Biaxially stretched polyester film and method for producing same

Abstract

It is provided that a biaxially stretched polyester film suitable for uses for which nylon films and other flexible films have conventionally been used and a method for producing the film. A biaxially stretched polyester film made of a polyester resin composition (A) containing not less than 60 mass % of polybutylene terephthalate and having yield stress in a MD of not more than 70 MPa, yield stress in a TD of not more than 70 MPa, rupture strength in the MD of not less than 160 MPa, rupture strength in the TD of not less than 160 MPa, and rupture elongation in the MD and TD of not less than 100%.

Claims

1. A biaxially stretched polyester film made of a polyester composition (A) containing not less than 60 mass % of a polybutylene terephthalate; wherein the biaxially stretched polyester film has a yield stress in a MD of not more than 70 MPa, yield stress in a TD of not more than 70 MPa, rupture strength in the MD of 160 MPa to 300 MPa, rupture strength in the TD of 160 MPa to 300 MPa, and rupture elongation in the MD and TD of 100% to 200%.

2. The biaxially stretched polyester film according to claim 1, wherein the polyester resin (A) contains a polyester resin (B) other than polybutylene terephthalate.

3. A method for producing the biaxially stretched polyester film according to claim 2, wherein the biaxially stretched polyester film is obtained by biaxially stretching an un-stretched polyester sheet with a thickness of 15 to 2500 m which is obtained by multi-layering a same composition in not less than 60 layers and casting the layered body.

4. A method for producing the biaxially stretched polyester film according to claim 2, obtained by bringing an un-stretched polyester sheet into contact with a chill roll at not more than 20 C. to cool the sheet and biaxially stretching the sheet.

5. A method for producing the biaxially stretched polyester film according to claim 2, wherein the biaxially stretched polyester film is obtained by biaxially stretching an un-stretched polyester sheet containing spherulites with diameter of not more than 500 nm in the un-stretched polyester sheet.

6. The biaxially stretched polyester film according to claim 2, having a ratio of the rupture strength in the MD and the rupture strength in the TD of not more than 1.5 and a ratio of the rupture elongation in the MD and the rupture elongation in the TD of not more than 1.5.

7. A method for producing the biaxially stretched polyester film according to claim 4, wherein the biaxially stretched polyester film is obtained by sequentially biaxially stretching the un-stretched polyester sheet.

8. A method for producing the biaxially stretched polyester film according to claim 5, wherein the biaxially stretched polyester film is obtained by sequentially biaxially stretching the un-stretched polyester sheet.

9. A method for producing the biaxially stretched polyester film according to claim 1, wherein the biaxially stretched polyester film is obtained by biaxially stretching an un-stretched polyester sheet with a thickness of 15 to 2500 m which is obtained by multi-layering a same composition in not less than 60 layers and casting the layered body.

10. A method for producing the biaxially stretched polyester film according to claim 1, obtained by bringing an un-stretched polyester sheet into contact with a chill roll at not more than 20 C. to cool the sheet and biaxially stretching the sheet.

11. A method for producing the biaxially stretched polyester film according to claim 10, wherein the biaxially stretched polyester film is obtained by sequentially biaxially stretching the un-stretched polyester sheet.

12. A method for producing the biaxially stretched polyester film according to claim 1, wherein the biaxially stretched polyester film is obtained by biaxially stretching an un-stretched polyester sheet containing spherulites with diameter of not more than 500 nm in the un-stretched polyester sheet.

13. A method for producing the biaxially stretched polyester film according to claim 12, wherein the biaxially stretched polyester film is obtained by sequentially biaxially stretching the un-stretched polyester sheet.

14. The biaxially stretched polyester film according to claim 1, having a ratio of the rupture strength in the MD and the rupture strength in the TD of not more than 1.5 and a ratio of the rupture elongation in the MD and the rupture elongation in the TD of not more than 1.5.

Description

EXAMPLES

(1) Next, the present invention will be described in more detail with reference to Examples, but the present invention should not be limited to these Examples. Film evaluation was carried out by the following measurement methods.

(2) [Film Formability]

(3) Film formability of a biaxially stretched film was evaluated according to the following standard. If marked with and , it was determined that productivity was good.

(4) : A film was formed without rupture and continuous production was possible.

(5) : Film formability was more or less unstable and rupture rarely occurred but continuous production was possible.

(6) x: Rupture often occurred and continuous production was difficult.

(7) [Mechanical Characteristics (Yield Stress Value, Initial Elastic Modulus, Rupture Strength, Rupture Elongation)]

(8) Methods were carried out according to JIS K 7113. Each specimen was obtained by cutting each film in dimensional size of 10 mm width and 100 mm length in the longitudinal direction and in the width direction with a razor. Each specimen was left to stand in environments of 23 C. and 65% RH for 12 hours and thereafter, measurement was carried out in environments of 23 C. and 65% RH at pulling speed of 200 mm/min with chuck distance of 100 mm and the average value of 5 measurements was employed. Autograph AG 5000 A manufactured by Shimadzu Corporation was employed.

(9) [Spherulite Size]

(10) Each un-stretched sheet obtained by casting was sampled and Hv light scattering pattern of each un-stretched sheet was measured by using a light scattering measurement apparatus (Dyna-3000, manufactured by OTSUKA ELECTRONICS Co., LTD.) Using the HV light scattering pattern obtained when the measurement center angle was changed to be 0, 20, and 60, the spherulite radius was measured based on the spread of the scattering pattern. The unit was [nm].

(11) [Thickness]

(12) The thickness was measured by a method according to JIS-Z-1702.

(13) [Plane Orientation Coefficient]

(14) Ten specimens were sampled from each rolled sample in the width direction. According to JIS K 7142-1996 5.1 (A method), refractive index in the longitudinal direction (nx), refractive index in the width direction (ny), and refractive index in the thickness direction (nz) were measured for each specimen by using sodium D-ray as a light source and Abbe's refractometer and the plane orientation coefficient (P) was calculated according to the following expression. The average value of the measured plane orientation coefficients was employed as the plane orientation coefficient.
P=(nx+ny)/2nz

(15) The difference of plane orientation coefficient in the width direction was the difference between the maximum value and the minimum value of the above-mentioned ten specimens.

(16) [Drawing Formability]

(17) Each obtained film roll and an aluminum foil (8079 material, thickness of 40 m) were dry-laminated using a urethane type adhesive (TM-509, CAT10L, ethyl acetate at 33.6:4.0:62.4 (mass ratio), manufactured by Toyo-Morton, Ltd.) to produce a film/aluminum foil laminated body. The obtained laminated body was set in a die set mold (90 mm50 mm projection shape) in such a manner that the polyester film was in the outer side and pressurized at 23 C. by a pressing machine to carry out drawing formation. The drawing depth at the time of the formation was increased every 0.2 mm and the maximum depth to the extent that the laminated body was not broken was determined to the drawing depth.

(18) [Piercing Strength]

(19) Measurement was carried out according to 2. Tensile Strength-Testing Method defined by Third: Instruments and Container Wrapping, Standards for Food and Additives (the Ministry of Health and Welfare, Notice 20 in 1982) in Food Sanitation Act. Each film was pierced by a needle with the tip end diameter of 0.7 mm at piercing speed of 50 mm/min and the strength at the time of piercing the film with the needle was measured to give the piercing strength. The measurement was carried out at normal temperature (23 C.) and the unit was [N/m].

(20) [Impact Strength]

(21) The strength of each film in environments at 23 C. against impact punching was measured by using an impact tester manufactured by TOYO SEIKI SEISAKU-SHO, LTD. The tester employed had impact sphere with diameter of inch. The unit was [J/m].

(22) [Thermal Shrinkage]

(23) The thermal shrinkage of each polyester film was measured by a dimensional change testing method described in JIS-C-2318, except that the testing temperature was at 150 C. and the heating time was 15 minutes. The thermal shrinkage of each nylon film was measured by a dimensional change testing method described in JIS-C-2318, except that the testing temperature was at 160 C. and the heating time was 10 minutes. The unit was [%].

(24) [Haze]

(25) Haze was measured at 3 different points by a method according to JIS-K-7105 using a haze meter (NDH 2000, manufactured by NIPPON DENSHOKU INDUSTRIES Co., LTD.) and the average value was defined as haze.

(26) The unit was [%].

(27) [Pinhole Resistance]

(28) Each film according to the present invention was cut in a size of 20.3 cm (8 inch)27.9 cm (11 inch) and the obtained rectangular test film after the cutting was left to stand in the condition of 23 C. and 50% RH for 24 hours and thus conditioned. Thereafter, each rectangular test film was rolled into a cylindrical form with a length of 20.32 cm (8 inch). One end of the cylindrical film was fixed in the outer circumference of a disk-like fixed head of a Gelbo flex tester (NO. 901 Model, manufactured by Rigaku Corporation) (according to the standard of MIL-B-131C) and the other end of the cylindrical film was fixed in the outer circumference of a disk-like movable head set on the opposite to the fixed head at 17.8 cm (7 inch) interval. A bending test was performed by continuously repeating 2000 cycles at 40 cycles/min, each of which was carried out by rotating the movable head at 440 while moving the movable head closer to the fixed bed by 7.6 cm (3.5 inch) along the axis between both heads set on the opposite to each other in parallel, successively moving the movable head forward by 6.4 cm (2.5 inch) without rotating the movable head, executing these movements reversely to turn the movable head back to the initial position. The test was performed at 5 C. Thereafter, the number of pinholes generated in the portion of the tested film of 17.8 cm (7 inch)27.9 cm (11 inch) excluding the parts fixed in the outer circumferences of the fixed head and the movable head was measured (that is, the number of pinholes generated in 497 cm.sup.2 (77 square inch).

Example 1

(29) PBT (NOVADURAN 5020, melting point 220 C., manufactured by Mitsubishi Engineering-Plastics Corporation) as a polyester resin composition (A) was mixed with a master batch containing calcium carbonate as a lubricant in a lubricant concentration of 2000 ppm by using a single screw extruder and melted at 270 C. and the obtained melt line was introduced into a static mixer having 12 elements. Accordingly, the PBT melt body was separated and layered to obtain a multi-layer melt body made of a single raw material. The melt body was cast by a T-die at 270 C. and closely stuck to a chill roll at 10 C. by electrostatic adhesion method to obtain an un-stretched sheet. The surface temperature of the chill roll was measured at every 10 cm interval in the width direction (by a thermocouple) to find a distribution of not more than 3 C. Successively, 3.2 times roll stretching was carried out at 60 C. in the vertical direction and thereafter, 3.9 times stretching was carried out at 80 C. in the transverse direction by leading the obtained sheet to a tenter and then the sheet was subject to the heat tension treatment at 200 C. for 3 seconds and to relaxation treatment by 3% for 1 second and both end parts were cut to give a PBT film with thickness of 12 m.

(30) The film formation conditions, physical properties, and evaluation results of the obtained films are shown in Table 1.

Examples 2 to 9

(31) The same process as that in Example 1 was carried out except that the raw material composition and the film formation conditions were changed as described in biaxially stretched films of Table 1 in Example 1. (PBT: NOVADURAN 5020, manufactured by Mitsubishi Engineering-Plastics Corporation, melting point 220 C.) (ecoflex: polybutylene adipate-butylene terephthalate copolymer, manufactured by BASF)

(32) (GS 390, copolymerization components: polybutylene terephthalate, polycarbonate, manufactured by TOYOBO CO., LTD.)

(33) The film formation conditions, physical properties, and evaluation results of the obtained films are shown in Table 1.

Comparative Examples 1 to 4

(34) The same process as that in Example 1 was carried out except that the raw material composition and the film formation conditions were changed as described in biaxially stretched films of Table 2 in Example 1. (PBT: NOVADURAN 5020, manufactured by Mitsubishi Engineering-Plastics Corporation, melting point 220 C.) (ecoflex: polybutylene adipate-butylene terephthalate copolymer, manufactured by BASF)

(35) The film formation conditions, physical properties, and evaluation results of the obtained films are shown in Table 2.

Comparative Example 5

(36) PBT (NOVADURAN 5020, melting point 220 C., manufactured by Mitsubishi Engineering-Plastics Corporation) as a polyester resin and polyethylene terephtalate (intrinsic viscosity of 0.65) were used and the PBT and PET were melted respectively at 280 C. by using extruders and joined by a 1201 layered feed block to obtain a PBT/PET alternately multi-layered melt body. The alternately layered body was cast by a die at 280 C. and closely stuck to a chill roll at 20 C. by electrostatic adhesion method to obtain an un-stretched sheet. The obtained un-stretched film was biaxially stretched in the film formation condition shown in Table 2 to obtain a PBT/PET alternately layered biaxially stretched film.

(37) The physical properties and evaluation results of the obtained films are shown in Table 2.

Comparative Example 6

(38) PBT (NOVADURAN 5020, melting point 220 C., manufactured by Mitsubishi Engineering-Plastics Corporation) as a polyester resin was used, melted at 280 C. by using a single screw extruder, cast by a die at 270 C., and closely stuck to a chill roll at 15 C. by an electrostatic adhesion method to obtain an un-stretched sheet. Film formation was carried out while adjusting the rolling speed to give the thickness of 20 m.

(39) The physical properties and evaluation results of the obtained films are shown in Table 2.

Comparative Example 7

(40) A PBT film manufactured by Kansaikagakukogyo Co., Ltd. and commercialized as a representative inflation biaxially stretched PBT film was used.

(41) The physical properties and evaluation results of the obtained films are shown in Table 2.

Comparative Example 8

(42) An ester film E5100-12 m manufactured by TOYOBO CO., LTD. was used.

(43) The physical properties and evaluation results of the obtained films are shown in Table 2.

Comparative Example 9

(44) A nylon film N1100-15 m manufactured by TOYOBO CO., LTD. was used.

(45) The physical properties and evaluation results of the obtained films are shown in Table 2.

(46) TABLE-US-00001 TABLE 1 Example item unit 1 2 3 4 5 6 7 8 9 raw A name PBT PBT PBT PBT PBT PBT PBT PBT PBT mate- rate wt. % 100 100 100 90 80 60 60 90 90 rial B-1 name eco- GS390 GS390 eco- eco- eco- flex flex flex flex rate wt. % 10 20 40 10 10 10 B-2 name PET rate wt. % 30 film temperature of extruder C. 270 270 270 270 270 270 280 270 270 forma- ultra multi-layer or not Yes Yes Yes Yes Yes Yes Yes Yes Yes tion the number of the pieces 12 12 12 12 12 12 12 6 12 condi- elements tion the number of the layers layers 4096 4096 4096 4096 4096 4096 4096 64 4096 chill roll temperature C. 10 10 10 15 15 16 19 15 23 spherulite size nm 300 300 300 300 300 300 300 450 300 gravity of the center part g/cm.sup.3 1.285 1.288 1.285 1.296 1.290 1.292 1.294 1.298 1.305 stretching temperature C. 60 60 60 60 60 60 60 60 60 in the MD stretch ratio in the MD times 3.2 4 3.5 3.5 3.5 3.5 3.5 3.5 3.5 stretching temperature C. 70 70 70 70 70 80 80 70 70 in the TD stretch ratio in the TD times 3.9 3.9 3.9 4.0 4.1 4.1 4.2 4.0 4.0 heat fixation temperature C. 200 200 200 200 205 205 200 200 200 relaxation ratio % 5 5 5 5 5 5 5 5 5 film formability prop- thickness, m m 12 12 12 12 20 12 20 12 12 erties yield stress in the MD MPa 66 67 66 52 55 53 65 54 55 yield stress in the TD MPa 64 65 65 51 53 52 62 53 54 rupture MD MPa 170 261 220 250 225 236 230 223 222 strength TD MPa 168 171 210 242 230 228 240 212 213 MD/ 1.01 1.53 1.05 1.03 0.98 1.04 0.96 1.05 1.04 TD rupture MD % 178 131 132 179 141 151 115 130 143 elonga- TD % 117 122 123 144 121 139 105 102 124 tion MD/ 1.52 1.07 1.07 1.24 1.17 1.09 1.10 1.27 1.15 TD elastic modulus in the GPa 2.55 2.50 2.43 2.55 2.65 2.49 2.53 2.33 2.63 MD elastic modulus in the GPa 2.40 2.50 2.32 2.34 2.54 2.39 3.33 2.51 2.57 TD plane orientation 0.14 0.14 0.14 0.14 0.14 0.14 0.12 0.14 0.14 coefficient drawing formability mm 5.2 5.4 6.2 6.6 6.4 6.6 5.4 6.4 6.2 piercing strength N/m 0.975 1.075 1.083 1.250 1.005 1.230 0.900 0.850 1.005 impact strength J/m 0.080 0.088 0.095 0.101 0.097 0.092 0.075 0.092 0.095 moisture absorption % 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 thermal shrinkage of % 2.80 2.70 2.49 2.30 2.43 2.62 1.73 2.95 2.31 the film in the MD thermal shrinkage of % 2.50 2.60 2.45 2.27 2.55 2.30 1.37 2.80 2.48 the film in the TD haze % 4.5 5.0 5.5 15.0 10.7 9.6 13.0 15.0 17.0 Gelbo flex test pieces 3 3 4 0 1 0 5 1 1

(47) TABLE-US-00002 TABLE 2 Comparative Example item unit 1 2 3 4 5 6 7 8 9 raw A name PBT PBT PBT PBT PBT PBT PBT PET Ny mate- rate wt. % 100 90 50 100 50 100 100 ES100 N1100 rial B-1 name eco- PET PET manu- manu- flex factured factured rate wt. % 10 50 50 by by B-2 name TOYOBO TOYOBO rate wt. % CO., CO., LTD. LTD. film temperature of extruder C. 270 270 285 285 280 270 film forma- ultra multi-layer or not No No No Yes Yes No forma- tion the number of the pieces 12 feed block tion condi- elements by an tion the number of the layers layers single single single 4096 1201 inflation layer layer layer (A/B biaxial alternately stretching laminated) chill roll temperature C. 22 15 20 20 20 15 spherulite size nm 600 600 600 gravity of the center part g/cm.sup.3 1.32 1.298 1.308 1.355 1.308 1.28 stretching temperature C. 60 60 70 80 60 No in the MD stretch ratio in the MD times 3.5 3.5 3.5 3.1 3.3 stretching temperature C. 70 70 85 90 90 in the TD stretch ratio in the TD times 4 4 4 3.9 4 heat fixation temperature C. 200 200 200 210 235 relaxation ratio % 5 5 5 5 5 film formability X X prop- thickness, m m 12 12 15 20 15 12 15 erties yield stress in the MD MPa 75 116 84 62 71 117 52 yield stress in the TD MPa 73 111 85 62 69 113 50 rupture MD MPa 200 228 165 60 210 230 206 strength TD MPa 250 236 159 60 230 240 290 MD/ 0.80 0.97 1.04 1.00 0.91 0.96 0.71 TD rupture MD % 124 102 229 500 135 100 105 elonga- TD % 91 95 225 600 90 90 65 tion MD/ 1.36 1.07 1.02 0.83 1.50 1.11 1.62 TD elastic modulus in the GPa 2.53 3.7 3.5 1.5 2.26 3.9 1.5 MD elastic modulus in the GPa 2.51 3.9 4.8 1.5 1.76 4 1.0 TD plane orientation 0.13 0.16 0.13 0 0.08 0.16 0.06 coefficient drawing formability mm 4.5 4.2 4.4 6.8 4.6 4.0 7.0 piercing strength N/m 0.750 1.005 0.830 0.200 0.720 1.000 0.933 impact strength J/m 0.067 0.043 0.050 0.060 0.055 0.042 0.073 moisture absorption % 0.1 0.1 0.1 0.1 0.2 0.1 1.5 thermal shrinkage of % 2.50 1.50 2.30 0.00 0.70 1.40 1.01 the film in the MD thermal shrinkage of % 2.30 0.30 1.90 0.00 0.60 0.20 1.00 the film in the TD haze % 15.0 2.6 12.0 18.0 12.0 2.3 1.3 Gelbo flex test pieces 5 30 10 13 5 30 0

INDUSTRIAL APPLICABILITY

(48) The present invention makes it possible to obtain a biaxially stretched polyester film suitable for uses for which nylon films and other flexible films have conventionally been used and suitable for uses such as wrapping materials for retort food and external materials for lithium ion batteries for which drawing formation is carried out.