JP2000037771A - Aliphatic polyester-based biaxially stretched film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aliphatic polyester-based biaxially stretched film which has excellent printability as important characteristics in a wrapping film of perishables, processed foods, medicine medical instruments and electronic parts or the like. SOLUTION: The aliphatic polyester-based biaxially stretched film consists of a polymer containing aliphatic polyester in which a main repeating unit is shown by a formula -O-CHR-CO- (wherein, R shows H or 1-3 C alkyl group), as a main component. Refractive index in the thickness direction is 1.440-1.455 and surface tension is >=45 dyne/cm and furthermore coefficient of heat shrinkage at 130 deg.C is <=5%.

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, an important property in a packaging film for fresh foods, processed foods, pharmaceuticals, medical equipment, electronic parts and the like. The present invention relates to an aliphatic polyester-based biaxially stretched film having excellent printability.

[0002]

2. Description of the Related Art In recent years, with the increasing public awareness of environmental protection, plastics that do not degrade or disappear over time and are not detrimental to the natural environment for all plastic processed products when disposed in the natural environment. Products are required.

Conventionally, films for packaging various products including foods include aromatic polyesters represented by polyethylene, polypropylene and polyethylene terephthalate,
Various plastics such as polyamide are used. 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, in the case of incineration, the thermal power is too strong, the furnace is severely damaged, a large amount of fuel is required, and the cost is high. 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 such circumstances, demands for various packaging films having good biodegradability are increasing.

[0004] In recent years, in order to impart biodegradability to the above-mentioned polyethylene and the like, various studies have been made on blending a component having biodegradability 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 this method, the starch component is biodegradable and thus decomposed by microorganisms in soil, but the polymer portion other than starch is not decomposed, and does not ultimately become a fundamental solution to the above problem.

[0005] As a fundamental solution to the above problem, various biodegradable polymer materials in which the polymer itself has biodegradability have been studied. Among them, polylactic acid has been widely known as a hydrolysable polymer, and is used as a molded product for pharmaceutical use (JP-B-41-2734, JP-B-63-68155, etc.) Various applications have been studied as basic raw materials for versatile materials.

Above all, a biaxially stretched film using a polylactic acid-based polymer has excellent mechanical properties equivalent to a general-purpose film, and is therefore expected to be applied to a wide range of uses including general packaging materials.

However, when used as a food packaging material, a serious drawback of this film is the printability required for a film for packaging, particularly the occurrence of color shift and poor adhesion in the printing process.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide an aliphatic biaxially stretched film which is effective as general packaging equipment.

[0009]

The main repeating unit is a compound represented by the general formula -O-CHR-CO- (R is H or a group having 1 to 1 carbon atoms).
3 represents an alkyl group. ), And a refractive index (N) in the thickness direction.
z) is not less than 1.440 and not more than 1.455, the surface tension is not less than 45 dyne / cm, and the heat shrinkage at 130 ° C. is not more than 5%.
It has been found that general packaging equipment can be obtained.

That is, the present invention relates to a compound represented by the general formula -O-CHR-CO
-(R represents H or an alkyl group having 1 to 3 carbon atoms.)
An aliphatic polyester having a main repeating unit of
Examples thereof include, but are not limited to, polylactic acid, polyglycolic acid, and poly (2-oxybutyric acid). In some cases, these may be used alone, or a mixture or a copolymer may be used. Those having an asymmetric carbon in the polymer are L-form, DL-
There are optical isomers such as isomer and D-isomer, and any of them may be used, or a mixture of these isomers may be used. The above-mentioned polymers used as the material of these films are:
The corresponding dehydrated cyclic ester compound of α-oxy acid is produced by a known method such as ring-opening polymerization.

In the present invention, the biodegradable aliphatic polyester used has a viscosity 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 viscosity average molecular weight needs to be 5,000 or more. On the other hand, a high viscosity polymer having a viscosity 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 biodegradable aliphatic polyester of the present invention is preferably a film which is heat-set after biaxial stretching, and is produced by forming and stretching by a known method.

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. Conversely, if the temperature 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 performed either sequentially or simultaneously with the stretching of the first axis and the stretching of the second axis.

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 Tg + 50 ° C.
Exceeding the thickness is not preferable because the thickness uniformity and the mechanical strength of the obtained film decrease.

The stretching in the vertical and horizontal directions may be performed in one step or in multiple steps, but it is ultimately at least three 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. When the longitudinal and transverse stretching ratios are each 3 times or less and the area magnification is 9 times or less, a film having good thickness uniformity cannot be obtained, and improvement in physical properties such as mechanical strength is poor.

The refractive index (Nz) in the thickness direction in the present invention
The important thing to keep the heat shrinkage ratio within the specified range is
Longitudinal stretching is performed in two or more steps, and at least once at Tg + 20
C. to Tg + 40 ° C., the stretching speed is 10,000% /
Min, preferably 15000% / min, more preferably 2
The step of stretching at 0000% / min or more is included.

The biaxially stretched aliphatic polyester film of the present invention may be multi-layered by a co-extrusion 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 or flame treatment may be performed.

The aliphatic polyester of the present invention may contain known additives as required. For example,
A lubricant, an antiblocking agent, a heat stabilizer, an antioxidant, an antistatic agent, an anti-lighting agent, an impact resistance improving agent and the like may be contained. However, since the aliphatic polyester-based biaxially stretched film of the present invention needs to be transparent and its contents visible after the heat seal layer is formed, high transparency is required even before the heat seal layer is formed. Becomes

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; cross-linked polystyrene resins; cross-linked acrylic resins;
Particles which are inert to aliphatic polyester-based polymers such as particles made of an organic polymer such as a crosslinked polyester resin are exemplified.

Any one of these lubricants may be used alone, or two or more thereof may be used in combination. The average particle system of the lubricant used is 0.01 μm or more and 3.0 μm or less, particularly
It is preferably 0.05 μm or more and 2.5 μm or less, and the amount of addition is 0.0
It is preferably contained in an amount of from 0.05% by weight to 2% by weight, particularly preferably from 0.01% by weight to 1.0% by weight in order to achieve both transparency and slipperiness of the film.

Particularly, in order to achieve both transparency and slipperiness, it is preferable to use two or more lubricants in combination. In particular, lubricant particles that deform during film formation (for example, organic lubricants having a low degree of cross-linking such as cross-linked polystyrene and cross-linked acryl, and inorganic lubricants such as silica that is an aggregate of primary particles) and normal particles that do not deform during film formation Of lubricant particles are preferably combined.

The refractive index (Nz) in the thickness direction of the aliphatic polyester-based biaxially stretched film in the present invention is 1.440.
It is necessary to be not less than 1.455 and more preferably not more than 1.445 and not more than 1.455. Nz is 1.4
If it is less than 40, breakage is likely to occur in the step of forming a film, and furthermore, printing misregistration tends to occur in the width direction. On the other hand, a value of 1.455 or more is not preferable because printing shift occurs in the longitudinal direction.

The aliphatic polyester-based biaxially stretched film of the present invention has a surface energy of 45 dyne /
cm or more, more preferably 47 dyne / cm
That is all. If the surface energy is less than 45 dyne / cm, the adhesion to the printing layer becomes insufficient, which is not preferable.

The aliphatic polyester-based biaxially stretched film of the present invention has a heat shrinkage at 130 ° C. of 5%.
Or less, more preferably 4% or less. If the heat shrinkage is more than 5%, printing misregistration occurs, which is not preferable.

The printing layer in the present invention is made of a nitrocellulose-based, urethane-based, or acrylic-based ink, and is printed by a gravure method, a flexo method, or the like.

[0027]

EXAMPLES Hereinafter, the contents and effects of the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to the following examples unless departing from the gist thereof. The methods for evaluating physical properties in the following examples and comparative examples are as follows.

(1) Refractive index in the thickness direction (Nz) The refractive index in the thickness direction was measured using an Abbe refractometer 4T manufactured by Atago Co., Ltd.

(2) Surface energy Wet index standard solution (manufactured by Nacalai Tesque Co., Ltd.) with a width of 1c
m, 6 cm in length, a reagent was selected to be in a state of being dropped in 2 seconds, and the surface energy was measured.

(3) Heat Shrinkage A film was taken 10 mm wide and 250 mm long, and 200 m thick
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 130 degrees for 30 minutes without load was determined, and the heat shrinkage was determined by the following equation. (AB) / A × 100 (%)

(3) Printability A nitrocellulose ink and a one-component urethane ink were printed on the surface of the aliphatic polyester film in two colors, red and white, by a gravure method. ○: Small color shift Δ: Medium color shift ×: Large color shift

(4) Ink Adhesion A cellophane tape was adhered to the print surface obtained in (3) and peeled off at 90 degrees. ○: No peeling △: Partially peeled ants ×: Fully peeled ants

Example 1 100 parts by weight of poly-L-lactic acid having a viscosity average molecular weight of 250,000 and an average particle system as a lubricant for forming surface projections
A polymer to which 0.06 parts by weight of 1.8 μm aggregated silica particles was added was extruded at a resin temperature of 210 ° C. using a 30 mm diameter extruder with a T-die, and then cooled with a chill roll at 20 ° C. A stretched film was obtained. 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 4 times in the transverse direction at 100 ° C. by a tenter-type stretching machine, heat-fixed at 155 ° C., and then 3% at 135 ° C.
Lateral relaxation treatment was performed. Further, the obtained film was heated to 40 ° C. and subjected to a corona treatment to obtain a stretched film having a thickness of 20 μm. Table 1 shows the physical properties.

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

Comparative Example 2 A biaxially stretched film was obtained in exactly the same manner as in Example 1, except that the longitudinal stretching was carried out 3.5 times at 65 ° C. by 3.5 times. Table 1 shows the physical properties.

Comparative Example 3 In Example 1, N, N'-ethylenebis (stearylamide) was used as a lubricant in an amount of 0.1% by weight based on 100 parts by weight of polylactic acid.
A biaxially stretched film was obtained in exactly the same manner except that 15 parts by weight were blended. Table 1 shows the physical properties.

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

[0038]

[Table 1]

[0039]

The aliphatic ester film of the present invention is
It is excellent in printability, which is important as a practical characteristic of a packaging film, and is extremely useful as an environmentally friendly general packaging film.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C08L 67/04 C08L 67/04 4J038 C09D 101/08 C09D 101/08 133/08 133/08 175/08 175/08 / / B29K 67:00 B29L 7:00 (72) Inventor Tadashi Okuhira 2-1-1 Katata, Otsu-shi, Shiga F-term in Toyobo Co., Ltd. Research Laboratory (reference) 3E086 AA23 AC07 BA04 BA15 BA24 BA33 BB62 BB90 CA01 CA17 CA18 CA22 CA27 CA28 CA31 DA02 4F071 AA44 AB18 AD02 AE11 AF13Y AF31Y AF61Y AH04 BA01 BB06 BB08 BC01 BC10 4F100 AA20H AJ06B AK25B AK41A AK51B AR00B BA01 BA02 CA19 CC00B DE01H EH17 A10A30 J01A01A30 J01A01A30J01A30A01 CF191 FD170 GG02 4J038 BA081 CG141 DG001 PB04 PC08

Claims (4)

[Claims] (1) a main repeating unit represented by the general formula -O-CH
R-CO- (R represents H or an alkyl group having 1 to 3 carbon atoms), which is composed of a polymer mainly containing an aliphatic polyester, and has a refractive index (Nz) in the thickness direction of 1.44.
0 or more and 1.455 or less, and the surface tension is 45 dyne / cm
The aliphatic polyester-based biaxially stretched film, wherein the heat shrinkage at 130 ° C. is 5% or less. 2. The biaxially stretched aliphatic polyester film according to claim 1, further comprising a print layer. 3. The aliphatic polyester-based biaxially stretched film according to claim 2, wherein the printing layer is a nitrocellulose-based, urethane-based, or acrylic-based ink. 4. The biaxially stretched aliphatic polyester film according to claim 1, wherein the aliphatic polyester is polylactic acid.