JPH0733053B2 - Method for producing thermoplastic polyester resin foam - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a thermoplastic polyester resin foam.

(Prior Art) A thermoplastic polyester resin (hereinafter referred to as PAT) is a high-molecular chain polyester obtained as a result of a condensation reaction of an aromatic dicarboxylic acid and a dihydric alcohol. A typical example thereof is polyethylene terephthalate produced by condensing terephthalic acid and 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,
Depending on the molding method, molded products having different crystallinity are produced, and as the crystallinity increases, heat resistance and rigidity improve, but on the other hand, printability, adhesion, and secondary processing Since the ease and the like decrease, the properties of the molded body can be changed to some extent according to the purpose.

Since PAT has such high mechanical strength and excellent heat resistance, it was attempted to use it as a foam to make a lightweight and tough heat insulating material. However, PAT has a characteristic that it is difficult to foam. The reason is that PAT is a crystalline resin as described above, so if you heat it, PAT
Is melted rapidly and becomes a liquid with low viscosity, and therefore PAT has an extremely narrow temperature range in which the viscosity is suitable for foaming.

However, the difficulty of foaming was gradually eliminated by subsequent improvements. The improvement was mainly to add various auxiliaries to PAT to increase the melt viscosity of PAT to give PAT a viscosity suitable for foaming. For example, an epoxy compound is added to PAT, a compound of a metal belonging to Group Ia or Group IIa of the periodic table is added to PAT, diglycidyl terephthalate is added to PAT, and sodium carbonate is added to PAT. It was in line with such a way of thinking.

The extrusion foaming method is known as a method for obtaining a PAT foam. The extrusion foaming method is a method in which PAT is put in an extruder and melted, a foaming agent is mixed in the molten 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, it was still true that PAT was difficult to foam.

It has been said that various foaming agents can be used.
Broadly speaking, there were chemical foaming agents and physical foaming agents.
A chemical foaming agent decomposes when heated and generates gas,
The generated gas is a foaming agent that causes the resin to generate bubbles. 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 foaming agents were used in many cases.

There were various physical foaming agents. Roughly speaking,
It was divided into organic compounds and inorganic compounds. Inorganic compounds include elements such as nitrogen and compounds such as carbon dioxide,
It contained an airy mixture. 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 contained various ketones. Of these, many organic compounds were used. In particular, aliphatic hydrocarbons and halogenated aliphatic hydrocarbons were often used.

Although these blowing agents do not all give successful results in the foaming of PAT, they are described in the literature as if they all had comparable effects. That is, only specific examples using aliphatic hydrocarbons and halogenated aliphatic hydrocarbons as the foaming agent are mentioned, and as the foaming agent, an inorganic gas such as nitrogen or carbon dioxide can be similarly used as the foaming agent. Has been done. JP-A-59-210955 and JP-B-61-48409 are examples thereof. But,
Since inorganic gases such as nitrogen and carbon dioxide and organic compounds such as butane and methyl chloride have completely different affinities for PAT, it is too apparent that they both act on PAT in the same way. Target. In other words, even the difference in blowing agent could not be considered for PAT.

On the other hand, halogenated aliphatic hydrocarbons, especially fluorinated aliphatic hydrocarbons, have become a problem in that they destroy the ozone layer of the earth. Recently, it is trying to totally prohibit the use of fluorinated aliphatic hydrocarbons. Therefore, it became necessary to stop the use of such a foaming agent and find a method for obtaining a PAT foam by using a safe foaming agent instead.

(Problems to be Solved by the Invention) The present invention has been made in order to obtain a good PAT foam by an extrusion foaming method, using an inorganic gas as a foaming agent instead of an organic substance.

(Means for Solving the Problem) This inventor uses an inorganic gas as a foaming agent to
An attempt was made to obtain a foam. In fact, the inventor has attempted to use nitrogen as a blowing agent in PAT extrusion foaming. As a result, the inventor releases nitrogen as soon as the PAT is extruded from the extruder into the low pressure region, thus not only being difficult to foam, but once foaming inside,
It was confirmed that the cell wall was immediately broken and the cells were continuous, and a good foam was not obtained.

As described above, since PAT has a narrow temperature range in which it has a viscosity suitable for foaming, it has been a long-term effort to keep PAT at a proper foaming viscosity. For this reason, it is said that it is necessary to strictly control the temperature of PAT, and the study was conducted in the direction of naturally reducing the extrusion speed.
In particular, when an inorganic gas is used as a foaming agent, the inorganic gas has a lower affinity for PAT than an organic compound,
As compared with the case where an organic compound was used as a foaming agent, it was common sense to further extrude and foam at a lower extrusion speed.

On the other hand, the present inventor tried to increase the extrusion amount of the resin, contrary to the common sense described above, when the inorganic gas was used as the foaming agent. Specifically, the amount of resin extruded per unit time per unit cross-sectional area of the extrusion hole in the die was set to 25 Kg / cm ² .hr or more. As a result, the inventor has found that the rupture of the cell walls inside the foam is reduced, and thus a good foam having many independent cells can be obtained. The present invention was made based on such knowledge.

(Summary of the Invention) The invention is to melt PAT by putting PAT in an extruder and melting the PAT.
Mix the foaming agent into the
In the method of making PAT foam by extruding PAT to a low pressure region, an inorganic gas having a boiling point of -50 ° C or less is used as a foaming agent,
By increasing the PAT extrusion speed, the amount of PAT extruded per unit time from the unit cross-sectional area of the extrusion hole in the die is 25 Kg /
The gist is a method for producing a PAT foam, which is characterized in that it is at least cm ² .hr.

(Explanation of Requirements) The resin used in the present invention is PAT. As described above, PAT is a high molecular weight chain polyester obtained by esterifying an aromatic dicarboxylic acid with a dihydric alcohol. As the dicarboxylic acid, in addition to terephthalic acid,
It is also possible to use isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyl ether dicarboxylic acid, diphenoxydicarboxylic acid. In addition to ethylene glycol, diethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexane dimethylol, 2,2-bis (4-β-hydroxyethoxyphenyl) propane can be used as the dihydric alcohol. . Such PAT is commercially available.
In the present invention, such commercially available PAT can be used.

In this invention, an inorganic gas is used as the foaming agent. The inorganic gas used has a boiling point of -50 ° C or lower. Examples are nitrogen, carbon dioxide, helium, neon, krypton, xenon and the like. These can be used alone or as a mixture.

In the method of the present invention, the operation of mixing the foaming agent into the melted PAT in the extruder and extruding the PAT into the low-pressure region from the die attached to the tip of the extruder is basically the same as the conventional extrusion foaming operation. The difference is that an inorganic gas is used as a foaming agent to increase the PAT extrusion rate.
It only reduces the total cross-sectional area of the extrusion holes in the die as compared to the extrusion capability of the extruder.

By increasing the PAT extrusion speed, the amount of resin extruded in a unit time from the unit cross-sectional area of the extrusion hole in the die to 25
Various measures can be taken to achieve kg / cm ² · hr.
One means is to increase the extrusion capability of the extruder while using the same die, and therefore, for example, it is possible to increase the screw rotation speed of the extruder. It is also possible to take a means of reducing the cross-sectional area of the extrusion hole in the die. It has been so far vaguely thought that the use of an inorganic gas as the blowing agent for PAT would work just as well as the use of an organic compound as the blowing agent. However, in the present invention, it has been confirmed that when an inorganic gas is used as the foaming agent, unlike other organic foaming agents, there is a difference in that the cell wall is broken and the cells are easily connected. Based on this confirmation, it has been found that it is necessary to increase the extrusion speed of the resin in order to prevent the destruction of the bubble wall. Such a relationship has not been easily predicted. Especially, when the extrusion speed is higher than the limit of 25 kg / cm ² · hr per unit cross-sectional area of the extrusion hole in the die, closed cells are likely to be generated, and a good PAT foam is easily obtained. The fact that is will be totally new.

Moreover, when the extrusion speed is not less than the above value, the bubbles of the obtained foam become uniform and fine. This is also an unexpected fact. Because the bubbles are uniform and fine,
The foam has a beautiful appearance, excellent printability, and excellent heat insulation. Therefore, the foam obtained by the method of the present invention has high quality and high quality.

In carrying out the method of the present invention, various auxiliaries which have been used so far can be used. For example, in order to add a small amount of talc powder as a bubble control agent or to improve the melting characteristics of PAT, an acid dianhydride such as pyromellitic dianhydride, a compound of a metal of Group Ia or Group IIa of the periodic table. , Sodium carbonate and the like can be added alone or in a mixture. The amount is within the range of 0.1-5 parts by weight with respect to 100 parts by weight of PAT.

(Effects of the Invention) According to the present invention, PAT is put into an extruder and melted, a foaming agent is mixed into the melted resin, and the resin is extruded from a die attached to the tip of the extruder to a low pressure region to form a resin foam. Since the extrusion foaming method of making a resin is adopted, it is possible to easily obtain a continuous and uniform foam, and the resin is PAT.
Therefore, a tough foam having good heat resistance can be obtained. In this invention, the boiling point of the foaming agent is -50.
Since an inorganic gas at or below 0 ° C is used, environmental pollution will not occur even if the foaming agent escapes into the air. Furthermore, by increasing the resin extrusion speed, the amount of resin extruded in a unit time from the unit cross-sectional area of the extrusion hole in the die is 25 kg / cm ^2.
Since it is not less than hr, the foam wall of the extruded PAT is less likely to be broken, so that a foam having a small number of open cells and a large number of closed cells can be obtained, and a foam having uniform cells can be obtained. Since it is possible to obtain a foam with many closed cells in this way, it has excellent properties such as excellent heat insulation, low water absorption and oil absorption, excellent gas barrier properties, and high compression strength. Furthermore, since the bubbles are uniformly fine, a good foam having a beautiful appearance can be obtained. The present invention provides such advantages.

Hereinafter, the advantages of the method of the present invention will be specifically described with reference to Examples and Comparative Examples. In the following, simply "parts" means "parts by weight". The average cell diameter was measured according to ASTM D2842-69, and the open cell diameter was measured according to ASTM D2856.

Example 1 Polyethylene terephthalate (manufactured by Teijin Ltd., trade name TR 8580) was used as PAT to prepare the following composition.

PAT 100 parts Talc fine powder 0.6 parts Pyromellitic anhydride 0.4 parts Sodium carbonate 0.1 parts The above composition is put into an extruder of 65 mmΦ, the temperature of the feeding part of the extruder is 280 ° C., the temperature of the compression part is 285 ° C., The temperature of the melting part and the temperature of the head part were both 275 ° C, and the temperature of the die was 270 ° C. Also, the screw rotation speed is 40 rpm,
The resin extrusion rate was 37.0 kg / hr. From the middle of the barrel of the extruder, nitrogen (boiling point -195.8
C.) at a rate of 0.23% by weight, and extruded from the mouthpiece into the atmosphere.

The die has an annular extrusion hole with a diameter of 60m.
m and width was 0.6 mm. At this time, the weight of PAT extruded per unit time per cross-sectional area of the extrusion hole is 33.0 kg / cm ² · hr.
Was calculated.

In addition, a plug with a diameter of 205 mm and a length of 740 mm is provided at the tip of the mouthpiece, cold water is circulated in the plug to cool the plug, and the PAT foam slides on the plug, resulting in PAT foaming. I tried to cool my body quickly. The annular sheet thus obtained was cut open to obtain a flat PAT foam sheet.

The obtained PAT foam sheet had a density of 0.34 g / cc, an average cell diameter of 0.29 mm, and an open cell rate of 10.9%, and it was recognized as a fine and uniform foam.

Example 2 In Example 1, carbon dioxide (boiling point −78.5 ° C.) was used as the blowing agent instead of nitrogen, and the press-fitting amount was 0.64% by weight.
Example 1 was carried out in exactly the same manner as in Example 1 except that
At this time, the amount of resin extruded from the unit cross-sectional area of the extrusion hole in the die in a unit time is 33.0 kg / cm ² · hr.
Met.

The obtained PAT foam sheet had a density of 0.27 g / cc, an average cell diameter of 0.35 mm, and an open cell rate of 7.0%. Therefore, it was recognized that the bubbles were fine and there were few open cells.

Example 3 In Example 1, the screw rotation speed of the extruder was 25 rpm, the PAT discharge rate from the extrusion hole of the die was 21.7 kg / hr,
The procedure of Example 1 was repeated, except that the amount of nitrogen injected was 2.0% by weight, a flat die was used as the die, and a flat cooling plate was used instead of the plug.

The extrusion hole of the die had a width of 65 mm and a thickness of 1 mm. Therefore, at this time, the amount of PAT extruded from the unit cross-sectional area of the extrusion hole within the unit time was 33.4 kg / cm ² · hr.

The cooling plate has a length of 400 mm and a width of 120 mm.
It was cooled by circulating water at 30 ° C.

The obtained PAT foam sheet had a density of 0.18 g / cc, an average cell diameter of 0.25 mm, and an open cell rate of 13.2%, which were confirmed to be good.

Comparative Example 1 The same as Example 1 except that isobutane (organic compound, boiling point −0.5 ° C.) was used as the blowing agent in place of nitrogen, and this was injected at a rate of 1.1% by weight. It was carried out. At this time, the amount of resin extruded in a unit time from the unit cross-sectional area of the extrusion hole in the die was 33.0 kg / cm ² · hr.

The obtained PAT foam sheet had a density of 0.27 g / cc, an average cell diameter of 0.47 mm, and an open cell rate of 6.9%. In this comparative example, since the organic foaming agent was used as the foaming agent, the breakage of bubbles was small.

Comparative Example 2 The procedure of Example 1 was repeated, except that the screw rotation speed was 10 rpm and the PAT extrusion rate was 10.2 kg / hr. At this time, the amount of resin extruded in a unit time from the unit cross-sectional area of the extrusion hole in the die was 19.6 kg / cm ² · hr.

The obtained PAT foam sheet had a density of 0.34 g / cc, an average cell diameter of 0.42 mm, and an open cell rate of 17.1%. Therefore, it was recognized that the bubbles were coarse and there were many open cells.

Comparative Example 3 The procedure of Example 1 was repeated, except that the width of the extrusion hole in the die was increased from 0.6 mm to 0.9 mm. At this time, the amount of resin extruded in a unit time from the unit cross-sectional area of the extrusion hole was 22.2 kg / cm ² · hr.

The obtained PAT foam sheet had a density of 0.33 g / cc, an average cell diameter of 0.61 mm, and an open cell rate of 18.5%. Therefore, it was recognized that the bubbles were coarse and there were many open cells.

Comparative Example 4 In Example 1, the amount of promellitic anhydride used was 0.4.
Part to 0.45 part, and changed the die from an annular one to a flat one, so that the extrusion hole has a width of 75 mm and a thickness of 1.5 mm, and the amount of resin extruded from the extrusion hole is 22.3 mm.
A PAT foam sheet was obtained in exactly the same manner as in Example 1 except that the rate was kg / hr and a flat cooling plate was used instead of the plug. At this time, the amount of resin extruded in a unit time from the unit cross-sectional area of the extrusion hole was 19.8 kg / cm ² · hr.

The obtained PAT foam sheet had a density of 0.18 g / cc, an average cell diameter of 0.71 mm, and an open cell rate of 20.4%. Therefore, it was recognized that the bubbles were coarse and there were many open cells.

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area C08L 67:02

Claims (1)

[Claims] 1. A thermoplastic polyester resin is put into an extruder and melted, a foaming agent is mixed into the melted resin, and the resin is extruded from a die attached to the tip of the extruder to a low pressure region to form a resin foam. In the method, the boiling point of the foaming agent is −
It is characterized by using an inorganic gas of 50 ° C. or less, increasing the resin extrusion speed, and setting the amount of resin extruded in a unit time from the unit cross-sectional area of the extrusion hole in the die to 25 Kg / cm ² · hr or more. , A method for producing a thermoplastic polyester resin foam.