JP2002248677A - Polylactic acid thermoforming product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoforming product having toughness, good transpar ency, excellent heat resistance and aging shape stability without problem of a discarding treatment or an environmental contamination. SOLUTION: The polylactic acid thermoforming product is obtained by molding a sheet made of a polylactic acid polymer having a weight mean molecular weight of 100,000 or more and a glass transition temperature of 50 deg.C or higher at a molding temperature of a range of 95 to 140 deg.C, and an area stretching ratio of a range of 2 to 20 times. A mean degree of orientation ΔP in plane of the molding part of the molding is in a range of 2×10<-3> to 30×10<-3> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoformed article made of a polylactic acid-based polymer such as a blister container or a PTP container having degradability.

[0002]

2. Description of the Related Art Processed products such as blister containers, which are widely used for display and packaging of various products, are prepared by forming a resin sheet, and then forming the sheet by a thermoforming method such as vacuum forming or pressure forming. It is common to make it. As the processed product such as the blister container, a transparent product is preferably used so that the inside product can be seen through the package. From such a point, sheets of polyvinyl chloride, polyethylene terephthalate, polystyrene and the like are often used as material sheets for processed products such as blister containers that are actually used.

[0003] A PTP (press-through pack) packaging container used for packaging tablets and capsules of pharmaceuticals is also formed by the same thermoforming method. From the viewpoint of barrier properties, sheets of polyvinyl chloride, polyethylene terephthalate, polypropylene and the like are frequently used.

[0004]

However, since these materials are chemically and biologically stable, they remain and accumulate 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 landfilled as garbage, thereby shortening the life of the landfill.

Therefore, the present invention is to provide a thermoformed product which is free from problems of disposal and environmental pollution, is tough, has good transparency, and is excellent in heat resistance and shape stability over time. Aim.

[0006]

According to the present invention, a sheet made of a polylactic acid polymer having a weight average molecular weight of 100,000 or more and a glass transition temperature of 50 ° C. or more is formed at a molding temperature of 95 ° C.
~ 140 ° C, stretched area magnification of 2 to 20 times, the average of the in-plane orientation degree ΔP of the molded part of this molded product is 2 × 10
^The above problem was solved by setting the range of ⁻³ to 30 × 10 ⁻³ .

The above-mentioned polylactic acid-based polymer has a so-called biodegradability, in which hydrolysis progresses spontaneously in the soil, the original form does not remain in the soil, and it becomes a harmless decomposed product by microorganisms. In addition, since a molecular orientation is imparted to a molded portion of the processed product, the obtained thermoformed product has a sufficient strength.

[0008]

Embodiments of the present invention will be described below.

According to the present invention, a polylactic acid-based thermoformed product (hereinafter, referred to as “polylactic acid-based thermoformed product”) is formed by molding a predetermined polylactic acid-based polymer under certain conditions.
It is referred to as "thermoformed product". ).

The above-mentioned polylactic acid-based polymer is a polylactic acid which is a homopolymer of lactic acid, a copolymer of lactic acid and another hydroxycarboxylic acid, or a mixture thereof, which does not impair the effects of the present invention. However, other polymer materials may be mixed. In addition, additives such as plasticizers, lubricants, inorganic fillers, and ultraviolet absorbers, and modifiers can be added for the purpose of adjusting moldability and physical properties of sheets and processed products.

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. 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. Further, a small amount of a chain extender, for example, A diisocyanate compound, a diepoxy compound, an acid anhydride and the like may be used.

The weight average molecular weight of the polylactic acid-based polymer is preferably in the range of 100,000 to 1,000,000, and is preferably 140,000 to 25,000,000.
0,000 is preferred. If the ratio is less than the above range, practical physical properties are hardly exhibited, and problems may occur such that the sheet cannot maintain strength during thermoforming. If it exceeds, the melt viscosity may be too high and the molding processability may be poor.

The sheet made of the above-mentioned polylactic acid-based polymer (hereinafter referred to as “material sheet”) is obtained by sufficiently drying the polylactic acid-based polymer to remove water, and then extruding, calendering, and pressing. It is obtained by molding into a sheet by a general melt molding method such as that described above, and then quenching. Practically, a polylactic acid-based polymer melt-extruded into a sheet is cast on a rotating casting drum (cooling drum).
It is preferable to quench the mixture by contacting with water. The temperature of the casting drum is suitably 50 ° C. or less. If it is higher than this, the polymer may adhere to the casting drum to make it difficult to take it off. In addition, crystallization is promoted, spherulites develop, transparency decreases, and thermoforming becomes difficult.
Therefore, it is preferable to rapidly cool the sheet in the above temperature range to make it a substantially amorphous sheet.

Further, the glass transition temperature of the obtained sheet
(Hereinafter abbreviated as “Tg”) is preferably 50 ° C. or higher, and 55 to 70 ° C.
Is preferred. If the Tg is less than 50 ° C, after forming into a thermoformed product, the heat resistance in an atmosphere of 50 ° C or more is insufficient,
Even at room temperature, dimensional changes are likely to occur over time, which is not preferable. In addition, spherulites may grow on a material sheet or a processed product while being left at room temperature, which may cause problems such as difficulty in forming the material sheet, embrittlement of the processed product, and reduction in transparency. Tg mainly depends on the composition, molecular weight, amount of contained oligomer, kind and amount of additives such as plasticizer, etc. of the polylactic acid-based polymer.

Next, the material sheet includes an infrared heater,
Thermoforming can be performed by preheating to a forming temperature with a hot plate heater, hot air or the like. Examples of the thermoforming method include a vacuum forming method, a plug assist forming method, a pressure forming method,
There are a male and female mold forming method, a method of expanding a formed male mold after deforming a sheet along the formed male mold, and the like. The thickness of the material sheet is not particularly limited as long as it can be used for ordinary thermoforming technology. Specifically, the range of about 30 to 1000 μm is included.

The thermoformed product thermoformed by the above-mentioned method comprises a convex portion subjected to the thermoforming process and a flat portion on which the material sheet remains as it is. Since the flat portion is not stretched during thermoforming, the physical properties are not improved and the strength is inferior. However, the flat portion is generally supported by bonding a support such as paper. on the other hand,
The convex portion is stretched during thermoforming, but its shape requires strength and it is necessary to improve brittleness. In the present invention, by increasing the molecular orientation of the projections, the strength can be improved and the brittleness can be improved. The in-plane orientation ΔP is a measure of the molecular orientation.

The degree of in-plane orientation ΔP represents the degree of orientation in the plane direction with respect to the thickness direction of the formed part wall, and is usually calculated by the following formula (1) by measuring the refractive index in three orthogonal directions.

ΔP = {(γ + β) / 2} −α (1) (α <β <γ) Here, γ and β are the refractive indexes of two orthogonal axes parallel to the sheet surface (wall surface), and α is the sheet thickness Is the refractive index in the vertical direction.

The ΔP depends on the degree of crystallinity and the crystal orientation, but largely depends on the in-plane molecular orientation. That is, by increasing the molecular orientation with respect to the in-plane, ΔP of less than 1.0 × 10 ⁻³ in the non-oriented sheet is 2 × 10 ⁻³ or more on average,
Preferably, it can be increased to 3 × 10 ⁻³ or more. However, if an average of ΔP exceeding 30 × 10 ⁻³ is to be obtained, stable molding cannot be performed, and the sheet may be frequently broken.

It is important that a thermoformed product such as a blister product is transparent in its use, and it is necessary to avoid whitening during thermoforming. Transparency can be represented by haze, and a thermoformed product having a haze of 20% or less, preferably 10% or less can be obtained under the thermoforming conditions described below.

The thermoforming conditions for obtaining a processed product having a ΔP and a haze in the above ranges are as follows:
The temperature is preferably in the range of 0 ° C, more preferably in the range of 95 to 120 ° C. The stretch area ratio of the thermoformed portion is preferably in the range of 2 to 20 times, and more preferably in the range of 4 to 15 times. If the thermoforming temperature (that is, the sheet temperature during molding) is less than 95 ° C, the heat resistance of the obtained thermoformed product is not sufficiently obtained, and if it is higher than 140 ° C, the material sheet is drawn down by heating and molding is performed. In some cases, transparency may be lost due to difficulty or whitening due to crystallization.

If the stretch area ratio of the thermoformed portion is smaller than twice, ΔP does not reach 2 × 10 ^-3 and no improvement in physical properties is observed. On the other hand, if the stretch area ratio exceeds 20 times, the thermoformed product may be broken, and the thermoformed product may not be stably obtained.

The thermoformed product according to the present invention is required to have a transparent content such as a blister package or a PTP container by utilizing the strength, transparency and water vapor barrier properties of the thermoformed portion. It is suitable for use in contact with a support such as paper.

For example, in the case of a blister package used for packaging and displaying products, it is customary to store the product in a convex molded portion and attach a backing paper to the opening from the molded portion to the surrounding unprocessed portion. It is. As this backing, in addition to cardboard, metal foil, various plastic sheets, etc. can be applied.If it is assumed that the blister-processed product is discarded together with the backing, it is preferable that the backing is made of biodegradable paper. It is.

The above-mentioned backing sheet is heat-sealed with the blister-processed product, or by using an adhesive, preferably a biodegradable adhesive such as unvulcanized natural rubber or protein such as casein, starch or glue. It is closely bonded. Alternatively, both side edges of the unformed portion (so-called flange) may be bent 180 ° to the back side, and another mount may be slidably mounted in the groove.

The PTP container is usually sealed with a lid made of aluminum foil. Since aluminum does not pollute the environment and is naturally reducing, it can be discarded even in a state of being bonded to the polylactic acid-based polymer sheet.

[0028]

The present invention is not limited by the following examples. The measured values shown in the examples were calculated by measuring under the following conditions.

(1) Average value of ΔP A portion corresponding to the stretching area magnification of the molded portion, that is, a sheet-like portion starting from several portions having a thickness corresponding to a value obtained by dividing the thickness of the original sheet by the stretching area magnification. Sample was cut out, and 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 sample plane β: Refractive index in the direction perpendicular to the sample α: Refractive index in the sample thickness direction

(2) Stretching Area Magnification The surface area of the molded portion after molding was divided by the area of the stretched original sheet to obtain a stretching area magnification.

(3) Haze Measured according to JIS-K7105.

(4) Formability (Drawdown Property) When the sheet is drawn down and cannot be formed at the time of thermoforming preheating, x indicates that the sheet can be drawn but can be formed, and x indicates that the sheet hardly draws down. And

(5) Heat resistance The molded article was left in an oven controlled at 50 ° C. for 30 minutes, and the volume before and after the test was measured by adding water. Thereafter, the volume retention was determined by the following equation, and was used as an index of heat resistance. Volume retention (%) = (volume after test) / (volume before test) × 100

(6) Brittleness Judgment was made by tactile sensation, and those with no brittleness were indicated by ○, slightly brittle by Δ, and brittle by X.

(7) Comprehensive Evaluation The above evaluation items (4), (5) and (6) were comprehensively judged, and a good one was evaluated as ○, a slightly poor one as Δ, and a poor one as ×.
And

(8) Glass transition temperature JIS-K71 using Perkin Elmer DSC-7
21.

(Examples 1-2 / Comparative Examples 1-4) Tg55
Melt extruded poly-L-lactic acid (Lacty 5000, manufactured by Shimadzu Corporation) having a weight average molecular weight of about 200,000 from a T-die at 180 ° C, quenched on a casting drum maintained at 50 ° C, and obtained an unstretched sheet with a thickness of 500 µm. I got

The obtained sheet was clamped to a thermoforming machine (PLAVAC-FE36PH, manufactured by Sanwa Kogyo Co., Ltd.), preheated to the molding temperature shown in Table 1 by an infrared heater, and then pressed into a mold by a plug to be preliminarily prepared. Molding and stretching were performed, and then the inside of the mold was evacuated to form a cup. The stretching was performed simultaneously with the molding.

Samples shown in Table 1 were obtained by changing the molding temperature and the stretching area ratio. The stretching area magnification was changed by variously changing the plug and the mold.

Comparative Example 5 Poly L having a Tg of 40 ° C. and a weight average molecular weight of about 200,000 plasticized by adding 6% of lactide.
-Lactic acid (manufactured by Shimadzu Corporation: Lacti 5000) at 180 ° C for T
It was melt-extruded from a die and quenched on a casting drum maintained at 50 ° C. to obtain an unstretched sheet having a thickness of 500 μm.
The obtained sheet was molded in the same manner as in Example 1 and evaluated.

[0041]

[Table 1]

[0042]

According to the present invention, by forming a thermoformed product having specific characteristics from a polylactic acid-based polymer which is a degradable polymer, the brittleness is improved in the formed portion and the strength is excellent. The unmolded portion is brought into contact with the support, exhibits the same practical strength, and can be obtained as a thermoformed product that is tough enough to withstand distribution and storage as a whole, and has good heat resistance.

Continued on front page F term (reference) 3E033 BA30 CA18 FA04 4F208 AA24A AE10 AR06 MA01 MA02 MB01 MC04 MG11 MH06 MK06

Claims (1)

[Claims] 1. A sheet comprising a polylactic acid-based polymer having a weight average molecular weight of 100,000 or more and a glass transition temperature of 50 ° C. or more, at a molding temperature of 95 to 140 ° C. and a stretching area magnification of 2 to 20 times. A polylactic acid-based thermoformed product which is formed and has an average degree of in-plane orientation ΔP of a molded portion of the molded product in the range of 2 × 10 ⁻³ to 30 × 10 ⁻³ .