JPH10305540A - Deep drawn thermoforming polyester container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a deep drawn container made of polyester multilayer sheet, having improved transparency, strength and irregular section. SOLUTION: The deep drawn container is made of polyester sheet of a three- layer structure and provided with 0.8 or more of a ratio of a depth to an opening diameter. A thickness of the sheet is 1 mm or more. Glass transition temperature of a skin layer is 90 deg.C or higher. The skin layer is made of polyester resin composition having a limiting viscosity of 0.6 or more. A core layer is made of polyethylene terephthalate resin having a limiting viscosity of 0.6 or more. The skin layer of 10 wt.% or more in the polyester container.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester container having good deep drawability and improved transparency, uneven thickness and strength of the container.

[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. P
A molded article made from a sheet made of ET as a raw material is easily moldable and has good transparency, gloss, and mechanical strength, and recently, attempts have been made to use it as a container for packaging various products. I have.

However, since the conventional sheet made of PET has crystallinity, if heated excessively during thermoforming, whitening due to crystallization occurs, and the original transparency is lost. is there. In particular, when a deep-drawn container having a ratio of the depth of the container to the diameter of the opening (hereinafter referred to as a drawing ratio) of 0.8 or more is thermoformed, it is necessary to perform sufficient heating as compared with normal thermoforming. In the conventional PET sheet, clouding of the container due to whitening and uneven thickness due to overheating are apt to occur, and improvement has been desired. Further, in consideration of the practical strength of a deep drawing container having a drawing ratio of 0.8 or more, a thick sheet having a thickness of 1 mm or more is necessary. In the case of such a thick sheet, more sufficient heating is performed. In addition, there is a problem that clouding of the container due to whitening and uneven thickness due to overheating are more likely to occur.

As a method for improving the thermoformability of a polyester sheet, a method has been proposed in which a component which inhibits the crystallinity of polyester is copolymerized to prevent crystallization during heating (Japanese Patent Laid-Open No. 51-81857). Gazette, JP-A-51-38
No. 335). However, by copolymerizing a component that inhibits crystallinity, whitening due to crystallization of the sheet is improved, but uneven thickness due to overheating cannot be improved.
Further, the physical properties of the sheet are deteriorated due to the blending of the copolymer component, which is not preferable.

[0005] Also, Japanese Patent Application Laid-Open No. Hei 8-1766 discloses that
A method of improving thermoformability by a sheet obtained by laminating a polyester layer and a PET layer obtained by copolymerizing 1,4-cyclohexanedimethanol has been proposed. However, even such a laminated sheet has a thickness of less than 1 mm. Although the moldability can be improved, the effect is not seen for a thick sheet having a thickness of 1 mm or more and uneven thickness occurs. That is, in a thick sheet, the difference between the surface layer temperature during heating and the temperature inside the sheet is large, and the surface layer temperature when the inside of the sheet is heated to a temperature at which thermoforming is possible greatly exceeds the glass transition temperature of the copolymerized polyester layer. It is considered that uneven thickness occurs due to deformation of the surface layer portion.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of a sheet made of PET, to obtain a transparent sheet obtained by deep drawing a sheet having a thickness of 1 mm or more.
An object of the present invention is to provide a polyester container having improved strength and uneven thickness.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies for this purpose and as a result, have found that a reinforcing layer made of a polyester resin composition having a glass transition temperature of 90 ° C. or more is provided on both sides of a main constituent layer made of PET resin. It has been found that a multi-layered sheet provided with a polyester container is excellent in deep drawability and that a polyester container having improved transparency, strength, and uneven thickness can be obtained, and has reached the present invention.

That is, the present invention is a polyester container comprising a polyester sheet having a three-layer structure, wherein the ratio of the depth to the opening diameter is 0.8 or more, wherein the thickness of the multilayer polyester sheet is 1 mm or more, The glass transition temperature of the layer is 90 ° C. or higher, and the skin layer is made of a polyester resin composition having an intrinsic viscosity of 0.6 or more, and the core layer is made of polyethylene terephthalate having an intrinsic viscosity of 0.6 or more. A polyester container having a weight ratio of 10% or more.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The PET resin used for the core layer of the multilayer polyester sheet used in the present invention comprises terephthalic acid or an ester-forming derivative thereof (for example, lower alkyl ester) and ethylene glycol or an ester-forming derivative thereof. It is obtained by polycondensing a derivative (for example, monocarboxylic acid ester ethylene oxide or the like) by a known method, but may contain other copolymer components as long as the original physical properties are not impaired.

[0010] 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.

[0011] The skin layer of the container of the present invention must have a glass transition temperature of 90 ° C or higher. Glass transition temperature 9
If the temperature is lower than 0 ° C., shrinkage occurs due to preheating when the sheet is formed to produce a container, and the appearance is impaired.

In the present invention, the limiting viscosity of the polyester resin composition used for the skin layer of the multilayer structured polyester sheet is 0.6 or more. When the intrinsic viscosity is lower than 0.6, the mechanical strength of the container is low, and particularly, the impact strength at low temperature is inferior. In addition, the sheet is drawn down during thermoforming, resulting in uneven thickness of the molded product, and the crystallization speed of the sheet is increased, so that the thermoformed product becomes opaque.

The resin composition having such an intrinsic viscosity can be obtained by solid-state polymerization of each resin. However, in consideration of the operability during solid-state polymerization, the intrinsic viscosity should be 0.9 or less. Is preferred.

The polyester resin composition used for the skin layer of the container of the present invention includes, for example, a polyester resin composition comprising 40 to 90 parts by weight of a polyethylene terephthalate resin and 10 to 60 parts by weight of a polyarylate resin.
And a polyester resin composition comprising 0 to 70 parts by weight of a PET resin and 30 to 100 parts by weight of a polyethylene naphthalate resin.

In the case of using the former polyester resin composition, in order to make the intrinsic viscosity of the skin layer 0.6 or more, P
It is preferable that the intrinsic viscosity of the ET resin is 0.6 or more, and the intrinsic viscosity of the polyarylate resin is 0.5 to 0.7.

When the latter polyester resin composition is used, the intrinsic viscosity of both the PET resin and the polyethylene naphthalate resin should be 0.6 or more in order to make the intrinsic viscosity of the skin layer 0.6 or more. Is preferred.

In the present invention, the intrinsic viscosity of the PET resin composition used in the core layer of the multilayer polyester sheet is 0.6 or more. When the intrinsic viscosity is lower than 0.6, the mechanical strength of the container is low, and particularly, the impact strength at low temperature is inferior. Further, the sheet is drawn down during thermoforming, and the molded product is likely to be uneven in thickness. Further, the intrinsic viscosity is preferably set to 0.9 or less from the viewpoint of suppressing the occurrence of uneven thickness in the molded product.

The polyester resin used in the present invention includes an antistatic agent, a heat-resistant agent, and the like as long as the original physical properties are not impaired.
An antioxidant and the like can be added. These additives may be added at the time of polymerizing the polymer, may be re-melted the polymerized polymer chip and blended using a twin-screw kneader or the like, or may be added to the molten polymer at the time of sheet production. Good.

The multilayer polyester sheet used in the present invention is a substantially unstretched sheet obtained by the above-mentioned composition by a usual film-forming means. The unstretched sheet of the present invention preferably has a density of 1.34 g / cm ³ or less and is substantially amorphous. The density of the sheet is 1.34 g / cm
^{A value of 3} or less is preferable because the transparency of the sheet is good and the impact strength of the sheet is sufficiently high. Such an amorphous polyester sheet can be obtained by melt-mixing the resin composition of the present invention with an extruder, then discharging the resin composition from a general multilayer extrusion die and rapidly cooling it with a cooling drum.

The structure of the multilayer polyester sheet used in the present invention is a three-layer sheet having a skin layer on both sides of a core layer. If the skin layer is only on one side of the core layer,
Heating during molding causes the PET of the core layer to whiten, thereby impairing the transparency of the molded article.

It is necessary that the weight ratio of the skin layer of the multilayered polyester sheet used in the present invention to all the layers is 10% or more. When the weight ratio of the skin layer is less than 10%, the effect of improving the deep drawing thermoformability is not sufficient, and whitening and uneven thickness of the molded product occur. Further, in consideration of the operability and economy at the time of molding, the ratio of the skin layer is preferably 20% or less.

As described above, the multilayer structured polyester sheet used in the present invention is a three-layer sheet having skin layers on both sides of the core layer. This is preferable because unevenness of the sheet surface during film formation is reduced. Therefore, the weight ratio of the skin layers on both sides is preferably in the range of 40:60 to 50:50.

The multi-layered polyester sheet used in the present invention is a thick sheet having a thickness of 1 mm or more. When the thickness is less than 1 mm, the strength of the obtained deep drawn container is so low that it cannot be practically used. That is, when the container is filled with the contents, the container is deformed by its own weight, or the container is deformed just by holding the container.

The polyester container of the present invention can be obtained from the multilayer structured polyester sheet by deep drawing thermoforming with a drawing ratio of 0.8 or more. As a thermoforming method, a sheet is heated and softened, pressed against a desired mold, air in a gap between the mold and the material is removed, and the sheet is closely adhered to the mold by atmospheric pressure to form the sheet. Pneumatic molding in which the sheet is brought into close contact with the mold, and molding using both vacuum and compressed air can be applied.

[0025]

The polyester container of the present invention has transparency,
Maintain the original properties of PET sheet such as mechanical properties,
Ideal for beverage cups without uneven thickness.

[0026]

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) 0.5 g of a sample 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 20 ° C.

(2) Density (ρ) Measured at 23 ° C. by a density gradient method.

(3) Glass transition temperature (Tg) About 10 mg of a sample obtained by cutting a skin layer portion of a polyester container with a microtome was used in a DS manufactured by PerkinElmer.
At C, the temperature was measured at a rate of 10 ° C./min in a nitrogen stream.

(4) Transparency (Haze) Using a body part of a polyester container, a haze meter manufactured by Nippon Denshoku Co., Ltd. measured according to JIS-K7105. A sample having a measured value of 3% or less was evaluated as "O", and a sample exceeding 3% was evaluated as "X".

(5) Thermoformability 90 m depth by a single-cavity pressure forming machine with plug assist
m, an opening diameter of 60 mm, and a draw ratio of 1.5 were prepared.
The case where a complete container was completed was evaluated as ○, and the case where shape improper or uneven thickness occurred was evaluated as ×.

(6) Container Strength A container was filled with 150 g of water and dropped on a concrete surface from a position having a height of 2.5 m for evaluation. When the drop test was performed 20 times and the number of times the container was cracked was 1 or less, it was rated "○", and when it was broken 2 or more times, it was rated "x".

Examples 1 to 9 Comparative Examples 1 to 3 Using a multilayer sheet extruder having a T-die of 80 cm in width equipped with three single-screw extruders, using the raw materials shown in Table 1, a thickness of 1.5 mm Was extruded. The intrinsic viscosities of the PET resin, polyarylate resin, and PEN resin used for the skin layer were 0.85, 0.51, and 0.63, respectively. The temperature of the cylinder of the extruder was 285 ° C., the temperature of the T-die was 280 ° C., and the temperature of the cooling roller was 40 ° C. Table 2 shows the physical properties of the obtained sheet.

Next, the above-mentioned sheet is preheated to a temperature not lower than the glass transition temperature of the resin composition for the skin layer and not higher than the melting point, and has a depth of 90 mm and an opening diameter of 6 using a single-cavity pressure forming machine with plug assist.
A container having 0 mm and a draw ratio of 1.5 was produced. Table 2 shows the evaluation results of the containers.

Comparative Example 4 The same resin composition as in Example 1 was used for the skin layer and the core layer, and the same extruder was used. Under the same conditions, the skin layer was laminated only on one side of the core layer. A layer sheet was prepared. A container was produced from this two-layer sheet in the same manner as in Example 1, and the container was evaluated. The above results are shown in Tables 1 and 2.

[0036]

[Table 1]

[0037]

[Table 2]

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B65D 1/26 B65D 1/26 Z // B29K 67:00 B29L 22:00 C08L 67:00

Claims (3)

[Claims] 1. A polyester container comprising a polyester sheet having a three-layer structure and having a ratio of depth to opening diameter of 0.8 or more, wherein the multilayer polyester sheet has a thickness of 1
mm or more, the glass transition temperature of the skin layer is 90 ° C. or more, and the skin layer is made of a polyester resin composition having an intrinsic viscosity of 0.6 or more, and the core layer is made of polyethylene terephthalate having an intrinsic viscosity of 0.6 or more. A polyester container, wherein the weight ratio of all the layers in the layer is 10% or more. 2. A polyester resin composition comprising: a polyethylene terephthalate resin having an intrinsic viscosity of 0.6 or more;
The polyester container according to claim 1, which is a polyester resin composition comprising 0 parts by weight and 10 to 60 parts by weight of a polyarylate resin having an intrinsic viscosity of 0.5 to 0.7. 3. A polyester resin composition comprising a polyethylene terephthalate resin having an intrinsic viscosity of 0.6 or more.
The polyester container according to claim 1, which is a polyester resin composition comprising parts by weight and 30 to 100 parts by weight of a polyethylene naphthalate resin having an intrinsic viscosity of 0.6 or more.