JP2003025344A - Method for manufacturing aromatic polyamide molded object - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple method for manufacturing an aromatic polyamide molded object lighter and tougher than a conventional one. SOLUTION: The method for manufacturing the aromatic polyamide molded object includes a stage for charging a dope, which contains a polymer (A) constituted of an aromatic polyamide, a foaming agent (B) and an organic solvent (C), in a mold and a stage for heating the dope (D) to evaporate the organic solvent (C) from the mold while pyrolizing the foaming agent (B).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an aromatic polyamide molded article and a method for producing the same. In particular, the present invention relates to an aromatic polyamide molded product having a low density and a low specific gravity and a method for producing the same.

[0002]

BACKGROUND ART Aramid, that is, wholly aromatic polyamide is a polymer generally having a melting point of 300 ° C. or higher and excellent in heat resistance and mechanical properties. However, its high melting point remarkably restricts moldability. Even now, the technology has come into practical use in a wide range only for liquid crystal spinning molding and wet molding fibers and films. Other molding methods include a molding method in which powdered aramid is press-molded at a high temperature of a glass transition temperature or higher under high pressure.

However, according to this method, only a high-density aromatic polyamide molded body can be obtained, and the lightness required for conventional plastic molded bodies is insufficient.

Under these circumstances, we have developed a lightweight aromatic polyamide molding having voids in the aramid powder by using a slurry in which a swelling solvent and water are slightly contained. It has been found that it will be possible to obtain.

However, when the above method is used,
A problem may be considered in terms of strength such that the aramid powder on the surface is easily peeled off. Further, there is a demand for a lighter weight aromatic polyamide molded product having a smaller apparent specific gravity, and it is the current situation that such a request cannot be satisfied satisfactorily.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a light and durable aromatic polyamide molding.

Still another object and advantage of the present invention are:
It will be apparent from the following description.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the inventors of the present invention have obtained a method for producing an aromatic polyamide molding which is lighter and stronger than conventional ones.

That is, according to one aspect of the present invention, a dope (D) containing a polymer (A) composed of an aromatic polyamide, a foaming agent (B) and an organic solvent (C) is put into a molding die. Provided is a method for producing an aromatic polyamide molded body, which comprises a step and a step of heating the dope (D) to evaporate the organic solvent (C) from the mold to thermally decompose the foaming agent (B).

According to another aspect of the present invention, there is provided an aromatic polyamide molding having a density of 0.1 to 1.0 g / cm ³ . This aromatic polyamide molded body can be manufactured by the manufacturing method according to the present invention. In many cases, even if 5% by weight or less of the organic solvent remains in the aromatic polyamide molded body, there is no problem in terms of physical properties.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to examples and the like. It should be noted that these examples and explanations are intended to exemplify the present invention and do not limit the scope of the present invention. It goes without saying that other embodiments may belong to the scope of the present invention as long as they match the gist of the present invention.

The polymer (A) used in the present invention is generally composed mainly of what is called an aromatic polyamide or aramid, and in particular the following formula (1)

[0013]

[Chemical 2]

Those comprising the repeating unit shown in are preferred.

As a raw material for the aromatic polyamide,
A compound selected from the group represented by the following formula (a) and a compound obtained by reacting a compound represented by the following formula (b) as a monomer are preferable, and a compound selected from the group (a) has a higher molecular weight. A compound represented by the following formula (A-1), which is easy to obtain an aromatic polyamide, is preferable.

[0016]

[Chemical 3]

Further, the aromatic polyamide may have a copolymerization component to the extent that the physical properties are not impaired. Examples of such components include the divalent components described in the structural formulas (C) and (D) below.

[0018]

[Chemical 4]

The derivative into which the above-mentioned components can be introduced may be any one as long as it can form an amide bond.
Examples of the group (c) include terephthalic acid, terephthalic acid dimethyl ester, terephthalic acid diethyl ester, terephthalic acid chloride, 2,6-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid dimethyl ester, and 2,6-naphthalenedicarboxylic acid. Examples thereof include diethyl ester and 2,6-naphthalenedicarboxylic acid chloride, and examples of the (D) group include 3,4′-diaminodiphenyl ether, p-phenylenediamine, xylylenediamine, cyclohexylenediamine, piperazine and the like.

Further, the polymer (A) used in the present invention
May be a blend of the aromatic polyamide with other polymers in a molten or solid state to the extent that the physical properties are not impaired (for example, a ratio of 30% by weight or less based on the total weight).

Polymers that can be blended are, for example, aromatic polyesters, aromatic polyimides, aliphatic polyamides and aliphatic polyesters, preferably aromatic polyesters, aromatic polyimides and aliphatic polyamides.

The other polymer may be included in the dope (D) independently of the polymer (A) without being blended with the aromatic polyamide.

The aromatic polyamide in the present invention preferably has a molecular weight of 1,000 to 50,000. If the amount is out of this range, the mechanical properties of the obtained aromatic polyamide molded article deteriorate, which is not preferable. More preferably 3000-40
000, and more preferably 5,000 to 30,000.

In the present invention, a mixed solution in which the polymer is dissolved, suspended or dispersed in the organic solvent (C) together with the foaming agent (B), that is, the dope (D) is prepared.

The dope (D) does not necessarily have to be in a completely liquid state and may contain a solid component, but the organic solvent (C) may evaporate before or after it is charged into the mold. Prior to this, it is preferable that the polymer (A) is once in a substantially dissolved state, since a molded product having a uniform composition can be easily provided. Therefore, the organic solvent (C) is preferably one that can dissolve the polymer (A).

The role of the foaming agent (B) in the dope (D) is
This is to generate gas by thermal decomposition of the foaming agent (B) to form bubbles in the molded body, and this action makes it possible to fill the molding die with the aramid body having closed cells.

If the foaming agent (B) is decomposed after evaporating the organic solvent (C) and increasing the viscosity of the dope, the generated bubbles are less broken, and the bubbles can be substantially eliminated. It is desirable that the gas generation temperature by decomposition is equal to or higher than the boiling point of the organic solvent (C). It can be seen by observing the cross section of the formed molded body whether or not the breakage is substantially eliminated. By this observation, any 10
If the number of bubbles in which a plurality of bubbles were connected was one or less, it was determined that the bubbles were not substantially broken.

From the viewpoint of the viscosity of the dope (D), it is desirable that the breakage of bubbles be substantially eliminated by the time the pyrolysis gas of the foaming agent (B) is generated.

The viscosity of the dope (D) can be adjusted by changing the heating rate, the heating method, the type of the foaming agent (B), the type of the organic solvent (C), the volume of the molding die and the like. Therefore, the size and / or amount of the bubbles formed by the pyrolysis gas of the foaming agent (B) can be determined by the heating rate, the heating method, the type of the foaming agent (B), the type of the organic solvent (C), and the molding die. It is possible to adjust by adjusting the change in volume. By changing the heating rate and the heating method depending on the part of the mold, it is possible to obtain a molded product having partially different densities.

The size and / or amount of the bubbles may be adjusted by adjusting the internal pressure of the molding die. As a method for this, a known method of sealing the molding die and blowing an inert gas into the molding die can be adopted.

As an example of a concrete method, dope (D)
Is charged into the molding die, the organic solvent (C) is evaporated and the foaming agent (B) is pyrolyzed, and the molding die is pressurized to generate a pressure generated by the generated gas. The degree of air bubbles,
The amount can be kept within a predetermined range. That is, it is possible to adjust the density of the manufactured molded body.

The foaming agent (B) to be used may be any of organic and inorganic substances, but organic substances having a high degree of freedom in thermal decomposition temperature are often preferable. A foaming agent whose organic substance is selected from any of an azo compound, a nitroso compound and a sulfonyl hydrazide compound can be used.

Specific examples include azodicarbonamide, azobisisobutyronitrile, N, N'-dinitrosopentamethylenetetramine, p-toluenesulfonylhydrazine and p, p'-oxybis (benzenesulfohydrazide). Of these, azodicarbonamide and p, p′-oxybis (benzenesulfohydrazide) are preferred, and azodicarbonamide is more preferred.

The organic solvent (C) used is preferably a compound selected from aprotic polar solvents, and specific examples thereof include N-methylpyrrolidone, dimethylsulfoxide, dimethylacetamide, dimethylformamide and sulfolane. Of these, N-methylpyrrolidone, dimethylacetamide and dimethylformamide are preferable, and dimethylformamide is more preferable.

The mixing ratio of the polymer (A), the foaming agent (B) and the organic solvent (C) in the dope (D) of the present invention depends on the apparent specific gravity required for the finally obtained aromatic polyamide molded article. Dependent.

The polymer (A) has a weight ratio (A / (A + B + C)) of 0.0 with respect to the total weight of (A + B + C).
A ratio of 5 to 0.95 is preferable because the fluidity is good. If it is out of this range, the fluidity becomes insufficient and the intended aromatic polyamide molded article cannot be obtained, or
The mechanical properties of the obtained aromatic polyamide molded article may be deteriorated, which may not be preferable. More preferably 0.1
0 to 0.90, more preferably 0.15 to 0.8
It is 0.

When the weight ratio (B / A) of the foaming agent (B) is 0.01 to 0.99 with respect to the weight of the polymer (A), good foaming is obtained, which is preferable. If the amount is out of this range, foaming may be insufficient, the desired aromatic polyamide molded article may not be obtained, or the mechanical properties of the obtained aromatic polyamide molded article may deteriorate, which is not preferable in some cases. It is more preferably 0.10 to 0.90, and even more preferably 0.15 to 0.80.

The organic solvent (C) has a weight ratio (C / (A + B + C)) of 0.3 to 0.99 with respect to the total weight of (A + B + C), depending on the ratio with the polymer (A).
The ratio is preferably good because the fluidity is good. When it is out of this range, the fluidity becomes insufficient, the desired aromatic polyamide molded article cannot be obtained, and the mechanical properties of the obtained aromatic polyamide molded article deteriorate, which is not preferable. It is more preferably 0.10 to 0.90, still more preferably 0.50 to 0.80.

The term "having fluidity" as used herein means that it is used in a generally known manner, for example, a single screw type extruder, a twin screw type extruder, a piston type extruder, a mono pump type extruder, etc. When extruded at a specific pressure, it means that the mold has a certain degree of fluidity such that it can be supplied through an injection port.

The dope (D) used in the present invention is rheologically a Newtonian fluid in many cases. However, the viscosity also greatly changes due to the temperature change.

Therefore, it may not be sufficient to specify the physical properties of the dope only by the viscosity, but at room temperature (25
In the measurement conditions in (° C.), a value of approximately 100 poises to 10,000 poises is preferable.

The prepared dope (D) is put into a molding die for obtaining a desired molded body.

The mold used in the present invention is 50 to 400.
It is preferable that the mold has a temperature adjusting function in the range of ° C. However, even if the mold does not have the function, an oven capable of adjusting the temperature so that the mold can be put in and taken out can be used.

Further, when the molding die is equipped with a degassing mechanism, the organic solvent (C), which will be described later, is smoothly degassed, so that it can be preferably used. For degassing, a so-called vent port can be used without special use, and the number thereof may be plural. Incidentally, even if it is desired to pressurize the inside of the mold later, the molded body portion overflowing the vent port is solidified,
In many cases, it is possible to maintain the pressure, but it is also useful to positively provide a shutoff mechanism at the vent port.

As the mold, known molds such as ordinary injection molding, cast molding, BMC, and reaction injection molding can be used as long as the object of the present invention is not impaired. As the material, a metal or an alloy can be used, and a cast product can also be used.

The pressurization in the molding die makes it difficult to escape the gas generated by the evaporation of the organic solvent (C) and the thermal decomposition of the foaming agent (B) inside the molding die by pressurizing the molding die itself. It is possible to obtain it. It is also possible to introduce an inert gas or the like into the molding die by a known method.

The pressurization in the molding die is for adjusting the amount and size of the bubbles due to the gas generated by the thermal decomposition of the foaming agent (B). It is preferable that the bubble is formed, but it may be before and after.

The pressure in the mold is 1 KPa to 10 MPa.
It is preferable to adjust between.

Here, the pressurization to the molding die itself is not directly related to the pressurization inside the molding die, and liquid leakage from a parting line or the like when the dope (D) is introduced into the molding die is prevented. It is usually determined in consideration of the pressure for controlling and the expansion of the molded body, and it may be too high for adjusting the pressure in the desired molding die. In such a case, it is useful to appropriately change the mold clamping pressure during the molding.

In order to largely expand the air bubbles generated by the thermal decomposition gas of the foaming agent (B), a mold capable of changing the depth of the mold (corresponding to the thickness of the molded product) is used.
A known method of changing the volume of the mold by retracting the mold once clamped halfway can be incorporated in the present invention. That is, in the usual case, when the dope is put into the mold, the inside of the mold is not filled, but the inside of the mold is filled by expansion due to the generation of bubbles,
When using a mold that can change the depth of such a mold, it may be possible to fill the mold first. Needless to say, any known method other than the above can be applied as the method of changing the volume of the molding die for the expansion of the bubbles, as long as it does not violate the object of the present invention.

After the dope is added, the temperature inside the molding die is raised to obtain the molded body by carrying out steps 1, 2 and 3 below.

(Step 1) The dope (D) is put into a molding die and then heated. The temperature inside the mold rises,
The organic solvent (C) in the dope (D) is preferentially distilled off as a normal gas, and the concentration of the aromatic polyamide (A) in the dope increases. That is, it is important that the viscosity of the dope (D) rises to such an extent that the foam film of bubbles formed by the thermal decomposition gas of the foaming agent (B) is not broken by the evaporation of the organic solvent (C). is there. The organic solvent (C)
Gas escapes from the vent and parting line to the outside.

The preferred temperature at this stage is 90-200.
℃. If the amount is out of this range, the mechanical properties of the obtained aromatic polyamide molded article deteriorate, which is not preferable. The temperature is more preferably 100 to 190 ° C., further preferably 11
It is 0 to 180 ° C.

(Step 2) When the concentration is increased and the viscosity is increased by distilling off the organic solvent (C), the temperature is further raised and heated. The preferable temperature of the dope (D) at this stage is equal to or higher than the gas generation start temperature by the thermal decomposition of the foaming agent (B) in the dope (D), and preferably equal to or higher than the boiling point of the organic solvent (C).

By these actions, it becomes possible to fill the aramid body having closed cells in the molding die. Specifically, depending on the boiling point of the organic solvent (B), the glass transition temperature of the aromatic polyamide used, the solubility of the aromatic polyamide in the organic solvent, and the like, it is substantially preferably 100 to 300 ° C.

If it is out of this range, the mechanical properties, hue, etc. of the obtained aromatic polyamide molded article are deteriorated, which is not preferable in many cases. The temperature is more preferably 110 to 250 ° C, and further preferably 120 to 220 ° C.

The surface of the heated dope (D) has swelling and plasticity due to both the effect of increasing the temperature and decreasing the concentration of the organic solvent (C). At that time, it is preferable to pressurize the molding die in that state so that the powders of the polymer can be more firmly bound to each other.

More specifically, the pressure applied to the molding die at this stage depends on the properties of the aromatic polyamide used and the properties of the surface of the molded product in the same manner as the temperature, but it is substantially 1 KPa.
It is -10 MPa. When it is out of this range, the mechanical properties, hue, etc. of the obtained aromatic polyamide molded article are deteriorated, which is not preferable. The pressure is more preferably 10 KPa to 5 MPa, further preferably 50 KPa to 1 MPa.

As described above, through the steps 1 and 2, the organic solvent (C) which dissolves and / or swells the polymer is evaporated by heating after the dope (D) is put into the mold, It is one of the features of the present invention that it exerts a thickening effect, increases the viscosity of at least the inner surface portion of the bubbles of the polymer, and efficiently forms the foam by the decomposition of the foaming agent (B) as independent cells.

(Step 3) After the above steps are completed, the inside of the molding die is preferably cooled to a temperature not higher than the glass transition temperature of the aromatic polyamide to obtain the aromatic polyamide molding of the present invention. A higher temperature may be used in the case of performing shape imparting such as pressing after shape taking out.

According to the present invention, a very lightweight aromatic polyamide molding having a density of 0.1 to 1.0 g / cm ³ can be obtained by the above method.

It is possible to add various additives to the molded article according to the present invention within a range not deviating from the object of the present invention.

Examples of such additives include processing stabilizers, heat resistance stabilizers, antioxidants, light stabilizers, ultraviolet absorbers, metal deactivators, metal soaps, nucleating agents, antistatic agents. , Slip agents, anti-blocking agents, lubricants, flame retardants, mold release agents, anti-mold agents, colorants, anti-fog agents, natural oils, synthetic oils, waxes, organic fillers, inorganic fillers, epoxy compounds. be able to.

[0064]

According to the present invention, by a simple method,
It is possible to provide an aromatic polyamide molded body that is lighter and stronger than before. Further, it is often possible to maintain the flame retardancy of the aromatic polyamide.

[0065]

[Reference Example 1] (Production of aromatic polyamide) Isophthalic acid chloride 2
028 parts by weight (10 mol) was dissolved in 15 liters of tetrahydrofuran, and 1080 ml of metaphenylenediamine (10 mols) was dissolved in 15 liters of a homogeneous solution. As the mixing exotherm started, the reaction solution became cloudy due to the reaction precipitate.

After the reaction cloudy solution was allowed to cool, it was poured into a separately prepared 0.1N sodium hydroxide aqueous solution 110 liter bath with stirring.

Stirring was continued until the exothermic reaction subsided.

The reaction product obtained was separated by filtration, and water,
It was washed in order of acetone. After drying, a white powder of aromatic polyamide was obtained. Number average molecular weight Mn of the obtained polymer
Was 23000, and the average particle size of the obtained powder was about 100 μm.

Reference Example 2 (Preparation of Dope) 1.4 parts by weight of azodicarbonamide,
After mixing 70 parts by weight of dimethylacetamide, the mixture was cooled to 4 ° C with ice water. 30 parts by weight of the aromatic polyamide powder obtained in Reference Example 1 was added thereto and stirred, and then 60
By heating to ℃, a transparent and uniform dope was prepared.

Example 1 Dope 10 prepared in Reference Example
Part by weight was put into a molding die (lower die), and the molding die (upper die) was closed. While applying a pressure of 50 KPa to the molding die (upper mold), the entire molding die was placed in an oven adjusted to 200 ° C. After the dimethylacetamide distillate from the mold settles,
The temperature was raised to 250 ° C and the temperature was raised to 300 ° C over 1 hour. After the gasses of azodicarbonamide and dimethylacetamide had subsided, the mold was taken out of the oven and allowed to cool. The molded body was taken out from the molding die, the size and weight were measured, and the density was calculated. The results are summarized in Table 1 below.

The flame retardancy was 30 in LOI value.

Although 4% by weight of dimethylacetamide remained in the molded body immediately after the molding, the physical properties were improved as compared with the case where dimethylacetamide was reduced to 0.1% by weight in a vacuum heating dryer. No change was observed. No abnormalities were observed in paintability.

As the molding die, an aluminum die having a shape capable of obtaining a plate-shaped molding having a length of 50 cm, a width of 50 cm and a thickness of 5 mm was used. An injection port was provided in the central portion of the plate-shaped portion having a length of 50 cm, the mold was placed horizontally, and the dope was injected with the mold closed. The vent port is 1 cm in length and 1 cm in width at the center of 50 cm length on the side opposite to the injection port.
It was set in the size of. The amount of dope charged was 1/3 of the internal volume of the mold, but the molded product was filled inside the mold.

[Comparative Example 1] The procedure of Example 1 was repeated, except that the aromatic polyamide powder was directly charged into the molding die instead of the dope. The results are summarized in Table 1 below.

[0075]

[Table 1]

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4F204 AA30 AB02 AB19 AR02 AR06                       AR08 EA01 EA04 EB01 EE02                       EE03 EK10 EK13 EL15

Claims (13)

[Claims] 1. A step of introducing a polymer (A) composed of an aromatic polyamide, a dope (D) containing a foaming agent (B) and an organic solvent (C) into a mold, and the dope (D). A step of heating to evaporate the organic solvent (C) from the mold to thermally decompose the foaming agent (B), and a method for producing an aromatic polyamide molded body. 2. The method for producing an aromatic polyamide molded body according to claim 1, wherein the organic solvent (C) can dissolve the polymer (A). 3. The method for producing an aromatic polyamide molded article according to claim 1, wherein the aromatic polyamide is mainly composed of a repeating unit represented by the following formula (1). [Chemical 1] 4. A foaming agent by adjusting at least one of a heating rate, a heating method, a foaming agent (B) type, an organic solvent (C) type, an internal pressure of a molding die, and a volume of the molding die. The size and / or the amount of bubbles formed by the pyrolysis gas of (B) are adjusted.
A method for producing an aromatic polyamide molded body according to any one of 1. 5. The gas generation temperature by the thermal decomposition of the foaming agent (B) in the dope (D) is equal to or higher than the boiling point of the organic solvent (C). A method for producing an aromatic polyamide molded article. 6. The viscosity of the dope (D) increases before the temperature of the dope (D) reaches the gas generation temperature due to the thermal decomposition of the foaming agent (B) due to the evaporation of the organic solvent (C).
The production of the aromatic polyamide molded product according to any one of claims 1 to 5, wherein the foaming agent (B) is increased to such an extent that breakage of a film of bubbles formed by the pyrolysis gas is substantially eliminated. Method. 7. The mold is pressurized after the dope (D) is introduced into the mold and at least while the bubbles are formed by the pyrolysis gas of the foaming agent (B). Item 7. A method for producing an aromatic polyamide molded article according to any one of Items 1 to 6. 8. The aromatic compound according to claim 1, wherein the foaming agent (B) is a foaming agent selected from any one of azo compounds, nitroso compounds and sulfonylhydrazide compounds. Method for producing polyamide molded body. 9. The method for producing an aromatic polyamide molded article according to claim 1, wherein the organic solvent (C) is an aprotic amide solvent. 10. The aromatic polyamide molded article according to claim 1, wherein the foaming agent (B) is azodicarbonamide and the organic solvent (C) is dimethylacetamide. Production method. 11. The method for producing an aromatic polyamide molded article according to claim 1, wherein the amount of residual organic solvent in the aromatic polyamide molded article is 5% by weight or less. 12. An aromatic polyamide molding having a density of 0.1 to 1.0 g / cm ³ . 13. An aromatic polyamide molding produced by the production method according to claim 1, which has a density of 0.1 to 1.0 g / cm ³ .