JPH0733049B2 - Method for producing thermoplastic polyester-based resin foam 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 method for producing a thermoplastic polyester resin foam sheet.

[0002]

2. Description of the Related Art A thermoplastic polyester resin (hereinafter referred to as PAT) is a high molecular weight chain polyester obtained by carrying out an esterification reaction between an aromatic dicarboxylic acid and a dihydric alcohol. is there. A typical example of PAT is polyethylene terephthalate obtained by reacting terephthalic acid with ethylene glycol.

PAT has excellent properties not found in other resins. For example, PAT has high mechanical strength, good shape stability, and excellent heat resistance to withstand 200 ° C. In addition, PAT is a crystalline resin and produces molded articles having different crystallinity depending on the molding method. The higher the crystallinity, the better the heat resistance and rigidity, but the PAT is printed. The easiness, easiness of adhesion, ease of secondary processing, etc. deteriorate. Therefore,
The properties of the molded body can be changed to some extent depending on the purpose.

Since PAT has such high mechanical strength and excellent heat resistance, it was attempted to mold it into a foam to make a lightweight and tough molded product. However, PAT has a characteristic that it is difficult to foam. The reason is that since PAT is a crystalline resin, when it is heated, it rapidly melts and becomes a liquid with low viscosity. In other words, PAT has an extremely narrow temperature range in which it exhibits a viscosity suitable for foaming.

However, the difficulty of foaming was gradually eliminated by the subsequent improvements. The improvement is mainly to add various auxiliaries to the PAT to increase the melt viscosity of the PAT and to give the PAT a viscosity suitable for foaming.
For example, an epoxy compound may be added to PAT, a metal compound of Group Ia or IIa of the periodic table may be added to PAT, diglycidyl terephthalate may be added to PAT, or sodium carbonate may be added to PAT to foam. It has been improved to make it easier.

The extrusion foaming method is known as a method for obtaining a PAT foam. What is extrusion foaming method?
Is put in an extruder and melted, a foaming agent is mixed in the melted resin, and the resin is extruded into a low pressure region from a die attached to the tip of the extruder to make a foam. However, even with this method, there was no change in that PAT was difficult to foam.

It has been said that it is convenient to make the foamed sheet of PAT by extrusion foaming of PAT. At that time, as a die, theoretically, a T-die having a linear slit could be used, but in reality, it was difficult to make a PAT foam sheet using the T-die. Therefore,
Circular dies with annular slits were mainly used to make PAT foam sheets. The circular die is composed of a core and an outer ring surrounding the core in order to form an annular slit, and PAT is extruded from the slit to form a tubular shape.

The inherent difficulties associated with extruding and foaming PATs using a circular die. The difficulty is that stripes are generated in the obtained foamed sheet and the quality is deteriorated, and bubbles in the foamed sheet are difficult to be fine. The occurrence of streaks occurs when the extruded sheet in the form of a tube increases in width as it expands, but it is difficult to hold the tube in a circular cross-section to match the increase in width, so It happens from bending to. The generation of stripes is not compatible with the miniaturization of bubbles, and when the stripes are not generated, the bubbles become coarse, and when the bubbles are made fine, the stripes become remarkable. Therefore, PAT with fine bubbles and no stripes
It was difficult to make a foamed sheet with a circular die.

[0009]

DISCLOSURE OF THE INVENTION The present invention is intended to obtain a good quality foam sheet having no bubbles and having fine bubbles by using a circular die.

[0010]

Heretofore, no particular attention has been paid to the temperature difference between the core and the outer ring in the circular die when the PAT is extruded and foamed by using the circular die. However, the inventor focused on the temperature difference. As a result of actually measuring the temperature difference, the inventor has found that when the PAT is extruded and foamed according to the conventional technique, the tip temperature of the core is considerably higher than the tip temperature of the outring.

The inventor has noted that at the tip of the circular die, the core has a temperature equal to or lower than the outring.
It was found that, when PAT is extruded and foamed, the obtained PAT foamed sheet unexpectedly has fine bubbles and has less streaks. Furthermore, as a result of repeated experiments, the present inventor conducted an experiment to output a portion of about 1/4 to 2/3 of C from the core tip to the extruder shaft based on the outer diameter C at the core tip. When maintained at a temperature equal to or lower than the ring tip temperature, it was confirmed that a good quality PAT foam sheet having fine bubbles and no stripes was obtained.

The inventor has also found that in order to maintain the core tip within the above-mentioned range at a lower temperature than the tip of the outring, the core has a cavity extending from the tip to the extruder. Digging, the depth of the cavity is 1/8 of the outer diameter C
It has been found that it is effective to blow the cooling gas into the holes with the above two-thirds or less. The present invention has been completed based on such knowledge.

[0013]

SUMMARY OF THE INVENTION According to the present invention, a die having a ring-shaped gap is attached to the end of an extruder, and a PAT containing a foaming agent is extruded and foamed from the gap to form a foam sheet. The extruder has a cavity extending to the tip of the core, and cooling gas is blown into the cavity so that the temperature of the tip of the core is equal to the temperature of the tip of the outer ring surrounding the core. Characterized by extruding PAT while maintaining a temperature lower than that, PA
The present invention relates to a method for manufacturing a T foam sheet.

[0014]

[Explanation of each requirement] The greatest feature of the present invention is to use a die having a cavity at the tip of the core. Therefore, first, the structure of the base will be described with reference to the drawings.

FIG. 1 is a front view of a die used in the present invention, and FIG. 2 is a sectional view taken along the line II-II in FIG. The die shown in FIGS. 1 and 2 is a circular die. This circular die inserts a core 1 into an outer ring 2 between which an annular gap 3
Is formed by forming. Reference numeral 4 denotes a mouthpiece portion forming a bridge, which supports a core 1 with a bolt 5 and an outer ring 2 with a bolt 6, and is fixed to a base portion 7. In this circular die, the resin proceeds from the exit 8 of the extruder in the direction of arrow A, passes through the passage 9, and is extruded from the annular slit 3.

At the tip of the core 1, there is provided a cavity 10 extending into the extruder. A bottom plate 11 is fitted in the cavity 10 to regulate the depth B of the cavity 10. Bottom plate 1
Reference numeral 1 denotes a screw provided on the outer periphery, which engages with a screw carved in the wall surface of the cavity 10 along the circumferential direction and is fixed so as to be displaceable in the cavity.

A support member 12 is fitted at the tip of the cavity 10. Like the bottom plate 11, the support member 12 has a screw on the outer circumference and is screwed to the wall surface of the cavity 10. The support member 12 is positioned such that its tip end surface is substantially flush with the tip end surface of the core 1. The support member 12 supports the pipe 13 by penetrating the pipe 13 at the center thereof.

The pipe 13 is for blowing a cooling gas into the cavity 10. The end of the pipe 13 located inside the cavity 10 is closed, and a small hole 14 is formed in the wall surface of the pipe 13. Therefore, when the cooling gas is blown into the pipe 13, the cooling gas is mainly ejected toward the wall surface of the cavity 10. The support material 12 is provided with a hole 15 for allowing the gas thus ejected to escape to the outside of the cavity 10.

As the cooling gas, nitrogen or carbon dioxide can be used in addition to air. The temperature of the cooling gas is preferably room temperature, but is not particularly limited.

As shown in FIG. 2, the cavity 10 was originally formed so as to extend deeply into the extruder, but the bottom plate 11 is fitted therein, and the depth is regulated by the bottom plate 11. . The depth B of the cavity 10 to the bottom plate 11 is about 1/8 or more and 2/3 of the outer diameter C of the tip of the core 1.
It is said that

In the present invention, the PAT is extruded and foamed by using the die shown in FIGS. 1 and 2. At this time, air at room temperature is sent from the pipe 13 to cool the tip of the core 1 so that the temperature of the tip of the core 1 is equal to the temperature of the portion of the outer ring 2 surrounding that portion, or Adjusted to be lower than that.

Up to now, PA using a circular die
In extrusion foaming of T, the temperature of the core 1 is higher than the temperature of the outer ring 2, for example, when the temperature of the outer ring 2 is 267 ° C. at the tip of the die, the temperature of the core 1 is 296 ° C., and the difference is large. It was Therefore, the difference could never be zero. However, in the present invention, the core 1 is cooled as described above so that the temperature of the core 1 is equal to or lower than the temperature of the outring 2. Therefore, the method of the present invention is quite different from the conventional method in that the temperature of the core is equal to or lower than the temperature of the outring. The temperature difference between the core 1 and the outer ring 2 is preferably 1 ° C to 17 ° C. If this state is called the temperature of the core, the temperature of the core 1 is 258 ° C to 275 ° C. At this time, the temperature of the outer ring is set to 275 ° C. or lower.

The resin used in this invention is PAT. As described above, PAT is a high-molecular chain polyester obtained by esterifying an aromatic dicarboxylic acid with a dihydric alcohol. As the dicarboxylic acid, in addition to terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyletherdicarboxylic acid, diphenoxydicarboxylic acid can also be used. Also,
As the dihydric alcohol, in addition to ethylene glycol, diethylene glycol, trimethylene glycol,
Tetramethylene glycol, cyclohexane dimethylol, and 2,2-bis (4-β-hydroxyethoxyphenyl) propane can also be used. Such a PAT
Is commercially available. In the present invention, such commercially available P
AT can be used.

Since PAT is generally a resin which is easily hydrolyzed at high temperatures, it is desirable to dry it before foaming it. For drying, for example, a dehumidifying dryer may be used. In that case, the drying condition is, for example, that air having a dew point of −30 ° C. is heated to 160 ° C. and PAT is exposed to this air for about 4 hours.

In the present invention, various materials which have been used as a foaming agent can be used. The foaming agent is roughly classified into a chemical foaming agent and a physical foaming agent. The chemical foaming agent is a foaming agent of a type that decomposes when heated to generate gas, and the generated gas causes bubbles in the resin. On the other hand, the physical foaming agent is a foaming agent of a type that generates bubbles in the resin only by being vaporized as it is in the resin. Of these, physical blowing agents are suitable for use.

There are various physical foaming agents. Broadly speaking, it is divided into organic compounds and inorganic compounds. Inorganic compounds include elements such as nitrogen, compounds such as carbon dioxide, and mixtures such as air. Organic compounds include aliphatic hydrocarbons such as butane, halogenated aliphatic hydrocarbons such as methyl chloride, alicyclic hydrocarbons such as cyclohexane, ethers such as ethyl ether, and acetone. It contains various ketones. Among these, organic compounds are suitable for use, and aliphatic hydrocarbons and halogenated aliphatic hydrocarbons are particularly suitable.

In the present invention, the PAT is extruded in a tubular shape. The extruded PAT foams at the same time as it leaves the circular die, extends in the lengthwise direction and increases the thickness, and also increases the width and the diameter. In order to increase the diameter, the tube will bend in the circumferential direction. Therefore, it is desirable to install a cylindrical mandrel at the tip of the circular die to enlarge the inner diameter of the tube so that the tube will not bend in the circumferential direction. At this time, at the tip of the circular die, since the core is kept at a temperature lower than that of the outring, stripes are less likely to occur. Nevertheless, the tube is uniformly and finely foamed so that the bubbles are fine. The tube is then cut along the extrusion direction and spread in a plane to form a foam sheet.

In carrying out the method of the present invention, various auxiliaries which have been used so far can be added. For example, in order to add a small amount of talc powder as a cell regulator or to improve the melting characteristics of PAT, an acid dianhydride such as pyromellitic dianhydride, Group Ia or II of the periodic table is used.
A compound of a group a metal, sodium carbonate, etc. can be added alone or after mixing. The amount is PAT10
It is in the range of 0.1-5 parts by weight with respect to 0 parts by weight.

[0029]

According to the method of the present invention, a die having a ring-shaped gap is attached to the tip of the extruder, and the PAT containing the foaming agent is extruded and foamed from the gap to form a foam sheet. Therefore, a uniform foamed sheet can be efficiently manufactured. Further, in the present invention, the extruder is provided with a cavity at the tip of the core that constitutes the gap and extends into the cavity, and since the cooling gas is blown into the cavity, only the tip of the core is appropriately cooled, The tip of the outer ring is maintained at a temperature lower than that of the ring. As a result, the PAT is extruded in the form of a tube to increase its length and thickness and spread in the diametrical direction, so that it tends to bend in the circumferential direction, but it is still less bendable and moreover it is uniformly finely foamed. Become. Therefore, it is possible to easily obtain a foam sheet having fine bubbles and no stripes. In addition, the obtained foamed sheet has high rigidity and good mechanical properties. The present invention provides such advantages.

[0030]

[Examples] Hereinafter, the reason why the method of the present invention is excellent will be specifically described by giving Examples and Comparative Examples. In the following, simply "parts" means "parts by weight".

[0031]

Example 1 In this example, polyethylene terephthalate as PAT (manufactured by Teijin Limited, trade name TR8580)
(Hereinafter, this is called PET) was used.

First, PET was placed in a dehumidifying dryer and dried at 160 ° C. for 4 hours while circulating air having a dew point of −30 ° C. Then, 100 parts of PET, 1 part of talc powder, 0.31 part of pyromellitic dianhydride, and 0.05 parts of sodium carbonate.
Parts and mixed well with a tumbler.

This mixture has a diameter of 65 mm and an L / D of 3
No. 5 extruder, the screw rotation speed is about 45 rpm, the temperature of the feeding section of the extruder is 280 ° C., the temperature of the compression section is 285.
℃, the temperature of the measuring part is 267 ℃, the temperature of the head is 270
The mixture was mixed well at 0 ° C., and butane as a foaming agent was pressed into the mixture at a ratio of 1.3 parts per 100 parts of the mixture from the middle of the barrel. Thus, PET containing a foaming agent was heated at 285 ° C. from a circular die as shown in FIGS.
It was extruded into a tube at a rate of 50 kg / hr in the air.

The circular die has an annular gap of 0.4.
mm, and the outer diameter C of the tip of the core 1 was 80 mm. Core 1
Has a cavity 10 with an inner diameter of 40 mm and a depth of 40 mm at its tip.
Is dug, and the bottom plate 11 is fitted into it, and the depth B is set to 3
It was set to 0 mm. A support material 12 is attached to the cavity 10, and a pipe 13 is fixed to the support material 12. 25 in pipe 13
The temperature of the tip of the core 1 was set to 263 ° C. by flowing air at 30 ° C./min. At this time, the tip temperature of the outer ring 2 was 267 ° C, and there was a difference of 4 ° C.

PET extruded from a circular die
Foamed and remained in the shape of a cylinder while advancing while coming into contact with the outer surface of the cylindrical mandrel and then taken off. The mandrel had an outer diameter of 205 mm and was cooled by circulating cooling water of 30 ° C. inside. The foam tube cooled by this mandrel was cut along the extrusion direction to form a flat sheet.

The obtained sheet had a width of 643 mm, an apparent density of 0.25 g / cc, and a basis weight of 300 g / m ² ,
The surface was free of streaks, foamed uniformly, and the bubbles were fine, and thus it was a good quality foamed sheet.

From this foam sheet, 250 × 250 mm
The sample is cut out, brought into contact with an overheated plate having a surface temperature of 140 ° C. for 6 seconds to preheat, and subsequently sandwiched between a convex mold and a concave mold heated at 180 ° C. for 8 seconds to form a container shape. At the same time, crystallization was promoted, and immediately thereafter, it was sandwiched between a convex mold and a concave mold having the same shape at room temperature for 6 seconds and cooled to obtain a container. The obtained container is uniformly and finely foamed,
The surface was beautiful, and it was strong.

[0038]

Example 2 This example was carried out in the same manner as in Example 1, except that the temperature at the tip of the circular die was slightly increased. Specifically, a PET foam sheet was obtained by treating in exactly the same manner as in Example 1 except that the tip end temperature of the outer ring was 272 ° C. and the tip end portion of the core was 270 ° C.

The obtained sheet had a width of 643 mm, an apparent density of 0.25 g / cc, and a basis weight of 350 g / m ² ,
It was a beautiful sheet with no bubbles on the surface and fine bubbles.

From the PET foam sheet thus obtained,
A container was made in the same manner as in Example 1. The obtained container was uniformly and finely foamed, had a beautiful surface, and was strong.

[0041]

COMPARATIVE EXAMPLE 1 This comparative example is the same as the pipe 1 in Example 1.
A PET foam sheet was obtained in the same manner as in Example 1 except that cooling air was not sent from 3. At this time, at the tip of the circular die, the core is 296 ° C,
The out ring was 267 ° C.

The PET foam sheet obtained had a width of 643.
mm, apparent density 0.26 g / cc, basis weight 350 g
It had 26 stripes extending in the extrusion direction at / m ² and also had coarse bubbles.

A container was made from this foamed sheet in the same manner as in Example 1, but the container had a weak rigidity.

[Brief description of drawings]

FIG. 1 is a front view of a mouthpiece that can be used in the present invention.

FIG. 2 is a sectional view taken along line II-II in FIG.

[Explanation of symbols]

 1 Core 2 Outring 3 Gap 4 Bridging Part 5 and 6 Bolt 7 Base 8 Extruder Exit 9 Resin Passage 10 Cavity 11 Bottom Plate 12 Supporting Material 13 Pipe 14 Small Hole

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B29K 105: 04 B29L 7:00 C08L 67:00

Claims (2)

[Claims] 1. A method for producing a foamed sheet by attaching a mouthpiece having an annular gap to the end of an extruder and extruding a thermoplastic polyester resin containing a foaming agent from the gap to form a foamed sheet. The extruder is provided with a cavity at the tip of the core that constitutes the core, and a cooling gas is blown into the cavity to bring the temperature of the tip of the core to the temperature of the tip of the outer ring that surrounds the core. A method for producing a thermoplastic polyester-based resin foam sheet, which comprises extruding the above resin while maintaining a temperature equal to or lower than that. 2. The method according to claim 1, wherein the depth of the cavity is not less than ⅛ and not more than ⅔ of the outer diameter of the tip of the core.