JP2005125803A - Multilayer biodegradable plastic film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayered biodegradable plastic film with an improvement in heat sealing properties made of conventional polylactate polymer films. <P>SOLUTION: The multilayer biodegradable plastic film comprises a film (polylactate film) with a composition formed or mainly formed of a polylactate polymer and biodegradable films as both outermost layers of the polylactate film. The surface orientation ΔP of the polylactate film ranges from 3.0×10<SP>-3</SP>to 30×10<SP>-3</SP>, the difference (ΔHm-ΔHc) of the amount of heat between those of crystal meltdown ΔHm and crystallization ΔHc on heating up is 20J/g or higher, and (ΔHm-ΔHc)/ΔHm is 0.75 or higher. The fusion temperature Tm of the biodegradable plastic film making both the outermost layers is lower than that of the polylactate film by 10°C or more. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a multilayer biodegradable plastic film excellent in heat sealability.

  A film having excellent heat sealability is required for a wide range of uses such as agricultural materials, building materials, and medical materials, including general packaging materials using a snack bag as a typical example.

  A film excellent in heat sealability means a desired adhesive strength when a so-called "heat seal" is used in which a film is bonded or bonded with heat and pressure using a heating bar, a heating plate or a heating roll. A film with a wide temperature range that can be obtained stably. That is, the film excellent in heat sealability can easily obtain various film processed products by performing heat seal.

  If the temperature is below the above temperature range during heat sealing, the film substrate is hard and sufficient adhesive strength cannot be obtained, and if it exceeds, the film substrate becomes too soft and causes pinholes or wrinkles to cause deterioration of the appearance. At the same time, the adhesive strength decreases due to them.

  Also, if the heat sealability is poor, heat sealing work must be performed in a narrow temperature range, high temperature control capability is required, equipment becomes expensive, productivity is poor, defect rate is high, and the mind and body of the worker Various problems such as severe fatigue occur.

  Therefore, for general-purpose films such as polyolefin, PET (polyethylene terephthalate), PVC (polyvinyl chloride), etc., for applications that require heat sealing, use raw materials with special polymer designs, or blend and laminate different types of raw materials. In many cases, films with improved heat sealability are used.

  On the other hand, in recent years, there is a demand for plastic products that do not adversely affect the natural environment that decomposes and disappears over time when rejected in the natural environment for all processed plastic products due to the increase in environmental issues.

  However, conventional plastic film products are stable in the natural environment for a long time and have a low bulk specific gravity, which promotes the shortening of the life of the landfill site and damages the natural landscape and the living environment of wild animals and plants. Problems were pointed out.

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

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

  Examples of aliphatic polyesters include poly (hydroxybutyric acid / valeric acid) as a microbial production polymer, polycaprolactone, a condensed dimer of aliphatic dicarboxylic acid and aliphatic diol as a synthetic polymer, and semisynthetic. A polylactic acid polymer is known as a polymer.

  Each of these biodegradable plastics has unique characteristics and can be used for various applications. Among them, polylactic acid polymers are more transparent, rigid, and heat resistant than other biodegradable plastics. Because of its excellent properties, workability, etc., development to hard transparent film applications in which hard PVC or PET has been used has been attempted.

In particular, biaxially stretched heat-set films using polylactic acid polymers have mechanical properties that are the same as or better than general-purpose films and are completely biodegradable, so they are expected to be applied to a wide range of applications including general packaging materials. Has been.
JP-A-8-85194 JP-A-7-18063 JP-A-6-256480

  In the present invention, a film made of a conventional polylactic acid-based polymer has poor heat sealability and has been a serious problem in practical use when used in various fields such as film processed products. Therefore, the present invention provides a biodegradable plastic film that improves the heat sealability of a film made from a conventional polylactic acid polymer and is excellent in heat sealability.

The gist of the present invention is (1) a film (polylactic acid film) comprising a polylactic acid polymer or a composition containing the same as a main component (both outermost layers of the polylactic acid film are biodegradable plastics). A multi-layer biodegradable plastic film that is a film, wherein the polylactic acid film has a plane orientation degree ΔP of 3.0 × 10 ⁻³ to 30 × 10 ⁻³ , and the polylactic acid film is heated The difference (ΔHm−ΔHc) between the amount of heat of crystal melting ΔHm and the amount of heat of crystallization ΔHc generated by crystallization during heating is 20 J / g or more and {(ΔHm−ΔHc) / ΔHm} is 0.75 or more. And the melting temperature Tm of the biodegradable plastic film forming both outermost layers is 10 ° C. or more lower than the melting temperature of the polylactic acid-based film. Is Irumu.

(2) Multilayer biodegradation having a polylactic acid polymer or a film (polylactic acid film) made of a composition containing the same as a main component, and both outermost layers of the polylactic acid film being biodegradable plastic films Crystal melting heat amount when the polylactic acid film has a plane orientation degree ΔP of 3.0 × 10 ⁻³ to 30 × 10 ⁻³ and the polylactic acid film is heated. The difference between ΔHm and the crystallization heat amount ΔHc generated by crystallization during heating (ΔHm−ΔHc) is 20 J / g or more and {(ΔHm−ΔHc) / ΔHm} is 0.75 or more and the polylactic acid system The multi-layer biodegradable plastic film is characterized in that the film has a melting temperature Tm, and the biodegradable plastic film forming both outermost layers is an amorphous film.

  (3) The multilayer biodegradable plastic film according to (1) or (2), wherein the polylactic acid film has a melting temperature Tm of 100 ° C. or higher.

  The multilayer biodegradable plastic film of the present invention has excellent heat-sealability and can be used for general packaging materials and the like, and because it has biodegradability, it is environmentally friendly.

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

  Examples of lactic acid include L-lactic acid and D-monolactic acid, and examples of hydroxycarboxylic acid include glycolic acid, 31-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyhydroxyvaleric acid, and 6-hydroxycaproic acid. Is a typical example.

  As the polymerization method, a known method such as a condensation polymerization method or a ring-opening polymerization method can be adopted. Furthermore, for the purpose of increasing the molecular weight, a small amount of a chain extender such as a diisocyanate compound, diepoxy compound, acid anhydride is used. Alternatively, 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. When the polymer is below this range, problems such as almost no practical physical properties appear. In the case of exceeding, the melt viscosity becomes too high and the molding processability is poor.

  Here, it is important that the melting temperature Tm of a polylactic acid polymer or a film composed of a composition containing the same as a main component (hereinafter referred to as polylactic acid film for short) is 100 ° C. or higher. If the Tm is less than 100 ° C., the heat resistance is lowered, causing wrinkles or the like in secondary processing or the like, which is not practical. Moreover, Tm of poly L-lactic acid homopolymer is 195 degreeC, and Tm falls as copolymerization components, such as D-lactic acid, glycolic acid, and 6-hydroxycaproic acid, increase. Therefore, in practice, the Tm of the polylactic acid film used in the present invention is 100 ° C. or higher and 195 ° C. or lower.

  In addition, 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 rise tends to increase and the melting temperature Tm tends to decrease. At the temperature at which Tc> Tm, Tm is substantially not observed. That is, depending on the selection of the comonomer, Tm may disappear before the temperature drops to 100 ° C., but in the present invention, the polylactic acid film needs to have Tm.

  The biodegradable plastic film laminated on the polylactic acid-based film described above is a biodegradable plastic film that is 10 ° C. or more lower than the melting temperature Tm of the polylactic acid-based film used, or a biodegradable plastic that is amorphous. It is a film. Examples of the biodegradable plastic film that can be used include polylactic acid, aliphatic polyesters other than polylactic acid, modified PVA, and cellulose ester compounds.

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

  As described above, the desired polylactic acid film having a melting temperature Tm of 10 ° C. or more lower than that of the polylactic acid film used as the substrate is D or L-lactic acid, glycolic acid, 6- By adding a copolymer component such as hydroxycaproic acid, the melting temperature Tm can be lowered. As the laminated film, since the melting temperature Tm of the homopolymer is 195 ° C., a polylactic acid film having a temperature of 185 ° C. or less is used. Further, in order to obtain a polylactic acid film that is amorphous, the copolymerization ratio may be further increased.

  Aliphatic polyesters other than polylactic acid used as a biodegradable plastic film laminated in the present invention have alkylene and ester bonds as a basic skeleton, and in a range that does not substantially affect biodegradability, urethane bonds, An amide bond, an ether bond, etc. can also be introduced. In particular, an isocyanate compound can be used to introduce a urethane bond into the main chain to jump up the molecular weight.

  Specifically, a polymer obtained by condensing an aliphatic diol and an aliphatic dicarboxylic acid is first mentioned. Examples of the aliphatic diol include ethylene glycol, 1,4-butanediol, and 1,4-cyclohexanedimethanol. Examples of the aliphatic dicarboxylic acid include succinic acid, adipic acid, suberic acid, sebacic acid, and dodecanedioic acid. Is a typical example. A polymer in which one or more of these are selected and subjected to condensation polymerization and then jumped up to a weight average molecular weight of 50,000 or more with an isocyanate compound, if necessary, is usually similar to Tm of 60 to 110 ° C. and polyethylene. It has basic physical properties 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. Representative examples of the monomer include ε-caprolactone, δ-valerolactone, β-methyl-δ-valerolactone, β-propiolactone, pivalolactone, β-butyrolactone, γ-butyrolactone, and the like. And glycolide. One or more types are selected from these, and the polymerization is carried out by adjusting the conditions so that the weight average molecular weight is 30,000 or more. Although control of Tm is performed by selection of a monomer, it is 50-170 degreeC normally.

  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 2-methylene-1 which is ethylene and cyclic ketene acetal. , 3-dioxolane and a radical polymer with 2-methylene-1,3-dioxepane.

  In addition, aliphatic polyesters that are biosynthesized with acetyl coenzyme A (acetyl CoA) in bacterial cells including Alkali genus eutrophus are known. This aliphatic polyester is mainly poly-β-bidoxybutyric acid (poly-3HB), but in order to improve the practical properties as a plastic, the fermentation process is devised and usually valeric acid units (HV) are copolymerized. It is industrially advantageous to make a copolymer of poly (3HB-co-3HV). The HV copolymerization ratio is generally 0 to 40%, and in this range, Tm is 130 to 165 ° C. 4HB may be copolymerized instead of HV, or a long-chain hydroxyalkanoate may be copolymerized.

  Polyvinyl alcohol (PVA) used as a biodegradable plastic film laminated in the present invention is relatively excellent in biodegradability among existing petroleum-derived synthetic polymers, but PVA homopolymers are molecular Since the cohesive force is too large and does not have a melting point and cannot be melt-extruded, there is a restriction on the molding process when forming a film. Therefore, ethylene can be copolymerized or a vinyl acetate unit usually disappearing in the saponification step can be left to be modified so as to have a Tm of about 50 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 received a certain evaluation as a biodegradable plastic material, and is called modified PVA.

  The cellulose ester compound used as a biodegradable plastic film laminated in the present invention is usually a compound obtained by acetic esterifying a hydroxyl group of cellulose, and the degree of substitution is between 2 and 3. The cellulose ester compound has substantially no Tm. In order to impart melt molding processability, a plasticizer may be added. The plasticizer also functions to adjust the Tg (glass transition temperature) of the material. As the plasticizer, in view 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 mentioned.

  The biodegradable plastic film laminated on the polylactic acid-based film also has a plasticizer, a lubricant, an inorganic filler, an ultraviolet absorber, etc. for the purpose of adjusting the physical properties and processability of the film within the range that does not impair the effects of the present invention. It is also possible to add additives, 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 film is used as a base material and the film forming both outermost layers is a biodegradable plastic film. In order to provide sealability and curl resistance, a laminated film of two types and three layers comprising a polylactic acid film excellent in mechanical properties as an inner layer and both outermost layers as other biodegradable plastic films. be able to.

  Further, a multilayer structure of three or more layers may be used for the purpose of providing other functions such as gas barrier property and water vapor barrier property. Further, for the purpose of lowering the price or for applications where it is preferable to have curl properties, the layer structure may be a non-target layer structure from the center layer.

  As a method of laminating a biodegradable plastic film on a polylactic acid film, a commonly used method can be employed. For example, a method in which a plurality of extruders are connected to one die and so-called co-extrusion, a method in which a different kind of material is coated on a kind of unwound film, a plurality of kinds of films at an appropriate temperature on a roll or a press machine, etc. Typically, a method of thermocompression bonding, a method of bonding films together using an adhesive, or the like can be given.

  As an adhesive in the case of so-called dry lamination or wet lamination, vinyl type, acrylic type, polyamide type, polyester type, rubber type, urethane type, etc. are generally used, but when making the adhesive also biodegradable, Polysaccharides such as starch, amylose and amylopectin, proteins and polypeptides such as glue, gelatin, casein, zein and collagen, unvulcanized natural rubber, aliphatic polyester, etc. are preferably employed.

In order to significantly improve the brittleness inherent in the polylactic acid-based polymer and further improve the film strength, the degree of plane orientation ΔP of the polylactic acid-based film used as the substrate is set to 3.0 × 10 ⁻³ to It is desirable to adjust 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 equation by measuring the refractive index in the three orthogonal directions.
ΔP = {(γ + β) / 2} −α
(Α <β <γ)
Here, γ and β are the refractive indexes of two orthogonal axes parallel to the film surface, and α is the refractive index in the film thickness direction.

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

  As a method of increasing ΔP, in addition to all known film stretching methods, a molecular orientation method using an electric field or a magnetic field can be employed.

  Usually, a sheet or cylindrical material melt-extruded from a T die, I die, round die, etc. is rapidly cooled with a cooling cast roll, water, compressed air, etc. and solidified in an amorphous state, and then a roll method, a tenter A method of stretching uniaxially or biaxially by a method, a tubular method or the like is desirably employed industrially.

  In the production of a stretched multilayer biodegradable plastic film, in the case of multilayering by lamination, so-called dry lamination or wet lamination, a pre-stretched polylactic acid film may be used, and in the case of co-extrusion, extrusion is performed. What is necessary is just to stretch | stretch the multilayer film made on suitable conditions.

  The stretching conditions when focusing only on the polylactic acid film are generally a stretching temperature of 50 to 100 ° C., a stretching ratio of 1.5 to 5 times, and a stretching speed of 100% / min to 10,000% / min. However, since this appropriate range varies depending on the composition of the polymer and the thermal history of the unstretched sheet, it can be appropriately determined while looking at the value of ΔP.

  The polylactic acid film stretched in this way has inherently improved brittleness and improved mechanical strength. It is a heat-shrinkable film and can be used for shrink packaging, shrink-bound packaging, or shrink labels.

However, in the multilayer biodegradable plastic film using the polylactic acid-based film having ΔP of 3.0 × 10 ⁻³ to 30 × 10 ⁻³ as described above, it can be used for many applications where thermal dimensional stability is required. Can not. Therefore, in order to impart thermal dimensional stability to the polylactic acid-based film, the difference (Hm−ΔHc) between the heat of crystal fusion ΔHm when the film is heated and the heat of crystallization ΔHc generated by crystallization during the temperature rise. ) Is controlled to 20 J / g or more and {(ΔHm−ΔHc) / 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 there is a problem that the film is shrunk during secondary processing steps such as bonding, drying, and aging, and during storage in summer. It is likely to occur and is not practically used. If this condition is exceeded, the thermal dimensional stability will be good and there will be no practical problems.

  ΔHm and ΔHc are determined by differential scanning calorimetry (DSC) of the film sample, and ΔHm is the amount of heat necessary to melt all the crystals when the temperature is raised at a heating rate of 10 ° C./min, It is determined from the area of the endothermic peak due to crystal melting that appears in the vicinity of the crystal melting point of the polymer. ΔHc is determined from the area of the exothermic peak generated during crystallization that occurs during the temperature raising process.

  ΔHm mainly depends on the crystallinity of the polymer itself, and takes a large value for a polymer with high crystallinity. Incidentally, the complete homopolymer of L-lactic acid or D-lactic acid without a copolymer is 60 J / g or more, and ΔHm varies depending on the composition ratio of these two lactic acid copolymers. ΔHc is an index related to the crystallinity of the film at that time with respect to the crystallinity of the polymer. When ΔHc is large, the crystallization of the film proceeds in the temperature rising process. That is, it represents that the degree of crystallinity of the film was relatively low based on the crystallinity of the polymer. Conversely, when ΔHc is small, it indicates that the degree of crystallinity of the film is relatively high based on the crystallinity of the polymer.

  That is, one direction for increasing (ΔHm−ΔHc) is to form a film having a relatively high degree of crystallinity from a polymer having high crystallinity as a raw material. The degree of crystallinity of the film depends not a little on the composition of the polymer, and in order to make the polymer itself ΔHm 20 J / g or more, in the case of making a co-child combination 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. In order to reduce ΔHc, that is, in order to increase the crystallinity of the film, it is necessary to select film forming conditions.

  In order to increase the degree of crystallinity of the film in the molding process, particularly the tenter method biaxial stretching, it is useful to increase the stretching ratio and promote orientation crystallization, or to heat-treat in an atmosphere at or above the crystallization temperature after stretching. As ΔP is larger, the crystallization temperature tends to decrease. In the present invention, as a result of intensive investigations, heat treatment is performed at a temperature of at least 70 ° C., preferably 90 ° C. to 170 ° C. for 3 seconds or longer. 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.

  Examples are shown below, but the present invention is not limited to these examples.

(Experimental example 1)
Co-extrusion was performed using a two-type three-layer T die die so that the melt from the 50 mmφ single-screw extruder was in the inner layer and the melt from the 30 mmφ single-screw extruder was in both outer layers. The thickness ratio of the outer layer / inner layer / outer layer was adjusted to 1/8/1, and an unstretched sheet having a total thickness of 250 μm was rapidly cooled after being extruded and collected.

  The inner layer (base material) is L-form / D-form = 98/2, polylactic acid (Lacty manufactured by Shimadzu Corporation) (Tm = 170 ° C.) having a weight average molecular weight of 200,000, and the outer layer is aliphatic polyester. Showa Highpolymer Co., Ltd. Bionore 1010 (Tm = 114 ° C.), Daicel Chemical Industries, Ltd. Plaxel H-7 (Tm = 60 ° C.), Zeneca Biopol D300G (Tm = 162 ° C.) and the same D400G (Tm = 153 ° C.) was used. Similarly, polylactic acid was extruded using a 30 mmφ single-axis extruder to obtain a 250 μm sheet composed of a single layer of polylactic acid.

  The above-described sheet was longitudinally stretched 1.5 times, then 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 of each zone of stretching and heat treatment was 30 seconds.

  Since the polylactic acid film layer used as the inner layer has a Tm of 170 ° C., among the above examples of the aliphatic polyester used in the outer layer, the present invention can form an outer layer that is 10 ° C. lower than the Tm of the polylactic acid film layer. Included were Bionore 1010 (Tm = 114 ° C.), Plaxel H-7 (Tm = 60 ° C.), and Biopol D400G (Tm = 153 ° C.). On the other hand, those using a multilayer film using Biopol D300G (Tm = 162 ° C.) and a film having a single layer structure of polylactic acid were designated as Comparative Examples 1 and 2.

  The evaluation results of the film are shown in Table 1. The measured values shown in the table were calculated under the following conditions.

(1) ΔP
The refractive index (α, β, γ) in the three orthogonal directions was measured with an Abbe refractometer and calculated by the following equation.

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 to it α: refractive index in the film thickness direction In the present invention, ΔP defines the polylactic acid polymer film. Therefore, when the film was stretched and heat-treated after being laminated by coextrusion or the like, film layers other than the polylactic acid film layer were removed as necessary, and the polylactic acid film was measured.

(2) Thermal analysis Based on JIS-K7122, a thermogram obtained by heating a raw pellet or a polylactic acid film layer 10 mg at a heating rate of 10 ° C./min using DSC-7 manufactured by PerkinElmer. The glass transition temperature Tg, the melting temperature Tm, the heat of crystal melting ΔHm, and the heat of crystallization ΔHc were determined and calculated.

(3) Heat seal strength A film sample is cut into a strip of 10 mm width × 100 mm length with MD (film flow direction) as the longitudinal direction, and the two strip samples are overlapped to have a heat seal bar of 10 mm width. After setting so as to be orthogonal to the heat sealer, it was heated from one side at a predetermined temperature, and heat sealed at a pressure of 1.178 Kg / cm ² for 15 seconds. At this time, when the laminated film was used, it was set so that the easy-adhesion treated surfaces were inside.

  The sample was subjected to a T-type peel test using an Intesco Universal Tester 205 type machine in accordance with JISK-6854 until it broke at a peel rate of 100 mm / min or until the adhesive part remained at 1 mm. The peak value of the obtained time-stress is defined as the heat seal strength. For easy understanding, the seal is not sealed at all, or even if the value is less than 50 g / cm, it is less than 50 g / cm and less than 500 g / cm. The thing was shown as (triangle | delta), and the thing over 500 g / cm was shown as (circle).

  As is apparent from Table 1, it can be seen that in Examples 1 to 3 in which the difference in Tm between the inner layer (base material) and the outer layer is 10 ° C. or more, suitable heat sealing performance is 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 seal performance.

(Experimental example 2)
An unstretched sheet of a multilayer biodegradable plastic film, which is a three-layered bionore 1010 provided in the outer layer, used in Example 1, was stretched in the longitudinal direction, then in the transverse direction, and further heat-treated. 4 to 8 sheets were obtained. In addition, Example 4 is an unstretched sheet.

  When the heat sealing performance of the obtained Examples 4 to 8 was examined in the same manner as in Experimental Example 1, it was found that suitable heat sealing performance was obtained in a wide temperature range. Further, Table 2 shows the tensile strength at break and heat shrinkability. In addition, the measured values shown in the table were calculated under the following conditions.

(4) Tensile breaking strength Tensile strength was measured based on JIS-K7127 using a Toyo Seiki Tensilon II type machine. MD indicates the film flow direction, and TD indicates the direction perpendicular to the film flow.

(5) Heat shrinkability A film sample was cut out to 100 mm × 100 mm and immersed in a hot water bath at 80 ° C. for 300 seconds, and then its dimensions were measured to calculate the ratio (%) of heat shrinkage to the original dimensions.

Since Example 4 is an unstretched sheet, the shrinkage rate is small, but the tensile strength is insufficient. Since Example 5 has a plane orientation degree ΔP in the range of 3 × 10 ⁻³ to 30 × 10 ⁻³ and is stretched, it is suitable as a heat shrinkable film having moderate tensile strength. Example 6 is a heat-shrinkable film excellent in both tensile strength and heat-shrinkability because the degree of plane orientation ΔP is in the above range and the heat treatment after stretching is appropriate. On the other hand, in Examples 7 and 8, ΔP is 3 × 10 ⁻³ to 30 × 10 ⁻³ , (ΔHm−ΔHc) is 20 J / g or more, and {(ΔHm−ΔHc) / ΔHm} is 0.75 or more. It is a thermal dimensional stability film excellent in both tensile strength and thermal dimensional stability.

That is, as is apparent from Table 2, the multilayer biodegradable plastic film of the present invention has excellent heat sealability depending on the stretching conditions, has an appropriate tensile strength, and has heat shrinkability or thermal dimensional stability. A degradable plastic film can be obtained.

Claims (3)

A multi-layer biodegradable plastic film having a polylactic acid polymer or a film (polylactic acid film) made of a composition containing the same as a main component, wherein both outermost layers of the polylactic acid film are biodegradable plastic films And the degree of plane orientation ΔP of the polylactic acid-based film is 3.0 × 10 ⁻³ to 30 × 10 ⁻³ , and the crystal melting heat amount ΔHm is increased when the polylactic acid-based film is heated. The difference (ΔHm−ΔHc) from the crystallization heat amount ΔHc generated by crystallization during warming is 20 J / g or more and {(ΔHm−ΔHc) / ΔHm} is 0.75 or more, and both the outermost layers are formed. The multilayer biodegradable plastic film is characterized in that the melting temperature Tm of the biodegradable plastic film is 10 ° C. or more lower than the melting temperature of the polylactic acid film. A multi-layer biodegradable plastic film having a polylactic acid polymer or a film (polylactic acid film) made of a composition containing the same as a main component, wherein both outermost layers of the polylactic acid film are biodegradable plastic films And the degree of plane orientation ΔP of the polylactic acid-based film is 3.0 × 10 ⁻³ to 30 × 10 ⁻³ , and the crystal melting heat amount ΔHm is increased when the polylactic acid-based film is heated. The difference (ΔHm−ΔHc) from the crystallization heat amount ΔHc generated by crystallization during warming is 20 J / g or more and {(ΔHm−ΔHc) / ΔHm} is 0.75 or more, and the polylactic acid film is melted. A biodegradable plastic film having a temperature Tm and forming the two outermost layers is an amorphous film.   The multilayer biodegradable plastic film according to claim 1 or 2, wherein the polylactic acid film has a melting temperature Tm of 100 ° C or higher.