WO2004003077A1

WO2004003077A1 - Container formed by stretch forming

Info

Publication number: WO2004003077A1
Application number: PCT/JP2002/006624
Authority: WO
Inventors: Takurou Itoh; Hiroto Watanabe
Original assignee: Toyo Seikan Kaisha,Ltd.
Priority date: 2002-06-28
Filing date: 2002-06-28
Publication date: 2004-01-08
Also published as: AU2002313314A1

Abstract

A container formed by stretch forming from a resin consisting mainly of polylactic acid, wherein the resin has a crystallization initiation temperature of 75°C or higher, has substantially two peaks when examined with a differential scanning calorimeter in the temperature range of 75 to 160°C where heat of crystallization is observed, and can hence be formed by stretch forming. The container is excellent in transparency and heat resistance.

Description

Specification

Stretched container Field of the invention

The present invention relates to a stretch-formed container formed from a resin mainly composed of polylactic acid, and more particularly, to a stretch-formed container having excellent stretch-moldability and improved heat resistance and transparency of the container. The present invention relates to a stretch-formed container formed from a resin mainly composed of polylactic acid. Conventional technology

As an ideal solution for plastic waste, degradable plastics that disappear in the natural environment are attracting attention, and among them, bacterium and fungi are among the most important. Biodegradable plastics, which break down by the action of enzymes released outside the body, have been used for some time.

However, this biodegradable plastic is excellent in harmony with the environment such as biodegradability, but it has good moldability and mechanical strength of stretch-formed products. However, they could not be satisfied with such points.

For example, even among the biodegradable plastics, aliphatic polyesters have poor melt properties of resin, and can be used for direct blow molding, injection stretch molding, and sheet thermoforming. There is a problem that it is difficult to form such as a foam. For this reason, the melt tension is improved by adding an inorganic filler (Japanese Patent Application Laid-Open No. Hei 5-289263). Higher molecular weight by chain stretching using acid anhydride (Japanese Patent Application Laid-Open No. Hei 7-250278) has been proposed.

Conventionally, aliphatic polyesters include, for example, P-hydroxybutyrate (PHB), and 3-hydroxybutyrate (3HB). And 3 — Hydroxylate Rate (3 HV) with random copolymers, poly (ε — force pro- lectone) (PCL), polybutylene Known are xinate (PBS), polybutylene succinate (ADBA), polylactic acid (LLA) and the like.

Among these aliphatic polyesters, they are industrially mass-produced, easy to obtain, and environmentally friendly. Lactic acid is listed. Polylactic acid (PL-A) is a resin made from cereal starch such as corn. Fermented starch, fermented lactic acid, and lactic acid are treated as monomers. It is a polymer. It is generally produced by a ring-opening polymerization method of lactide, which is a dimer, and a direct polycondensation method. This polymer is decomposed by water and carbon dioxide by natural microbes, and it is expected to become a complete recycling system type resin. It has been done. In addition, the glass transition point (T g) has an advantage that the glass transition point (T g) is about 60 ° C., which is close to the T g of polyethylene terephthalate. .

However, polylactic acid, which is generally used in the field of packaging containers, like other aliphatic polyesters, still has to be solved in terms of moldability and the like. Have a problem That is, as described below, polylactic acid includes D-lactic acid, L-lactic acid, and DL-lactic acid, and among them, polylactic acid composed of monolactic acid is also used. (L-lactic acid) can be used in the field of packaging containers because it forms oriented crystals by stretching and improves mechanical strength such as yield point strength, elastic modulus, and thermal dimensional stability. On the other hand, polylactic acid, which consists solely of L-lactic acid, has high optical purity and high crystallinity, and forms crystals upon heating the preform and subsequent stretching. And overstretching cause whitening, making it difficult to combine orientational crystallinity and transparency, which poses a practical problem. Disclosure of the invention

Accordingly, an object of the present invention is to provide a stretch container having transparency, stretch moldability, and thermal dimensional stability in a stretch-molded container formed of a resin mainly composed of polylactic acid. 0% to provide a molded container.

According to the present invention, in a stretch-formed container formed of a resin mainly composed of polylactic acid, the crystallization start temperature is 75 ° C or more, and the temperature measured by a differential scanning calorimeter is 7 ° C. A stretch-formed container characterized by having substantially two peaks in a crystallization exothermic temperature range of 5 to 160 ° C. is provided.

In the stretch-formed container of the present invention,

1. Polylactic acid has a higher ratio of optically active isomer (d) and a lower ratio of optically active isomer (d) Is a pre-

2. The axial shrinkage of the side wall at a temperature of 55 ° C is 4% or less,

3. The light transmittance at a wavelength of 465 nm on the side wall is 60% or more.

Is preferred. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a general polylactic acid DSC curve.

FIG. 2 is a view showing the DSC curve of polylactic acid used in Example 1.

FIG. 3 is a view showing a DSC curve of polylactic acid used in Comparative Examples 1 and 2. BEST MODE FOR CARRYING OUT THE INVENTION The stretch-formed container of the present invention has a crystallization onset temperature of 75 ° C. or higher and a temperature of 75 to 160 ° C. measured by a differential scanning calorimeter (DSC). Some are characterized by having substantially two peaks in the crystallization exothermic temperature range of ° C.

Polylactic acid has the following formula (1) Chemical 1

C H 3 O

I II

― [-O-CH-C] Poly (L-lactic acid) composed of repeating units represented by one (1), composed of only L-lactic acid, and D-lactic acid only Poly (D-lactic acid), and poly (DL-lactic acid) in which L-lactic acid unit and D-lactic acid unit are present at an arbitrary ratio.

As mentioned above, it is desirable to use polylactic acid with high optical purity in order to improve the mechanical strength of the container.However, because of its high crystallinity, stretch molding is preferred. It is easy to whiten due to thermal crystallization. On the other hand, optically pure (low optical purity) polylactic acid, which is excellent in stretch moldability, is less likely to be oriented and crystallized in stretch molding, resulting in poor heat resistance. In the present invention, polylactic acid having a crystallization start temperature of 75 ° C. or higher is used to disperse the optically active isomer (d) in the molecular chain unevenly. Thus, it is possible to provide a stretch-molded container having transparency, stretch-moldability, and heat resistance while having biodegradability.

On the other hand, when the amount of the optically active isomer (d) is small, crystallization proceeds during the stretch molding, and excellent transparency cannot be obtained. As a result, stretch molding becomes difficult. It will not be possible to provide transparency.

Further, the polylactic acid used in the present invention has the composition It is also important that the crystallization onset temperature is 75 ° C or higher, and if the crystallization temperature is lower than 75 ° C, whitening due to excessive elongation occurs during molding. This makes it difficult to stretch.

Further, the stretch-formed container of the present invention has substantially two peaks in a crystallization range temperature range of 75 to 160 ° C. measured by a differential scanning calorimeter (DSC). And are important.

Figure 1 shows a typical DSC curve of polylactic acid, and Figure 3 shows a DSC curve of polylactic acid containing 2.0% of the optically active isomer (d). Also has only one peak in the crystallization temperature range. On the other hand, the polylactic acid used in the present invention has two peaks in the crystallization temperature range, as shown in FIG. That is, since the stretch-formed container of the present invention has both a low-temperature crystallization component and a high-temperature crystallization component, stretch-forming can be performed while maintaining transparency. At the same time, it becomes possible to provide an oriented crystal, and at the same time, it is possible to improve the heat resistance. This is also evident from the results of the examples described below. Even for polylactic acid having an optically active isomer (d) ratio of 2.0%, a single peak is observed. The polylactic acid that is present causes whitening during the stretch molding process and cannot impart transparency (Comparative Examples 1 and 2), whereas the double peaks do not. In the stretch-formed container of the present invention having the following properties, it does not cause whitening and has excellent transparency. Equipment can be provided. (Examples 1 and 2).

(Polylactic acid)

Polylactic acid used in the present invention is, of course, not limited to, but is preferably in the range of 100,000 to 3,000,000, in particular, 2,0000 to 2,500,000. It is preferred to have a weight average molecular weight of The density is 1.26 to 1.20 gcm ³ , the melting point is 1665 to 200 ° C, and the melt flow rate (ASTMD 1238, 190 ° C) is 2 to It is preferably in the range of 20 g Z 10 minutes.

In the stretch molded container of the present invention, polylactic acid (A) having a high ratio of the optically active isomer (d) and polylactic acid having a low ratio of the optically active isomer (d) are used. It is desirable to use (B) by blending it. A high ratio of the optically active isomer (d) means that the optically active isomer (d) is generally contained in the range of 4 to 10%, and the optically active isomer (d) is contained. Is low when the content of the optically active isomer (d) is generally in the range of 0.5 to 1.5%.

In the present invention, it is desirable to mix the optically active isomers in a ratio within the range of 1.5 to 3.5 / ₀ . Examples of the blending method include a dry blend and a melt blend, and, if necessary, a solid phase polymerization. It is also possible to apply.

In the container of the present invention, the above-mentioned polylactic acid can be used alone, or it can be used as a blend with another aliphatic polyester or another resin. It can also be used as Other aliphatic polyesters include 3—hydroxybutyrate, 3—hydroxyvalerate, and 3—hydroxyprolate. , 3-Hydrogen heptanoate, 3-Hydroxy octanoate, 3-Hydroxycinanoate, 3-Hydroxy Polycyanate, r-butyrolactone, δ-valerolactone, ε-force proton, etc. Or one of these copolymers.

Further, the container of the present invention can be used as a single layer of the above polylactic acid resin composition or, depending on the properties of the contents, ethylene. By forming layers such as vinyl alcohol copolymer saponified compound, mexylylene adipamide (ΜXD6), cyclic olefin copolymer, etc. In addition, it is possible to provide a metal oxide coating layer.

In addition, other resins that can be used in the form of a blend or a laminate include a barrier resin, for example, a hydroxyl group that exhibits a barrier property to oxygen. Thermoplastic resin contained, Nylon resin, P / R, Polyester resin, High-trile resin, and exhibits barrier properties to water vapor Cyclic olefin-based copolymers and the like can be mentioned.

Among these, a hydroxyl group-containing resin is preferred in terms of biodegradability, and any resin can be used as long as thermoforming is possible. This resin has, in its molecular chain, a repeating unit having a hydroxyl group and a unit for imparting thermoformability to the resin. Hydroxyl-containing repeating units are vinyl alcohol units and hydroxyalkyl (meta) acrylate units. Although it does not matter, vinyl alcohol units are preferred in terms of biodegradability. Other units contained in this hydroxyl "a" resin include olefin units such as ethylene and propylene, and vinyl esters such as vinyl acetate. And alkyl (meta) acrylate units, etc. These hydroxyl group-containing resins are at least sufficient to form a film. It must be a molecule.

Suitable hydroxyl-containing resins are 10 to 40 mol% of ethylene units, 40 to 88 mol% of vinyl alcohol units, and 50 mol % Or less of the ester-containing vinyl unit.

By using such a hydroxyl group-containing polymer as a preform or a laminate, it is possible to improve the gas barrier properties of the stretched molded product. However, the advantage that biodegradability is not substantially impaired is achieved.

The container of the present invention may contain various coloring agents, fillers, mechanical or organic reinforcing agents, lubricants, plasticizers, leveling agents, surfactants, etc., depending on the intended use. Thickeners, thinners, stabilizers, antioxidants, ultraviolet absorbers, antioxidants and the like can be blended according to known formulations.

(Stretch molding container and its manufacturing method)

The stretch blow molded article of the present invention is obtained by biaxially stretching a preform (preform) provided with a layer made of the above-mentioned resin composition of polylactic acid. Manufactured from this.

The manufacture of preforms is known to the public. 200

It can be manufactured by extrusion molding, injection molding, or compression molding.

For example, by extruding the molten resin through a τ die, the thin film of the stretched film, and the compressed air to the film and the cup Molding Sheets for plug-assist molding are molded. In addition, by extruding the molten resin through a ring die, it is possible to mold a pipe-shaped preform for container molding. .

Furthermore, the molten resin is injected into a mold composed of a cavity mold and a core mold by a screw or a plunger. In this way, a preform for a three-dimensional container such as a bottle is formed. Also, by compressing the molten resin with a cavity mold and a core mold, a three-dimensional preform such as a bottle can be obtained.

In order to manufacture a preform formed from a laminate of polylactic acid and another resin, for example, a hydroxyl group-containing resin, a technique known per se is used, for example, extrusion molding. In the case of the method, a multi-layer preform is manufactured by co-extrusion using a multi-layer die using an extruder corresponding to the resin.

Further, in the injection molding, a multilayer preform can be formed by a simultaneous co-extrusion method or a sequential co-extrusion method known per se. Furthermore, even in the compression molding method, a multi-layered preform can be produced by forming a multi-layered molten resin by co-extrusion or the like. Wear .

The obtained preforms are infrared heating, hot air heating, After being heated by heating means such as frequency induction heating or ultrasonic heating, a stretched molded article is obtained by stretching and blowing in a mold.

Although the stretching temperature varies depending on the type of polylactic acid and the blend or the resin to be laminated, the glass transition point (Tg) of polylactic acid is generally used. ), A temperature of T g + 10 ° C. to T g + 20 ° C. is appropriate. Generally speaking, the stretching ratio in the machine direction (the direction of the container axis) is 1.4 to 4.0 times, and the stretching ratio in the transverse direction (the container circumferential direction) is 1.4 to 4.0 times. Therefore, it is preferable that the stretching is performed so that the area stretching ratio becomes 2 to 16 times.

As is clear from the results of the examples described later, the stretch-molded container of the present invention has an axial shrinkage of the side wall portion at a temperature of 55 ° C of 4% or less, particularly 3% or less. Excellent heat resistance, especially dimensional stability.

Further, the stretch-formed container of the present invention is free from whitening due to overstretching or overheating, and has a light transmittance of 60% or more, particularly 70%, at a wavelength of 465 nm on the side wall. % And excellent transparency. Examples Examples of the present invention are shown below. Note that the present invention is not limited to the following embodiments.

(resin) According to Shimadzu Corporation, polylactic acid having a weight-average molecular weight of 160,000 and an optically active isomer (d) ratio of 1.2% (L acty 9100) , 2.0% of a polylactic acid resin (Lacty 900), and 5.0% of a polylactic acid flour (Lacty500).

(Bottle molding)

By using an injection molding machine, a preform having a diameter of 28 mm0 is injection molded at a mold temperature of 15 ° C under the conditions of 190 ° C to 200 ° C. Was Next, the preform was reheated to 80 to 90 ° C using an infrared heating heater, and the area stretch ratio was 4 to 10 times using a mold blow molding machine. By stretching, a bottle having a mean wall thickness of 300 OjUm with a volume of 500 ml was prepared.

(Evaluation of appearance of molding pot)

Immediately after the blow molding, the presence of microvoid whitening due to overstretching and the presence of crystal whitening due to overheating were confirmed. In this case, let X be the pot (light transmittance power less than 60% at 465 nm) generated by overstretching and whitening due to crystal formation, and let X be the transparency. The bottle whose light transmittance was maintained (the light transmittance at 465 nm was 60% or more) was designated as 〇.

(Differential scanning calorimetry)

Using a SEIKO differential scanning calorimeter, a 10 mg polylactic acid sample cut out of the preform was used, and the temperature range was 40 ° C to 200 ° C. At a heating rate of 10 ° C. In this case, the base line of the crystallization peak is heated to a high temperature after the end of the glass transition point endothermic peak. Large side of oil tree ο out ο 9 つ 8 1 1

The point of rising from this baseline was defined as the crystallization onset temperature.

Heat-resistant)

The obtained injection molded container was stored in a 55 ° C constant temperature bath for 5 hours, and the dimensional deformation of the container side wall was observed. X was defined as one that shrunk well by 4% in dimension, and one with shrinkage of 4% or less.

Example 1

Specific power of optically active form (d) 1.2% of polylactic acid tree and 5.0% of optically active isomer (d) of polylactic acid were respectively 78% and 2% by weight. The blend was adjusted to 2%, and a polylactic acid resin composition pellet having an average optically active isomer (d) ratio of 1.% was prepared. Next, using an injection molding machine, the mold temperature was set at 190 ° C to 200 ° C.

A preform having a diameter of 28 mm 0 was injection molded at 5 ° C. The obtained preform was reheated to 0 ° C using an infrared heating heater, and the area was stretched at a stretching ratio of 4 to 10 times. Average wall thickness of 0 ml volume 3

A 0 m bottle was molded.

Example 2

Specific power of optically active compound (d): 1.2 o _{/ o} polylactic acid resin and optically active isomer (d): 5.0% % And 22%, and then use a stirring-type vacuum dryer.

Solid-state polymerization in the temperature range up to 0 ° C and average optically active isomer (d.) Polylactic acid resin composition pellets with specific power << 1. '8% were prepared. Next, using an injection molding machine, a preform having a diameter of 28 mm0 was injection-molded at a mold temperature of 15 ° C under conditions of 190 ° C to 200 ° C. did . After the obtained preform was reheated to 90 ° C using an infrared heating heater, a blow molding machine was used at an area stretching ratio of 4 to 10 times. , 500 m

A bottle with an average thickness of 3 volume of 3 O O jU m was formed.

(Comparative Example 1)

A polylactic acid tree having a ratio of the optically active isomer (d) of 2.0% was used. Using an injection molding machine, a preform with a diameter of 28 mm0 was injection-molded at a mold temperature of 15 ° C under conditions of 190 ° C to 200 ° C. . After the obtained preform was reheated to 90 ° C with an infrared heating heater, a blow molding machine was used at an area stretching ratio of 4 to 10 times. First, a pot with a mean wall thickness of 300 jUm having a volume of 500 ml was formed.

(Comparative Example 2)

Polylactic acid resin having an optically active isomer (d) ratio of 2.0 / ₀ was used. Using an injection molding machine, a preform having a diameter of 28 mm ø was injection-molded at a mold temperature of 15 ° C under conditions of 190 ° C to 200 ° C. After reheating the resulting et a pli off O over arm to 8 0 ⁰ C by an infrared pressurized thermal heat COMPUTER at the area draw ratio 4 to 1 0 times the draw ratio, use the blanking B over molding machine A 500 ml bottle with an average wall thickness of 300 jUm was molded.

(Comparative Example 3)

Polylactic acid tree containing 1.2% of optically active isomer (d) A polylactic acid resin having a ratio of fat and photoactive isomer (d) of 5.0 / ₀ was melt blended to give a weight ratio of 78% and 22%, respectively. , The average optically active isomer (d) ratio power << 1.

An 8% polylactic acid resin composition pellet was prepared. Next, a preform having a diameter of 28 mm0 was formed by injection molding using a mold at a temperature of 190 ° C to 200 ° C and a mold temperature of 15 ° C. . Using the preform as an infrared heating heater

After reheating at 90 ° C, using a blow molding machine at a draw ratio of 7 to 25 times the area draw ratio, a pot with an average wall thickness of 500 mI and a thickness of 200 jum Molded.

table 1

'Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Preform 90 ° C 90. C 90X 80 ° C 90 ° C Heating temperature Whitening state. O OXX ― X Crystallization start 8 OV 80 ° C 80 ° C 80. C 80 ° C Temperature Crystallization peak Double Double Single. Single layer Double pattern Peak peak Peak ^al peak Peak Heat resistance 〇 o

Claims

Range of request

1. In a stretch-formed valley formed from a polylactic acid-based resin, the crystallization start temperature is 75 ° C or higher, and the temperature measured with a differential scanning Amami thermometer. A crystallization exotherm in the range of 75 to 160 ° C) Dish iiz. A stretch-formed container characterized by having substantially two peaks.

2. Polylactic acid is a blend of polylactic acid with a high ratio of optically active isomer (d) and polylactic acid with a low ratio of optically active isomer (d). The stretch-formed container according to claim 1, characterized in that:

3 says

The stretch-formed container according to claim 1 or 2, characterized in that the shrinkage in the axial direction of the side wall portion at a pan degree of 55 ° C is 4% or less.

4. Light transmittance at a wavelength of 4 65 nm on the side wall 60

%. The stretch-formed container according to any one of claims 1 to 3, wherein the stretch-formed container is at least 0.1%.