KR100611845B1 - Biaxially oriented polyester film having good cold-resistance and preparation thereof - Google Patents

Abstract

The present invention relates to a biaxially oriented polyester film having excellent flexibility and cold resistance, and a method for producing the same, which is prepared from a polyester resin containing 1,3-propanediol in an amount of 60 mol% or more in all diol components, and has a storage modulus (E ', -20 to 5 ℃ temperature range) is a polyester film of the present invention, characterized in that 0.5 × 10 ⁹ to 4.0 × 10 ⁹ Pa is excellent in flexibility, cold resistance, puncture strength, impact resistance and pinhole resistance, etc. Or as a refrigerated food packaging material.

Description

Biaxially oriented polyester film having excellent cold resistance and manufacturing method thereof {BIAXIALLY ORIENTED POLYESTER FILM HAVING GOOD COLD-RESISTANCE AND PREPARATION THEREOF}

The present invention relates to a biaxially oriented polyester film excellent in flexibility and cold resistance and useful as a packaging material for frozen or refrigerated foods and a method for producing the same.

Most polymer films deteriorate from room temperature and rapidly harden to lower mechanical properties. As a representative example, biaxially oriented polyethylene terephthalate (PET) film is useful as a packaging material because it has excellent printability, processability, heat resistance, dimensional stability, and deposition property, but at low temperatures, stiffness is increased to increase the resistance to pitting and resistance. Impact resistance and pinhole resistance rapidly decrease.

In addition, polyolefin-based cast polypropylene (CPP) film, which is useful as a sealant film, has excellent heat resistance and is suitable for food retort pouches. Biaxially oriented nylon films have been widely used as packaging materials because of their high flexibility. Both of them have the drawback that the deterioration of physical properties at low temperatures occurs frequently and is frequently ruptured when applied to the packaging of processed foods stored and transported at low temperatures.

Accordingly, as a film having further improved flexibility, Japanese Patent Application Laid-Open No. 2000-63537 has a biaxially oriented film having a thickness direction refractive index (Nz) of 1.570 or less and a density of 1.315 g / cm ³ or more, mainly comprising polytrimethylene terephthalate. However, in the film forming method according to the embodiment, the elastic modulus is too high to obtain a film having low flexibility, and as a result, the film is not suitable for low temperature storage.

Japanese Patent Application Laid-Open No. 2000-63538 also proposes a Young's modulus of 110 kg / mm ² or more and an elongation of bidirectional fracture of 90% or more in producing a biaxially oriented film mainly composed of polytrimethylene terephthalate having excellent flexibility. The film forming method according to the example has a problem that a film having low flexibility and pinhole resistance is obtained by having a Young's modulus of 300 kg / mm ² or more and having a rigidity of almost PET level.

Therefore, the object of the present invention is to focus on the fact that cold resistance is directly related to flexibility, and that flexibility is directly related to the storage modulus that viscoelastic polymers may have, and thus the basic properties of the film (moisture resistance, printability, dimensional stability, processability) Of course, there is provided a polyester film that can be usefully used as a frozen or refrigerated food packaging material having excellent flexibility, cold resistance (flexibility at low temperature), puncture resistance, impact strength, and pinhole resistance, and a method of manufacturing the same.

In order to achieve the above object, in the present invention, a storage elastic modulus (E ') prepared from a polyester resin containing 1,3-propanediol in an amount of 60 mol% or more in all the diol components and in a temperature range of -20 to 5 ° C. The biaxially-oriented polyester film which is this 0.5 * 10 <^9> -4.0 * 10 <^9> Pa is provided.

The present invention will be described in more detail below.

According to a preferred embodiment of the present invention, the biaxially oriented polyester film is prepared by the film composition having the composition, and then melt-extruded and quenched and solidified to obtain an unstretched sheet, which is 9 to 16 times the stretched surface ratio (final margin). Mystery x transverse stretching ratio) and a transverse stretching speed of 30 to 90 times / min, followed by heat setting.

In the biaxially oriented polyester film composition according to the present invention, 1,3-propanediol is contained in the total diol component of 60 mol% or more, preferably 70 mol% or more. When 1,3-propanediol is contained in less than 60 mol%, flexibility falls and the impact strength, puncture strength, and pinhole strength at low temperatures are poor.

Polyester film according to the present invention, in addition to 1,3-propanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), dipropanediol, diethylene glycol, triethylene glycol, weight average molecular weight 200 40 mol% or less of polyethylene glycol, 1,4-butanediol, 2-methyl-1,3-propanediol, 1,4-cyclohexanedimethanol, propylene glycol and the like within a range of not impairing flexibility By including it, it is possible to control the crystallization rate and lower the storage modulus.

In addition, as the acid component forming the polyester, terephthalic acid, naphthalenedicarboxylic acid, isophthalic acid, a linear aliphatic divalent acid having two or more methyl groups (eg, succinic acid, glutaric acid, adipic) Acids (adipic acid, suberic acid, azelaic acid, sebacic acid and ester derivatives thereof) and mixtures thereof can be used.

The composition of the polyester film of the present invention can be achieved by copolymerizing each monomer component or blending polymers. Moreover, additives, such as a crosslinking agent, antioxidant, a heat stabilizer, and a ultraviolet absorber, can be added in a normal amount in the range which does not impair the objective of this invention.

The film according to the invention is produced as follows. First, a polyester resin of a suitable composition is melt-extruded and quenched and solidified to obtain an unstretched sheet, and the unstretched sheet has a stretch surface ratio of 9 to 16 times (long stretch ratio x transverse stretch ratio) and 30 to 90 times / min, preferably Preferably, the film is drawn at a transverse stretching speed of 40 to 60 times / minute. At this time, you may carry out by either the method of sequential biaxial or simultaneous biaxial stretching. Regarding the longitudinal stretching speed, in the case of sequential stretching, it is difficult to express it in the concept of speed, and in the case of simultaneous stretching, it almost coincides with the transverse stretching speed. If the drawn surface magnification is lower than 9 times, the mechanical properties are lowered, so that the impact strength and the puncture strength are poor, and when the drawn surface magnification is higher than 16 times, breakage occurs frequently and the thickness is uneven. Further, when the stretching speed in the lateral direction is slower than 30 times per minute, the productivity is lowered, and when it is faster than 90 times per minute, the orientation crystallinity is sharply increased in the stretching direction, thereby increasing the rigidity of the film and decreasing the flexibility.

In order to impart dimensional stability after stretching, cooling is performed after heat setting the stretched film, but heat setting is generally performed at a temperature of 30 to 50 ° C. lower than the resin melting temperature, but in the present invention, heat treatment is performed at a temperature close to the melting point. The heat setting is performed at a temperature of 10 to 30 ° C. lower than the resin melting temperature in order to lower the heat shrinkage rate and to re-freeze the crystals to increase elongation and improve flexibility. If the heat setting temperature is lower than 30 ° C compared to the resin melting temperature, the heat shrinkage rate is high, resulting in poor dimensional stability, resulting in a problem of inconsistency in printing. If the temperature is lower than 10 ° C compared to the resin melting temperature, crystallization by heat Progresses rapidly, the mechanical properties are drastically deteriorated, and the fracture property is deepened, resulting in poor productivity.

Thus prepared, the biaxially oriented polyester film of the present invention having a polytrimethylene terephthalate as a main component may have a thickness of 7 to 30㎛, but is not limited thereto.

The polyester film according to the present invention has a storage modulus (E ′) in the temperature range of −20 to 5 ° C. of 0.5 × 10 ⁹ to 4.0 × 10 ⁹ Pa, preferably 1.0 × 10 ⁹ to 3.0 × 10 ⁹ Pa . Furthermore, in the film of the present invention, the amount of change in storage modulus (ΔE ', absolute value of the difference in modulus at 20 ° C and -20 ° C) between 20 ° C and -20 ° C is 0.4 x 10 ⁹ Pa or less, preferably 0.3 x 10 ⁹ Pa or less. The film of the present invention not only has a low storage modulus but also does not increase rapidly at low temperatures, thereby maintaining flexibility at low temperatures.

If the storage modulus is less than 0.5 × 10 ⁹ Pa, the resistance to mechanical stress is insufficient in the printing and laminating process, so that breakage occurs during driving and wrinkles occur in the driving direction, and 4.0 × 10 ⁹ If the thickness is larger than Pa, the film has high rigidity, and thus the flexibility is reduced, thereby reducing the pinhole resistance and the puncture resistance.

In addition, if the change in storage modulus (ΔE ') between 20 ° C and -20 ° C is greater than 0.4 × 10 ⁹ Pa, the pinhole strength, impact strength, and sting strength at low temperatures all drop rapidly, so that the holes are easily drilled at low temperatures. Torn.

As described above, the biaxially oriented polyester film of the present invention is not only basic properties such as moisture resistance, printability, dimensional stability, processability, but also flexibility, cold resistance (flexibility at low temperature), puncture resistance, impact resistance, pinhole resistance, etc. It is excellent in that it can be usefully used as a frozen or refrigerated food packaging material. In addition, the film of the present invention may be used as a packaging material by laminating one or more various polyester or olefin film layers thereon.

Through the following examples and comparative examples will be described in more detail the present invention. However, the following examples are not intended to limit the invention only.

Preparation Example 1 Preparation of Polymer A

130 mole parts of 1,3-propanediol were added to an esterification reactor with respect to 100 mole parts of terephthalic acid, and tributylene titanate was added at 0.07% by weight relative to terephthalic acid as a catalyst, followed by esterification. Trimethyl phosphate as a stabilizer was added 0.06% by weight to terephthalic acid as a stabilizer, and silica particles having an average particle diameter of 2.5 μm were added as a slip agent to 0.07% by weight with respect to terephthalic acid, followed by polycondensation reaction under high vacuum to carry out polytrimethylene terephthalate. (Polymer A) was obtained by pellets.

Preparation Example 2 Preparation of Polymer B

The same method as in Preparation Example 1, except that 100 mol parts of 1,3-propanediol and 25 mol parts of 2-methyl-1,3-propanediol were used as the diol component (about 80 mol% of 1,3-propanediol). Was carried out to obtain 2-methyl-1,3-propanediol copolymerized polytrimethylene terephthalate (polymer B) as a pellet.

Preparation Example 3 Preparation of Polymer C

As polybutylene terephthalate, LUPOX HV-1010 manufactured by LG Chem was used.

Example 1

Polymer A (melting point: 225 ° C.) obtained in Preparation Example 1 was dried at 160 ° C. for 3 hours and melt-extruded at 245 ° C. to prepare an amorphous sheet on a cooling roll maintained at 20 ° C. The amorphous sheet was stretched 2.8 times in the longitudinal direction using the circumferential speed difference between the rolls maintained at 55 ° C, and then stretched 3.6 times in the transverse direction at 60 ° C at 40 times per minute in a transverse stretching apparatus, and then opened at 200 ° C. It cooled, and cooled at 40 degreeC, and obtained the biaxially-oriented polyester film of thickness 15micrometer.

Comparative Examples 1 to 3

A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the longitudinal and transverse draw ratios, the transverse draw speeds, and the heat setting temperatures were changed as shown in Table 1 below.

Example 2

The polymers A and B obtained in Production Examples 1 and 2 were mixed at 25% by weight and 75% by weight, respectively (about 85 mol% of 1,3-propanediol) (melting point of the mixture: 205 ° C) and dried at 160 ° C for 3 hours. After melt extrusion at 235 ℃ to prepare an amorphous sheet on a cooling roll maintained at 20 ℃. The amorphous sheet was stretched 2.8 times in the longitudinal direction using the circumferential speed difference between the rolls held at 65 ° C, and then stretched 3.6 times in the transverse direction at 40 ° C per minute in 70 ° C and then opened at 190 ° C. It cooled, and cooled at 40 degreeC, and obtained the biaxially-oriented polyester film of thickness 15micrometer.

Comparative Example 4

A biaxially oriented polyester film was obtained in the same manner as in Example 2 except that the longitudinal and transverse draw ratios, the transverse draw speeds, and the heat setting temperatures were changed as shown in Table 1 below.

Example 3

Amorphous sheets were prepared in the same manner as in Example 2, cut into 9 cm and 9 cm horizontally and vertically, respectively, and mounted in a simultaneous biaxial stretching machine (Toyoseiki Co., Ltd.), followed by injecting hot air at 75 ° C. in the longitudinal direction. And 3.8 times each in the transverse direction were stretched at a rate of 60 times per minute to obtain a film. The obtained film was mounted on a heat setting mold and heat-fixed in a 210 ° C. air circulation oven for 15 seconds and then cooled at 40 ° C. to obtain a biaxially oriented polyester film having a thickness of 15 μm.

Example 4

The polymers A and C obtained in Production Examples 1 and 3 were mixed at 70% by weight and 30% by weight, respectively (about 70 mol% of 1,3-propanediol) (melting point of the mixture: 220 ° C) and dried at 160 ° C for 3 hours. After melt extrusion at 240 ℃ to prepare an amorphous sheet on a cooling roll maintained at 20 ℃. The amorphous sheet was stretched 3.3 times in the longitudinal direction using the circumferential speed difference between the rolls maintained at 60 ° C, and then stretched 3.8 times in the transverse direction at a rate of 50 times per minute at 65 ° C in a transverse stretching apparatus, and then opened at 195 ° C. It cooled, and cooled at 40 degreeC, and obtained the biaxially-oriented polyester film of thickness 15micrometer.

Comparative Example 5

A biaxially oriented polyester film was obtained in the same manner as in Example 4 except that the longitudinal and transverse draw ratios, the transverse draw speeds, and the heat setting temperatures were changed as shown in Table 1 below.

Test Example

Properties of the films prepared in Examples 1 to 4 and Comparative Examples 1 to 5 were measured as follows, and the results are shown in Table 1 below.

(1) storage modulus

Dynamic mechanical analyzer The elastic modulus of the sample film was measured using a TA Instrument DMA SS6100 (Seiko Co., Ltd.) at a frequency of 1H z and a heating rate of 10 ° C / min in a stress mode. At this time, the storage modulus (E ') in the temperature range of -20 ° C to 5 ° C and the absolute value of the difference between the storage modulus values at 20 ° C and -20 ° C were taken to determine the amount of change in the modulus of elasticity (ΔE').

(2) Pinhole resistance

Using Gelbo Flex of Gelbo, USA, the sample film was rotated and reciprocated 2700 times (about 60 minutes) at a rotation angle of 420 degrees at room temperature. Subsequently, the sample film was laid flat on the white paper, the oil ink was applied using the doctor blade on the film, and the ink dots appearing on the white paper were counted as the number of pinholes when the film was removed. At this time, the average value obtained by repeating 3 times for each sample was taken.

(3) unit shock absorption energy

Measurements were made in accordance with ASTM D3420, and the apparatus used a Film Impact Tester manufactured by Toyoseiki. Pendulum Tip used a hemispherical shape with a diameter of 1 inch, the sample film was mounted on a sample stage having a circular hole of about 50mm in diameter. The impact absorption energy (kgf-cm) measured in this way was divided into the thickness (micrometer) of a sample film, and it was set as unit shock absorption energy (kgf-cm / micrometer). At this time, 10 times was measured for each sample, and the average value was taken.

(4) inner stick strength

Measurements were made in accordance with ASTM D882, and the apparatus used UTM (Shimadzu AGS-500D, compression mode). A tip having a diameter of 1 mm was used, and the compression speed was set to 50 mm / min to obtain the puncture resistance (kgf). At this time, 10 times was measured for each sample, and the average value was taken.

From the results of Table 1, in the embodiment according to the present invention, the desired film excellent in flexibility, cold resistance (flexibility at low temperature), shock absorption energy, pinhole resistance, puncture strength, etc. of the film can be obtained. In case of departing from the scope of the invention (comparative example) it can be seen that the physical properties are very poor.

As described above, the biaxially oriented polyester film according to the present invention is excellent in flexibility, cold resistance, puncture strength, impact resistance and pinhole resistance, and thus may be usefully used as a frozen or refrigerated food packaging material.

Claims (9)

It is made from a polyester resin containing at least 60 mol% of 1,3-propanediol in the total diol component, and has a storage modulus (E ′) of 0.5 × 10 ⁹ to 4.0 × 10 ⁹ Pa in the temperature range of -20 to 5 ° C. Phosphorus, biaxially oriented polyester film. The method of claim 1, A biaxially oriented polyester film, wherein the amount of change in storage modulus (ΔE ′) between 20 ° C. and −20 ° C. is 0.4 × 10 ⁹ Pa or less. The method of claim 1, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), dipropanediol, diethylene glycol, triethylene glycol, polyethylene glycol having a weight average molecular weight of 200 to 100,000, 1,4-butanediol, A biaxially oriented polyester, characterized in that the diol component selected from the group consisting of 2-methyl-1,3-propanediol, 1,4-cyclohexanedimethanol, propylene glycol, and mixtures thereof is contained in 40 mol% or less. film. After melt-extruding the polyester resin which contains 1, 3- propanediol in 60 mol% or more in all the diol components, the obtained sheet | seat is 9-16 times the stretch surface magnification (longitudinal draw ratio x transverse mystery), and 30-90 times The manufacturing method of the biaxially-oriented polyester film of Claim 1 which includes heat-setting after extending | stretching at the lateral stretch rate of / min. The method of claim 4, wherein Heat-setting at a temperature of 10 to 30 DEG C lower than the resin melting temperature. The method of claim 4, wherein Sequential biaxial stretching or simultaneous biaxial stretching during stretching. A packaging material comprising the biaxially oriented polyester film according to any one of claims 1 to 3. The method of claim 7, wherein A packaging material comprising the biaxially oriented polyester film as a base layer, and further comprising a polyester or olefin film layer thereon. The method of claim 7, wherein A packaging material used for the packaging of refrigerated or frozen food.