JP2000238128A - Aliphatic polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aliphatic polyester biaxially stretched film suitable as a packaging material of perishable foods, processed foods, pharmaceuticals, medical equipment, electronic parts or the like and excellent in procesability not generating the deterioration of flatness or printing shift in a printing or laminating process. SOLUTION: An aliphatic biaxially stretched film comprises a polymer based on an aliphatic polyester having a main repeating unit represented by general formula -O-CHR-CO- (wherein R is hydrogen or a 1-3C alkyl group) and the value (Nx-Ny) calculated by subtracting the refractive index (Ny) in the lateral direction thereof from the refractive index (Nx) in the longitudinal direction thereof is -0.0215-0 and the irregulality of Nx-Ny in the longitudinal direction thereof is 0.0050 or less and the heat shrinkage factor thereof at 120 deg.C is 5.0% or less.

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-based resin, and more particularly, to a film or a film suitable for packaging of fresh foods, processed foods, pharmaceuticals, medical equipment, electronic parts and the like. The present invention relates to an aliphatic polyester-based biaxially stretched film which is excellent in workability and does not cause deterioration in flatness or misregistration in a laminating step.

[0002]

2. Description of the Related Art Conventionally, biodegradable aliphatic polyester films such as polylactic acid have been rejected in a natural environment.
It is known that after being naturally hydrolyzed, it becomes a harmless decomposition product by microorganisms.

[0003] An example of such a biodegradable aliphatic polyester film such as polylactic acid is a film made of a polylactic acid polymer, and the degree of plane orientation ΔP of the film is 3.0 × 10 ^−3. The difference (ΔHm−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 20.
A biodegradable aliphatic polyester film having a J / g or more is known (JP-A-7-207041).

However, in the case of a film made of the above-mentioned polylactic acid-based polymer, the degree of plane orientation of the film {P is not less than 3.0 × 10 ^-3 and the heat of crystal fusion when the film is heated} The difference (ΔHm−ΔHc) between Hm and the heat of crystallization △ Hc generated by crystallization during temperature rise is 20 J.
/ G or more is prioritized to be decomposed in the natural world, so that the orientation and crystallization of the film may prevent hydrolysis and decomposition by microorganisms. Only films with insufficient properties were obtained.

[0005] Therefore, fresh foods, processed foods, pharmaceuticals,
When used as a packaging film for medical equipment, electronic components, etc., such a film, even if decomposed in nature,
There have been problems such as dimensional changes and wrinkles occurring in the printing and laminating steps required for films for packaging.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, and is useful as a packaging film for fresh foods, processed foods, pharmaceuticals, medical equipment, electronic parts, and the like, and decomposed in the natural world. An object of the present invention is to provide a polyester-based biaxially stretched film.

[0007]

An aliphatic polyester whose main repeating unit is a general formula -O-CHR-CO- (wherein R represents hydrogen or an alkyl group having 1 to 3 carbon atoms) is mainly used. A biaxially stretched film comprising a polymer as a component, wherein the biaxially stretched film has a refractive index (N
x) minus the refractive index in the width direction (Ny) (Nx-N
y) is -0.0215 to 0, and Nx-
The variation in Ny is 0.0050 or less and 120
The thermal shrinkage at 5.0 ° C is 5.0% or less,
The present inventors have found that a general packaging machine having excellent processability without causing dimensional change or wrinkling in a printing or laminating process can be obtained, and has reached the present invention.

The aliphatic polyester-based biaxially stretched film of the present invention has the following constitution. (1) The main repeating unit has the general formula -O-CHR-CO
-(Wherein, R represents hydrogen or an alkyl group having 1 to 3 carbon atoms), which is a biaxially stretched film made of a polymer mainly composed of an aliphatic polyester. The value (Nx-Ny) obtained by subtracting the refractive index (Ny) in the width direction from the refractive index (Nx) in the longitudinal direction is -0.0215 to 0, and the variation in Nx-Ny in the longitudinal direction is 0.0.
050 or less, and the heat shrinkage at 120 ° C is 5.
An aliphatic polyester-based biaxially stretched film having a content of 0% or less. (2) The biaxially stretched aliphatic polyester film according to claim 1, wherein the heat shrinkage at 120 ° C. is 3.0% or less. 3. The biaxially stretched aliphatic polyester-based film according to claim 1, wherein a refractive index (Nz) in a thickness direction is from 1.440 to 1.455. 4. The biaxially stretched aliphatic polyester film according to claim 1, wherein the aliphatic polyester is polylactic acid.

In the present invention, the film is a so-called film.
Including

According to the aliphatic polyester-based biaxially stretched film of the present invention, it is possible to obtain a product excellent in processability without causing dimensional change or wrinkling in a printing or laminating process.

The aliphatic polyester which is a material for forming the aliphatic polyester film of the present invention has a main repeating unit represented by the general formula -O-CHR-CO- (where R is hydrogen or a group having 1 to 3 carbon atoms). Alkyl group.) Aliphatic polyester. Here, examples of the alkyl group having 1 to 3 carbon atoms include alkyl groups such as methyl, ethyl and propyl. Examples of such aliphatic polyesters include aliphatic polyesters such as polylactic acid, polyglycolic acid, poly (2-oxybutyric acid), poly (2-oxyvaleric acid), and poly (2-oxycaproic acid). Examples include, but are not limited to:

As the aliphatic polyester which is a material forming the aliphatic polyester film of the present invention, polylactic acid is preferred.

The aliphatic polyester resins used in the present invention include fatty acids such as polylactic acid, polyglycolic acid, poly (2-oxybutyric acid), poly (2-oxyvaleric acid) and poly (2-oxycaproic acid). Group polyester resin alone,
Alternatively, a mixture of these or a copolymer of monomers such as lactic acid and glycolic acid to be used may be used.

When the aliphatic polyester used in the present invention has an asymmetric carbon, optical isomers such as L-form, DL-form and D-form exist, but the aliphatic polyester used in the present invention is These optical isomers are also included.

The method for producing the polyester which is the raw material for forming the aliphatic polyester film of the present invention is not particularly limited, and it is produced by a conventionally known method or the like. For example, glycolic acid, 2-oxybutyric acid, 2-oxyvaleric acid, 2-
The dehydrated cyclic ester compound of α-hydroxy acid such as oxycaproic acid is produced by a known method such as ring-opening polymerization.

In the present invention, the aliphatic polyester used is preferably a polymer having a weight average molecular weight of 10,000 to 500,000. When it is less than 10,000, the physical properties of the film obtained from the aliphatic polyester are remarkably inferior, and it is difficult to achieve the object of the present invention for use as a packaging container. The weight average molecular weight is preferably 10,000 or more because the extrudability when producing a film from the aliphatic polyester (at the time of film formation) and the biaxial stretchability of the formed film are also reduced. On the other hand, when the weight average molecular weight is 50
If it exceeds 10,000, there is a problem that the melt extrusion becomes difficult because the aliphatic polyester becomes a high-viscosity polymer. The weight average molecular weight is more preferably from 50,000 to 300,000.

In the aliphatic polyester used in the present invention, the content of the heat seal layer must be transparent so as to be transparent after the heat seal layer is formed. Various additives are contained within a necessary range for maintaining high transparency even before formation. Examples of the additives include a lubricant, an antiblocking agent, a heat stabilizer, an antioxidant, an antistatic agent, a lightfast agent, and an impact resistance improver.

Examples of the lubricant include metal oxides such as silica, titanium dioxide, talc and kaolinite; salts of metals such as calcium carbonate, calcium phosphate and barium sulfate; crosslinked polyethylene resins; crosslinked acrylic resins; silicone resins; crosslinked polyester resins. And the like which are inert to the aliphatic polyester resin used in the present invention.

Any one of these lubricants may be used alone, or two or more of them may be used in combination. The average particle system of the lubricant used is 0.01 μm to 3.0 μm.
Is preferably 0.05 μm to 2.5 μm, and the amount of the lubricant used is 0.005% by weight to 2% by weight (more preferably 0.01% by weight to 1% by weight) based on the weight of the entire polyester. 0% by weight) is preferable in order to achieve both transparency and slipperiness of a film required as a packaging container for fresh food or the like. It is preferable to use two or more lubricants in combination in order to achieve both transparency and slipperiness of the film. Such two or more kinds of lubricants are lubricant particles which deform a film from an aliphatic polyester during film formation (for example, organic lubricants having a low degree of crosslinking such as cross-linked polyethylene and cross-linked acrylic, and inorganic lubricants such as silica which is a primary particle aggregate). It is preferable to combine the polyester resin with ordinary lubricant particles that do not deform a film from a polyester resin during film formation.

The method for producing the aliphatic polyester-based biaxially stretched film of the present invention is not particularly limited. For example, the aliphatic polyester-based resin is melted and extruded into a sheet shape (film formation). After the stretched film is obtained, the unstretched film is biaxially stretched, preferably subjected to a heat setting treatment and then subjected to a relaxation treatment.

In the above-mentioned production method, the heat-setting treatment is preferably carried out at a temperature of 145 ° C. or higher, more preferably at a temperature of 150 ° C. or higher. Good from the point.

The thickness of the biaxially stretched film used in the present invention is not particularly limited, and is appropriately set according to the material used, desired physical properties, and the like.

As the extrusion method for forming (forming a film) the aliphatic polyester resin of the present invention into a film, a known T-die method, inflation method and the like can be applied. The extrusion temperature is from the melting temperature (Tm) of the polyester used to Tm.
+ 70 ° C is preferable, and Tm + 20 ° C to Tm + 50
C. is more preferred. If the extrusion temperature is lower than the above range, it is difficult to obtain extrusion stability, and it is easy to overload. Conversely, if the extrusion temperature is higher than the above range, the decomposition of the polyester becomes severe, which is not preferable. The die of the extruder used in the present invention has an annular or linear slit, and the temperature of the die is preferably about the same as the extrusion temperature range.

The obtained unstretched film is biaxially stretched in two directions, longitudinal and transverse.

The stretching method is not particularly limited, and it can be carried out by a generally known method, for example, a roll stretching method, a long gap stretching method, a tenter stretching method, a tubular stretching method, or the like. In any of these methods, stretching in the longitudinal and transverse directions may be performed simultaneously (simultaneous biaxial stretching), or sequential biaxial stretching in which one of the longitudinal and transverse directions is performed first.

The film is preferably stretched in a temperature range of glass transition temperature (Tg) to Tg + 50 ° C., more preferably in a temperature range of (Tg) to Tg + 40 ° C., which the polymer (aliphatic polyester) used has. If the stretching temperature exceeds Tg + 50 ° C., the uniformity of the thickness of the obtained stretched film and the mechanical strength of the obtained stretched film are undesirably reduced.

The stretching in the longitudinal and transverse directions may be carried out in one stage or in multiple stages, but ultimately in each stretching direction is preferably at least three times, more preferably at least 3.5 times. Good to do. In addition, biaxial stretching in the vertical and horizontal directions
It is preferable in view of the uniformity of the thickness and the mechanical properties of the stretched film that can be stretched to a transverse area magnification of 9 times or more, more preferably 12 times or more. If the stretching ratio in the longitudinal and transverse directions is less than 3 times for each, and the ratio of the longitudinal and transverse area by stretching is less than 9 times, a stretched film having good uniformity in thickness cannot be obtained, and the mechanical strength by stretching is also improved. For it is scarce.

As described above, the stretching in the vertical and horizontal directions may be performed in one stage or in multiple stages, but the stretching in the vertical direction is preferably performed in two or more stages.

In the present invention, for example, longitudinal stretching is performed in two or more stages, and at least one longitudinal stretching is performed at a stretching temperature Tg + 2.
In the range of 0 ° C. to Tg + 40 ° C., the stretching speed is 10,000%
/ Min, preferably 15,000% / min, more preferably 20,000% / min or more, whereby the biaxially stretched film having the desired physical properties of the present invention can be obtained.

The refractive index (Nz) in the thickness direction of the biaxially stretched aliphatic polyester-based film in the present invention is 1.44.
00 to 1.4550, and preferably 1.445.
More preferably, it is 0 to 1.4550. If Nz is less than 1.4400, breakage is likely to occur in the step of forming a film. On the other hand, when the thickness exceeds 1.4550, flatness is disturbed when the film is heated in a printing or laminating step, which is not preferable.

Further, the variation of Nx-Ny in the longitudinal direction of the aliphatic polyester film in the present invention needs to be 0.0050 or less, preferably 0.050.
030 or less, more preferably 0.0020 or less. N
When the variation of x-Ny is larger than 0.0050, when the film is heated in a state where a transport tension is applied in a printing or laminating process, a place where good flatness and a place where the flatness is bad are mixed in the longitudinal direction of the film. , Which is not preferable because the yield of the final product is reduced.

The value (Nx-Ny) obtained by subtracting the refractive index (Ny) in the width direction from the refractive index (Nx) in the longitudinal direction of the biaxially stretched film in the present invention needs to be -0.0215 to 0. And preferably -0.0150 to 0. If the value is less than -0.0215, when the biaxially stretched film is heated in a printing or laminating step, the film is stretched due to the transport tension of the film, and printing deviations and ripples are generated, which is not preferable because flatness is deteriorated. Also, (N
If (x-Ny) exceeds 0, the thickness unevenness tends to increase.

Further, the heat shrinkage at 120 ° C. of the aliphatic polyester-based biaxially stretched film used in the present invention needs to be 5.0% or less, and preferably 3.0% or less. If the heat shrinkage of the stretched film is more than 5.0%, the film is not preferred because printing misregistration occurs in a printing step and wrinkles occur during heat sealing.

Further, the aliphatic polyester-based biaxially stretched film of the present invention may be used as a single layer, or may be used as a multilayer by a co-extrusion method or a coating method in a production process. When used in multiple layers, the materials used for each layer may be the same or different. Further, the film of the present invention may be subjected to a corona treatment, a plasma treatment, a flame treatment or the like for the purpose of improving the surface energy.

[0035]

EXAMPLES Hereinafter, the contents and effects of the present invention will be specifically described with reference to Test Examples, Examples, and Comparative Examples, but the present invention is not limited to these without departing from the gist thereof. Test Examples The following tests were performed on the biaxially stretched films obtained in Examples 1, 2, and 3, and Comparative Examples 1, 2, and 3. 1. Test method (1) Refractive index in the thickness direction, longitudinal direction and width direction (Nz,
Nx, Ny) Measurement Each refractive index was measured using an Abbe refractometer 1T manufactured by Atago Co., Ltd. (2) Measurement of variation (unevenness) of (Nx-Ny) in the longitudinal direction Using an Abbe refractometer 1T manufactured by Atago Co., Ltd., the absolute value of 3 m of Nx-Ny was measured at 10 cm intervals in the longitudinal direction of the film. The thickness unevenness was calculated from the equation. Unevenness of (Nx-Ny) = (Maximum value of Nx-Ny)-(N
(Minimum value of x-Ny) (3) Measurement of heat shrinkage The film was 10 mm wide and 250 mm long, and 200 m long
Mark at m intervals and measure interval A at a constant tension of 5 g. Subsequently, the interval B between marks after being placed in an oven in an atmosphere of 120 ° C. for 30 minutes with no load was determined, and the heat shrinkage was determined by the following equation. Heat shrinkage = (AB) / A × 100 (%) (4) Measurement of processability On the films obtained in Examples 1-3 and Comparative Examples 1-3, gravure ink (Lamiace 61 white two-liquid type) And Toyo Ink Co., Ltd.) to form a printing ink layer by gravure printing, and then apply an adhesive (AD585 / CAT-10, Toyo Morton Co., Ltd.) at 2 g / m ^2, and then unstretched polypropylene film according to a conventional method. A sealant layer of 60 μm (P1120, manufactured by Toyobo Co., Ltd.) was attached by a dry lamination method to obtain an aliphatic polyester film laminate. In this step, the state of the film was observed, and the following three-stage evaluation was visually performed. ；: Good condition of the film △: slight wrinkles and print misregistration occurred in the film ×: poor flatness was observed in the film, and wrinkles and print misregistration occurred. 2. Test Results The results of the above tests (1) to (4) are shown in Table 1.

[0036]

[Table 1]

Example 1 To 100 parts by weight of poly-L-lactic acid having a weight average molecular weight of 250,000, 0.06 parts by weight of aggregated silica particles having an average particle size of 1.8 μm was added as a lubricant for forming surface projections. The polyester resin was extruded at a resin temperature of 210 ° C. using a 30 mm extruder with a T-die and then cooled with a chill roll at 20 ° C. to obtain an unstretched film having a thickness of 300 μm. The film temperature was preheated to 95 ° C. by a plurality of ceramic rolls, stretched 1.5 times in the machine direction at a stretching speed of 30000% / min between the rolls, and further stretched 2.7 times in the machine direction at 99 ° C. Next, 80 ° C in the transverse direction using a tenter-type stretching machine.
After stretching 3.8 times at 156 ° C., heat-setting at 156 ° C.
A 3% transverse relaxation treatment was performed at 6 ° C. A stretched film having a thickness of 20 μm was obtained, and was set as Example 1. Example 2 A biaxially stretched film was obtained in the same manner as in Example 1 except that the longitudinal stretching was performed at 8000% / min. Example 3 A biaxially stretched film was obtained in exactly the same manner as in Example 1 except that the heat setting was performed at 151 ° C., and this was designated as Example 3. Comparative Example 1 Example except that the longitudinal stretching was preheated to a film temperature of 99 ° C. by a plurality of ceramic rolls, and one-stage stretching was performed 2.5 times in the machine direction at a stretching speed of 30,000% / min between the rolls.
A biaxially stretched film was obtained in exactly the same manner as in Example 1, and Comparative Example 1 was used. Comparative Example 2 A biaxially stretched film was obtained in exactly the same manner as in Example 1 except that longitudinal stretching was performed at 68 ° C. by 3.5 times in one-step stretching. Comparative Example 3 A biaxially stretched film was obtained in the same manner as in Example 1 except that the heat setting was performed at 141 ° C., and Comparative Example 3 was obtained.

[0038]

The aliphatic polyester-based biaxially stretched film of the present invention is excellent in processing suitability such as not causing deterioration in flatness or printing deviation in a printing or laminating step,
It is extremely useful as a packaging film for fresh foods, processed foods, pharmaceuticals, medical equipment, electronic components and the like.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) B29L 7:00 (72) Inventor Hisato Kobayashi 2-1-1 Katata, Otsu-shi, Shiga Prefecture Toyobo Co., Ltd. (72) Inventor Tadashi Okuhira 2-1-1 Katata, Otsu City, Shiga Prefecture F-Term in Toyobo Co., Ltd. Research Laboratory (Reference) 3E086 BA04 BA15 BA33 BB22 BB51 BB62 BB67 BB75 BB90 CA01 CA17 CA18 CA22 CA25 CA31 4F100 AK41A AT00B AT02 BA10A BA10B EJ38A GB15 GB23 GB41 GB66 JA03A JC00A JL01 JN18A 4F210 AA24 AB17 AE01 AG01 QA02 QA03 QC05 QG01

Claims (4)

[Claims] (1) a main repeating unit represented by the general formula -O-CH
A biaxially stretched film comprising a polymer containing an aliphatic polyester as a main component, which is R-CO- (wherein R represents hydrogen or an alkyl group having 1 to 3 carbon atoms). The value (Nx-Ny) obtained by subtracting the refractive index (Ny) in the width direction from the refractive index (Nx) in the longitudinal direction of the stretched film is -0.02.
An aliphatic polyester-based biaxially stretched film having a Nx-Ny variation in the longitudinal direction of not more than 0.0050 and a heat shrinkage at 120 ° C of not more than 5.0%. . 2. The aliphatic polyester-based biaxially stretched film according to claim 1, wherein the heat shrinkage at 120 ° C. is 3.0% or less. 3. The refractive index (Nz) in the thickness direction is 1.440.
3. The biaxially stretched aliphatic polyester film according to claim 1, wherein the thickness is 0 to 1.455. 4. The biaxially stretched aliphatic polyester film according to claim 1, wherein the aliphatic polyester is polylactic acid.