JPH07207041A - Polylactic acid film - Google Patents

Abstract

PURPOSE:To obtain a polylactic acid film excellent in strengths and hot dimensional stability from a polyLactic acid polymer being a degradable polymer. CONSTITUTION:This film is one made of a polyLactic acid polymer and having a surface orientation degree DELTAP of 3.0X10<-3> or above and a difference (DELTAHm-DELTAHc) of 20J/g or above (wherein DELTAHm is the heat of crystal melting as measured when the film is heated, and DELTAHc is the heat of crystallization generated when the heated crystal is crystallized).

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a film made of a polylactic acid polymer.

[0002]

2. Description of the Related Art At present, as a film having excellent transparency, strength and thermal dimensional stability, many polymer material films including polyethylene terephthalate stretched film are known and widely used in industry. Have been consumed. However, when these films are discarded in the natural environment, they remain without being decomposed due to their stability, causing problems such as spoiling the landscape and polluting living environments such as fish and wild birds.

Therefore, there is a demand for a material composed of a decomposable polymer that does not cause these problems.
Development is underway. One example is polylactic acid. It is known that polylactic acid is hydrolyzed naturally in soil, does not remain in its original form in soil, and then becomes a decomposition product harmless by microorganisms.

However, regarding the polylactic acid film,
Up to now, little has been known, and no industrially useful film excellent in both strength and thermal dimensional stability has been known.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a polylactic acid film having practical strength and thermal dimensional stability.

[0006]

Means for Solving the Problems As a result of intensive investigations by the present inventors, the present inventors have made a polylactic acid-based polymer, have a plane orientation degree ΔP of 3.0 × 10 ⁻³ or more, and raise the film. Difference between heat of crystal fusion ΔH _m when heated and heat of crystallization ΔH _c generated by crystallization during heating (ΔH _m −ΔH _c ).
Of 20 J / g or more, it was found that a polylactic acid film excellent in strength and thermal dimensional stability can be obtained,
The present invention has also been completed.

The present invention will be described in detail below. The polylactic acid-based polymer used in the present invention is polylactic acid or a copolymer of lactic acid and another hydroxycarboxylic acid, or a mixture thereof, and other polymer materials within a range that does not impair the effects of the present invention. May be mixed. Further, for the purpose of adjusting molding processability and film physical properties, a plasticizer, a lubricant,
It is also possible to add additives such as inorganic fillers and ultraviolet absorbers, and modifiers.

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. Typical examples include 6-hydroxycaproic acid and the like.

As these polymerization methods, any known method such as condensation polymerization method and ring-opening polymerization method can be adopted. Furthermore, a small amount of a chain extender for the purpose of increasing the molecular weight, for example, You may use a diisocyanate compound, a diepoxy compound, an acid anhydride. The weight average molecular weight of the polymer is preferably from 10,000 to 1,000,000. When the weight average molecular weight is less than this range, practical physical properties are hardly exhibited, and when it exceeds the above range, the melt viscosity becomes too high and the moldability becomes poor.

The polylactic acid film in the present invention is obtained by converting these polymers into a flat or cylindrical unstretched sheet or a sheet-like melt by a general melt molding method such as an extrusion method, a calender method or a pressing method. Then, it is obtained by uniaxially or biaxially stretching it by a roll method, a tenter method, a cubula method, an inflation method or the like.

In the present invention, the degree of plane orientation ΔP of the film is determined by the balance between the composition of the polymer and the molding processing conditions.
And the difference between the heat of crystal fusion and the heat of crystallization of the film (ΔH
It is most important that _m −ΔH _c ) and a certain value or more. That is, in the polylactic acid-based film, the original brittleness of the material is improved by increasing ΔP, and the thermal dimensional stability that decreases with the increase of ΔP is increased (ΔH _m −ΔH _c ). This can be improved.

ΔP represents the degree of orientation in the plane direction relative to the thickness direction of the film, and is usually calculated by the following formula by measuring the refractive index in the directions of three orthogonal axes. ΔP = {(γ + β) / 2} -α (α <β <γ) Here, γ and β are biaxial refractive indices orthogonal to the film surface, and α is a refractive index in the film thickness direction.

ΔP depends on the crystallinity and the crystal orientation, but largely depends on the molecular orientation in the film plane. That is, by increasing the molecular orientation in the plane of the film, particularly in one or two directions of the flow direction of the film and / or the direction orthogonal thereto, in the non-oriented sheet / film, ΔP is 1.0 × 10 ⁻³ or less. Can be increased to 3.0 × 10 ⁻³ or more specified in the present invention. As a method for increasing ΔP, in addition to all known film stretching methods, a molecular orientation method using an electric field or a magnetic field can be adopted.

When biaxial stretching by the tenter method is adopted, the stretching conditions are as follows: stretching temperature 50 to 100 ° C., stretching ratio 1.5 to 5 times, stretching speed 100% / min to 10000.
% / Min is generally used, but the appropriate range varies depending on the composition of the polymer and the thermal history of the unstretched sheet, so it can be appropriately determined while looking at the value of ΔP. The same applies to the case where another stretching method such as the cubula stretching method is adopted. ΔP
When it is less than 3.0 × 10 ⁻³ , the polylactic acid-based film is poor in strength and brittle, so it is difficult to put it to practical use.
When it is set to × 10 ^-3 or more, strength and brittleness are improved and practically no problem occurs.

However, if ΔP is 3.0 × 10 ^-3 or more, the thermal dimensional stability of the film becomes poor, and the practical properties of the film are greatly impaired. What is thermal dimensional stability?
It is an indicator of whether the film can retain its original dimensions without shrinking when exposed to an atmosphere at a temperature slightly higher than room temperature.In many applications where the film is used, the thermal dimensional stability is usually High prices are required.

In a polylactic acid type film having a ΔP of 3.0 × 10 ⁻³ or more, the (ΔH _m −ΔH _c ) of the film is controlled to 20 J / g or more in order to obtain practical thermal dimensional stability. This is very important. That is, (ΔH _m −ΔH
_{When c} ) is less than 20 J / g, the thermal dimensional stability of the film is poor and it cannot be put to practical use in many applications.
If it is at least J / g, the thermal dimensional stability will be good.

ΔH _m and ΔH _c are obtained by differential scanning calorimetry (DSC) of the film sample, and ΔH _m and ΔH _c are
H _m is the amount of heat required to melt all the crystals when the film is heated at a temperature rising rate of 10 ° C./min, and is calculated from the area of the endothermic peak due to crystal melting that appears near the crystal melting point of the polymer. . Further, ΔH _c can be obtained from the area of the exothermic peak generated during crystallization that occurs during the temperature rising process.

ΔH _m mainly depends on the crystallinity of the polymer itself, and takes a large value in a polymer having a large crystallinity. By the way, in the homo-L-lactic acid polymer without copolymerization, about 50
J / g. Further, ΔH _c is an index relating to the crystallinity of the film at that time with respect to the crystallinity of the polymer, and ΔH _c is
When the H _c is large, the crystallization of the film proceeds during the temperature rising process, that is, the crystallinity of the film is relatively low based on the crystallinity of the polymer. Conversely, Δ
When H _c is small, it means that the crystallinity of the film was relatively high based on the crystallinity of the polymer.

That is, one direction for increasing (ΔH _m -ΔH _c ) is to use a polymer having high crystallinity as a raw material.
To make a film with a relatively high degree of crystallinity. The crystallinity of the film depends to a large extent on the composition of the polymer, but is also greatly influenced by the processing conditions of the film.

In order to increase the crystallinity of the film in the molding step, especially in the biaxial stretching by the tenter method, the stretching ratio is increased to promote oriented crystallization, and after the stretching, heat treatment is performed in an atmosphere having a crystallization temperature or higher. The method is effective.

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. (1) By ΔP Atsube refractometer, the refractive index (α, β,
γ) was measured and calculated by the following formula.

ΔP = {(γ + β) / 2} −α (α <β <γ) γ: Maximum refractive index in the film plane β: Refractive index in the in-plane direction of the film orthogonal thereto α: Refraction in the film thickness direction rate

(2) ΔH _m -ΔH _c Using DSC-7 manufactured by Perkin Elmer, a film sample 10 mg was heated according to JIS-K7122 at a temperature rising rate of 10 ° C./min from a thermogram to determine the heat of crystal fusion. ΔH _m and heat of crystallization ΔH _c were calculated and calculated.

(3) Tensile strength and brittleness The tensile strength was measured using a Toyo Seiki Tensilon II machine according to JIS
-Measured based on K7127. Further, the brittleness was judged by touch. MD indicates the flow direction of the film, and TD indicates the direction orthogonal to the flow of the film. (4) Thermal Dimensional Stability A film sample is cut into 100 mm x 100 mm, immersed in a hot water bath at 80 ° C for 10 seconds, and then the vertical and horizontal dimensions are measured. Was used as an index.

[0025]

【Example】

(Examples 1 and 2) Poly L-lactic acid having a weight average molecular weight of 100,000 was extruded from a T-die with a 30 mmφ uniaxial extruder and rapidly cooled with a casting roll to a thickness of 200 μm.
To obtain an unstretched sheet. Then roll stretching in the longitudinal direction,
Then, it was stretched in the tenter in the width direction and subsequently heat-treated in the tenter. The stretching conditions and the subsequent heat treatment conditions were variously changed to obtain film samples shown in Table 1.
The flow rate of the film is 3 m / min, and the passing time through each stretching / heat treatment zone is 20 seconds.

[0026]

[Table 1]

From the results of Table 1, ΔP and (ΔH _m −Δ
It can be seen that the film having H _c ) within the range of the present invention is not brittle and has excellent strength, and also has good thermal dimensional stability.

(Example 3) Polylactic acid was prepared in the same manner as in Example 1 except that a copolymer of 97% by weight of L-lactic acid and 3% by weight of glycolic acid having a molecular weight of 200,000 was used and the stretching and heat treatment conditions were changed. Table 2 shows the results of obtaining the system films.

[0029]

[Table 2]

[0030]

According to the present invention, a film having excellent strength and thermal dimensional stability can be obtained from a polylactic acid polymer which is a degradable polymer.

Claims (1)

[Claims] 1. A plane orientation degree Δ comprising a polylactic acid-based polymer.
P is 3.0 × 10 ⁻³ or more, and the difference between the heat of crystal fusion ΔH _m when the film is heated and the heat of crystallization ΔH _c generated by crystallization during temperature increase (ΔH _m −ΔH A polylactic acid film characterized in that _c ) is 20 J / g or more.