JPS6148410B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a string-like aromatic polyester foam, and its object is to provide a method for producing a string-like aromatic polyester foam that is easy to mold and post-process. Traditionally, plastics such as polystyrene,
Many methods have been proposed for producing foams from polyethylene and the like. In particular, string-like foams such as string-like foamed polystyrene, string-like foamed polyethylene, etc. are industrially produced primarily for use as cushioning materials. However, these string-like foams do not have sufficient mechanical properties such as heat resistance and strength, and their fields of use are limited. On the other hand, aromatic polyesters include polystyrene,
Foams have been developed and proposed because they have superior mechanical properties such as heat resistance and strength compared to polyethylene and the like. As one method, a mixture of an aromatic polyester and a diepoxy compound is fed to an extrusion foam molding machine, and a low boiling point blowing agent is injected from a nozzle provided in the center of the extrusion foam molding machine. A method has been proposed for producing a foam by extruding a molten resin composition containing ).
However, these publications do not provide specific explanations about the method for producing string-like foam;
Rather, the emphasis is on producing foams with larger shapes than cord-like moldings, and only specific examples thereof are shown. According to the study results of the present inventors, the foam molded products obtained in these specific examples have advanced crystallization, high resin density, and extremely low post-processability, such as stretchability, and are similar to aromatic polyesters. It cannot be said that the original excellent mechanical properties are fully utilized. In addition, if rapid cooling conditions are selected to prevent the progress of crystallization, a molded product with post-addition properties can be obtained, but the molded product has a large cooling shrinkage and is not a foam with uniform cells with an excellent appearance. It's hard to say. In addition, a liquid mixture of a large amount of a low-boiling solvent, an expanding agent, and polyester is extruded into a low-pressure, low-temperature region under conditions that provide sufficient cooling to adiabatically evaporate the solvent and precipitate an ultrafine porous structure. A method has been proposed in which the film-like pore walls made of the individual polymers formed at that time are oriented in one plane (Japanese Patent Publication No. 43-3993). However, the ultrafine porous structure produced by this method has a high expansion ratio and the individual film-like pore walls are oriented, so the structure has high strength. The strength cannot be further increased by post-processing, such as stretching, and
There are problems such as difficulty in obtaining a structure with a medium density of about 0.05 to 0.5. The present inventors have repeatedly investigated the production of string-like aromatic polyester foam that is easy to mold and process and has greater strength. When a melted aromatic polyester having the ability to foam is extruded through a die such that the semi-crystallization time of the polyester and the cross-sectional area of the foam satisfy a specific relationship,
The inventors have discovered that a string-like aromatic polyester foam can be obtained that can be easily subjected to post-processing such as stretching and heat processing, and have thus arrived at the present invention. That is, the present invention provides an aromatic polyester melt containing 1 to 50% by weight of a substance with a boiling point of 90°C or lower at normal pressure and having a melt viscosity of 8000 poise or higher at a temperature 15°C higher than the melting point, using the following formula t 〓≧20D ² In the formula, t〓 is the half crystallization time (seconds) at the temperature showing the maximum crystallization rate of the aromatic polyester, and D is the effective diameter (cm) of the foam. This is a method for producing a string-like aromatic polyester foam having a cross-sectional area of 1 to 200 ^mm2 , which is characterized by extrusion from a die and foaming. The aromatic polyester used in the present invention mainly contains aromatic dicarboxylic acids (85 mol% of dicarboxylic acids).
Polyester containing a dicarboxylic acid component (accounting for the above). Representative examples of the aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, and diphenoxyethane dicarboxylic acid. . The diol components preferably used in the polyester include ethylene glycol, trimethylene glycol, tetramethylene glycol, neopentylene glycol, hexamethylene glycol, cyclohexane dimethylol, tricyclodecane dimethylol,
Examples include 2,2-bis(4·β-hydroxyethoxyphenyl)propane, 4,4'-bis(β-hydroxyethoxy)diphenylsulfone, and diethylene glycol. The polyester includes
A small proportion of oxyacids such as p-oxybenzoic acid (15 mol% or less based on the dicarboxylic acid component), aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, etc. (15 mol% or less based on the dicarboxylic acid component) Alternatively, in a small proportion, a polyfunctional compound such as pentaerythritol, trimethylolpropane, trimellitic acid, pyromellitic acid, etc. or a monofunctional compound such as benzoic acid may be copolymerized. In the present invention, it is necessary that the viscosity of the resin melt in the extrusion foam molding machine be 8000 poise or more at a temperature 15° C. higher than the melting point. If the viscosity of the resin melt is lower than 8000 poise, it is difficult to obtain a foam in which fine bubbles are uniformly dispersed. We speculate that this is because obtaining a foam with uniformly dispersed cells requires that each individual cell in the foam have adequate resistance to the foaming pressure when the melt is extruded from the die. be done. In order to obtain such a melt viscosity, it is preferable to use the following method. (1) Use aromatic polyester with a high degree of polymerization. This aromatic polyester can be obtained, for example, by solid phase polymerization or by adding a polymerization accelerator, chain extender, etc. during the polymerization step. (2) Use aromatic polyester whose melt viscosity has been increased by copolymerizing a branching agent. Examples of the branching agent include polyfunctional compounds such as pentaerythritol and glycerin. (3) Increase the melt viscosity of the aromatic polyester in the extruder. For example, a highly polymerized or crosslinked aromatic polyester is produced in an extruder by feeding together with the aromatic polyester a compound which increases its molecular weight or causes crosslinking. Examples of this include a method of adding a diepoxy compound in combination with a metal of group a or group a of the periodic table or a compound thereof, as described in JP-A No. 53-24364; A method of adding a diepoxy compound and a montan wax salt or a montan wax ester salt in combination as described in JP-A-54-
As described in Japanese Patent No. 70364, there is a method of adding a combination of a diepoxy compound of polyalkylene glycol and a metal of groups a to a of the periodic table or a compound thereof. Among these methods, method (3) is particularly preferred because it has the advantage that a foam can be produced using an aromatic polyester with a relatively low degree of polymerization. In order to impart foaming ability to the extruded melt, a method is preferably used in which a gas inert to aromatic polyester or a liquid substance with a low boiling point is contained in the melted resin. At that time, 90℃ at normal pressure
If a substance with a higher boiling point is used, the shrinkage rate of the cells will increase when the string-like foam is cooled to room temperature, which is not preferable. It is preferable to use a substance having a boiling point of 90°C or less at normal pressure. Preferred examples of such substances include carbon dioxide, inert gases such as nitrogen, helium, xenon, neon, etc., organic compounds with a boiling point of 90°C or less at normal pressure, such as saturated aliphatic hydrocarbons, saturated alicyclics, etc. Examples include group hydrocarbons, halogenated saturated hydrocarbons, ethers, ketones, etc. Particularly preferably used organic compounds include hydrocarbons having 7 or less carbon atoms (for example, aliphatic saturated hydrocarbons such as methane, ethane, propane, butane, hexane, etc., and alicyclic saturated hydrocarbons such as cyclohexane, methylcyclopentane, etc.). ), chlorinated saturated hydrocarbons with a carbon number of 2 or less (e.g. methyl chloride, methylene chloride, chloroform carbon tetrachloride, ethyl chloride, dichloroethane, dichloroethylene, etc.), fluorinated saturated hydrocarbons with a carbon number of 2 or less (e.g. tetrafluorocarbons), chlorocarbon, ethyl fluoride, ethane tetrafluoride, etc.), chlorinated fluorinated hydrocarbons having 2 or less carbon atoms (e.g. chlorodifluoromethane,
Dichlorofluoromethane, chlortrifluoromethane, dichlordifluoromethane, trichlorofluoromethane, dichlortetrafluoroethane,
(trichlorotrifluoroethane, tetrachlorodifluoroethane, etc.), ethers such as ethyl ether, methylal, acetaldehyde dimethyl acetal, and ketones such as acetone and methyl ethyl ketone. These may be used alone or in combination of two or more. The proportion of an inert gas or a substance that is liquid at room temperature (hereinafter referred to as a blowing agent) added to provide foaming ability is 1 to 50% by weight based on the aromatic polyester. If the blowing agent is less than 1% by weight, the melt extrudate will hardly foam, making it impossible to obtain a practical foam molded product.
If the amount is more than 1% by weight, the blowing agent will not be uniformly contained in the molten resin, and the gas will blow out, making it difficult to obtain a foamed product with a predetermined shape, which is not preferable. A more preferable addition range of the blowing agent is 2 to 40% by weight. As a method for incorporating a blowing agent, the following method is preferably used. a Press fit through the vent provided in the middle of the cylinder of the extruder. b Press fit from two places: the vent part and the die part. c Press fit into two parts using the die part. d Press fit from 3 places: the vent part and the die part. The string-like foam produced according to the present invention is not crystallized or has only a small degree of crystallization, and has a characteristic that it can be easily subjected to treatments such as stretching and heat processing. In order to obtain such characteristics, the half-crystallization time t〓 (seconds) at the temperature of the maximum crystallization rate of the aromatic polyester and the effective diameter D (cm) of the string-like foam are required.
It is necessary that the relationship satisfies the following formula: t≧20D ² (1). Table 1 shows t〓≧
The relationship between the effective diameter (D: cm) and half crystallization time (t: seconds) when 20D ² is shown.

[Table] The half-crystallization time at the temperature showing the maximum crystallization rate of aromatic polyester is determined by the acid component, glycol component, copolymerization component, degree of polymerization, catalyst, various additives, etc. For polyethylene terephthalate, which is most widely used in polyethylene terephthalate, it is possible to increase the half-crystalization time to 40 seconds or more at the temperature that exhibits the maximum crystallization rate, depending on the selection of the catalyst system and thickening means. The relationship of formula (1) can be satisfied over a cross-sectional area of 1 mm ² to 200 mm ² . What should be noted here is the selection of the foaming nucleating agent. That is, in order to reduce the cell diameter and obtain a uniform foam, a foam nucleating agent that is insoluble and inert to aromatic polyester is usually added, but some of these agents can also be used as crystal nucleating agents. and tends to shorten the half-crystallization time. Typical crystal nucleating agents are arranged in descending order of half-crystallization time as follows. Talc < graphite < kaolin < magnesium carbonate ≒ zinc oxide < manganese dioxide ≒ molybdenum disulfide < aluminum oxide < antimony trioxide <
Triiron tetroxide<calcium carbonate≒calcium sulfate≒
Silica < barium sulfate. When producing polyethylene terephthalate string-like foam, the half-crystallization time is measured by simple preliminary experiments such as differential calorimetry and depolarized intensity method in the absence of a blowing agent, and the effective diameter is determined. It is preferable to select a foam nucleating agent so as to determine the half-crystallization time accordingly. In addition, polybutylene terephthalate is a typical aromatic polyester that crystallizes quickly, but in this case, it is impossible to use conventional methods for 5 seconds at a temperature that exhibits the maximum crystallization rate. Since it is not possible to obtain a half-crystallization time longer than
From (1), D≦0.5cm. In this case, by replacing part of the acid component or glycol component of the polyester with another dicarboxylic acid component or diol component, the half-crystallization time can be increased and the diameter D
It is possible to increase the As a string-like foam of aromatic polyester, 1
Those having a cross-sectional area of mm ² to 200 mm ² are suitable. That is, if the thickness is less than 1 mm ² , the majority of the skin layer is unfoamed, and an effective foam cannot be obtained. On the other hand, string-like foams larger than 200 mm ² lose their bendability, making it difficult to process such as weaving and knitting, and unable to perform their original functions. A more preferable range of cross-sectional area is 3
~ ^150mm2 . The most common cross-sectional shape here is a circle, an ellipse, or a rectangular shape.
Although it is possible to manufacture a die with a star shape or other irregularities, the shape approaches the above shape due to the foaming force. The cross-sectional shape of the above-mentioned foam excludes foams in the form of films or sheets, so it usually has a major axis/minor axis or width/thickness of 10 or less, and furthermore, this effective diameter is

[Formula] However, D: effective diameter, S: cross-sectional area, π: defined as pi. A die for producing a foamed continuous body having a cross-sectional area of 1 mm ² to 200 mm ² can be designed by conducting preliminary experiments in consideration of the balance effect of the composition, expansion ratio, appropriate draft, etc.
The foamed continuous body extruded from the die is cooled appropriately depending on its thickness. That is, immediately after the expansion of the foam extruded from the die is completed, it is cooled by means such as water cooling or air cooling. Although it depends on the type of blowing agent used, if the extruded foam is cooled too rapidly, the shrinkage of the extruded foam will increase, so the equation (1)
It is desirable to select a cooling method with this in mind.
The smaller the effective diameter (D), the more gentle the cooling method is preferably used. The string-like aromatic polyester foam continuum thus obtained has a low crystallinity and is easily subjected to treatments such as stretching and heat processing. Stabilizers, pigments, foam nucleating agents, flame retardants, antistatic agents, and other additives may be added to the string-shaped foamed molded product obtained by the present invention to the extent that the purpose of the present invention is not impaired.
It can be made to contain. The present invention will be explained in more detail with reference to Examples below. Note that parts in the examples represent parts by weight. Examples 1 to 5 After drying 100 parts of polyethylene terephthalate pellets with an intrinsic viscosity of 0.65 with hot air at 130°C for 8 hours, 0.6 parts of 1,2-diglycidylhexahydrophthalate and 0.5 parts of silica as a foaming nucleating agent were added to a V-type blender. 1,2 to the pellets.
- Diglycidyl hexahydrophthalate and silica as a foaming nucleating agent were uniformly deposited. The pellets obtained above are made into a cylinder with a diameter of 40 mm.
Extrusion foam molding was carried out using an extrusion foam molding machine equipped with a die having 8 nozzles with a diameter of 1.5 mm and a diameter of 1.5 mm. In extrusion foam molding, 15 parts of dichlorodifluoromethane (per 100 parts of polymer) is injected into the center of the cylinder of the molding machine using a plunger pump, and the temperature of the cylinder is adjusted to the supply zone.
280℃, plasticization zone 280℃, metaling zone
The temperature was set at 270°C, the die part was set at 270°C, the screw rotation speed was 30 rpm, and the force was 90 Kg/cm ² . As shown in Table 2, the average diameter of the string-like foam was varied by changing the draft rate. In addition, water cooling method and air cooling method were used as the cooling method. Table 2 shows foaming extrusion conditions such as draft rate and cooling method, and physical properties such as the achieved crystallinity and specific gravity of the foam. The melt viscosity of the extrusion composition (melting point: 253°C) at 273°C was 28,000 poise. Furthermore, when the above extrusion was carried out without adding a blowing agent, the half-crystallization time was 50 seconds at 180°C.

[Table] In each of the examples, all the conditions of t≧20D ² described above are satisfied, and in this case, no crystallization occurs even when slow cooling conditions such as air cooling are selected. Examples 6 and 7 and Comparative Examples 1 and 2 Foam molding was carried out in the same manner as in Example 1, except that talc was used instead of silica as a foam nucleating agent. The melt viscosity of the extrusion composition (melting point: 253°C) at 273°C was 26,000 poise. Furthermore, when this extrusion was carried out without adding a blowing agent, the half-crystallization time was 12 seconds at 140°C. Table 3 shows the extrusion foaming conditions and the physical properties of the product obtained.

[Table] A comparison between Table 3 and Table 2 reveals that by replacing the foaming nucleating agent with talc, which is also effective as a crystal nucleating agent, those with a large effective diameter can be amorphous even with the most effective cooling method. It can be seen that the condition cannot be maintained and stretching becomes difficult. Examples 8 to 10 and Comparative Examples 3 and 4 100 parts of polyethylene terephthalate pellets with an intrinsic viscosity of 0.65 were dried with hot air at 130°C for 8 hours, and then 2,2-bis(4-hydroxyphenyl)propane was added to the pellets. Sprinkle 0.8 parts of zyl ether, 0.3 parts of sodium montanate, and 0.5 parts of talc uniformly using a V-type blender,
Using a tandem extruder consisting of 40mm and 50mm,
It was extruded through a die having eight nozzles with a hole diameter of 1.5 mm, and foam molded. During foam molding, carbon dioxide gas was injected from the center of the first extruder at a rate of 7 parts per 100 parts of polyethylene terephthalate under a pressure of 45 kg/cm ² . As for the extrusion conditions, the cylinder temperature of the first extruder was set at 280°C, the cylinder temperature of the second extruder was set at 265°C, and the die temperature was set at 270°C. The screw rotation speed is
The first extruder is set at 30 rpm, the second extruder is set at 23 rpm,
The extrusion pressure was 120Kg/cm ² . The above-mentioned sodium montanate was added as a thickening reaction accelerator, and talc was added as a foaming nucleating agent, both of which are substances conventionally known as crystal nucleating agents for polyethylene terephthalate. Table 4 shows the extrusion foaming conditions and the physical properties of the product obtained. The melt viscosity of the extrusion composition (melting point: 253°C) at 273°C was 25,000 poise. Further, when this extrusion was carried out without adding a blowing agent, the half crystallization time was 7 seconds at 140°C.

[Table] From the above table, it can be seen that the range in which an amorphous open foam can be obtained is narrower than in Example 1, and that the thickening reaction accelerator and foam nucleating agent must be carefully selected. Example 11 and Comparative Examples 5 to 8 100 parts of polybutylene terephthalate pellets with an intrinsic viscosity of 1.45 obtained by solid phase polymerization were heated at 130°C.
After drying with hot air for 8 hours, sprinkle 0.5 part of silica evenly with a V-type blender as a foaming nucleating agent, and then use an extrusion foam molding machine equipped with a die with a cylinder diameter of 40 mm, L/D 32, and 8 nozzles with a hole diameter of 1.5 mm. Extrusion foam molding was performed using. In extrusion foam molding, a mixed blowing agent of methylene chloride: trichlorotrifluoroethane (trade name: Freon 113) (mixing ratio 1:3) was injected at a ratio of 15 parts (per 100 parts of polymer) using a plunger pump. . In addition, the cylinder temperature is 220℃ in the supply zone and 220℃ in the plasticization zone.
The temperature was set at 240°C, the metering zone at 240°C, and the die section at 230°C, the screw rotation speed was 35 rpm, and the discharge pressure was 80 Kg/cm ² . Table 5 shows the extrusion foaming conditions and the physical properties of the product obtained. The melt viscosity of the extrusion composition (melting point: 225°C) at 245°C was 18,000 poise. Further, the half-crystallization time after extrusion of the above composition without adding a blowing agent was 7 seconds at 80°C and 4 seconds at 60°C.

[Table] From the above table, it can be seen that in the case of polybutylene terephthalate, it is necessary to strengthen the cooling and reduce the diameter of the strings in order to obtain an amorphous foam continuum.

Claims (1)

[Scope of Claims] 1. An aromatic polyester melt containing 1 to 50% by weight of a substance with a boiling point of 90°C or less at normal pressure and having a melt viscosity of 8000 poise or more at a temperature 15°C higher than the melting point is prepared by the following formula: t〓≧20D ² In the formula, t〓 is the half-crystallization time (seconds) at the temperature showing the maximum crystallization rate of the aromatic polyester, and D is the effective diameter (cm) of the foam. A method for producing a string-like aromatic polyester foam having a cross-sectional area of 1 to 200 ^mm2 , which comprises extruding it through a die and foaming it.