JP4734071B2 - Molding film - Google Patents

Description

  The present invention relates to a molding film made of polylactic acid and having biodegradability.

  Polylactic acid is a highly transparent and tough polymer, but it is easily hydrolyzed in the presence of water due to its chemical structure. Therefore, after disposal, it is decomposed without polluting the environment, and the load on the environment is small. Taking advantage of this property, a film-like product is subjected to a vapor deposition treatment and is beginning to be used as a food packaging material and a sealing material.

  However, the melting point of polylactic acid is usually about 170 ° C., and heat setting cannot be performed at a sufficiently high temperature when forming a stretched film. Therefore, the film obtained is a film that easily undergoes heat shrinkage, and lacks dimensional stability and heat resistance. Polylactic acid films have poor flexibility and do not have moldability as molding materials.

  As a method for improving the heat resistance of polylactic acid, poly-L-lactic acid (hereinafter referred to as “PLLA”) consisting only of L-lactic acid units and poly-D-lactic acid (hereinafter referred to as “PDLA”) consisting only of D-lactic acid units. Is known to form stereocomplex polylactic acid by mixing in solution or in a molten state. In order to obtain a stretched film having practical strength using this stereocomplex polylactic acid, it is necessary that the molecular weights of PLLA and PDLA be 100,000 or more. No stereocomplex polylactic acid can be obtained. In addition, in solution blending, a method of forming stereocomplex polylactic acid from PLLA and PDLA having a molecular weight of 100,000 or more has been attempted, but this method needs to be maintained in a solution state for a long period of time, and there is a problem in productivity. is there. Further, an amorphous polymer having a molecular weight of about 200,000 having 70 to 95 mol% of L-lactic acid units and an amorphous polymer having a molecular weight of about 200,000 having 70 to 95 mol% of D-lactic acid units are melt-blended to produce stereo. A method for producing complex polylactic acid is also known, but even if it is used as a stretched film, it has poor moldability.

JP-A 63-264913 JP 2000-17163 A

  The object of the present invention is a polylactic acid film having biodegradability, but has good moldability that can be used by bonding to a paper container, a decorative board, woodwork furniture, etc., and has dimensional stability and heat resistance. An object of the present invention is to provide a film for molding that is excellent in performance.

That is, the present invention is Ri Do from the layer B of the polylactic acid substantially unoriented structure, the layer A of the polylactic acid of the alignment structure disposed on both sides in contact with the layer,
The polylactic acid of layer A is a stereocomplex polylactic acid having a melting point of 190 to 220 ° C.
The polylactic acid of layer B has a melting point of 160-200 ° C.
The melting point of the polylactic acid in layer A is 15 ° C. or higher than the melting point of the polylactic acid in layer B.
It is a film for molding.

  According to the present invention, although it is a polylactic acid film having biodegradability, it has good moldability that can be used by being attached to a paper container, a decorative board, woodwork furniture, etc., and has dimensional stability and heat resistance. It is possible to provide a molding film that is excellent in performance.

Hereinafter, the present invention will be described in detail.
[Polylactic acid layer A]
The polylactic acid layer A is a layer having an orientation structure, and this orientation structure is formed by stretching. The stretching may be either uniaxial stretching or biaxial stretching. The melting point of the polylactic acid in layer A is preferably 190 to 220 ° C. When the melting point is less than 190 ° C, the heat resistance is inferior, and when it exceeds 220 ° C, the moldability is inferior.

  The melting point of the polylactic acid of layer A is at least 15 ° C., preferably at least 20 ° C., particularly preferably at least 30 ° C. higher than the melting point of the polylactic acid of layer B. If the difference in melting point is less than 15 ° C., the polylactic acid in the layer B cannot be made into a substantially non-oriented structure while maintaining the oriented structure of the polylactic acid in the layer A. In this case, part of the polylactic acid in the layer A starts to melt, and the film is likely to be cut in the film production process, or the film wound up in a roll shape is likely to be fused. In order to satisfy the condition of the melting point of the polylactic acid of the layer A, it is preferable to use stereocomplex polylactic acid as the polylactic acid of the layer A.

  In order to maintain the dimensional stability, deformation resistance and curl resistance of the molding film of the present invention and a processed product using the same at a high level, the glass transition temperature of the polylactic acid of the layer A is preferably 40 ° C. or higher. More preferably, it is 50 ° C. or higher. This glass transition temperature is a glass transition temperature observed when a polylactic acid is once melted, rapidly cooled and solidified, and then heated at a rate of 20 ° C./min with a differential scanning calorimeter. Change (specific heat change) temperature.

[Polylactic acid layer B]
The polylactic acid layer B is a substantially non-oriented layer. This non-oriented layer can be formed by heat-treating a polylactic acid layer having an oriented structure once formed by the stretching step of the step of producing the molding film of the present invention at a temperature equal to or higher than the melting point. . The melting point of the polylactic acid of the layer B is, for example, 160 to 200 ° C., preferably 165 to 195 ° C., and is at least 15 ° C. lower than the polylactic acid constituting the layer A of polylactic acid. When the melting point is less than 160 ° C, the heat resistance and strength are poor, and when it exceeds 200 ° C, the moldability is poor. The melting point is a melting point observed when a polylactic acid is once melted, then rapidly cooled and solidified, and the sample is heated at a rate of 20 ° C./min with a differential scanning calorimeter, which is a melting endothermic peak temperature.

In the molding film of the present invention, the respective melting endothermic peaks of the polylactic acid of layer A and layer B are detected. The glass transition temperature of the polylactic acid in layer B is preferably 40 ° C. or higher, more preferably 50 ° C. or higher. If the glass transition temperature is less than 40 ° C., a problem of adhesion in the film production process occurs, which is not preferable.
As polylactic acid satisfying such conditions, poly-L lactic acid that can be polymerized with L-lactic acid as the main component and / or poly-D lactic acid that can be polymerized with D-lactic acid as the main component are preferably used.

[Layer structure]
The molding film of the present invention comprises a polylactic acid layer B having a substantially non-oriented structure and a polylactic acid layer A having an oriented structure provided on both sides in contact with this layer, preferably having a uniaxial or more axis. It has a laminated structure of a polylactic acid layer B in which the stretched orientation structure is made into a non-oriented structure by heat treatment and a polylactic acid layer A having a uniaxial stretched orientation structure. The surface layer of the molding film of the present invention is composed of a polylactic acid layer A having an oriented structure. When the surface layer has a substantially non-oriented structure, not only the heat resistance of the film is inferior, but also the production process becomes inconvenient because the film tends to stick to the rolls in the process.

  For example, A / B / A (where “/” indicates the layer configuration) type, A / B / A / B / A type, as a configuration including the polylactic acid layer A having an oriented structure on the surface layer. A multi-layer structure such as a five-layer structure, a seven-layer structure, a nine-layer structure, and a 2n + 1 (n is a natural number) structure can be given. Of these configurations, a three-layer or five-layer configuration is preferable, and a three-layer configuration is particularly preferable.

  The polylactic acid layer B has a non-oriented structure by heat treatment. In this heat treatment, in the state where the polylactic acid layer A is laminated on both sides of the polylactic acid layer B, the polylactic acid layer B is lower than the melting point of the polylactic acid layer A and The temperature is higher than the melting point of the lactic acid layer B. By this heat treatment, the polylactic acid in the layer B becomes a molten state, and the oriented structure becomes a substantially non-oriented structure. This heat treatment is preferably performed by setting the temperature during the heat setting treatment after the stretching treatment in the coextrusion film forming method to a temperature lower than the melting point of the polylactic acid of the layer A and higher than the melting point of the polylactic acid of the layer B. It can be carried out.

  In the molding film of the present invention, the ratio (a / b) of the total thickness (a) of the layer A having an oriented structure and the total thickness (b) of the layer B having a substantially non-oriented structure is, for example, 0.01 to It is 0.60, preferably 0.02 to 0.43, more preferably 0.05 to 0.17.

  This total thickness ratio is, for example, when the layer structure is composed of three layers of A1 (thickness: a1) / B (thickness: b) / A2 (thickness: a2), that is, the total thickness ratio of layer A and layer B, that is, (a1 + a2) ) / (B). When the layer structure is composed of five layers of A1 (thickness: a1) / B1 (thickness: b1) / A2 (thickness: a2) / B2 (thickness: b2) / A3 (thickness: a3), layer A and layer The total thickness ratio of B, that is, (a1 + a2 + a3) / (b1 + b2). When the total thickness ratio (A / B) is less than 0.01, the outermost layer thickness of layer A is small, and it is difficult to control the thickness during film production, and the polylactic acid layer B is partially exposed to the surface layer. Unsatisfactory dimensional stability and poor heat resistance. When the total thickness ratio exceeds 0.60, the proportion of the polylactic acid layer B having a substantially amorphous structure is small and the moldability is lowered. For example, when the film for molding is subjected to vacuum suction molding with heating or preheating. This is not preferable because the processability of the moldability becomes insufficient.

  The total thickness of the molding film of the present invention is, for example, 20 to 100 μm, preferably 25 to 80 μm, and more preferably 30 to 60 μm. When the total thickness is less than 20 μm, film breakage and thickness unevenness occur during film formation, which is not preferable. If the total thickness exceeds 100 μm, the moldability at the time of molding the molding film under heating or preheating is not preferable.

[Inert particles]
The molding film of the present invention preferably contains inert particles in the polylactic acid of the layer A in order to obtain the slipperiness of the film. The average particle diameter of the inert particles is preferably 0.05 to 5 μm, more preferably 0.1 to 2 μm. When the average particle size is less than 0.05 μm, sufficient slipperiness cannot be imparted to the molding film, and when it exceeds 5 μm, the transparency of the molding film is lost. The shape of the inert particles is preferably spherical. By using spherical particles as inert particles, light scattering can be reduced and high light transmittance can be obtained.

  The inert particles preferably contain any element of Al, Si, Ca and Mg. As the inert particles, for example, when Si is contained, two types of spherical silicas having different average particle sizes may be combined, and spherical silica and spherical silicones having different particle sizes may be used in combination.

[Production method]
The polylactic acid itself constituting the layer A and the layer B can be produced by a known polylactic acid polymerization method. For example, it can be produced by ring-opening polymerization of lactide and dehydration condensation of lactic acid. These methods may be combined with solid phase polymerization.

  The molding film of the present invention is preferably produced by a coextrusion film forming method. For example, a case of producing a three-layer film (A / B / A) will be described. First, a polylactic acid chip used for the layer A is dried and melted, and in parallel with this, a polylactic acid chip used for the layer B Dry and melt. Subsequently, the molten polylactic acid is laminated in three layers so as to be A / B / A inside the die provided with the feed block, and then cast on a cooling drum to form an unstretched three-layer film. Subsequently, this unstretched three-layer film is stretched to obtain a three-layer stretched film having an oriented structure. This stretching may be performed under the condition that the polylactic acid layer A forms a desired alignment structure. For example, the layer A is stretched at a temperature of Tg (glass transition temperature) of −10 ° C. to Tg + 50 ° C. of the polylactic acid by 2.5 times or more, preferably 3-6 times in the machine direction, and then at a temperature of Tg + 10 to Tg + 50 ° C. The film is stretched 2.5 times or more in the transverse direction, preferably 3 to 6 times. At this time, the draw ratio is preferably 8 times or more, more preferably 9 times or more in terms of area magnification.

  The three-layer stretched film thus obtained is subjected to heat treatment. The heat treatment is performed at a temperature higher than the melting point of the polylactic acid in layer B. By this heat treatment, the polylactic acid of the layer B having the stretched orientation structure is melted and changed into a substantially non-oriented structure. The temperature of this heat treatment is preferably a temperature that is 5 ° C. or more higher than the melting point of the polylactic acid in the layer B and a temperature that is 10 ° C. or more lower than the melting point of the polylactic acid in the layer A. By performing this heat treatment, the polylactic acid layer A has the same effect as the heat setting treatment. As the heat treatment method, for example, a method in which heat treatment is performed in the process immediately after the film is stretched, or a method in which the film is wound into a roll after completion of the film stretching can be applied.

Hereinafter, the present invention will be described more specifically with reference to examples.
In addition, the measuring method and evaluation method of the characteristic used in the Example and the comparative example are as follows.

(1) Vacuum suction moldability Evaluation by vacuum suction molding was performed as an evaluation of molding processability. Using a commercially available product from As One Co., Ltd., Bifnel funnel AF3 (φ105mm), paste the film for evaluation to the upper mouth of this funnel with a double-sided tape etc., and set it at 100mm above the film with a 1200W industrial dryer for about 60 seconds. The film was heated until the temperature near the film surface reached 80 ° C. Then, using a Tokyo Rika Kikai Co., Ltd. aspirator A-3S, the film was suction-molded for 10 seconds under a vacuum degree of 50 mmHg from the lower part of the funnel to prepare a sample for evaluating the shape of the container. . The vacuum suction moldability was evaluated by measuring the followability and film thickness of the bottom end portion of the funnel that is most tensile molded.
(Circle): The film is shape | molded so that it may fully follow a funnel end bottom part, and the film thickness of this end bottom part is kept at 10% or more of the original film thickness.
(Triangle | delta): Although the film is shape | molded so that it may fully follow a funnel end bottom part, the film thickness of this end bottom part is thin, and is less than 10% of the original film thickness.
X: Even if the film is not sufficiently follow-molded to the funnel end bottom part, or the film is follow-formed, breakage of the film at the end bottom part is confirmed.

(2) Heat resistance The shape of the container after putting 50 cc of olive oil into the film sample in the shape of the container obtained by the method for evaluating vacuum suction formability of (1) above and heating in a 1500 W microwave oven for 3 minutes. The film samples were observed and the heat resistance was evaluated according to the following evaluation criteria.
○: No significant change.
Δ: Change such as deformation.
X: It is torn or melts.

(3) Film thickness 100 points were measured with an external micrometer, and the average value was obtained as the film thickness.

(4) Thickness of each layer A sample was cut into a triangle, fixed in an embedded capsule, and then embedded in an epoxy resin. The embedded sample was microtomed (ULTRACUT-S), and the cross-section parallel to the longitudinal direction was made into a thin film section having a thickness of 50 nm, and then observed and photographed with a transmission electron microscope at an acceleration voltage of 100 kV. From these, the thickness of each layer was measured, and the average thickness and relative standard deviation were determined.

(5) Melting point About 10 mg of sample was sealed in an aluminum pan for measurement and attached to a differential calorimeter (DuPont V4.OB2000 DSC), and the temperature was raised from 25 ° C. to 300 ° C. at a rate of 20 ° C./min. It was warmed and held at 300 ° C. for 5 minutes, then taken out, immediately transferred onto ice and rapidly cooled. This pan was again attached to the differential calorimeter, and the melting point (Tm) (unit: ° C) was measured by raising the temperature from 25 ° C at a rate of 20 ° C / min.

(6) Thermal contraction rate It computed from the change of the space | interval of the mark on a film before and behind heat-processing a film sample at 150 degreeC x 10 minutes.

[Reference Example] Production of polylactic acid Polylactic acid was produced by the following method.
200 wtppm of tin octylate was added to 100 wt% of L-lactide, and polymerization was performed at 190 ° C to produce pellets, which were designated as PLLA-1. The obtained PLLA-1 had a weight average molecular weight of 130,000 and a melting point of 170 ° C.
PLLA-2 was prepared by adding 200 wt ppm of tin octylate to 97.5 wt% of L-lactide and 2.5 wt% of D-lactide, and performing polymerization at 190 ° C. to produce pellets. . The obtained PLLA-2 had a weight average molecular weight of 120,000 and a melting point of 158 ° C.
200 wt ppm of tin octylate was added to 95 wt% of L-lactide and 5 wt% of D-lactide, and polymerization was performed at 190 ° C. to produce pellets, which were designated as PLLA-3. The obtained PLLA-3 had a weight average molecular weight of 120,000, but a melting point of 146 ° C.
200 wt ppm of tin octylate was added to 80 wt% of L-lactide and 20 wt% of D-lactide, and polymerization was performed at 180 ° C. to produce pellets, which were designated as PLLA-4. The obtained PLLA-4 had a weight average molecular weight of 110,000, but the melting point could not be clearly detected.

To 100% by weight of D-lactide, 200 wt ppm of tin octylate was added, and polymerization was performed at 190 ° C. to produce pellets, which were designated as PDLA-1. The obtained PDLA-1 had a weight average molecular weight of 130,000 and a melting point of 170 ° C.
200 wtppm of tin octylate was added to 97.5 wt% of D-lactide and 2.5 wt% of L-lactide, and polymerization was performed at 190 ° C to prepare pellets, which were referred to as PDLA-2. . The obtained PDLA-2 had a weight average molecular weight of 120,000 and a melting point of 158 ° C.
200 wt ppm of tin octylate was added to 95 wt% of D-lactide and 5 wt% of L-lactide, and polymerization was carried out at 190 ° C. to produce pellets, which were designated as PDLA-3. The obtained PDLA-3 had a weight average molecular weight of 120,000, but a melting point of 146 ° C.
200 wt ppm of tin octylate was added to 80 wt% of D-lactide and 20 wt% of L-lactide, and polymerization was performed at 180 ° C. to prepare pellets, which were referred to as PDLA-4. The obtained PDLA-4 had a weight average molecular weight of 110,000, but the melting point could not be detected clearly.

[Example 1]
A blend of PLLA-2 and PDLA-2 in the above reference example in a one-to-one ratio in a chip state is dried at 120 ° C. for 6 hours, and then supplied to an extruder hopper and melted at a melting temperature of 260 ° C. While supplying the inside of the die to form polylactic acid layer A, the above PLLA-1 was dried at 120 ° C. for 6 hours, then supplied to the extruder hopper, melted at a melting temperature of 240 ° C., and supplied to the inside of the die. As the polylactic acid layer B, a molten polymer was laminated on three layers of A / B / A, extruded onto a cooling drum having a surface temperature of 20 ° C., and rapidly cooled to obtain an unstretched three-layer film. At this time, the melting point of the stereocomplex polylactic acid formed in the polylactic acid layer A was 205 ° C.

  Subsequently, this unstretched three-layer film was successively biaxially stretched 3.0 times at 70 ° C. in the machine direction and 3.2 times at 90 ° C. in the transverse direction, then heat-set at 195 ° C., and A / B / A molding film having the structure of A was obtained. The thickness of the molding film was 50 μm in total, with the surface polylactic acid layer A on both sides made of stereocomplex polylactic acid being 2 μm and the inner polylactic acid layer B being 46 μm. Table 1 shows the evaluation results of vacuum suction moldability, heat resistance and heat shrinkage under heating. Both were good results.

[Example 2]
An unstretched three-layer film having an A / B / A configuration in the same manner as in Example 1 except that PLLA-3 is used instead of PLLA-2 and PDLA-3 is used instead of PDLA-2. Got. At this time, the melting point of the stereocomplex polylactic acid formed in the polylactic acid layer A was 195 ° C. Subsequently, this film was sequentially biaxially stretched in the same manner as in Example 1, and then heat-set at 185 ° C. to obtain a molding film having the same thickness structure as in Example 1. Table 1 shows the evaluation results of vacuum suction moldability, heat resistance and heat shrinkage under heating. Both were good results.

[Example 3]
In Example 1, a molding film having an A / B / A configuration was obtained in the same manner as in Example 1 except that PDLA-1 was used instead of PLLA-1 in the polylactic acid layer B. Table 1 shows the evaluation results of vacuum suction moldability, heat resistance and heat shrinkage under heating. Both were good results.

[Example 4]
A blend of PLLA-1 and PDLA-1 of the above reference example in a one-to-one ratio in a chip state is dried at 120 ° C. for 6 hours, supplied to an extruder hopper, and melted at a melting temperature of 270 ° C. To the polylactic acid layer A, and the above-mentioned PLLA-3 and PDLA-3 blended in the chip state at a ratio of 1: 1, dried at 120 ° C. for 6 hours, and then subjected to another extrusion. It is supplied to the machine hopper, melted at a melting temperature of 260 ° C., and supplied to the inside of the die. As the polylactic acid layer B, the molten polymer is laminated on three layers of A / B / A and placed on a cooling drum having a surface temperature of 20 ° C. Extruded and quenched to obtain a three-layer unstretched film. At this time, the melting point of the stereocomplex polylactic acid formed into the polylactic acid layer A was 220 ° C., and the melting point of the stereocomplex polylactic acid formed into the polylactic acid layer B was 195 ° C.

  Subsequently, the three-layer unstretched film was successively biaxially stretched 3.0 times in the longitudinal direction at 70 ° C. and 3.2 times in the transverse direction at 90 ° C., and then heat-set at 205 ° C. A molding film having the same thickness as that of the film was obtained. Table 1 shows the evaluation results of vacuum suction moldability, heat resistance and heat shrinkage under heating. In particular, good characteristics were obtained in the heat shrinkage rate.

[Comparative Example 1]
In Example 1, except that PLLA-4 is used instead of PLLA-2 and PDLA-4 is used instead of PDLA-2, a polylactic acid layer A and a polylactic acid layer B are obtained in the same manner as in Example 1, and A An unstretched film having a configuration of / B / A was obtained. At this time, the melting point of the stereocomplex polylactic acid formed in the polylactic acid layer A was 180 ° C.
Subsequently, the three-layer unstretched film was successively biaxially stretched in the same manner as in Example 1, and then heat-set at 170 ° C. to obtain a molding film having the same thickness structure as in Example 1. The evaluation results are shown in Table 1. None of the properties were satisfactory.

[Comparative Example 2]
After the PLLA-1 of the above reference example is dried at 120 ° C. for 6 hours, it is supplied to an extruder hopper, melted at a melting temperature of 200 ° C., and supplied to the inside of the die, and the molten polymer is placed on a cooling drum having a surface temperature of 20 ° C. Extrusion and rapid cooling yielded a single-layer unstretched film. Subsequently, this single-layer unstretched film was successively biaxially stretched 3.0 times at 70 ° C. in the machine direction and 3.2 times at 90 ° C. in the transverse direction, and then heat-set at 150 ° C., and the thickness was 50 μm. A stretched film was obtained. None of the properties were satisfactory.

[Comparative Example 3]
While the polylactic acid layer A is produced in the same manner as in Example 1, the polylactic acid layer B is produced in the same manner as in Example 4, and a molten polymer is laminated on three layers of A / B / A, and a surface temperature of 20 It was extruded on a cooling drum at 0 ° C. and quenched to obtain a three-layer unstretched film. At this time, the melting point of the stereocomplex polylactic acid formed into the polylactic acid layer A was 205 ° C., and the melting point of the stereocomplex polylactic acid formed into the polylactic acid layer B was 195 ° C. Subsequently, this three-layer unstretched film was successively biaxially stretched 3.0 times at 70 ° C. in the machine direction and 3.2 times at 90 ° C. in the transverse direction, and then heat-set at 195 ° C. A three-layer film having a similar thickness structure was obtained. The evaluation results are shown in Table 1. None of the properties were satisfactory.

Claims (3)

A layer B of substantially non-oriented structure polylactic acid, Ri Do from the layer A of the polylactic acid of the alignment structure disposed on both sides in contact with the layer,
The polylactic acid of layer A is a stereocomplex polylactic acid having a melting point of 190 to 220 ° C.
The polylactic acid of layer B has a melting point of 160-200 ° C.
The melting point of the polylactic acid in layer A is 15 ° C. or higher than the melting point of the polylactic acid in layer B.
Film for molding.   The film for molding according to claim 1, wherein the heat shrinkage rate at 150 ° C for 10 minutes is 1.5 to 3.8%.   The film for molding according to claim 1, which is for vacuum suction molding.