JP2005330008A - Film case - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film case that can be used in a microwave oven and can be composted. <P>SOLUTION: The microwave-proof film case is formed, for example, by pressing a film of polylactic acid copolymer in which plane orientation ΔP is 3.0×10<SP>-3</SP>to 30×10<SP>-3</SP>, a difference (ΔHm-ΔHc) between a crystal fusion heat ΔHm when the temperature of the film is increased and a crystallization heat ΔHc generated by crystallization during the increase of the temperature is not less than 20 J/g, and ä(ΔHm-ΔHc)/ΔHm} is not less than 0.7. As for the microwave-proofness of the film case, tested by filling the film case with water to its half capacity and then heating the case for five minutes in a microwave oven with a rated high frequency output 500 W, the rate of a size change is 20% or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a film case that can be used in a microwave oven and can be composted.

Conventionally, an aluminum foil case has been used as a case to serve side dishes in lunch boxes sold at convenience stores and supermarkets. Since then, with the development of convenience stores, etc., it has become frequent to warm lunches in the microwave on the spot, and metal aluminum foil cases are no longer used.
Although the case was temporarily replaced by a paper cup, the paper case also has the disadvantage that side dishes containing a lot of water cannot be served due to its water resistance. Excellent plastic films such as polypropylene and polyethylene terephthalate have been developed.

However, since the sheet for producing the case described above is chemically and biologically stable, it remains and accumulates almost without being decomposed even if left in the natural environment. In addition to polluting the living environment, there is a problem that when it is buried as garbage, it remains almost undecomposed and shortens the life of the landfill.
In convenience stores, a system for so-called composting of unsold lunches has been established at each store, but those made of polypropylene and polyethylene terephthalate cannot be composted.

  Therefore, various packaging materials for lunch boxes are required to be made of materials that can be composted, and many researches and developments have been conducted. One of them is polylactic acid. It is known that polylactic acid is naturally hydrolyzed in the soil, the original form does not remain in the soil, and then becomes a harmless degradation product by microorganisms.

Since polylactic acid is inherently brittle, even if it is made into a sheet or film, sufficient strength cannot be obtained, and in particular, heat resistance is difficult to put into practical use.
Therefore, the present invention provides a biodegradable film case that has sufficient heat resistance and water resistance and can be composted with a microwave oven.

As a result of intensive studies to solve the above problems, the present inventors have completed the present invention. That is, the gist of the present invention is that the degree of plane orientation ΔP is 3.0 × 10 ⁻³ to 30 × 10 ⁻³ , and is generated by the amount of crystal melting heat ΔHm when the film is heated and crystallization during the temperature increase. A film case made of a polylactic acid polymer having a difference from the crystallization heat amount ΔHc (ΔHm−ΔHc) of 20 J / g or more and {(ΔHm−ΔHc) / ΔHm} of 0.7 or more, When the film case is filled with half of the water and heated in a microwave oven with a rated high-frequency output of 500 W for 5 minutes, the dimensional change rate obtained by the following formula is 20% or less.

Dimensional change rate (%) = {(B−A) / A} × 100
A: Diameter of the upper opening of the film case before heating (mm)
B: Diameter of the upper opening of the film case after heating (mm)

  As described above, the polylactic acid plastic cup of the present invention can be heated in a microwave oven and composted.

BEST MODE FOR CARRYING OUT THE INVENTION

  The present invention will be described in detail below.

The polylactic acid-based polymer used in the present invention is polylactic acid, a copolymer of lactic acid and other hydroxycarboxylic acid, or a mixture thereof, and other polymer materials as long as the effects of the present invention are not impaired. May be mixed.
In addition, additives such as plasticizers, lubricants, inorganic fillers, ultraviolet absorbers, and modifiers may be added for the purpose of adjusting the molding processability and physical properties of the sheet or molded body.

  Examples of lactic acid include L-lactic acid and D-lactic acid, and other hydroxycarboxylic acids include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, A typical example is 6-hydroxycaproic acid.

  As these polymerization methods, any known method such as a condensation polymerization method or a ring-opening polymerization method can be adopted. Furthermore, for the purpose of increasing the molecular weight, a small amount of chain extender, for example, a diisocyanate compound, an epoxy is used. A compound, an acid anhydride, or 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. Below this range, practical properties are hardly expressed, and the film cannot maintain strength during plastic cup molding. Cause problems. In the case of exceeding, the melt viscosity becomes too high and the molding processability is poor.

The polylactic acid-based film used in the present invention is formed into a sheet by a general melt-molding method such as an extrusion method, a calendar method, or a press method after sufficiently drying the above-described polymer to remove moisture. Then, it is obtained by quenching.
Practically, it is preferable that the polymer melt-extruded into a sheet is brought into contact with a rotating casting drum (cooling drum) and rapidly cooled. The temperature of the casting drum is suitably 60 ° C. or lower. If the temperature is higher than this, the polymer will stick to the casting drum and it will be difficult to take off, and crystallization will be promoted to develop spherulites and transparency. In addition to the decrease, thermoforming becomes difficult. Therefore, it is preferable to quench the sheet at 60 ° C. or lower to obtain a substantially amorphous sheet.

In addition, in the present invention, in order to significantly improve the inherent brittleness of the polylactic acid polymer and prevent cracking during plastic cup molding, the plane orientation degree ΔP of the polylactic acid film is set to 3.0 ×. Adjust to 10 ⁻³ to 30 × 10 ⁻³ .
Here, the degree of plane orientation ΔP represents the degree of orientation in the plane direction with respect to the thickness direction of the film, and is usually calculated by the following formula (1) by measuring the refractive index in the orthogonal three-axis direction.

ΔP = {(γ + β) / 2} −α (1)
(However, α <β <γ, where γ and β are the biaxial refractive indexes parallel to the film surface, and α is the refractive index in the film thickness direction.)

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

  As a method of increasing the degree of plane orientation ΔP, in addition to all known stretching methods, a molecular orientation method using an electric field or a magnetic field can be employed. Usually, the sheet or cylindrical material melt-extruded from the above-described T die, I die, round die or the like is rapidly cooled by a cooling cast roll, water, compressed air, etc., and solidified in a state close to amorphous. Thereafter, a method of stretching uniaxially or biaxially by a roll method, a tenter method, a tubular method or the like is desirably employed industrially.

As stretching conditions for an unstretched polylactic acid-based sheet, 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% / min are common. The appropriate range varies depending on the composition of the polymer and the thermal history of the unstretched sheet, and can be appropriately determined while looking at the value of the plane orientation degree ΔP.
By setting the degree of plane orientation ΔP to 3.0 × 10 ⁻³ or more, it is possible to prevent cracks during case molding. The upper limit is practically about 30 × 10 ⁻³ , and if it is attempted to increase the degree of plane orientation ΔP from this, stretching becomes unstable or impossible, and even if it can be stretched, it becomes difficult to form a film case. .
In a polylactic acid film having a plane orientation degree ΔP of 3.0 × 10 ⁻³ to 30 × 10 ⁻³ , the crystal when the film is heated in order to obtain practical thermal dimensionality in a microwave oven. It is possible to control the difference (ΔHm−ΔHc) between the heat of fusion ΔHm and the heat of crystallization ΔHc generated by crystallization during temperature elevation to 20 J / g or more and {(ΔHm−ΔHc) / ΔHm} to 0.7 or more. is important.

The amount of heat of crystal fusion ΔHm and the amount of heat of crystallization ΔHc are determined by differential scanning calorimetry (DSC) of the film sample. The amount of heat of crystal fusion ΔHm melts all crystals when the temperature is raised at a rate of temperature increase of 10 ° C./min. This is the amount of heat necessary for the heat treatment, and is obtained from the area of the endothermic peak due to crystal melting that appears in the vicinity of the crystal melting point of the polymer.
The amount of heat of crystallization ΔHc is determined from the area of the exothermic peak generated during crystallization that occurs during the temperature rising process, and it is important to control the (ΔHm−ΔHc) of the film to 20 J / g or more. That is, when (ΔHm−ΔHc) is less than 20 J / g, the thermal dimensional stability of the film case is poor and deformation occurs when the microwave oven is used. On the other hand, if it is 20 J / g or more, the thermal dimensional stability will be good.

  The amount of heat of crystal fusion ΔHm mainly depends on the crystallinity of the polymer itself, and takes a large value for a polymer with high crystallinity. Incidentally, the complete homopolymer of L-lactic acid or D-lactic acid having no copolymer component is 60 J / g or more, and in the copolymer of these two kinds of lactic acid, the heat of crystal fusion ΔHm varies depending on the composition ratio.

  The crystallization heat amount ΔHc is an index related to the crystallinity of the film at that time with respect to the crystallinity of the polymer. When the crystallization heat amount ΔHc is large, the crystallization of the film proceeds in the temperature rising process. In other words, the crystallinity of the film was relatively low based on the crystallinity of the polymer. Conversely, when the amount of heat of crystallization ΔHc is small, the crystallinity of the polymer is used as the standard. This means that the degree of crystallinity is relatively high.

  Here, one direction for increasing (ΔHm−ΔHc) is to form a film having a relatively high degree of crystallinity from a polymer having high crystallinity as a raw material. Depends on the composition.

In order to increase the heat of crystal melting ΔHm of the polymer itself to 20 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 in the range of 0: 100 to 6:94. It is good to.
In order to reduce the amount of heat of crystallization ΔHc, that is, to increase the degree of crystallinity of the film, it is necessary to select film forming conditions. In order to increase the crystallinity of the sheet in the forming process, particularly the tenter method biaxial stretching, it is useful to increase the stretching ratio and promote orientation crystallization, or to heat-treat in an atmosphere above the crystallization temperature after stretching. is there.

  In addition, since the crystallization temperature tends to decrease as the degree of plane orientation ΔP increases, in the present invention, the heat treatment is performed at 70 ° C. or higher, preferably 90 ° C. to 170 ° C. for 3 seconds or longer. The higher the heat treatment temperature and the longer the heat treatment time, the better the thermal dimensional stability. (ΔHm−ΔHc) / ΔHm is an index indicating the degree of crystallinity of the sheet. If the value is smaller than 0.7, deformation occurs when the microwave oven is used, which is not preferable.

In the present invention, the polylactic acid film produced as described above is case-molded to obtain a film case.
Although the thickness of the film suitable for the film case is not particularly limited, 0.01 mm to 0.10 mm is preferably used from the viewpoint of use. Especially preferably, it is the range of 0.02 mm-0.05 mm.

  The case may be formed by pressing using a normal hydraulic press or mechanical press. Moreover, at the time of shaping | molding, in order to improve a moldability, you may shape | mold after preheating between the glass transition point Tg (degreeC)-melting | fusing point Tm (degreeC) of a polylactic acid polymer.

  Examples are shown below, but the present invention is not limited thereto. The measured values shown in the examples were measured and calculated under the following conditions.

-Degree of plane orientation ΔP
The refractive indexes (α, β, γ) in the three orthogonal directions were measured with an Abbe refractometer, and calculated by the following equation (1).

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

・ (ΔHm−ΔHc) / ΔHm
From a thermogram when a differential scanning calorimeter DSC-7 (manufactured by Perkin Elmer) was used to heat 10 mg of a film sample at a heating rate of 10 ° C./min based on JIS-K7122, ΔHm and crystallization heat amount ΔHc were obtained, and (ΔHm−ΔHc) / ΔHm was calculated.

-Suitability for microwave oven About half of the water in the film case was put and heated in a microwave oven with a rated high-frequency output of 500 W for 5 minutes. The deformation state after heating was determined from the dimensional change of the diameter of the upper opening. The dimensional change rate is expressed by the following equation (2).

Dimensional change rate (%) = {(BA) / A} × 100 (2)
(Here, diameter before test: A (mm) Diameter after test: B (mm))

The evaluation is
A: 0 to 10% = no problem in practical use
○: 11-20% = no problem in practical use
Δ: 21-30% = can be used depending on conditions
X: 31% or more
And Δ or more was regarded as acceptable.

(Examples 1-4)
Polylactic acid having a composition ratio of L-lactic acid and D-lactic acid as shown in Table 1 and having a weight average molecular weight of about 200,000 was extruded at 200 ° C. using a 90 mmφ uniaxial extruder, width 300 mm, and thickness after stretching. Was set to have a thickness of 0.04 mm to produce a sheet.
The unstretched sheet was sequentially stretched by a biaxial stretching machine under the conditions shown in Table 1 to obtain a desired stretched film.

  ΔP of the obtained stretched polylactic acid film was measured by the method described above to obtain ΔP. Moreover, (DELTA) Hm and (DELTA) Hc were obtained by measuring with the above-mentioned method. A film case having a bottom diameter of 45 mm, a top opening diameter of 70 mm, and a height of 30 mm was formed from the polylactic acid film.

(Comparative Examples 1-3)
As in the examples, polylactic acid having a weight-average molecular weight of about 200,000 was extruded at 200 ° C. at a composition ratio of L-lactic acid and D-lactic acid shown in Table 1 at 200 ° C., width 300 mm, stretched The thickness was set so that the subsequent thickness was 0.04 mm, and a sheet was produced.

  ΔP of the obtained stretched polylactic acid film was measured by the method described above to obtain ΔP. Moreover, (DELTA) Hm and (DELTA) Hc were obtained by measuring with the above-mentioned method. A film case having a bottom diameter of 45 mm and a height of 30 mm was formed from the polylactic acid film.

As is apparent from Table 1, Examples 1, 2, and 3 satisfying the conditions of the present invention are excellent in moldability and suitability for microwave ovens.
In Example 4, since (ΔHm−ΔHc) was small, the suitability for the microwave oven was inferior, but not at a level where it could not be used.
On the other hand, in Comparative Example 1, (ΔHm−ΔHc) / ΔHm was small, so the suitability for the microwave oven was poor, and it was not resistant to use.
In Comparative Example 3, (ΔHm−ΔHc) and (ΔHm−ΔHc) / ΔHm were satisfied, but since ΔP was small, cracking occurred at the time of case molding, and molding could not be performed.

(Example 5)
Using the film case prepared in Example 1 as a sample, water, humus, and nutrients were placed in a household conposter and allowed to stand at 60 ° C., whereupon rapid degradation started after 2 weeks and weight retention after 4 weeks. Was 10% or less.

(Comparative Example 4)
As a comparative example, a film case made of OPP was composted under the same conditions as in Example 5. However, even after 4 weeks, the physical property retention was 100% and was not decomposed at all.

Claims (6)

The degree of plane orientation ΔP is 3.0 × 10 ⁻³ to 30 × 10 ⁻³ , and the difference between the amount of heat of crystal melting ΔHm when the film is heated and the amount of heat of crystallization ΔHc generated by crystallization during the temperature increase ( ΔHm−ΔHc) is 20 J / g or more and {(ΔHm−ΔHc) / ΔHm} is a film case made of a polylactic acid polymer having 0.7 or more,
A film case having suitability for a microwave oven, in which half the water is placed in the film case and heated for 5 minutes in a microwave oven with a rated high-frequency output of 500 W, the dimensional change rate obtained by the following formula is 20% or less.
Dimensional change rate (%) = {(B−A) / A} × 100
A: Diameter of the upper opening of the film case before heating (mm)
B: Diameter of the upper opening of the film case after heating (mm) The degree of plane orientation ΔP is 3.0 × 10 ⁻³ to 30 × 10 ⁻³ , and the difference between the amount of heat of crystal melting ΔHm when the film is heated and the amount of heat of crystallization ΔHc generated by crystallization during the temperature increase ( 2. The film case according to claim 1, comprising a polylactic acid film having [Delta] Hm- [Delta] Hc) of 20 J / g or more and {([Delta] Hm- [Delta] Hc) / [Delta] Hm} of 0.7 or more.   A polylactic acid in which the composition ratio of L-lactic acid to D-lactic acid is 100: 0 to 94: 6 or 0: 100 to 6:94, and the polylactic acid itself has a crystal melting heat ΔHm of 20 J / g or more. 3. The film case according to claim 2, comprising a lactic acid film.   The film case according to any one of claims 1 to 3, wherein the polylactic acid film having a thickness of 0.01 mm to 0.10 mm made of the polylactic acid is pressed.   A film is formed from polylactic acid containing L-lactic acid and D-lactic acid in a composition ratio of 99.5: 0.5 to 94.9: 5.1, and after biaxial stretching at 100 to 140 ° C. The film case according to any one of claims 1 to 4, wherein the polylactic acid film obtained by heat treatment is pressed. The plane orientation degree ΔP of the polylactic acid film is 11.5 × 10 ^{−3 to} 12.4 × 10 ⁻³ , the difference from the crystallization heat amount ΔHc (ΔHm−ΔHc) is 28 to 44 J / g, and The film case according to claim 1, wherein {(ΔHm−ΔHc) / ΔHm} is 0.84 to 0.97.