JP2000080199A - Method for separating polyamide and glass fiber from glass fiber-containing polyamide molded article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently separate and recover a polyamide and glass fibers from a glass fiber-containing polyamide molded article. SOLUTION: In the method for adding a solvent to a glass fiber-containing polyamide molded article, heating the mixture while stirring to dissolve a polyamide and then, separating a polyamide solution and glass fibers, the polyamide and the glass fibers are separated by using, as the solvent, an aqueous solution of phosphoric acid having a concentration of not less than 70 wt.% at a solvent ratio which simultaneously meets the following formula (I): solvent ratio >=0.0625 ×dissolution temperature ( deg.C)+9.75 and formula (II): solvent ratio >=1 (wherein the solvent ratio is a weight of the phosphoric acid aqueous solution to a weight of the polyamide in the polyamide molded article; and the dissolution temperature is a liquid phase temperature in dissolving the polyamide molded article).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating and recovering polyamide and glass fiber from a polyamide molded article containing glass fiber.

[0002]

2. Description of the Related Art Polyamides are used as engineering plastics in automobile parts and home electric parts because of their excellent mechanical properties such as strength and elastic modulus.
In applications where strength is particularly required in such fields,
Glass fiber is added as a reinforcing agent. The addition ratio of the glass fiber depends on the required characteristic value, but is usually added to the polyamide resin in an amount of 10% by weight to 60% by weight. As a method of incorporating glass fiber into polyamide, a method of blending polyamide pellets and chopped strands of glass fiber and melt-blending with an extruder is general.

[0003] In recent years, from the viewpoints of global environmental problems and securing resources, there is a demand for recycling of molded articles. As one method of recycling a resin from a used molded article, there is a method of recovering the resin by melting, which is called a material recycling method. For example, in this method, a polyamide molded article containing glass fibers is pulverized into a flake shape by a crusher or the like, and then heated and melted by an extruder or the like to obtain a pellet, and the molded article is manufactured again using the pellet as a raw material. As another method, there is a method called a chemical recycling method. In this method, polyamide is heated in the presence of an acid catalyst such as phosphoric acid to depolymerize and recover as a monomer.

[0004] In general, the material recycling method is easy to carry out, but the quality of the recovered product obtained is inferior.
In many cases, the number of reuses and applications are limited. On the other hand, in the chemical recycling method, it is possible to return to a monomer and, if necessary, to purify a monomer, so that the reuse application is not limited at all. In particular, polyamides are easier to depolymerize than other resins, and it is estimated that this recycling method will increase in the future.

[0005]

In order to depolymerize waste polyamide molded products containing glass fibers and recover polyamide monomers, it is necessary to separate polyamide and glass fibers prior to depolymerization. Almost no studies have been made on the method of separating polyamide and glass fibers. Therefore, the present inventors have diligently studied a method for efficiently separating polyamide and glass fibers from waste polyamide molded articles containing glass fibers, and have reached the present invention. That is, the present invention provides a method for efficiently separating polyamide and glass fibers from waste polyamide molded articles containing glass fibers.

[0006]

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention provides a polyamide molded article containing glass fiber, wherein a polyamide is dissolved by adding a solvent and heating while stirring. A method for separating a polyamide solution and glass fiber, wherein a phosphoric acid aqueous solution having a concentration of 70% by weight or more is used as the solvent in a solvent ratio that simultaneously satisfies the following formulas (I) and (II). Solvent ratio ≧ −0.0625 × solution temperature (° C.) + 9.75 (I) Solvent ratio ≧ 1 (II) (where solvent ratio = weight of aqueous phosphoric acid solution) / Weight of polyamide in polyamide molded article, dissolution temperature = temperature of liquid phase when polyamide molded article is dissolved)).

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. In the present invention, “weight” means “mass”. Glass fiber is a fibrous glass added to enhance the physical properties of a polyamide resin, and some fibers have different lengths and diameters depending on the degree of dispersion and reinforcement effect in polyamide.
Generally, chopped strands are often used in terms of handling and the like. Also, to improve the convergence of the fiber,
Some are surface-treated, but are not particularly limited.

Polyamides include lactams such as ε-caprolactam and nylons 6, 11, and 12 obtained by polymerizing amino acids such as aminocaproic acid, and diamines such as hexamethylenediamine and dicarboxylic acids such as adipic acid. Nylon 66,
Nylon 46, nylon 610, nylon 612, and the like. These copolymers are also included. Nylon 6 is particularly preferred from the viewpoint of implementing in combination with chemical recycling.

Additives which are usually added to the polyamide include viscosity stabilizers such as acetic acid, coloring agents such as titanium oxide, heat-resistant agents such as hindered amines, light-proofing agents, weathering agents, and flame-retardants such as melamine. May be. Of course, in order to obtain a pure polyamide and a glass component by separation and recovery, it is preferable that such an additive is not added. When an additive is contained, the amount of the added additive is small, and when the quality of the recovered polyamide or glass fiber is not affected, the operation of separating is not necessary. When the added amount is large and affects the quality of the recovered polyamide or glass fiber, it is necessary to separate the additive separately.

The solvent added for dissolving the polyamide component is a phosphoric acid aqueous solution having a phosphoric acid concentration of 70% by weight or more, and the phosphoric acid concentration is preferably 75% by weight or more. 70
If the amount is less than 10% by weight, the polyamide will not be dissolved or it will take an extremely long time to dissolve.
The intended purpose of the present invention cannot be achieved.

The amount of the solvent (aqueous phosphoric acid solution) to be used for dissolution must satisfy the following formulas (I) and (II) specified in relation to the dissolution temperature. Solvent ratio ≧ −0.0625 × dissolution temperature (° C.) + 9.75 ·· (I) Solvent ratio ≧ 1 ·· (II) where solvent ratio = weight of phosphoric acid aqueous solution / weight of polyamide in polyamide molded article The dissolution temperature is the temperature of the liquid phase when the polyamide molded article is dissolved.

When the solvent ratio is below the lower limit specified by the formulas (I) and (II), the polyamide does not dissolve or it takes an extremely long time to dissolve, and the dissolution efficiency is poor. The intended purpose of the invention cannot be achieved. The melting temperature is the maximum temperature of the liquid phase when a polyamide molded article containing glass fibers is melted. The higher the melting temperature and the lower the amount of solvent used, the less the amount of solvent used, but the quality of polyamide is likely to deteriorate due to heat. Therefore, it is necessary to determine the dissolution temperature by comprehensively judging the economics such as the amount of solvent used and the quality deterioration of the polyamide due to the temperature.

The boiling point of the solvent (for example, a phosphoric acid concentration of 75
(Phosphoric acid aqueous solution having a boiling point of 140 ° C. or less) is advantageous in terms of equipment because the dissolving operation can be performed at normal pressure, and is generally 60 to 140 ° C.

The melting equipment may be of a continuous type or a batch type. In order to heat the solvent in order to dissolve the polyamito component, it is necessary to provide a jacket or an internal coil in which a heat medium enters. In order to promote the dissolution, it is necessary to install a stirring device in the dissolution tank. The stirrer is not particularly limited, and may be a propeller type, an irrigator type, or the like.

After dissolving the polyamide, it is necessary to separate the polyamide solution from the glass fibers. The separation method may be any method such as centrifugation, decantation, and filtration. If necessary, the separated glass fiber may be washed and removed with a polyamide solvent or the like, if necessary.

The polyamide solution separated and recovered is added with a polyamide poor solvent such as water to precipitate the polyamide, and the precipitated polyamide can be recovered. The recovered polyamide can be used as a raw material for material recycling.

The recovered polyamide solution can also be used as a raw material for chemical recycling, which is recovered as a monomer by depolymerization. In general, phosphoric acid is often used as a catalyst for depolymerization, so this method is particularly advantageous for this method. In this case, the polyamide phosphoric acid aqueous solution from which the glass fibers have been separated and removed does not require the operation of precipitating and separating the polyamide as in the material used for material recycling. It can be used as a raw material for charging and depolymerization.

[0018]

EXAMPLES The effects of the present invention will be described below with reference to examples. [Examples 1 to 5 and Comparative Examples 1 to 6] In a 1 L heatable container equipped with a stirrer, a thermometer and a condenser, 15 glass fibers were placed.
Nylon 6 pellets containing 2.5% by weight (diameter: 2.5 m
m, length: 2.5 mm), further added an aqueous phosphoric acid solution, and heated with stirring to dissolve the polyamide. A dissolution test was performed by changing the phosphoric acid concentration, dissolution temperature, and solvent ratio of the phosphoric acid aqueous solution at that time. The results are shown in Table 1. If the phosphate concentration is too low,
When the solvent ratio was too low, the polyamide did not dissolve, and the polyamide and the glass fiber could not be separated.

[0019]

[Table 1] Example No. Phosphoric acid concentration Dissolution temperature Solvent ratio Dissolution time Formula (I) (%) (° C) In relation Comparative Example 1 65 60 7 embodiment the insoluble range Comparative Example 2 〃 100 4 embodiment the insoluble range Example 1 70 60 6 400 range Example 2 〃 100 3.5 180 range between (min) Example 3 75 606 6 Within the range Comparative Example 3 〃 〃 5 Insoluble range outside Example 4 〃 100 3.5 150 Within the range Comparative Example 4 〃 〃 3 Insoluble range outside Example 5 １４０ 140 1 150 Comparative Example 5 within the range 〃 〃 0.8 Insoluble Out of range

Examples 6 and 7: 15% by weight of glass fiber
Examples 1-5 using nylon 66 pellets contained
A dissolution test was performed using the same apparatus as in Example 1, and the results are shown in Table 2. Nylon 66 could be efficiently dissolved by the method of the present invention.

[0021]

[Table 2] Example No. Phosphoric acid concentration Dissolution temperature Solvent ratio Dissolution time Formula (I) (%) (° C) (Min) relationship between Example 6 75 100 3.5 200 range Example 7 〃 140 1 200 within the range

[0022]

According to the method of the present invention, it is possible to efficiently separate and recover polyamide and glass fibers from a polyamide molded article containing glass fibers.

Claims (4)

[Claims] 1. A method for dissolving a polyamide by adding a solvent to a polyamide molded article containing glass fiber and heating while stirring, and then separating a polyamide solution and a glass fiber, wherein the solvent has a concentration of 70%.
The phosphoric acid aqueous solution having a concentration of not less than 10 wt%
Wherein the solvent ratio satisfies the following conditions: Solvent ratio ≧ −0.0625 × dissolution temperature (° C.) + 9.75 (I) Solvent ratio ≧ 1 (II) (where, solvent ratio = weight of phosphoric acid aqueous solution / polyamide in polyamide molded article) Weight, dissolution temperature = temperature of the liquid phase when dissolving the polyamide molded article.) 2. The method according to claim 1, wherein the polyamide is nylon 6. 3. The method for separating polyamide and glass fibers according to claim 1, wherein the melting temperature is 60 to 140 ° C. 4. A method for depolymerizing a polyamide molded product, comprising depolymerizing a polyamide solution separated and recovered by the method according to claim 1.