KR101485692B1 - A method of preparing and processing sizing agent comprising thermoplastic resin - Google Patents

Abstract

The present invention relates to a method for preparing a sizing agent comprising thermoplastic resin which is stable at low temperature through gelated thermoplastic resin and for preparing a reinforced fiber composite material having an enhanced impregnation property by sizing on a surface of a fiber with the sizing agent. The present invention can increase an impregnation degree of the sizing agent by preparing a sizing agent comprising thermoplastic resin, which maintains stability around room temperature. Thus, in the case where the sizing agent of the present invention is used, binding ability of an interface between the fiber and the thermoplastic resin is increased so that a physical property of the reinforced fiber composite material can be improved and a process can be performed at room temperature and is thus economical.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a thermoplastic resin sizing agent,

More particularly, the present invention relates to a thermoplastic resin sizing agent which is stable even at a low temperature through a gelled thermoplastic resin, and sizing the thermoplastic resin sizing agent on the surface of the fiber by using the thermoplastic resin sizing agent. To a method of manufacturing a material.

Recently, due to the necessity of recycling due to environmental problems and shortening of molding time for mass production, the short molding time of thermoplastic resin and the merit of being able to be recycled have been actively studied, and fiber-reinforced thermoplastic resin composite materials have been actively studied . However, impregnation between fiber bundles is difficult because the melt viscosity of the thermoplastic resin is much higher than that of the thermosetting resin.

Therefore, in recent years, a method for improving impregnability has become a major issue in industry and academia. In general, various methods such as film lamination, powder impregnation, and solution impregnation are used for producing a fiber-reinforced thermoplastic resin composite material.

Film lamination is the most common method for producing composite materials, which is easy to manufacture, but it is difficult to overcome the impregnation problem. On the other hand, the solution impregnation can improve the impregnation property because the resin used as the matrix can be dissolved in the solvent to lower the viscosity. However, crystalline polymers such as isoterpic polypropylene with high solvent resistance and crystallinity can not be dissolved in ordinary solvents at room temperature. And the complete removal of the solvent used is also difficult, which can cause porosity after impregnation.

On the other hand, isotopic polypropylene is a crystalline resin and has a lower solubility than other thermoplastic resins. Such a crystalline phase of polypropylene has very dense chains, making it difficult to impregnate the solvent. On the other hand, the amorphous phase has a higher solubility in solvents than the crystalline state. Therefore, it is important to increase the amorphous phase in order to increase the solubility of the polypropylene. Conventional crystalline polymers can increase the amorphous phase in the same way as quenching. However, in the case of polypropylene having a very high crystallization rate, it is impossible to increase the amorphous phase by a general quenching method.

Korean Patent Laid-Open Publication No. 10-2011-124783 (November 17, 2011) discloses a water-based reinforcing film-forming agent used in a glass fiber sizing composition and a fiber-reinforced composite material containing the same. The above-mentioned patent discloses that polyolefin resin is used as a sizing agent, and no method for increasing the amorphous phase of a polymer used as a sizing agent is disclosed.

The present invention provides a thermoplastic resin sizing agent which can be treated even at room temperature to improve the impregnability of the matrix in a fiber-reinforced thermoplastic resin composite material and to improve interfacial strength through the impregnation property.

The present invention provides a sizing agent which is stably dissolved even at a melting point (crystallization temperature) or lower of a crystalline polymer.

One aspect of the present invention is

Dissolving the thermoplastic resin in a solvent;

Quenching the solution to produce a gel; And

And then re-dissolving the gel in the solvent.

In another aspect, the present invention relates to a sizing agent wherein the crystalline thermoplastic resin is dissolved in a solvent, wherein the sizing agent is maintained at a temperature lower than the melting point of the thermoplastic resin from room temperature to the sizing agent.

In another aspect, the present invention provides a method comprising: impregnating a fiber with a sizing agent prepared by the method;

And removing the solvent from the fibers impregnated with the sizing agent.

In another aspect, the present invention is produced by alternately laminating a thermoplastic resin film and a carbon fabric, followed by squeezing, wherein the carbon fabric relates to the method of making the sized carbon fiber composite material.

In another aspect, the present invention relates to a method of making a carbon fiber composite material by impregnating a sizing agent with a carbon fabric.

The present invention can increase the degree of impregnation of a sizing agent by preparing a thermoplastic sizing agent that maintains stability at about room temperature. Therefore, when the sizing agent of the present invention is used, the interfacial bonding force between the fiber and the thermoplastic resin increases, so that the mechanical properties of the fiber-reinforced composite material can be increased.

1 shows a process for producing a thermoplastic sizing agent including a quenching and redissolution process.
Fig. 2 is a graph showing a molding cycle for producing a composite material in Comparative Example 1 and Example 1. Fig.
3 shows XRD results of the thermoplastic resin gel and thermoplastic resin pellets prepared in Example 1 and the thermoplastic resin gel dried in a vacuum oven for 12 hours.
Fig. 4 shows the tensile test results of a film made of a thermoplastic resin gel and a solution prepared according to Example 1. Fig.
FIG. 5 is a graph showing the results of thermogravimetric analysis (TGA) after removal of the solvent and solidification of the fibers impregnated in the thermoplastic sizing agent according to Example 1 through microwave.
FIG. 6A is a photograph showing the result of SEM observation of the surface of the fiber not subjected to the sizing treatment on the surface according to Comparative Example 1, FIG. 6B is a photograph showing the surface of the fiber treated with the thermoplastic sizing agent according to Example 1, This is a photograph showing the result.
FIG. 7 is a graph showing the results of measurement of interfacial shear strength of the fiber-reinforced thermoplastic resin composite material prepared in Comparative Examples 1 to 1. FIG.
Fig. 8A is a photograph showing the result of SEM observation of the cross-section of the fiber-reinforced thermoplastic resin composite material produced in Comparative Example 1, Fig. 8B is a photograph of the cross- This is a photograph showing the result.

Hereinafter, embodiments of the present invention will be described in detail.

1 shows a method for producing a sizing agent according to the present invention. Referring to FIG. 1, the sizing agent manufacturing method of the present invention includes a dissolving step, a gel producing step, and a redissolving step.

The dissolving step is a step of dissolving the thermoplastic resin in a solvent.

The thermoplastic resin may be a crystalline polymer, preferably a highly crystalline polymer.

The thermoplastic resin may be selected from the group consisting of isotactic polypropylene, nylon, polyethylene, polyetheretherketone, polyethylene terephthalate, polytetrafluoroethylene, polyphenyletherketone, It may be polyphenylene sulfide.

The solvent suitable for the thermoplastic resin can be appropriately selected and used. Examples of the solvent include 1,2-dichlorobenzene, cyclohexane, ethylbenzene, methylcyclohexane, acetone, methanol, and the like. Methylene Chloride, Dimethylformamide, Trichlorobenzene, Tetrahydrofuran, Dimethylacetamide can be used.

The dissolving step is a step of heating the thermoplastic resin to a temperature at which the thermoplastic resin can be dissolved in the solvent. For example, in the case of isotopic polypropylene, the melting point is in the range of 130 to 171 ° C. When it is dissolved in 1,2-dichlorobenzene, the thermoplastic resin can be melted at 100 to 120 ° C.

The step of preparing the gel comprises quenching the solution in which the thermoplastic resin is dissolved in the dissolving step to prepare a gel.

The quenching may be performed at a temperature of 5 ° C or less, preferably 0 to -273 ° C. The solution may be quenched in liquid nitrogen.

After the quenching process, the thermoplastic resin and the solvent are mixed and solidified into a gel state.

The step of preparing the gel includes a stabilization step in which the solution is quenched and then stored for a predetermined time.

The stabilization step may be performed at a temperature higher than the quenching temperature, preferably at a temperature in the range of -50 to 10 ° C for a predetermined time, more preferably at a temperature near the melting point of the solvent used . There is no particular limitation on the time of the stabilization step, and for example, 12 to 48 hours can be performed.

The gel may be maintained in a gel state at room temperature through rapid cooling and stabilization. That is, the solidified gel after quenching does not maintain the gel shape at room temperature unless the stabilization step is performed.

Generally, the thermoplastic resin has a very high crystallization rate and it is difficult to obtain an amorphous phase by a normal quenching process.

In order to solve this problem, in the present invention, a thermoplastic resin is first dissolved in a solvent at a high temperature (in the vicinity of the melting point of the thermoplastic resin) and quenched. In this rapid quenching process, a solvent is rapidly permeated between the chains of the thermoplastic resin, And then the thermoplastic resin is still in a gel state at room temperature through a stabilization step in which the solution is stored at a low temperature near the melting point of the used solvent for a day.

The re-dissolving step is a step of re-dissolving the gel prepared above in the solvent.

Unlike the dissolving step, the re-dissolving step may add the re-dissolution temperature to a temperature lower than the dissolution temperature of the thermoplastic resin. Preferably, the re-dissolution step is performed at a temperature lower than the normal temperature to the dissolution temperature, Lt; / RTI >

Here, the melting temperature is a temperature at which the thermoplastic resin is melted using a solvent in the melting step. For example, in the case of isotactic polypropylene, 1,2-dichlorobenzene may dissolve the thermoplastic resin at 100 to 120 ° C in the dissolution step, Lt; / RTI >

That is, the thermoplastic resin may be present in a solution state even if the re-dissolution step is maintained at a temperature ranging from room temperature to less than the dissolution temperature of the thermoplastic resin.

The sizing agent obtained through the redissolving step may have a concentration of the thermoplastic resin in the range of 2 to 20 wt%.

INDUSTRIAL APPLICABILITY The present invention can stably dissolve a thermoplastic resin at room temperature, so that impregnation and process efficiency can be improved when a carbon fiber composite material is produced.

The sizing agent of the present invention is a sizing agent in which the crystalline thermoplastic resin is dissolved in a solvent, and the temperature of the sizing agent can be maintained at a temperature lower than the room temperature to the melting temperature of the thermoplastic resin.

The sizing agent may be in a solution state and may have a temperature range from room temperature to a temperature lower than the melting temperature of the thermoplastic resin, preferably from room temperature to 60 ° C.

The thermoplastic resin may be an isotactic polypropylene, a nylon, a polyethylene, a polyetheretherketone, a polyethylene terephthalate, or a polytetrafluoroethylene .

Examples of the solvent include 1,2-dichlorobenzene, cyclohexane, ethyl benzene, methylcyclohexane, acetone, and methanol methylene chloride Methylene chloride, dimethylformamide, trichlorobenzene, tetrahydrofuran, and dimethylacetamide may be used.

The sizing agent may have a concentration of the thermoplastic resin in the range of 2 to 20 wt%.

As for the sizing agent, the above description can be referred to.

The present invention relates to a sizing treatment method using a sizing agent produced by the above method.

The sizing treatment method of the present invention includes a step of impregnating fibers with a sizing agent prepared by the above method and a step of removing the solvent from the fibers impregnated with the sizing agent.

The sizing treatment of the fibers is a step of impregnating the thermoplastic resin sizing agent with the fibers and drying the fibers. More specifically, the fibers pass through a treatment bath containing a sizing agent to impregnate the sizing agent into the fibers.

As described above, the sizing agent may be a solution state in which the crystalline thermoplastic resin is dissolved in a solvent, and the temperature of the sizing agent may range from room temperature to less than the melting point of the thermoplastic resin. Preferably, the solution is maintained at a temperature below which no recrystallization occurs.

The step of removing the solvent from the fibers impregnated with the sizing agent may heat or irradiate microwaves. It is preferable to irradiate microwave. Microwaves are absorbed by dielectric materials with charge and dipole, heated by the vibration of microwave frequency, converted to thermal energy, and generate energy, which enables rapid heating. Therefore, the solvent in the impregnated sizing agent can be removed more effectively. In addition, when a solvent having a boiling point similar to the melting point of the thermoplastic resin is used, the thermoplastic resin sizing agent can be re-dissolved together with the microwave to be coated on the fiber surface.

The sizing treatment method of the present invention can increase the interfacial bonding strength between the fiber and the thermoplastic resin by previously impregnating the thermoplastic resin between the bundles of the fibers.

In another aspect, the present invention relates to a method for producing a carbon fiber composite material.

The present invention comprises alternately laminating a thermoplastic resin film and a carbon fabric and then pressing to produce a carbon fiber composite wherein the carbon fabric is sized by the sizing agent. As noted above, the sizing treated carbon fabric can increase the interfacial bonding force during crimping of the carbon fabric and the thermoplastic resin, because the thermoplastic resin is previously impregnated between the fiber bundles.

The carbon fiber composite material according to the present invention can be produced through a film lamination method using a thermoplastic resin film and a carbon fiber fabric sized by a thermoplastic resin sizing agent obtained by the above method.

The present invention can be applied not only to carbon fiber but also to general fiber form, and it can be applied to various thermoplastic composite material manufacturing methods as well as film lamination method depending on the type of fiber or resin.

The present invention can produce a carbon fiber composite material by impregnating a sizing agent with a carbon fabric. By adjusting the concentration of the sizing agent, a composite material can be produced without using a thermoplastic resin. That is, the sizing agent may be a thermoplastic resin of a carbon fiber composite material. In this case, the concentration of the thermoplastic resin in the sizing agent may range from 10 to 50 wt%.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

Comparative Example  One

Seven sheets of isotactic polypropylene having a thickness of 0.2 mm and six sheets of PAN-based carbon fabrics (12 k, woven fabrics) without sizing were alternately laminated and subjected to a molding cycle as shown in Fig. 2 using hot press Lt; 0 > C for 30 minutes to prepare a carbon fiber-reinforced polypropylene composite material.

Example  One

The isotactic polypropylene pellets were placed in 1,2-dichlorobenzene at 130 ° C and dissolved for 1 hour to prepare a 20 wt% polypropylene solution. The polypropylene solution at 130 캜 was quenched in liquid nitrogen and stabilized at 0 캜 for 24 hours to prepare a polypropylene gel. The prepared polypropylene gel was put into 1,2-dichlorobenzene and redissolved at 50 DEG C for 1 hour to prepare a sizing agent of 8 wt% polypropylene. A non-sizing PAN-based carbon fabric (12k, woven fabric) was impregnated with the prepared polypropylene sizing agent at 50 DEG C for 10 minutes. The carbon fiber impregnated in the polypropylene sizing agent was irradiated with a microwave for 15 minutes (wavelength: 60 mm, frequency: 2450 MHz, output: 800 W) to dry and solidify the solvent. The carbon fibers thus-sized were subjected to the same procedure as in Comparative Example 1 to prepare a composite material.

Experimental Example  One

The degree of crystallization of the polypropylene gel and the polypropylene pellet prepared in Example 1 and the polypropylene gel dried in a vacuum chamber for 12 hours was investigated by XRD. The results are shown in Fig.

The dried specimen of polypropylene gel showed the same crystal structure as polypropylene pellet. The crystallization degree of gel was almost similar to 51.6% and 47.5% of dry specimen and pellet, respectively. On the other hand, the polypropylene gel which had not undergone the drying process was found to be amorphous without crystal structure. In general, the isotactic polypropylene has a very high crystallization rate, so that an ordinary amorphous polypropylene can not be obtained by a quenching process. However, in the case of the solution mixed with the solvent, the solvent is already permeated between the chains of the polypropylene polymer, so that the polypropylene gel is maintained at an amorphous state even at a low temperature through the quenching process. Therefore, a complete amorphous structure can be confirmed as shown in FIG.

Experimental Example  2

The process of preparing a polypropylene gel and a solution of the polypropylene gel prepared in Example 1, proceeding with a tensile test, and dissolving and quenching the polypropylene sizing agent, confirmed the effect on the physical properties of the polypropylene. The gel and the solution were dried in a vacuum chamber at 30 캜 for 12 hours to completely remove the solvent, and then a 0.07 mm film was produced using a hot press. The tensile test was performed with a universal material testing machine (INSTRON 5969, MA, USA) based on ASTM D638 method for measuring the tensile properties of polymers. The results are shown in Fig.

The tensile strength of the film made from polypropylene gel was almost the same as that of the film made using polypropylene pellets. However, the tensile strength of the film prepared using the solution showed a slight decrease of about 0.7%. These results demonstrate that the preparation of the polypropylene sizing agent, including the dissolution and quenching process, has little effect on the physical properties of the polypropylene.

Experimental Example  3

The carbon fiber impregnated in the polypropylene sizing agent according to Example 1 was subjected to solvent removal and solidification through a microwave and then thermogravimetric analysis (TGA, Q600, TA instruments, USA) and scanning electron microscope (SEM , and scanning electron microscope (SEM). The thermogravimetric analysis was carried out by measuring the mass loss with temperature change in the temperature range of 40 to 600 ° C. The results are shown in Fig. 5 and Figs. 6A and 6B, respectively.

Microwave - dried polypropylene sizing agent showed no weight loss by solvent in thermogravimetric analysis. From this, it can be confirmed that the microwave effectively evaporated the solvent. However, when compared to pure polypropylene pellets, pyrolysis started at a faster point. Carbon fibers are heated by absorbing microwave energy. This is because some sized polypropylene is pyrolyzed by the temperature of the carbon fiber.

Further, as shown in FIGS. 6A and 6B, the results of the scanning electron microscopic analysis confirmed the difference between the untreated fiber and the polypropylene sized fiber surface. When sizing with polypropylene sizing agent, polypropylene particles adhere to the surface of the carbon fiber, and a large number of fine polypropylene strands are connected to the carbon fiber in the form of a spider web, as compared with the surface of the carbon fiber without sizing treatment .

Experimental Example  4

Based on the carbon fiber-reinforced polypropylene composite material prepared in Example 1, the interlaminar shear strength was measured according to ASTM D2334 using a universal material tester (INSTRON 5969, MA, USA) The cross-section of the fiber-reinforced polypropylene composite material was observed to evaluate impregnation properties. The results are shown in Fig. 7 and Figs. 8A and 8B, respectively.

As shown in FIG. 7, the interfacial shear strength (SF) of the carbon fiber-reinforced polypropylene composite material subjected to the sizing treatment with the polypropylene sizing agent was found to be higher than that of the non-sizing carbon fiber reinforced polypropylene composite It can be confirmed that the interface shear strength (UF) of the material increased by 38.5%.

8A and 8B, the impregnation properties of polypropylene were evaluated by scanning electron microscopy. As a result, in the case of the carbon fiber composite material not subjected to polypropylene sizing, impregnation of fibers into the bundle did not occur, but polypropylene sizing treatment It was confirmed that the impregnation into the bundle was improved. This indicates that the polypropylene sizing agent was impregnated into the bundle beforehand in the polypropylene sizing process.

While the preferred embodiments of the present invention have been described in detail, the present invention is not limited thereto.

Claims (15)

Dissolving the thermoplastic resin in a solvent;
Quenching the solution to produce a gel; And
And then re-dissolving the gel in the solvent. The method of manufacturing a sizing agent according to claim 1, wherein the dissolution step is maintained at a temperature equal to or higher than the dissolution temperature of the thermoplastic resin, and the dissolution step is maintained at a temperature lower than the dissolution temperature of the thermoplastic resin. The method of claim 1, wherein the redissolving step dissolves the gel at room temperature. 2. The method of claim 1, wherein the step of preparing the gel comprises a stabilization step in which the solution is quenched and then stored for a predetermined period of time. 5. The method of claim 4, wherein the stabilizing step is performed near the melting point of the solvent. The method of claim 1, wherein the quenching temperature is 5 ° C to -273 ° C. The method of claim 1, wherein the method comprises quenching the solution in liquid nitrogen. The method of claim 1, wherein the thermoplastic resin is selected from the group consisting of isotactic polypropylene, nylon, polyethylene, polyetheretherketone, polyethylene terephthalate and polytetrafluoroethylene (Polytetrafluoroethylene). ≪ / RTI > The method of claim 1, wherein the solvent is selected from the group consisting of 1,2-dichlorobenzene, cyclohexane, ethyl benzene, methylcyclohexane, acetone, methanol Wherein the solvent is at least one selected from the group consisting of methanol, methylene chloride, dimethylformamide, trichlorobenzene, tetrahydrofuran, and dimethylacetamide. delete delete delete Impregnating the fibers with a sizing agent prepared by the process of any one of claims 1 to 9; And removing the solvent from the fibers impregnated with the sizing agent. 14. The method of claim 13, wherein removing the solvent comprises irradiating microwaves to remove the solvent. Wherein the carbon fiber composite material is produced by alternately laminating a thermoplastic resin film and a carbon fabric, followed by compression, and the carbon fabric is subjected to the sizing process of the aforementioned item 13.

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