JP2001151907A - Polylactic acid-based shrink film or sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biodegradable polylactic acid-based shrink sheet product for package which has a satisfactory shrinkage rate and is excellent in impact resistance (breakage resistance) and, especially, in transparency and is free of irregularity of thickness upon stretching. SOLUTION: The shrink film or sheet is obtained by shaping a plastic material, which is made of a mixture of a polylactic acid material having a ratio between D-lactic acid and L-lactic acid within a given range sand an aliphatic polyester wherein the aliphatic polyester has a heat quantity ΔHm of melting of crystals of 55 J/g or below and an apparent melt viscosity of the polymer is in a constant relation when an apparent shearing rate is 102 (1/sec). The film or sheet has a skin layer made mainly of the polylactic acid material and has a thermal shrinkage rate in a uniaxial direction of, at least, 10% or over in hot water of 80 deg.C/10 seconds.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a shrinkable film or sheet containing polylactic acid as a main component.

[0002]

2. Description of the Related Art Sheets and films of polyvinyl chloride, styrene-butadiene copolymer, polyethylene terephthalate, etc. are known as heat-shrinkable sheets or films used for shrink wrapping, shrink-wrapping wrapping, shrink labels and the like. It is also widely used and consumed in industry. However, when these sheets and films are rejected in the natural environment, they remain without being decomposed due to their stability.
It causes problems such as spoiling the landscape and polluting the living environment of fish and birds.

[0003] Therefore, there is a demand for a material made of a degradable polymer which does not cause these problems.
Development is taking place. One example is polylactic acid. It is known that polylactic acid naturally undergoes hydrolysis in soil, does not remain in its original form in soil, and then becomes a harmless degradation product by microorganisms.

[0004]

However, polylactic acid is inherently brittle, so that even if it is used as a sheet or film, it does not have sufficient strength to be practically used. In particular, in producing a uniaxially contractible film from polylactic acid by substantially uniaxially stretching, the brittleness in the direction in which the film is not stretched is not improved, so that the film is easily torn when subjected to an impact in that direction.

[0005] Japanese Patent Application Laid-Open No. 5-221790 discloses a heat-shrinkable film made of polylactic acid for labels. However, this heat-shrinkable film has a high shrinkage temperature of 140 to 150 ° C. and is a high-temperature shrinkable film that can be used as a label for a glass bottle or the like. For this reason, when shrink-wrapping or shrink-wrapping a packaged object which is likely to be thermally deformed such as a fresh food or a paper box, or various containers containing food or medicine, low-temperature shrinkage processing at about 60 to 120 ° C is performed. It is necessary to have sufficient heat shrinkage under these conditions. Furthermore, even if the label is shrinkable at high temperatures, the shrinkage finish is poor, and a portion that floats without contacting the shrinkable object may be formed, so that sufficient performance may not be exhibited. further,
Unless the crystallinity of polylactic acid is taken into account, stretching at a temperature as described in the gazette becomes very difficult. That is, the film crystallizes and whitens during stretching, or a polylactic acid having a low melting point easily causes a problem such as melting and breaking of the film during stretching, and it is difficult to manufacture the film in a substantially stable manner.

[0006] Japanese Patent Application Laid-Open No. 7-256755 discloses a heat-shrinkable film made of a polylactic acid-based polymer that satisfies predetermined requirements and that is low-temperature shrinkable. But,
This heat-shrinkable film has a poor shrinkage finish, and may have a floating portion without contacting the shrinkable object.

The present inventors have disclosed a stretched film comprising a mixture of a polylactic acid-based polymer and another aliphatic polyester in JP-A-9-157408. This stretched film is obtained by heat-setting a stretched film of a mixed resin of a predetermined polylactic acid-based polymer and a predetermined biodegradable aliphatic polyester, and has slipperiness, heat sealing performance, fusing sealing performance, and thermal dimensional stability. It is shown that it is excellent. However, this stretched film is disclosed to improve the thermal dimensional stability and the like by heat setting, but the stretched film before the heat setting is subjected to shrinkage, shrink finish, and fusing property. And the like as a heat-shrinkable film.

On the other hand, Japanese Patent Application Laid-Open No. 9-169896 discloses a shrink film comprising the composition of the above-mentioned polylactic acid and aliphatic polyester. The purpose is to smooth the shrinkage curve by mixing aliphatic polyester with polylactic acid, and to suppress wrinkles generated during shrinkage. However, films based on the methods and examples disclosed in the present invention do not always provide films with excellent transparency. If the aliphatic polyester to be mixed is not carefully selected, the transparency of the film is remarkably reduced, which poses a practical problem. In particular, in applications such as shrink labels, characters and designs are printed on the back surface of the film and characters and patterns are read through the film. Therefore, if the film is cloudy or has low gloss, the beautiful appearance of the label is impaired.

Accordingly, the present invention provides a biodegradable polylactic acid-based shrinkage for packaging having a sufficient shrinkage, excellent impact resistance (breaking resistance) and particularly excellent transparency, and having no variation in thickness when stretched. It is intended to provide a sheet-like material.

[0010]

A first gist of the present invention is as follows.
Polylactic acid-based polymer (A) in which the composition ratio of D-lactic acid and L-lactic acid is 100: 0 to 92: 8 or 0: 100 to 8:92.
A mixture of 10 to 60 parts by weight of the aliphatic polyester (B) represented by the following formula with respect to 100 parts by weight, and
(1) The heat of crystal melting ΔHm of the aliphatic polyester is 55
J / g or less, and (2) the apparent shear rate is 10 ²
Assuming that the apparent melt viscosities of the polymers A and B at (1 / sec) are SVa and SVb, respectively, a film formed by molding a plastic material having a relation of 1 ≦ (SVa / SVb) ≦ 2 or The sheet is provided with (3) a skin layer containing a polylactic acid-based polymer (A) as a main component, and (4) at least a uniaxial heat shrinkage of 10% or more in warm water at 80 ° C./10 seconds. According to another aspect of the present invention, there is provided a heat-shrinkable film or sheet.

[0011]

Embedded image (In the formula, R ¹ and R ² are an alkylene group or a cycloalkylene group having 2 to 10 carbon atoms. N is a degree of polymerization necessary for a weight average molecular weight of 20,000 to 300,000.
The n R ¹ or R ² may be the same or different. Further, in the formula, a urethane bond residue and / or a carbonate bond residue can be contained up to 5% of the weight average molecular weight in place of the ester bond residue. As a second point, the film is stretched at a stretching temperature of 70.
〜95 ° C., at least uniaxial stretching ratio 2.5２．５
The above problem was solved by being a film or sheet stretched at 6.0.

In addition, it is important that the haze of the film or sheet is 10% or less.

[0013]

Embodiments of the present invention will be described below.

The polylactic acid-based film or sheet for packaging according to the present invention (hereinafter sometimes referred to as "sheet-like material") is a biodegradable polymer mainly composed of a polylactic acid-based polymer and a biodegradable aliphatic polyester. It is a sheet-like material formed from a biodegradable resin composition containing an aliphatic polyester as a main component.

The above-mentioned biodegradable resin composition refers to a polymer which is biodegradable, that is, a polymer which is finally decomposed by microorganisms.

The above-mentioned polylactic acid-based polymer refers to lactic acid, specifically, a homopolymer of D-lactic acid or L-lactic acid or a copolymer thereof. That is, poly (L-lactic acid) whose structural unit is L-lactic acid, and poly (D-lactic acid) whose structural unit is D-lactic acid
Lactic acid) Furthermore, there is poly (DL-lactic acid) which is a copolymer of L-lactic acid and D-lactic acid. Also, a mixture of these is included.

The above-mentioned polylactic acid-based polymer can be produced by a known method such as a condensation polymerization method or a ring-opening polymerization method. For example, in the polycondensation method, D-lactic acid, L-lactic acid or a mixture thereof is directly subjected to dehydration polymerization to obtain polylactic acid having an arbitrary composition. Further, in the ring-opening polymerization method, lactide, which is a cyclic dimer of lactic acid, is subjected to ring-opening polymerization in the presence of a predetermined catalyst while using a polymerization regulator or the like as necessary, and polylactic acid having an arbitrary composition is obtained. Is obtained. The lactide includes L-lactide, which is a dimer of L-lactic acid, and D, which is a dimer of D-lactic acid.
-Lactide, DL which is a dimer of D-lactic acid and L-lactic acid-
There is lactide, and a polylactic acid-based polymer having any composition and crystallinity can be obtained by mixing and polymerizing these as needed.

The biodegradable aliphatic polyester is a biodegradable aliphatic polyester excluding the polylactic acid-based polymer. This biodegradable aliphatic polyester is
The glass transition point (hereinafter abbreviated as “Tg”) is preferably 0 ° C. or lower.

If the Tg is too high, the breaking resistance is low, and the elongation does not exceed 10% even when a tensile test is performed on the sheet. Excellent break resistance means that the sheet does not break easily even when subjected to an impact, which can be replaced by elongation in a tensile test of the sheet. It is important that the elongation is 10% or more, preferably 50% or more, and more preferably the elongation is about 100% or more. In order to realize this, the Tg of the aliphatic polyester to be compounded (depending on the amount) is required. 0 ° C. or lower, preferably −10 ° C. or lower, more preferably −20 ° C. or lower, and the mixing amount is also 10 to 100 parts by weight, preferably 20 to 60 parts by weight per 100 parts by weight of the polylactic acid-based polymer. is there.

On the other hand, when the amount of the aliphatic polyester to be mixed increases, the film gradually shrinks unintentionally by the user at room temperature, so-called spontaneous shrinkage occurs, and the flatness of the sheet before use may be lost. It is not preferable. Further, the transparency of the sheet material is also reduced. Especially when the amount is 50
When the amount is more than the weight part, transparency for shrink labels cannot be secured.

There are other important factors that affect the transparency of the sheet. That is, as much as possible, a transparent aliphatic polyester is used and mixed with a polylactic acid-based polymer. As the aliphatic polyester to be applied, an aliphatic polyester obtained by condensing an aliphatic dicarboxylic acid and an aliphatic diol, an aliphatic polyester obtained by ring-opening polymerization of a cyclic lactone, a synthetic aliphatic polyester,
There is an aliphatic polyester biosynthesized in the cells. Among them, those having the highest transparency are aliphatic polyesters obtained by condensing an aliphatic dicarboxylic acid and an aliphatic diol.

Examples of the aliphatic dicarboxylic acid include succinic acid, adipic acid, suberic acid, sebacic acid, dodecane diacid, and the like. Examples of the aliphatic diol include ethylene glycol and 1,4-butanediol. ,
1,4-cyclohexanedimethanol and the like.
The aliphatic polyester is produced by esterifying any of these aliphatic dicarboxylic acids and aliphatic diols. Here, the selection of the dicarboxylic acid and the diol is important. Crystallization occurs in aliphatic polyesters having a Tg of 0 ° C. or lower, and particularly when the polyester has high crystallinity, it becomes spherulite, causing irregular reflection of light and devitrification. In order to make the sheet-like material transparent, it is necessary to lower the crystal. The rule is that the heat of fusion ΔHm when the temperature of the aliphatic polyester is raised is 55%.
J / g or less. If ΔHm exceeds 55 J / g, the aliphatic polyester becomes opaque, and even if it is mixed with polylactic acid, it does not provide a degree of transparency that can be used as a label. A preferred combination of the above dicarboxylic acid and diol is one obtained by condensation polymerization of ethylene glycol or 1,4-butanediol using succinic acid and adipic acid as the dicarboxylic acid component. In particular, when it is desired to lower the crystallinity and Tg, the latter is more preferable.

In the above various polymerization steps, a small amount of a chain extender, for example, a diisocyanate compound, an epoxy compound, a diphenyl compound, an acid anhydride and the like can be used for the purpose of increasing the molecular weight. The preferred range of the weight-average molecular weight of the polylactic acid-based polymer or the biodegradable aliphatic polyester is 60,000 to 1,000,000, and if it is less than 60,000, the physical properties of the obtained sheet are low, and 1,000,000. If it exceeds, the moldability is poor.

Here, the melt viscosity depending on the weight average molecular weight will be described. The melt viscosity means a viscosity when a resin is heated and melted to be in a fluidized state. Although there are several methods for measuring the melt viscosity, here (JIS K
7199) "Method of testing flow characteristics of thermoplastics by capillary rheometer"
It is expressed by the "apparent shear viscosity" determined by the following formula. This is a numerical value calculated from the shear rate and the shear stress when the molten resin passes through a thin circular tube, and is generally expressed in comparison with the shear rate. In the present invention, it has been found that the transparency of the sheet material is significantly different due to the difference between the melt viscosity (apparent shear viscosity) of the polylactic acid-based polymer to be mixed and the melt viscosity (apparent shear viscosity) of the aliphatic polyester. The relationship in obtaining a perfect sheet-like material was derived and completed.

That is, when the apparent shear rate is 10
The apparent melt viscosities of the polylactic acid-based polymer and the aliphatic polyester at ² (1 / sec) were SVa and S, respectively.
When Vb is satisfied, the transparency of the sheet is improved when the relationship is 1 ≦ (SVa / SVb) ≦ 2. In particular, 100 μm which is the thickest one generally used as a shrink label
Even with m, the haze of the sheet can be reduced to 10% or less. The preferred haze of the shrink label is 10% or less, preferably 7% or less, more preferably 5% or less. If this area is carefully studied, it can be within such a range.

If the above (SVa / SVb) is less than 1 or more than 2, a transparent film cannot be obtained. In order to achieve a transparent sheet, an aliphatic polyester having a melt viscosity satisfying the above formula must be selected according to the polylactic acid-based polymer used.

The most important point of the present invention is that a skin layer of a polylactic acid-based polymer which is a component of the sheet is provided on one or both surfaces of the sheet. Since the polylactic acid-based polymer and the aliphatic polyester constituting the sheet-like material have different deformation behaviors during stretching,
Raise the surface. Haze is calculated by the following formula

Haze (%) = (diffuse transmittance (%) / total light transmittance (%)) × 100 The greater the amount of the aliphatic polyester contained, the more easily the surface roughness occurs, and the diffusion of transmitted light occurs, so that the haze increases and the transparency decreases.

The method of suppressing the diffusion of the transmitted light on the surface of the sheet is to suppress the surface roughness, which is solved by laminating a highly transparent polylactic acid-based polymer.
Compared to the sheet without the lamination, the sheet will have more transparency.

It is necessary that the skin layer has a thickness at least larger than the size of the irregularities on the surface, specifically, 1 μm or more, preferably 2 μm or more. The upper limit is not particularly limited, but if the skin layer is too thick in view of the thickness composition ratio of the sheet-like material, the effect of mixing the aliphatic polyester is weakened, and the rupture resistance is reduced.
In the case of a 50 μm thick sheet, the thickness of the skin layer is 2 to 10
It is preferable to set to about μm. Although providing the skin layer only on one side of the sheet-like material has an effect of reducing the haze of the entire sheet-like material, it is preferably provided on both surface layers.

The above-mentioned sheet-like material means a sheet or a film. By definition in JIS, a sheet is a flat product whose thickness is thin and its thickness is generally small compared to its length and width. A film is extremely small in thickness compared to its length and width, and its maximum thickness Is an optionally defined thin flat product, usually supplied in roll form (JI
SK 6900). Therefore, it can be said that a sheet having a particularly small thickness among the sheets is a film. However, since the boundary between the sheet and the film is not clear and cannot be clearly distinguished, in the present application, as described above, the term “sheet-like material” is used as a concept including both the sheet and the film.

In the polylactic acid-based polymer, the composition ratio of L-lactic acid and D-lactic acid is 100: 0 to 92: 8 or 0: 100 to
8:92 is good, 98: 2-94: 6 or 6: 94-
2:98 is preferred. If the ratio is out of the above range, the thickness tends to vary at the time of stretching, so that printing cannot be performed neatly. The stretching ratio of the sheet is preferably at least a uniaxial stretching ratio of 2.5 to 6.0, and is preferably 3.0 to 5.0 times. Outside this range, the film tends to have uneven thickness.

The shrinkage of the obtained sheet is 80 ° C.
It is preferably 10% or more in 10 seconds, and 20% or more.
~ 100% is preferred. If the shrinkage is less than 10%,
This is because it tends to be insufficient for use in shrink wrapping or shrink wrapping wrapping. In general, in shrink wrapping and shrink wrapping, the shrinkage rate of the polylactic acid-based shrinkable sheet is as follows:
It may be about 10%, and in the case of a label such as a PET bottle, a contraction rate of 30% or more is good.

Next, a method for forming a polylactic acid-based shrinkable sheet for packaging according to the present invention will be described. The mixing of the polylactic acid-based polymer and the aliphatic polyester is performed by charging the respective raw materials into the same extruder. There is a method of directly extruding from a die to directly produce a sheet-like material, or a method of extruding into a strand shape to produce pellets, and producing the sheet-like material again by an extruder. In any case, the reduction in molecular weight due to decomposition must be taken into consideration, but it is better to select the latter for uniform mixing. The polylactic acid-based polymer and the aliphatic polyester are sufficiently dried to remove water, and then melted by an extruder. The polylactic acid-based polymer is L
The melt extrusion temperature is appropriately selected in consideration of the fact that the melting point changes depending on the composition ratio of the lactic acid structure and the D-lactic acid structure, and the melting point of the aliphatic polyester and the mixing ratio. Actually 10
A temperature range from 0 to 250 ° C is usually chosen.

For the purpose of adjusting various physical properties, a heat stabilizer, a light stabilizer, a light absorber, a lubricant, a plasticizer,
Inorganic fillers, colorants, pigments and the like can also be added.

As a lamination method, a commonly used method can be adopted. For example, a method of so-called co-extrusion in which a plurality of extruders are connected to one die in a feed block type or a multi-manifold type, and another type of sheet-like material is heated on a surface of a rolled mixed film using a roll or a press plate. There is a method of crimping.

The biodegradable resin composition melt-molded into a sheet is fed to a rotating casting drum (cooling drum).
It is preferable to quench the mixture by contacting with water. The temperature of the casting drum is 6 depending on the nature and proportion of the polymer to be mixed.
0 ° C. or lower is appropriate. If it is higher than this, the polymer sticks to the casting drum and may not be removed.
In addition, since crystallization of the polylactic acid portion is promoted and stretching cannot be performed, it is preferable to set the temperature to 60 ° C. or lower and quench to make the polylactic acid portion substantially amorphous.

The resulting sheet is stretched in at least one direction. The stretching ratio of the sheet material is, for example, the stretching ratio in the transverse (width) direction is in the range of 2.5 to 6 times, the stretching ratio in the longitudinal (longitudinal) direction is in the range of 1 to 3 times, and the stretching temperature is 7 times.
It can be appropriately selected within the range of 0 to 95 ° C. The stretching step is a roll stretching in which the sheet-like material is stretched between two rolls having a difference in peripheral speed and / or a tenter in which a tenter is used to stretch the clip-like material while stretching the gap between the clip rows while holding the sheet-like material with clips. This is performed by stretching. In the case of biaxial stretching, it is not particularly limited,
Simultaneous or sequential stretching methods may be used.

The polylactic acid-based shrinkable sheet obtained according to the present invention can be used as a packaging material or a shrinkable label material. Containers, foods such as fresh foods, and the like are used as objects to be packaged using the packaging material and the shrinkable label material. Examples of the container include a container having high hardness such as a glass bottle, a glass container, and a hard plastic container, and a container formed of paper or a plastic such as polystyrene, polyethylene, or polyethylene terephthalate.
These containers are used for any purpose such as food, beverage, and medicine.

The object to be packaged is shrink-wrapped or shrink-wrapped by the above-mentioned packaging material. At this time, since the polylactic acid-based shrinkable sheet has a sufficient shrinkage rate and no thickness unevenness at the time of stretching, the packaging material has a good finish when shrink-wrapped and has a good appearance in a wrapped state. Further, even if a heat treatment is performed after the packaging, the packaging materials do not fuse with each other, so that the handling becomes easy. In addition, the above-mentioned polylactic acid-based shrinkable sheet is excellent in transparency, and after printing on the back surface of the sheet-like material, it is excellent in clearness of printed characters and designs when reading from the front surface. By shrinking and adhering to the packaging material, it can be used effectively as a label.

As a method for producing this laminated stretched film, a sheet-like material or a cylindrical material extruded from a T-die, an I-die, a round die, or the like is rapidly cooled by a cooling cast roll, water, pressurized air, or the like, and is cooled to an amorphous state. After solidification, a method of stretching uniaxially or biaxially by a roll method, a tenter method, a tubular method, or the like can be given. Usually, in the production of a uniaxially stretched film, the tenter method is used. In the production of a biaxially stretched film, the longitudinal stretching is performed by a roll method and the transverse stretching is performed by a tenter method. Axial stretching method is common

[0041]

[Examples] Evaluation method-Apparent melt viscosity (SVa, SVb) Measured based on (JIS K7199). The sample was inserted into the measuring device, and heated and melted at a measuring temperature of 200 ° C. The heating time at this time was 5 minutes.

Heat of crystallization and melting ΔHm Using DSC-7 manufactured by PerkinElmer (JIS K
7122), the heat of fusion was measured. That is,
After conditioning the test piece 10 mg from the film under standard conditions, the nitrogen gas flow rate was 25 ml / min, and the heating temperature was 10
The endothermic peak area was read from a DSC curve drawn while the temperature was raised to 200 ° C. at a rate of ° C./min, and was defined as ΔHm (J / g).

The total light transmittance and the diffuse transmittance were determined based on haze (JIS K 7105), and were calculated by the following equations.

[0044]

Haze (%) = (diffuse transmittance (%) / total light transmittance (%)) × 100 A tensile test is performed based on rupture resistance (JIS K 7127), and the sheet at that time The elongation of the material was measured and used as a substitute evaluation of the breaking resistance. Test conditions were No. 2 test piece, tensile speed 2
The measurement was performed five times at 00 mm / min, and the average value was determined.
If the elongation of the sheet is low, the breaking resistance is low, and if the elongation is high, the breaking resistance is high. Those having an elongation of 50% or more were marked with "O" in good results. If it is less than 10% or more, it is slightly good. If it is less than 10%, it is unsuitable and indicated as x.

The "elongation" is represented by the following equation.

[0046]

(Equation 2) ・ Shrinkage rate The sheet-shaped sample was tested for a length of 140
mm, width 10mm, length 1 in the test direction
After putting a rating line between 00 mm and immersing in a hot water bath at 80 ° C. for 10 seconds, the dimension between the rating lines was measured, and the heat shrinkage was calculated according to the formula.

[0047]

(Equation 3) -Thickness variation The thickness of the obtained sheet-like material was measured with a dial gauge at a total of 200 points at 10 points at equal intervals in the width direction and 20 points at 500 mm intervals in the length direction, and the average value of the thickness ( X) and standard deviation (σ) were obtained, and (3σ / X) × 100 (%) was obtained. Those having a value of less than 15% were represented by (○) as having good thickness, and those having a value of 15% or more were represented by (x).

Example 1 100 parts by weight of a polylactic acid polymer having a structural unit of L-lactic acid: D-lactic acid = 99.5: 0.5, having a glass transition point (Tg) of 58 ° C. and a melting point of 175 ° C. The transition point (Tg) is-
After drying 10 parts by weight of polybutylene succinate / adipate which is a biodegradable aliphatic polyester having a melting point of 94 ° C. at 45 ° C., each was dried, mixed and melt-extruded to form pellets. The obtained pellets were extruded as an intermediate layer from a multi-manifold die at 210 ° C. with a single-screw extruder of 40 mmφ, and dried over 100 parts by weight of the polylactic acid-based polymer to obtain a granular silica having an average particle size of 1.4 μm. 0.1
Parts by weight were mixed and extruded at 210 ° C. as front and back layers from the above die with a 25 mmφ same-direction twin-screw extruder. This co-extruded sheet is rapidly cooled by a casting roll at about 43 ° C.
An unstretched sheet was obtained. Then, at 65 ° C in the longitudinal direction, 1.0
Roll stretching twice, and then stretching in the width direction with a tenter. The temperature of the heat treatment zone in the tenter was kept constant at 50 ° C., and a sheet material substantially not heat-set was produced. The stretching temperature and stretching ratio of the sheet material are as shown in Table 2, and the sheet is a uniaxially stretched film stretched substantially in the width direction. The discharge amount of the molten resin from the extruder and the line speed were adjusted so that the average thickness of the film was about 50 μm. The line speed is about 6 to 17 m / min, and the width of the obtained film also depends on the stretching ratio in the width direction.
The film was dropped from m to 300 mm wide to about 1200 mm.

Examples 2 to 5 and Comparative Examples 3 to 7 The same procedure as in Example 1 was repeated except that the polylactic acid-based polymer and the biodegradable aliphatic polyester shown in Table 2 were used. I got something. The discharge amount of the molten resin from the extruder and the line speed were adjusted so that the average thickness of the sheet was approximately 40 to 60 μm. Table 1 shows details of the resins used. The polylactic acid used in Example 5 was obtained by melting the polylactic acid in a non-dried state at 220 ° C., extruding and pelletizing to reduce the molecular weight. Mixing with the aliphatic polyester was performed in the same manner as in Example 1 in a dry state.

Comparative Examples 1 and 2 In Example 2, the single-layer sheet without the aliphatic polyester and the single-layer sheet with the aliphatic polyester mixed are described in Comparative Examples 1 and 2. Use a single-layer base, 40
A sheet-like material was produced in the same manner as in Example 2 except that only the mmφ single screw extruder was used.

The resulting polylactic acid-based shrinkable sheet was measured for transparency, impact resistance (break resistance), and thickness variation.
Table 2 shows the results.

[0052]

Industrial Applicability According to the present invention, a biodegradable polylactic acid-based shrinkable sheet for packaging having a sufficient shrinkage rate, excellent impact resistance (break resistance), and particularly excellent transparency, and having no thickness unevenness when stretched. An article can be provided.

[0053]

[Table 1]

[0054]

[Table 2]

Continued on the front page F-term (reference) 4F071 AA43 AA44 AA87 AA88 AF61Y AH04 AH06 BB07 BC01 4F100 AA20H AK41A AK41B AK41J AL01A AL05A BA02 BA03 CA23 EJ38 GB17 JA03 JA06A JA20A JC00 JK10 JN01 J02Y02 CF02

Claims (3)

[Claims] 1. The composition ratio of D lactic acid and L lactic acid is 100: 0.
A mixture of 10 to 60 parts by weight of an aliphatic polyester (B) represented by the following general formula with respect to 100 parts by weight of a polylactic acid-based polymer (A) having a ratio of 0 to 92: 8 or 0: 100 to 8:92. And the polymer A when (1) the heat of crystal fusion ΔHm of the aliphatic polyester is 55 J / g or less, and (2) the apparent shear rate is 10 ² (1 / sec).
And apparent melt viscosities of SVa and S, respectively.
Assuming that Vb is Vb, in a film or sheet formed by molding a plastic material having a relationship of 1 ≦ (SVa / SVb) ≦ 2, (3) a skin layer containing a polylactic acid-based polymer (A) as a main component is provided. (4) A heat-shrinkable film or sheet having a heat shrinkage in at least one direction of 10% or more in hot water at 80 ° C./10 seconds. Embedded image (In the formula, R ¹ and R ² are an alkylene group or a cycloalkylene group having 2 to 10 carbon atoms. N is a degree of polymerization necessary for a weight average molecular weight of 20,000 to 300,000.
The n R ¹ or R ² may be the same or different. Further, in the formula, a urethane bond residue and / or a carbonate bond residue can be contained up to 5% of the weight average molecular weight in place of the ester bond residue. ) 2. The shrinkable film or sheet according to claim 1, wherein the film is stretched at a stretching temperature of 70 to 95 ° C. in at least a uniaxial direction at a stretching ratio of 2.5 to 6.0. 3. The shrinkable film or sheet according to claim 1, wherein the haze is 10% or less.