AU2013245537A1

AU2013245537A1 - Method for producing heat shrinkable polyester film

Info

Publication number: AU2013245537A1
Application number: AU2013245537A
Authority: AU
Inventors: Tsan-Chin Chang; Kuan-Hua Su
Original assignee: Far Eastern New Century Corp
Current assignee: Far Eastern New Century Corp
Priority date: 2013-01-31
Filing date: 2013-10-18
Publication date: 2014-08-14
Anticipated expiration: 2033-10-18
Also published as: TWI454371B; BR102013029726A2; AU2013245537B2; TW201429698A

Abstract

METHOD FOR PRODUCING HEAT SHRINKABLE POLYESTER FILM A method for producing a heat shrinkable polyester 5 film includes the following steps: (a) providing a polyester film that has a glass transition temperature (Tg) C; (b) preheating the polyester film at a preheating temperature ranging from (Tg+20) 'C to (Tg+30) C; (c) drawing the preheated polyester film 10 along a transverse direction which is perpendicular to a machine direction with a draw ratio ranging from 2.7 to 7.7; and (d) annealing the drawn polyester film at an annealing temperature ranging from (Tg-10) 0C to Tg0 C, followed by cooling to room temperature so as to obtain 15 the heat shrinkable polyester film.

Description

1 METHOD FOR PRODUCING HEAT SHRINKABLE POLYESTER FILM The invention relates to a method for producing a heat shrinkable film, more particularly to a method for producing a heat shrinkable polyester film. 5 Heat shrinkable films are widely used as packaging and labeling materials. Among these, heat shrinkable polyester films, which have good mechanical properties and are odorless and nontoxic, have currently been adopted for replacing polyvinyl chloride films due to 10 environmental protection issues. For example, heat shrinkable polyethylene terephthalate (PET) films may be adopted for packaging or labeling bottles that are made of PET as well, so that the heat shrinkable PET films can be recycled together with the PET bottles. 15 However, the heat shrinkage ratio of conventional polyester films is less than 30%. In order to obtain higher heat shrinkage ratio, modifiers such as isophthalic acid (IPA), Neopentyl glycol (NPG) and 1,4-cyclohexanedimethanol (CHDM), are commonly used. 20 Conventionally, the polyester films will be heated to a temperature above 100'C for performing the heat shrinking process during packaging or labeling, but such high temperature results in high energy consumption and increases production cost. US Patent 25 No.7008698 discloses a modified polyester film which has a heat shrinkage ratio of 50% at 80'C for 10 seconds, but requires at least two drawing steps to achieve such 2 heat shrinkage ratio at the temperature of lower than 100 0 C. European Patent No.1055506B1 discloses a method for lowering the heat shrinking temperature. The method includes a step of drawing the polyester film at a 5 temperature ranging from (Tg-5) 0 C to (Tg+15) 0 C with a draw ratio ranging from 1.05 to 1.2 along a machine direction, and a step of drawing the polyester films twice along a transverse direction which is perpendicular to the machine direction. The heat 10 shrinkable polyester film produced by this method has a heat shrinkage ratio ranging from 50% to 60% at 800 C, but has a heat shrinkage ratio of greater than 20% at 70 0 C for 5 seconds and a heat shrinkage ratio of greater than 35% at 75 0 C for 5 seconds. Such high heat shrinkage 15 ratio(s) at 70 0 C (and 75 0 C) may result in unwanted deformation of the heat shrinkable polyester film during cargo transportation since the temperature while being transported in cargo containers may reach 70 0 C. 20 Therefore, there is a need in the art to provide a heat shrinkable polyester film that not only has relatively high heat shrinkage ratio which is greater than 60% at 80 0 C for 5 seconds, but also has a heat shrinkage ratio lower than 0.5% at 70 0 C for 5 seconds 25 to attain good dimensional stability. Therefore, the object of the present invention is to provide a method for producing a heat shrinkable 3 polyester film that may alleviate the aforementioned drawbacks. Accordingly, a method for producing a heat shrinkable polyester film of the present invention 5 includes the following steps of: (a) providing a polyester film that has a glass transition temperature (Tg) C; (b) preheating the polyester film at a preheating temperature ranging from (Tg+20) C to (Tg+30) C; 10 (c) drawing the preheated polyester film along a transverse direction which is perpendicular to a machine direction with a draw ratio ranging from 2.7 to 7.7; and (d) annealing the drawn polyester film at an 15 annealing temperature ranging from (Tg-10) 0 C to Tg C, followed by cooling to room temperature so as to obtain the heat shrinkable polyester film. The preferred embodiment of a method for producing a shrinkable polyester film according to the present 20 invention includes the following steps of: (a) providing a polyester film that has a glass transition temperature (Tg) C; (b) preheating the polyester film at a preheating temperature ranging from (Tg+20) C to (Tg+30) C; 25 (c) drawing the preheated polyester film along a transverse direction which is perpendicular to a machine direction with a draw ratio ranging from 2.7 4 to 7.7; and (d) annealing the drawn polyester film at an annealing temperature ranging from (Tg-10) 'C to Tg C, followed by cooling to room temperature so as to obtain 5 the heat shrinkable polyester film. In step (a) , the polyester film may be prepared by commonly known techniques, such as by meltingpolyester or modified polyester through a single or twin screw extruder under a working temperature ranging from 200 C 10 to 300 0 C, followed by extruding the melt through a T-die. Preferably, the polyester film is made of a modified polyester, and the modified polyester is made by polymerizing a diol, a diacid and a crystallinity modifier. The modified polyester may be one disclosed 15 in US Patent Nos. 6939616 and 7829655 and Taiwanese Patent No. 1335922, preferably a modified polyethylene terephthalate (PET). Preferably, the diacidmay be, but not limited to, terephthalic acid (TPA) . The diol may preferably be, but not limited to, one of ethylene 20 glycol (EG) , propylene glycol (PG) , and butylene glycol (BG) , and more preferably ethylene glycol (EG) . The crystallinity modifier is adopted for lowering the crytallinity of the modified polyester, and is preferably selected from the group consisting of 25 2-methyl-1,3-propanediol (MPDO), neopentyl glycol (NPG), isophthalic acid (IPA), 1,4-cyclohexanedimethanol (CHDM), and combinations 5 thereof, more preferably neopentyl glycol (NPG). In this embodiment, the glass transition temperature of the modified polyester film preferably ranges from70'C to 800 C, more preferably from 73 0 C to 79 0 C. 5 In this embodiment, preferably, the preheating temperature in step (b) ranges from 90 0 C to 110 0 C as determined based on the glass transition temperature of the modified polyester film, more preferably from 93 0 C to 109 0 C, most preferably from 99 0 C to 108 0 C. It 10 should be noted that the purpose of step (b) is to preheat the polyester film so as to soften the polyester film uniformly. Drawing should not be performed in the step (b) , so the draw ratio of the preheated polyester film is not greater than 1.05, and is more preferably 15 1. Preferably, the polyester film is preheated for 5 to 9 seconds, more preferably for 7 to 9 seconds. In this embodiment, in step (c) the preheated polyester film is drawn at a temperature preferably ranging from 70 0 C to 90 0 C, more preferably from 80 0 C 20 to 850 C. In step (c), the draw ratio of the preheated polyester film preferably ranges from 3.5 to 6.5, more preferably from 4.5 to 5.2. In this embodiment, the preheated polyester film may be drawn for not greater than 15 seconds, preferably from 1 to 12 seconds, more 25 preferably from 5 to 11 seconds. In this embodiment, the annealing temperature of the drawn polyester film in step (d) ranges from 60 0 C to 6 80'C as determined based on the preferable range of Tg of the polyester film, preferably from 63 0 C to 790 C, more preferably from 70 0 C to 780 C. In this embodiment, the draw ratio of the annealed polyester film in step 5 (d) is not greater than 1.05, and is more preferably 1 (i.e., completely without being drawn in step (d)). Preferably, the drawn polyester film in step (d) is annealed for not greater than 10 seconds, more preferably from 1 to 8 seconds. In this embodiment, the 10 room temperature in step (d) ranges from 20 0 C to 300 C. <Examples> [Synthesis Example 1 (SE 1): Modified Polyester] 80 mol% of TPA, 100 mol% of EG and 20 mol% of IPA were placed in a stirrer and stirred to form a paste-like 15 mixture, followed by adding 75 ppm of heat stabilizer (phosphoric acid) to the paste-like mixture. The paste-like mixture was then placed into an esterification reactor and was stirred under heating to perform esterification reaction, with a controlled 20 reactor pressure of not greater than 3 Kg/cm2. Water, as a reaction by-product, was rectified out of the esterification reactor by a rectification tube during the esterification reaction. An esterified product was obtained at a temperature of 250 0 C after 6 to 7 hours 25 of esterification reaction. The esterification product was then placed into a condensation reactor together with 300 ppm of antimony trioxide serving as a catalyst, 7 followed by gradually increasing the temperature to 285'C and simultaneously vacuuming the condensation reactor to approximately 1 torr in two hours to perform the condensation reaction. The condensation reaction 5 was performed for 4 to 5 hours until the intrinsic viscosity of the product ranges from 0.6 to 0.9, followed by shaping, cooling, cutting the product so as to obtain the modified polyester of SE 1 in a granular form. 10 [Synthesis Examples 2 and 3 (SE2 and SE3): Modified Polyester] The method for preparing the modified polyester of each of SE2 and SE3 according to the present invention is similar to that of SE 1, except for the reactant 15 compositions thereof. The reactant compositions of SE2 and SE3 are listed in Table 1. [Physical Property Analysis] 1. Glass Transition Temperature (Tg): The glass transition temperature of each of 20 Synthesis Examples was measured by differential scanning calorimetry (MODEL: DSC 2910 modulated DSC, commercially available from TA Instruments Inc.). The results of SE1, SE2 and SE3 are recorded in Table 1. 2. Intrinsic Viscosity (IV): 25 1 gram of the modified polyester of each of Synthesis Examples 1, 2 and 3 was dissolved into 100 grams of a phenol/tetrachloroethane solvent (50/50) to form a 8 dilute solution, followed by measuring the intrinsic viscosity of the solution using Ubbelohde Viscosimeter at 30 0 C. The results of SE 1, SE2, and SE3 are recorded in Table 1. 5 Table 1 Synthesis Example(SE) 1 2 3 Diacid TPA 80 100 100 Diol EG 100 82 70 Reactant IPA 20 - (mol%) Crystallinity NPG - 18 15 Modifier MPDO - - 15 Physical IV(ml/g) 0.723 0.691 0.647 Property Tg( 0 C) 74.5 79.0 73.0 [Example (EX) 1)] The heat shrinkable polyester film of EX1 according to the present invention was produced by a method including the following steps of: 10 (a) melting and extruding the modified polyester of SE2 through a single screw extruder under a working temperature of above 200 0 C and through a T-die to form a polyester film; (b) preheating the polyester film at 99 0 C for 7.2 15 seconds with a draw ratio of 1 (i.e., without drawing the polyester film) to obtain a preheated polyester film; (c) drawing the preheated polyester film along the transverse direction (TD) which is perpendicular to the 9 machine direction (MD) at 80 C with a draw ratio of 4.7 for 10.8 seconds, so as to obtain a drawn polyester film; and (d) annealing the drawn polyester film at 76'C for 5 7.2 seconds with a draw ratio of 1 (i.e., without drawing the drawn polyester film) , followed by cooling to room temperature (about 25 0 C) so as to obtain the heat shrinkable polyester film of EX1. [Examples (EXs) 2 to 5] 10 The method for producing the heat shrinkable polyester film of each of EX2 to EX5 is similar to that of EX1, except for the modified polyester adopted in step (a) , the preheating temperature in step (b) , and the annealing temperature in step (d) . The process 15 parameters of the method for producing each of EX2 to EX5 are recorded in Table 2. [Comparative Examples (CEs) 1 to 6] The method for producing the heat shrinkable polyester film of each of CE1 to CE6 is similar to that 20 of Example 1, except for the preheating temperature in step (b) and the annealing temperature in step (d) . The process parameters of the method for each of CE1 to CE6 are recorded in Table 2. Method of Measuring Heat Shrinkage Ratio 25 The heat shrinkable polyester film of each of the Examples (EXs) and the Comparative Examples (CEs) was subjected to measurement of heat shrinkage ratio in 1 0 accordance with Japanese Industrial Standard JIS-Z1709. Multiple 100mmxlOOmm (along MD and TD) square samples were taken from the heat shrinkable polyester film of each of the Examples and Comparative Examples and were 5 subjected to hot water bath separately at 60 0 C, 70 0 C, and 80 0 C for 5 seconds for measuring the heat shrinkage ratio thereof by applying the following formula(I): Heat Shrinkage Ratio(%)=[(Lo-L 1 )/Lo]x100% (I) wherein LO represents an original length of the samples 10 and Li represents a length of the samples after shrinking. The heat shrinkage ratio of the heat shrinkable polyester film of each of the Examples and Comparative Examples is recorded in Table 2. Table 2 Modified Step(b) Step(c) Shrinkage Rate(%) Polyester Preheating Annealing (5 seconds) SE Tg( 0 C) Temperature Temperature 60 0 C 70 0 C 80 0 C

(T

1 0

C)[T

1 -Tg] (T 2 0

C)[T

2 -Tg] EX 1 2 79 99[+20] 76[-3] 0 0.2 63.4 EX 2 2 79 108[+29] 78[-1] 0 0 61.8 EX 3 2 79 100[+21] 70[-9] 0 0.4 69.5 EX 4 1 74.5 102[+27.5] 74[-0.5] 0 0.3 64.9 EX 5 3 73 99[+26] 70[-3] 0 0.1 67.5 CE 1 2 79 93[+14] 76[-3] 0 0.8 64.8 CE 2 2 79 93[+14] 82[+3] 0 1.2 58.3 CE 3 2 79 99[+20] 82[+3] 0 2.4 57.1 CE 4 2 79 94[+15] 85[+6] 0 1.0 55.6 1 1 CE 5 2 79 85[+6] 78[-1] 0 1.8 63.2 CE 6 2 79 100[+21] 65[-14] 0 3.6 71.3 According to industrial demands, the shrinkage ratio is preferably 0% at 60 0 C, <0.5% at 70 0 C and >60% at 800 C. As shown in Table 2, the preheating temperature of 5 each of CE1 and CE5 in step (b) is lower than (Tg+20) C, and the shrinkage ratio of the heat shrinkable polyester film thereof at 70 0 C is greater than 0.5% and does not meet the requirements of dimensional stability for cargo transportation. 10 As for CE2 and CE4, the preheating temperatures are lower than (Tg+20) 0 C and the annealing temperatures are higher than Tg 0 C. Thus, not only the shrinkage ratio of the heat shrinkable polyester film is lower than 60% at 80 0 C for 5 seconds, but the shrinkage ratio of the 15 heat shrinkable polyester film is also higher than 0.5% at 70 0 C for 5 seconds, which does not meet the requirements of dimensional stability for cargo transportation. As for CE3, the preheating temperature is in the 20 range of between (Tg+20) 0 C and (Tg+30) 0 C, but the annealing temperature is higher than Tg 0 C, which is not in the preferable range of the annealing temperature according to the present invention. Thus, the shrinkage ratio of the heat shrinkable polyester film is lower 25 than 60% at 80 0 C for 5 seconds.

12 As for CE6, the annealing temperature is lower than (Tg-10) 'C, which is not in the preferable range according to the present invention, so the shrinkage ratio of the heat shrinkable polyester film is higher 5 than 0.5% at 70 0 C for 5 seconds and does not meet the requirements of dimensional stability for cargo transportation. In contrast, the shrinkage ratio of the heat shrinkable polyester film of each of the Examples (EXs) 10 is smaller than 0.5% at 70 0 C for 5 seconds andis greater than 60% at 80 0 C for 5 seconds. To sum up, by controlling the preheating temperature in the range of between (Tg+20) 0 C to (Tg+30) 0 C and the annealing temperature in the range of between (Tg-10) 0 C 15 to (Tg) 0 C accompanied with a single drawing step, the heat shrinkable polyester film produced by the method according to the present invention has met the industrial demands to assure the dimensional stability of the film while transporting in cargo containers, as 20 well as effectively reducing the shrinking temperature to 800 C. For the purpose of this specification, it will be clearly understood that the word "comprising" means "including but not limited to, " and that the word 25 "comprises" has a corresponding meaning. It is to be understood that, if any prior art publication is referred to herein, such reference does 1 3 not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

Claims

1. A method for producing a heat shrinkable polyester film comprising the following steps of: (a) providing a polyester film that has a glass 5 transition temperature (Tg) C; (b) preheating the polyester film at a preheating temperature ranging from (Tg+20) C to (Tg+30) C; (c) drawing the preheated polyester film along a transverse direction which is perpendicular to a 10 machine direction with a draw ratio ranging from 2.7 to 7.7; and (d) annealing the drawn polyester film at an annealing temperature ranging from (Tg-10) 0 C to Tg C, followed by cooling to room temperature so as to obtain 15 the heat shrinkable polyester film.

2. The method as claimed in Claim 1, wherein, in step (a) , the polyester film is made of a modified polyester, the modified polyester being made by polymerizing a 20 diol, a diacid, and a crystallinity modifier.

3. The method as claimed in Claim 2, wherein the crystallinity modifier is selected from the group consisting of 2-methyl-1,3-propanediol, neopentyl 25 glycol, isophthalic acid, 1,4-cyclohexanedimethanol and combinations thereof. 15

4. The method as claimed in Claim 2, wherein the diol is one of ethylene glycol, propylene glycol and butylene glycol.

5 5. The method as claimed in Claim 4, wherein the diol is ethylene glycol.

6. The method as claimed in Claim 2, wherein the diacid is terephthalic acid. 10

7. The method as claimed in any one of Claims 1 to 6, wherein the glass transition temperature of the polyester film ranges from 70 0 C to 80 0 C. 15

8. The method as claimed in any one of Claims 1 to 7, wherein a draw ratio of the preheated polyester film in step (b) is not greater than 1.05.

9. The method as claimed in any one of Claims 1 to 8, 20 wherein, in step (b) , the polyester film is preheated for 5 to 9 seconds.

10. The method as claimed in any one of Claims 1 to 9, wherein, in step (c) , the preheated polyester film is 25 drawn at a temperature ranging from 80 0 C to 85 0 C.

11. The method as claimed in any one of Claims 1 to 10, 1 6 wherein, in step (c) , the preheated polyester film is drawn for not greater than 15 seconds.

12. The method as claimed in any one of Claims 1 to 11, 5 wherein, in step (c) , the draw ratio of the preheated polyester film ranges from 4.5 to 5.2.

13. The method as claimed in any one of Claims 1 to 12, wherein, in step (d) , a draw ratio of the annealed 10 polyester film is not greater than 1.05.

14. The method as claimed in any one of Claims 1 to 13, wherein, in step (d) , the drawn polyester film is annealed for not greater than 10 seconds. 15

15. The method as claimed in Claim 14, wherein, in step (d), the drawn polyester film is annealed for 1 to 8 seconds. 20