JP2023020666A - Blended yarn of recycled carbon fiber and thermoplastic resin fiber, and carbon fiber reinforced thermoplastic resin pellet - Google Patents

Abstract

To provide a blended yarn of recycled carbon fiber and thermoplastic resin fiber, which can be stably produced from a raw material recycled carbon fiber obtained through decomposition by heat treatment.SOLUTION: A blended yarn comprises a recycled carbon fiber and a thermoplastic resin fiber. The recycled carbon fiber has a single fiber tensile strength of 3.0 GPa or more, and a Weibull shape coefficient of 6.0 or more. The recycled carbon fiber contains a residual carbon component at a content of more than 0 wt.% and 5.0 wt.% or less relative to the recycled carbon fiber.SELECTED DRAWING: None

Description

The present disclosure relates to blended yarns of recycled carbon fibers and thermoplastic resin fibers, and carbon fiber reinforced thermoplastic resin pellets formed from the blended yarns. The invention also relates to methods for their production.

BACKGROUND ART Carbon fibers are used as reinforcing fibers for thermoplastic resins because they are excellent in specific strength and specific modulus and are lightweight. Carbon fiber reinforced resin composite materials (or carbon fiber reinforced plastics, CFRP) are used not only for sports and general industrial applications, but also for a wide range of applications such as aerospace applications and automobile applications.

One form of carbon fiber reinforced resin composite material is carbon fiber reinforced thermoplastic resin pellets. Carbon fiber reinforced thermoplastic resin pellets are made from long fiber reinforced pellets produced by cutting resin strands in which continuous carbon fibers are coated with thermoplastic resin, and resins in which discontinuous carbon fibers are kneaded and dispersed in thermoplastic resin. There are two short fiber reinforced pellets produced by cutting strands. Since long fiber reinforced pellets contain relatively long carbon fibers compared to short fiber reinforced pellets, they are supplied to injection molding machines, etc. to produce carbon fiber-containing products with excellent mechanical properties. can do.

In recent years, there has been an increasing demand for recycled carbon fibers recovered from used carbon fiber-containing products. Many recycled carbon fibers are discontinuously cut carbon fibers, and as a raw material for carbon fiber-containing products such as carbon fiber reinforced resin composite materials, recycled carbon fibers are treated in the same way as unused continuous carbon fibers. Methods for producing spun yarn from

Patent Document 1 discloses a method for producing a spun yarn by blending a carbonized material containing recycled carbon fibers obtained by heat-treating scraps of a carbon fiber reinforced resin composite material at a temperature of 900° C. or higher with thermoplastic resin fibers. is described.

In Patent Document 2, instead of recycled carbon fibers recovered by heat treatment of a carbon fiber reinforced resin composite material, imitation of recycled carbon fibers that do not contain carbide, cut unused discontinuous carbon fibers are treated as synthetic fibers. It describes how to utilize the blended spun yarn.

Patent Literature 3 describes a method for producing spun yarn from carbon fibers or recycled carbon fibers alone without blending with thermoplastic fibers.

JP 2018-35492 A JP 2018-123438 A Japanese Unexamined Patent Application Publication No. 2020-90738

Methods of decomposing a used carbon fiber reinforced resin composite material to obtain recycled carbon fibers include a method of decomposing a resin component by heat treatment, a method of dissolving and removing using a solvent, and a method of electrolysis. However, as a widely used method, there is a method of decomposing by heat treatment.

However, there have been cases where it is not possible to produce blended yarn with thermoplastic resin fibers using recycled carbon fibers obtained by a method of decomposing by heat treatment as a raw material.

An object of the present disclosure is to provide a blended yarn with a thermoplastic resin fiber that is stably produced using recycled carbon fiber obtained by a method of decomposing by heat treatment as a raw material. Another object of the present disclosure is to provide carbon fiber reinforced thermoplastic resin fiber pellets formed from the blended yarn.

According to the following aspects of the present invention, the above problems can be solved:
<Aspect 1>
A blended yarn containing recycled carbon fibers and thermoplastic resin fibers,
The recycled carbon fiber has a single fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more, and the recycled carbon fiber contains a residual carbon component, and the content of the residual carbon component is more than 0% by weight and 5.0% by weight or less with respect to the recycled carbon fiber;
A blended yarn characterized by
<Aspect 2>
The blended yarn according to aspect 1, wherein the content of the recycled carbon fiber is more than 50% by weight and not more than 98% by weight with respect to the blended yarn.
<Aspect 3>
The blended yarn according to mode 1 or 2, wherein the recycled carbon fibers and the thermoplastic resin fibers each have an average length of 20 mm or more and 80 mm or less.
<Aspect 4>
The thermoplastic resin fibers contained in the blended yarn are polyolefin resin fibers, polyester resin fibers, polyamide resin fibers, polyetherketone resin fibers, polycarbonate resin fibers, phenoxy resin fibers, polyphenylene sulfide resin fibers, and mixtures thereof. The blended yarn according to any one of aspects 1-3, selected from:
<Aspect 5>
It has a core-sheath structure,
The blended yarn according to any one of aspects 1 to 4 is a core component, and a thermoplastic resin is a sheath component,
A carbon fiber reinforced thermoplastic resin pellet characterized by:
<Aspect 6>
6. Aspect 5, wherein the thermoplastic resin as the sheath component is selected from polyolefin resins, polyester resins, polyamide resins, polyetherketone resins, polycarbonate resins, phenoxy resins, and polyphenylene sulfide resins, and mixtures thereof. Carbon fiber reinforced thermoplastic resin pellets.
<Aspect 7>
The melting point T0 (° C.) of the thermoplastic resin as the sheath component is lower than the melting point T1 (° C.) of the thermoplastic resin fiber contained in the blended yarn, and T1−T0>10 is satisfied. The carbon fiber reinforced thermoplastic resin pellet according to aspect 5 or 6.
<Aspect 8>
The carbon fiber reinforced thermoplastic resin pellet according to any one of aspects 5 to 7, having a cut length of 3 mm or more and 10 mm or less.
<Aspect 9>
decomposing a plastic component contained in a carbon fiber-containing plastic product by a semiconductor thermal activation method to produce recycled carbon fibers; and blending the recycled carbon fibers and thermoplastic resin fibers;
A method of making a blended yarn, comprising:
<Aspect 10>
A method for producing carbon fiber-reinforced thermoplastic resin pellets having a core-sheath structure, comprising coating the blended yarn obtained by the method according to aspect 9 with a thermoplastic resin.

According to the present invention, it is possible to provide a blended yarn with a thermoplastic resin fiber that is stably produced using recycled carbon fibers obtained by a method of decomposing by heat treatment as a raw material. Moreover, according to the present invention, it is possible to provide carbon fiber reinforced thermoplastic resin pellets formed from the blended yarn.

FIG. 1 is a schematic diagram of carbon fiber reinforced thermoplastic resin pellets according to the present disclosure and carbon fiber reinforced thermoplastic resin strands used in the process of making pellets according to the present disclosure. FIG. 2 is a conceptual cross-sectional view for explaining the disassembly method according to the present invention. FIG. 3 is a cross-sectional schematic diagram that schematically illustrates one embodiment of the disassembly method according to the present disclosure. FIG. 4 is a photograph of the CFRP plate before heat treatment. FIG. 5 is a photograph of the CFRP plate after undergoing the treatment according to Reference Example 4. FIG. FIG. 6 is a photograph of the CFRP plate after undergoing the treatment according to Reference Comparative Example 2. FIG.

The blended yarn of recycled carbon fiber and thermoplastic resin fiber according to the present disclosure is
The recycled carbon fiber has a single fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more, and the recycled carbon fiber contains a residual carbon component, and the content of the residual carbon component is be more than 0% by weight and 5.0% by weight or less with respect to the fiber,
characterized by

The blended yarn according to the present disclosure can be produced by common spinning methods. The spinning process may include carding, drawing and roving steps. Here, the carding step may be a step in which aggregates of discontinuous fibers are separated and opened, and the mixed single fibers are oriented in one direction to produce a thick sliver. The roving step can be a step of winding a blended yarn by further stretching and twisting the sliver.

The tensile strength of the sliver is given by the frictional force due to the contact or entanglement of the single fibers, so that each fiber spreads well and the contact area or entanglement between the single fibers increases, which improves the tensile strength. A decrease in tensile strength can be suppressed by suppressing single fiber breakage and increasing the number of joints between single fibers. Strengthening the twist also increases the contact area between the single fibers, thereby improving the tensile strength. In order to supplement the frictional force, each fiber or sliver may be oiled as necessary.

In general, carbon fibers have no crimp and have high surface smoothness, so the entanglement between single fibers is weak, and furthermore, they are hard with high elastic modulus and low elongation, so they are relatively easy to break and cut. . The thermoplastic resin fiber blended with the recycled carbon fiber has the effect of increasing the entanglement of the single fibers, and even by blending a small amount of the thermoplastic resin fiber, the tensile strength of the sliver is greatly improved.

Although not intended to be limited by theory, the blended yarn according to the present disclosure has a high Weibull shape factor in the single fiber tensile strength of the recycled carbon fiber, so the variation in tensile strength is small, and a general Compared to unused carbon fibers, there are relatively few single fibers with low tensile strength, so it is thought that single fiber breakage of recycled carbon fibers is relatively suppressed.

In addition, as a general feature of recycled carbon fibers obtained by a method of heat treatment and decomposition, the tensile strength tends to decrease due to the generation of oxidation defects in the recycled carbon fibers, and the carbide of the resin component serves as a residual carbon component. May be contained in recycled carbon fiber. The residual carbon component may strongly bind the monofilaments of the recycled carbon fibers. In the production of spun yarn, residual carbon content is believed to interfere with fiber opening and entanglement of single fibers during the carding process.

Although not intending to be limited by theory, the blended yarn according to the present disclosure is made from recycled carbon fibers having a relatively low content of residual carbon components, so that single fibers are easily entangled with each other.

For the reasons described above, the blended yarn according to the present disclosure can easily obtain a frictional force due to the entanglement of the single fibers, so that the yarn is not pulled out due to the tension in the spinning process, and the tensile strength for stable production is high. It is considered to be easy to obtain.

The present disclosure also includes carbon fiber reinforced thermoplastic resin pellets having the blended yarns described above. This carbon fiber reinforced thermoplastic resin pellet is
having a core-sheath structure;
The blended yarn is the core component, and the thermoplastic resin is the sheath component,
characterized by

The carbon fiber-reinforced thermoplastic resin pellets according to the present disclosure are produced by producing a blended yarn in the same manner as in a general method for producing long fiber-reinforced pellets, except that the blended yarn according to the present disclosure is used as a substitute for continuous carbon fibers. Since it can be produced by cutting resin strands obtained by coating with thermoplastic resin, short fiber reinforcement produced by cutting resin strands in which discontinuous carbon fibers are kneaded and dispersed in thermoplastic resin Compared to pellets, it can contain recycled carbon fibers having a relatively long fiber length. That is, the carbon fiber-reinforced thermoplastic resin pellets according to the present disclosure can be supplied to an injection molding machine or the like to produce a carbon fiber-containing product having excellent mechanical properties and the like.

Hereinafter, the invention according to the present disclosure will be described in further detail.

<Recycled Carbon Fiber>
Regenerated carbon fibers (recycled carbon fibers) contain carbon fiber components and carbon components other than the carbon fiber components (in particular, residual carbon components). Generally, in recycled carbon fibers, carbon components other than the carbon fiber components adhere to the surface of the carbon fiber components.

The recycled carbon fiber according to the present disclosure has a single fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more, and contains a residual carbon component, and the content of the residual carbon component is It is characterized by being more than 0% by weight and not more than 5.0% by weight with respect to the fiber.

The method of regeneration is not particularly limited as long as the recycled carbon fiber has such characteristics. For example, it may be a recycled carbon fiber obtained by heat-treating a carbon fiber-containing plastic product such as carbon fiber reinforced plastic (CFRP). .

Particularly preferably, the recycled carbon fiber is a recycled carbon fiber obtained by a semiconductor thermal activation method. That is, a particularly preferred embodiment of the present disclosure includes recycled carbon fibers produced by decomposing plastic components contained in carbon fiber-containing plastic products by a semiconductor thermal activation method.

The "semiconductor thermal activation method" (TASC method) is a method of decomposing a compound to be decomposed such as a polymer by utilizing the thermal activation of semi-conductors (TASC).

A method for obtaining recycled carbon fibers having properties according to the present disclosure using the semiconductor thermal activation method is described below.

<Single fiber tensile strength>
Single fiber tensile strength is preferably 3.1 GPa or more, 3.2 GPa or more, 3.3 GPa or more, or 3.4 GPa or more. Although the upper limit of the single fiber tensile strength is not particularly limited, it may be 6.0 GPa or less.

Single fiber tensile strength can be measured in accordance with JIS R7606 as follows:
taking at least 30 single fibers from the fiber bundle;
Measure the diameter of the single fiber in the side image of the single fiber taken with a digital microscope, calculate the cross-sectional area,
Fixing the sampled single fiber to a perforated mount with an adhesive,
The mount on which the single fibers are fixed is attached to a tensile tester, and a tensile test is performed with a sample length of 10 mm and a strain rate of 1 mm/min to measure the tensile breaking stress.
Calculate the tensile strength from the cross-sectional area and tensile breaking stress of the single fiber,
The average tensile strength of at least 30 single fibers is taken as the single fiber tensile strength.

<Weibull Shape Factor>
The Weibull shape factor is preferably 6.5 or greater, 7.0 or greater, 7.5 or greater, 8.0 or greater, or 8.5 or greater. Although the upper limit of the Weibull shape factor is not particularly limited, it may be 15.0 or less. A high Weibull shape factor of the single fiber tensile strength means that the variation of the single fiber tensile strength is small.

The Weibull shape factor can be calculated according to the following formula:
lnln {1/(1−F)}=m×lnσ+C
In the formula, F is the fracture probability determined by the symmetric sample cumulative distribution method, σ is the single fiber tensile strength (MPa), m is the Weibull shape factor, and C is a constant.

Weibull plotting is performed with lnln {1/(1−F)} and lnσ, and the Weibull shape factor m can be obtained from the linearly approximated slope.

<Carbon fiber component>
The carbon fiber component in the recycled carbon fiber is usually derived from the carbon fiber contained in the carbon fiber-containing product or the like that is the raw material of the recycled carbon fiber. The carbon fiber component in the recycled carbon fiber may be modified by being subjected to heat treatment or the like during the manufacturing process of the recycled carbon fiber.

The carbon fiber component in the recycled carbon fiber may be, for example, PAN-based carbon fiber or pitch-based carbon fiber.

The form of the carbon fiber component in the recycled carbon fiber is not particularly limited, but may be in the form of a carbon fiber bundle composed of a plurality of single yarns (single fibers, filaments). The number of filaments constituting the carbon fiber bundle may range from 1,000 to 80,000 or from 3,000 to 50,000. In addition, the diameter of the filaments constituting the carbon fiber component in the recycled carbon fiber may be 0.1 μm to 30 μm, 1 μm to 10 μm, or 3 μm to 8 μm.

<Residual carbon component>
The residual carbon component contained in the recycled carbon fiber is, in particular, residual carbon derived from the resin contained in the carbon fiber-containing plastic product used as a raw material when producing the recycled carbon fiber.

In the present disclosure, the residual carbon component is more than 0% by weight and 5.0% by weight or less with respect to the recycled carbon fiber. In this case, it is possible to obtain a blended yarn with improved yarn pull-out resistance against the tension in the spinning process.

In addition, when the residual carbon component is more than 0% by weight and 5.0% by weight or less, contamination due to a relatively large amount of carbon components (especially charcoal) can be avoided, and the blended yarn is used as a material. It is possible to reduce the carbon component that may become a foreign substance when manufacturing a carbon fiber-containing product or the like.

Preferably, the residual carbon content is 4.0% by weight or less, 3.0% by weight or less, or 2.0% by weight or less with respect to the recycled carbon fiber. It is preferable that the residual carbon component is reduced as much as possible. 0.8% by weight or more, 1.0% by weight or more, or 1.2% by weight or more.

The content of residual carbon components in the recycled carbon fiber can be measured by thermogravimetric analysis (TGA method).

The residual carbon content by thermogravimetric analysis can be measured by the following procedure:
(i) A sample piece of 1 to 4 mg obtained by pulverizing recycled carbon fiber was measured with a thermogravimetric analyzer at an air supply rate of 0.2 L / min, a heating rate of 5 ° C / min, and 1/ At a recording speed of 6s,
temperature increase from room temperature to 100° C.,
hold at 100° C. for 30 minutes,
raising the temperature from 100°C to 400°C, and
Perform thermogravimetric analysis with a step of holding at 400 ° C. for a total of 300 minutes,
(ii) In a graph plotting the weight loss rate against time, identify the inflection point of the slope, and subtract the weight loss rate during the holding period at 100 ° C. from the weight loss rate value at the inflection point. Calculate the amount of residual carbon by

If the inflection point of the slope cannot be specified under the above conditions, instead of thermogravimetric analysis for a total of 300 minutes, thermogravimetric analysis is performed for a total of about 600 minutes accompanied by holding at 400 ° C. for 480 minutes. Further, instead of holding at 400° C. for 480 minutes, it may be held at a specific temperature in the range of greater than 400° C. and up to and including 500° C. for 480 minutes.

Further, when the recycled carbon fiber contains a resin derived from a sizing agent or the like, the above measurement can be performed after removing the resin.

<Thermoplastic resin fiber>
The thermoplastic resin fibers contained in the blended yarn according to the present disclosure include polyolefin resin fibers (e.g., polypropylene resin fibers and polyethylene resin fibers), polyester resin fibers (e.g., polyethylene terephthalate resin fibers, polybutylene terephthalate resin fibers, and polylactic acid resin fiber), polyamide resin fiber, polyetherketone resin fiber, polycarbonate resin fiber, phenoxy resin fiber, and polyphenylene sulfide resin fiber. The thermoplastic resin fibers may be of only one type, or may be a mixture of two or more thermoplastic resin fibers.

≪Blended Yarn≫
A blended yarn is a spun yarn containing recycled carbon fibers and thermoplastic resin fibers. The blended yarn can also contain, for example, a binder or the like that is applied to the recycled carbon fiber. Also, the blended yarn may be a spun yarn substantially composed of recycled carbon fiber and thermoplastic resin fiber.

<Content of recycled carbon fiber>
The content of the recycled carbon fiber is preferably more than 50% by weight and not more than 98% by weight with respect to the blended yarn. Particularly preferably, it may be more than 55% by weight, more than 60% by weight, more than 65% by weight or more than 70% by weight and/or up to 97% by weight, up to 96% by weight, up to 95% by weight, up to 94% by weight % or less, 93 wt.% or less, 92 wt.% or less, 91 wt.% or less, or 90 wt.% or less.

If the content of the recycled carbon fiber exceeds 50% by weight, when producing the carbon fiber reinforced thermoplastic resin pellets according to the present disclosure using the recycled carbon fiber, the thermoplastic resin is used for the purpose of increasing the carbon fiber content. There is no need to reduce the coating amount in , and the stability of the coating treatment is improved. If the content of the recycled carbon fiber is 98% by weight or less, the entanglement with the blended thermoplastic resin fiber is sufficient, and the yarn pull-out due to the tension in the spinning process is less likely to occur.

The content of thermoplastic resin fibers may be 50 wt% or less, 40 wt% or less, or 30 wt% or less, and/or more than 3 wt%, more than 4 wt%, 5 It may be greater than 6 wt%, greater than 7 wt%, greater than 8 wt%, greater than 9 wt%, or greater than 10 wt%.

<Average fiber length>
The recycled carbon fibers contained in the blended yarn may have an average length of 20 mm or more and 80 mm or less. Fibers having lengths in this range can be obtained, for example, by cutting fibers having relatively long dimensions. The average length of the recycled carbon fibers may be 20 mm or more, 30 mm or more, or 40 mm or more, and/or may be 80 mm or less, 70 mm or less, or 60 mm or less, respectively.

The thermoplastic resin fibers contained in the blended yarn can have an average length of 20 mm or more and 80 mm or less. Fibers having lengths in this range can be obtained, for example, by cutting fibers having relatively long dimensions. The thermoplastic fibers may each have an average length of 20 mm or more, 30 mm or more, or 40 mm or more, and/or may be 80 mm or less, 70 mm or less, or 60 mm or less.

In the production of the blended yarn, if the average length of the recycled carbon fiber and the thermoplastic resin fiber is 20 mm or more, it is possible to improve the yarn dropout resistance against the tension during the spinning process of the sliver.
When the average length of the recycled carbon fiber and the thermoplastic resin fiber is 80 mm or less, it is possible to reduce the winding around parts of manufacturing equipment.

The average length of the recycled carbon fiber and the thermoplastic resin fiber is measured by visually using a vernier caliper or the like, or by measuring the length of 50 fibers in an image obtained with a digital camera or an optical microscope. It can be calculated by averaging the values.

<Method for producing blended yarn>
As described above, the blended yarn of recycled carbon fiber and thermoplastic resin fiber according to the present disclosure can be produced by a general spinning method. That is, the method for producing a blended yarn according to the present disclosure includes a carding step of separating and opening aggregates of discontinuous fibers and orienting the mixed single fibers in one direction to produce a thick sliver. It may include a drawing step in which the sliver is combined and stretched to further improve the degree of fiber orientation, and a roving step in which the sliver is further stretched and twisted to wind the blended yarn.

A binder can be applied when producing the blended yarn. The binder, in particular, has a role of promoting bonding of the recycled carbon fibers to the thermoplastic resin fibers. The timing of applying the binder is not particularly limited, but it may be applied directly to the recycled carbon fiber, or may be applied to the blended yarn containing the recycled carbon fiber and the thermoplastic resin fiber. The binder may be, for example, an epoxy resin. The method of applying the binder is not particularly limited, and a known method can be used. For example, the binder can be applied by immersing the recycled carbon fiber or blended yarn in a binder solution or dispersion and drying. can. The amount of the binder may be 0.1% to 25% by weight, or 1% to 20% by weight with respect to the recycled carbon fiber.

≪Carbon fiber reinforced thermoplastic resin pellets≫
According to the present invention, carbon fiber reinforced thermoplastic resin pellets having a core-sheath structure are provided, in which the blended yarn according to the present disclosure is used as the core component and the thermoplastic resin is used as the sheath component. The pellets according to the present disclosure contain recycled carbon fibers with a relatively long fiber length compared to short fiber reinforced pellets obtained by kneading and dispersing recycled carbon fibers in a thermoplastic resin, so they are supplied to injection molding machines and the like. By doing so, a carbon fiber-containing product having excellent mechanical properties and the like can be produced.

<Method for producing carbon fiber reinforced thermoplastic resin pellets>
The core-sheath structure carbon fiber reinforced thermoplastic resin pellets according to the present disclosure include producing a carbon fiber reinforced thermoplastic resin strand by coating a blended yarn with a thermoplastic resin, and cutting the strand. More specifically, as described above, except that the blended yarn according to the present disclosure is used instead of continuous carbon fibers, similar to the method for producing general long fiber reinforced pellets, It can be produced by cutting a resin strand coated with a thermoplastic resin. That is, a coating process in which the blended yarn that is continuously conveyed while being rewound is passed through a die that is continuously supplied with a molten thermoplastic resin from a supply port different from the blended yarn, and a carbon fiber reinforced extruded from the die It can be manufactured by a method that includes a cutting step in which the thermoplastic resin strands are cooled and then cut.

<Thermoplastic resin>
The thermoplastic resin used for the coating treatment in the production of the pellets (that is, the thermoplastic resin constituting the sheath component of the pellet) includes polyolefin resins (e.g., polypropylene resins and polyethylene resins), polyester resins (e.g., polyethylene terephthalate resins, poly butylene terephthalate resin, and polylactic acid resin), polyamide resin, polyetherketone resin, polycarbonate resin, phenoxy resin, and polyphenylene sulfide resin. The thermoplastic resin may be of only one type, or may be a mixture of two or more thermoplastic resins.

Also, the thermoplastic resin that constitutes the sheath component of the pellet may be of the same type as the thermoplastic resin fibers contained in the blended yarn according to the present disclosure, or may be of a different type. In particular, the melting point (T0 (°C)) of the thermoplastic resin constituting the sheath component of the pellet is lower than the melting point (T1 (°C)) of the thermoplastic resin fiber contained in the blended yarn according to the present disclosure by more than 10%. is preferred. In this case, when producing the carbon fiber reinforced thermoplastic resin pellets according to the present disclosure, the thermoplastic resin fibers contained in the blended yarn are suppressed from melting, and only the thermoplastic resin covering the blended yarn melts. Since it becomes easier to set the manufacturing conditions, the blended yarn may be stably threaded in the die.

In addition, various types of thermoplastic resins may be added to the above-mentioned thermoplastic resins used for the coating treatment within the range that does not impair the mechanical strength for the purpose of improving fluidity, appearance gloss, flame retardancy, thermal stability, weather resistance, impact resistance, etc. Polymers, fillers, stabilizers, pigments, etc. may be incorporated.

<Core-sheath structure of pellet>
The carbon fiber reinforced thermoplastic resin pellets according to the present disclosure are produced by cutting (slicing) the carbon fiber reinforced thermoplastic resin strands obtained by coating the blended yarn according to the present disclosure with a thermoplastic resin. The blended yarn is the core component, and the thermoplastic resin is the sheath component.

Regarding the ratio of the thermoplastic resin as the sheath component in the core-sheath structure carbon fiber reinforced thermoplastic resin pellets, the thermoplastic resin as the sheath component is 50 parts by weight per 100 parts by weight of the recycled carbon fiber contained in the blended yarn. It is preferably 100 parts to 1000 parts by weight, more preferably 100 parts to 750 parts by weight, and most preferably 250 parts to 500 parts by weight.

<Cut length of pellet>
The cut length of the pellet is preferably 3 mm or more and 10 mm or less. Particularly preferably, it may be 5 mm or less. The cut length of the pellet particularly corresponds to the length in the axial direction of the core structure of the pellet.

If the cut length of the pellet is 3 mm or more, the average length of the recycled carbon fiber is relatively long, so that the mechanical properties of the carbon fiber-containing product using the pellet as a molding raw material can be further improved. If the cut length of the pellet is 10 mm or less, the recycled carbon fiber can be easily dispersed during molding, and the mechanical properties of the carbon fiber-containing product can be further improved.

The diameter of the core-sheath type pellet is not particularly limited, but it may be 1/10 or more and 2 times or less of the cut length of the pellet, and it is preferably 1/4 or more and 1 time or less of the cut length of the pellet. preferable. If the diameter of the pellet is too small, there may be areas that cannot be coated. Conversely, if the diameter of the pellet is too large, it may be difficult to mold because it may not be properly bitten into the molding machine.

For the cut length and diameter of the pellet, measure the cut length or diameter of 30 or more pellets visually using a vernier caliper or the like, or in an image acquired with a digital camera or an optical microscope, and average the measured values. can be calculated by

FIG. 1 is a schematic diagram that schematically illustrates a carbon fiber reinforced thermoplastic resin pellet 200 having a core-sheath structure according to the present disclosure. The figures are schematic diagrams for illustration purposes and are not to scale. The core-sheath structured pellet 200 has a core component 210 and a sheath component 220 . The pellet 200 also has a cut length L and a diameter R. Core-sheath structure pellets 200 are obtained by cutting (cutting treatment, “C” in FIG. ) can be manufactured by

≪Manufacturing method of recycled carbon fiber by semiconductor thermal activation method≫
A method for obtaining recycled carbon fibers having properties according to the present disclosure using the semiconductor thermal activation method is described below. In the following, first, a method for decomposing plastic-containing materials will be described, and then, using this decomposition method, a method for recovering inorganic materials (carbon fibers) from plastic-containing materials containing plastics and inorganic materials (carbon fibers). explain.

<Method for decomposing materials containing plastic>
A method for decomposing a plastic-containing material according to the present disclosure comprises:
The plastic-containing material is heated to a first surface temperature in the presence of a semiconductor material in an atmosphere in a heating furnace into which a low-oxygen gas having an oxygen concentration of less than 10% by volume is introduced, and the plastic in the plastic-containing material is to decompose
including.

FIG. 2 is a conceptual cross-sectional view for explaining the disassembly method according to the present invention. The decomposition mechanism of the plastic-containing material according to the present invention will be described below. No theory is intended to limit the present invention.

When the semiconductor material 11 is heated in an oxygen atmosphere, holes h ⁺ and electrons e ⁻ are generated in the semiconductor material 11, and the electrons e ⁻ react with oxygen O ₂ in the atmosphere to form O ₂ ⁻ radicals (active oxygen ) is thought to occur. Then, in the plastic-containing material 12 arranged adjacent to the semiconductor material 11, radical propagation occurs, and the plastic-containing material 12 is decomposed into low-molecular-weight components, furthermore, CO ₂ , H ₂ O, CH ₄ and the like. is oxidatively decomposed into decomposition gases of Radicals are believed to promote the oxidative decomposition of plastics by abstracting hydrogen from them.

By using a semiconductor material, the heat introduced for decomposition of the plastic can be reduced compared to the case where the semiconductor material is not used, and as a result, energy consumption can be reduced.

In the conventional plastic decomposition method based on the thermal activation of semiconductors, excessive oxidation heat may occur in the heat treatment process. In the conventional method, the heat treatment was carried out in the air where the oxygen concentration was not controlled, so it is believed that excessive radicals were generated and as a result, excessive oxidation heat was generated.

In contrast, the inventors of the present invention have found that even in the presence of a semiconductor material, by setting the oxygen concentration to a relatively low value, it is possible to efficiently heat-treat the plastic while suppressing excessive oxidation heat generation. I found what I can do.

Especially in the early stages of the thermal decomposition of plastics, there is a high possibility that excessive oxidation heat will be generated due to the relatively large amount of plastics. On the other hand, according to the method according to the present disclosure, the heat treatment is efficiently performed at a relatively low oxygen concentration, so even in the initial stage of decomposition, excessive oxidation heat generation can be suppressed. .

Therefore, according to the method according to the present disclosure, since the heat treatment is performed in the presence of the semiconductor material, good decomposition efficiency can be obtained even with a relatively low oxygen concentration, and the oxygen concentration in the heating furnace is relatively low. By setting the value, it is possible to suppress excessive oxidation heat generation and achieve a decomposition treatment with improved stability.

The decomposition method according to the invention will now be described with reference to the drawings depicting exemplary embodiments.

FIG. 3 is a cross-sectional view that schematically illustrates one embodiment of the disassembly method according to the present disclosure. The heating furnace 20 shown in FIG. 3 has a heat source (heater) 23 , a gas supply section 24 , an exhaust port 25 and an internal space 26 . A porous carrier 21 is arranged in the interior space 26 of the heating furnace 20 and the semiconductor material is carried on the surface of the carrier 21 . In the embodiment of FIG. 3 a plastic-containing material 22 is placed in contact with this carrier 21 .

The temperature of the atmosphere in the interior space 26 of the furnace 20 can be controlled via the heat source (heater) 23 of the furnace 20 so that the surface temperature of the plastic-containing material 22 is at a specific temperature. . The surface temperature of the plastic-containing material 22 can be measured via a temperature sensor 27 placed within 5 mm of the surface of the plastic-containing material 22 .

A low oxygen concentration gas having an oxygen concentration of less than 10% by volume is introduced into the internal space 26 of the heating furnace 20 through the gas supply section 24 . By setting the introduction speed of the low-oxygen-concentration gas according to the volume in the furnace, the oxygen concentration in the atmosphere inside the heating furnace 20 can be controlled. The hypoxic gas can be forced into the furnace, for example, via a gas supply provided in the furnace, or can be sucked into the furnace by applying suction pressure to the exhaust port 25. can be done.

Low oxygen concentration gas is, for example, a mixed gas of air and nitrogen gas. By selecting the ratio of air and nitrogen gas, the oxygen concentration in the furnace can be controlled.

The plastic-containing material is heated to a first surface temperature, for example, 300° C. to 600° C., in an atmosphere in which the oxygen concentration is controlled to less than 10% by volume by introducing a low oxygen concentration gas. As a result, the plastic contained in the plastic-containing material 22 is decomposed into cracked gases such as water vapor, carbon dioxide, and methane, and the cracked gases are discharged from the exhaust port 25 of the heating furnace 20 .

After the heat treatment with an oxygen concentration of less than 10% by volume, a heat treatment with an oxygen concentration of 10% by volume or more can be further performed.

In addition, the inorganic material contained in the plastic-containing material can be recovered after the heat treatment.

The decomposition method according to the present disclosure is described in more detail below.

<Materials containing plastic>
The plastic-containing material contains plastic. The plastic-containing material may be a plastic material or a plastic composite material.

The plastics contained in the plastic-containing material include thermoplastic resins and thermosetting resins.

Examples of the thermoplastic resin contained in the plastic-containing material include polycarbonate (PC) resin, polyethylene (PE) resin, polypropylene (PP) resin, polyvinyl chloride (PVC) resin, polystyrene (PS) resin, polyethylene terephthalate ( PET) resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide (PA) resin, polylactic acid (PLA) resin, polyimide (PI) resin, polymethyl methacrylate (PMMA) resin, methacrylic resin, polyvinyl alcohol (PVA) resin , polyacetal resin, petroleum resin, AS resin, modified polyphenylene ether resin, polybutylene terephthalate (PBT) resin, polybutene (PB) resin, fluorine resin, polyacrylate resin, polyether ether ketone (PEEK) resin, polyphenylene sulfide (PPS) resin.

Examples of thermosetting resins contained in plastic-containing materials include phenol resins, urethane foam resins, polyurethane resins, urea resins, epoxy resins, unsaturated polyester resins, melamine resins, alkyd resins, vinyl ester resins, and cyanate resins. mentioned.

The plastic-containing material can contain at least one selected from the group consisting of the above thermoplastic resins and thermosetting resins.

(plastic composite material)
Plastic-containing materials are, in particular, plastic composite materials. The plastic composite material is, for example, fiber reinforced plastic (FRP). Examples of reinforcing fibers contained in fiber-reinforced plastics include carbon fibers.

(carbon fiber reinforced plastic)
Plastic composite materials are in particular carbon fiber-containing plastic products such as carbon fiber reinforced plastics (CFRP). Carbon fiber reinforced plastics contain plastic and carbon fiber material. Carbon fiber reinforced plastics may contain other members and/or materials (for example, reinforcing fibers other than carbon fibers, resin moldings, metals, ceramics, etc.).

The carbon fibers contained in the carbon fiber reinforced plastic are not particularly limited, but include PAN-based carbon fibers and pitch-based carbon fibers. The carbon fiber may be of one type or may be composed of two or more types.

The carbon fiber material contained in the carbon fiber reinforced plastic may be in any form, and may be, for example, carbon fiber bundles, woven fabrics formed from carbon fiber bundles, or non-woven fabrics of carbon fibers.

<Introduction of low oxygen concentration gas>
In the method according to the present disclosure,
A low oxygen concentration gas having an oxygen concentration of less than 10% by volume is introduced into the atmosphere of the heating furnace.

Preferably, the oxygen concentration of the low oxygen concentration gas introduced into the atmosphere of the heating furnace is more than 0% by volume, 1% by volume or more, 2% by volume or more, 3% by volume or more, or 4% by volume or more, and/or , 9% by volume or less, 8% by volume or less, or 7% by volume or less.

The timing of introducing the low oxygen concentration gas into the heating furnace can be determined according to the type of plastic contained in the plastic-containing material, the surface temperature at which decomposition of the plastic starts, and the like. In addition, the timing of introducing the low-oxygen concentration gas into the heating furnace can be determined based on previously acquired data regarding the self-heating of the plastic-containing material.

In one preferred embodiment of the present disclosure, a hypoxic gas is introduced into the atmosphere of the furnace while the surface temperature of the plastic-containing material held within the furnace is below 300°C.

More preferably, while the surface temperature of the plastic-containing material held in the heating furnace is 250° C. or lower, 200° C. or lower, or 150° C. or lower, in the atmosphere of the heating furnace, the oxygen concentration is less than 10% by volume. A hypoxic gas is introduced.

More preferably, a low oxygen concentration gas having an oxygen concentration of less than 10% by volume is introduced into the atmosphere of the furnace holding the plastic-containing material having a surface temperature of less than 300° C., thereby to less than 10% by volume of oxygen.

More preferably, a low oxygen concentration gas having an oxygen concentration of less than 10% by volume is introduced into the atmosphere of the furnace holding the plastic-containing material having a surface temperature of less than 300° C., thereby The oxygen concentration in the Control below.

The oxygen concentration in the heating furnace can be directly measured by an oxygen concentration meter (oxygen monitor), or can be determined based on the volume inside the furnace and the amount of gas introduced into the furnace. The oxygen concentration in the furnace is preferably the average oxygen concentration over the course of the heat treatment.

Introduction of the low-oxygen gas into the furnace can be performed, for example, by pushing the low-oxygen gas into the furnace via a gas supply provided in the heating furnace, or a suction provided in the furnace. This can be done by providing suction through a port (or exhaust port) so that gas flows into the furnace from a gas supply provided at a location different from the suction port. The gas supply of the furnace may, for example, have openings and/or comprise a gas permeable material.

The amount of gas introduced into the furnace can be set based on the unit resin amount of the resin (for example, epoxy resin) to be decomposed, depending on the capacity of the heating furnace, the desired oxygen concentration, and the like.

For example, the amount of gas introduced into the furnace per unit amount of resin is in the range of 1 to 1000 (L/min)/kg or less, preferably in the range of 2 to 700 (L/min)/kg or less. can be done. Also, the time for replacing the atmosphere in the furnace with the introduced gas can be determined based on the determined amount of gas to be introduced and the volume of the heating furnace to be used.

In particular, the introduction amount of the low oxygen concentration gas is set with respect to the volume of the furnace so that the atmosphere in the heating furnace is maintained while the surface temperature of the plastic-containing material held in the heating furnace is less than 300 ° C. , can be replaced by the introduced hypoxic gas.

The low oxygen concentration gas introduced into the heating furnace may contain a diluent gas, particularly a mixture of air and diluent gas. Examples of the diluent gas include nitrogen gas, carbon dioxide gas, steam, and superheated steam. Note that superheated steam is steam heated to a temperature equal to or higher than the boiling point. Superheated steam has the advantage of relatively high heat transfer to the object to be decomposed.

(heating furnace)
The heating furnace may be a combustion furnace or an electric furnace. The heating furnace has, for example, an internal space for containing the plastic-containing material and the semiconductor material, a heat source (heater) for heating the atmosphere in the heating furnace, and a gas supply for introducing a low oxygen concentration gas into the heating furnace. , an exhaust port for discharging cracked gases, and, optionally, a suction port for applying suction pressure to the interior of the furnace. Note that one structure can also be used as an exhaust port and a suction port. As an exhaust port and/or a suction port, for example, one or a plurality of openings provided in the heating furnace can be used.

(Surface temperature)
The "surface temperature" of the plastic-containing material can be determined by measuring the temperature within 5 mm of the plastic-containing material during heat treatment.

The surface temperature of the plastic-containing material can be controlled, for example, by controlling the temperature in the furnace via the heat source of the furnace, and/or by introducing a cold gas into the furnace, and/ Alternatively, it can be controlled by lowering the oxygen concentration to suppress oxidation heat generation.

In addition, by measuring the surface temperature of the plastic-containing material via a temperature sensor placed within 5 mm from the surface of the plastic-containing material and feeding back this measured value to the heat source of the heating furnace, the surface temperature can be measured with higher accuracy. can also be controlled.

Furthermore, for example, data on the correlation between the temperature in the heating furnace and/or the output of the heat source and the surface temperature measured by the sensor is obtained in advance, and the heat treatment may be performed based on this data. .

<Heat treatment>
A method according to the present disclosure includes:
The plastic-containing material is heated to a first surface temperature in the presence of a semiconductor material in an atmosphere in a heating furnace into which a low-oxygen gas having an oxygen concentration of less than 10% by volume is introduced, and the plastic in the plastic-containing material is to decompose
including.

Preferably, this heat treatment is performed in an atmosphere in which the oxygen concentration is less than 10% by volume by introducing a low oxygen concentration gas, particularly more than 0% by volume, 1% by volume or more, 2% by volume or more. , at an oxygen concentration of 3% by volume or more, or 4% by volume or more, and/or at an oxygen concentration of 9% by volume or less, 8% by volume or less, or 7% by volume or less.

(First surface temperature)
"First surface temperature" is the surface temperature of the plastic-containing material. The "first surface temperature" can be determined by measuring the temperature within 5 mm around the plastic-containing material during heat treatment, similarly to the "surface temperature" above.

The first surface temperature may be 300°C or higher, 325°C or higher, or 350°C or higher, and/or may be 600°C or lower, 550°C or lower, 500°C or lower, or 450°C or lower. The first surface temperature is, for example, 300°C to 600°C, 300°C to 550°C, 300°C to 500°C, or 300°C to 450°C.

If the first surface temperature is less than the above range, decomposition of the plastic may not occur. Further, when the first surface temperature exceeds the above range, when the plastic-containing material contains a valuable substance such as carbon fiber, the deterioration and/or burning of the carbon fiber due to heating in the presence of oxygen is remarkable. can be. By setting the first surface temperature to a relatively low temperature, the effect of suppressing excessive oxidation heat generation is further enhanced.

In a preferred embodiment of the present disclosure, the first surface temperature is brought to a temperature of 450° C. or higher during the heat treatment with an oxygen concentration of less than 10% by volume. When the heating temperature is relatively low, the carbides formed on the surface of the plastic-containing material may inhibit further decomposition of the plastic. Carbide can be removed even if the is low. Therefore, it becomes possible to further improve the decomposition efficiency of the plastic.

Preferably, the heat treatment under the introduction of a low-oxygen concentration gas is performed for a predetermined period of time. This predetermined time may be between 1 minute and 600 minutes, preferably between 30 minutes and 300 minutes, more preferably between 60 minutes and 180 minutes. The time when the temperature of the heating furnace reaches 300° C. or the time when the start of decomposition of the plastic is confirmed can be set as the starting point of the above-mentioned “predetermined time”.

(semiconductor material)
The semiconductor material may be placed in the furnace together with the plastic-containing material, or the semiconductor material may be placed in the furnace beforehand and the plastic-containing material then placed adjacent to or in contact with the semiconductor material. can be placed.

In one embodiment according to the present disclosure, the plastic-containing material and the semiconductor material undergoing heat treatment are spaced apart from each other by a distance of 50 mm or less. For this purpose, for example, spacers arranged between the plastic-containing material and the semiconductor material can be used.

The distance between the plastic-containing material and the semiconductor material can be measured where they are closest together.

In another preferred embodiment of the present disclosure, a plastic-containing material and a semiconductor material that are to undergo heat treatment are placed in contact with each other.

The mode of contact between the plastic-containing material and the semiconductor material is not particularly limited. For example, the two can be brought into contact by placing a plastic-containing material over the semiconductor material. A plastic-containing material may also be placed over the semiconductor material carried on the surface of the carrier. Furthermore, the two can be brought into contact by surrounding or covering at least a portion or the entirety of the plastic-containing material with a semiconducting material.

The semiconductor material is not particularly limited as long as it is stable at the temperature and oxygen concentration of the present invention. The semiconductor material contains, for example, at least one selected from the group consisting of the following substances:
BeO, MgO _, CaO _, SrO, _BaO , _CeO2 , _ThO2 , _{UO3 , U3O8 ,} TiO2 _{, ZrO2} , _V2O5 , _Y2O3 , _Y2O2S , _Nb2O5 , _{Ta2O5 , MoO3 , WO3 ,} MnO2 _{, Fe2O3 ,} MgFe2O4, _{NiFe2O4 , ZnFe2O4 , ZnCo2O4} , ZnO _, CdO, _{Al2O3 ,} MgAl _{2O4 , ZnAl2O4 , Tl2O3} , _In2O3 , _{SiO2 , SnO2 , PbO2} , _UO2 , _{Cr2O3 , MgCr2O4} , _FeCrO4 , _{CoCrO4 , ZnCr2O 4} , _WO2 , MnO, _{Mn3O4 , Mn2O3} , FeO, NiO, CoO _{, Co3O4} , _{PdO ,} CuO, _Cu2O , _Ag2O , _CoAl2O4 , _{NiAl2O4 , Tl2O} , GeO, PbO, TiO, _Ti2O3 , _VO , _MoO2 , IrO2, _RuO2 , _CdS , CdSe, CdTe, _Cu2O , _{Sb2O3 , MnO3} , and _CoCrO4 .

Preferably, the semiconductor material is an oxide semiconductor material. Preferred oxide semiconductor materials include chromium oxide, titanium oxide, zinc oxide, vanadium oxide, tungsten oxide, molybdenum oxide, cobalt oxide, iron oxide, and copper oxide.

The form of the semiconductor material is not particularly limited, and may be plate-like, granular, or honeycomb-like, for example. From the viewpoint of promoting decomposition of the plastic, it is preferable that the semiconductor material is supported on the surface of the air-permeable carrier. The air-permeable carrier may be a porous body made of ceramics or the like, a honeycomb-shaped support, or the like. The semiconductor material may be a semiconductor sintered body.

<Two-step heating>
A heat treatment method according to one preferred embodiment of the present disclosure comprises:
heating the plastic-containing material subjected to the heat treatment at the first surface temperature in the presence of the semiconductor material in an atmosphere having an oxygen concentration of 10% by volume or more;
including.

Heat treatment at an oxygen concentration of 10% by volume or more is preferably performed at an oxygen concentration of more than 10% by volume, 12% by volume or more, 15% by volume or more, or 20% by volume or more, and / or 30% by volume. or less, or at an oxygen concentration of 25% by volume or less.

In this embodiment, also referred to as two-step heating, the plastic-containing material that has been heat treated at a relatively low oxygen concentration is further heat treated under an increased oxygen concentration.

During the early stages of the pyrolysis of plastics, due to the relatively large amount of plastics, there is a high likelihood that excessive oxidation heat will be generated. In contrast, in the above-described embodiment involving two-step heating, the heat treatment at relatively low oxygen concentration is followed by the heat treatment with increased oxygen concentration. That is, at the stage when the decomposition of the plastic has progressed and the amount of the plastic has been reduced, the heating is performed with the oxygen concentration increased, so it is possible to suppress the generation of excessive oxidation heat.

Also, in the heat treatment at a relatively low oxygen concentration, part of the plastic may remain as carbide without being vaporized. On the other hand, in the above-described embodiment involving two-step heating, the oxygen concentration is increased and the heat treatment is further performed, so the remaining carbide can be efficiently decomposed and removed, and as a result, the decomposition efficiency is improved. It can be improved further.

The heat treatment under introduction of a low oxygen concentration gas and the heat treatment at an oxygen concentration of 10% by volume or more can be performed continuously in the same heating furnace. That is, for example, after heating the plastic-containing material to the first surface temperature, the oxygen concentration can be increased to 10% by volume or more in the same heating furnace, and heat treatment can be further performed. In the conventional plastic decomposition method, it was necessary to perform processing such as shredding of the processing object following batch processing, but heat processing under the introduction of low oxygen concentration gas and heating at an oxygen concentration of 10% by volume or more The number of steps can be reduced by continuously performing the treatments in the same heating furnace.

An atmosphere with an oxygen concentration of 10% by volume or more can be formed, for example, by introducing a high oxygen concentration gas with an oxygen concentration of 10% by volume or more into the heating furnace, in particular, air and / or oxygen gas into the heating furnace. can be formed by introducing The oxygen concentration of the oxygen-rich gas may be more than 10% by volume, 12% by volume or more, 15% by volume or more, or 20% by volume or more, and/or 30% by volume or less, or 25% by volume or less. you can

In the heat treatment at an oxygen concentration of 10% by volume or more, the semiconductor material used in the heat treatment at the first surface temperature can be used.

(Second surface temperature)
In particular, the plastic-containing material that has been subjected to the heat treatment at the first surface temperature is heated to the second surface temperature in the presence of the semiconductor material in an atmosphere having an oxygen concentration of 10% by volume or more.

"Second Surface Temperature" is the surface temperature of the plastic-containing material being treated. The "second surface temperature" can be determined by measuring the temperature within 5 mm around the plastic-containing material during heat treatment, similarly to the above "surface temperature" and "first surface temperature".

The second surface temperature may range from 400°C to 600°C. More preferably, the second surface temperature is between 425°C and 575°C, or between 450°C and 550°C.

If the second surface temperature is less than the above range, the decomposition efficiency may not be improved. Further, when the second surface temperature exceeds the above range, when the plastic-containing material contains a valuable substance such as carbon fiber, the deterioration and/or burning of the carbon fiber, etc. due to heating in the presence of oxygen is significant. can be.

The second surface temperature may be substantially the same temperature as the first surface temperature.

Also, the second surface temperature may be greater than or equal to the first surface temperature, or at least 5°C, at least 10°C, at least 25°C, at least 50°C, or at least 75°C higher than the first surface temperature. good.

Heat treatment at an oxygen concentration of 10% by volume or more can be performed for a predetermined period of time. This predetermined time can be, for example, 1 minute to 600 minutes, 60 minutes to 360 minutes, or 90 minutes to 300 minutes.

<Application>
According to the method for decomposing a plastic-containing material according to the present disclosure, it is possible to efficiently vaporize and decompose a wide variety of plastics. In addition, the decomposition method according to the present disclosure can also be applied to volatile organic compounds (VOC), flue gas, particulate matter (PM), etc., and can be used for exhaust gas treatment.

<<Method of collecting inorganic materials>>
Methods according to the present disclosure for recovering inorganic materials contained in plastic composites are described below.

In one embodiment of the recovery method of the present disclosure, the plastic-containing material, which is a plastic composite material, contains plastic and inorganic material, and the recovery method comprises:
recovering the inorganic material by decomposing the plastic in the plastic-containing material by the decomposition method;
including.

For the decomposition method according to the present disclosure that can be used in the recovery method according to the present disclosure and details thereof, the above description regarding the decomposition method for plastic-containing materials can be referred to.

As described above, according to the decomposition method according to the present disclosure, it is possible to efficiently decompose plastic. Therefore, according to the recovery method according to the present disclosure, the plastic contained in the plastic composite material can be efficiently and selectively decomposed, so that inorganic materials having good physical properties can be efficiently recovered. can.

Moreover, in the recovery method according to the present disclosure, the inorganic material can be recovered without crushing the plastic composite material. It should be noted that crushing of the plastic composite material is not specifically excluded and crushing can be carried out at will.

Furthermore, when recovering an inorganic material from a plastic composite material, it is necessary to suppress the influence of heat treatment on the inorganic material as much as possible from the viewpoint of maintaining the quality of the recovered inorganic material. In this regard, in the decomposition method according to the present disclosure, excessive oxidation heat generation is suppressed due to the relatively low oxygen concentration. Therefore, according to the recovery method according to the present disclosure, it is possible to recover an inorganic material having relatively good physical properties.

(Two-stage heating)
In another embodiment of the recovery method of the present disclosure, the plastic-containing material as a plastic composite is subjected to two-step heating. That is, by subjecting the plastic composite material to heating under the introduction of a low oxygen concentration gas and subsequent heat treatment at an oxygen concentration of 10% by volume or more, the plastic is decomposed and the inorganic material is recovered.

When recovering inorganic materials, it is desirable to suppress deterioration of the physical properties of the inorganic materials due to excessive heat generated by oxidation. Furthermore, it is desirable to suppress deterioration of the physical properties of the inorganic materials due to carbonization of the plastic and remaining attached to the inorganic materials. is preferred. In this regard, in the embodiment in which the plastic composite material is subjected to two-stage heating, the physical property deterioration of the inorganic material due to the excessive oxidation heat generation is prevented by making the oxygen concentration relatively low in the initial stage where excessive oxidation heat generation is likely to occur. suppressed. Furthermore, since heat treatment is performed after that with an increased oxygen concentration, the carbonized resin remaining on the inorganic material can be efficiently removed. As a result, the method of recovering inorganic materials via two-step heat treatment can ensure better physical properties of the recovered inorganic materials.

(inorganic material)
Plastic composite materials containing inorganic materials and plastics include carbon fiber reinforced plastics.

The inorganic material is in particular carbon fiber (carbon fiber material).

(Carbon fiber)
The carbon fibers contained in the carbon fiber reinforced plastic are not particularly limited, but include PAN-based carbon fibers and pitch-based carbon fibers. The carbon fiber may be of one type or may be composed of two or more types.

The carbon fibers contained in the carbon fiber reinforced plastic may be in any form, such as carbon fiber bundles, woven fabrics formed from carbon fiber bundles, or carbon fiber non-woven fabrics.

(Recovered material)
According to one embodiment of the recovery method according to the present disclosure, the plastic-derived residual carbon recovered together with the inorganic material is reduced, and in particular, the residual carbon is 5% by weight or less of the recovered inorganic material. is. Preferably, the residual carbon is 4 wt% or less, 3 wt% or less, 2 wt% or less, 1 wt% or less, 0.9 wt% or less, 0.5 wt% or less, or It is 0.1% by weight or less. The residual carbon content is preferably reduced as much as possible, but the lower limit may be 0.001% by weight or more.

Furthermore, according to the recovery method according to the present disclosure, it is possible to recover a carbon fiber material having physical properties superior to those of the carbon fiber material before manufacturing the carbon fiber reinforced plastic.

In particular, according to the recovery method according to the present disclosure, carbon fibers having a single fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more can be obtained as inorganic materials from carbon fiber reinforced plastics.

(single fiber tensile strength)
Single fiber tensile strength is preferably 3.1 GPa or more, 3.2 GPa or more, 3.3 GPa or more, or 3.4 GPa or more. Although the upper limit of the single fiber tensile strength is not particularly limited, it may be 6.0 GPa or less.

Single fiber tensile strength can be measured in accordance with JIS R7606 as follows:
taking at least 30 single fibers from the fiber bundle;
Measure the diameter of the single fiber in the side image of the single fiber taken with a digital microscope, calculate the cross-sectional area,
Fixing the sampled single fiber to a perforated mount with an adhesive,
The mount on which the single fibers are fixed is attached to a tensile tester, and a tensile test is performed with a sample length of 10 mm and a strain rate of 1 mm/min to measure the tensile breaking stress.
Calculate the tensile strength from the cross-sectional area and tensile breaking stress of the single fiber,
The average tensile strength of at least 30 single fibers is taken as the single fiber tensile strength.

(Weibull shape factor)
The Weibull shape factor is preferably 6.5 or greater, 7.0 or greater, 7.5 or greater, 8.0 or greater, or 8.5 or greater. Although the upper limit of the Weibull shape factor is not particularly limited, it may be 15.0 or less.

The Weibull shape factor can be calculated according to the following formula:
lnln {1/(1−F)}=m×lnσ+C
In the formula, F is the fracture probability determined by the symmetric sample cumulative distribution method, σ is the single fiber tensile strength (MPa), m is the Weibull shape factor, and C is a constant.

Weibull plotting is performed with lnln {1/(1−F)} and lnσ, and the Weibull shape factor m can be obtained from the linearly approximated slope.

<Application>
According to the recovery method according to the present disclosure, for example, only matrix resins such as fiber reinforced plastics (FRP), solar cell panels, and electronic circuits are efficiently decomposed, and valuables such as reinforcing fibers and rare metals are efficiently recovered. can do.

≪Recycled carbon fiber materials≫
The recycled carbon fiber material (recycled carbon fiber) according to the present disclosure can be produced by recovering the carbon fiber material from carbon fiber reinforced plastic. In one embodiment of the present disclosure, this recycled carbon fiber material can have physical properties that are superior to those of the carbon fiber before manufacturing the carbon fiber reinforced plastic.

The method for producing the recycled carbon fiber material is not particularly limited. For example, the recycled carbon fiber material can be produced by recovering the recycled carbon fiber material from the carbon fiber reinforced plastic by the recovery method according to the present disclosure.

In one embodiment, the recycled carbon fiber material has a single fiber tensile strength of 3.0 GPa or greater and a Weibull shape factor of 6.0 or greater. Single fiber tensile strength and Weibull shape factor can be measured and determined by the methods previously described.

Single fiber tensile strength of the recycled carbon fiber material is preferably 3.1 GPa or more, 3.2 GPa or more, 3.3 GPa or more, or 3.4 GPa or more.

The Weibull shape factor of the recycled carbon fiber material is preferably 6.5 or higher, 7.0 or higher, 7.5 or higher, 8.0 or higher, or 8.5 or higher.

(Method for producing recycled carbon fiber material)
In particular, it has a single fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more, and the content of the residual carbon component is more than 0% by weight and 5.0% by weight or less with respect to the recycled carbon fiber. A method for producing a recycled carbon fiber material comprising:
The plastic-containing material is heated to a first surface temperature in the presence of a semiconductor material in an atmosphere in a heating furnace into which a low-oxygen gas having an oxygen concentration of less than 10% by volume is introduced, and the plastic in the plastic-containing material is to decompose
including
Here, the plastic-containing material is carbon fiber reinforced plastic containing carbon fiber material.

In particular, it has a single fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more, and the content of the residual carbon component is more than 0% by weight and 5.0% by weight with respect to the recycled carbon fiber. A method for producing recycled carbon fiber is
A plastic-containing material is heated to a first surface temperature in the presence of a semiconductor material in an atmosphere in a heating furnace into which a low oxygen concentration gas having an oxygen concentration of less than 10% by volume is introduced, and the first surface temperature is Decomposing the plastic in the plastic-containing material by heating the plastic-containing material subjected to the heat treatment in the presence of the semiconductor material in an atmosphere with an oxygen concentration of 10% by volume or more,
including
Here, the plastic-containing material is carbon fiber reinforced plastic containing carbon fibers.

In one preferred embodiment of the method for producing a recycled carbon fiber material according to the present disclosure, a hypoxic gas is introduced into the furnace atmosphere while the surface temperature of the plastic-containing material is below 300°C.

(residual carbon)
Preferably, the recycled carbon fiber material according to the present disclosure has a reduced amount of residual carbon, in particular, the residual carbon is 5% by weight or less relative to the recycled carbon fiber material. More preferably, the residual carbon is 4% by weight or less, 3% by weight or less, 2% by weight or less, 1% by weight or less, 0.9% by weight or less, or 0.5% by weight or less with respect to the recycled carbon fiber material. , or 0.1% by weight or less.

“Residual carbon” is a carbonized component derived from plastic contained in the carbon fiber reinforced plastic, which is the raw material for manufacturing the recycled carbon fiber material.

The amount of residual carbon in recycled carbon fiber materials can be determined by thermogravimetric analysis (TGA).

Determination of residual carbon content by thermogravimetric analysis can be performed by the following procedure:
(i) For a sample piece of 1 to 4 mg obtained by pulverizing a recycled carbon fiber material, in a thermogravimetric analyzer, an air supply rate of 0.2 L / min, a heating rate of 5 ° C. / min, and 1 /6s recording speed,
temperature increase from room temperature to 100° C.,
hold at 100° C. for 30 minutes,
raising the temperature from 100°C to 400°C, and
Perform thermogravimetric analysis with a step of holding at 400 ° C. for a total of 300 minutes,
(ii) In a graph plotting the weight loss rate against time, identify the inflection point of the slope, and subtract the weight loss rate during the holding period at 100 ° C. from the weight loss rate value at the inflection point. Calculate the amount of residual carbon by

If the inflection point of the slope cannot be identified under the above conditions, instead of the thermogravimetric analysis for a total of 300 minutes, a thermogravimetric analysis for a total of about 600 minutes with a hold at 400° C. for 480 minutes may be performed. Furthermore, instead of holding at 400° C. for 480 minutes, a specific temperature in the range of greater than 400° C. and up to and including 500° C. may be held for 480 minutes.

EXAMPLES The present invention will be described more specifically below using examples. It should be noted that the examples are illustrative, and the present application is not limited thereto.

<<Example 1>>
<Preparation of materials>
(recycled carbon fiber)
In Example 1, as the recycled carbon fiber, by the method according to the present disclosure, CFRP was used as a raw material and regenerated by the semiconductor thermal activation method. , a Weibull shape factor of 7.0 and a residual carbon content of 0.6% by weight.

(single fiber tensile strength)
The single fiber tensile strength was measured according to JIS R7606 as follows:
taking at least 30 single fibers from the fiber bundle;
Measure the diameter of the single fiber in the side image of the single fiber taken with a digital microscope, calculate the cross-sectional area,
Fixing the sampled single fiber to a perforated mount with an adhesive,
The mount on which the single fibers are fixed is attached to a tensile tester, and a tensile test is performed with a sample length of 10 mm and a strain rate of 1 mm/min to measure the tensile breaking stress.
Calculate the tensile strength from the cross-sectional area and tensile breaking stress of the single fiber,
The average tensile strength of at least 30 single fibers was taken as the single fiber tensile strength.

(Weibull shape factor)
The Weibull shape factor was calculated according to the following formula:
lnln {1/(1−F)}=m×lnσ+C
(Wherein, F is the fracture probability determined by the symmetric sample cumulative distribution method, σ is the single fiber tensile strength (MPa), m is the Weibull shape factor, and C is a constant.).
Weibull plotting was performed with lnln {1/(1−F)} and lnσ, and the Weibull shape factor m was obtained from the linearly approximated slope.

(Residual carbon content)
The amount of residual carbon components in the recycled carbon fiber was determined by thermogravimetric analysis (TGA method) as follows:
(i) For a 4 mg sample piece obtained by pulverizing recycled carbon fiber, in a thermogravimetric analyzer, an air supply rate of 0.2 L / min, a heating rate of 5 ° C. / min, and a heating rate of 1/6 s Thermogravimetric analysis was performed with the steps of ramping from room temperature to 100° C., holding at 100° C. for 30 minutes, ramping from 100° C. to 400° C., and holding at 400° C. for 480 minutes at recording speed. , for a total of about 600 minutes,
(ii) In a graph plotting the weight loss rate against time, identify the inflection point of the slope, and subtract the weight loss rate during the holding period at 100 ° C. from the weight loss rate value at the inflection point. The amount of residual carbon was calculated by

After the above recycled carbon fiber is immersed in an aqueous dispersion of epoxy resin and pulled out, it is dried in a dryer. was applied.

(Thermoplastic resin fiber)
In Example 1, as the thermoplastic resin fiber, polyamide 66 resin fiber (PA66 resin fiber (manufactured by Toray Industries, Inc., 1401-1.3T-38 E9) with an average length of 38 mm, single yarn fineness 1.3 dtex, number of crimps 17 crests/25 mm, melting point 265°C) was used.

<Production of blended yarn>
80% by weight of the recycled carbon fiber with a binder and 20% by weight of the PA66 resin fiber are mixed and spun through each process of carding, drawing, and roving to obtain a weight of 0.86 g / m. A continuous blended yarn (blended yarn according to Example 1) could be produced. A twist of 200 turns/m was applied in the roving process.

<Production of carbon fiber reinforced thermoplastic resin pellets>
Next, the blended yarn obtained above is coated with polyamide 6 (manufactured by DSM: Akulon (registered trademark) FX9182, melting point 220° C.) using a crosshead die for wire coating with an exit diameter of 3 mm. is cut to a length of 3 mm, the carbon fiber content is 17% by mass (463 parts by mass of polyamide 6 per 100 parts by mass of carbon fiber), the diameter is 2.6 mm, and the cut length is 3 mm. Pellets (carbon fiber reinforced thermoplastic resin pellets according to Example 1) were obtained.

<Injection molding evaluation>
Using the obtained carbon fiber reinforced thermoplastic resin pellets as a raw material, a 110-ton electric injection molding machine (manufactured by Japan Steel Works, Ltd., J110AD) was used to set cylinder temperatures C1 / C2 / C3 / C4 / N = 265 ° C. / 270 ° C. / 280. C./280.degree. C./280.degree. C. (where C1 to C4 are cavities and N is a nozzle), and injection molding was performed with a molding cycle of 40 seconds to obtain a dumbbell for tensile test (molded article according to Example 1) having a thickness of 4 mm. The resulting molded product had a good appearance without any lumps of fibrous substances or air bubbles due to poor dispersion.

Using the obtained dumbbell as a test piece, the tensile strength was measured according to ISO 527 (JIS K7161). The tensile strength was 200 MPa, showing excellent mechanical properties.

Further, the average fiber length of the recycled carbon fibers contained in the compact was 0.33 mm.

Evaluation of the average fiber length of the recycled carbon fibers in the compact was carried out as follows:
A test piece of 20 mm×10 mm was cut out from the obtained molded article and heated at 550° C. for 1.5 hours in an oxygen atmosphere to burn off the resin component. The remaining carbon fibers were put into water and sufficiently stirred by ultrasonic vibration. The stirred dispersion is randomly collected with a measuring spoon to obtain a sample for evaluation, and the length of 3000 fibers is measured with an image analysis device Luzex AP manufactured by Nireco, the length average is calculated, and the molding is performed. The average fiber length of carbon fibers in the body was determined.

The results for Example 1 are shown in Table 1 below.

<<Comparative Example 1>>
An attempt was made to produce a blended yarn in the same manner as in Example 1, except that recycled carbon fibers with a residual carbon content of 7.1% by weight were used. The single fiber tensile strength and Weibull shape factor of the recycled carbon fibers could not be evaluated because the single fibers were strongly bound to each other by the residual carbon and the single fibers could not be separated and collected.

In Comparative Example 1, in the carding process, it was observed that the binding between the single fibers of the recycled carbon fibers was not sufficiently opened, and the entanglement between the single fibers was small, and the yarn came off. could not be manufactured. The results are shown in Table 1 below.

<<Reference Examples 1 to 3 and Reference Comparative Example 1>>
In Reference Examples 1 to 3 and Reference Comparative Example 1, a carbon fiber reinforced plastic (CFRP) plate as a plastic-containing material was heat-treated to evaluate the plastic decomposition efficiency.

<Reference Example 1>
Reference Example 1 was carried out as follows.

(Provision and arrangement of materials)
As the semiconductor material, a carrier having a honeycomb structure and chromium oxide (Cr ₂ O ₃ , purity of 99% or more, manufactured by Junsei Chemical Co., Ltd.) applied to the surface was used. The carrier with honeycomb structure had 13 cells/25 mm.

A CFRP plate with an epoxy resin content of 41% by weight was used as the plastic-containing material.

The furnace internal volume of the heating furnace was 9L. Inside the heating furnace, a CFRP plate was placed on a carrier carrying chromium oxide as a semiconductor material. The carrier and CFRP plate were placed in contact with each other.

The surface temperature of the CFRP plate was measured by a sensor arranged within 5 mm from the surface of the CFRP plate.

(Heat treatment)
The internal temperature of the furnace was increased by controlling the internal temperature of the furnace via the heater output of the furnace.

Before the surface temperature of the CFRP plate reached 300° C., a mixed gas of air and nitrogen gas with an oxygen concentration of 6% by volume was introduced into the heating furnace. The mixed gas is introduced into the heating furnace by sucking from the suction port provided in the upper part of the heating furnace at a gas introduction rate of 70 L / min, and the mixed gas is introduced from the gas supply port provided in the lower part of the heating furnace. This was done by inflowing The oxygen concentration in the heating furnace was measured by an oxygen monitor.

Heat treatment was performed for 30 minutes in an atmosphere in which the oxygen concentration was controlled to 6% by volume by introducing the mixed gas. During the heat treatment, the heater power of the heating furnace was adjusted to raise the surface temperature of the CFRP plate to a first surface temperature of 376°C.

(evaluation)
Evaluation of the plastic decomposition efficiency in the method according to Reference Example 1 was performed by calculating the weight reduction rate (wt%) from the difference between the weight of the CFRP plate before heat treatment and the weight of the CFRP plate after heat treatment. . Table 2 shows the results.

<Reference Example 2>
The same as Reference Example 1 except that the carrier and the CFRP plate were separated from each other by 30 mm in the heating furnace, and the surface temperature of the CFRP plate was raised to 377° C. during the heat treatment. Then, the heat treatment and evaluation of Reference Example 2 were performed. Table 2 shows the results.

<Reference Example 3>
Heating of Reference Example 3 in the same manner as in Reference Example 1, except that the heat treatment time was 60 minutes and the surface temperature of the CFRP plate was increased to 371 ° C. during the heat treatment. Processing and evaluation were carried out. Table 2 shows the results.

<Reference Comparative Example 1>
Heat treatment and evaluation of Reference Comparative Example 1 were performed in the same manner as in Reference Example 1, except that no semiconductor material was used and the surface temperature of the CFRP plate was raised to 370 ° C. during the heat treatment. did Table 2 shows the results.

As can be seen in Table 2, Reference Examples 1 to 3, which were heated to a surface temperature of 371° C. to 377° C. in the presence of a semiconductor material and under the introduction of a low oxygen concentration gas with an oxygen concentration of 6 vol. The decomposition efficiency of the plastic-containing material was higher than that of Reference Comparative Example 1, which did not use the material.

In Reference Example 3, the treatment time was extended to 60 minutes, but the increase in the weight reduction rate was limited compared to Reference Example 1 in which the treatment time was 30 minutes. This is believed to be due to the fact that the sample surface was covered with carbides during the heat treatment, resulting in reduced decomposition efficiency.

<<Reference Example 4 and Reference Comparative Example 2>>
<Reference Example 4>
The treatment and evaluation according to Reference Example 4 were performed in the same manner as in Reference Example 1, except that heating was performed at a surface temperature of 500° C. for 60 minutes. The results are shown in Table 3 below.

<Reference Comparative Example 2>
Processing and evaluation according to Reference Comparative Example 2 were performed in the same manner as in Reference Example 4, except that no semiconductor material was used. The results are shown in Table 3 below.

Photographs of the samples after the treatments according to Reference Example 4 and Reference Comparative Example 2 are shown in FIGS. 5 and 6, respectively. Also, a photograph of the sample before treatment is shown in FIG.

As can be seen in Table 3, Reference Example 4, in which heat treatment was performed under a semiconductor material under the introduction of a low oxygen concentration gas with an oxygen concentration of 6% by volume, is a semiconductor material under the introduction of a low oxygen concentration gas with an oxygen concentration of 6% by volume. Compared to Reference Comparative Example 2 in which heat treatment was performed without any material, high plastic decomposition efficiency was exhibited.

In addition, as can be seen in FIG. 6, residual carbon derived from plastic adheres to the surface of the sample after the treatment according to Reference Comparative Example 2 in a lump. In the sample after the treatment according to Example 4, such attachment of residual carbon was not confirmed, and the surface was relatively smooth and highly uniform, similar to the surface of the sample before treatment shown in FIG. rice field.

<<Reference Examples 5 to 9>>
In Reference Examples 5 to 9, the CFRP plate or pressure vessel as the plastic-containing material was subjected to two-step heat treatment. Then, the decomposition efficiency was evaluated, and the physical properties of the carbon fiber material obtained by the heat treatment were evaluated.

<Reference Example 5>
Reference Example 5 was carried out as follows.

(Provision and arrangement of materials)
As the semiconductor material, a carrier having a honeycomb structure and chromium oxide (Cr ₂ O ₃ , purity of 99% or more, manufactured by Junsei Chemical Co., Ltd.) applied to the surface was used. The carrier with honeycomb structure had 13 cells/25 mm.

A CFRP plate with an epoxy resin content of 41% by weight was used as the plastic-containing material. Table 4 shows the physical properties of the carbon fiber material contained in the CFRP plate before treatment as Reference Example 1.

The furnace internal volume of the heating furnace was 0.0525 m ³ . Inside the heating furnace, a CFRP plate was placed on a carrier carrying chromium oxide as a semiconductor material. The carrier and CFRP plate were placed in contact with each other.

The surface temperature of the CFRP plate was measured by a sensor placed within 5 mm from the surface of the CFRP plate.

(Heat treatment)
The internal temperature of the furnace was increased by controlling the internal temperature of the furnace via the heater output of the furnace. Then, before the surface temperature of the CFRP plate reached 300° C., a mixed gas of air and nitrogen gas with an oxygen concentration of 8% by volume was introduced into the heating furnace. The mixed gas was introduced into the heating furnace by sucking at a gas introduction rate of 190 L/min and allowing the mixed gas to flow from a gas supply section provided in the heating furnace.

In Reference Example 5, and Reference Example 6 and Reference Comparative Example 4 below, the oxygen concentration in the heating furnace was measured by an oxygen monitor installed in the heating furnace. Regarding Reference Examples 7 to 9, the in-furnace oxygen concentration was determined based on the in-furnace volume and the amount of gas introduced.

When the surface temperature of the CFRP plate reached 300°C, generation of cracked gas was confirmed.

Heat treatment was performed for 120 minutes in an atmosphere in which the oxygen concentration was controlled to 8% by volume by introducing the mixed gas. During the heat treatment, the heater power of the heating furnace was adjusted to raise the surface temperature of the CFRP plate to a first surface temperature of 450°C.

(Secondary heat treatment)
Then, while maintaining the gas suction pressure, the supply of nitrogen gas was stopped and only air was supplied. After confirming that the oxygen concentration in the heating furnace reached 10% by volume or more, heat treatment was further performed. The surface temperature of the CFRP plate was raised to 500° C. during the heat treatment for 260 minutes. The average oxygen concentration over 260 minutes was 14% by volume, and the maximum oxygen concentration was 18% by volume.

In Reference Example 5, a 0.8 kg CFRP plate was treated. The throughput to the furnace internal volume was 15.2 kg/m ³ .

(Residual carbon content)
The amount of residual plastic-derived carbon in the carbon fiber material recovered after heat treatment was determined by thermogravimetric analysis.

Thermogravimetric analysis was performed as follows:
(i) For a sample piece of 1 to 4 mg obtained by pulverizing the recovered carbon fiber material, in a thermogravimetric analyzer, an air supply rate of 0.2 L / min, a heating rise rate of 5 ° C. / min, and Thermogravimetric analysis with the steps of ramping from room temperature to 100°C, holding at 100°C for 30 minutes, ramping from 100°C to 400°C, and holding at 400°C at a recording speed of 1/6 s. for a total of 300 minutes,
(ii) In a graph plotting the weight loss rate against time, identify the inflection point of the slope, and subtract the weight loss rate during the holding period at 100 ° C. from the weight loss rate value at the inflection point. The amount of residual carbon was calculated by

Further, for the carbon fiber material recovered after the heat treatment, the fiber single yarn diameter and single fiber tensile strength were measured, and the Weibull shape factor was calculated.

(single fiber tensile strength)
The single fiber tensile strength was measured according to JIS R7606 as follows:
taking at least 30 single fibers from the fiber bundle;
Measure the diameter of the single fiber in the side image of the single fiber taken with a digital microscope, calculate the cross-sectional area,
Fixing the sampled single fiber to a perforated mount with an adhesive,
The mount on which the single fibers are fixed is attached to a tensile tester, and a tensile test is performed with a sample length of 10 mm and a strain rate of 1 mm/min to measure the tensile breaking stress.
Calculate the tensile strength from the cross-sectional area and tensile breaking stress of the single fiber,
The average tensile strength of at least 30 single fibers was taken as the single fiber tensile strength.

(Weibull shape factor)
The Weibull shape factor was calculated according to the following formula:
lnln {1/(1−F)}=m×lnσ+C
(Wherein, F is the fracture probability determined by the symmetric sample cumulative distribution method, σ is the single fiber tensile strength (MPa), m is the Weibull shape factor, and C is a constant.)

Weibull plotting was performed with lnln {1/(1−F)} and lnσ, and the Weibull shape factor m was obtained from the linearly approximated slope.

Table 4 shows the evaluation results. The fiber single yarn diameter is the average diameter of the single fibers measured for at least 30 single fibers as described above.

<Reference Example 6>

Except that a pressure vessel was used as the plastic-containing material, the mixed gas was sucked at a gas introduction rate of 127 L / min, and the oxygen concentration, surface temperature, and heat treatment time were as shown in Table 4 below. Then, the treatment was carried out in the same manner as in Reference Example 5.

The pressure vessel treated in Reference Example 6 had an aluminum liner and 44 wt% FRP (fiber reinforced plastic), which contained 31 wt% reinforcing fibers and 13% epoxy resin. . The reinforcing fibers consisted primarily of carbon fibers with minor amounts of glass fibers. The volume of the pressure vessel was 2.0L.

The amount of FRP treated in Reference Example 6 was 0.47 kg. The processing amount with respect to the furnace internal volume was 9.0 kg/m ³ .

Table 4 shows the evaluation results of the plastic decomposition efficiency and the evaluation results of the physical properties of the recovered carbon fiber material in Reference Example 6. The average oxygen concentration over 180 minutes of secondary heat treatment was 18% by volume, and the maximum oxygen concentration was 20% by volume.

Table 4 shows the physical properties of the carbon fiber material contained in the pressure vessel before treatment as Reference Example 2.

<Reference Example 7>
The furnace volume of the heating furnace was 0.1435 m ³ , the mixed gas of superheated steam and air was introduced into the heating furnace at a gas introduction rate of 29 L / min, and the surface temperature and heat treatment time were as follows. Heat treatment was performed in the same manner as in Reference Example 5, except that it was as shown in Table 4.

The internal temperature of the heating furnace and the surface temperature of the sample were controlled via the heater output of the heating furnace and the temperature of the superheated steam.

In Reference Example 7, a 1.0 kg CFRP plate was treated. The throughput for the volume inside the furnace was 7.0 kg/m ³ .

Table 4 shows the evaluation results of the plastic decomposition efficiency and the physical property evaluation results of the recovered carbon fiber material in Reference Example 7. In the secondary heat treatment, only air was forced into the furnace at 29 L/min.

<Reference Example 8>
The treatment was carried out in the same manner as in Reference Example 7, except that a pressure vessel was used as the plastic-containing material, and the surface temperature and heat treatment time were as shown in Table 4 below.

The pressure vessel used in Reference Example 8 is the same as the pressure vessel used in Reference Example 6.

The amount of FRP treated in Reference Example 8 was 0.47 kg. The throughput for the volume inside the furnace was 3.3 kg/m ³ .

Table 4 shows the evaluation results of the plastic decomposition efficiency and the evaluation results of the physical properties of the recovered carbon fiber material in Reference Example 8. In the secondary heat treatment, only air was forced into the furnace at 29 L/min.

<Reference Example 9>
The furnace volume of the heating furnace was 0.049 m ³ , the mixed gas of superheated steam and air was introduced into the heating furnace at a gas introduction rate of 25 L / min, the surface temperature and the heat treatment time are shown in the table below. Processing was carried out in the same manner as in Reference Example 7, except that 4 was used.

In Reference Example 9, a CFRP plate with an epoxy resin ratio of 38% was treated. The throughput for the volume inside the furnace was 1.6 kg/m ³ .

Table 4 shows the evaluation results of the plastic decomposition efficiency and the physical property evaluation results of the recovered carbon fiber material in Reference Example 9. In the secondary heat treatment, while continuing to supply superheated steam, the amount of air was increased, and gas with an oxygen concentration of 11% by volume was forced into the furnace at 38 L/min.

Table 4 shows the physical properties of the carbon fiber material contained in the above CFRP plate according to Reference Example 9 before treatment as Reference Example 3.

<<Reference Comparative Example 3>>
In Reference Comparative Example 3, materials were provided and arranged in the same manner as in Reference Example 5, and then the internal temperature of the heating furnace was raised without adjusting the oxygen concentration of the atmosphere in the heating furnace.

As a result, when the surface temperature of the CFRP plate reached 300.degree. The results are listed in Table 4.

In Reference Comparative Example 3, a 0.8 kg CFRP plate was treated. The throughput to the furnace internal volume was 15.2 kg/m ³ .

<<Reference Comparative Example 4>>

Processing was carried out in the same manner as in Reference Example 6, except that no semiconductor material was used.

The amount of FRP processed in Reference Comparative Example 4 was 0.47 kg. The processing amount with respect to the furnace internal volume was 9.0 kg/m ³ .

Regarding Reference Comparative Example 4, Table 4 shows the evaluation results of physical properties of the recovered carbon fiber material. The average oxygen concentration over 180 minutes of secondary heat treatment was 18% by volume, and the maximum oxygen concentration was 20% by volume.

As can be seen in Table 4, a low oxygen concentration gas with an oxygen concentration of 6-8% by volume was introduced, a primary heat treatment was performed in the presence of the semiconductor material, and a secondary heat treatment was performed under an increased oxygen concentration. Reference Examples 5 to 9, which were further carried out, showed low residual carbon content and excellent plastic decomposition efficiency.

In addition, in Reference Comparative Example 3 in which the oxygen concentration was not controlled, excessive self-heating occurred, whereas Reference Example 5 in which a low oxygen concentration gas with an oxygen concentration of 6 to 8% by volume was introduced into the heating furnace. ~9, no excessive self-heating was observed. In Reference Comparative Example 3, the oxygen concentration was excessive because the decomposition treatment was started without lowering the oxygen concentration in advance, and as a result, it was not possible to appropriately control the decomposition temperature in the presence of the semiconductor material. Conceivable.

Furthermore, the carbon fiber materials recovered in Reference Examples 5 to 9 have comparable fiber single yarn diameters and single fiber tensile strengths compared to the carbon fiber materials before treatment (Reference Examples 1 to 3). In addition, the Weibull shape factor of the single fiber tensile strength was increased. That is, in Reference Examples 5 to 9, carbon fiber materials having physical properties superior to those of carbon fiber materials before production of carbon fiber reinforced plastics were recovered.

Furthermore, the carbon fiber material recovered in Reference Example 6 with heat treatment in the presence of a semiconductor material was found to be particularly monofilamentary compared to the carbon fiber material recovered in Reference Comparative Example 4 in which heat treatment was performed without a semiconductor material. It had excellent quality in terms of tensile strength and Weibull shape factor.

100 carbon fiber reinforced thermoplastic resin strand 110 core component of strand 120 sheath component of strand 200 carbon fiber reinforced thermoplastic resin pellet 210 core component of pellet 220 sheath component of pellet L pellet cut length R pellet diameter C cutting treatment 11 semiconductor Materials 12 plastic-containing material 20 furnace 21 carrier with semiconductor material 22 plastic-containing material 23 heat source (heater)
24 Gas supply part 25 Exhaust port 26 Internal space of heating furnace 27 Temperature sensor

Claims (10)

A blended yarn containing recycled carbon fibers and thermoplastic resin fibers,
The recycled carbon fiber has a single fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more, and the recycled carbon fiber contains a residual carbon component, and the content of the residual carbon component is more than 0% by weight and 5.0% by weight or less with respect to the recycled carbon fiber;
A blended yarn characterized by The blended yarn according to claim 1, wherein the content of the recycled carbon fiber is more than 50% by weight and not more than 98% by weight with respect to the blended yarn. The blended yarn according to claim 1 or 2, wherein the recycled carbon fibers and the thermoplastic resin fibers each have an average length of 20 mm or more and 80 mm or less. The thermoplastic resin fibers contained in the blended yarn are polyolefin resin fibers, polyester resin fibers, polyamide resin fibers, polyetherketone resin fibers, polycarbonate resin fibers, phenoxy resin fibers, polyphenylene sulfide resin fibers, and mixtures thereof. The blended yarn according to any one of claims 1 to 3, selected from It has a core-sheath structure,
The blended yarn according to any one of claims 1 to 4 is a core component, and a thermoplastic resin is a sheath component,
A carbon fiber reinforced thermoplastic resin pellet characterized by: 6. The method of claim 5, wherein said thermoplastic resin as said sheath component is selected from polyolefin resins, polyester resins, polyamide resins, polyetherketone resins, polycarbonate resins, phenoxy resins and polyphenylene sulfide resins, and mixtures thereof. of carbon fiber reinforced thermoplastic resin pellets. The melting point T0 (° C.) of the thermoplastic resin as the sheath component is lower than the melting point T1 (° C.) of the thermoplastic resin fiber contained in the blended yarn, and T1−T0>10 is satisfied. The carbon fiber reinforced thermoplastic resin pellet according to claim 5 or 6. The carbon fiber reinforced thermoplastic resin pellet according to any one of claims 5 to 7, having a cut length of 3 mm or more and 10 mm or less. decomposing a plastic component contained in a carbon fiber-containing plastic product by a semiconductor thermal activation method to produce recycled carbon fibers; and blending the recycled carbon fibers and thermoplastic resin fibers;
A method of making a blended yarn, comprising: A method for producing carbon fiber reinforced thermoplastic resin pellets having a core-sheath structure, comprising coating the blended yarn obtained by the method according to claim 9 with a thermoplastic resin.

Images