JPH07179642A - Foamed polyester sheet and its production - Google Patents

Abstract

PURPOSE:To provide a foamed polyester sheet having heat resistance at a temperature as high as 150 deg.C or above and adapted for an electronic oven-proof food container. CONSTITUTION:This sheet is made from a resin composition comprising 100 pts.wt. polyethylene 2,6-naphthalate of an intrinsic viscosity of 0.5 or above and 0.01-5 pts.wt. inorganic nucleator selected from the group consisting of glass, a mineral material and a mixture thereof.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a foamed polyester sheet and a method for producing the same. More specifically, the present invention relates to a foamed polyester sheet which has uniform fine bubbles and a high expansion ratio and is excellent in high-temperature stability at 150 ° C. or higher and which can be used as a food container compatible with a microwave oven, and a method for producing the same.

[0002]

2. Description of the Related Art Aromatic polyesters, especially polyethylene terephthalate (hereinafter referred to as PET), have mechanical properties
Due to its excellent heat resistance, chemical resistance, dimensional stability, etc.,
Used in fibers, films, injection molded products, etc.

In recent years, various foaming agents have been added to thermoplastic polyesters for foam molding (JP-A-52-438).
No. 71) or a uniform mixture of PET and polycarbonate is heated to a temperature of 250 to 350 ° C. and reacted,
A method has been proposed in which the heating temperature is maintained until CO ₂ is liberated, and then the reaction mixture is expanded (see Japanese Patent Publication No. 47-38875).

However, the former method has drawbacks such as coloring due to a foaming agent, foaming unevenness, and deterioration of mechanical properties, and the latter method requires a long reaction time at a high temperature, so that the reaction mixture is colored and mechanically colored. There is a drawback that the deterioration of characteristics cannot be avoided.

Further, a method of producing a foamed molded article by heating and melting PET containing a polyolefin and mixing an inert gas into the molten resin composition (JP-A-2-28672).
However, uniform and fine bubbles cannot be obtained by this method, and the expansion ratio is as low as 3 times or less.

Further, a foamed sheet of thermoplastic polyester characterized in that the crystallinity of the front surface and the back surface of the sheet differ by 1% or more (see Japanese Patent Publication No. 47570/1993) is also proposed. The polyester used in the product has a low melt viscosity and must be used in combination with a melt property modifier such as pyromellitic dianhydride, which causes the sheet to turn yellow when operated for a long time and is not suitable for recycling. There is a point.

On the other hand, polyethylene 2,6-naphthalate (hereinafter referred to as PEN) has higher heat resistance than PET described above, and various proposals for use in fields requiring heat resistance at high temperatures (Japanese Patent Laid-Open No. 47-47). -35087, JP-A-50-
No. 14818, No. 50-74652, No. 52-45466, No. 2-202925.
Japanese Patent Laid-Open No. 5-70569), but no attempt has been made to foam PEN and use it in a food container compatible with a microwave oven.

[0008]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention
An object of the present invention is to provide a foamed polyester sheet which has a high temperature heat resistance of 0 ° C. or higher and can be used as a food container for microwave oven. Another object of the present invention is to have a high expansion ratio,
An object of the present invention is to provide a foamed polyester sheet that is lightweight and has excellent mechanical properties. Still another object of the present invention is to provide a method capable of industrially advantageously and easily producing the present polyester sheet. Further objects and advantages of the present invention will be apparent from the following description.

[0009]

According to the present invention, the above objects and advantages of the present invention are as follows: (a) 100 parts by weight of polyethylene 2,6-naphthalate resin having an intrinsic viscosity of 0.5 or more; and (b) glass. And a foamed polyester sheet comprising a resin composition containing 0.01 to 5 parts by weight of an inorganic nucleating agent selected from the group consisting of mineral materials and mixtures thereof.

The PEN resin (a) used in the present invention is obtained by polycondensing a dicarboxylic acid component and a glycol component by a known method, and the dicarboxylic acid used as the acid component is 91 mol% thereof.
The above is preferably 2,6-naphthalenedicarboxylic acid.

Although dicarboxylic acids other than 2,6-naphthalenedicarboxylic acid can be used, it is preferable that these are less than 9 mol% of the acid component. Such dicarboxylic acids include terephthalic acid, isophthalic acid,
Phthalic acid, 2,7-naphthalenedicarboxylic acid, 1,5-
Naphthalenedicarboxylic acid, diphenyl-4,4'-dicarboxylic acid, 3.3'-dimethyldiphenyl-4,4'-
Dicarboxylic acids and the like are exemplified, and these dicarboxylic acids are 1
Only one species may be used or two or more species may be used in combination.

Further, it is preferable that 90 mol% or more of the glycol component is ethylene glycol. Other diol components can also be used, but it is preferable to keep these to less than 10 mol% of the diol component. Examples of such diols include diethylene glycol, triethylene glycol, hexamethylene glycol, bis-β-hydroxybisphenol A,
1,4-Cyclohexanedimethanol and the like are disclosed. These diols may be used alone or in combination of two or more.

The inorganic nucleating agent (b) used in the present invention is selected from glass, mineral materials and mixtures thereof.
Preferred mineral materials include talc, silica and mica. The glass is, for example, fibrous glass.

The amount of the inorganic nucleating agent used is PEN resin 1
It is 0.01 to 5 parts by weight per 00 parts by weight. When the amount of the inorganic nucleating agent is less than 0.01 part by weight, the polyester cannot be substantially foamed, while the action and effect of the nucleating agent exceeding 5 parts by weight is saturated.

The intrinsic viscosity of the PEN resin used in the present invention is 0.5 or more, preferably 0.6 to 0.9. When the intrinsic viscosity is less than 0.5, not only the moldability in sheet molding is deteriorated but also the physical properties of the obtained sheet are remarkably deteriorated. On the other hand, a resin exceeding 0.9 is economically disadvantageous because the polymerization takes too long.

The expanded polyester sheet of the present invention is preferably 0.01 to 1.5 g / cm ³ , more preferably,
It is provided as being in the range of 0.03 to 1.3 g / cm ³ .

The thermoplastic resin composition used in the present invention can further have a foaming effect by adding a specific foaming aid. As such foaming aid, organic acid, organic acid Ca salt, Zn salt, Mg salt, Ba salt, Al salt, Pb salt,
And a compound selected from Mn salts and organic acid esters, and two or more of these foaming aids may be used in combination.

The amount of the foaming aid used is the same as that of PEN resin 1.
It is 0.01 to 5 parts by weight per 00 parts by weight. If the amount of the foaming aid is less than 0.01 part by weight, the effect of further foaming the polyester is small, while if it is more than 5 parts by weight, the physical properties of the obtained foamed molded product are remarkably deteriorated, which is not preferable.

Any method may be used for adding the foaming nucleating agent and the foaming auxiliary agent, but the foaming nucleating agent and the foaming auxiliary agent are uniformly dispersed in the polyester composition to be pelletized, and then subjected to foam molding. Is most preferable for practical use.

According to the present invention, the expanded polyester sheet of the present invention comprises: (1) 100 parts by weight of (a) polyethylene 2,6-naphthalate resin having an intrinsic viscosity of 0.6 or more; and (b) glass, a mineral material. And 0.01 to 5 parts by weight of an inorganic nucleating agent selected from the group consisting of a mixture thereof are supplied to a melt extruder to be melt-mixed, and (2) while the resulting mixture in a molten state is in the melt extruder. Mixed with an inert gas,
And (3) extruding from the forming die to produce a foamed polyester sheet;

In the step (1), other components used as necessary can be added and mixed. Examples of such other components include a foam nucleating agent and a foaming auxiliary agent as described above.

In the method of the present invention, after carrying out the step (1), the steps (2) and (3) can be continuously carried out, or the step (1) can be carried out to prepare the polyester resin composition, for example, as pellets. It is also possible to obtain once in the form and then perform the steps (2) and (3).

In the melt extruder, the raw material components of step (1) are mixed and heated in the solid transfer zone and transferred to the melting zone. The melting zone is maintained at a temperature well above the melting point of the molten resin so that melting and mixing occur simultaneously.

Next, in step (2), the molten resin is carried to the melt transfer zone. In the melt transfer zone, an inert gas is pressed into the molten resin and sufficient agitation is provided so that the bubbles of the inert gas are uniformly dispersed throughout the molten resin. The resin entering the melt transfer zone from the melt zone is set at a slightly lower temperature and therefore the melt viscosity is higher. This prevents the inert gas from back mixing through the extruder and escaping from the solid phase transfer zone via the hopper.

As the inert gas, those which do not react with the resin composition produced in the step (1) and which are in a gaseous or liquid state when mixed are used. Examples of such an inert gas include freon gas, nitrogen, carbon dioxide, helium, neon, argon, krypton, and propane,
Aliphatic hydrocarbons such as butane, pentane, hexane are mentioned. Of these, nitrogen is preferable because of its low cost.

The molten thermoplastic resin composition in the melt transfer zone is typically fed to a metering pump and extruded from the forming die in step (3) to form the desired shape.
The metering pump and sheet forming die are kept below the temperature of the barrel surrounding the melt transfer zone to minimize bubble breakage and diffusion of the inert gas in the thermoplastic. . Upon exiting the sheet forming die, the sheet extrudate expands to a level that depends on the melt temperature, the die length to open ratio and the shear stress at the die wall.

The forming die can be, for example, a sheet forming die or a circular die. The use of a circular die allows slit opening and thermoforming. The produced foamed sheet is cooled without stretching by air cooling, water cooling or passing through a chilled roll. The foamed sheet thus produced is generally amorphous, and its thickness is usually about 0.1 to 10 mm. As the melt extruder, for example, a single screw extruder,
A twin-screw extruder or a multi-screw extruder can be used.

The foam sheet can be thermoformed into heat set thin wall articles using conventional thermoforming equipment.
Such thermoforming methods include: 1. Preheating the foam sheet until it softens and positioning in the mold; 2. The step of drawing the preheated sheet onto the heated mold surface; 3. Heat setting the formed sheet by contacting the sheet with a heated mold for a time sufficient to be partially crystallized; The step of removing the molded product from the cavity of the mold is included.

[0029]

EXAMPLES The present invention will be described in detail below with reference to examples. In addition, the intrinsic viscosity of the PEN resin, the melt viscosity of the resin composition, and the heat distortion temperature of the molded product in the examples were measured by the following methods. (1) Intrinsic viscosity of resin: Measured at 20 ° C using a solution prepared by melting 1.0 g of a polymer in 100 cc of a mixed solvent of phenol / tetrachloroethane = 60/40. (2) Melt viscosity Shimadzu FLOWTESTER (model CFT-50
No. 0) was used and the measurement was performed with a nozzle diameter of 1 mm and a load of 100 kg / cm ² . (3) Heat distortion temperature A TMA (Thermal Mechanical) manufactured by Rigaku Co., Ltd.
l Analyzer; TAS-100) in compression mode.

Example 1 100 parts by weight of PEN resin (intrinsic viscosity: 0.63) was blended with 0.6 part by weight of talc. Prepared thermoplastic resin composition with screw diameter 65 mm, screw L / D
Extruder was used. Extruder speed 5
The temperature of the melting zone was kept at 290 ° C., the temperature of the die was kept at 280 ° C., the nitrogen gas was injected at 80 kg / cm ² from the vent of the melting zone at 0 rpm. At this time, the melt viscosity of the resin in the melting zone is 8,000 poise.

The thickness of the produced foam sheet is 1.0 mm,
The size of bubbles is 60-80 μm, and the density is 0.40 g / cm
³ , the expansion ratio was 3.33 times. The obtained sheet was molded at a molding temperature of 140 ° C. using a Kiefeld thermoforming machine.
Heat set temperature 180 ℃, vertical 120mm, width 16
It was molded into 10 thermoformed products of 0 mm in height and 37 mm in height. Add water and salad oil to this molded product and microwave for 10 minutes.
Table 1 shows the result of heating for a minute and checking the deformation of the appearance of the container.

Example 2 A foamed sheet was produced in the same manner as in Example 1 except that 100 parts by weight of PEN resin (intrinsic viscosity 0.85) was used. At this time, the resin melt viscosity in the melting zone is 1
It is 2,000 poise. The thickness of the produced foamed sheet was 2.0 mm, the size of bubbles was 40 to 60 μm, the density was 0.20 g / cm ³ , and the expansion ratio was 6.65 times. Table 1 shows the heat resistance evaluation results of the molded products.

Example 3 A foamed sheet was produced in the same manner as in Example 1 except that 0.4 part by weight of Zn stearate was further added. At this time, the melt viscosity of the resin in the melting zone is 9,000 poise. The thickness of the produced foamed sheet was 1.5 mm, the size of cells was 40 to 50 μm, the density was 0.23 g / cm ³ , and the expansion ratio was 5.78 times. Table 1 shows the heat resistance evaluation results of the molded products.

Comparative Example 1 100 parts by weight of a PET resin having an intrinsic viscosity of 0.70 was blended with 0.6 part by weight of talc and 0.4 part by weight of Zn stearate. The prepared thermoplastic resin composition was extruded using an extruder having a screw diameter of 65 mm and a screw L / D of 30. Keep the extruder speed at 50 rpm, the melting zone temperature at 290 ° C, and the die temperature at 280 ° C.
Nitrogen gas was injected at 80 kg / cm ² from the vent of the melting zone. At this time, the melt viscosity of the resin in the melting zone is 3,300 poise. No foaming occurred and no foamed sheet was obtained.

Comparative Example 2 100 parts by weight of PEN resin (intrinsic viscosity 0.43), 0.6 parts by weight of talc, and 0.4 parts by weight of Zn stearate were blended. The prepared thermoplastic resin composition was extruded using an extruder having a screw diameter of 65 mm and a screw L / D of 30. Keep the extruder speed at 50 rpm, the melting zone temperature at 290 ° C, and the die temperature at 280 ° C.
Nitrogen gas was injected at 80 kg / cm ² from the vent of the melting zone. At this time, the melt viscosity of the resin in the melting zone is 6,300 poise. The thickness of the produced foam sheet is 0.3 mm, the size of the bubbles is 60 to 150 μm,
The density was 0.65 g / cm ³ , and the expansion ratio was 2.00. The obtained sheet had large unevenness of foaming and could not be thermoformed.

[0036]

[Table 1]

[0037]

EFFECT OF THE INVENTION It is possible to provide a foamed polyester sheet which has uniform fine bubbles and a high expansion ratio, is excellent in high temperature stability and can be used as a food container compatible with a microwave oven, and a method for producing the same.

Claims (3)

[Claims] 1. An inorganic nucleating agent selected from the group consisting of (a) 100 parts by weight of a polyethylene 2,6-naphthalate resin having an intrinsic viscosity of 0.5 or more and (b) glass, a mineral material and a mixture thereof. A foamed polyester sheet comprising a resin composition containing 01 to 5 parts by weight. 2. The expanded polyester sheet according to claim 1, which has a density in the range of 0.01 to 1.5 g / cm ³ . 3. An inorganic nucleus selected from the group consisting of (1) (a) 100 parts by weight of a polyethylene 2,6-naphthalate resin having an intrinsic viscosity of 0.5 or more and (b) glass, a mineral material and a mixture thereof. 0.01 to 5 parts by weight of the agent is supplied to a melt extruder for melt mixing, (2) an inert gas is mixed in while the resulting mixture in a molten state is in the melt extruder, and (3) formation A method for producing a foamed polyester sheet, comprising extruding from a die to produce a foamed polyester sheet.