JPH10316785A - Method for producing polyethylene terephthalate resin foam sheet - Google Patents

Abstract

(57) [Abstract] [Problem] To have a clean appearance without wrinkles or tears on the surface, and to be excellent in heat resistance, heat insulation, weather resistance, etc.
Provided is a foam sheet suitable for various uses such as a heat insulating container and a buffer packaging material. SOLUTION: A composition comprising a polyethylene terephthalate resin (A), a polyvalent carboxylic acid having at least three carboxylic acid groups (B) and a compound having two or more oxazoline groups in one molecule (C). A method for producing a foamed sheet by kneading a melt obtained by melting a material with an extruder and a foaming agent at a high temperature and a high pressure and extruding the kneaded material through a circular die to a low pressure region and molding with a mandrel, The surface temperature of the foamed sheet until the temperature reaches the mandrel is maintained at 180 ° C. or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyester resin foam, and more particularly, to a method for producing a polyethylene terephthalate resin foam sheet which can be suitably used for, for example, heat-resistant containers, heat-insulating containers, buffer packaging materials and the like. About the method.

[0002]

2. Description of the Related Art Linear aromatic polyester resins such as polyethylene terephthalate have mechanical properties, heat resistance,
Because of its excellent chemical resistance and dimensional stability, it is used in a wide range of applications such as injection molded products, blow molded products, films and fibers. However, it is extremely difficult to obtain a good foam because extrusion viscoelasticity at the time of melting is insufficient to perform extrusion foaming using the linear aromatic polyester resin. There are drawbacks.

[0003] As a method of remedying such drawbacks, when extrusion-molding a linear aromatic polyester resin,
A method of mixing a compound having two or more acid anhydride groups in one molecule with the resin (Japanese Patent Publication No. 5-15736),
A method in which a similar acid anhydride and a specific metal compound are combined and mixed with the resin (Japanese Patent Publication No. 5-47575) has been proposed.

[0004] By the way, for example, a container molded from a foamed sheet is required to be beautiful in appearance without wrinkles on the surface. Further, in order to obtain a molded container having a beautiful appearance without wrinkles on the surface as described above, it is necessary to obtain a foam sheet having a beautiful appearance without wrinkles. Further, in order to improve the processability of the polyester resin, the degree of crystallinity is suppressed to a low level. However, in order to suppress the degree of crystallinity, rapid cooling is generally performed. However, in the study of foam production, the present inventors found that if the foamed sheet immediately after extrusion was rapidly cooled, uneven cooling or insufficient cooling could not be performed, so that the foamed sheet surface had wrinkles and tears due to uneven cooling (unevenness). And a problem that a foamed sheet with a beautiful appearance cannot be obtained.

[0005] For example, in Japanese Patent Publication No. 5-83573, a hot foam immediately after foaming is rapidly cooled to a glass transition temperature or less to reduce the crystallinity to 30% or less.
A method for producing a thermoplastic polyester resin foam characterized by heating to 0 ° C. or higher has been proposed. However, when the sheet is formed by the manufacturing method, uneven cooling (non-uniformity) occurs when the foamed sheet is rapidly cooled. As a result, the expansion ratio varies, a portion having a high degree of crystallinity is generated, and the sheet surface is wrinkled or torn. There is a problem that occurs.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, has good secondary workability due to the low crystallinity, and has the problem of uneven cooling during sheet formation. An object of the present invention is to provide a method for stably producing a foamed sheet which is free from wrinkles and tears, has a beautiful surface, and has excellent cushioning properties, mechanical properties and heat resistance.

[0007]

That is, the present invention relates to a polyethylene terephthalate resin (A), a polyvalent carboxylic acid (B) having at least three carboxylic acid groups, and two or more oxazolines in one molecule. After the composition comprising the compound having a group (C) is melted by an extruder and a foaming agent is kneaded at a high temperature and a high pressure, the kneaded material is extruded through a circular die to a low pressure region and molded with a mandrel to form a foam. A method for producing a sheet, wherein the surface temperature of a foamed sheet from an extruder to a mandrel is set to 180.
A method for producing a foamed polyethylene terephthalate resin sheet characterized in that the sheet is maintained at a temperature of not less than ° C.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The polyethylene terephthalate resin used in the present invention is a polyester obtained by polycondensing a carboxylic acid containing terephthalic acid as a main component and an alcohol containing ethylene glycol as a main component. Terephthalic acid as the main component means that the carboxylic acid contains 70% by weight or more of terephthalic acid, and ethylene glycol as the main component means that the alcohol contains ethylene glycol at 70% by weight.
It means that it is contained above.

Specific examples of the carboxylic acid include, in addition to terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, and the like. A mixture of more than one species can be used.

Specific examples of the alcohol include, besides ethylene glycol, propylene glycol, butanediol, neopentylene glycol, hexamethylene glycol, cyclohexane dimethylol, tricyclodecane dimethylol, 2,2-bis (4- β-hydroxyethoxyphenyl) propane, 4,4′-bis (β-
(Hydroxyethoxy) diphenyl sulfone and the like, and these can be used alone or in combination of two or more.

The polyethylene terephthalate-based resin preferably has a number average molecular weight of 10,000 to 50,000 and an intrinsic viscosity of 0.5 to 1.1 dl / g from the viewpoint of easy industrial processing. Such a polyethylene terephthalate-based resin can be produced by a method of melt polycondensation or solid phase polymerization usually used for producing a polyester. In general, in the case of melt polycondensation, a high-molecular-weight product tends to be difficult to obtain, so that a higher molecular weight may be obtained by solid-phase polymerization. It tends to be higher. In the present invention, since a polyethylene terephthalate resin having a relatively small molecular weight obtained by melt polycondensation can be used, if simplicity or low cost is required, a polyethylene terephthalate resin obtained by melt polycondensation is used. It may be preferable to use.

The polyvalent carboxylic acid having at least three carboxylic acid groups used in the present invention is not particularly limited as long as it is a compound having at least three, preferably three to four carboxylic acid groups in one molecule. However, from the viewpoint of improving the compatibility after melt mixing with the polyethylene terephthalate resin, the molecular weight is preferably 500 or less, more preferably 15 or less.
It is preferably from 0 to 350.

Specific examples of the polycarboxylic acid include trimellitic acid, pyromellitic acid, naphthalene tricarboxylic acid, and naphthalene tetracarboxylic acid. These may be used alone or in combination of two or more. Among the polyvalent carboxylic acids, pyromellitic acid is preferred because it can be uniformly and easily melt-mixed with a polyethylene terephthalate resin. The polyvalent carboxylic acid is melt-mixed with a polyethylene terephthalate-based resin to produce a polyester having a carboxylic acid group at a molecular terminal through a transesterification reaction.

The polycarboxylic acid is used in an amount of 0.05 to 5 parts by weight based on 100 parts by weight of the polyethylene terephthalate resin (A).
Parts by weight, preferably 0.1 to 3 parts by weight, more preferably 0.2 to 2 parts by weight. When the amount of the polyvalent carboxylic acid is less than the above range, the effect of stabilizing the melt viscoelasticity that is improved when the composition used in the present invention is melted becomes insufficient, and when the amount exceeds the above range. Tends to be difficult to melt-process the composition used in the present invention.

The compound having two or more oxazoline groups in one molecule used in the present invention is a compound in which two or more oxazoline rings are bonded to an aliphatic group or an aromatic group, and has the following general formula (I) ).

[0016]

Embedded image

In the above general formula (I), R represents 1 carbon atom.
To 4, hydrocarbons, benzene rings, taphthalene rings, groups derived from benzene rings bonded to hydrocarbons, and the like. Specific examples thereof include a methylene group, an ethylene group, a trimethylene group, and a tetramethylene group. Group, phenylene group, naphthylene group and the like. In the general formula (I), R ¹ , R ² , R ³ and R ⁴ include hydrogen or an alkyl group such as methyl and ethyl. Furthermore,
In the above general formula (I), n is an integer of 2 or more, preferably 2 or 3.

A typical example of this compound is a condensate of a polycarboxylic acid or a derivative thereof such as an acid chloride and a 2-amino alcohol. Specific examples of the condensate of dicarboxylic acid or its acid chloride and 2-amino alcohol include 1,3-bis (2-oxazolin-2-yl) benzene derived from isophthalic acid, and 1,3-bis (2-oxazolin-2-yl) benzene.
Bis (4,4-dimethyl-2-oxazolin-2-yl) benzene, terephthalic acid, analogs derived from phthalic acid; naphthalenedicarboxylic acids such as 1,4-derived from naphthalene-1,4-dicarboxylic acid Bis (2-oxazolin-2-yl) naphthalene, 1,4-
Bis (4,4-dimethyl-2-oxazolin-2-yl) naphthalene; 1,2-bis (2-oxazolin-2-yl) ethane derived from succinic acid, 1,2-bis (4,4 -Dimethyl-2-oxazolin-2-yl)
Ethane; 1,3-bis (2-derived from glutaric acid
Oxazolin-2-yl) propane, 1,3-bis (4,4-dimethyl-2-oxazolin-2-yl) propane; 1,4-bis (2-
Oxazolin-2-yl) butane, 1,4-bis (4,
4-dimethyl-2-oxazolin-2-yl) butane and the like. Derivatives of tricarboxylic acid include 1,2,4-tris (2-oxazolin-2-yl) benzene derived from trimellitic acid. Of these, preferred are 1,3-bis (2-oxazolin-2-yl) benzene and 1,4-bis (2-oxazoline-2-) derived from isophthalic acid and terephthalic acid.
Il) It is benzene. These compounds having two or more oxazoline groups in one molecule can be used alone or in combination of two or more.

The compound (C) having two or more oxazoline groups in one molecule is obtained by melting the compound (A) with the polyethylene terephthalate resin (A) and the polycarboxylic acid (B) having at least three carboxyl groups. Used to improve viscoelasticity. This is because the carboxyl group present in the polyester molecule and the oxazoline group react with the polyethylene terephthalate-based resin and the polyvalent carboxylic acid and are produced, and the oxazoline group is opened and bonded to form the polyester. This is considered to be due to a structure in which the molecules are bonded to each other.

That is, in the present invention, since the polyester resin contains a polyvalent carboxylic acid component, the polyester resin has a large branched structure, and the viscoelasticity at the time of melting can be remarkably improved. . In the present invention, the compound having two or more oxazoline groups in one molecule is the polyethylene terephthalate resin 100.
0.1 to 10 parts by weight, preferably 0.2 to 10 parts by weight
To 5 parts by weight, more preferably 0.3 to 3 parts by weight. When the proportion of the compound having two or more oxazoline groups in one molecule is smaller than the above range, it becomes difficult to improve the melt viscoelasticity of the composition of the present invention to a melt viscoelasticity suitable for extrusion foam molding. If the amount is larger than the above range, it is difficult to control the properties of the resin at the time of foaming by uniformly controlling the reaction with the polyester-based resin. Tend to be unable to do so.

In the present invention, a foamed sheet using a polyethylene terephthalate-based resin as a base resin is manufactured, and the extrusion foaming method is suitable as the method. Extrusion foaming can be performed, for example, as follows. The polyethylene terephthalate-based resin composition is put into an extruder and melted, and a foaming agent is press-fitted from the middle of the extruder so that the melted polyethylene terephthalate-based resin contains the foaming agent. A circular die is attached to the tip of the extruder, and a polyethylene terephthalate-based resin containing a foaming agent is extruded from the extruded holes, and molded with a mandrel to form a foamed sheet.

The extruder used for extrusion foaming is a single screw extruder,
An extruder such as a multi-screw extruder or a tandem extruder can be used. From the viewpoint that the properties of the obtained foam can be easily adjusted, it is desirable to extrude and foam using a tandem extruder. Further, in the tandem extruder, the foaming agent is supplied from the first extruder and the first extruder. Although it can be injected from any position of the conveying pipe to the second-stage extruder and from any place of the second-stage extruder, a method of press-fitting from the first-stage extruder to improve the dispersion and kneading of the foaming agent in the molten resin. Is desirable.

In the production method of the present invention, the composition is prepared by first melting and kneading the polyethylene terephthalate resin (A) and the polyvalent carboxylic acid (B), and then two or more oxazolines in one molecule. The compound obtained by adding the compound (C) having a group is preferable because the melt viscoelasticity of the obtained composition is easily controlled industrially. In this case, the melt kneading of the polyethylene terephthalate resin (A) and the polyvalent carboxylic acid (B)
It can be carried out by stirring and kneading while maintaining the temperature required for melting using various kneading apparatuses usually used for resin melt processing, but from the viewpoint that melt kneading can be performed uniformly and easily, it is biaxial. It is preferable to use an extruder.

The thus obtained melt-kneaded product of the polyethylene terephthalate resin (A) and the polyvalent carboxylic acid (B) preferably has a number average molecular weight of 3,000 to 4,000.
0, more preferably 5,000 to 30,000. When the number average molecular weight is smaller than the above range, the melt viscoelasticity of the composition used in the present invention tends to be insufficiently improved, and when the number average molecular weight is larger than the above range, melt molding tends to be difficult. .

Examples of the foaming agent include a solid decomposition type foaming agent which decomposes by heating to generate a gas, a liquid volatile foaming agent which vaporizes by heating, and a gaseous gas type foaming agent which can be dissolved in a resin under pressure. Either can be used. Specific examples of the decomposable foaming agent include azodicarbonamide, dinitropentamethylenetetramine, hydrazodicarbonamide, sodium bicarbonate and the like, and these are used alone or in combination of two or more. Specific examples of volatile foaming agents include saturated aliphatic hydrocarbons such as butane, pentane and hexane, saturated alicyclic hydrocarbons such as cyclohexane, aromatic hydrocarbons such as benzene and xylene, and methylene chloride. Halogenated hydrocarbons,
Examples thereof include fluorochloro-substituted hydrocarbons such as Freon (trade name), and these are used alone or in combination of two or more. Further, specific examples of the gas-type blowing agent include nitrogen, carbon dioxide, and the like, and these may be used alone or in combination of two or more.

The amount of the foaming agent used is an amount necessary for the obtained polyethylene terephthalate resin foam to have a desired expansion ratio. For example, in order to obtain a foamed sheet, the amount is preferably 0.5 parts by weight or more, especially 1 part by weight or more, based on 100 parts by weight of a molten mixture obtained by melt-mixing a polyethylene terephthalate-based resin. In order not to reduce the dimensional stability during molding, 1 part by weight of the molten mixture is used.
It is preferably 0 parts by weight or less, especially 7.5 parts by weight or less.

The circular die is a die having an extrusion hole having an annular cross section. The mandrel is a cylindrical cooling plug, and its material may be any material as long as it does not physically or chemically change upon contact with the foam sheet, but may be made of aluminum or stainless steel having a high thermal conductivity. Is preferably used.

In the present invention, the extruded polyethylene terephthalate-based resin sheet has a surface of a foamed sheet extruded from a circular die of an extruder still at 180 ° C.
During the above, it is cooled by contact cooling with a mandrel to obtain a foamed sheet. The temperature of the polyethylene terephthalate resin sheet immediately after being extruded is 2
It is about 30 to 280 ° C. While the surface of the foamed sheet extruded from the circular die of the extruder is still at 180 ° C. or higher, it differs depending on the ambient temperature of the extruded low pressure region. For example, if the ambient temperature is about 15 to 25 ° C., Generally, it is from the immediately after to about 1 to 3 seconds. In the present invention, the surface temperature of the foamed sheet is measured using a non-contact radiation thermometer.

In the production of a foamed sheet of an amorphous resin such as a polystyrene resin, a high-temperature foamed sheet immediately after extrusion is cooled to a temperature close to the glass transition temperature by blowing air or the like to obtain a foamed sheet having a beautiful surface. Can be obtained. However, when producing a foamed sheet of polyethylene terephthalate-based resin, if the glass is crystalline, and if it is to be cooled to a temperature close to the glass transition temperature in the same manner as in the production of a foamed sheet of an amorphous resin, the crystallization rate will be reduced before that. Since the foamed sheet passes through a high temperature zone (about 130 to 160 ° C.), a part having a high degree of crystallinity is generated in the foamed sheet, and the foamed sheet is torn or wrinkled. In addition, due to cooling unevenness, foaming in a low temperature portion stops, uneven foaming ratio occurs, and wrinkles are generated on the foam sheet surface,
A foam sheet with a beautiful surface cannot be obtained.

Therefore, according to the present invention, the foamed sheet is extruded from the extruder until the mandrel forms the sheet so that the sheet is not broken or wrinkled due to the influence of crystallinity or the effect of uneven cooling. By maintaining the temperature and heating until the sheet reaches the mandrel, it is possible to obtain a foamed sheet with a beautiful surface without tearing or wrinkling of the sheet due to the crystallinity. That is, the foamed sheet having a beautiful surface can be obtained by maintaining the temperature at 180 ° C. or higher until the foamed sheet is extruded from the extruder and formed by the mandrel.

In the production method of the present invention, if the temperature of the foam sheet before reaching the mandrel is 180 ° C. or higher, crystallization proceeds uniformly, and wrinkles and tears occur on the surface of the foam sheet. But by slowing down the cooling,
A foam sheet having a beautiful surface without wrinkles or tears on the surface can be obtained. If the foamed sheet is cooled to less than 180 ° C. before reaching the mandrel from the extruder, foaming in the low-temperature portion will stop, and wrinkles will occur on the foamed sheet surface due to uneven foaming ratio, and further partial crystal growth will occur. Some parts cause crystallization, and wrinkles and tears occur due to variation in crystallization.

It takes 180 seconds for the polyethylene terephthalate resin foam sheet to reach the mandrel from the extruder.
Examples of the method for maintaining the temperature at a temperature of not less than ° C include the following methods, but the present invention is not limited thereto. For example, in order to insulate the foam sheet from the external environment, a method of covering the foam sheet between the mandrel and the extruder with a hood made of aluminum or the like, or foaming by blowing air at a temperature of 180 ° C. or more to the foam sheet immediately after extrusion. There is a method of preventing the temperature of the sheet surface from lowering.

The thickness of the foam sheet is preferably 0.5 mm or more because the foam after extrusion cannot maintain heat if the thickness of the foam sheet is too thin. Is difficult to form a sheet, and wrinkles are easily formed during the formation of the sheet.

In the manufacturing method of the present invention, when the outlet diameter of the circular die and the outer shape ratio of the cylindrical mandrel (hereinafter, referred to as blow-up ratio) are small, the foam after exiting the die has a small blow-up ratio. When the blow-up ratio is large, the foam is torn when the foam is applied to the mandrel in order to form the foam into a foamed sheet. Therefore, the blow-up ratio is desirably 2 to 5 times.

The polyethylene terephthalate-based resin foam sheet produced by the production method of the present invention preferably has a crystallinity of a mandrel-molded foam sheet in order to improve secondary workability such as container moldability. 20% or less,
More preferably, it is desirably 15% or less. The crystallinity of the foamed sheet produced by the production method of the present invention is usually at least 5% or more.

In the present invention, the crystallinity refers to the differential scanning calorimetry (hereinafter referred to as DSC method).
Using a differential scanning calorimeter / analyzer (DSC200 manufactured by Seiko Denshi Kogyo Co., Ltd.), at a heating condition of 10 ° C./min,
After measuring the melting point Tm (° C.) and the crystallization temperature Tc (° C.) of the polyethylene terephthalate resin, Tm and T
c Calorific value Hm (J / g) and Hc at each temperature
(J / g) refers to a value (absolute crystallinity) calculated according to the following equation. [Crystallinity (%)] = {(Hm−Hc) / Ho} × 10
0 In the formula, Ho represents the heat of fusion (J / g) per gram of the fully crystallized polyethylene terephthalate resin. Here, according to the Polymer Data Handbook (published by Baifukan), the heat of complete crystallization per mole of polyethylene terephthalate is 26.9 KJ. Converting this to the amount of heat of complete crystallization per gram gives 1
Since Ho is 40.1 J, Ho uses this value.

The foamed sheet of the present invention has a density of 0.7
By setting the g / cm ³ or less, preferably 0.5 g / cm ³ , it is possible to effectively realize the lightweight property, which is an advantage of the foam. The lower limit of the density is about 0.02 g / cm ³ . Further, by setting the closed cell ratio of the bubbles present in the foamed sheet to 70% or more, preferably 80% or more, the heat insulating property can be further enhanced. Further, when the size of the bubbles in the foam sheet is 0.5 mm or less, preferably 0.3 mm or less in diameter, the heat insulating property can be further enhanced. The foam sheet produced in this way has a beautiful appearance and a uniform fine cell structure, and is suitably used for applications such as heat-resistant containers, heat-insulated containers, and buffer packaging materials.

[0038]

EXAMPLES The present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the following description, “parts” means “parts by weight” unless otherwise specified.

Example 1 The number average molecular weight was 17000 and the intrinsic viscosity was 0.65 dl / g.
A mixture obtained by mixing 0.4 parts of pyromellitic acid and 0.2 parts of triphenyl phosphite with 100 parts of polyethylene terephthalate pellets was used to prepare a mixture having a cylinder diameter of 30 parts.
The mixture was extruded and kneaded with a twin-screw extruder having a diameter of 2 mm to prepare pellets of the polyethylene terephthalate resin (A-1). Cylinder diameter 45mm with foaming agent inlet in the rear half of the cylinder
The polyethylene terephthalate-based resin ( A-1) To 100 parts, 1.24 parts of 1,3-phenylenebisoxazoline,
A composition mixed at a rate of 0.25 parts of talc was supplied from a vibrating quantitative feeder at a rate of 15 kg / hr, and liquefied butane gas was used as a blowing agent at a rate of 2.2 parts per 100 parts of a melt from a blowing agent inlet. A cylindrical foam sheet was extruded from a circular die under the following conditions from an extruder equipped with a circular die having a diameter of 30 mm and a clearance of 0.6 mm, and the space between the extruder and the mandrel was covered with an aluminum hood. The tube was advanced while being in close contact with a stainless steel cylindrical mandrel having an outer diameter of 120 mm and adjusted to 50 ° C., and then the cylindrical foam sheet was cut open to obtain a flat foam sheet. First stage extruder cylinder temperature 265-290 ° C Conveyor tube temperature 280-285 ° C Second stage extruder cylinder temperature 270-280 ° C Second stage extruder head temperature 270-280 ° C Second stage extruder die temperature 270-280 ℃ The surface temperature of the foam sheet immediately before reaching the mandrel is 1
95 ° C. The foamed sheet obtained had an expansion ratio of 7.
It was three times and the thickness was 1.5 mm.

The crystallinity of the obtained foamed sheet, wrinkles on the surface of the foamed sheet, and moldability of the container were examined by the following methods. Table 1 shows the results.

1) Crystallinity 10 ° C./° C. using a differential scanning calorimeter (DSC200 manufactured by Seiko Instruments Inc.) in accordance with the DSC method.
After measuring the melting point Tm (° C.) and the degree of crystallinity Tc (° C.) of the polyethylene terephthalate-based resin under the conditions of temperature rise for one minute, the calorific value Hm (J /
g) and Hc (J / g) were measured and calculated according to the following conditional expressions. [Crystallinity (%)] = {(Hm−Hc) / Ho} × 10
0 In the formula, Ho represents the heat of fusion (J / g) per gram of the fully crystallized polyethylene terephthalate resin.

2) Wrinkles on the Surface of the Foamed Sheet The obtained foamed sheet was cut into a size of 30 cm × 30 cm, and wrinkles on both surfaces were visually observed and evaluated according to the following evaluation criteria. (Evaluation criteria) A: No wrinkles are observed on both sides of the foam sheet. B: One or two wrinkles are observed on one side of the foam sheet. C: Three or more wrinkles are observed on one side of the foam sheet.

3) Container moldability The foamed sheet was prepared by using a single-shot molding machine with an infrared heater.
The mixture was heated to 30 to 140 ° C., shaped in a mold controlled at 180 ° C., and promoted crystallization, and formed into a container having a diameter of 70 mm, a depth of 20 mm, and a bottom diameter of 55 mm. The state of the obtained molded container was visually observed, and evaluated based on the following evaluation criteria. (Evaluation Criteria) A: No crack, crack or wrinkle is observed in the container. B: Only molding wrinkles are observed in a part of the container. C: Cracks and cracks are observed in a part of the container.

Example 2 In Example 1, the ratio of the liquefied butane gas to 100 parts in the molten mixture was changed from 2.2 parts to 1.5 parts, and the clearance of the circular die was changed from 0.6 mm to 0.4 part.
In the same manner as in Example 1 except that the foaming ratio was changed to 6. mm.
A foam sheet 5 times in thickness and 1.2 mm in thickness was obtained. The surface temperature of the foam sheet immediately before reaching the mandrel was 188 ° C. The crystallinity, surface wrinkles, and container moldability of the obtained foamed sheet were examined in the same manner as in Example 1. Table 1 shows the results.

Example 3 In Example 1, the aluminum hood between the extruder and the mandrel was removed, and air heated to 200 ° C. was blown from both sides of the foamed sheet immediately after extrusion at a rate of 3 liters per minute. A foamed sheet having a foaming ratio of 7.5 times and a thickness of 1.4 mm was obtained in the same manner as in Example 1 except that spraying was performed from both sides of the sheet. The surface temperature of the foam sheet immediately before reaching the mandrel was 188 ° C. The crystallinity, surface wrinkles, and container moldability of the obtained foamed sheet were examined in the same manner as in Example 1. Table 1 shows the results.

Example 4 The same procedure as in Example 1 was carried out except that the temperature of the mandrel was changed from 50 ° C. to 140 ° C. to obtain a foam having an expansion ratio of 8.2 times and a thickness of 1.3 mm. I got a sheet. The surface temperature of the foam sheet immediately before reaching the mandrel was 192
° C. The crystallinity, surface wrinkles, and container moldability of the obtained foamed sheet were examined in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 1 The procedure of Example 1 was repeated, except that the foamed sheet immediately after being discharged from the extruder was blown from both sides of the foamed sheet at a rate of 3 liters / minute at 20 ° C. Similarly, a foam sheet having a foaming ratio of 7 times and a thickness of 1.3 mm was obtained. The surface temperature of the foam sheet immediately before reaching the mandrel was 165 ° C. The crystallinity, surface wrinkles, and container moldability of the obtained foamed sheet were examined in the same manner as in Example 1. Table 1 shows the results.

COMPARATIVE EXAMPLE 2 The procedure of Example 1 was repeated, except that the aluminum hood was removed between the extruder and the mandrel. I got a sheet. The surface temperature of the foam sheet immediately before reaching the mandrel was 173 ° C. The crystallinity, surface wrinkles, and container moldability of the obtained foamed sheet were examined in the same manner as in Example 1. Table 1 shows the results.

[0049]

[Table 1]

[0050]

According to the present invention, it is possible to obtain a foamed sheet having a clean appearance without wrinkles or tears on the surface. Furthermore, since the present invention is a method for producing a foamed sheet using a polyethylene terephthalate-based resin having excellent heat resistance as a base resin, the resulting foamed sheet has excellent heat resistance, heat insulation properties, weather resistance, etc. It is suitable for various uses such as containers and buffer packaging materials.

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Claims (5)

[Claims] 1. A polyethylene terephthalate-based resin (A), a polyvalent carboxylic acid (B) having at least three carboxylic acid groups, and a compound (C) having two or more oxazoline groups in one molecule. A method of manufacturing a foamed sheet by kneading a melt obtained by melting a composition with an extruder and a foaming agent at a high temperature and a high pressure, extruding the kneaded material through a circular die to a low pressure region and molding with a mandrel, and A method for producing a polyethylene terephthalate-based resin foam sheet, wherein the surface temperature of the foam sheet from the press to the mandrel is maintained at 180 ° C. or higher. 2. Polyethylene terephthalate resin (A) is melt-mixed with a polyvalent carboxylic acid (B) having at least three carboxylic acid groups, and then a compound having two or more oxazoline groups in one molecule ( The method according to claim 1, wherein the composition obtained by adding (C) is melted by an extruder. 3. The method according to claim 1, wherein the degree of crystallinity of the foamed sheet formed by the mandrel is 20% or less. 4. The polycarboxylic acid (B) having at least three carboxylic acid groups is blended in an amount of 0.05 to 5 parts by weight based on 100 parts by weight of the polyethylene terephthalate resin (A). 3. The production method according to 3. 5. The compound according to claim 1, wherein the compound (C) having two or more oxazoline groups in one molecule is 0.1 to 10 parts by weight based on 100 parts by weight of the polyethylene terephthalate resin (A). 5. The production method according to 3 or 4.