WO2006001659A1

WO2006001659A1 - Biaxially oriented polyester films and processing method thereof

Info

Publication number: WO2006001659A1
Application number: PCT/KR2005/001978
Authority: WO
Inventors: Sang-Hyun Baek; Do-Hyun Kim
Original assignee: Kolon Industries Inc.
Priority date: 2004-06-25
Filing date: 2005-06-24
Publication date: 2006-01-05
Also published as: TWI292409B; TW200606193A; KR100893721B1; KR20050122621A

Abstract

There are provided a biaxially oriented polyester film having 70 degrees or less of foldability (θ), wherein the foldability is obtained by folding a film in half by using Heat Gradient under conditions of 0.2 MPa of pressure, 1 sec and an ambient temperature, and after 30 mins, calculating the degree of the folded portion by using the following equation 1. Equation 1 θ = 2sin-1(F/2L) wherein, F is a distance of an imaginary line connecting both end points of film folded in half, and 2L is total distance of the folded film, and the biaxially oriented polyester film is useful for packaging materials for candies, caramels or chocolates packaging materials, since it has inherent and excellent mechanical properties, printabilities, transparencies, thickness uniformities, cutting properties, innoxious properties as well as twisting properties.

Description

BIAXIALLY ORIENTED POLYESTER FILMS AND PROCESSING METHOD THEREOF

Technical Field The present invention relates to a biaxially oriented polyester film having excellent twisting properties, and processing method thereof, and more particularly, to a biaxially oriented polyester film that is useful for packaging materials for candies, chocolates, caramels and the like by imparting twisting properties to a biaxially oriented polyester film having inherently excellent mechanical properties, printabilities, transparencies, thickness uniformities, cutting properties, innoxious properties and the like and processing method thereof.

Background Art Currently, industrially produced polyester moulded articles, in particular polyethyleneterephthalate (PET) moulded articles are used extensively in fibers, films and other moulded articles. Particularly, since the polyethyleneterephthalate films prepared from aromatic dicarboxylic acid and ethyleneglycol have excellent mechanical properties including heat resistance, tensile strength, elongation ratio, Young's modulus, elastic recovery, impact resistance and the like, dimensional stability, electric insulation properties, it can be used as industrial materials and agricultural materials, such as magnetic recording tapes, photographic films, insulating materials, vapor depositing films(films to be vapor deposited) and the like. Additionally, since the polyester films have chemical properties including chemicals resistance, durability, water resistance and the like, as well as transparencies, aroma retaining properties, water resistance, gas blocking properties and the like, utilization of the polyester films as packaging materials have been increased greatly. Generally, an industrial method of PET films comprises melt-extruding PET polymers and cooling a melt-extrudates in cooling drum to form an amorphous sheet; and then annealing the amorphous sheet to form biaxially oriented films. In an industrial method of PET polymers used in preparation of PET films, PET polymers are prepared by direct esterification reaction of dicarboxylic acid such as terephthalic acid and ethyleneglycol as major components at 200 to 280 ^°C and an ambient pressure or under pressurized conditions, or trans esterification reaction of dimethylcarboxylate such as dimethylterephthalate and ethyleneglycol as major components in the presence of catalysts at 140 to 240 ^°C, to obtain bis(j3 -hydroxyethyl)terephthalates and low molecular weight condensates thereof as major components, and successively heating it in combination with polycondensation catalysts at 260 to 300 ^°C to carry out polycondensation. It is well known that PET films have great industrial values due to their excellent physical properties as described above. However, their utilization is limited in some applications. Particularly, the films that are used as packaging materials for packaging candies, caramels, chocolates and the like should have excellent twisting properties, high stiffness, printabilities, innoxious properties to human body, cutting properties and the like, but PET films have very weak twisting properties due to their high recovery. Additionally, cellophanes, OPS, PVC films and the like have been used as packaging materials for candies, caramels, chocolates and the like in the past, since their twisting properties are excellent. However, in the case of the PVC films, since there are problems of environmental hormones caused by plasticizer and generation of dioxin on incineration, utilization of the PVC films has been regulated environmentally in many nations and regions, and utilization of the PVC films have also been regulated in some food packaging applications domestically. In the case of the OPS, its utilization has been limited due to its poor thickness uniformities, thermal stabilities(dimensional stabilities), mechanical roughness, and processabilities. Further, in the case of cellophane, since there is no manufacturer in domestic, it is very import-dependent, and various problems are occurred since a process for preparing cellophane polymer is considered as polluting industries. Especially, since the price of the cellophane polymer is very high, its utilization is limited. Recently, a co-extruded non-oriented polypropylene films have been developed partially and used, but their market share is very low due to their poor printabilities, thermal stabilities and the like. Therefore, if the PET films have also the twisting properties, the films can meet various physical properties including other mechanical properties, printabilities, transparencies, thickness uniformities, cutting properties, innoxious properties and the like that are necessary for packaging materials. However, so far the PET films having twisting properties have not been developed due to high resiliency (elastic recovery properties) of the PET films.

Disclosure of the Invention Therefore, an object of the present invention is to solve the problems involved in the prior art, and to provide a innoxious to human body and environment-friendly biaxially oriented polyester film that is useful for packaging materials for candies, chocolates, caramels and the like by imparting twisting properties to a biaxially oriented polyester film having inherently excellent mechanical properties, printabilities, transparencies, thickness uniformities, cutting properties, innoxious properties and the like and processing method thereof. To accomplish the object, the present invention provides a biaxially oriented polyester film having 70 degrees or less of foldability (θ), wherein the foldability is obtained by folding a film in half by using Heat Gradient under conditions of 0.2 MPa of pressure, 1 sec and an ambient temperature, and after 30 mins, calculating the degree of the folded portion by using the following equation 1.

Equation 1 θ = 2sin^"1(F/2L) wherein, F is a distance of an imaginary line connecting both end points of film folded in half, and 2L is total distance of the folded film.

Additionally, the present invention provides a process for preparing a biaxially oriented polyester film having 70 degrees or less of foldability (θ), wherein the foldability is obtained by folding a film in half by using Heat Gradient under conditions of 0.2 MPa of pressure, 1 sec and an ambient temperature and after 30 mins, calculating the degree of the folded portion by using the following equation 1,

Equation 1 θ - 2sin^"1(F/2L) wherein, F is a distance of an imaginary line connecting both end points of film folded in half, and 2L is total distance of the folded film, comprising melting a polymer obtained from polyethyleneterephthalate alone or mixtures in combination with at least one copolymerization components at temperature of melting point or more, and then rapid cooling the molten polymer at temperature of glass transition temperature or less to prepare an amorphous sheet; biaxially orienting the amorphous sheet with larger machine directional(MD) orientation ratio than transverse directional(TD) orientation ratio under conditions of a machine directional orientation temperature that satisfies the following equation 2 and a transverse directional orientation temperature that satisfies the following equation 3;

Equation 2 Tg ≤ machine directional orientation temperature (Tsm) ≤ Tg + 30^°C wherein, Tg is glass transition temperature,

Equation 3 Tsm ≤ transversal orientation temperature (Tst) ≤ Tsm + 30^°C wherein, Tsm is machine directional orientation temperature,

annealing the biaxially oriented film at the temperature that satisfies the following equation 4; and

Equation 4 Tg ≤ annealing temperature ≤ Tst + 30^°C wherein, Tg is glass transition temperature, and Tst is transverse directional orientation temperature. relaxing the annealed film under relaxing condition that satisfies the following equation 5. Equation 5 -3% ≤ relaxation ≤ 3%

Brief Description of the Drawings The above objects, other features and advantages of the present invention will become more apparent by describing the preferred embodiment thereof with reference to the accompanying drawings, in which:

Fig. 1 is a scheme for illustrating calculating method of foldability. < Brief description of reference numbers > W : a width of film L : a distance of film folded in half F : a distance of an imaginary line connecting both end points of film folded in half θ : a degree of portion folded in half, foldability

Best Mode for Carrying Out the Invention Reference will now be made in detail to preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The polyester film according to the present invention has 70° or less of foldability as defined following to increase twisting properties. Herein, the "foldability" of the present invention means degree (θ) obtained by folding a film in half by using Heat Gradient under conditions of 0.2 MPa of pressure, 1 sec and an ambient temperature, and after 30 mins, calculating the degree of the folded portion by using the following equation 1. Equation 1

wherein, F is a distance of an imaginary line connecting both end points of film folded in half, and 2L is total distance of the folded film.

That is, the polyester film of the present invention has 70 degrees or less of a foldability, and so when candies and the like are packaged with the polyester film used as packaging materials, the packages won't be disintegrated even after lapsing a long time. If the foldability is 70 degree or more, after somewhat lapsing time, the packages can be disintegrated and the content can be exserted. Therefore, the polyethylene film having 70 degrees of foldability cannot be suitable for packaging materials. Further, the polyester film of the present invention can be obtained from polyethyleneterephthalate alone, or mixtures in combination with at least one copolymerization components. Further, at least one copolymerization components is preferably selected from acids, esters or alcohols, more preferably is selected from acids including isophthalic acid and adipic acid; esters including naphtalenecarboxylicmethylester; alcohols including diethyleneglycol, polyethyleneglycol, polypropyleneglycol and polytetramethyleneglycol. Next, the process for preparing the polyester film is described. Twisting properties of a polyester film can be improved by optimizing preparation conditions of a polyester film. As described above, the polyester film of the present invention can be obtained from polyethyleneterephthalate alone, or mixtures in combination with at least one copolymerization components, therefore an addition of the copolymerization components can be carried out by any method including polymerizing method or blending method. ^"" ^{/ υ w} J y ψ ft Preparation conditions of the polyester film can be set depending on thermaf ' o behaviors of respective compositions. For the process for preparing the polyester film of the present invention, the first operation is melting a polymer obtained from polyethyleneterephthalate alone, or mixtures in combination with at least one copolymerization components at temperature of melting point or more, and then rapid cooling the molten polymer at temperature of glass transition temperature or less to prepare an amorphous sheet. Next, the second operation is biaxially orienting the amorphous sheet with larger machine directional orientation ratio than transverse directional orientation ratio under conditions of a machine directional orientation temperature that satisfies the above equation 2 and a transverse directional orientation temperature that satisfies the above equation 3. That is, for the orientation operation, a machine directional(MD) orientation temperature can be in the range of glass transition temperature of the composition to above 30 "C higher temperature than glass transition temperature. Preferably, the orientation can be carried out at temperature closing to glass transition temperature. A transverse directional(TD) orientation can be also carried out in the range of machine directional orientation temperature to higher temperature above 30^°C than machine directional orientation temperature. Wherein, the orientation is carried out in machine direction from 3 to 5 times, and then in transverse direction from 3 to 5 times. Preferably, a machine directional orientation ratio can be larger than transverse orientation ratio. Next, the biaxially oriented film is annealing at the temperature that satisfies the above equation 4, and then the annealed film is relaxed under conditions that satisfy the above equation 5. That is, the annealing temperature in the annealing operation is in a range from glass transition temperature to above 30O higher temperature than transverse direction orientation temperature, preferably transverse direction orientation temperature or less. In a post-process such as printing and the like after the preparation of the film, the heat treatment should be carried out at least at glass transition temperature or more to minimize shrinkage when heat is applied to the film. In relaxing zone, a relaxation (%) can be 3% or less, preferably 0%. Rather, it is also possible in even case that an orientation is carried out in heat fixation zone (relaxation (%): -3%). However, in case of orientation, crimples in appearance can be occurred. The present invention will be described in greater detail with reference to the following examples. The following examples are for illustrative purposes and are not intended to limit the scope of the invention.

Examples 1, 2 and comparative examples 1 to 4 An amorphous sheet was prepared by extruding polyethyleneterephthalate, and then rapid cooling extruded polyethyleneterephthalate. A film was prepared by biaxially orienting the amorphous sheet successively under conditions described in the following Table 1. A glass transition temperature of the rapid cooled non-oriented polyethyleneterephthalate was 68 ^°C according to the result as analyzed with differential scanning calorimetry (DSC). Table 1

In following examples, a folability measurement of the film was carried out as follows. It can be referred that the more a modified body by external force can not return to the original state, the more twisting properties is excellent. Therefore, we evaluated the foldability by folding a film with identical pressure for identical time period, releasing pressure, and then comparing folding degree of the film. (1) apparatus: Heat Gradient (manufactured by Toyoseiki) (2) measuring conditions : pressure - 0.2 MPa, time - lsec, temperature - ambient temperature (3) specimen : size (width x length) - 10 mm x 15 mm (4) evaluation method of foldability

As described above, we pressed a film with consistent pressure and after 30 mins, calculated degree of folded portion and compared with each other. Calculation method can be referred to FIG. 1 and based on the equation 1 above. For FIG. 1, W is 8 mm, and L is 8 mm. The foldability can be evaluated comparatively by using calculated θ. Under the above conditions, if the foldability is in the range of 0°<θ<70°, the twisting properties was shown to be excellent. The results evaluated as described above were shown in the following Table 2.

Table 2

As shown in the results of table 2, the foldability of the polyester film prepared according to the present invention was 70° or less, and the polyester film exhibited excellent folding properties.

Examples 3 to 7 and Comparative example 5 The examples relate to the biaxially oriented polyester film prepared in combination with copolymerization components. An amorphous sheet was prepared by extruding copolymerization polyester in combination with copolymerization components described in the following Table 3 and then rapid cooling it. The glass transition temperature of the amorphous polyester copolymer sheet was measured by DSC. The results were shown in the Table 3. The conditions for preparing the film are as follows, which are included in the scope of examples. - machine directional orientation ratio: 4.0 times, - transverse directional orientation ratio: 3.5 times, - machine directional orientation temperature: Tg + 25 ^"C , - transverse directional orientation temperature: machine directional orientation temperature + 10 ^°C , - relaxation (%): 0%, - annealing temperature: transverse directional orientation temperature + 10^°C .

For comparative example 5, the amorphous polyester copolymer sheet was prepared in a identical method to examples 3 to 7, except that heat treating temperature was transverse directional elongation temperature + 50^°C .

Table 3

As shown in the results of the Table 3, the foldability of the polyester film prepared according to the present invention was 70° or less, and the polyester film exhibited excellent folding properties.

Industrial Availability As described above, if the polyester film satisfies the foldability of desired range measured by method according to the present invention, the polyester film can be used usefully as a packaging materials for packaging candies, caramels or chocolates since the polyester film has inherently mechanical properties, printabilities, transparencies, thickness uniformities, cutting properties, innoxious properties and the like as well as twisting properties.

While the present invention has been described and illustrated herein with reference to the preferred embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made therein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of the appended claims and their equivalents.

Claims

■ u What is claimed is:

1. A biaxially oriented polyester film having 70 degrees or less of foldability (θ), wherein the foldability is obtained by folding a film in half by using Heat Gradient under conditions of 0.2 MPa of pressure, 1 sec and an ambient temperature, and after 30 mins, calculating the degree of the folded portion by using the following equation 1;

Equation 1 θ = 2sin^'1(F/2L) Wherein, F is a distance of an imaginary line connecting both end points of film folded in half, and 2L is total distance of the folded film.

2. The biaxially oriented polyester as claimed in claim 1, wherein the polyester film is obtained from polyethyleneterephthalate alone, or mixtures in combination with at least one copolymerization components.

3. The biaxially oriented polyester as claimed in claim 2, wherein the copolymerization components is at least one selected from acids including isophthalic acid and adipic acid; esters including naphtalenecarboxylicmethylester; or alcohols including diethyleneglycol, polyethyleneglycol, polypropyleneglycol, and polytetramethyleneglycol.

4. A process for preparing a biaxially oriented polyester film having 70 degrees or less of foldability (θ), wherein the foldability is obtained by folding a film in half by using Heat Gradient under conditions of 0.2 MPa of pressure, 1 sec and an ambient temperature and after 30 mins, calculating the degree of the folded portion by using the following equation 1 ;

Equation 1 θ = 2sin^"1(F/2L) Wherein, F is a distance of an imaginary line connecting both end points of film folded in half, and 2L is total distance of the folded film, comprising melting a polymer obtained from polyethyleneterephthalate alone or mixtures in combination with at least one copolymerization components at temperature of melting point or more, and then rapid cooling the molten polymer at temperature of glass transition temperature or less to prepare amorphous sheet; biaxially elongating the amorphous sheet with larger machine directional orientation ratio than transverse directional orientation ratio under conditions of a machine directional orientation temperature that satisfies the following equation 2 and a transverse directional orientation temperature that satisfies the following equation 3;

Equation 2 Tg ≤ machine directional orientation temperature(Tsm) ≤ Tg + 30^°C wherein, Tg is glass transition temperature,

Equation 3 Tsm ≤ transversal orientation temperature(Tst) ≤ Tsm + 30^°C wherein, Tsm is machine directional orientation temperature, annealing the biaxially oriented film at the temperature that satisfies the following equation 4; and Equation 4 Tg ≤ annealing temperature ≤ Tst + 30^°C wherein, Tg is glass transition temperature, and Tst is transverse directional orientation temperature. relaxing the annealed film under relaxing condition that satisfies the following equation 5.

Equation 5 -3% < relaxation < 3%

5. The process as claimed in claim 4, wherein the combination of the copolymerization components is carried out by polymerizing method or blending method.

6. The process as claimed in claim 4, wherein in operation biaxially orienting the amorphous sheet, the machine directional orientation ratio is the transverse directional orientation ratio or more.