TW201429698A - Method of preparing thermal shrinkage polyester thin film - Google Patents

Abstract

A method of preparing a thermal shrinkage polyester thin film comprises: a. providing a polyester thin film having X degrees Celsius glass transfer temperature; b. preheating the polyester thin film at a preheating temperature range from (X+20) degrees Celsius to (X+30) degrees Celsius to obtain a preheated polyester thin film; c. extending the preheated polyester thin film along a direction perpendicular to a machine direction under conditions of an extension ratio ranging from 2.7 to 7.7 and an extension time that is not greater than 15 seconds, thereby obtaining an extended thin film; d, annealing the extended thin film under an annealing temperature ranging from (X-10) degrees Celsius to X degrees Celsius and an annealing time that is not greater than 10 seconds so as to obtain an annealed thin film; and e. cooling the annealed thin film to the ambient temperature to prepare the thermal shrinkage polyester thin film. The thermal shrinkage polyester thin film obtained by the preparation method of the invention has lower shrinkage temperature during label thermal shrinkage process and has good size stability during transportation.

Description

Method for preparing heat shrinkable polyester film

The invention relates to a method for preparing a heat-shrinkable polyester film, in particular to a method for preparing a heat-shrinkable polyester film comprising a preheating, stretching and annealing step.

The heat shrinkable film is a widely used packaging and labeling material. Among them, the heat-shrinkable polyester film has been used to replace the polyvinyl chloride film which is less environmentally friendly because of its advantages of being odorless, non-toxic, mechanically good, and easy to recycle. Heat-shrinkable polyester film, such as polyethylene terephthalate (PET), can be recycled with the bottle body when used for packaging and labeling PET beverage bottles, which is more in line with market and environmental requirements.

Generally, the shrinkage rate of the unmodified polyester film is not more than 30%. Therefore, when applied to a heat shrinkable film, conventional techniques generally add a modifier such as isophthalic acid (IPA), new to the polyester. Neopentyl glycol (NPG), 1,4-cyclohexanedimethanol (CHDM), and the like. Furthermore, the polyester film must be subjected to a temperature higher than 100 ° C in the subsequent packaging and label heat shrinking process, and in order to achieve energy saving, the industry is now expected to reduce the shrinkage temperature and time of the heat shrinkable polyester film. For example, at 80 ° C and below, the desired heat shrinkage can be achieved. According to the various problems mentioned above, US 7,008,698 B2 proposes a heat shrinkage The polymer film comprises a modified polyester resin obtained by polymerizing a diacid and a diol containing 2-methyl-1,3-propanediol; the polymer film is melted and extruded into a sheet, and then passed through The cooling is carried out by performing multiple extensions at a temperature at which the glass transition temperature of the polymer is lower than the temperature at which the polymer is softened and melted. The process of this patent requires at least two extension steps to achieve a 50% shrinkage of the resulting polymer film at 80 ° C and 10 seconds. For the industry, the process of this patent case is still not economically viable and needs to be improved.

EP1055506 B1 also uses a process improvement method to reduce the shrinkage temperature. The process consists of making the polyester film at a temperature between [Tg-5] ° C and [Tg + 15] ° C and a draw ratio of 1.05 to 1.2 along the machine. The direction (MD) is first extended to obtain an extended polyester film; the stretched polyester film is preheated and the second and third extensions are respectively performed in a direction perpendicular to the machine direction (TD). The obtained heat-shrinkable polyester film has a shrinkage ratio of 50 to 60% at 80 °C. The above patents only use a two-stage extension process, which meets the need to reduce the shrinkage temperature, but still cannot effectively save energy and reduce carbon and reduce manufacturing costs. In addition, the heat-shrinkable polyester film produced in the above patents has a shrinkage ratio of >20% at 70 ° C and 5 seconds and a shrinkage of >35% at 75 ° C and 5 seconds, respectively, possibly during container transportation. It is deformed by heat shrinkage (the temperature in the container during transportation may be as high as 70 ° C), resulting in poor dimensional stability of the heat-shrinkable polyester film.

It can be seen from the above description how to reduce the shrinkage temperature of the heat-shrinkable polyester film while satisfying the dimensional stability that needs to be maintained during container transportation, there is still a great demand in the industry.

In view of the energy consumption of the EP1055506 B1 using a two-stage extension process and its inability to meet dimensional stability issues during container transport, the applicant of the present invention proposes a preheating and annealing step using a single extension step (EP1055506 B1 and The process of these steps has not been proposed to overcome all of the problems raised above while meeting the needs of the industry.

Accordingly, it is an object of the present invention to provide a method for producing a heat-shrinkable polyester film which can reduce the shrinkage temperature and which has good dimensional stability during transportation.

Thus, the method for preparing the heat-shrinkable polyester film of the present invention comprises: (a) providing a polyester film having a glass transition temperature of X ° C; (b) allowing the polyester film to be at (X + 20) ° C to (X) Preheating at a preheating temperature range of +30) °C to obtain a preheated polyester film; (c) preheating the polyester at an elongation ratio ranging from 2.7 to 7.7 and an extension time of not more than 15 seconds Extending the film in a direction perpendicular to the machine direction to obtain an extended film; (d) annealing the stretched film at an annealing temperature range of (X-10) ° C to X ° C and an annealing time of not more than 10 seconds, An annealed film is obtained; and (e) the annealed film is cooled to ambient temperature to produce the heat-shrinkable polyester film.

The preparation method of the invention has the shrinkage rate of the obtained heat-shrinkable polyester film at 70 ° C and 5 seconds <0.5% through the control of the preheating temperature, the extension condition and the annealing temperature, and can be good in container transportation. Dimensional stability Properties, and shrinkage at 80 ° C and 5 seconds > 60%, through the reduction of shrinkage temperature, the label heat shrinking process temperature can be reduced, while reducing energy consumption.

The preparation method of the heat-shrinkable polyester film of the invention comprises: (a) providing a polyester film having a glass transition temperature of X ° C; (b) making the polyester film at (X + 20) ° C to (X + 30) Preheating at a preheating temperature range of °C to obtain a preheated polyester film; (c) preheating the polyester film along an extension ratio ranging from 2.7 to 7.7 and an extension time of not more than 15 seconds Extending perpendicular to the machine direction to obtain an extended film; (d) annealing the stretched film at an annealing temperature range of (X-10) ° C to X ° C and an annealing time of not more than 10 seconds, to obtain an Annealing the film; and (e) cooling the annealed film to ambient temperature to produce the heat-shrinkable polyester film.

The polyester film of the step (a) can be produced according to the methods known in the art, for example, by passing the polyester or the modified polyester through a single-screw extruder or a twin-screw extruder at a processing temperature of 200 to 300 ° C. Melting is carried out, followed by formation of a polyester film through a die (T-die).

Preferably, the polyester film of the step (a) is made of a modified polyester which is polymerized by a composition. The composition comprises a diacid, a diol, and a modifier for destroying crystallinity. The type of the modified polyester can be disclosed, for example, in TW 1335922, US Pat. No. 6,396,616, and US Pat. The diacid can be, for example but not limited to, terephthalic acid (TPA); the diol can be, for example but not limited to, ethylene glycol (EG), propylene glycol (PG), butylene glycol (BG), and the like, preferably EG. Preferably, the modifier is selected from the group consisting of isophthalic acid (IPA), 2-methyl-1,3-propanediol (MPDO), neopentyl glycol (NPG), and 1,4-cyclohexane. Methanol (CHDM) or a combination of these, with NPG being preferred.

Preferably, the glass transition temperature X of the polyester film of step (a) ranges from 70 to 80 °C. In a preferred embodiment of the invention, X ranges from 73 to 79 °C.

Preferably, the preheating temperature of the step (b) ranges from 90 to 110 ° C according to the preferred range of X above. In a preferred embodiment of the invention, the preheating temperature of step (b) ranges from 93 to 109 °C. In a more preferred embodiment of the invention, the preheating temperature of step (b) ranges from 99 to 108 °C.

Step (b) is mainly to preheat the polyester film to have a uniform temperature on the surface of the film. In the preheating process of the step (b), the polyester film is not extended at the same time. Preferably, the elongation ratio of the step (b) is not more than 1.05; more preferably, the elongation ratio is 1 (ie, completely). No extension).

Preferably, the preheating time of the step (b) ranges from 5 to 9 seconds; more preferably, the preheating time ranges from 7 to 9 seconds.

Preferably, the temperature of the step (c) ranges from 70 to 90 °C. In a preferred embodiment of the invention, the temperature of step (c) is from 80 to 85 °C.

Preferably, the step (c) has an elongation ratio of 3.5 to 6.5; more preferably, the elongation ratio is 4.5 to 5.2.

The extension time of the step (c) is not more than 15 seconds; preferably, the extension time is 1 to 12 seconds; more preferably, the extension time is 5 to 11 seconds.

Preferably, the annealing temperature of the step (d) ranges from 60 to 80 ° C according to the preferred range of X above. In a preferred embodiment of the invention, the annealing temperature of step (d) ranges from 63 to 79 °C. In a more preferred embodiment of the invention, the annealing temperature of the step (d) ranges from 70 to 78 °C.

Preferably, the step (d) has an extension ratio of not more than 1.05; more preferably, the elongation ratio is 1.

The annealing time of the step (d) is not more than 10 seconds; preferably, the annealing time is 1 to 8 seconds.

Preferably, the ambient temperature of the step (e) ranges from 20 to 30 °C.

The heat-shrinkable polyester film prepared by the preparation method of the invention has a shrinkage ratio of <0.5% at 70 ° C and 5 seconds, and a shrinkage ratio of >60% at 80 ° C and 5 seconds, which fully meets the needs of the industry.

The present invention will be further illustrated by the following examples, but it should be understood that this embodiment is intended to be illustrative only and not to be construed as limiting.

<Example> [Preparation Example 1] Modified polyester

Pour 80 mol% of TPA, 100 mol% of EG and 20 mol% of IPA into a stirred tank to form a paste, and add 75 ppm of heat stabilizer (phosphoric acid), then pour the paste into the ester. The temperature is stirred in the polymerization tank, and the esterification reaction is carried out at the same time. The pressure in the tank is controlled to be within 3 kg/cm ² , and the water formed by the reaction is distilled off through the distillation tube. After 6~7 hours, the final esterification temperature is raised to 250 °C, then the esterification in the reaction tank is moved to the condensation reaction, and then 300 ppm of antimony trioxide is added as a catalyst, and the temperature is gradually raised to 285 °C. At the same time, evacuate to about 1 torr in 2 hours. The modified polyester ester granules are prepared until the ultimate viscosity is between 0.6 and 0.9, which lasts for 4 to 5 hours, followed by drainage, cooling, and pelletizing.

[Preparation Examples 2 and 3] Modified polyester

Except that the reactants and the proportions were changed according to the following Table 1, the other processes and procedures were the same as in Preparation Example 1, and finally the modified polyester was obtained.

[Property test]

1. Thermal properties: using a thermal differential scanning analyzer (DSC, TA) Manufactured by Instruments, Model DSC 2910 Modulated DSC) to test the glass transition temperature Tg (°C).

2. Ultimate viscosity [intrinsic viscosity, IV (ml / g)]: 1 g of the modified polyester was dissolved in 100 g of a 50/50 by weight phenol/tetrachloroethane mixed solvent and measured at 30 ° C using a Ubelode-viscosimeter.

Table 1

[Example 1] Heat shrinkable polyester film

(a) First, the modified polyester of Preparation Example 2 was passed through a single-screw extruder and melted at a processing temperature higher than 200 ° C, followed by a die to form a polyester film; (b) The polyester film was preheated at a preheating temperature of 99 ° C and an extension (extension ratio of 1), and a preheated polyester film was obtained after 7.2 seconds; (c) an elongation ratio of 4.7 and an elongation temperature of 80 ° C. Next, the preheated polyester film is stretched in a direction perpendicular to the machine direction, and after stretching for 10.8 seconds, an extended film is obtained; (d) the stretched film is annealed at 76 ° C and is not stretched (elongation ratio) Annealing is performed for 1), an annealed film is obtained after 7.2 seconds; and (e) the annealed film is cooled to ambient temperature (about 25 ° C) to obtain the heat-shrinkable polyester film.

[Examples 2 to 5 and Comparative Examples 1 to 6]

In addition to changing the process conditions according to Table 2 below, the remaining processes are the same as in Example 1. Similarly, the heat-shrinkable polyester films of Examples 2 to 5 and Comparative Examples 1 to 6 were finally prepared.

Thermal Shrinkage Test: The heat-shrinkable polyester films of Examples 1 to 5 and Comparative Examples 1 to 6 were each subjected to the following test. According to the JIS Z1709 standard method, a rectangular sample having a size of 100 mm × 100 mm was cut and marked along the MD and TD, respectively. The samples were placed in a constant temperature water bath at 60 ° C, 70 ° C and 80 ° C for 5 seconds to test, and then the sample was taken out and the heat shrinkage rate was calculated by the following formula: heat shrinkage rate = [(L _{0 -} L ₁ ) /L ₀ ] × 100% (L ₀ represents the original length of the sample, and L ₁ represents the length after shrinkage of the sample). According to the industry demand, the shrinkage at 60 ° C is optimally 0%, the shrinkage at 70 ° C is preferably <0.5%, and the shrinkage at 80 ° C is preferably >60%.

Table 2

As can be seen from the results of Table 2, the samples of Examples 1 to 5 have a shrinkage ratio of less than 0.5% at 70 ° C and 5 seconds and a shrinkage ratio of more than 60% at 80 ° C and 5 seconds, which proves that the control step (b) is passed. The preheating temperature range is (X+20) to (X+30) °C and the annealing temperature range of step (d) is (X-10) to (X) °C, which can effectively reduce the shrinkage temperature and improve the container transportation. The dimensional stability of the time.

The preheating temperature of Comparative Example 1 is lower than (X+20) °C, and the shrinkage ratio at 70 ° C is more than 0.5%, which cannot meet the size required for container transportation. Stability. The same was true in Comparative Example 5.

The preheating temperature of Comparative Example 2 was lower than (X + 20) ° C, the annealing temperature was greater than X, and the shrinkage ratio at 80 ° C was less than 60%, which could not meet the shrinkage requirement. The same was true in Comparative Example 4.

The annealing temperature of Comparative Example 3 was greater than X, and the shrinkage ratio at 80 ° C was less than 60%, which could not meet the requirements for shrinkage. The annealing temperature of Comparative Example 6 was lower than (X-10) ° C, and the shrinkage ratio at 70 ° C was much larger than 0.5%, which could not satisfy the dimensional stability required for container transportation.

In summary, the preparation method of the present invention controls the temperature range of the preheating step and the annealing step, and the stretching step of the obtained heat-shrinkable polyester film at 70 ° C and 5 seconds is <0.5%. And shrinkage at 80 ° C and 5 seconds > 60%, and can have good dimensional stability when transported in containers, while reducing the shrinkage temperature in the packaging and label heat shrinking process.

The above is only the preferred embodiment of the present invention, and the scope of the present invention is not limited thereto, that is, the simple equivalent changes and modifications made by the patent application scope and patent specification content of the present invention, All remain within the scope of the invention patent.

Claims (9)

A method for preparing a heat-shrinkable polyester film comprising: (a) providing a polyester film having a glass transition temperature of X ° C; (b) providing the polyester film at (X + 20) ° C to (X + 30) Preheating at a preheating temperature range of °C to obtain a preheated polyester film; (c) preheating the polyester film along the extension ratio in the range of 2.7 to 7.7 and an extension time of not more than 15 seconds Extending in the direction of the machine direction to obtain an extended film; (d) annealing the stretched film at an annealing temperature range of (X-10) ° C to X ° C and an annealing time of not more than 10 seconds to obtain an annealed a film; and (e) cooling the annealed film to ambient temperature to produce the heat-shrinkable polyester film. The method for producing a heat-shrinkable polyester film according to claim 1, wherein the polyester film of the step (a) is made of a modified polyester, and the modified polyester is made of a composition. The composition is prepared by polymerization, and the composition comprises a diacid, a diol, and a modifier for destroying crystallinity. The method for producing a heat-shrinkable polyester film according to claim 2, wherein the modifier is selected from the group consisting of 2-methyl-1,3-propanediol, neopentyl glycol, and 1,4-cyclohexane Methanol or a combination of these. The method for producing a heat-shrinkable polyester film according to claim 1, wherein X ranges from 70 to 80 °C. The method for producing a heat-shrinkable polyester film according to claim 1, wherein the step (b) has an elongation ratio of not more than 1.05. The method for producing a heat-shrinkable polyester film according to claim 1, wherein the preheating time of the step (b) is from 5 to 9 seconds. The method for producing a heat-shrinkable polyester film according to claim 1, wherein the temperature of the step (c) is in the range of 80 to 85 °C. The method for producing a heat-shrinkable polyester film according to claim 1, wherein the step (d) has an elongation ratio of not more than 1.05. The method for producing a heat-shrinkable polyester film according to claim 1, wherein the ambient temperature ranges from 20 to 30 °C.