JP2711205B2 - Composite foamed 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 foamed polyester sheet, and more particularly to a foamed polyester sheet excellent in thermoformability and heat sealability.

[0002]

2. Description of the Related Art Conventionally, thermoplastic resin foams, for example, foams of polyolefin, polyurethane and polyamide, have been widely used as a heat insulating agent, a buffer and a packaging material. Such a thermoplastic resin foam is usually produced by a method of mixing air bubbles, a method of using a decomposition gas of a foaming agent, a solvent diffusion method, a method of generating a gas by a chemical reaction, or the like.

On the other hand, aromatic polyesters, especially polyethylene terephthalate, are used for fibers, films, injection molded articles and the like because of their excellent mechanical properties, heat resistance, chemical resistance and dimensional stability. In recent years, a method of adding various foaming agents to these thermoplastic polyesters and subjecting them to foam molding (see JP-A-52-43871) or heating a homogeneous mixture of polyethylene terephthalate and polycarbonate to a temperature of 250 to 350 ° C. Let C
A method has been proposed in which the heating temperature is maintained until O ₂ is liberated, and then the reaction mixture is expanded (see Japanese Patent Publication No. 47-38875).

[0004] However, the former method has disadvantages such as coloring caused by the foaming agent, spots of foaming, deterioration of mechanical properties, and the like, and the latter method requires a long reaction time at a high temperature, and the reaction mixture is colored. There is a disadvantage that deterioration of characteristics is inevitable.

A method has also been proposed in which polyethylene terephthalate containing a polyolefin is heated and melted, and an inert gas is mixed into the molten resin composition to produce a foamed molded product (see Japanese Patent Application Laid-Open No. 2-286725). However, in this method, uniform fine bubbles cannot be obtained, and the expansion ratio is as low as 3 times or less.

The present inventors have eliminated the drawbacks associated with the above-mentioned foam molding method, and are capable of high-magnification (three times or more) foaming that is lightweight, has excellent mechanical properties, and has uniform cell sizes. As a result of intensive studies on a method for producing a flexible foamed polyester sheet, the melt viscosity at the flow starting temperature was 8,000.
After supplying a thermoplastic polyester resin and a foam nucleating agent of poise or more to an extruder, mixing with an inert gas while in a molten state, and extruding from a sheet forming die, the density becomes 0.01 to
It has been found that an ideal foamed sheet can be obtained as a polyester resin within the range of 1.5.

[0007] However, the high magnification power obtained by such a method is
Was further investigated foam sheet, Hitoshi the sheet can not vacuum forming or pressure forming the pin holes are generated at the time of thermoforming, due to the uneven surface of the product after the molding
A new problem, that is, the lowering of the reliability, has become apparent.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a foamed polyester sheet having excellent thermoforming properties and heat sealing properties and a high expansion ratio.

That is, the present invention is a composite foamed polyester sheet obtained by forming an unfoamed heat-sealing resin layer on at least one surface of a foamed polyester sheet.

In the present invention, the unfoamed heat seal resin layer laminated on the foamed polyester sheet is made of a polyester copolymer, polyethylene, polypropylene or the like. In particular, a polyester copolymer is preferable because of good adhesiveness of the laminate, and is obtained by polycondensing a dicarboxylic acid component and a diol component by a known method. More preferred is terephthalic acid.

As such dicarboxylic acids, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 2,2
7-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenyl-4,4-dicarboxylic acid, 3,3
-Dimethylphenyl-4,4'-dicarboxylic acid and the like. These dicarboxylic acids can be used even if only one kind is used.
More than one species may be used in combination.

It is more preferable that 50 mol% or more of the diol component is ethylene glycol. Although other diol components can be used, it is preferable that these are kept to less than 50 mol% of the diol component as much as possible. Examples of such diols include 1,4-butanediol, diethylene glycol, hexamethylene glycol, bis-β-hydroxybisphenol A, cyclohexane dimethanol, and the like.
These diols may be used alone or in combination of two or more.

Further, polypropylene is preferable because it has good heat sealability even in a container containing a liquid such as water. The unfoamed heat-sealing resin layer is a resin layer containing polypropylene as a main component (40% by weight or more), and a film grade having a molecular weight of 100,000 to 700,000 is preferable in terms of film-forming properties. Polybutene (more preferably low melting point type polybutene) for heat sealing at low temperature
Can also be mixed. As described above, copolymerization or blending with another resin can be performed within the range not losing the required properties aimed at by the present invention.

On the other hand, the foamed polyester sheet serving as a base material is made of, for example, (1) (a) a thermoplastic polyester resin 10
0 parts by weight, and (b) an inorganic nucleating agent selected from the group consisting of glass, mineral materials and mixtures thereof from 0.01 to 0.01 parts by weight.
5 parts by weight are fed to a melt extruder to melt and mix, (2) the resulting molten mixture is mixed with an inert gas while in the melt extruder, and (3) extruded from a forming die. Can be manufactured. The thickness is usually 0.1
0 to 1.0 mm. In order to obtain high-magnification foaming, conditions under which the thermoplastic polyester resin has a high melt viscosity are selected, or a polyfunctional glycidyl ester compound, a polyfunctional carboxylic anhydride, or the like is added (Japanese Patent Laid-Open No. 59-21095).
No. 5) is also effective. Further, a sheet provided with a known property by adding a resin layer such as polyester or polyolefin can also be used as the base material.

Preferred thermoplastic polyester resins to be used include polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polybutylene terephthalate elastomer, amorphous polyester,
Polycyclohexane terephthalate, polyarylate,
Polyethylene naphthalate and the like, and these resins may be used alone or a plurality of these resins may be used as a mixture.

The inorganic nucleating agent (b) is a fibrous glass or a mineral material such as talc, silica, mica and mica, and these nucleating agents may be used alone or in combination of two or more. . The addition ratio of the inorganic nucleating agent is 0.01 to 5 parts by weight per 100 parts by weight of the polyester composition. If the amount of the inorganic nucleating agent is less than 0.01 part by weight, it is difficult to substantially expand the polyester, while if it is more than 5 parts by weight, the physical properties of the obtained foam molded article are undesirably deteriorated.

Further, the foamed polyester sheet includes:
If necessary, a specific foaming aid can be added and mixed. Such foaming aids include organic acids and organic acids such as C
At least one compound selected from the group consisting of an a salt, a Zn salt, a Mg salt, a Ba salt, an Al salt, a Pb salt and a Mn salt, and an ester of an organic acid is exemplified.

The composite foamed polyester sheet of the present invention can be produced by a conventional method such as an extrusion lamination method and a coextrusion method.
Above at least one side of the foamed polyester sheet of the substrate
It is obtained by laminating or co-extruding an unfoamed heat seal resin layer . At this time, the thickness of the unfoamed heat sealing resin layer to be laminated or co-extruded is usually 5 μm or more, and preferably 10 to 50 μm. The thickness of the unfoamed heat seal resin layer is 5μ
If it is less than m, pinholes occur, or thickness unevenness due to surging occurs, and it is difficult to obtain a stable laminate or co-extruded layer, and sufficient adhesive strength with a foamed polyester sheet as a base material is obtained. It is difficult to obtain. On the other hand, when the thickness is 100 μm or more, the heat sealing property is saturated.

The expanded polyester sheet of the present invention
The expanded polyester sheet is substantially unstretched.
You.

The composite foamed sheet can be thermoformed into a heat-set thin article using a conventional thermoforming apparatus. Such thermoforming methods include: 1. pre-heating the foam sheet until it softens and positioning it in the mold; 2. drawing the preheated sheet onto the heated mold surface; 3. heat setting the formed sheet by leaving the sheet in contact with a heated mold for a time sufficient to partially crystallize; Removing the molded article from the cavity of the mold is included. In this step, the foamed polyester sheet of the present invention is excellent in moldability because there is no pinhole on the sheet surface as compared with the foamed sheet obtained from the conventional polyethylene terephthalate resin, and the pressure forming and vacuum forming are easy. Can be implemented.

In the container of the present invention, such a composite foamed sheet is thermoformed by a known method and under conditions to obtain a container body or a lid having a desired shape such as a tray or a cup. Next, the container body is filled with contents including water and the like, and the unfoamed heat of the container body and the lid is filled.
A sealed container is manufactured by heat sealing the sealing resin layer .
When a transparent part is required in a part of the container, the lid side may be made of an unfoamed polyester sheet.

[0022]

As described above, the composite foamed sheet according to the present invention is excellent in chemical resistance, heat resistance and heat insulation, has no pinholes on the sheet surface, is excellent in thermoformability and heat sealability, and is excellent in food quality. It can be suitably used for materials such as containers, packaging bags, packing materials and cases for electric products.

[0023]

The present invention will be described below in detail with reference to examples.

Incidentally, the resin melt viscosity is defined as a value in a mixed solution of phenol / tetrachloroethane = 1/1 at 20.degree.
g / 100 cc. The melt viscosity of the resin is measured by FLOWTESTER (model C
FT-500), nozzle diameter 1 mm, load 100
It is a value measured in kg / cm ² .

The thermoformability was evaluated according to the following evaluation criteria.

○: The entire sheet stretched uniformly and could be formed into the same shape as the press mold and could not be broken. △: Can be formed into the same shape as the press mold, but a part of the surface was torn and flack was formed. Resulting ×: Sheet is severely broken and cannot be formed

The heat sealability was determined according to JIS-Z-1526.
Was measured and evaluated in accordance with the heat sealing strength test. Heat sealability is usually required to be 1.0 kg / cm ² or more,
Preferably it is 2.0 kg / cm ² or more. The impact resistance is measured by thermoforming a composite foamed polyester sheet to make a container (16 cm long × 12 cm wide × 4.5 cm high), put 200 ml of water in it, and use the same composite foamed polyester sheet as a lid material, 130 ° C or 90 ° C, pressure 1k
The container was heat-sealed under the conditions of g / cm ² and a time of 1 second to form a sealed container, dropped from a height of 1.2 m, and evaluated whether the heat-sealed portion was damaged at that time. ○ ・ ・ ・ No damage △ ・ ・ ・ Some damage × ・ ・ ・ Damaged

Example 1 Polyethylene terephthalate resin (Intrinsic viscosity of resin 1.
2. Melt viscosity at a flow start temperature of 260 ° C is 11,3.
To 100 parts by weight (00 poise), 0.6 parts by weight of talc and 0.4 parts by weight of Zn stearate were dry-blended. Screw diameter of the prepared thermoplastic resin composition is 65 mm,
The screw was extruded using an extruder having an L / D of 30. The rotation of the extruder was kept at 100 rpm, the temperature of the melting zone was kept at 270 ° C., the temperature of the die was kept at 260 ° C., and nitrogen gas was injected at a pressure of 40 kg / cm ² from the vent of the melting zone. On one side of the manufactured foamed polyester sheet,
Polyethylene terephthalate copolymerized with 20% by mole of 2-bis (4-β-hydroxyethoxyphenyl) propane as a glycol component was laminated by an extrusion lamination method so as to have a thickness of 0.1 mm, and a foamed sheet shown in Table 1 was obtained. Manufactured. Kiefe
Using a thermoforming machine manufactured by Company l at a molding temperature of 100 ° C and a length of 160
The container was manufactured by molding into a thermoformed product having a height of 120 mm, a width of 120 mm and a height of 45 mm. The moldability and heat sealability were evaluated.
Table 1 shows the results.

Example 2 Polybutylene terephthalate resin (Intrinsic viscosity of resin 1.
4. The melt viscosity at a flow start temperature of 220 ° C is 13.0
Molding and evaluation were performed in the same manner as in Example 1 except that a foamed polyester sheet using (00 poise) was used. Table 1 shows the results.

Example 3 Molding and evaluation were performed in the same manner as in Example 1 except that a coextruded foamed sheet was manufactured using a multilayer extruder so that the thickness of the unfoamed heat-sealing resin layer was 0.1 mm. went.
Table 1 shows the results.

Comparative Example 1 Unfoamed polyester was added to the foamed polyester sheet produced in Example 1 .
The same molding and evaluation were performed without laminating the heat seal resin layer . Table 1 shows the results.

[0032]

[Table 1]

Sheets and containers were produced in the same manner as in Example 1 except that the unfoamed heat-sealing resin layer was changed to polypropylene (molecular weight: 600,000).

Except that the unfoamed heat seal resin layer was changed to a mixture of the same weight of polypropylene (molecular weight: 600,000) and polybutene (melting point: 71 ° C., density: 0.90), a sheet and a sheet were prepared in the same manner as in Example 1. A container was manufactured.

Sheets and containers were produced in the same manner as in Example 1, except that the unfoamed heat-sealing resin layer was changed to low-density polyethylene (MFR 5.1, density 0.919).

[0036]

[Table 2]

From the above results, it was found that the polyester sheet of the example had good heat sealability and impact resistance of the heat seal portion in addition to thermoformability .

Claims (2)

(57) [Claims] (A) a thermoplastic polyester resin 100
Parts by weight, and (b) 0.01 to 5 inorganic nucleating agents selected from the group consisting of glass, mineral materials and mixtures thereof.
It consists of a resin composition containing parts by weight and has a density of 0.01
~0.4g / cm in the range of ³ substantially unstretched foamed least heat unfoamed on one surface of the polyester sheet
A composite foamed polyester sheet formed with a sealing resin layer . 2. (a) Thermoplastic polyester resin 100
Parts by weight, and (b) 0.01 to 5 inorganic nucleating agents selected from the group consisting of glass, mineral materials and mixtures thereof.
Parts by weight and (c) organic acid, organic acid Ca salt, Zn salt, Mg
A resin composition containing 0.01 to 5 parts by weight of at least one compound selected from the group consisting of a salt, a Ba salt, an Al salt, a Pb salt, an Mn salt, and an ester of an organic acid; 01~0.4g / cm in the range of ³ substantially composite foam polyester Gite comprising brought forming at least a heat sealing resin layer of unfoamed on one surface of the foamed polyester sheet unstretched.