JP3073914B2 - Multilayer polyester sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer polyester sheet. More specifically, the present invention relates to a multilayered polyester sheet capable of efficiently producing a transparent container having excellent gas barrier properties.

[0002]

2. Description of the Related Art Polyesters, especially polyethylene terephthalate (hereinafter referred to as PET), are excellent in mechanical properties, heat resistance, chemical resistance, dimensional stability and the like.
Widely used as film and plastic. Recently, molded articles made from PET-based sheets are easily moldable and have good transparency, gloss, and mechanical strength. Has been made.

[0003] However, these packaging containers have a disadvantage that they do not have sufficient gas barrier properties against oxygen or the like and cannot be used for applications requiring high gas barrier properties such as food containers and small containers having a long storage period. And its improvement was desired.

On the other hand, polyethylene naphthalate (hereinafter referred to as P
EN) is excellent in heat resistance, weather resistance and gas barrier properties as compared with PET as already known in JP-A-52-45466, and is useful as a resin for producing fibers, films and other molded articles. It is.

[0005] Japanese Patent Application Laid-Open No. 49-1676 discloses that a thickness of 0.
Although a sheet made of PEN having a size of 5 mm or more has been proposed, such a sheet made of PEN is excellent in gas barrier properties, but has an extremely low elongation. Difficult to take,
There is a disadvantage that cracks are easily generated when the sheet is subjected to secondary processing.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of a sheet made of PET as a raw material, to have excellent gas barrier properties, to be able to be wound up at the time of film formation, and to be capable of being used in a container or the like. An object of the present invention is to provide a sheet having excellent workability.

[0007]

Means for Solving the Problems As a result of intensive studies for the purpose of the present inventors, the present inventors have found that by providing a reinforcing layer made of a high-viscosity PET resin on both sides of a main constituent layer made of a PEN resin, the gas barrier property is improved. Excellent, and sheet rewindability,
The inventors have found that a multilayer structure sheet having improved secondary workability is obtained, and have reached the present invention.

That is, the present invention relates to a polyester sheet having a multilayer structure, wherein the polyester layer has a skin layer made of a PET resin having an intrinsic viscosity of 0.8 to 0.9, and a PEN having an intrinsic viscosity of 0.5 to 0.7. a multilayer structure polyester sheet with a core layer made of resin, the weight ratio of the skin layer and the core layer 10: 90-20: about substantially multilayer polyester sheet of unstretched state, which is a 80 Things.

The PET resin used in the present invention includes terephthalic acid or an ester-forming derivative thereof (eg, a lower alkyl ester) and ethylene glycol or an ester-forming derivative thereof (eg, a monocarboxylic acid ester, ethylene oxide). Can be obtained by polycondensation according to the above method, but may contain other copolymer components in a range that does not impair the original physical properties.

Examples of such copolymerizable components include aromatic dicarboxylic acids such as isophthalic acid and naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and alicyclic rings such as 1,4-cyclohexanedicarboxylic acid. Diols such as aromatic dicarboxylic acids, diethylene glycol, 1,4-butanediol, neopentyl glycol, and 1,4-cyclohexanedimethanol; and polyalkylene glycols such as polyethylene glycol and polytetraethylene oxide glycol. The amount of these copolymer components is usually 10 mol% or less, preferably 5 mol%.
It is as follows.

The PEN resin used in the present invention is 2,6
-Obtained by polycondensation of naphthalenedicarboxylic acid or an ester-forming derivative thereof (e.g., a lower alkyl ester) and ethylene glycol or an ester-forming derivative thereof (e.g., a monocarboxylic acid ester ethylene oxide) by a known method. However, other copolymer components in a range not impairing the original physical properties may be contained.

Such copolymerizable components include aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid; aliphatic dicarboxylic acids such as adipic acid and sebacic acid;
-Alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, diethyleneglycol, 1,4-butanediol,
Examples thereof include diols such as neopentyl glycol and 1,4-cyclohexanedimethanol, and polyalkylene glycols such as polyethylene glycol and polytetraethylene oxide glycol. The amount of these copolymer components is usually 10 mol% or less, preferably 5 mol% or less.

In the present invention, the intrinsic viscosity of the PET resin used for the skin layer of the multilayer polyester sheet is 0.8 to 0.9. When the intrinsic viscosity is lower than 0.8, the thermoformed article becomes opaque because the crystallization rate of the obtained sheet is increased. In addition, the production of a PET resin having an intrinsic viscosity higher than 0.9 is not preferable because a long-term solid-state polymerization is required and the production cost increases.

In the present invention, the limiting viscosity of the PEN resin used for the core layer of the multilayer polyester sheet is 0.1.
5 to 0.7. When the intrinsic viscosity is lower than 0.5,
The elongation of the obtained sheet is remarkably reduced, and the production of a PEN resin having an intrinsic viscosity higher than 0.7 requires long-term solid-state polymerization, which is not preferable because the production cost increases.

The multilayer polyester sheet of the present invention is a substantially unstretched sheet obtained by using the above-mentioned composition by ordinary film forming means. The unstretched sheet of the present invention has a density of 1.34 g / cm ³ or less and is substantially amorphous. If the density of the sheet is higher than 1.34 g / cm ³ , the transparency of the sheet is reduced and the impact strength of the sheet is undesirably reduced. Such an amorphous polyester sheet can be obtained by melt-mixing the structure of the present invention with an extruder, discharging the mixture from a general multilayer extrusion die, and quenching with a cooling drum.

The structure of the multilayer structured polyester sheet of the present invention is a three-layer sheet having a skin layer on both sides of a core layer. And the weight ratio of the skin layer and the core layer is 10:90.
２０20: 80 is preferred. If the weight ratio of the skin layer is less than 10%, the elongation of the sheet is significantly reduced, and cracks frequently occur during secondary processing. On the other hand, when the content is more than 20% by weight, the gas composition deteriorates because the weight percentage of the PEN resin is low.

The multilayer structured polyester sheet of the present invention comprises:
As described above, it is a three-layer sheet having skin layers on both sides of the core layer. However, if the ratio of the skin layers on both sides is extremely different, unevenness of the sheet surface becomes remarkable at the time of film formation, which is not preferable. Weight ratio is 40:60 to 50: 5
It is preferable to set the range to 0.

A molded article having excellent gas barrier properties can be obtained from the multilayer structured polyester sheet of the present invention by thermoforming.
In thermoforming, the sheet is heated and softened, pressed against a desired mold to remove air in the gap between the mold and the material, and then adhered to the mold at atmospheric pressure to form the sheet, or the sheet is compressed with compressed air at atmospheric pressure or higher. Pneumatic molding in which the mold is brought into close contact with the mold, and molding using vacuum and compressed air together can be applied.

[0019]

Industrial Applicability The multilayer structured polyester sheet of the present invention can be widely used as a sheet having excellent gas barrier properties, excellent winding properties during film formation, and excellent secondary workability into containers and the like.

[0020]

The present invention will be described in more detail with reference to the following examples. In addition, the measurement of the main physical property value in an Example was performed by the method shown below. (1) Intrinsic viscosity (IV) A sample 0.5 was dissolved in 50 ml of a mixed solvent of 60% by weight of phenol and 40% by weight of 1,1,2,2-tetrachloroethane and measured at 20C. (2) Density (ρ) The sample was immersed in a density gradient tube made of carbon tetrachloride and n-heptane, and measured at 23 ° C. (3) Oxygen permeability Using a sheet piece having a thickness of 500 μm, JIS-K7126
It was measured according to. (4) Elongation JIS-K7113 using a 500 μm thick sheet piece
The elongation at break (%) obtained by measuring according to the above was determined. (5) Transparency (haze) JIS-K6714 using a 500 μm thick sheet piece
It was measured according to.

Examples 1 and 2 Comparative Example 1 A multilayer sheet extruder having an 80 cm wide T-die equipped with three single screw extruders was used.
PEN resin comprising ethylene glycol and 2,6-naphthalenedicarboxylic acid as a core layer and PET having an intrinsic viscosity of 0.85 comprising ethylene glycol and terephthalic acid
A resin having a thickness of 0.
A 5 mm three layer sheet was extruded. The temperature of the cylinder of the extruder was 300 ° C. , the temperature of the T-die was 290 ° C., and the temperature of the cooling roller was 30 ° C. The sheet was wound into a roll, but no break or crack occurred. Table 1 shows the measurement results of the intrinsic viscosity, density, oxygen permeability, elongation, and transparency of the obtained sheet.

Examples 3 and 4 Comparative Example 2 The procedure of Example 1 was repeated except that the intrinsic viscosity was 0.65, which was composed of ethylene glycol and 2,6-naphthalenedicarboxylic acid.
The test was performed in the same manner as in Example 1 except that N resin was used for the core layer and the weight ratio of the skin layer was set to the ratio shown in Table 1. Table 1 shows the results.

Comparative Example 3 In Example 1, the intrinsic viscosity of the same ethylene glycol and terephthalic acid used for the skin layer was 0.85.
The test was performed in the same manner as described in Example 1, except that the PET resin was also used for the core layer. Table 1 shows the results.

Comparative Example 4 The procedure of Example 1 was repeated, except that the same PEN resin having the intrinsic viscosity of 0.50, which was composed of ethylene glycol and 2,6-naphthalenedicarboxylic acid and used for the core layer, was also used for the skin layer. The test was performed in the same manner as described in Example 1.
When the sheet was wound into a roll, the sheet frequently broke. Table 1 shows the results.

[0025]

[Table 1]

Claims (2)

(57) [Claims] 1. A multilayer polyester sheet comprising a skin layer made of polyethylene terephthalate resin having an intrinsic viscosity of 0.8 to 0.9 and a core layer made of polyethylene naphthalate resin having an intrinsic viscosity of 0.5 to 0.7. The multilayer polyester sheet in a substantially unstretched state, wherein the weight ratio of the skin layer to the core layer is from 10:90 to 20:80. 2. An oxygen permeability of 1.0 cc · mm / m ² · day
The multilayer polyester sheet according to claim 1, which has an atm or less.