JP3206747B2 - Aliphatic polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film made of an aliphatic polyester resin, and more particularly to printing and printing which are important characteristics in packaging films for fresh foods, processed foods, pharmaceuticals, medical equipment, electronic parts and the like. The present invention relates to an aliphatic polyester film excellent in processing suitability such as lamination and heat sealing strength after bag making.

[0002]

2. Description of the Related Art Conventionally, various plastics such as polyethylene, polypropylene, polyethylene terephthalate, polyolefins represented by nylon 6, aromatic polyesters, polyamides and the like have been used for films for packaging various products including foods. . These films for packaging materials are collected after use, and disposed of either by incineration or burying in soil. However, it is well known that the collection requires a great deal of labor, and is actually left uncollected and causes various problems such as environmental pollution.
In addition, when incinerated, the thermal power is too strong, the furnace is severely damaged, and a large amount of fuel is required. On the other hand, when buried in the soil, there is a problem that the waste does not have biodegradability and remains semipermanently in the soil. Under these circumstances, there has been an increasing demand for various packaging films having good biodegradability.

[0003] Therefore, in order to impart biodegradability to the above polyethylene and the like, various studies have been made on blending a biodegradable component such as starch. Furthermore, a method of imparting photodegradability or a method of blending a biodegradable component of starch with photodegradable polyethylene and the like have been studied, and are attracting attention as a solution to the above-mentioned problem. However, in these methods, the starch component is biodegradable and thus decomposed by microorganisms in the soil.
The polymer parts other than starch are not decomposed. Therefore, it is not a fundamental solution to the above problem.

[0004] From these facts, with the increasing public awareness of environmental protection in recent years, when plastic products are generally disposed of in the natural environment, they are decomposed and disappear over time, adversely affecting the natural environment. There is a demand for a plastic product that does not affect the environment.

[0005] As a fundamental solution to the above problem, various biodegradable polymer materials in which the polymer itself has biodegradability have been studied. Above all, polylactic acid is easily degraded when rejected in the natural environment.For example, polylactic acid film has the advantage that it is naturally hydrolyzed in soil and then becomes a harmless degradation product by microorganisms. More and more have been developed. Specifically, for example, a polylactic acid film is used as a molded product for medicine (JP-B-41-2734).
Various applications have been studied as basic raw materials of biodegradable general-purpose materials for disposable uses other than pharmaceutical uses.

Above all, biaxially stretched aliphatic polyester films are expected to be applied to a wide range of uses including general packaging materials because they have transparency, biodegradability and excellent mechanical properties equivalent to general-purpose films. I have.

For example, Japanese Patent Application Laid-Open No. 7-207041 discloses a biodegradable film made of a polylactic acid-based polymer, having a plane orientation degree ΔP of 3.0 × 10 ^-3 or more, and heating the film. Between the heat of crystallization melting ΔHm at the time and the heat of crystallization ΔHc generated by crystallization during heating (ΔHc).
m-ΔHc) is 20 J / g or more, and describes a film having practical strength and thermal dimensional stability.

[0008] However, as a result of proceeding development with priority given to decomposition in the natural world, it has not been possible to sufficiently bring out the excellent properties inherent to aliphatic polyesters. That is, since importance was placed on biodegradability, orientation and crystallization of the film were not sufficient, and strength and thermal dimensional stability were still insufficient.

As a result, fresh foods, processed foods, pharmaceuticals,
When used as a packaging film for medical equipment, electronic parts, etc., such a film undergoes dimensional changes or wrinkles in the processing steps such as the printing step or laminating step necessary for a film for packaging. It became clear that there was a problem with suitability.

Generally, a film is required to have a winding property at the time of molding and a slip property at the time of using the product. If the slip property is insufficient, the handling property becomes poor during the production and processing of the film, and the slip property is poor due to the poor slip property in contact with the guide rolls during running of the film, thereby increasing the tension and causing scratches on the film surface. And running performance deteriorates. Examples of a film containing an organic lubricant such as a fatty acid ester, a fatty acid or a fatty acid amide, and an inorganic fine particle (anti-blocking agent) such as silica or calcium carbonate in order to improve the slipperiness. Are disclosed in JP-A-8-34913 and JP-A-9-2
No. 78997.

However, when used as a bag for packaging, it is necessary to laminate a sealant film made of a polyolefin resin or an aliphatic polyester resin on the aliphatic polyester film and seal the contents by heat sealing. To improve handling,
JP-A-8-34913 and JP-A-9-2789
No. 97, when the organic lubricant described in the aliphatic polyester-based film is added, the running property is improved, but the adhesive strength between the aliphatic polyester-based film and the sealant film is reduced and the adhesion becomes insufficient. It is difficult to use as a packaging bag.

As described above, the addition of the above-mentioned organic lubricant or anti-blocking agent alone maintains the transparency required for packaging applications while maintaining the workability and the adhesiveness of the heat-sealed portion after bag making. Was difficult to balance.

[0013]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems and provides an aliphatic polyester-based film having excellent suitability for printing, laminating and the like, and excellent heat-sealing strength, which is particularly suitable for packaging and the like. The purpose is to do.

[0014]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above situation, and an aliphatic polyester biaxially stretched film which can solve the above-mentioned problems is as follows. It is.

That is, the first invention of the present invention comprises, as a main component, an aliphatic polyester whose main repeating unit is a general formula -O-CHR-CO- (R is hydrogen or an alkyl group having 1 to 3 carbon atoms). And a refractive index (Nz) in the thickness direction of 1.440 or more and less than 1.455, and a surface energy of 45 dyne / cm or more.

A second invention is the aliphatic polyester film according to the first invention, wherein the film has a heat-sealing resin layer laminated thereon.

A third invention is the aliphatic polyester film according to the second invention, wherein the heat-sealing resin layer is a polyolefin resin or an aliphatic polyester resin.

A fourth invention is the aliphatic polyester film according to any one of the first to third inventions, wherein the aliphatic polyester is polylactic acid.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The aliphatic polyester used in the present invention has a main repeating unit of the general formula -O-CHR.
-CO- (R is hydrogen or an alkyl group having 1 to 3 carbon atoms)
Is a polyester.

Here, all the repeating units of the aliphatic polyester are preferably represented by the above general formula.
If necessary, a unit other than the repeating unit represented by the above general formula may be contained as long as the performance as the aliphatic polyester is not impaired. Specifically, for example, 70 mol% or more of the repeating units in the molecule are preferably the repeating units represented by the above general formula, more preferably 80 mol% or more, and still more preferably 90 mol% or more. Mol% or more, particularly preferably 95 mol% or more.

However, an aromatic component is not usually contained in the aliphatic polyester. If necessary, an aromatic component may be employed as long as the performance as the aliphatic polyester is not impaired.In that case, the ratio of the repeating unit containing the aromatic structure may be, of the repeating units in the molecule. 1
It is preferably 0 mol% or less, more preferably
It is at most 5 mol%, more preferably at most 3 mol%.

Specific examples of the aliphatic polyester include, but are not limited to, polylactic acid, polyglycolic acid, and poly (2-oxybutyric acid). Among them, polylactic acid is most preferable in terms of performance and price.
Further, the aliphatic polyester may be a homopolymer or a copolymer obtained by copolymerizing a plurality of types of repeating components selected from the above general formula. Further, the aliphatic polyester may be a single polymer or a mixture of a plurality of aliphatic polyesters.

When an asymmetric carbon is present in the constituent carbon atoms of the aliphatic polyester, optical isomers such as L-form, DL-form and D-form may exist, and any of them can be employed. Mixtures of these isomers can also be employed.

Further, other polymer materials may be mixed with the aliphatic polyester as long as the effects of the present invention are not impaired. When another polymer material is mixed, preferably, the aliphatic polyester is 70% by weight or more of the total weight of the aliphatic polyester and the other polymer material, and more preferably 80% by weight or more. , More preferably 90% by weight, particularly preferably 95% by weight or more. The aliphatic polyester described above (hereinafter, referred to as
Sometimes simply referred to as “polymer”. ) Is produced by a known method, for example, a method such as ring-opening polymerization of a corresponding dehydrated cyclic ester compound of α-oxyacid, and becomes a raw material of the film of the present invention.

The weight average molecular weight of the aliphatic polyester used in the present invention is preferably 10,000 to 500,000. More preferably, it is 40,000 to 300,000. Particularly preferably, 5
~ 300,000. If the weight average molecular weight is too small, the physical properties of the obtained film are liable to decrease, and the biodegradation rate tends to be too high, which is not preferable. In order to ensure sufficient extrudability from a film-forming machine during film production and stretchability with a biaxial stretching machine, the weight-average molecular weight is 1: 1.
Preferably, it is at least 10,000. On the other hand, when the weight average molecular weight is too high, there is a problem that melt extrusion of the aliphatic polyester becomes difficult.

Known additives can be added to the aliphatic polyester as required. For example, a lubricant, an antiblocking agent, a heat stabilizer, an antioxidant, an antistatic agent, a light resistance agent, an impact resistance improver, a crystal nucleating agent, a coloring prevention agent, a pigment, a dye, an ultraviolet absorber, a release agent, An antimicrobial agent or a flame retardant may be contained. For example, anionic surfactants such as potassium lauryl phosphate, cationic surfactants such as quaternary ammonium salts, ethylene oxide addition of aliphatic higher alcohols and higher fatty acids, if necessary, in consideration of antistatic properties and the like. Nonionic surfactants such as products, polyalkylene glycols such as polyethylene glycol, polyethylene glycol / polypropylene glycol block copolymers, and silicone oils such as dimethyl polysiloxane, polyether-modified silicone oil, and higher alkoxy-modified silicone oil. Alternatively, two or more kinds can be contained.

In the present invention, in order to improve the handleability of the film, inert particles such as inorganic particles, organic salt particles or heat-resistant polymer particles, which are inert to the aliphatic polyester, are added to the aliphatic polyester. It is preferable that the film is contained in polyester to impart appropriate surface irregularities to the film surface.

Examples of the inorganic particles include metal oxides such as silica, titanium dioxide, aluminum oxide, zirconium oxide, talc, kaolinite, calcium carbonate, magnesium carbonate, barium carbonate, calcium phosphate, magnesium phosphate, lithium phosphate, and sulfuric acid. And salts of metals such as barium and lithium fluoride.

In particular, in order to obtain a film having excellent transparency while maintaining good handling properties, it is preferable to use silica, which is a particle having a refractive index close to that of the aliphatic polyester. Agglomerated silica particles, crushed silica, and glass filler are particularly preferred.

Examples of the organic salt particles include calcium oxalate and terephthalates such as calcium, barium, zinc, manganese and magnesium.

Examples of the heat-resistant polymer particles include homo- or copolymers of vinyl monomers such as divinylbenzene, styrene, acrylic acid, methacrylic acid and acrylic acid. Specifically, for example, crosslinked polymer particles such as crosslinked polystyrene resin, crosslinked acrylic resin, crosslinked polyester resin, and silicone resin, polytetrafluoroethylene, benzoguanamine resin, thermosetting epoxy resin, unsaturated polyester resin, thermosetting Heat-resistant organic particles such as a urea resin and a thermosetting phenol resin are exemplified.

One of these inert particles may be used alone, or two or more of them may be used in combination. Further, the average particle diameter of the inert particles in the film is 0.01 to
3.0 μm is preferred, and more preferably 0.05 to
2.5 μm. The average particle size of the inert particles can be determined by an electron microscope. Further, the content of the inert particles with respect to the aliphatic polyester is 0.005 to 2
% By weight, more preferably 0.01 to 1.0% by weight.
% By weight. Above all, a relatively large inert particle having a refractive index close to that of the aliphatic polyester and having an average particle diameter of 1.0 to 2.5 μm is 0.01 to 2.5 μm to the polyester.
It is particularly preferable to contain 0.1% by weight in order to achieve both transparency and slipperiness of the film.

In order to achieve both transparency and handleability of the film, it is preferable to use two or more kinds of inert particles in combination. In particular, large particles of inert particles (for example, crosslinked polymer particles having a low degree of crosslinking, such as crosslinked polystyrene and crosslinked acryl, and silica that is an aggregate of primary particles, etc.) that are deformed during film formation, and film formation. It is preferred to combine ordinary inert particles of small particle size that do not deform into them.

The method of adding the inert particles to the aliphatic polyester is not particularly limited, and any known method can be used. Specifically, for example, if polylactic acid is used as the aliphatic polyester, before polymerizing lactide, a method of dispersing inert particles in molten lactide, and inert particles during the polymerization reaction of lactide Are dispersed.

The aliphatic polyester composition for a film thus prepared is formed into a film by a conventionally known method. Preferably, the film is further stretched after molding. Specifically, a biaxial stretching method such as a uniaxial stretching method in which the film is stretched in a longitudinal direction or a transverse direction, an inflation method, a simultaneous biaxial stretching method, or a sequential biaxial stretching method is used. As the sequential biaxial stretching method, for example, longitudinal stretching and transverse stretching may be performed in order, or transverse stretching and longitudinal stretching may be performed in order. Further, a stretching method such as a horizontal / longitudinal / longitudinal stretching method, a vertical / horizontal / longitudinal stretching method, a vertical / longitudinal / horizontal stretching method can be applied. Further, if necessary, a heat setting treatment, a vertical relaxation treatment, a horizontal relaxation treatment, or the like may be performed. More preferably, it is heat-set after biaxial stretching.

For example, when an aliphatic polyester film is produced by an extrusion method, a known T-die method,
An inflation method or the like can be applied, and an unstretched film can be obtained by these methods. The extrusion temperature is from the melting temperature (Tm) of the aliphatic polyester used to Tm + 7.
0 ° C. range, more preferably Tm + 20 to Tm + 50
It is in the range of ° C. If the extrusion temperature is too low, an excessive load is applied to the extruder, which makes it difficult to perform stable extrusion. Conversely, if the extrusion temperature is too high, the aliphatic polyester tends to decompose, which is not preferable. As the die of the extruder used for producing the aliphatic polyester film, a die having an annular or linear slit can be used. As for the temperature of the die, the same temperature as the extrusion temperature is applied.

In the biaxial stretching of the unstretched film made of the aliphatic polyester, the uniaxial stretching and the biaxial stretching may be performed sequentially or simultaneously. The stretching temperature ranges from Tg (glass transition point) to Tg + 50 of the aliphatic polyester used.
C. is preferred. More preferably, Tg + 10 to T
g + 40 ° C. If the stretching temperature is too low, stretching is difficult, while if it is too high, the thickness uniformity or the mechanical strength of the obtained film decreases, which is not preferable.

The stretching in the longitudinal and transverse directions may be carried out in one step or in multiple steps. However, the stretching is ultimately performed at least three times, more preferably at least 3.5 times in each stretching direction. -9 times or more in horizontal area magnification, more preferably 1
Stretching at least two times is preferable in terms of thickness uniformity and mechanical properties. If the longitudinal and transverse stretching ratios are each 3 times or less and the area magnification is 9 times or less, it becomes difficult to obtain a film having good thickness uniformity, and it is difficult to obtain sufficient improvement in physical properties such as mechanical strength. . The thickness of the base film mainly composed of an aliphatic polyester is preferably from 10 to 250 μm, more preferably from 12 to 250 μm.

In the biaxially stretched film, the longitudinal direction refers to the longitudinal stretching direction, and the width direction refers to the transverse stretching direction. The upper limit of the stretching ratio is not particularly limited. However, it is preferable that the film is controlled so as not to break during stretching.

The aliphatic polyester film may be formed into a multilayer film by providing a co-extrusion step with another resin or a coating step during the production process.

In the present invention, the refractive index (N
z) can be adjusted to a predetermined range by an arbitrary method. Specifically, for example, longitudinal stretching is performed in two or more stages, and at least one of them is performed at Tg + 20 ° C. to Tg +
Stretching speed of 10,000% / min or more in a temperature range of 40 ° C.,
Preferably at least 15000% / min, more preferably 2
A process including a step of stretching at 0000% / min or more is employed.

In the present invention, the refractive index (Nz) of the aliphatic polyester film in the thickness direction is 1.440 or more .
Must be less than 455, more preferably 1.4
45 to 1.455. When Nz is less than 1.440,
Breakage is likely to occur in the process of forming a film, wrinkles and deterioration in flatness are generated in a printing process, a laminating process, a heat sealing process, and the like, which is not only unfavorable but also results in poor heat sealing strength. Also, 1.4
If it is more than 55, it is not preferable because wrinkling, deterioration of flatness, elongation, etc. occur in the printing step, laminating step, heat sealing step and the like, resulting in poor workability.

The surface energy of the aliphatic polyester film in the present invention is at least 45 dyne / cm, more preferably at least 47 dyne / cm. When the surface energy is less than 45 dyne / cm, the heat sealing strength becomes insufficient, which is not preferable.

In order to make the surface energy of the aliphatic polyester film 45 dyne / cm or more, it is preferable to perform corona discharge treatment, coating treatment, plasma treatment or flame treatment.

The heat seal layer in the present invention comprises a polyolefin resin or an aliphatic polyester resin, and is laminated by a method such as dry lamination or extrusion lamination. When an aliphatic polyester-based resin is used as the heat seal layer, a great advantage that biodegradability can be imparted to the entire laminated product is obtained. Dry lamination is generally performed by applying an adhesive layer by a gravure coat method, a reverse kiss roll coat method, or a reverse roll coat method, drying, and then laminating the resin film having heat sealability.

Examples of the adhesive to be used include a two-component reaction type urethane adhesive and another isocyanate adhesive which are used by mixing a main agent having an OH group and a curing agent having an NCO group. . Examples of the polyolefin-based resin include polyethylene, polypropylene, and copolymers thereof.

Specific examples of the aliphatic polyester having heat sealability include, but are not limited to, polylactic acid, polyglycolic acid, poly (2-oxybutyric acid) and the like. Among them, polylactic acid is most preferable in terms of performance and price. The aliphatic polyester may be a homopolymer or a copolymer in which a plurality of types of repeating components are copolymerized. Further, the aliphatic polyester may be a single polymer or a mixture of a plurality of aliphatic polyesters. When an asymmetric carbon is present in the constituent carbon atoms of the aliphatic polyester, optical isomers such as L-form, DL-form and D-form may exist, and any of them may be employed. Also, a mixture of these isomers can be employed.

[0048]

EXAMPLES Hereinafter, the contents and effects of the present invention will be described specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. First, methods for evaluating physical properties in the following examples and comparative examples will be described.

(1) Refractive index in the thickness direction (Nz) The refractive index of the aliphatic polyester film in the thickness direction was measured using an Abbe refractometer 1T manufactured by Atago Co., Ltd.

(2) Surface energy Various wetting index standard solutions (manufactured by Nacalai Tesque, Inc.) were applied to the surface of the aliphatic polyester film at a width of 1 cm and a length of 6 cm.
cm, a reagent that shrinks the film in 2 seconds was selected, and the surface energy was measured.

(3) Processing Suitability Gravure ink (Ramiace 61 white two-part type, manufactured by Toyo Ink Co., Ltd.) was gravure-printed on the aliphatic polyester films obtained in Example 1 and Comparative Examples 1-4. A printing ink layer was formed. Then, the adhesive (AD585 / C
AT-10, manufactured by Toyo Morton Co., Ltd.) at 2 g / m ^2, and a 60 μm-thick unstretched polypropylene film (P1120, manufactured by Toyobo Co., Ltd.) is laminated by a dry lamination method according to a conventional method to form a sealant layer. An aromatic polyester-based film laminate was obtained. The states of the obtained laminate and the laminate obtained in Example 2 were observed, and a three-step evaluation was performed. ；: Good film condition without wrinkles and print misregistration;
Wrinkles and / or print misregistration slightly occurred ×; deterioration of flatness was observed, and wrinkles and print misregistration occurred

(4) Heat Seal Strength The peel strength of the laminate prepared in (3) was measured when dry (without water) and when wet (with water). The measurement was performed by a 90 ° peel test at a tensile speed of 100 mm / min. "No water" described in Table 1 indicates a temperature of 23 ° C and a humidity of 65.
It is a measured value in% RH. “Water present” is a value measured by dropping a water drop on a measurement sample with a dropper and keeping the film in a wet state.

(5) Film Formation Situation was evaluated by the number of breaks of the aliphatic polyester film when the film was continuously biaxially stretched for 3 hours. The case where no breakage of the film occurs or the case where it occurs once was judged to be good.

Example 1 0.06 weight of aggregated silica particles having an average particle size of 1.8 μm as inert particles for forming surface projections was added to 100 weight parts of poly-L-lactic acid having a weight average molecular weight of 250,000. A part-containing polylactic acid polymer was obtained. This polymer is
Using a 30 mm extruder with a die and a resin temperature of 21
After extruding at 0 ° C., it was cooled with a chill roll at 20 ° C. to obtain an unstretched film having a thickness of 275 μm. The film temperature was preheated to 95 ° C. by a plurality of ceramic rolls, stretched 1.4 times in the machine direction at a stretching speed of 30,000% / min between the rolls, and further stretched 2.5 times in the machine direction at 97 ° C. Next, the film was stretched four times in the transverse direction at 100 ° C. by a tenter-type stretching machine, and then heat-set at 150 ° C. Then 3% at 130 ° C
Lateral relaxation treatment was performed. The obtained film was heated to 40 ° C. and subjected to corona treatment to obtain a biaxially stretched film having a thickness of 20 μm. Table 1 shows the physical properties.

Comparative Example 1 A biaxially stretched film was obtained in the same manner as in Example 1 except that the longitudinal stretching speed was 5000% / min. Table 1 shows the physical properties.

Comparative Example 2 A biaxially stretched film was obtained in the same manner as in Example 1 except that longitudinal stretching was performed at 65 ° C. by 3.5 times in one-step stretching, and the second-stage longitudinal stretching was not performed. Was. Table 1 shows the physical properties.

COMPARATIVE EXAMPLE 3 Without adding inert particles, N, N
N'-ethylenebis (stearylamide)
A biaxially stretched film was obtained in the same manner as in Example 1 except that 0.15 parts by weight was added to 00 parts by weight. Table 1 shows the physical properties.

Comparative Example 4 A biaxially stretched film was obtained in the same manner as in Example 1 except that the corona treatment was not performed. Table 1 shows the physical properties.

Example 2 A gravure ink (Lamiace 61 white two-part type, manufactured by Toyo Ink Co., Ltd.) was gravure-printed on the biaxially stretched film obtained in Example 1 to form a printing ink layer. Then, 2 g / m ^{2 of} an adhesive (AD585 / CAT-10, manufactured by Toyo Morton Co., Ltd.) was applied. Further, as a sealant layer, poly-D, L-lactic acid having a weight average molecular weight of 180,000 (L-form / D-form =
80/20; weight ratio) was extruded from a 30 mm extruder equipped with a T-die at a resin temperature of 200 ° C., and an unstretched film having a thickness of 60 μm obtained by dry lamination according to a conventional method. The same physical property evaluation as in the examples was performed. Table 1 shows the results.

[0060]

[Table 1]

[0061]

The aliphatic ester film of the present invention is
It is extremely useful as an environmentally friendly general packaging film because it is excellent in processability of printing and lamination and heat seal strength after bag making, which are important as practical properties of the packaging film.

────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI B29L 7:00 B29L 7:00 9:00 9:00 (56) References JP-A-2000-37771 (JP, A) 8-3333 (JP, A) JP-A-10-100353 (JP, A) JP-A-7-205278 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 55/00 -55/30 B32B 1/00-35/00 C08J 5/18 C08L 67/04

Claims (4)

(57) [Claims] (1) a main repeating unit represented by the general formula -O-CH
A film mainly composed of an aliphatic polyester which is R-CO- (R is hydrogen or an alkyl group having 1 to 3 carbon atoms), and has a refractive index (Nz) in the thickness direction of 1.440 or more and 1.455. And the surface energy is 45 dy
an aliphatic polyester-based film having a thickness of at least ne / cm. 2. The aliphatic polyester film according to claim 1, wherein the film has a heat-sealing resin layer laminated thereon. 3. The aliphatic polyester film according to claim 2, wherein the heat-sealing resin layer is a polyolefin resin or an aliphatic polyester resin. 4. The aliphatic polyester film according to claim 1, wherein the aliphatic polyester is polylactic acid.