymer and improve the impact resistance of the molded article, the degree of plane orientation of the sheet of the polylactic acid-based polymer (△ P) is adjusted to 3.0 × 10 ⁻³ to 30 × 10 ⁻³ . The plane orientation degree (△ P) represents the degree of orientation in the plane direction with respect to the thickness direction of the sheet, and is usually calculated by measuring the refractive indices (α, β, γ) in orthogonal three-axis directions and according to a predetermined formula described later. . By setting the plane orientation degree (ΔP) to 3.0 × 10 ⁻³ or more, the impact resistance is remarkably improved, and the non-oriented sheet is mainly generated when exposed to a high-temperature and high-humidity atmosphere. Embrittlement and whitening caused by spherulite growth can be prevented. Note that the upper limit of the plane orientation degree (実 際 P) is practically about 30 × 10 ^−3.
If the ratio is increased, stretching becomes unstable or impossible. Even if stretching is possible, thermoforming of the sheet becomes difficult. Although the degree of plane orientation (ΔP) also depends on the degree of crystallinity and crystal orientation, it largely depends on the molecular orientation in the sheet plane.
Therefore, adjustment of ΔP can be achieved by increasing the molecular orientation in the sheet plane, particularly in one or two directions, ie, in the direction of sheet flow and / or in the direction perpendicular thereto, to 1.0 × 10 ⁻ for non-oriented sheets. ^The degree of plane orientation of ³ or less (△
P) can be increased to 3.0 × 10 ⁻³ or more. In the present invention, any known stretching method can be adopted to increase the degree of plane orientation (ΔP).
In addition, a molecular orientation method using an electric field or a magnetic field can be employed. Normally, a sheet or cylindrical material that has been melt-extruded from a T-die, I-die, round die, etc., is quenched by a cooling cast roll, water, pressurized air, etc., and solidified in an amorphous state, and then rolled. A method of uniaxially or biaxially stretching by a tenter method, a tubular method, or the like is desirably employed industrially. The conditions for stretching the unstretched polylactic acid-based polymer sheet are as follows: a stretching temperature of 50 to 100 ° C., a stretching ratio of 1.5 to 5 times, and a stretching speed of 100% / min to 10,000.
Although it is generally 00% / min, the appropriate range of the stretching conditions varies depending on the composition of the polymer and the heat history of the unstretched sheet. Therefore, the appropriate range is appropriately determined while checking the value of the degree of plane orientation (ΔP). be able to.

In the present invention, the polylactic acid-based polymer sheet produced as described above is thermoformed to obtain a molded article. The thickness of the sheet suitable for thermoforming is not particularly limited, but is preferably in the range of 0.05 mm to 2 mm from the application.

The molded article of the present invention has high impact resistance of 80 kgf · mm or more, and more preferably 100 kgf · mm or more. The molded article of the present invention has high heat resistance, and has a volume shrinkage of 5% or less after drying in a hot air dryer at 80 ° C. for 20 minutes.

A molding apparatus and a molding method used in the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view schematically showing one embodiment of a molding device used in the present invention. In the present invention, the polylactic acid polymer sheet 1
Is heated to a predetermined temperature in advance by the heating device 2 and then placed on the upper surface of the compressed air chamber 4 below the heating mold 3. There is no particular limitation on the method of placing the sheet. For example, after a sheet having a predetermined size is preheated, the sheet is placed in the compressed air chamber 4.
May be moved to a predetermined position on the upper surface of the sheet, or one sheet may be continuously heated using one continuous sheet.
, And may be preheated, transferred and placed on the compressed air chamber 4. The heating device 2 is provided with a suitable heating means. After the mounting, the heating mold 3 is lowered to fix the sheet 1 between the heating mold 3 and the compressed air chamber 4, and then the sheet 1 is brought into contact with the heating mold 3 by blowing compressed air from the compressed air holes 5 on the compressed air chamber 4 side. Form along. The compressed air blown from the compressed air holes 5 is maintained as it is, and is brought into contact with the heating mold 3 for a predetermined time to perform heat treatment. Heating type 3
Is connected to an electric heater 6 so that a predetermined temperature can be maintained. Next, the cooling mold (male mold) 7 having a shape corresponding to the heating mold (female mold) 3 is raised by the shaft 8 in the pressurized air chamber 4 to be fitted with the heating mold 3. By blowing compressed air from the compressed air holes 5 ′ and discharging air from the compressed air holes 5 on the compressed air chamber 4 side, the heat-treated molded product is forcibly transferred to the cooling mold 7 and brought into contact with the cooling mold 7 to be cooled. In the cooling mold 3, water or the like is circulated from the cooling liquid pipe 10 into the cooling mold 3 so that the cooling temperature can be maintained. The molded body thus formed is taken out after returning the heating mold 3 to the state shown in FIG. 1 by raising the heating mold 3 by the shaft 9 and lowering the cooling mold 7 by the shaft 8 in the compressed air chamber 4. . FIG. 1 shows an embodiment in which the heating type is a female type and the cooling type is a male type, but the present invention is not limited to these. The molding apparatus used in the present invention is described in
-27850 discloses this in detail.

In the present invention, the polylactic acid-based polymer sheet needs to be heated in advance so that the temperature is in the range of (Tg) to (Tg + 50 ° C.). Here, Tg represents the glass transition temperature of the polylactic acid-based polymer. If the preheating temperature of the sheet is lower than the glass transition temperature (Tg), softening is insufficient, while if it exceeds (Tg + 50 ° C.), the orientation of the sheet is lost, resulting in poor impact resistance and transparency. In addition, sheet forming and heat treatment are performed using (Tc−
(20 ° C.) to (Tm−20 ° C.). Here, Tc represents the crystallization temperature of the polylactic acid-based polymer, and Tm represents the melting point of the polylactic acid-based polymer. The heating mold 3 uses the electric heater 9 and (Tc-2
It is necessary to heat in advance to a temperature in the range of 0 ° C to (Tm-20 ° C). If the temperature is lower than (Tc-20 ° C.), the crystallization of the sheet does not proceed sufficiently in a short time, and the desired heat resistance cannot be obtained. If the temperature is higher than (Tm-20), the orientation is lost and the impact resistance is poor. It will be. By molding along a heating mold heated to a predetermined temperature as in the present invention, it is possible to prevent the sheet temperature from decreasing and the sheet tension from increasing, so that the compressed air pressure required for molding is reduced. There is also an effect that can be suppressed.
The molding pressure is practical in terms of the pressure-resistant structure of the device.
It is preferable to select an appropriate value within a range of 40 kgf / cm ² or less.

In order to remove the molded body that has been molded and crystallized by the heat treatment from the heating mold, it is necessary to sufficiently remove the molded body so that the molded body does not shrink and deform due to residual heat. In the present invention, the cooling mold 7 is fitted to the heating mold 3,
By blowing compressed air from the heating mold 3 side to the molded product sandwiched between the two molds and forcibly transferring the molded body to the cooling mold and cooling it along, the mold can be quickly transferred and the mold can be shrunk without shrinkage deformation. A molded article faithful to the above can be obtained.

The obtained molded article is suitably used as, for example, a food container, a blister pack container, and a display package, but is not limited thereto. The molded article of the present invention can be adapted to various uses by appropriately selecting the size and shape. Here, the blister pack container refers to a container used for a so-called blister pack in which the contents are stored and the bottom or the lid is sealed with a heat-sealed sheet or the like.

[0016]

EXAMPLES Examples are shown below, but the present invention is not limited to these examples. The measured values shown in the examples were measured and calculated under the following conditions. (1) Degree of plane orientation (ΔP) The refractive index (α, β, γ) of the sheet in three orthogonal directions was measured by an Appe refractometer and calculated by the following equation. ΔP = {(γ + β) / 2)} − α (α <β <
γ) γ: maximum refractive index in the sheet plane β: refractive index in the direction orthogonal to the direction of γ in the sheet plane α: refractive index in the sheet thickness direction (2) glass transition temperature (Tg), crystallization temperature ( Tc),
Melting point (Tm) Differential scanning calorimeter "DSC-7" (manufactured by PerkinElmer)
Was used to measure the glass transition temperature (Tg), crystallization temperature (Tc), and melting point (Tm) of the polylactic acid-based polymer based on JIS-K7122. However, the glass transition temperature (T
g), melting point (Tm) is measured in a pellet state,
The crystallization temperature (Tc) was measured in a sheet state. (3) Impact resistance Hydroshot high-speed impact tester “HTM-1”
The impact resistance was measured using (manufactured by Shimadzu Corporation).
A sample having a size of 100 mm × 100 mm was cut out from the bottom of the molded body, a weight was dropped at the center of the sample to give an impact, and the breaking energy when the sample was broken was read. However, the measurement temperature is 23 ° C and the falling speed of the weight is 3 m
/ Sec. The smaller the maximum load and the energy when the sample breaks, the lower the impact resistance and the brittleness. (4) Heat resistance (stability during heating) The volume (Vt) of the molded body after standing for 20 minutes in a hot air dryer at a temperature of 80 ° C. was measured, and the volume (V ₀ ) before leaving and the volume after standing were measured. From the volume <Vt), the volume change rate (△
V) was determined, and this value was regarded as heat resistance. Volume change rate (△
The smaller the value of V), the better the heat resistance. ΔV = [(Vo−Vt) / Vo] × 100 (%)

Example 1 The composition ratio of L-lactic acid to D-lactic acid was about 99.5: 0.5, and the glass transition temperature (T
g) 60 ° C, melting point (Tm) 174 ° C, weight average molecular weight 2
(0000,000 polylactic acid) was extruded at 200 ° C. using a 90 mmφ uniaxial extruder to prepare an unstretched sheet of a polylactic acid-based polymer having a width of 300 mm and a thickness of 0.3 mm after stretching. The obtained unstretched sheet was stretched using a sequential biaxial stretching machine under the conditions shown in Table 1 to obtain a stretched sheet of a polylactic acid-based polymer. The plane orientation degree (ΔP) of the obtained stretched sheet of polylactic acid-based polymer was determined to be 9.1 × 1
0 was ^-3. The obtained stretched sheet of polylactic acid-based polymer was 130 m in length using a pressure forming apparatus shown in FIG.
m, a width of 130 mm and a depth of 30 mm were molded into a box-shaped molded body. However, the temperature of the heating device (sheet heating temperature), the compressed air pressure from the compressed air holes, and the temperature of the heating mold (heat treatment temperature)
Was molded as shown in Table 1. About the obtained molded object, evaluation of moldability and measurement of impact resistance and heat resistance were performed. Table 1 shows the results. The evaluation criteria for moldability were indicated by “○” for those that could be molded, and “X” for those that could not be molded. In addition, a comprehensive evaluation was performed in consideration of the results of impact resistance and heat resistance. However, those which were not usable or those which could not be formed were indicated by "x", those which were at or above the practical level were indicated by "o", and those which were extremely excellent were indicated by "o".

(Examples 2 to 4) Unstretched sheets were produced in the same manner as in Example 1. Then, Example 1 was repeated except that the stretching conditions of the obtained unstretched sheet were changed as shown in Table 1.
In the same manner as in the above, a stretched sheet of a polylactic acid-based polymer was produced. Next, using the obtained stretched sheet of polylactic acid-based polymer, the sheet heating temperature, the pneumatic pressure, and the heat treatment temperature are shown in Table 1.
A molded article was obtained in the same manner as in Example 1 except that the composition was changed as shown in (1). ΔP, crystallization temperature (Tc), evaluation of moldability, impact resistance and heat resistance (ΔV) were determined in the same manner as in Example 1. Table 1 shows the results.

(Comparative Examples 1 to 6) Unstretched sheets were produced in the same manner as in Example 1. Then, for Comparative Examples 1 to 4, and 6, a stretched sheet was produced in the same manner as in Example 1 except that the stretching conditions were changed as shown in Table 1. Next, using the obtained stretched sheet, a molded article was obtained in the same manner as in Example 1 except that the sheet heating temperature, the air pressure, and the heat treatment temperature were changed as shown in Table 1. However, for Comparative Example 5, a molded article was produced in the same manner as described above with the unstretched sheet.

[0020]

[Table 1]

As is clear from Table 1, all of the molded articles of Examples 1 to 4 have an impact resistance of 80 kgf · mm or more and a heat resistance (ΔV) of 5% or less. It was found to be a very excellent molded article. On the other hand, in Comparative Example 1, since the sheet heating temperature was low, molding was not possible, and in Comparative Example 2, the sheet heating temperature was too high, and the impact resistance and heat resistance were poor. In Comparative Example 3, the heat treatment temperature was low, so the heat resistance was poor. In Comparative Example 4, the heat treatment temperature was too high.
Poor impact resistance. Comparative Example 5 has a small ΔP.
Inferior in impact resistance, Comparative Example 6 was too large in plane orientation (ΔP) and could not be molded. The shape of the obtained molded body can be appropriately selected depending on the application,
Appropriate shapes were selected to produce food containers and blister pack containers, which were found to be biodegradable containers having excellent impact resistance and heat resistance.

[0022]

As described in detail above, the biodegradable molded article obtained from the polylactic acid-based polymer sheet of the present invention has excellent impact resistance and wet heat resistance, and can be used in a wide range of fields. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view schematically showing one embodiment of a molding apparatus used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sheet 2 Heating device 3 Heating type 4 Compressed air chamber 5 Compressed air hole 5 'Compressed air hole 6 Electric heater 7 Cooling type 8 axis 9 axis 10 Coolant pipe

Claims (5)

[Claims] 1. A plane orientation degree (ΔP) of 3.0 × 10 ⁻³ or more.
A sheet of a polylactic acid-based polymer having a size of 30 × 10 ⁻³ is ^subjected to a temperature equal to or higher than the glass transition temperature (Tg) of the polylactic acid-based polymer (Tg).
g + 50 ° C.) or less, and then kept in contact with a heating mold {the crystallization temperature (Tc) of the polylactic acid-based polymer −20 ° C.) or more, {the polylactic acid-based polymer Molding method and heat treatment at a temperature in the range of -20 ° C. or lower, followed by cooling. 2. The degree of plane orientation (ΔP) is 3.0 × 10 ⁻³ or more.
A sheet of a polylactic acid-based polymer having a size of 30 × 10 ⁻³ is ^subjected to a temperature equal to or higher than the glass transition temperature (Tg) of the polylactic acid-based polymer (Tg).
(g + 50 ° C.) or less before heating to a temperature in the range of not more than the following range, followed by molding along a heating mold with compressed air, and keeping the obtained molded article in contact with the heating mold. [Crystallization of the polylactic acid-based polymer] A heat treatment is performed at a temperature in a range of not less than a temperature (Tc) -20 ° C and not more than a melting point (Tm) of the polylactic acid-based polymer -20 ° C}, and then fitted into a cooling mold having a shape substantially corresponding to a heating mold. A method of molding a polylactic acid-based polymer, comprising blowing compressed air from the heating mold side, transferring the molded article to the cooling mold, and cooling while contacting the cooling mold. 3. The impact resistance is 80 kgf · mm or more, and the heat resistance is 5% or less in volume shrinkage when dried in a hot air dryer at 80 ° C. for 20 minutes. A molded article of a polylactic acid-based polymer. 4. A molded article of a polylactic acid-based polymer produced by using the molding method of claim 1. 5. A food container made of a polylactic acid-based polymer, produced by using the molding method according to claim 1.