JPH08323946A - Multi-layer biodegradable plastic film - Google Patents

Abstract

PURPOSE: To improve heat properties by setting the melting temperature for a biodegradable plastic film forming the outermost layer lower by at least specified temperature than the melting temperature of a film composed of a polylactic polymer or a composition having polylactic polymer as its main component. CONSTITUTION: A multi-layer biodegradable plastic film comprises a film composed of a polylactic polymer or a composition having the same as main component, and at least one outermost layer of a biodegradable plastic film, and the melting temperature Tm for the biodegradable plastic film forming the outermost layer is lower by at least 10 deg.C than the m.p. Tm for the film comprising the polylactic copolymer or the composition having the same as main component. The polylactic polymer to be used is a copolymer of polylactic acid or lactic acid and other hydroxycarboxylic acid, or a composition thereof, and other polymeric materials may be mixed in the range not inhibiting the effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer biodegradable plastic film having excellent heat sealability.

[0002]

[Prior Art and Problems to be Solved by the Invention]
Films with excellent heat-sealing properties are required for a wide range of applications including general packaging materials, which use snack confectionery bags as a typical example, as well as agricultural materials, construction materials, and medical materials.

A film excellent in heat-sealing property means a desired adhesion in so-called "heat-sealing", in which films are bonded or bonded by heat and pressure using a heating bar, a heating plate, a heating roll or the like. A film with a wide temperature range that provides stable strength. That is, for a film having excellent heat sealability, various film processed products can be easily obtained by heat sealing.

When the temperature is lower than the above temperature range during heat sealing, the film base material is hard so that sufficient adhesive strength cannot be obtained. When the temperature is higher than the above temperature range, the film base material becomes too soft and pinholes or wrinkles are formed, resulting in appearance. While causing deterioration of the adhesive strength, they also reduce the adhesive strength.

If the heat-sealing property is poor, the heat-sealing work must be performed within a narrow temperature range, which requires a high temperature control capability, which makes the apparatus expensive, the productivity is low, and the defective rate is high. Various problems such as severe physical and mental fatigue occur.

Therefore, general-purpose films such as polyolefin, PET (polyethylene terephthalate), and PVC (polyvinyl chloride) are used for heat seal applications.
In many cases, films with improved heat-sealing properties are used by using raw materials with a special polymer design or by blending or laminating different raw materials.

[0007] On the other hand, in recent years, there has been a demand for a plastic product which does not adversely affect the natural environment, which decomposes and disappears with time when it is discarded in the natural environment due to the recent increase in environmental problems.

However, conventional plastic film products are stable in the natural environment for a long period of time and have a low bulk specific gravity, so that they promote the shortening of the life of waste landfills and the natural environment and the living environment of wild animals and plants. It was pointed out that there was a problem such as damage to the.

Therefore, biodegradable plastic materials are attracting attention today. It is known that biodegradable plastics gradually disintegrate / decompose in soil or water due to hydrolysis or biodegradation, and finally become harmless decomposition products by the action of microorganisms.

Biodegradable plastics that are currently being put into practical use are roughly classified into aliphatic polyesters, modified PVA (polyvinyl alcohol), cellulose ester compounds, starch modified products, and blends thereof.

Examples of the aliphatic polyester include poly (hydroxybutyric acid / valeric acid) as a microbial-produced polymer, polycaprolactone or a condensate of aliphatic dicarboxylic acid and an aliphatic diol as a synthetic polymer, and
Polylactic acid-based polymers are known as semi-synthetic polymers.

[0012] Each of these biodegradable plastics has its own characteristic, and it is possible to develop applications according to them.
Among them, polylactic acid-based polymers are superior in transparency, rigidity, heat resistance, processability, etc. as compared with other biodegradable plastics, and thus rigid PVC and PET have been conventionally used. It is about to be developed for film applications.

In particular, a biaxially stretched heat-setting film using a polylactic acid polymer has mechanical properties equivalent to or superior to those of a general-purpose film and is completely biodegradable, so that it can be applied to a wide range of applications including general packaging materials. Is expected.

However, a film made of a polylactic acid-based polymer has a poor heat-sealing property and has been a serious problem in practical use when it is used in various fields such as film-processed products. Therefore, an object of the present invention is to provide a biodegradable plastic film having excellent heat sealability.

[0015]

The gist of the present invention is to have a film made of a polylactic acid polymer or a composition containing the polylactic acid polymer as a main component, and at least one outermost layer is a biodegradable plastic film. In a certain multilayer biodegradable plastic film, the melting temperature Tm of the biodegradable plastic film forming the outermost layer is the melting temperature Tm of the film made of the polylactic acid polymer or a composition containing the polylactic acid polymer as a main component. It is a multilayer biodegradable plastic film characterized by having a temperature of 10 ° C. or higher. A different gist of the present invention is a multilayer biodegradable plastic film having a film made of a polylactic acid-based polymer or a composition containing the polylactic acid-based polymer as a main component, and at least one outermost layer of which is a biodegradable plastic film. The film made of the polylactic acid-based polymer or the composition containing the polylactic acid-based polymer as a main component has a melting temperature Tm, and the biodegradable plastic film forming the outermost layer is an amorphous film. It is a multilayer biodegradable plastic film. The melting temperature Tm of the film made of the polylactic acid-based polymer or the composition containing the polylactic acid-based polymer as a main component is 10
It is preferably 0 ° C. or higher.

The polylactic acid-based polymer used in the present invention is
It is polylactic acid or a copolymer of lactic acid and other hydroxycarboxylic acid, or a composition thereof, and other polymer materials may be mixed within a range that does not impair the effects of the present invention. It is also possible to add additives such as plasticizers, lubricants, inorganic fillers, ultraviolet absorbers and modifiers for the purpose of adjusting the physical properties and processability of the film.

Examples of lactic acid include L-lactic acid and D-lactic acid, and examples of hydroxycarboxylic acid include glycolic acid and 3-
Typical examples are hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, 6-hydroxycaproic acid and the like.

As the polymerization method, a known method such as a condensation polymerization method or a ring-opening polymerization method can be adopted, and further, a small amount of a chain extender such as a diisocyanate compound or a diepoxy compound for the purpose of increasing the molecular weight. An acid anhydride, an acid chloride or the like may be used. The weight average molecular weight of the polymer is preferably in the range of 60,000 to 1,000,000, and if it falls below such a range, problems such as practically exhibiting no physical properties occur. On the other hand, if it exceeds, the melt viscosity becomes too high and the moldability becomes poor.

Here, it is important that the melting temperature Tm of the film (hereinafter, abbreviated as polylactic acid-based film) made of the polylactic acid-based polymer or the composition containing the polylactic acid-based polymer as a main component is 100 ° C. or higher. If the Tm is less than 100 ° C., the heat resistance is lowered and wrinkles or the like are caused in the secondary processing or the like, which is not practical. In addition, T of poly L-lactic acid homopolymer
m is 195 ° C., and Tm decreases as the amount of copolymerization components such as D-lactic acid, glycolic acid, and 6-hydroxycaproic acid increases. Therefore, practically, the Tm of the polylactic acid-based film used in the present invention is 100 ° C. or higher and 19
It is 5 ° C or lower.

When the copolymerization ratio of a crystalline polymer such as a polylactic acid polymer is increased, the crystallization temperature Tc at the time of temperature increase tends to increase and the melting temperature Tm tends to decrease. .
At the temperature where Tc> Tm, Tm is substantially not observed. That is, depending on the selection of the comonomer,
In some cases, the Tm may disappear before the Tm reaches 100 ° C.
It is necessary to have

The biodegradable plastic film laminated on the above-mentioned polylactic acid-based film is a biodegradable plastic film lower than the melting temperature Tm of the polylactic acid-based film used by 10 ° C. or more, or an amorphous biodegradable plastic film. It is a degradable plastic film. As the biodegradable plastic film, for example, polylactic acid, aliphatic polyester other than polylactic acid, modified PVA, cellulose ester compound and the like can be used.

When the polylactic acid film is used as the biodegradable plastic film laminated on the polylactic acid film (base material), it means that the polylactic acid film is multilayered.

The desired polylactic acid-based film having a melting temperature Tm of 10 ° C. or more lower than that of the polylactic acid-based film used as a substrate is, as described above, a D-based homopolymer.
Alternatively, by adding a copolymerization component such as L-lactic acid, glycolic acid or 6-hydroxycaproic acid, the melting temperature T
It can be obtained by reducing m. As the film to be laminated, a polylactic acid film having a melting temperature Tm of the homopolymer of 185 ° C. or lower is used because the homopolymer has a melting temperature Tm of 195 ° C.
Further, in order to obtain an amorphous polylactic acid based film, the copolymerization ratio may be further increased.

The aliphatic polyester other than polylactic acid, which is used as the biodegradable plastic film laminated in the present invention, has alkylene and an ester bond as a basic skeleton, and has a range that does not substantially affect biodegradability. It is also possible to introduce a urethane bond, an amide bond, an ether bond or the like. In particular, an isocyanate compound can be used to introduce a urethane bond into the main chain to jump up the molecular weight.

Specific examples include a polymer obtained by condensing an aliphatic diol and an aliphatic dicarboxylic acid.
Aliphatic diols include ethylene glycol, 1,4
-Butanediol, 1,4-cyclohexanedimethanol, and the like, and examples of the aliphatic dicarboxylic acid include:
Representative examples thereof include succinic acid, adipic acid, suberic acid, sebacic acid and dodecanedioic acid. After selecting one or more from each of them and subjecting them to condensation polymerization, if necessary, an isocyanate compound is used to adjust the weight average molecular weight to 50,000.
The polymer jumped up to 0 or more is usually 60 to 11
It has a Tm of 0 ° C. and basic physical properties similar to polyethylene, and can be preferably used in the present invention.

Further, a series of aliphatic polyesters obtained by ring-opening polymerization of cyclic lactones using an organometallic catalyst can be mentioned. As the monomer, ε-caprolactone, δ-valerolactone, β-methyl-δ-valerolactone, β-propiolactone, pivalolactone, β-butyrolactone,
Typical examples include γ-butyrolactone, and further include lactide and glycolide. One or more kinds are selected from these, and the conditions are adjusted so that the weight average molecular weight is 30,000 or more and the polymerization is performed. The Tm is controlled by selecting the monomer, but it is usually 50 to 170 ° C.

Other synthetic aliphatic polyesters include:
Cyclic acid anhydrides and oxiranes, for example, polymers of succinic anhydride and ethylene oxide, propion oxide or allyl glycidyl ether, and ethylene and cyclic ketene acetals 2-methylene-1,3-dioxolane and 2-methylene-1. , 3-dioxepane and the like radical polymer.

In addition, acetyl coenzyme A (acetyl C) in cells such as Alcaligenes eutrophus
Aliphatic polyesters biosynthesized by oA) are known. This aliphatic polyester is mainly poly-β-hydroxybutyric acid (poly3HB), but in order to improve the practical properties as a plastic, the fermentation process was devised and usually valeric acid unit (HV) was copolymerized. , Poly (3
HB-co-3HV) is industrially advantageous. The HV copolymerization ratio is generally 0 to 40%, and in this range, the Tm is 130 to 165 ° C. Instead of HV, 4HB may be copolymerized, or a long chain hydroxyalkanoate may be copolymerized.

Polyvinyl alcohol (P, used as a biodegradable plastic film laminated in the present invention)
VA) is relatively excellent in biodegradability among existing petroleum-derived synthetic polymers, but PVA homopolymers have too large a cohesive force of molecules and have no melting point and thus cannot be melt-extruded. There is a restriction on the forming process when it is made into a material. Therefore, by copolymerizing ethylene or leaving a vinyl acetate unit that normally disappears in the saponification step,
It can be used after being modified so as to have a Tm of 0 to 150 ° C. A composition in which starch or the like is dispersed in order to enhance biodegradability based on such a PVA polymer has been evaluated as a biodegradable plastic material, and is called modified PVA.

The cellulose ester compound used as the biodegradable plastic film to be laminated in the present invention is usually a compound in which the hydroxyl groups of cellulose are converted into acetic acid ester, and the substitution degree thereof is between 2 and 3. The cellulose ester compound has substantially no Tm. A plasticizer may be added to impart melt moldability. The plasticizer also has a function of adjusting the Tg (glass transition temperature) of the material. As the plasticizer, in consideration of biodegradability, aliphatic esters and oils and fats such as dibutyl adipate, dioctyl adipate, glycerin acetate, soybean oil, castor oil, and linseed oil are preferably used.

For a biodegradable plastic film laminated on a polylactic acid-based film, a plasticizer, a lubricant, an inorganic filler, and an ultraviolet absorber are also used for the purpose of adjusting the physical properties and processability of the film within a range that does not impair the effects of the present invention. Additives such as agents
It is also possible to add modifiers or other polymeric materials.

The layer structure of the multilayer biodegradable plastic film of the present invention is not particularly limited as long as a polylactic acid type film is used as a substrate and at least one film forming the outermost layer is a biodegradable plastic film. In order to impart double-sided heat sealability and curl resistance, a polylactic acid-based film having excellent mechanical properties is used as an inner layer, and both outer layers are other biodegradable plastic films. can do.

Further, a multi-layered structure of three or more layers may be used for the purpose of imparting other functionality such as gas barrier property and water vapor barrier property. Further, in order to reduce the cost and to use for which curling property is preferable, the layer structure may be asymmetrical with respect to the central layer.

As a method for laminating the biodegradable plastic film on the polylactic acid type film, a commonly used method can be adopted. For example, a method of connecting a plurality of extruders to one die and so-called co-extrusion, a method of coating another kind of material on one kind of unwound film, a plurality of kinds of films at an appropriate temperature with a roll or a press. A typical example is a method of thermocompression bonding or a method of bonding films together using an adhesive.

As the adhesive in the case of so-called dry laminating or wet laminating, vinyl-based, acrylic-based, polyamide-based, polyester-based, rubber-based, urethane-based, etc. are generally used. When the adhesive is also made to be biodegradable Include polysaccharides such as starch, amylose and amylopectin,
Proteins and polypeptides such as glue, gelatin, casein, zein, and collagen, unvulcanized natural rubber, and aliphatic polyester are preferably used.

In order to greatly improve the inherent brittleness of the polylactic acid type polymer and further improve the film strength, the polylactic acid type film used as the substrate has a plane orientation degree ΔP of 3.0 ×. It is desirable to adjust to 10 ⁻³ to 30 × 10 ⁻³ .

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 by measuring the refractive index in the directions of three orthogonal axes. ΔP = {(γ + β) / 2} -α (α <β <γ) where γ and β are biaxial refractive indexes 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 any known film stretching method, a molecular orientation method utilizing an electric field or a magnetic field can be adopted.

Usually, a sheet-shaped material or a cylindrical material melt-extruded from a T-die, an I-die, a round die or the like is rapidly cooled by a cooling cast roll, water, compressed air or the like to be solidified in a state close to an amorphous state, and then the roll. Industrially, a method of uniaxially or biaxially stretching by a method, a tenter method, a tubular method, or the like is industrially adopted.

In the case of producing a stretched multilayer biodegradable plastic film, in the case of laminating, that is, so-called dry laminating or wet laminating, a polylactic acid-based film that has been stretched in advance may be used, or when coextruding. For, the extruded multilayer film may be stretched under appropriate conditions.

Stretching conditions when paying attention only to the polylactic acid film are as follows: stretching temperature 50 to 100 ° C., stretching ratio 1.5 to 5 times, stretching speed 100% / min to 10,000.
% / 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 thus-stretched polylactic acid-based film has its original brittleness significantly improved and its mechanical strength improved. It is a heat-shrinkable film, and can be applied to shrink-wrapping, shrink-bonding packaging, shrink-wrapping, and the like.

However, the above-mentioned ΔP is 3.0 × 10 ^-3.
A multilayer biodegradable plastic film using a polylactic acid-based film of ˜30 × 10 ⁻³ cannot be used in many applications requiring thermal dimensional stability. Therefore, in order to impart thermal dimensional stability to the polylactic acid-based film,
The difference between the heat of crystal fusion ΔHm when the film is heated and the heat of crystallization ΔHc generated by crystallization during temperature increase (ΔH
m-ΔHc) is 20 J / g or more and {(ΔHm-ΔH
c) / ΔHm} is controlled to 0.75 or more.

That is, if these conditions are not satisfied,
The thermal dimensional stability of the film is poor, and problems such as lamination, drying, aging, and other secondary processing steps that are heated and shrinkage during storage in the summer are likely to occur, and are not put to practical use. If this condition is exceeded, the thermal dimensional stability will be good, and there will be no practical problems.

ΔHm and ΔHc are obtained by differential scanning calorimetry (DSC) of a film sample, and
Hm is the amount of heat required to melt all the crystals when the temperature is raised at a heating rate of 10 ° C./minute, 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, ΔHc is obtained from the area of the exothermic peak generated during crystallization that occurs during the temperature rising process.

ΔHm mainly depends on the crystallinity of the polymer itself, and takes a large value for a polymer having high crystallinity. Incidentally, the complete homopolymer of L-lactic acid or D-lactic acid without a copolymer has a content of 60 J / g or more, and in the copolymer of these two types of lactic acid, ΔHm changes depending on the composition ratio. ΔHc is an index relating to the crystallinity of the film at that time with respect to the crystallinity of the polymer, and when ΔHc is large, the crystallization of the film proceeds in the temperature rising process. That is, it means that the crystallinity of the film was relatively low based on the crystallinity of the polymer. On the contrary, when ΔHc 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 (ΔHm-ΔHc) 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, and in order to make ΔHm of the polymer itself to be 20 J / g or more, in the case of making a copolymer from L-lactic acid and D-lactic acid, It has been experimentally confirmed that the composition ratio needs to be adjusted within the range of 100: 0 to 94: 6 or within the range of 0: 100 to 6:94. Further, in order to reduce ΔHc, that is, in order to increase the crystallinity of the film, it is necessary to select the film processing conditions.

In order to increase the crystallinity of the film in the molding process step, especially in the biaxial stretching by the tenter method, it is useful to increase the stretching ratio to promote oriented crystallization and to perform heat treatment after stretching in an atmosphere having a crystallization temperature or higher. Is. It should be noted that the larger the ΔP, the lower the crystallization temperature tends to be, and in the case of the present invention, as a result of intensive studies, at least 70 ° C. or higher, and preferably 90 ° C. to 170 ° C. for 3 seconds or more by heat treatment. Thermal dimensional stability can be imparted. Within this range, the higher the heat treatment temperature and the longer the heat treatment time, the better the thermal dimensional stability.

[0050]

EXAMPLES Examples will be shown below, but the present invention is not limited thereto.

(Experimental Example 1) Coextrusion was carried out using a two-layer, three-layer T-die die so that the melt from the 50 mmφ uniaxial extruder was the inner layer and the melt from the 30 mmφ uniaxial extruder was the outer layers. went. The thickness ratio of outer layer / inner layer / outer layer was adjusted to ⅛ / 1, and an unstretched sheet of 250 μm in total was extruded and then rapidly cooled and collected.

As the inner layer (base material), L body / D body = 98 /
2. Polylactic acid having a weight average molecular weight of 200,000 (Lacty manufactured by Shimadzu Corporation) (Tm = 170 ° C.), and an outer layer of aliphatic polyester manufactured by Showa High Polymer Co., Ltd. Bionole 1010 (Tm = 114 ° C.) , Daicel Chemical Industries, Ltd.
Praxel H-7 (Tm = 60 ° C.), Zeneca Biopol D300G (Tm = 162 ° C.) and D
400 G (Tm = 153 ° C.) was used. Further, similarly, polylactic acid was extruded by a 30 mmφ single-screw extruder to obtain a 250 μm sheet composed of a single layer of polylactic acid.

The above-mentioned sheet was longitudinally stretched 1.5 times, then horizontally stretched 1.5 times, and then heat-treated at 160 ° C. The flow rate of the film after stretching was 2 m / min, and the passing time through each zone of stretching and heat treatment was 30 seconds.

Since the Tm of the polylactic acid type film layer used as the outer layer is 170 ° C., an inner layer lower than the Tm of the polylactic acid type film layer by 10 ° C. or more can be formed among the above examples of the aliphatic polyester used as the inner layer. Included in the present invention are Bionore 1010 (Tm = 114 ° C.), Praxel H-7 (Tm = 60 ° C.), Biopol D300G.
It is a film using (Tm = 162 ° C.), and these are Examples 1 to 3. On the other hand, Biopol D400G
Comparative examples 1 and 2 were a multilayer film using (Tm = 153 ° C.) and a film having a single-layer structure of polylactic acid.

The evaluation results of the film are shown in Table 1. In addition,
The measured values shown in the table are measured under the following conditions,
Calculated.

(1) ΔP Using Abbe refractometer, the refractive indices (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 film in-plane direction orthogonal thereto α: Refraction in the film thickness direction Note that, in the present invention, ΔP is defined for a polylactic acid-based polymer film, and therefore, when it is stretched and heat-treated after being laminated by coextrusion or the like, the polylactic acid-based film is optionally used. Remove the film layers other than the layers,
It measured about the polylactic acid type film.

(2) Thermal analysis Using DSC-7 manufactured by Perkin Elmer, raw material pellets,
Or film sample 10 of polylactic acid type film layer
Based on JIS-K7122, mg is heated at a rate of 10 ° C /
From the thermogram when the temperature is raised in minutes, the glass transition temperature Tg
-Melting temperature Tm-Crystal heat of heat ΔH _m -Crystal heat of heat ΔH
_c was calculated and calculated.

(3) Heat Seal Strength A film sample was cut into a strip of 10 mm width × 100 mm length with MD (the film flow direction) as the longitudinal direction, and two strip samples were stacked together to form 10 mm.
After setting so that it intersects perpendicularly with the heat sealer having the width heat seal bar, heat from one side at a predetermined temperature,
Heat sealing was performed for 15 seconds at a pressure of 1.178 Kg / cm ² . At this time, in the case of using a laminated film, the surfaces for easy adhesion treatment were set to be inside.

The above sample is used as an Intesco universal testing machine 20.
According to JIS K-6854, a T-type peeling test was performed using a 5 type machine until breakage at a peeling speed of 100 mm / min or until the bonded portion remained 1 mm. The obtained time-stress peak value is taken as the heat-sealing strength, and for the sake of simple understanding, if it is not sealed at all, or if the value is less than 50 g / cm, it is x, 50 g / cm or more and 500 or more.
Those with less than g / cm are shown with Δ, and those with more than 500 g / cm are shown with ◯.

[0061]

[Table 1] As is clear from Table 1, T of the inner layer (base material) and the outermost layer
It can be seen that in Examples 1 to 3 in which the difference in m is 10 ° C. or more, suitable heat sealing performance can be obtained in a wide temperature range. On the other hand, Comparative Example 1 having a Tm difference of 10 ° C. or less and Comparative Example 2 having a single layer are inferior in heat sealing performance.

(Experimental Example 2) A biaxially stretched heat-fixing polylactic acid film having a thickness of 40 μm obtained by the same method as in Comparative Example 2 was used as a base (base material), and an inflation film described later was formed on one side of the base by a dry laminating method. Pasted on
A two-layer laminated film was produced.

As a crystalline modified PVA system, Matterby AF-05H (Tm = 13) manufactured by Nippon Synthetic Chemical Industry Co., Ltd.
6 ° C.), a composition of cotton acetate L-40 manufactured by Daicel Chemical Industries, Ltd. as an amorphous cellulose ester compound and 43 parts of dibutyl adipate (no Tm / Tg = 103).
C), an amorphous polylactic acid-based polymer, L-form / D-form = 86/14, a polymer having a weight average molecular weight of 200,000 (Tm not included, Tg = 55 ° C), and polylactic acid used as a base. Using a 30 mmφ single-screw extruder equipped with equipment for blown film, a BUR (blow-up ratio) of 2.5 to 4.4 and a thickness of 10 to 15 μm.
m blown film was produced.

On a biaxially stretched heat-fixed polylactic acid film,
A mixture of Nippon Polyurethane Industry Co., Ltd. Nipporan 3022 / Coronate L = 9/1 was used as an adhesive, and after coating with a coater to a thickness of 2 to 5 μm, the above three kinds of inflation films were pressure bonded to 40 ° C. × 2. The adhesive was cured by aging for days to obtain multilayer biodegradable plastic films of Examples 4 to 6 and Comparative Example 3.

Table 2 shows the evaluation results of these laminated films.

[0066]

[Table 2] As is clear from Table 2, the Tm of the polylactic acid-based film and the biodegradable plastic film which is the outermost layer on one side
In Example 1 in which the difference in temperature is 10 ° C. or more and Examples 2 and 3 in which the biodegradable plastic film that is the outermost layer on one side is amorphous, suitable heat sealing performance is obtained in a wide temperature range. You can see that On the other hand, Comparative Example 3 having no difference in Tm is inferior in heat sealing performance.

(Experimental Example 3) An unstretched sheet of a multilayer biodegradable plastic film which was used in Example 1 and had the bionole 1010 as an outer layer and which had three layers was longitudinally stretched under the conditions shown in Table 3 and then laterally stretched. Example 8 after further heat treatment
~ 11 sheets were obtained. In addition, Example 7 is an unstretched sheet.

When the heat sealing performance of the obtained Examples 7 to 11 was examined in the same manner as in Experimental Examples 1 and 2, it was found that suitable heat sealing performance was obtained in a wide temperature range. Further, Table 3 shows the tensile breaking strength and the heat shrinkability. The measured values shown in the table were calculated by measuring under the following conditions.

(4) Tensile breaking strength The tensile strength was measured using a Toyo Seiki Tensilon II machine according to JIS
-Measured based on K7127. MD indicates the flow direction of the film, and TD indicates the direction orthogonal to the flow of the film.

(5) Heat-shrinkable film sample was cut into a size of 100 mm × 100 mm, immersed in a hot water bath at 80 ° C. for 300 seconds, the size was measured, and the ratio (%) of the heat-shrinkable portion to the original size was calculated. .

[0071]

[Table 3] Although Example 7 is a non-stretched sheet, the shrinkage rate is small,
Insufficient tensile strength. Example 8 has a plane orientation degree ΔP in the range of 3 × 10 ⁻³ to 30 × 10 ⁻³ and is stretched, and thus is suitable as a heat-shrinkable film having a moderate tensile strength. Example 9 is a heat-shrinkable film having excellent tensile strength and heat-shrinkability because the degree of plane orientation ΔP is in the above range and the heat treatment temperature after stretching is appropriate.
On the other hand, in Examples 10 and 11, ΔP was 3 × 10 ⁻³ to 30 ×.
10 ⁻³ , (ΔHm−ΔHc) is 20 J / g or more,
{(ΔHm-ΔHc) / ΔHm} is 0.75 or more, and the thermal dimensional stability film is excellent in both tensile strength and thermal dimensional stability.

That is, as is clear from Table 3, the multilayer biodegradable plastic film of the present invention has excellent heat-sealing properties depending on the stretching conditions, has appropriate tensile strength, and has heat-shrinkability or thermal dimensional stability. A multilayer biodegradable plastic film having the same can be obtained.

[0073]

EFFECT OF THE INVENTION The multilayer biodegradable plastic film of the present invention has an excellent heat-sealing property, so that it can be used for general packaging materials and the like, and since it has biodegradability, it is environmentally friendly.

Claims (3)

[Claims] 1. A multi-layer biodegradable plastic film comprising a film made of a polylactic acid polymer or a composition containing the polylactic acid polymer as a main component, and at least one outermost layer of which is a biodegradable plastic film. The melting temperature Tm of the biodegradable plastic film forming the outermost layer is 10 ° C. or more lower than the melting temperature Tm of the film made of the polylactic acid polymer or a composition containing the polylactic acid polymer as a main component. Multi-layer biodegradable plastic film. 2. A multilayer biodegradable plastic film having a film made of a polylactic acid-based polymer or a composition containing this as a main component, and at least one outermost layer of which is a biodegradable plastic film. A film made of the polylactic acid polymer or a composition containing the polylactic acid polymer as a main component has a melting temperature Tm, and the biodegradable plastic film forming the outermost layer is an amorphous film. Multi-layer biodegradable plastic film. 3. The melting temperature Tm of a film made of the polylactic acid polymer or a composition containing the polylactic acid polymer as a main component is 1.
3. The multilayer biodegradable plastic film according to claim 1, which has a temperature of 00 ° C. or higher.