JPH0583573B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing a thermoplastic polyester resin foam. More specifically, in this invention, when a thermoplastic polyester resin is first foamed, it is rapidly cooled to form a foam with a low degree of crystallinity, and then this foam is heated to further expand the foam. The present invention relates to a method for producing a low-density thermoplastic polyester resin foam.

(Prior Art) Some thermoplastic resins are suitable for use in foams, while others are not. Among thermoplastic resins, polystyrene is said to be the most suitable resin for making foams because it exhibits a viscosity suitable for making foams over a wide temperature range when heated. In addition, polyethylene does not show a viscosity suitable for foaming as it is, but when it is irradiated with radiation or a chemical crosslinking agent is added, it easily crosslinks and shows an appropriate viscosity. It is said that this resin is suitable for making into foam. Therefore, polystyrene foams and polyethylene foams have been produced in large quantities and have come to be widely used as heat insulating materials, cushioning materials, packaging materials, molded articles, and the like.

On the other hand, thermoplastic polyester resin (hereinafter referred to as PAT) has excellent properties not found in polystyrene or polyethylene.
For example, it has high rigidity and good shape stability,
It has excellent heat resistance, being able to withstand temperatures of 200℃. Therefore, attempts were made to use PAT as a foam material to make heat-resistant and strong insulation materials, cushioning materials, packaging containers, etc. However, unlike polystyrene and polyethylene, it was not easy to foam PAT. Even if foaming was achieved, the foaming ratio remained low. Here, PAT
means a high molecular weight chain polyester obtained by reacting an aromatic dicarboxylic acid such as terephthalic acid with a dihydric alcohol such as ethylene glycol.

The reason PAT is difficult to foam is that when melted, PAT does not exhibit a suitable viscosity for foaming, like polystyrene or polyethylene. Specifically, when PAT is heated, it rapidly softens and becomes a liquid with low viscosity. Therefore,
This is because the temperature range in which the viscosity is suitable for foaming is narrow, and therefore temperature control is difficult, and because the viscosity is low, the gas that acts as a foaming agent quickly dissipates. Therefore, attempts have been made to improve the viscosity properties during melting to facilitate foaming, thereby obtaining a low-density PAT foam.

As an improvement plan, it was proposed to mix various things into PAT. For example, it has been proposed to mix a diepoxy compound with PAT, or to use a mixture of group a and group a metal compounds of the periodic table with a diepoxy compound. Although this proposal certainly made foaming easier, it was still not possible to obtain a low-density foam that expanded to a high ratio.

JP-A-55-2045 describes a method for obtaining a low-density foam by introducing high-temperature PAT containing a foaming agent immediately after extrusion from an extruder into a reduced pressure zone and foaming it under reduced pressure. There is. However, since foams generally have uneven surfaces or are significantly deformed due to foaming, it is not easy to construct a vacuum zone through which such foams can be passed continuously. In particular, it is difficult to provide a sufficient vacuum seal at the foam outlet. Therefore, this method has the disadvantage that it is not easy to implement.

JP-A-59-135237 recommends using a high molecular weight linear aromatic polycarbonate as a blowing agent to make PAT foams. However, with this method, only a low expansion ratio can be obtained. In fact, this publication only cites a density of 0.83 g/cc as one example of the resulting foam. In addition, this publication states that when PAT foam is held at high temperatures, PAT crystallization progresses.
By keeping the foam at a high temperature of 204℃ or higher,
It is also stated that a PAT foam with high heat resistance can be obtained.

Although PAT is a crystalline resin, it is known that the degree of crystallinity varies depending on the molding method. It is also known that the higher the degree of crystallinity, the better the heat resistance. Furthermore, its crystallinity is determined by the density of the resin,
Based on line diffraction images, nuclear magnetic resonance spectra, etc.
It is also known that it can be measured. However, P.A.T.
Since the foam contains air bubbles, the degree of crystallinity cannot be easily measured by these methods. Therefore, crystallinity was not a problem when making PAT foams.

(Problems to be Solved by the Invention) This invention aims to obtain a PAT foam that is expanded to a high magnification. More specifically, the present invention was made in an attempt to provide a method for easily producing a low-density PAT foam having uniform, fine cells.

(Means for Solving the Problem) The inventor attempted to foam PAT to a high magnification by foaming PAT twice. At that time, the inventor said that the lower the degree of crystallinity, the easier it is to deform due to heat.
I came up with the idea of using the characteristics of PAT. As a result of various experiments, the inventor found that although the initial foaming, that is, the primary foaming, may be performed by any means, the degree of crystallinity of the primary foam obtained by the primary foaming should be kept low. It has been found that foaming when the foam is subsequently heated and foamed, that is, secondary foaming, is facilitated, and that foaming can be achieved at a high magnification. The inventor also confirmed that the degree of crystallinity of a PAT foam can be reliably measured from the cold crystallization heat and fusion heat. Furthermore, the inventor found that when the crystallinity of the primary foam is measured by the thermal method described above, by rapidly cooling the foam obtained by primary foaming, the crystallinity of the primary foam can be suppressed to 30% or less. They found that the secondary foam can be easily foamed by heating it to 60°C or higher. This invention was made based on such knowledge.

(Summary of the Invention) This invention rapidly cools the softened PAT foam to below the glass transition point immediately after foaming to reduce the degree of crystallinity.
30% or less, and then heating the PAT foam to 60° C. or higher.

(Description of each requirement of the invention) In the present invention, in order to produce a softened PAT foam, PAT that has been softened at high temperatures and contains a blowing agent may be transferred to a low pressure region. It softens when exposed to high temperatures and contains a foaming agent.
To make PAT, heat and melt PAT.
A blowing agent may be mixed into this under pressure. For this purpose, various methods that have been employed up to now can be used. Among them, it is easy to use an extruder to melt PAT in the extruder, press-in a blowing agent during extrusion and knead it, and then extrude this kneaded material from a mold attached to the extruder. This is an easy method to implement.

As described above, PAT that can be used in this invention is a high molecular weight chain polyester obtained by reacting an aromatic dicarboxylic acid with a dihydric alcohol. As the dicarboxylic acid, terephthalic acid is most often used, but isophthalic acid and 2,6-naphthalene dicarboxylic acid are also used. In addition, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, and diphenoxy dicarboxylic acid can also be used. Ethylene glycol is mainly used as the dihydric alcohol, but trimethylene glycol, tetramethylene glycol, neopentylene glycol, hexamethylene glycol, cyclohexane dimethylol, tricyclodecane dimethylol, 2,2-bis(4 -β-hydroxyethoxyphenyl)propane, 4,4′-bis(β-
Some use hydroxyethoxy) diphenyl sulfone and diethylene glycol. Such PATs are commercially available. In this invention, commercially available PAT can be used.

Among the above-mentioned PATs, those suitable for use in the present invention include polyethylene terephthalate, polybutylene terephthalate, polybutylene terephthalate elastomer, amorphous polyester, polycyclohexane terephthalate, and the like. These resins can be used alone or in combination. Further, resins other than PAT can be mixed with these resins. When other resins are mixed, the amount of the other resins needs to be less than that of PAT.

Since PAT is a resin that easily hydrolyzes at high temperatures, it is desirable to dry it beforehand when foaming it. For example, a dehumidifying dryer may be used for drying. In that case, the drying conditions are, for example, air with a dew point of -30°C is heated to 160°C,
It is sufficient to expose the PAT to this air for about 4 hours.

Various foaming agents can be used. Broadly speaking, solid compounds that decompose to generate gas at temperatures above the softening point of PAT, liquids that vaporize within PAT when heated, and inert gases that can be dissolved in PAT under pressure. can also be used. The solid compounds mentioned above are, for example, azodicarbonamide, dinitrosopentamethylenetetramine, hydrazocarbonamide, sodium bicarbonate, and the like. The liquid that vaporizes in PAT is
For example, saturated aliphatic hydrocarbons such as hexane, pentane, butane, saturated alicyclic hydrocarbons such as cyclohexane, aromatic hydrocarbons such as benzene, xylene, halogenated hydrocarbons such as methylene chloride, Freon(R) It is a hydrocarbon. Examples of the inert gas include carbon dioxide and nitrogen.
In addition, as the blowing agent, a high molecular weight chain aromatic polycarbonate can also be used, as taught in Japanese Patent Application Laid-Open No. 59-135237.

When the softened PAT mixed with a blowing agent is transferred to a low pressure area, the PAT foams. This foaming is
This is primary foaming in this invention, and the obtained foam is primary foaming. The primary foaming is conveniently carried out by extrusion from an extruder as described above. However, primary foaming has a low expansion ratio and usually has a high density. The expansion ratio varies depending on the shape of the foam, but when the foam is a sheet, it is about 5 times at most. In this invention, the primary foam obtained in this way is immediately after being made and while it is still at a high temperature.
This is rapidly cooled to a temperature below the glass transition point of PAT. The glass transition point of PAT varies depending on the type of carboxylic acid and alcohol that make up PAT, but roughly speaking, it is within the range of 30-90°C.
Therefore, the primary foam is usually rapidly cooled to below 60°C.

When the primary foam is rapidly cooled, it solidifies because there is no metal to form crystals, so the degree of crystallinity is low.
The degree of crystallinity depends on the degree of quenching. For example, the results vary depending on the type of cooling medium, the temperature of the cooling medium, the state of contact with the cooling medium, etc. When a primary foam made by extrusion is cooled by direct contact with water at room temperature, the primary foam will have a crystallinity of several percent to several tens of percent, usually 30%.
% or less. However, when the primary foam made by extrusion is guided into a mold and shaped, if the mold is not forcibly cooled, the crystallinity is over 30% because the foam is not rapidly cooled. becomes. In particular, thick-walled primary foams have a low degree of crystallinity.
30% or more. Therefore, when producing a primary foam using an extruder, the primary foam is rapidly cooled by advancing along a forcedly cooled mold.

In order to effectively cool the primary foam, it is desirable that the primary foam has a large surface area compared to its volume. That is, it is preferable to form the material into a sheet, and to have a thickness of 10 mm or less, particularly 3 mm or less. In that case, when the sheet is cylindrical, a mandrel is provided inside the cylinder, the sheet is made to advance along the mandrel, the mandrel is cooled with water, and the length of the mandrel is made as long as possible. On the other hand, when the sheet is in the form of a flat plate, the sheet is sandwiched between a pair of rolls and allowed to advance while being cooled, the rolls are cooled with water, and the diameter of the rolls is made as large as possible. In this way, the crystallinity of the primary foam can be reduced by 30%.
Hold below.

Generally, the crystallinity of a resin can be measured by density, X-ray diffraction pattern, nuclear magnetic resonance absorption spectrum, etc., as mentioned above, but resin foams contain air bubbles within them. Therefore, crystallinity cannot be measured by these methods.
Therefore, in the primary foam of PAT, the heat of fusion is
Thermal methods must be used, such as by measuring the heat of cold crystallization. The principle is that when PAT foam is heated at a constant rate, the crystals first increase and then melt. When the crystals increase, they generate heat, and when they melt, they absorb the heat of fusion, so this property is utilized. That's what I do. Specifically, the amount of heat of cold crystallization emitted during crystallization and the amount of heat of fusion absorbed during melting are measured, and this is compared with the amount of heat of fusion derived from the theory of perfect crystals to determine the degree of crystallinity. Calculate.

In order to actually measure the heat of cold crystallization and heat of fusion of the PAT foam, it is preferable to use differential scanning calorimetry. In differential scanning calorimetry, the heaters for the measurement sample and the standard sample operate independently, and when a temperature difference occurs between them during the constant-rate heating process, one of the mechanisms to increase or suppress heat flow is automatically activated. This difference in heat rate is now recorded directly. The degree of crystallinity is theoretically calculated according to the following formula.

(Absolute value of heat of fusion per mole - absolute value of cold crystallization heat per mole) ÷ Heat of fusion per mole of fully crystalline PAT x 100 = Crystallinity (%) Here, the heat of fusion per mole of fully crystalline PAT According to the Polymer Data Handbook (published by Baifukan), the heat of fusion is 26.9 KJ, so this will be used.

In this invention, a PAT primary foam having a crystallinity of 30% or less is selected and subjected to the second foaming. This is secondary foaming. During secondary foaming,
Heat this to 60℃ or higher. The heating means is not particularly limited. Any of heating by conduction, heating by radiation, heating by convection, and heating by high frequency power can be used. Moreover, any heating medium can be used as long as it does not particularly attack the PAT. Among them, a preferred heating method is to heat the primary foam of PAT by contacting it with heated metal or air, or by contacting it with steam or heated water.

The heating time during secondary foaming is appropriately determined depending on the properties of PAT, the shape and the type and temperature of the heating medium. Generally, when the temperature of the heating medium is low, the heating time is lengthened, and conversely, when the temperature is high, the heating time is shortened. Further, if the foam is thick, the heating time is increased, and if the foam is thin, the heating time is shortened.

When heating the primary foam by contacting it with a metal plate, the temperature of the metal plate is 60 to 200°C, and the contact is preferably for 5 seconds or more. Further, when the primary foam is heated by contacting with air, it is desirable to place the primary foam in an oven and heat the oven for 10 seconds to 5 minutes at a temperature of 100 to 230°C. When heating with a metal plate or air, it is preferable to avoid performing secondary foaming immediately after primary foaming, and to wait at least 24 hours, usually about 3 days, after primary foaming before performing secondary foaming.

On the other hand, when the primary foam is heated by contact with steam or heated water, secondary foaming can be carried out immediately after primary foaming. in this case,
The steam or water is at a temperature of 60°C to 125°C and the contact time is 10 seconds to 5 minutes. Steam or water above 125°C may hydrolyze the primary foam, so it is best to avoid using it.

To contact PAT foam with steam or water,
Various aspects can be adopted. The foam may be immersed in heated water, as shown in FIG. Alternatively, as shown in FIG. 2, a wire gauze may be placed above the surface of the heated water, and the foam may be placed on the wire gauze so that the foam is brought into contact with the water vapor evaporating from the water. Furthermore, as shown in Figure 3,
Pressurized steam may be blown into the container containing the foam.

When heating the foam in contact with water or steam, it is desirable to mold the foam into a desired shape. When a mold is used, water or steam enters the mold and directly contacts the foam.

In this way, when the PAT foam is brought into contact with water or steam at 60° C. or higher and heated, the PAT foam undergoes large secondary foaming and becomes a low-density foam.
In general, heating with water or steam is more likely to cause secondary foaming than heating with air, and steam is more likely to cause secondary foaming than water. According to water or steam, the magnification of secondary foaming is small
It is 1.3 times, and if it is large, it becomes more than 4 times.
Moreover, foaming can be performed uniformly, and the obtained secondary foam has fine and uniform cells. In this way, a low density foam of good quality can be obtained.

Various additives can be incorporated into the PAT in practicing this invention. For example, adding a small amount of talc powder as a bubble control agent,
To improve the solubility properties of PAT, acid dianhydrides such as pyromellitic anhydride, periodic table a,
Group A metal compounds or sodium carbonate, etc. alone or in combination, 0.1-5 parts by weight per 100 parts by weight of PAT.
It can be added in parts by weight.

Further, when carrying out the method of this invention, the obtained secondary foam is maintained at a high temperature, for example, 200°C or higher,
By increasing the crystallinity of PAT, it is also possible to obtain a secondary foam with further improved heat resistance.

(Effects of the Invention) According to the method of the invention, since foaming is performed twice, it is possible to obtain a highly foamed, low-density foam. That is, in primary foaming, foaming is performed using a normal method to obtain a foamed product with the conventional expansion ratio, and at the same time, the softened foamed material immediately after foaming is rapidly cooled to below the glass transition point.
The foam will have a low degree of crystallinity. In this way, a primary foam with a crystallinity of 30% or less can be obtained. In secondary foaming, the primary foam with such a low degree of crystallinity is heated to 60°C or higher, so the primary foam foams again and becomes a secondary foam with a low density. In this way, a low-density foam having uniform, fine cells can be obtained. Moreover, when water or steam is used as a heating medium during secondary foaming, secondary foaming can be performed following primary foaming, so that a low-density foam can be produced industrially easily. Furthermore, since the foam thus obtained is made of PAT, PAT itself is a strong and heat-resistant resin, so the resulting secondary foam is strong and heat-resistant. Therefore, it can be used as a lightweight plate or container that has both heat resistance and heat insulation properties. This invention brings such benefits.

Next, the reasons why the method of this invention is superior will be explained with reference to Examples and Comparative Examples. In the following, parts and % simply mean parts by weight and % by weight, respectively.

Example 1 (Primary foaming) Polystyrene terephthalate resin (trade name TR8580 manufactured by Teijin) as PAT (hereinafter referred to as PET)
) was used.

First, put the PET in a dehumidifying dryer and dry it at a dew point of -30℃.
PET at 160℃ for 4 hours while circulating air.
dried. Thereafter, 0.6 part of talc, 0.35 part of pyromellitic anhydride, and 0.1 part of sodium carbonate were mixed with 100 parts of PET, and the mixture was thoroughly mixed in a tumbler. This mixture was put into an extruder with a diameter of 65 mm and an L/D of 35, and mixed well at a screw rotation speed of 25 rpm and a barrel temperature of 270-290°C. Butane was added as a blowing agent from the middle of the barrel at 1.3 parts per 100 parts of the mixture. It was press-fitted in a proportion of 50%. In this way, it contains a blowing agent.
PET was extruded into the atmosphere from a circular mold in a cylindrical shape. The mold has an annular outlet distance of 0.4 mm and a diameter of
60 mm and maintained at 270-285°C. The PET extruded into the atmosphere foamed and was pulled out while contacting the outer surface of the cylindrical mandrel while remaining in a cylindrical shape. The mandrel had an outer diameter of 205 mm, and 30°C cooling water was circulated inside to rapidly cool the PAT foam. PET quenched in this way
The foam was cut open and rolled up as a flat foam sheet, which was used as a primary foam sheet. The primary foam sheet has a width of 643 mm, an apparent density (hereinafter simply referred to as density) of 0.26 g/cc, and a thickness of 1.5 mm.
The crystallinity was 9%.

(Secondary foaming) A 100 mm x 100 mm piece was cut out from the above-mentioned primary foaming sheet, and this was subjected to secondary foaming. For secondary foaming, as shown in Figure 1, the sample was immersed in warm water at 63°C for 5 minutes. As a result, the original sheet with a thickness of 1.5 mm became 2.1 mm thick, a density of 0.19 g/cc, a degree of crystallinity of 9%, and a secondary foamed sheet of 137%. The secondary foamed sheet was finely foamed and was good as a foam.

Example 2 In this example, secondary foaming was performed using the same primary foam sheet obtained in Example 1, but only the temperature of the hot water in secondary foaming was changed to 83°C, and it was heated for 5 minutes. Secondary foaming was performed by dipping.

The obtained secondary foam sheet has a thickness of 3.02 mm and a density of
It was 0.13g/cc, crystallinity was 10%, and secondary foaming was 200%. The secondary foamed sheet was also foamed uniformly and finely, had a low density, and was a good foam.

Example 3 In this example, secondary foaming was carried out using the same primary foam sheet obtained in Example 1, but at that time, the primary foam sheet was brought into contact with water vapor as shown in FIG. That's it. Specifically, secondary foaming was performed by contacting with water vapor at 62° C. for 5 minutes.

The resulting secondary foam sheet had a thickness of 2.51 mm.
The density was 0.16 g/cc, and secondary foaming was 163%.

Example 4 This example was conducted in the same manner as Example 3, but
However, the temperature of the steam was changed to 75°C to perform secondary foaming.

The resulting secondary foamed sheet had a thickness of 2.73 mm, a density of 0.14 g/cc, and was 186% secondary foamed.

Example 5 This example was carried out in the same manner as Example 3, except that the steam temperature and contact time during secondary foaming were changed, with the steam temperature being 100°C and the contact time being 0.5 minutes. Next, foaming was performed.

The resulting secondary foam sheet had a thickness of 2.78 mm.
The density is 0.14g/cc, the crystallinity is 10%,
There was secondary foaming of 186%.

Example 6 This example was carried out similarly to Example 5, but
The only change was the contact time with water vapor during secondary foaming. That is, as shown in Figure 2, 100
Secondary foaming was carried out by contacting with water vapor at .degree. C. for 2 minutes.

The resulting secondary foam sheet had a thickness of 3.92 mm.
The density is 0.10g/cc, the crystallinity is 16%,
There was secondary foaming to 260%.

Example 7 This example was carried out in the same manner as Examples 5 and 6, except that the only difference was the contact time with water vapor during secondary foaming. That is, secondary foaming was performed by contacting with water vapor at 100° C. for 5 minutes.

The resulting secondary foam sheet had a thickness of 5.63 mm.
The density is 0.065g/cc, the crystallinity is 26%,
Secondary foaming occurred at 377%.

Example 8 This example was carried out in the same manner as Examples 5 to 7, except that the contact time with water vapor during secondary foaming was changed. That is, secondary foaming was performed by contacting with water vapor at 100° C. for 7 minutes.

The resulting secondary foam sheet had a thickness of 5.96 mm.
It had a density of 0.065 g/cc and was secondary foamed to 400%.

Example 9 In this example, as in Example 8, secondary foaming was performed by contacting with steam at 100° C. for 7 minutes. At that time, 210 mm of primary foam with a size of 200 mm x 280 mm was
It was placed in an aluminum mold with 5 × 290 mm mold cavities and subjected to secondary foaming.

The resulting secondary foam sheet had a thickness of 5.00 mm.
A flat foam board with a density of 0.078 g/cc and secondary foaming of 333% was obtained.

Example 10 In this example, secondary foaming was performed using the same primary foam sheet obtained in Example 1, but the secondary foaming was performed by blowing pressurized steam as shown in Figure 3. I went there. Specifically, the primary foamed sheet was brought into contact with steam at 110° C. for 3 minutes to perform secondary foaming.

The resulting secondary foam sheet had a thickness of 3.41 mm.
The density was 0.11 g/cc, and 236% was secondary foamed.

Example 11 This example was carried out similarly to Example 10, but
However, the temperature of the pressurized steam during secondary foaming and the contact time with the steam were changed. in particular,
Secondary foaming was performed by contacting with steam at 120°C for 0.5 minutes.

The resulting secondary foam sheet had a thickness of 3.00 mm.
It had a density of 0.13 g/cc and was secondary foamed to 200%.

Example 12 This example uses carbon dioxide instead of butane as the foam and changes the injection rate of carbon dioxide.
Primary foaming was carried out in the same manner as in Example 1, except that the amount was 1.1 parts, and a primary foamed sheet was obtained. The primary foam sheet had a width of 643 mm, a density of 0.26 g/cc, a thickness of 1.5 mm, and a crystallinity of 9%.

Secondary foaming was carried out in exactly the same manner as in Example 7 to obtain a secondary foamed sheet. The thickness of the secondary foam sheet is
It had a diameter of 3.00 mm, a density of 0.13 g/cc, and was secondary foamed to 200%.

Example 13 This example was carried out almost in the same manner as Example 1, except that during the secondary foaming, 80 °C hot water was used instead of 63 °C hot water.
A secondary foamed sheet was obtained in the same manner as in Example 1, except that hot air at a temperature of 0.degree. C. was used and the hot air was contacted for 5 minutes.

The secondary foam sheet has a thickness of 2.1 mm and a density of
It was 0.19 g/cc, the secondary foaming rate was 137%, and the crystallinity was 10%.

Example 14 In this example, secondary foaming was carried out by bringing hot air into contact with the primary foam sheet in the same manner as in Example 13, but
The only difference was that the temperature of the hot air was raised to 100°C, and otherwise the procedure was carried out in exactly the same manner as in Example 13 to obtain a secondary foamed sheet.

The secondary foam sheet has a thickness of 2.6mm and a density of 0.15.
g/cc, primary foaming rate is 173%, crystallinity is 10%
It was hot.

Example 15 In this example, secondary foaming was carried out by bringing hot air into contact with the primary foam sheet in the same manner as in Example 13, but
The only difference was that the temperature of the hot air was increased to 110°C, and otherwise the process was carried out in exactly the same manner as in Example 13 to obtain a secondary foamed sheet.

The secondary foam sheet has a thickness of 2.8mm and a density of 0.14
g/cc, the secondary foaming rate was 186%, and the crystallinity was 12%.

Example 16 In this example, secondary foaming was carried out by bringing hot air into contact with the primary foam sheet in the same manner as in Example 13, but
The only difference was that the temperature of the hot air was increased to 140°C, and otherwise the process was carried out in exactly the same manner as in Example 13 to obtain a secondary foamed sheet.

The secondary foam sheet has a thickness of 3.01mm and a density of 0.13.
g/cc, the secondary foaming rate was 200%, and the crystallinity was 25%.

Example 17 In this example, secondary foaming was carried out by bringing hot air into contact with the primary foam sheet in the same manner as in Example 13.
The only difference was that the temperature of the hot air was raised to 230°C, and otherwise the procedure was exactly the same as in Example 13 to obtain a secondary foam sheet.

The secondary foam sheet has a thickness of 4.04mm and a density of
It was 0.097 g/cc, the secondary foaming rate was 268%, and the crystallinity was 26%.

Example 18 (Primary foaming) In this example, primary foaming was carried out in almost the same manner as in Example 1, except that the mold attached to the tip of the extruder was changed from a circular mold to a flat mold, and the mandrel was This was different from Example 1 in that a flat plate was used instead of . The flat mold had a linear extrusion port with a width of 150 mm and a distance of 0.7 mm. As a flat plate, 500×500
mm aluminum plates were cooled with water at 30°C, and the extruded foam sheet was sandwiched between the aluminum plates for rapid cooling. A primary foam sheet was obtained in the same manner as in Example 1 except for the above. The primary foam sheet is 200mm wide, 200mm thick, and has a density of 0.52g/cc.
The crystallinity was 12%.

(Secondary Foaming) The above-mentioned primary foam sheet was brought into contact with steam at 100° C. for 7 minutes to perform secondary foaming in exactly the same manner as in Example 8. The resulting secondary foam sheet has a thickness of
It had a diameter of 12.5 mm, a density of 0.204 g/cc, and was secondary foamed to 255%.

Example 19 (Primary foaming) In this example, primary foaming was carried out in almost the same manner as in Example 18, except that the temperature of the aluminum plate was slightly raised and the cooling rate of the foam sheet was made higher than in Example 18. A primary foam sheet was obtained in the same manner as in Example 18 except that the size was reduced.
The primary foam sheet had the same width, thickness, and density as Example 18, but had a crystallinity of 25%.

(Secondary foaming) The above-mentioned primary foamed sheet was subjected to secondary foaming in exactly the same manner as in Example 13 to obtain a secondary foamed sheet. The obtained secondary foam sheet has a thickness of 11.0 mm and a density of
It was 0.232 g/cc and had secondary foaming of 224%.

Comparative Example 1 This comparative example was carried out in the same manner as Example 1, but
However, the difference from Example 1 was that during the secondary foaming, hot air at 59°C was used instead of hot water at 63°C, and the secondary foaming was performed by contacting the hot air for 5 minutes. Other than that, the procedure was exactly the same as in Example 1 to obtain a secondary foamed sheet.

The secondary foam sheet has a thickness of 1.5 mm and a density of 0.26.
g/cc, and the secondary foaming rate was 100%, with no secondary foaming actually occurring.

Comparative Example 2 This comparative example was carried out in almost the same manner as Example 1, except that the temperature of the water during secondary foaming was lowered to 53°C.
A secondary foamed sheet was obtained in the same manner as in Example 1, except that the procedure was different from Example 1 in that the following points were used.

The secondary foam sheet has a thickness of 1.5 mm and a density of 0.26.
g/cc, and as in Comparative Example 1, the secondary foaming rate is
At 100%, there was virtually no secondary foaming.

Comparative Example 3 This comparative example was carried out in almost the same manner as in Example 3, except that the temperature of the steam was lowered to 58°C, and other than that, the experiment was carried out in the same manner as in Example 3. , a secondary foamed sheet was obtained.

The secondary foam sheet has a thickness of 1.5mm and a density of 0.26.
g/cc, the secondary foaming rate was 100%, and there was virtually no secondary foaming.

Comparative Example 4 In this comparative example, a primary foamed sheet was obtained in almost the same manner as in Examples 13 and 14, except that the temperature of the aluminum plate was further raised than in Examples 13 and 14, and the cooling rate of the extruded sheet was A primary foam sheet was obtained in the same manner as in Examples 13 and 14, except that the size of the sheet was made smaller. The primary foam sheet is
The width, thickness, and density were the same as those of Examples 13 and 14, but the crystallinity was 32%.

The above-mentioned primary foamed sheet was brought into contact with steam at 100° C. for 7 minutes to perform secondary foaming to obtain a secondary foamed sheet. The secondary foam sheet has a thickness of 5 mm and a density of
The secondary foaming rate was 0.52 g/cc, and the secondary foaming rate was 100%, with no secondary foaming actually occurring.

Example 20 In this example, as schematically shown in FIG. 4, primary foaming and secondary foaming were carried out successively.

In FIG. 4, the extruder 1 operated in exactly the same manner as described for the primary foaming in Example 1, and continuously fed out the primary foaming sheet. The primary foam sheet was subsequently introduced into the steam tank 2 without being rolled up. Primary foam sheet is steam tank 2
The surface had cooled to 30°C before entering.

The primary foamed sheet was brought into contact with steam at 100° C. for 5 minutes in a steam tank 2 to cause secondary foaming, and then cooled to form a secondary foamed sheet.

The secondary foam sheet has a width of 645mm and a density of 0.07g/
cc, 5.5mm thick, foamed to a high magnification, and was a beautiful, low-density sheet with fine, uniform air bubbles.

[Brief explanation of the drawing]

1 to 3 are sectional views showing specific embodiments of secondary foaming in the present invention.
FIG. 4 is a schematic diagram showing successive embodiments of the present invention.

Claims (1)

[Claims] 1. Rapidly cooling the high-temperature thermoplastic polyester resin foam immediately after foaming to below the glass transition point of the resin to reduce the degree of crystallinity to 30% or less, and then heating this polyester resin foam to 60°C or higher. A method for producing a thermoplastic polyester resin foam, characterized by: