JP3217240B2 - Polylactic acid based molded body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molded article made of polylactic acid which is excellent in impact resistance, transparency and wet heat resistance and decomposes in a natural environment.

[0002]

2. Description of the Related Art Blister-processed products used for display and packaging of various products are obtained by obtaining a resin sheet and forming the sheet by a thermoforming method such as vacuum forming or pressure forming. Is common. As the blister-processed product, a product having excellent transparency that allows the inside product to be seen through the package is preferable. Therefore, polyvinyl chloride, polyethylene terephthalate, and polystyrene sheets are used as material sheets for blister products.

[0003] However, the above-mentioned sheet is chemically,
Since it is biologically stable, it remains and accumulates without being substantially decomposed even when left in a natural environment. These are not only scattered in the natural environment and pollute the living environment of animals and plants, but also hardly decompose when buried as garbage, which has a problem of shortening the life of the landfill.

[0004] Therefore, there is a demand for a material made of a degradable polymer which does not cause these problems, and much research and development has been carried out. One of them is known as polylactic acid.

[0005] Japanese Patent Application Laid-Open No. 6-122148 discloses a method for obtaining a blister-processed product using polylactic acid, which is disclosed in JP-A-6-122148. A method for obtaining an L-lactic acid-based polymer molded article from a polymer sheet by vacuum suction, air pressure or vacuum air pressure is disclosed, and discloses that the obtained molded article has excellent transparency and moldability.

[0006]

However, the conventionally known molded article made of polylactic acid has insufficient strength and impact resistance, and causes problems such as perforation during handling. In addition, when the product is exposed to a high temperature and high humidity environment during transportation, storage and use of the product due to insufficient moisture and heat resistance, the molded product may be deformed or the transparent molded product may be whitened. Occurs.

[0007] For this reason, the use of a molded article made of polylactic acid that decomposes in a natural environment is expected due to environmental problems and the like, but has not been put to practical use due to the above-mentioned matters.

Accordingly, an object of the present invention is to provide a polylactic acid-based molded article having excellent impact resistance and heat and humidity resistance.

[0009]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a polylactic acid-based polymer (excluding a polymer consisting of L-lactic acid or D-lactic acid alone) and having a plane orientation degree ΔP of 3.0 ×.
10 ⁻³ to 30 × 10 ⁻³ , and the difference (ΔHm−ΔHc) between the heat of crystallization melting 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 and {(ΔHm−ΔHc) / ΔHm} is not more than 0.1.
A polylactic acid-based polymer obtained by thermoforming an oriented polylactic acid-based sheet of 75 or more. In addition, the gist of the present invention is that it is made of a polylactic acid-based polymer, has a plane orientation degree ΔP of 3.0 × 10 ⁻³ to 30 × 10 ⁻³ , and has a heat of crystallization and melting ΔHm when the sheet is heated. Difference (ΔHm−ΔH) from the amount of heat of crystallization ΔHc generated by crystallization during temperature rise
c) is 20 J / g or more and ｛(ΔHm−ΔHc) / ΔH
A polylactic acid-based molded article characterized in that an oriented polylactic acid-based sheet having m｝ of 0.75 or more is thermoformed so that the sheet temperature immediately before molding is in a range of 145 to 170 ° C.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The polylactic acid-based polymer used in the present invention is polylactic acid, a copolymer of lactic acid and another hydroxycarboxylic acid, or a mixture thereof, and does not impair the effects of the present invention. Other polymer materials may be mixed within the range. It is also possible to add additives such as plasticizers, lubricants, inorganic fillers and ultraviolet absorbers, and modifiers for the purpose of adjusting the moldability and the physical properties of the sheet or the molded article.

Lactic acid includes L-lactic acid and D-lactic acid, and other hydroxycarboxylic acids include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, and 4-hydroxyvaleric acid. Representative examples include valeric acid and 6-hydroxycaproic acid.

As these polymerization methods, any known methods such as condensation polymerization and ring-opening polymerization can be employed. Further, a small amount of a chain extender such as diisocyanate is used for the purpose of increasing the molecular weight. Compounds, epoxy compounds, acid anhydrides and the like may be used.

The weight average molecular weight of the polylactic acid-based polymer is preferably in the range of 50,000 to 1,000,000, and below this range practical properties are hardly exhibited, and the sheet retains strength during thermoforming. It causes problems such as inability to do so. On the other hand, if it exceeds, the melt viscosity becomes too high, resulting in poor moldability.

The polylactic acid-based sheet used in the present invention comprises:
After sufficiently drying the above-mentioned polymer to remove water, the polymer is formed into a sheet by a general melt molding method such as an extrusion method, a calender method, a press method, and the like, and then rapidly cooled.

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 it is higher than this, the polymer sticks to the casting drum and it becomes difficult to take it off. In addition, crystallization is promoted and spherulites develop and transparency increases. As the temperature decreases, thermoforming becomes difficult. Therefore, it is preferable to rapidly cool the sheet at a temperature of 60 ° C. or less to obtain a substantially amorphous sheet.

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 product, the degree of plane orientation ΔP of the polylactic acid-based sheet is set to 3.
It is adjusted to 0 × 10 ⁻³ to 30 × 10 ⁻³ .

The degree of plane orientation ΔP represents the degree of orientation in the plane direction with respect to the thickness direction of the sheet, and is usually calculated by the following formula by measuring the refractive index in three orthogonal directions. ΔP = {(γ + β) / 2} −α (α <β
<Γ) Here, γ and β are the refractive indices of two orthogonal axes parallel to the sheet surface,
α is the refractive index in the sheet thickness direction.

The degree of plane orientation ΔP also depends on the degree of crystallinity and crystal orientation, but largely depends on the molecular orientation in the sheet plane.
In other words, by increasing the molecular orientation in the sheet plane, particularly in one or two directions of the sheet flow direction and / or the direction perpendicular thereto, the non-oriented sheet has a 1.0 ×
ΔP which is 10 ⁻³ or less is defined as 3.0 × defined by the present invention.
It can be increased to 10 ⁻³ or more.

As a method of increasing the plane orientation degree ΔP,
In addition to any known stretching method, a molecular orientation method using an electric field or a magnetic field can be employed.

Normally, a sheet or cylindrical material melt-extruded from a T die, an I die, a round die or the like is quenched by a cooling cast roll, water, pressurized air or the like and solidified in a state close to amorphous. A method of uniaxially or biaxially stretching by a roll method, a tenter method, a tubular method, or the like is desirably employed industrially.

The stretching conditions of the unstretched polylactic acid-based sheet include a stretching temperature of 50 to 100 ° C. and a stretching ratio of 1.5 to 5 times.
In general, the stretching speed is 100% / min to 10,000% / min, but the appropriate range varies depending on the composition of the polymer and the heat history of the unstretched sheet.
It can be determined as appropriate while looking at the value of P.

By setting the degree of plane orientation ΔP to 3.0 × 10 ⁻³ or more, the impact resistance is remarkably improved, and
It is possible to prevent embrittlement and whitening mainly caused by spherulite growth, which occur when the non-oriented sheet is exposed to a high-temperature and high-humidity atmosphere. The upper limit of the plane orientation degree ΔP is actually 30 × 1
0 is about ^-3, when you raise from the surface orientation degree ΔP this, it is impossible to there is no instability stretching. Even if it can be stretched, it becomes difficult to thermoform the sheet.

The degree of plane orientation ΔP is 3.0 × 10 ⁻³ to 30 ×
By setting the range to 10 ^-3 , the above-described effects can be obtained, but on the other hand, thermal dimensional stability becomes poor, and deformation tends to occur. For example, in hot summer months or in high-temperature, high-humidity warehouses, vehicles, ships, and the like, sheets and molded articles undergo natural shrinkage, causing deformation such as sagging and waving. Even if thermoforming is performed using the deformed sheet, a molded product having a desired shape cannot be obtained. Therefore, it is important that the polylactic acid-based sheet does not shrink at a temperature slightly higher than room temperature, that is, at a temperature of about 50 ° C. or more, that is, it has thermal dimensional stability.

For this reason, the plane orientation degree ΔP is set to 3.0 × 10
^-3 to 30 × 10 ^-3 polylactic acid-based sheet,
In order to obtain practical thermal dimensional properties, 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 and {(ΔHm−ΔHc) / ΔHm} is 0.75
It is important to control above.

Heat of crystal melting ΔHm, heat of crystallization ΔHc
Is obtained by differential scanning calorimetry (DSC) of the sheet sample, and the heat of crystal fusion ΔHm is 1
This is the amount of heat required to melt all crystals when the temperature is raised at 0 ° C./min, and is determined from the area of the endothermic peak due to crystal melting that appears near the crystal melting point of the polymer. Further, the heat of crystallization ΔHc is determined from the area of the exothermic peak generated at the time of crystallization generated in the process of raising the temperature.

The heat of crystal fusion ΔHm mainly depends on the crystallinity of the polymer itself, and takes a large value for a polymer having high crystallinity. By the way, L-lactic acid or D without copolymer component
In the case of a complete homopolymer of lactic acid, it is 60 J / g or more, and in a copolymer of these two lactic acids, the heat of crystal fusion ΔHm changes depending on the composition ratio.

The heat of crystallization ΔHc is an index relating to the crystallinity of the polymer and the crystallinity of the sheet at that time.
When the heat of crystallization ΔHc is large, the crystallization of the sheet proceeds during the heating process. That is, it indicates that the crystallinity of the sheet was relatively low based on the crystallinity of the polymer. Conversely, when the heat of crystallization ΔHc is small, it indicates that the crystallinity of the sheet is relatively high based on the crystallinity of the polymer.

1 for increasing (ΔHm−ΔHc)
One direction is to make a sheet having a relatively high crystallinity from a polymer having high crystallinity, and the crystallinity of the sheet depends to a large extent on the composition of the polymer.

The heat of crystal fusion ΔHm of the polymer itself is 2
To achieve 0 J / g or more, the composition ratio of L-lactic acid and D-lactic acid is in the range of 100: 0 to 94: 6 or 0: 100 to
6:94.

Further, in order to reduce the heat of crystallization ΔHc, that is, to increase the crystallinity of the sheet, it is necessary to select the sheet forming conditions. In order to increase the crystallinity of the sheet in the forming process, particularly in the biaxial stretching by the tenter method, it is useful to increase the stretching ratio to promote oriented crystallization, or to heat-treat after stretching in an atmosphere at a crystallization temperature or higher. is there. In addition, since the crystallization temperature tends to decrease as the degree of plane orientation ΔP increases, in the case of the present invention, the heat treatment is performed at 70 ° C. or more, preferably 90 ° C. to 17 ° C.
It is good to carry out for 3 seconds or more in the range of 0 ° C. The higher the heat treatment temperature and the longer the heat treatment time, the better the thermal dimensional stability.

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

The method of thermoforming includes any known method of thermoforming a sheet, for example, vacuum forming, pressure forming,
Vacuum pressure molding, male and female molding, plug assist vacuum molding,
It can be arbitrarily adopted from CD (Cuspation Dilation: tip expansion) molding or the like.

Since the sheet of the present invention tends to have a relatively large forming stress, in order to obtain a molded article having a complicated shape with detailed details and corners, it is possible to apply a large force to the sheet. Molding, plug assist vacuum molding and the like are preferably employed.

A suitable pressure for the pressure forming is generally in the range of 1.5 to 20 kg / cm ² . If it is below this range, depending on the shape of the mold, depending on the shape of the mold, it may not be possible to mold sufficiently to the details and corners.On the contrary, if it is over, before the sheet is formed and reaches the mold surface, it will be compressed by air pressure. The sheet often breaks.

The temperature of the sheet immediately before molding is adjusted to 60 to 175 ° C., more preferably 145 to 145, by adjusting the preheating temperature and time.
The temperature range is 170 ° C. The mold temperature is preferably 60 ° C. or lower, which is the glass transition temperature of polylactic acid.

[0036]

EXAMPLES Examples will be shown below, but the present invention is not limited to these examples. The measurement values shown in the examples were calculated by measuring under the following conditions.

(1) ΔP The refractive index (α, β,
γ) was measured and calculated by the following equation.

ΔP = {(γ + β) / 2} −α
(Α <β <γ) γ: Maximum refractive index in the film plane β: Refractive index in the direction perpendicular to the film α: Refractive index in the film thickness direction (2) ΔHm−ΔHc and (ΔHm−ΔHc) / ΔH
m Using DSC-7 manufactured by Perkin-Elmer, the heat of crystal fusion ΔHm and the heat of crystallization ΔHc were determined from a thermogram obtained by heating a 10 mg film sample at a rate of 10 ° C./min according to JIS-K7122. Obtained and calculated.

(3) Impact resistance Hydroshot high-speed impact tester HTM-1 (trade name)
The impact resistance was measured using Shimadzu Corporation. 100m
A weight was dropped at the center of a sample cut into a size of mx 100 mm to give an impact, and the breaking energy when the sample was broken was read. The measurement temperature was 23 ° C and the falling speed of the drop was 3m /
Seconds. The lower the maximum load and the energy at break, the lower the impact resistance and the more brittle.

(4) Moisture / heat resistance: 50 ° C., 80% R.C. H. After leaving the molded body in a thermo-hygrostat for 24 hours under the conditions of the above, the degree of whitening and deformation of the molded body was visually determined. × is a level that does not withstand use, Δ is better than × but does not meet the practical level, ○
Is above the practical level.

Example 1 The composition ratio of L-lactic acid to D-lactic acid was about 98: 2, the glass transition point was 58 ° C., and the melting point was 17
Extruded polylactic acid having a weight average molecular weight of 180,000 at 5 ° C at 200 ° C using a 90 mmφ single-screw extruder to obtain a width of 3
A sheet having a thickness of 00 mm and a thickness of 1.875 mm was produced.

The unstretched sheet was roll-stretched 2.5 times in the flow direction at 70 ° C., and then stretched 2.5 times in the width direction at 70 ° C. in the tenter. Subsequently, heat treatment was performed at 160 ° C. for 25 seconds in a tenter to prepare a polylactic acid-based sheet having a thickness of 300 μm. Table 1 summarizes the manufacturing conditions.

Example 2 A polylactic acid-based sheet was prepared in the same manner as in Example 1 and under the conditions shown in Table 1.

(Comparative Examples 1 to 5) Polylactic acid-based sheets were prepared in the same manner as in Example 1 and under the conditions shown in Table 1.

ΔP, Δ of the obtained stretched polylactic acid sheet
Hm and ΔHc were measured by the method described above, and ΔP, (H
m-ΔHc) and {(ΔHm-ΔHc) / ΔHm}. In addition, a cup-shaped molded body was manufactured from the polylactic acid-based sheet using an aluminum cup-shaped mold using a pressure molding machine. Using the obtained molded body, impact resistance and wet heat resistance were measured. Table 1 shows the results.
Shown in In addition, comprehensive evaluation was performed based on the results of the impact resistance and the wet heat resistance. As for the evaluation, × is a level that can not be used,
は was set to a practical level or higher.

[0046]

[Table 1] As is clear from Table 1, Examples 1 and 2, which satisfy the conditions of the present invention, are excellent in impact resistance and wet heat resistance. on the other hand,
In Comparative Example 1, the stretching was insufficient and the degree of plane orientation ΔP was small,
Impact resistance and wet heat resistance are not improved. Comparative Example 2
Has not been heat-treated, so the crystallinity is insufficient.
Although the impact resistance has been improved, it is still insufficient, and the impact resistance and wet heat resistance have not been improved.

In Comparative Example 3, since excessive stretching was performed,
The degree of plane orientation ΔP became too large, and molding was impossible. In Comparative Example 4, the degree of plane orientation ΔP and the degree of crystallinity were insufficient, and the impact resistance and the moist heat resistance were not improved. In Comparative Example 5, since the content of the D-form was large, the crystallinity was poor, and the molded body was deformed due to wet heat resistance.

[0048]

As described above, the polylactic acid-based molded article of the present invention has excellent impact resistance and wet heat resistance, so that a molded article made of polylactic acid can be used in a wide range of fields.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-122148 (JP, A) JP-A-6-298236 (JP, A) JP-A-6-23836 (JP, A) JP-A-8-208 11206 (JP, A) JP-A-8-73628 (JP, A) JP-A-7-205278 (JP, A) JP-A-7-207041 (JP, A) JP-A-7-308961 (JP, A) JP-A-8-198955 (JP, A) JP-A-8-323946 (JP, A) JP-A-9-12748 (JP, A) “The 88th Annual Meeting of the Plastic Film Research Society”, Plastics Society of Japan LUM Study Group, 1994, p. 7-10 (58) Field surveyed (Int. Cl. ⁷ , DB name) C08J 5/00-5/02 C08J 5/18 C08G 63/00-63/91 C08L 67/00-67/08 CA (STN ) REGISTRY (STN)

Claims (2)

(57) [Claims] 1. A polylactic acid-based polymer (provided that L-lactic acid and
Or a polymer consisting solely of D-lactic acid) , the degree of plane orientation ΔP is 3.0 × 10 ⁻³ to 30 × 10 ⁻³ , and the heat of crystallization and melting when the sheet is heated is ΔHm. The difference (ΔHm−ΔHc) from the heat of crystallization ΔHc generated by crystallization during temperature rise is 20 J / g or more and 以上 (ΔHm−
A polylactic acid-based molded article obtained by thermoforming an oriented polylactic acid-based sheet having ΔHc) / ΔHm｝ of 0.75 or more. 2. A polylactic acid-based polymer having a degree of plane orientation Δ
P is 3.0 × 10 ⁻³ to 30 × 10 ⁻³ , and the difference (ΔHm−) between the heat of crystallization fusion ΔHm when the sheet is heated and the heat of crystallization ΔHc generated by crystallization during the temperature rise. Δ
Hc) is 20 J / g or more and ｛(ΔHm−ΔHc) / Δ
An oriented polylactic acid-based sheet having an Hm｝ of 0.75 or more,
A polylactic acid-based molded article, which is thermoformed so that the sheet temperature immediately before molding is in the range of 145 to 170 ° C.