JP2000239410A - Aliphatic polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the processability in printing and laminating by forming a film from an aliphatic polyester so as to provide a specified variation in thickness in the longitudinal direction and a specified thermal shrinkage factor in the longitudinal direction. SOLUTION: An aliphatic polyester of which the main repeating units comprise the units of the formula -O-CHR-CO- and which has a weight-average molecular weight of 10,000 to 500,000, preferably 50,000 to 300,000, is extruded at a temperature from the melting temperature (Tm) of the polymer to Tm+70 deg.C to give an unstretched film. This film is biaxially stretched in a temperature range from the glass transition temperature (Tg) of the polymer to Tg+50 deg.C, preferably from Tg+10 deg.C to Tg+40 deg.C, at least 3-fold, preferably at least 3.5-fold, and by area at least 9-fold, preferably 12-fold. The stretched film is thermally fixed at a temperature from 150 deg.C to Tm, preferably from 155 deg.C to Tm, and then subjected to treatment for a transverse relaxation of 1-10% at a temperature from 120 deg.C to the thermal fixing temperature, thus giving a film having a variation in thickness in the longitudinal direction of at most 10% and a thermal shrinkage factor in the longitudinal direction of at most 5%. In the formula, R is H or a 1-3C alkyl.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel aliphatic polyester-based biaxially stretched film.

[0002]

2. Description of the Related Art Conventionally, aliphatic polyester films such as polylactic acid are easily decomposed when disposed in a natural environment. For example, polylactic acid films are naturally hydrolyzed in soil. Later, various methods have been developed with the advantage of becoming harmless decomposition products by microorganisms.

[0003] Such a biodegradable film is made of a polylactic acid polymer and has a plane orientation degree ΔP of 3.0 × 10 ^-3.
And a difference (ΔHm−ΔHc) between the heat of crystallization ΔHm when the film is heated and the heat of crystallization ΔHc generated by crystallization during the temperature rise is 20 J / g or more. A film having strength and thermal dimensional stability is known (JP-A-7-207041).

[0004] However, as a result of the development of the polylactic acid-based film with a priority on decomposing it in the natural world, the excellent properties inherent to aliphatic polyesters could not be fully obtained. That is, since importance was placed on biodegradability, orientation and crystallization of the film were not sufficient, and strength and thermal dimensional stability were insufficient.

As a result, fresh foods, processed foods, pharmaceuticals,
When used as a packaging film for medical devices, electronic components, etc., such a film has problems such as dimensional changes and wrinkles occurring in a printing or laminating process required as a packaging film. It became clear that there was.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel aliphatic polyester-based biaxially stretched film which solves the above-mentioned problems and has excellent workability in a printing or laminating process. It is in.

[0007]

Means for Solving the Problems The inventor of the present invention has made intensive studies to solve the problems of the prior art. As a result, by setting the thickness unevenness and the heat shrinkage in the longitudinal direction of the biaxially stretched film composed of a polymer containing a specific aliphatic polyester as a main component to a specific value or less, a dimensional change in a printing or laminating process is reduced. The present inventors have found that a film useful as a general packaging substrate having excellent processability without causing wrinkles or wrinkles can be obtained, and the present invention has been completed.

That is, in the present invention, the main repeating unit is
It consists of aliphatic polyester which is a unit represented by general formula -O-CHR-CO- (I) (wherein, R represents H or an alkyl group having 1 to 3 carbon atoms), The present invention relates to an aliphatic polyester-based biaxially stretched film having a thickness unevenness of 10% or less and a heat shrinkage in a longitudinal direction at 120 ° C of 5% or less.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As the aliphatic polyester in the present invention, an aliphatic polyester whose main repeating unit is a unit represented by the general formula (I), for example, polylactic acid, polyglycolic acid, poly (2-oxy Butyric acid) and the like, but are not limited thereto.

[0010] These aliphatic polyesters may be used alone or in a mixture. Further, a copolymer of the unit of the general formula (I) may be used. When the aliphatic polyester has an asymmetric carbon, L-form, D-form
There are optical isomers such as L-form and D-form, and any of them may be used, or a mixture of these isomers may be used. Further, other polymer materials may be mixed as long as the effects of the present invention are not impaired.

The above-mentioned aliphatic polyester (hereinafter, may be simply referred to as “polymer”) as a material of these films is obtained by subjecting the corresponding dehydrated cyclic ester compound of α-oxy acid to a known method such as ring-opening polymerization. Manufactured for

In the present invention, the aliphatic polyester used has a weight average molecular weight of 10,000 to 500,000. If it is less than 10,000, the physical properties of the obtained film are remarkably inferior, and the decomposition rate is too high to achieve the object of the present invention. In addition, since the extrudability and biaxial stretchability during film production are also reduced, the weight average molecular weight needs to be 10,000 or more. On the other hand, a high viscosity polymer having a weight average molecular weight of 500,000 or more has a problem that melt extrusion becomes difficult. A preferred range is from 50,000 to 300,000.

The film made of the aliphatic polyester of the present invention is preferably a film heat-set after extrusion molding and biaxial stretching, and is produced by forming a film by a known method and stretching.

The method for extruding the film of the present invention comprises:
Known T-die method, inflation method and the like can be applied,
An unstretched film can be obtained by these methods. The extrusion temperature is the melting temperature (Tm) of the polymer used.
To Tm + 70 ° C., more preferably Tm + 20 to
Tm + 50 ° C.

If the extrusion temperature is too low, it is difficult to obtain extrusion stability, and it is easy to fall into overload. On the other hand, if it is too high, the decomposition of the polymer becomes severe, which is not preferable. The die of the extruder used in the present invention may have an annular or linear slit. The temperature of the die may be as high as the extrusion temperature range.

The biaxial stretching of the unstretched film may be carried out sequentially or simultaneously with the stretching of the first axis and the stretching of the second axis.

In the biaxially stretched film of the present invention, the longitudinal direction means the longitudinal stretching direction, and the width direction means the transverse stretching direction.

The stretching temperature is preferably in the range of the glass transition temperature (Tg) of the polymer used to Tg + 50 ° C. More preferably, it is in the range of Tg + 10 to Tg + 40 ° C. If the stretching temperature is lower than Tg, stretching is difficult, and if it exceeds Tg + 50 ° C., the thickness uniformity and the mechanical strength of the obtained film are undesirably reduced.

The stretching in the vertical and horizontal directions may be performed in one stage or in multiple stages, but is ultimately at least 3 times, more preferably 3.5 times or more in each stretching direction. Stretching at a lateral area magnification of 9 times or more, more preferably 12 times or more is necessary from the viewpoint of uniformity of thickness and mechanical properties. If the longitudinal and transverse stretching ratios are each less than 3 times and the area magnification is less than 9 times, a film having good thickness uniformity cannot be obtained,
Also, the improvement of physical properties such as mechanical strength is poor. The upper limit of the stretching ratio is not limited as long as the film does not break during film formation.

It is important that the thickness unevenness and the heat shrinkage ratio in the present invention be within the predetermined ranges. Minutes, preferably 1500
The method includes a step of stretching at 0% / min, more preferably at 20,000% / min or more. The upper limit of the stretching speed is not limited as long as the film does not break during film formation.

After the above film is biaxially stretched, usually,
The heat setting is performed at a temperature of 150 ° C. or more and Tm or less, preferably 155 ° C. or more and Tm or less, and a lateral relaxation treatment is performed at a temperature of 120 ° C. or more and a heat fixing temperature of about 1 to 10%, preferably about 2 to 8%.

The biaxially stretched aliphatic polyester film of the present invention may be multi-layered by a coextrusion method or a coating method in the production process. Further, the film of the present invention, for the purpose of improving the surface energy, corona treatment,
Plasma treatment, flame treatment, or the like may be performed.

The raw material aliphatic polyester of the present invention may contain known additives as necessary. For example, it may contain a lubricant, an antiblocking agent, a heat stabilizer, an antioxidant, an antistatic agent, a lightfast agent, an impact resistance improver, and the like. However, since the aliphatic polyester-based biaxially stretched film of the present invention is required to be transparent and its contents visible after the heat seal layer is formed, high transparency is maintained even after the heat seal layer is formed. It is necessary to use it within the possible range.

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;
Alternatively, particles inert to aliphatic polyester such as particles made of an organic resin such as a crosslinked polystyrene resin, a crosslinked acrylic resin, a silicone resin, and a crosslinked polyester resin can be exemplified.

Any one of these lubricants may be used alone, or two or more thereof may be used in combination. The average particle size of the lubricant used is preferably 0.01 μm or more and 3.0 μm or less. The thickness is more preferably 0.05 μm or more and 2.5 μm or less. The amount of addition is preferably 0.005% by weight or more and 2% by weight or less, preferably 0.01% by weight or less.
More than 1.0% by weight is more preferable in order to achieve both transparency and slipperiness of the film.

In order to achieve both transparency and slipperiness, it is preferable to use two or more lubricants in combination. In particular, lubricant particles that are deformed during film formation (for example, organic lubricants having a low degree of crosslinking such as cross-linked polystyrene resin and cross-linked acrylic resin, and inorganic lubricants such as silica that is an aggregate of primary particles) and during film formation. It is preferable to combine ordinary lubricant particles that do not deform.

The thickness unevenness in the longitudinal direction of the aliphatic polyester-based biaxially stretched film of the present invention must be 10% or less, preferably 8% or less, more preferably 5% or less. This thickness unevenness is expressed as a percentage of the difference between the maximum value and the minimum value with respect to the average value of the thickness by continuously measuring the thickness in the longitudinal direction of the film. 1 uneven thickness
If it is larger than 0%, when the film is heated in a processing step such as printing or laminating while conveying tension is applied, the film becomes a film in which a place having good flatness and a place having poor flatness are mixed in the longitudinal direction of the film. It is not preferable because the yield (yield) of the product decreases. Here, the thickness of the film of the present invention is usually good to be about 5 to 50 μm.

The heat shrinkage in the longitudinal direction at 120 ° C. of the biaxially stretched aliphatic polyester-based film of the present invention needs to be 5% or less, and preferably 3% or less. If the heat shrinkage is more than 5%, printing deviation occurs in the printing step, and wrinkles occur during heat sealing, which is not preferable.

Further, the refractive index (Nz) in the thickness direction of the aliphatic polyester-based biaxially stretched film in the present invention is preferably from 1.440 to 1.455, more preferably from 1.445 to 1.455. It is as follows. When Nz is less than 1.440, breakage is likely to occur in the step of forming a film. On the other hand, if it exceeds 1.455, flatness is disturbed when the film is heated in a printing or laminating step, which is not preferable.

Further, in the aliphatic polyester-based biaxially stretched film of the present invention, a value obtained by subtracting the refractive index (Ny) in the width direction from the refractive index (Nx) in the longitudinal direction (Nx-Ny).
Is preferably −0.020 or more and 0 or less,
It is more preferably 0.015 or more and 0 or less. Nx-
When Ny is less than -0.020, when the film is heated in a printing or laminating step, the film is stretched due to the transport tension of the film, which causes printing misalignment and ripples, which deteriorates the flatness, which is not preferable. When Nx-Ny is 0 or more, thickness unevenness tends to increase.

[0031]

EXAMPLES Hereinafter, the contents and effects of the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples unless departing from the gist thereof. Absent.

The methods for evaluating physical properties in the following Examples and Comparative Examples are as follows.

(1) Thickness unevenness in the longitudinal direction Using a “film thickness continuous measuring device” manufactured by Anritsu Corporation, a thickness of 3 m was continuously measured in the longitudinal direction of the film, and the thickness unevenness was calculated from the following equation.

Thickness unevenness (%) = [(maximum thickness−minimum thickness) / average thickness] × 100 (2) Thermal shrinkage in the longitudinal direction A film having a width of 10 mm and a length of 250 mm was taken to have a thickness of 200 m.
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 measured at a constant tension of 5 g, and the heat shrinkage was determined by the following equation.

Heat shrinkage (%) = [(AB) / A] × 100 (3) Refractive index (Nz, thickness direction, longitudinal direction and width direction)
Nx, Ny) Each refractive index was measured using “Abbe refractometer 1T” manufactured by Atago Co., Ltd.

(4) Processing Suitability Gravure ink (“Lamiace 61 white two-part type”, manufactured by Toyo Ink Co., Ltd.) is gravure printed on the thermoplastic film obtained in each of the Examples and Comparative Examples to form a printing ink layer. After forming and then applying 2 g / m ^{2 of an} adhesive “AD585 / CAT-10” (manufactured by Toyo Morton Co., Ltd.), a 60 μm unstretched polypropylene film (“P112
0 "(manufactured by Toyobo Co., Ltd.) by a dry lamination method to form a sealant layer to obtain an aliphatic polyester film laminate. Observe the state of the film in this process, the processing suitability in the printing and lamination process,
Each item of wrinkles and print misregistration was evaluated on a three-point scale based on the following criteria.

[0037]

Printing shift: ず れ: No printing shift, good film condition, Δ: Slight printing shift, ×: Deterioration in flatness, printing shift occurred.

(5) Film-forming condition When biaxial stretching was carried out continuously for 3 hours, no breakage of the film was generated or it was determined that the film was broken once, and it was determined that the film was broken twice or more.

Example 1 Poly-L-lactic acid having a weight average molecular weight of 250,000 (Tg = 61.
(6 ° C., Tm = 170 ° C.) A composition in which 0.06 part by weight of aggregated silica particles having an average particle diameter of 1.8 μm as a lubricant for forming surface projections was added to 100 parts by weight of T
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 300 μm. The film temperature was preheated to 96 ° C with a plurality of ceramic rolls, stretched 1.5 times in the machine direction at a stretching speed of 30,000% / min between the rolls, and further stretched 2.7 times in the machine direction at 98 ° C. Then
The film was stretched 3.8 times in the transverse direction at 80 ° C. with a tenter-type stretching machine, heat-set at 155 ° C., and then subjected to a 3% transverse relaxation treatment at 135 ° C. Thus, a biaxially stretched film of the present invention having a thickness of 20 μm was obtained. Table 1 shows the physical properties.

COMPARATIVE EXAMPLE 1 In Example 1, longitudinal stretching was performed by preheating at a film temperature of 96 ° C. with a plurality of ceramic rolls.
A biaxially-stretched film for comparison was obtained in exactly the same manner as in Example 1 except that the stretching was performed in a single step at a stretching speed of 2.5% in the machine direction at a stretching speed of% / min. Table 1 shows the physical properties.

Comparative Example 2 A biaxially stretched film for comparison was obtained in exactly the same manner as in Example 1 except that longitudinal stretching was performed at 68 ° C. and 3.5-fold in one-step stretching. Table 1 shows the physical properties.

Example 2 A biaxially stretched film of the present invention was obtained in the same manner as in Example 1 except that longitudinal stretching was performed at 12,000% / min. Table 1 shows the physical properties.

Comparative Example 3 A comparative biaxially stretched film was obtained in the same manner as in Example 1 except that the heat setting was performed at 140 ° C. Table 1 shows the physical properties.

Example 3 A biaxially stretched film of the present invention was obtained in the same manner as in Example 1 except that the heat setting was performed at 150 ° C. Table 1 shows the physical properties.

[0046]

[Table 1]

[0047]

The aliphatic polyester film of the present invention has dimensional changes and wrinkles in the printing and laminating processing steps, which are important characteristics in packaging films for fresh foods, processed foods, pharmaceuticals, medical equipment, electronic parts and the like. It has excellent processability without causing flatness deterioration and print misregistration, and is extremely useful as a film for general packaging.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat 参考 (Reference) C08L 63:02 (72) Inventor Hisato Kobayashi 2-1-1 Katata, Otsu-shi, Shiga Toyobo Co., Ltd. Within the Research Institute (72) Inventor Tadashi Okuhira 2-1-1 Katata, Otsu-shi, Shiga F-Term in the Research Laboratory of Toyobo Co., Ltd. (Reference) 3E086 AD01 BA02 BA04 BA15 BA33 BB62 BB75 BB90 CA01 CA17 CA18 CA22 CA25 CA28 CA31 4F071 AA43 AA44 AA81 AA84 AA86 AF31Y AF52A AF61Y AH04 BA01 BB06 BB08 BC01 BC12 4F210 AA24A AB17 AE01 AG01 QA02 QA03 QC16 QD04 QD16 QG01 QG11 QG18 QW07 QW12

Claims (5)

[Claims] A main repeating unit is a unit represented by a general formula -O-CHR-CO- (I) (wherein, R represents H or an alkyl group having 1 to 3 carbon atoms). An aliphatic polyester-based biaxially stretched film comprising an aliphatic polyester, wherein the thickness unevenness in the longitudinal direction is 10% or less, and the heat shrinkage in the longitudinal direction at 120 ° C is 5% or less. 2. The method according to claim 1, wherein the refractive index (Nz) in the thickness direction is from 1.440 to 1.455, and the heat shrinkage in the longitudinal direction at 120 ° C. is 3% or less. 3. The biaxially stretched aliphatic polyester film according to item 1. 3. A value (Nx-Ny) obtained by subtracting a refractive index (Ny) in a width direction from a refractive index (Nx) in a longitudinal direction is -0.020.
The aliphatic polyester-based biaxially stretched film according to claim 1 or 2, wherein the number is 0 or less. 4. The weight average molecular weight of the aliphatic polyester is as follows:
The aliphatic polyester-based biaxially stretched film according to claim 1, 2 or 3, having a molecular weight of 10,000 to 500,000. 5. The biaxially stretched aliphatic polyester film according to claim 1, wherein the aliphatic polyester is polylactic acid.