JP2697224B2 - Rolled polyethylene terephthalate sheet, method for producing the same, and molded product thereof - Google Patents

Description

The present invention relates to a polyethylene terephthalate sheet having excellent heat resistance, transparency, impact resistance and thermoformability, a method for producing the same, and a transparent sheet obtained by thermoforming the sheet. The present invention relates to various molded articles, which can be usefully used as building materials and packaging containers.

[Conventional technology]

Conventional biaxially stretched films of polyethylene terephthalate have excellent heat resistance, transparency, and impact resistance, and are widely used in many applications such as base films for magnetic tapes. However, since such a biaxially stretched film has a high degree of molecular arrangement, it is difficult to perform three-dimensional shaping by thermoforming. On the other hand, an unstretched sheet obtained by extruding polyethylene terephthalate is excellent in thermoformability, but inferior in both heat resistance and impact resistance. For example, a container thermoformed from an unstretched sheet loses its shape when boiling water is added. For this reason, thermoforming and sufficient heat are applied to perform dimensional stabilization processing and are used as trays for microwave ovens.However, such containers have transparency due to crystallization generated during dimensional stabilization processing. Will be lost. Also, it has only insufficient properties in terms of impact resistance.

Therefore, in order to obtain a sheet excellent in heat resistance, transparency, impact resistance, and thermoformability, it is necessary to use an amorphous polymer having a high glass transition temperature, for example, a considerably expensive polymer such as polycarbonate and polysulfone. The current situation is that it cannot be obtained.

[Problems to be solved by the invention]

The present invention uses polyethylene terephthalate, a fairly inexpensive polymer widely used for synthetic fibers, films, bottles, and the like, and provides a sheet having excellent heat resistance, transparency, impact resistance, and thermoformability, and a method for producing the same. And a thermoformed product of the sheet.

[Means for solving the problem]

The present invention is a polyethylene terephthalate temperature tα showing the maximum value of the tan δ of dynamic elongation viscoelasticity defined in the following text of the polyethylene terephthalate is 84 ° C. or more, and the elongation strength ratio in one direction and the direction perpendicular thereto is 0.5 The present invention provides a transparent sheet having a thickness of from 2.0 to 2.0, a method for producing the same, and a transparent molded article obtained by thermoforming the sheet.

The polyethylene terephthalate referred to in the present invention is not limited to polyethylene terephthalate alone, but may be a copolymer containing 85 mol% or more of ethylene terephthalate units and 15 mol% or less of a different chemical structural unit, and greatly increases transparency. It may be a polymer blend or a polymer alloy containing polyethylene terephthalate as a main component and containing a heterogeneous polymer to such an extent as not to be lost.

As the copolymerizable component that can be used to form the copolymer, a part of terephthalic acid is isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylethanedicarboxylic acid, diphenyletherdicarboxylic acid, diphenylsulfone. Aromatic dicarboxylic acids such as dicarboxylic acids, alicyclic dicarboxylic acids such as hexahydroterephthalic acid and hexahydroisophthalic acid, aliphatic dicarboxylic acids such as adipic acid, sebacic acid and azelaic acid, p-β-hydroxyethoxy Benzoic acid, substituted with one or more other bifunctional carboxylic acids such as oxyacids such as ε-oxycaproic acid, and part of the ethylene glycol component, for example, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, Decamethylene glycol, neo pliers Len glycol, diethylene glycol, 1,1-cyclohexanedimethanol, 1,4-
Cyclohexanedimethanol, 2,2-bis (4'-β-
Hydroxyethoxyphenyl) propane, bis (4'-
(β-hydroxyethoxyphenyl) sulfonic acid or the like can be used. In addition, as the heterogeneous polymer that can be used to form the polymer blend or the polymer alloy, a polymer composed of the above monomers that can form a copolymer other than polyethylene terephthalate can be used.

A preferred rolling method for obtaining a transparent rolled sheet in the present invention will be described below.

Rolling, the polyethylene terephthalate after melt extrusion is directly rolled in one direction, for example, in the longitudinal direction or the width direction at a predetermined temperature state as it is, or after being cooled once after extrusion, once again held at a predetermined temperature by heating. After that, rolling may be performed in one direction, or any method may be used.

The temperature of polyethylene terephthalate when rolling is required to satisfy the range of 80 ° C. or more and 170 ° C. or less.
The reason is that if the temperature is lower than 80 ° C., rolling is possible but the heat resistance is lost, and if the temperature exceeds 170 ° C., a phenomenon occurs in which the material loses transparency called so-called whitening.

In addition, the thickness rolling ratio H1 / H2 (H1: material thickness,
H2: thickness after rolling) is larger than 1 but is limited to 3 or less. The reason for this is that as the rolling ratio increases, the heat resistance, transparency, and impact resistance of the rolled sheet increase, but when rolling is performed, for example, in the longitudinal direction, the strength in that direction increases, and the width direction changes. This is because the strength ratio in the longitudinal direction with respect to the width direction is too large, that is, the anisotropy is increased, thereby deteriorating thermoformability. As a result of many experiments, the present inventors have found that the thickness rolling ratio is greater than 1 and 3
The following corresponds to the strength ratio of 0.5 to 2 and thermoforming is possible,
On the other hand, although there are some differences depending on the shape of the molded product, it has been found that thermoforming of a practical shape cannot be performed due to its anisotropy at a higher rolling ratio, that is, at a strength ratio. A particularly preferred thickness rolling ratio is 1.3 to 1.7.

The method of heating the material may be direct contact heating by a heating roll having a built-in heater, or indirect heating by a heater.

Furthermore, the present invention is limited to unidirectional rolling elongation, but from the standpoint of thermoforming, bidirectional rolling, that is, rolling also in a direction perpendicular to the rolling direction, increasing the strength in that direction and reducing the strength ratio. It is desirable to have a sheet. However,
Realizing this two-way rolling requires a complicated process, rather, in unidirectional rolling, by limiting to the above rolling conditions, a practical process, and having transparency, heat resistance, etc. A sheet that also satisfies thermoformability can be manufactured.

The dynamic elongation viscoelasticity of the present invention refers to the sample length along the rolling direction.
Take 30mm (distance between clamps) and 10mm width, elongate viscoelastic properties measured at a frequency of 100Hz with a viscoelastic spectrometer VES-F-III manufactured by Iwaki Seisakusho at a rate of 2 ° C / min from room temperature. Say.

The elongation strength refers to the strength at the time of cutting when elongating in a 20 ° C. atmosphere at a constant speed of 100% / min with a sample length of 30 mm and a width of 10 mm.

The term “transparent” as used in the present invention means that the average transmittance of light in the wavelength range of visible light is at least 50% or more.

The thermoforming in the present invention is a thermoforming in which an object to be molded is heated to a temperature range not lower than its glass transition point and not higher than its melting point, and is pressure-bonded to an open mold by vacuum, air pressure or a combination of these and auxiliary mechanical means. The way to do it.

When tα <84 ° C., the sheet has poor heat resistance and insufficient impact resistance. When such a sheet is thermoformed, relatively large spherulites easily appear and become cloudy.
A particularly preferred range of tα is 86 ° C. or higher. The intensity ratio is 0.
When the ratio is outside the range of 5 to 2.0, the thermoformability is extremely poor due to the anisotropy of strength in the longitudinal direction and the width direction. In this respect, a particularly preferred rolling ratio range is 1.3 to 1.7.

In the present invention, it is particularly important to realize a transparent sheet having tα ≧ 84 ° C. and a strength ratio of 0.5 to 2.0 by a rolling method instead of a stretching method usually used for film production. Ordinary stretched films are mechanically stretched between rolls or clips, or formed into a tubular shape and expanded by air pressure. In the case of polyethylene terephthalate, when uniaxial stretching is performed by such a method, heat resistance does not appear unless a stretching ratio of 3.5 or more is set. However, when stretched under these conditions, the strength ratio goes out of the range of 0.5 to 2.0,
Thermoformability deteriorates significantly. When biaxially stretched in this manner, a film having characteristics of tα ≧ 84 ° C. and a strength ratio of 0.5 to 2.0 can be easily obtained, but as described above, thermoformability is significantly deteriorated due to a high degree of molecular orientation. I will.

A particularly preferred method for thermoforming using the sheet according to the present invention is described below.

According to the present invention, the rolled polyethylene terephthalate sheet holds both ends of the sheet and has a temperature suitable for thermoforming.
Heat to 80 ° C or higher and 170 ° C or lower. Preferably 100 ° C or higher 15
The range of 0 ° C is good. The heating may be any of hot air heating, infrared heating, high frequency heating, and hot plate heating.

As soon as the sheet is heated to an appropriate temperature range, it is transferred to the mold of the molded product and shaped into a molded product. The shaping may be performed by vacuum, pressurized air, or pressurization using a plug, and these methods may be used in combination.

In this case, the mold is preferably heated to a temperature range of 90 ° C. or more and 180 ° C. or less. Thereby, the stretching stress at the time of shaping is relieved, and heat setting is performed, and the heat resistance of the molded product is improved. Moreover, the molded product maintains transparency.

The transparent sheet product according to the present invention is a useful sheet using relatively inexpensive polyethylene terephthalate as a raw material and having excellent transparency, heat resistance, impact resistance, and thermoformability. For example, when this is thermoformed into a food packaging container, the food can be hot-filled and the transparency is not lost. Therefore, the filling can be performed efficiently, and at the same time, there is an appealing effect that the filled food can be seen well. The present container is also characterized by having retort resistance.

Since the sheet of the present invention is made by a rolling method, a sheet having a thickness of 300 μm or more can be made. Since a normal polyethylene terephthalate film is stretched in the width direction by a stenter, it is difficult to produce a film having a thickness of 300 μm or more. Therefore, the sheet of the present invention can be used for building materials. For example, a sheet obtained by laminating and adhering the sheets of the present invention so that the rolling directions intersect each other in order to increase the isotropy is particularly useful for building materials.

〔Example〕

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.

Example 1 A polyethylene terephthalate resin having an intrinsic viscosity [η] of 0.65 was melt-extruded from a flat die to obtain an unstretched transparent sheet having a width of 500 mm and an average thickness of a flat portion excluding both ears of 0.83 mm.

This was heated again to 90 ° C. and rolled to 0.5 mm in the longitudinal direction (rolling ratio: 1.6) by a roll heated to 100 ° C.
The tα of this sheet was 89 ° C., and the strength ratio between the longitudinal direction and the width direction was 1.5.

Using a vacuum forming machine manufactured by Toyobo Research Institute,
It was molded into a tray-shaped container under the following molding conditions.

Molding conditions Heating temperature 200 ° C (ceramic heater) Heating time 15 seconds Heated sheet measured temperature 150 ° C Molding cycle 30 seconds Container dimensions W × D × H = 125 × 90 × 30mm Capacity 300cc The molded container maintains transparency. Was.

Further, after the curry of the container was filled and the lid was heat-sheeted, heat treatment was performed at 120 ° C. for 30 minutes using a high temperature and high pressure cooking sterilization tester RCS 40RTG manufactured by Hisaka Seisakusho. As a result, all 30 containers were not deformed in appearance, and the volume change was 2
% Was very good.

〔The invention's effect〕

Rolled polyethylene terephthalate sheet of the present invention,
It has excellent properties in all of transparency, heat resistance, impact resistance, and thermoformability, so it is particularly useful for food packaging containers, and it is easy to manufacture high-thickness sheets. Can be used, and the present invention can provide an industrially extremely useful sheet.

Continuation of front page (72) Inventor Koichiro Goto 2-6-3 Otemachi, Chiyoda-ku, Tokyo Nippon Steel Corporation (56) References JP-A-51-30855 (JP, A) JP-A-1 JP-A-189809 (JP, A) JP-A-53-86762 (JP, A) JP-A-62-183329 (JP, A) JP-A-52-138275 (JP, A) JP-A-53-16086 (JP, A) ) Tokuhyo Hei 4-500933 (JP, A) Tokiko 46-19198 (JP, B1)

Claims (3)

(57) [Claims] The transparent elongation obtained by rolling at a temperature tα at which the maximum value of tan δ of dynamic elongation viscoelasticity is 84 ° C. or more, and an elongation strength ratio between one direction and a direction perpendicular thereto is in the range of 0.5 to 2.0. Polyethylene terephthalate rolled sheet. 2. A transparent molded article obtained by thermoforming the sheet according to claim 1. 3. The unstretched polyethylene terephthalate sheet obtained by melt extrusion is unidirectionally stretched at a temperature of 80 ° C. or more and 170 ° C. or less at a thickness rolling ratio of more than 1 and 3 or less. The method for producing a sheet according to claim 1, wherein the sheet is rolled and elongated.