KR20010055363A - Polyester film having gas-barrier property - Google Patents

Abstract

PURPOSE: A gas blocking polyester film is provided which has excellent basic properties such as mechanical strength, heat-resistance, chemical-resistance and size stability, particularly very good gas isolating property. And it is thus useful as various packing materials, coating materials and protecting materials. CONSTITUTION: The gas blocking polyester film consists of: (i) a first polymer resin layer which is made of polyester having a limit viscosity of 0.55-0.75 deciliter per gram; and (ii) a second polymer resin layer which is laminated on one side of the first polymer resin layer and is made of polyester thermotropic liquid crystalline polymer.

Description

Polyester film having gas-barrier property

The present invention relates to a gas barrier polyester film, and more particularly, has excellent basic properties such as mechanical strength, heat resistance, chemical resistance, and dimensional stability, and in particular, has excellent gas barrier properties, and thus, various packaging materials, coating materials, and protections. A polyester film useful for reuse.

Recently, films or sheets made of gas barrier resins or processed products thereof have been used in place of conventional paper or cellophane as food packaging, various component packaging, coating materials and protective materials. Products made with these gas barrier resins not only have excellent processability and transparency, but also have the advantages of being light and inexpensive. However, the film made of the conventional general-purpose polymer resin has a gas barrier property is limited, so the gas barrier property is inferior to that of the packaging material using glass or metal materials, and thus, the film is limited in application to a packaging field requiring long-term storage. Therefore, studies have been actively conducted to produce films having excellent gas barrier properties while satisfying basic physical properties.

For example, as a water support material for gas barrier films, thermoplastic resins having high crystallinity, that is, ethylene-vinyl alcohol copolymer resins, polyvinyl alcohol resins, polyvinylidene chloride resins, polyamide resins, polyester resins, and the like To provide a film produced using. If the film is made of a resin having a high crystallinity, the gas barrier property may be improved to some extent, but there is a limit. This has been proposed.

For example, US Pat. No. 2,698,240 discloses a method of coating polyvinylidene chloride on a polyester film. US Pat. No. 5,472,792 laminates a copolymerized polyolefin resin and a polyester film to impart gas barrier properties. Is disclosed. However, there is a limit to the gas barrier properties imparted to the film even by such a method, and there is a problem that it must go through post processing. In particular, in case of polyvinylidene chloride-based resin, there is a problem in that environmental hormones such as dioxins are discharged during incineration.

Therefore, the technical problem to be solved by the present invention is to solve the above problems, not only excellent basic properties such as mechanical strength, heat resistance, chemical resistance, dimensional stability, but also particularly excellent gas barrier properties useful for various packaging materials, coating materials and protective materials It is to provide a polyester film.

In order to achieve the above technical problem, the present invention, the first polymer resin layer formed of a polyester having an intrinsic viscosity of 0.55 to 0.75 dl / g; And a second polymer resin layer laminated on one surface of the first polymer resin layer and formed of a polyester-based thermotropic liquid crystal polymer.

In the gas barrier polyester film according to the present invention, the polyester-based thermotropic liquid crystal polymer is a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid or a copolymer of p-hydroxybenzoic acid and ethylene terephthalate. It is preferable to include a copolymer.

In addition, the copolymer of p-hydroxybenzoic acid and ethylene terephthalate is more preferably composed of 60 to 80 mol% of p-hydroxybenzoic acid and 20 to 40 mol% of ethylene terephthalate.

Hereinafter, a gas barrier polyester film and a method of manufacturing the same according to the present invention will be described in more detail.

The present invention, the first polymer resin layer formed of a polyester having an intrinsic viscosity of 0.55 to 0.75 dl / g; And a second polymer resin layer laminated on one surface of the first polymer resin layer and formed of a polyester-based thermotropic liquid crystal polymer.

It is a feature of the present invention to orient the crystals of the resin molding of the film uniaxially in order to impart high gas barrier properties to the film. The most important factors for high gas barrier films are the crystallinity and orientation of the films. In the present invention, in order to optimize the crystallization element, the polyester polymer having a thermal orientation of 0.55 to 0.75 dl / g is formed of a first polymer resin layer and has molecular orientation in molten state on one surface of the first polymer resin layer. By forming the liquid crystal polymer into the second polymer resin layer, a polyester film having high gas barrier property is provided.

Polyester constituting the first polymer resin layer of the present invention is ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-propanediol, 1,4-butanediol, 2-methyl-1, Polyhydroxy and terephthalic acid, isophthalic acid such as 5-pentanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, para-xylene glycol, bisphenol A-ethylene glycol, polytetramethylene glycol, polytetramethylene oxide glycol Esters using dicarboxylic acids such as ortho-phthalic acid, phthalic acid, 4,4'-diphenyldicarboxylic acid, 5-sodium-sulfo-isophthalic acid, para-hydroxybenzoic acid, sobaic acid After carrying out the polymerization or transesterification, it can be prepared by condensation polymerization at high temperature and high pressure. It is preferable that the intrinsic viscosity of the polyester is 0.55 to 0.75 dl / g. If the intrinsic viscosity is lower than 0.55 dl / g, the crystallization of the polymer proceeds too fast and the molecular weight is small so that the workability such as breaking or tearing in the film state is poor. If the intrinsic viscosity is greater than 0.75dl / g, the molecular weight of the polymer is too large, making the resin itself difficult, and it is difficult to obtain a uniform sheet due to the high viscosity when forming the film.

The first polymer resin layer is preferably formed of any one resin selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate. These resins are physicochemically stable, have good mechanical strength, and have good heat resistance, durability, chemical resistance, and dimensional stability.

In forming the 1st polymer resin layer of this invention, an inorganic fine particle can be added in order to give glossiness and processability of a film. These inorganic fine particles have a refractive index similar to that of polyester and have less voids formed inside the film to improve transparency, and form appropriate protrusions on the surface of the film so that the reflection of light is somewhat irregular so that the kind and amount of addition are not shiny. I can regulate it.

Titanium dioxide, calcium carbonate, barium sulfate, silica, talc, zeolite and the like can be used as the inorganic particles, and silica is particularly preferable.

The average particle diameter of the inorganic particles is preferably 2.0 to 6.5 µm using silica as an example, and the amount of the inorganic particles added is more preferably 0.5 to 3.5% by weight based on the total weight of the first polymer resin layer. If the added amount of the inorganic particles is less than 0.5% by weight, the transparency of the film is good, but the glossiness increases, and thus the slipperiness between films decreases, resulting in poor film formability. If the added amount of the inorganic particles exceeds 3.5% by weight, the glossiness is appropriate, but the light transmittance is lowered. Considering the light transmittance and glossiness of the film, the addition amount of the most preferable inorganic particles, especially silica is 1.0 to 2.0% by weight and the average particle diameter is 3.0 to 5.0㎛. Such glossiness and light transmittance are not particularly limited because the desired degree varies depending on the color or pattern of the adherend or individual. However, in the case of light colors, the light transmittance is 75 to 95% and the glossiness is about 30 to 50%. The color of the adherend is also enhanced and there is little glare or eye fatigue.

The second polymer resin layer of the present invention is formed of a polyester-based thermotropic liquid crystal polymer and has a high gas barrier property.

Thermotropic liquid crystal polymer is a polymer that forms a liquid crystal state according to temperature change, and can be melt-molded and has excellent mechanical properties such as high strength, high elasticity, and low linear thermal expansion coefficient. In particular, since the polyester-based thermotropic liquid crystal polymer has a rod-like form in which the repeating unit of the monomer is linear, it has mechanical anisotropy and excellent crystal orientation. The film has a gas barrier property of 200 to 300 times better than that of a conventionally used polyester film such as polyethylene terephthalate film. However, there is a problem in film formability in forming a film using a polyester-based thermotropic liquid crystal polymer alone, but in the present invention, the polyester-based thermotropic liquid crystal polymer is laminated on a first polymer resin layer made of a conventional polyester, It was intended to produce a film with high gas barrier properties.

The polyester-based thermotropic liquid crystal polymer forming the second polymer resin layer of the present invention preferably includes a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid represented by the following formula (1).

In Formula 1, x and y are the moles of p-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA), respectively.

As the copolymer of Chemical Formula 1 used as the thermotropic liquid crystal polymer of the present invention, for example, a copolymer having x and y of 73 mol% and 27 mol% may be used.

In addition, a copolymer of p-hydroxybenzoic acid represented by the following formula (2) and ethylene terephthalate may be used as the polyester-based thermotropic liquid crystal polymer forming the second polymer resin layer of the present invention.

In Formula 2, x and y are the moles of p-hydroxybenzoic acid (HBA) and ethylene terephthalate (ET), respectively.

The copolymer of p-hydroxybenzoic acid and ethylene terephthalate is more preferably composed of 60 to 80 mol% of p-hydroxybenzoic acid and 20 to 40 mol% of ethylene terephthalate.

Thus, as the polyester-based thermotropic liquid crystal polymer forming the second polymer resin layer of the present invention, for example, Vectra A 950 from Hoechst Celanese, Rodrun 5000 and 3000 from Unitika, etc. And DuPont's HX.

The thickness of the gas barrier polyester film of the present invention is not particularly limited and may vary depending on the use thereof, but is preferably 10 to 38 μm. In addition, the thickness ratio of the first polymer resin layer and the second polymer resin layer is not particularly limited, but is preferably 4: 1 to 8: 1 in consideration of gas barrier properties and film properties.

The gas barrier polyester film of the present invention can be produced, for example, by the following method.

Polyester resins having an intrinsic viscosity of 0.55 to 0.75 dl / g prepared by condensation polymerization of an acid component and a diol component in a conventional manner, p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid or p-hydroxybenzoic acid and ethylene Copolymers obtained by copolymerizing terephthalate are formed and melted, respectively, and these are laminated in two layers in a feed block and discharged through an extrusion die. Subsequently, the first polymer resin layer is used as a drum surface in a cooling drum and cooled while being electrostatically applied. The sheet thus produced is biaxially stretched sequentially according to the draw ratio required for the product according to the application. In addition, in some cases, the heat setting step may be further performed to further increase the crystallinity and orientation of the second polymer resin layer while maintaining the physical properties of the first polymer resin layer. Considering the processability of the film, the melting point of the polyester forming the first polymer resin layer of the present invention is preferably 200 to 250 ℃, the melting point of the thermotropic liquid crystal polymer forming the second polymer resin layer is 220 to 280 ℃. Is preferred.

In order to obtain the desired high gas barrier property in manufacturing the gas barrier polyester film of this invention, it is necessary to consider the following conditions in order to raise the crystallinity degree and orientation degree of a film.

First, the amorphous tie molecules of the polymer forming the first polymer resin layer and the second polymer resin layer should be elongated.

Second, the polymer crystals constituting the second polymer resin layer should be uniaxially oriented.

Third, the crystallinity of the polymer resin forming the film should not be lowered.

Therefore, the forming temperature of the film must be lower than the melting point of the crystal region and higher than the glass transition temperature of the amorphous region.

Forming with a roll at a temperature higher than the melting point of the crystal region is well known in the art, such as roll extrusion, but according to this method, since the crystal region is stretched at the melting temperature, the degree of crystal orientation is lowered. It is not suitable for producing the film of the invention. That is, forming the film at an excessively high or low temperature is limited in improving gas barrier properties. It is good film formability to increase the forming temperature to be close to the melting point between the melting point and the glass transition temperature, but since the melting point of the polymer does not appear clearly compared to the low molecule, a part of the crystal may melt even below the melting point. Therefore, it is preferable to perform shaping | molding of a film about 10 degrees C or less than crystallization temperature.

The preferable range of the elongation of a film can be determined considering the following points.

Microscopic deformation mechanisms of crystalline (strictly semicrystalline) resins include deformation of the amorphous regions (stretching relaxation), rotation and reorientation of the crystal regions, shear deformation of the crystal regions (tilting), molecular slips of Thai molecules in the crystal regions, and It is performed in the order of separation or segregation of crystal regions. The sequence of steps in these micro processes takes place at a temperature between the melting point and the glass transition temperature. In the film of the present invention, it is preferable that the initial deformation mechanism of the deformation mechanism, that is, deformation of the amorphous region (relaxation) and rotation and reorientation of the crystal region are sufficiently performed. In other words, insufficient stretching results in insufficient rotation in the crystal region, resulting in unsatisfactory gas barrier properties. When the stretching is excessive, the molecular slip of amorphous molecules is initiated from the crystal region and the crystal separation is performed, thereby reducing the crystallinity. Therefore, the gas barrier property of the film is also lowered.

In consideration of this point, the draw ratio of the film according to the present invention is set based on the degree of orientation of the film, in particular, the degree of orientation of the polyester-based thermotropic liquid crystal polymer which is a constituent of the second polymer resin layer. desirable.

When extending | stretching in the width direction after extending | stretching in the longitudinal direction according to sequential stretching, the extending | stretching temperature of the longitudinal direction is normally preferable to 90-100 degreeC, If extending | stretching temperature is lower than this, extending | stretching of a 1st polymer resin layer is uneven, and extending | stretching If the temperature is higher than this, the molecular orientation of the second polymer resin layer may be lowered. The stretching temperature at the time of stretching in the width direction should be in harmony with the stretching temperature in the longitudinal direction, but is preferably 120 to 140 ° C.

In addition, a heat setting step may be further performed to increase the thermal stability, crystallinity, molecular orientation, and gas barrier properties of the film, and it is preferable to perform about 5 to 10 seconds at 180 to 250 ° C.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, it is a matter of course that the scope of the present invention is not limited to the following examples.

EXAMPLE

Example 1

Terephthalic acid as a dicarboxylic acid component and ethylene glycol as a diol component were mixed in a 1: 2 equivalent ratio, and then 0.07% by weight of a conventional polycondensation catalyst and silica having an average particle diameter of 1.5 µm were added to the mixture to complete the polycondensation reaction. To prepare a polyester having an inherent viscosity of 0.64 dl / g.

Vectra, Hoechst Celaness, a copolymer of 73 mol% p-hydroxybenzoic acid and 27 mol% 6-hydroxy-2-naphthoic acid, which is a thermotropic liquid crystal polymer forming a second polymer resin layer. A 950 (Vectra A950) was used.

The two resins were melted and extruded through two extruders, laminated in two layers in a feed block, and then stretched 3.6 times in the length direction and 4.0 times in the width direction using a conventional T-die and a biaxial stretching apparatus. Subsequently, heat setting was performed at 220 ° C. to prepare a biaxially stretched coextruded polyester film having a thickness of 12 μm.

Example 2

A thermotropic liquid crystal polymer forming the second polymer resin layer except that Rodika 5000 manufactured by Unitika, which is a copolymer composed of 80 mol% p-hydroxybenzoic acid and 20 mol% ethylene terephthalate, is used. Then, a film was prepared in the same manner as in Example 1.

Example 3

A thermotropic liquid crystal polymer for forming the second polymer resin layer, except that Rodran 3000 manufactured by Unitika, which is a copolymer composed of 60 mol% of p-hydroxybenzoic acid and 40 mol% of ethylene terephthalate, was used. Then, a film was prepared in the same manner as in Example 1.

Examples 4-5

Films were prepared in the same manner as in Example 1, except that Xydra and Dupont's HX, each of which was used as the thermotropic liquid crystal polymer forming the second polymer resin layer, were used. It was.

Comparative Example 1

After mixing terephthalic acid as a dicarboxylic acid component and ethylene glycol as a diol component in a 1: 2 equivalent ratio, a polycondensation reaction was completed by adding a conventional polycondensation catalyst to the mixture to prepare a chip, followed by a melt extrusion process. After the amorphous sheet was prepared. Subsequently, the amorphous sheet was stretched 3.6 times at 100 ° C. in the longitudinal direction and then stretched 4.0 times at 130 ° C. in the lateral direction (width direction). Then, heat setting was performed at 230 ° C. for 7 seconds to prepare a single layer polyester film having a thickness of 12 μm.

Comparative Example 2

A water-soluble composition obtained by dispersing a polyvinylidene chloride emulsion in water at a concentration of 20.0% by weight on one surface of an amorphous sheet prepared in the same manner as in Comparative Example 1 at 3.6 ° C. in a longitudinal direction was applied by a Meyer bar coating method. Subsequently, the film was stretched 4.0 times at 130 ° C. in the transverse direction and then heat-set at 230 ° C. for 7 seconds to prepare a polyvinylidene chloride coated polyester film having a thickness of 12 μm.

Comparative Example 3

After preparing a single-layer polyester film having a thickness of 9 ㎛ in the same manner as in Comparative Example 1, using a conventional extrusion coating method on one side was prepared a film laminated with a 3 ㎛ ethylene vinyl alcohol copolymer film.

Comparative Example 4

A polyvinyl alcohol film was laminated in the same manner as in Comparative Example 4 except that polyvinyl alcohol was used instead of the ethylene vinyl alcohol copolymer.

Comparative Example 5

After preparing a single-layer polyester film having a thickness of 9 μm by the same method as in Comparative Example 1, laminate a propylene / butadiene-1 copolymer (REXTAC of Rexene Co. of USA) film on one surface thereof using a conventional dry lamination method. To prepare a 12 μm polyester-propylene / butadiene-1 copolymer lamination film.

Oxygen permeability and moisture permeation rate of the films prepared according to the above Examples and Comparative Examples were measured using the OX-TRAN apparatus of MOCON, according to ASTM 1434 and ASTM F 372, the results are shown in Table 1.

Oxygen Permeability (cm3 / m2.24hr.atm) Moisture permeability (g / ㎡.24hr) Example 1 4.5 3.4 Example 2 5.8 3.9 Example 3 7.1 4.5 Example 4 5.5 3.0 Comparative Example 5 5.4 2.9 Comparative Example 1 40.0 30.0 Comparative Example 2 11.0 11.0 Comparative Example 3 32.3 2.1 Comparative Example 4 35.4 5.7 Comparative Example 5 24.1 19.4

Referring to Table 1, the polyester film of the present invention laminated the second polymer resin layer made of a polyester thermotropic liquid crystal polymer was low in oxygen permeability and moisture permeability was excellent gas barrier properties. This is presumably because the crystallinity and crystal orientation of the thermotropic liquid crystal polymer forming the second polymer resin layer are large, and thus the gas barrier property is improved.

On the other hand, in the case of the polyester film coated with polyvinylidene chloride of Comparative Example 2, the oxygen permeability and moisture permeability are significantly improved compared to the general single-layer polyester film of Comparative Example 1, but environmental pollution due to dioxin generated during decomposition of the film The problem is serious, the film according to Comparative Examples 3 to 5 is expensive and there is a problem that the gas barrier properties change depending on the relative humidity.

As described above, the polyester film laminated with the second polymer resin layer made of the polyester-based thermotropic liquid crystal polymer according to the present invention is not only excellent in basic properties such as mechanical strength, heat resistance, chemical resistance, dimensional stability, in particular, It has excellent gas barrier property and is useful for various packaging materials, coating materials and protective materials.

Claims (9)

A first polymer resin layer formed of polyester having an intrinsic viscosity of 0.55 to 0.75 dl / g; And And a second polymer resin layer laminated on one surface of the first polymer resin layer and formed of a polyester-based thermotropic liquid crystal polymer. The gas barrier polyester film of claim 1, wherein the first polymer resin layer is formed of any one resin selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. The gas barrier polyester film of claim 1, wherein the first polymer resin layer comprises at least one inorganic particle selected from the group consisting of titanium dioxide, calcium carbonate, barium sulfate, silica, talc, and zeolite. . The gas barrier polyester film of claim 3, wherein the inorganic particles are present in an amount of 0.5 to 3.5 wt% based on the total weight of the first polymer resin layer. The gas barrier polyester film of claim 1, wherein the polyester-based thermotropic liquid crystal polymer comprises a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. The gas barrier polyester film of claim 1, wherein the polyester-based thermotropic liquid crystal polymer comprises a copolymer of p-hydroxybenzoic acid and ethylene terephthalate. The gas barrier polyester according to claim 6, wherein the copolymer of p-hydroxybenzoic acid and ethylene terephthalate is composed of 60 to 80 mol% of p-hydroxybenzoic acid and 20 to 40 mol% of ethylene terephthalate. film. The thermotropic liquid crystal polymer of claim 1, wherein the polyester-based thermotropic liquid crystal polymer is at least one selected from the group consisting of Vectra A. 950 of Hoechst Celanese, Rodrun 5000 and 3000 of Unitika. Gas-blocking polyester film made into. The gas barrier polyester film of claim 1, wherein a thickness ratio of the first polymer resin layer and the second polymer resin layer is 4: 1 to 8: 1.