JP2001303456A - Method of surface-treatment for aramid fiber and surface-treated fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface-treated reinforcing fiber that has excellent fiber- resin adhesion and can meet a wide variety of matrix resins by treating the aramid fiber on its surface with supercritical fluid. SOLUTION: Aramid fiber is characteristically controlled in its crystal structure or the gaps between its crystals and its water content and impregnated or soaked with a film former, a, silane coupling agent or a mixture thereof as a surface treatment agent in a supercritical fluid, followed by heat treatment. The effect of the surface treatment can also be attained in the same way by carrying out the treatment in an aqueous medium instead of the supercritical fluid in the case where the aramid fiber has high water content.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an excellent method for surface treating aramid fiber and the use of the surface-treated aramid fiber.

[0002]

2. Description of the Related Art Aramid fiber is an organic polymer material having high strength, high elastic modulus and excellent heat resistance. Therefore, using this aramid fiber as a reinforcing material, a matrix is used as a thermosetting resin and a thermoplastic resin. Fiber-reinforced composite materials used as resins are used in various fields, and utilization in other fields is desired.

[0003] However, it is known that aramid fiber is inferior in adhesiveness to a resin as compared with other practical reinforcing fibers such as glass fiber and carbon fiber.

For example, glass fibers are subjected to a surface treatment with a silane coupling agent. In the case of carbon fiber, a method of plasma treatment or anodic oxidation is used.

Aramid fibers have been subjected to various chemical treatments (JP-A-59-184232, M. Takayanagi, T. Kajiyam).
a, T. Katayose, J. Appl.Polym.Sci., 27, 3903 (19
77)) and chemical surface treatment by plasma treatment (H. Ishid
a, G. Kumar, "Molecular Characterization of Compo
site Interfaces ", Prenum Press (1985)).

In such a treatment, there is a problem that the fiber is deteriorated due to an excessive reaction, and in the plasma treatment, the surface modifying group regresses with time in a short term.

In addition to the chemical treatment, plasma discharge (Japanese Patent Publication No. 1-12867) and excimer laser (Japanese Patent Application Laid-Open No.
-136267) is known.

[0008] These methods also reduce the crystallinity of the surface when changing the surface morphology, and impair high strength, high elastic modulus and heat resistance. It is known that the surface treatment as described above significantly reduces the crystallinity in the vicinity of the surface of an aramid fiber having high crystallinity, and the fiber fibrillation phenomenon becomes remarkable. As a result, when used in a composite material, fiber breakage due to fibrillation is likely to occur. It is known that even if the interfacial adhesion is improved, fiber embrittlement due to fibrillation leads to deterioration of composite material properties.

As a method for preventing the surface from being chemically or physically changed directly, for example, a method in which an epoxy resin is directly coated on a fiber (Japanese Patent Application Laid-Open No. 56-94640) is known.

[0010] In this method, since there is no aggressive measure regarding the bonding mode between the coating material and the fiber, there is a problem that the effect of improving the adhesion is not exhibited when the coating material is dissolved. In addition, since a large amount of organic solvent is required for coating, there is a problem in practical use in terms of industry, resources, and environment and safety.

As industrially said, practical surface treatment of aramid fibers improves the interfacial strength by removing the oil applied during spinning by extraction. This method simply removes the oil agent acting as a lubricant at the interface, and is an extremely passive process. However, although the adhesiveness at the interface is not sufficient, a polymer-based composite material can be produced without impairing at least the crystallinity and orientation of the aramid fiber.

As described above, aramid fiber has high crystallinity,
A fiber-reinforced composite material having high strength, high elastic modulus, and heat resistance is expected depending on the orientation, but sufficient strength, adhesiveness, or adhesion at the fiber-matrix resin interface becomes poor due to the inertness of the aramid fiber surface. Any of the above methods of activating an inactive surface become surface active and reduce the crystallinity and orientation of the fiber structure. As a result, the properties of the composite material are significantly reduced.

When the adhesion and adhesion between the fiber and the matrix resin are low in the fiber reinforced composite material, not only the mechanical properties of the composite material but also the permeation of a medium such as water into the interface between the fiber and the matrix resin is allowed. become. In aramid fibers that are highly hygroscopic, water penetration can vary not only the electrical properties of the composite, but also the dimensions of the composite, and can even cause microscopic destruction of the matrix resin.

[0014] Under such circumstances, the application of the reinforcing fiber for aramid fiber composite material and the use of the composite material must be naturally limited.

[0015]

SUMMARY OF THE INVENTION The present invention has been achieved as a result of studying to solve the above-mentioned problems in the prior art technically.

Accordingly, an object of the present invention is to provide a surface treatment method for aramid fibers using a supercritical fluid, and to provide a surface-treated reinforced fiber for a composite material which has excellent adhesion and can cope with a wide range of thermoplastic and thermosetting resins. An object of the present invention is to provide a reinforcing fiber composite material having excellent properties.

[0017]

Means for Solving the Problems A first invention of the present invention for achieving the above object is to provide a film former as a surface treatment agent, a silane coupling agent in a supercritical fluid or an aqueous medium in an aramid fiber. Alternatively, there is provided a surface treatment method for aramid fibers, which comprises treating with a film former and a silane coupling agent.

The above-mentioned silane coupling agent includes aminopropyltriethoxysilane, which is conventionally used,
The compound is selected from the compounds represented by the following general formula (1) including phenylaminopropyltrimethoxysilane, glycidylpropyltriethoxysilane, methacryloxypropyltrimethoxysilane, and vinyltriethoxysilane. R in the formula (1) is preferably an organic group that reacts or strongly interacts with the resin, and R ′ is preferably an alkyl group having 1 to 4 carbon atoms.

R-Si- (OR ') ₃ (1) The above-mentioned film former is a highly functional urethane or epoxy type film used as a fiber surface treating agent for composite materials. It is selected from water-dispersed emulsion-type oligomers such as formers, starch-based, polyvinyl alcohol-based, and acrylic film formers. At that time, a film former having a reaction or strong interaction with the matrix resin is desirable.

Further, in a mixed system of a silane coupling agent and a film former, it is desirable that strong interaction or reaction between the silane coupling agent and the film former occurs.

In the above treatment, the solid content of the surface treating agent to the aramid fiber is 0.01 to 20% by weight.
Is desirably within the range.

In the surface-treated aramid fiber of the present invention, the crystal size of the aramid fiber (110 planes)
Is less than 50 angstroms, the water content of the aramid fiber is 15 to 200% by weight, and the crystal size of the fiber is obtained by heat-treating the aramid fiber (110 planes).
It is a preferable condition to use an aramid fiber having a particle size of 50 Å or more.

Furthermore, the surface treatment method for aramid fibers of the present invention comprises the steps of:
After neutralization, without drying until the water content is less than 15% by weight, this fiber is treated in an aqueous medium or a supercritical fluid with the above surface treatment agent, and after the treatment, the water content of the aramid fiber Less than 15% by weight, and the crystal size of the aramid fiber is 50 Å or more,
The heat treatment of the surface-treated aramid fiber is characterized in that the surface treatment is preferably performed in a supercritical fluid such as carbon dioxide, and the heat treatment is preferably performed at a temperature of 80 ° C to 200 ° C.

The moisture content of the surface treatment is 15% by weight.
The above aramid fiber form may be not only a long fiber form after spinning but also a short fiber form cut after spinning.

A second invention of the present invention is a surface-treated aramid fiber treated by the above-mentioned treatment method, and a third invention is a fiber-reinforced composite obtained by impregnating the surface-treated aramid fiber with a matrix resin. A wide variety of composite materials can be made by selecting the conventional surface treatment agent used in the method of the present invention according to the matrix resin.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The surface treatment method for aramid fibers according to the present invention is capable of penetrating a conventional surface treatment agent for reinforcing fibers such as glass fibers and carbon fibers into aramid fibers having a high impregnating property and having a crystal size of less than 50 angstroms. It is characterized by impregnating and then returning to the conventional crystal size and fixing the surface treatment agent.

At this time, a method of immersing the aramid fiber in an aqueous solution or an emulsion may be used as a method of infiltrating and impregnating the surface treatment agent, but it is preferable that the treatment is performed in a supercritical fluid in order to improve the effect. .

In the supercritical fluid method, the liquid silane agent is attached to a suitable carrier powder such as silica,
The emulsion film former is solidified and coexists with the aramid fiber, and the fluid is flowed to promote the penetration and impregnation of the surface treatment agent into the aramid fiber.

In penetrating and impregnating the aramid fiber with the surface treating agent, it is important that the aramid fiber be smaller than a normal crystal size. In a fiber structure with a crystal size of less than 50 angstroms, the intercrystalline space is widened, so that not only low-molecular-weight silane coupling agent but also film former molecules of molecular size (less than 10,000) penetrate into this wide space. Can be.

By using a supercritical fluid, the silane coupling agent and the film former molecules are slightly dissolved on the fluid side and penetrate into the atmosphere containing moisture near the surface of the gap. A large amount of the agent can be permeated into the gap according to the distribution rule.

Although the permeation based on this distribution rule is expected to be exhibited even when an appropriate organic solvent is used, it is environmentally unfavorable in view of practical application. Since the supercritical fluid is generated only under a high pressure, the penetration of the surface treatment agent can be more effectively performed, and after the treatment, the supercritical fluid is vaporized when the pressure is reduced to a low pressure.

After the infiltration treatment of the surface treatment agent, at 80 ° C.
Heat treatment at ~ 200 ° C is a preferred condition. At this heat treatment temperature, it is important to lower the water content of the aramid fiber, increase the crystal size, and narrow the intercrystalline space. The surface treatment agent can be sufficiently inserted into and fixed to the aramid fiber by narrowing the gap between the crystals by heat treatment.

Accordingly, the fixing mechanism of the surface treatment agent by this surface treatment method is described as an intercalation of an aramid fiber in which a silane coupling agent or a film former, which is a surface treatment agent, is heat-treated in the inter-crystal space to form a normal inter-crystal space. Is obtained. As a result, the anchoring of the present invention is not a mechanism in which the silane coupling agent is chemically bonded to the substrate, as in the conventional surface treatment of glass fibers and other filler particles, but rather the spatial spacing of the physical intercrystalline gaps. It uses change. This makes it possible to impart useful functional surface treatment properties while maintaining the original physical properties of the aramid fiber.

Incidentally, referring to the mechanism of strengthening the interface between the aramid fiber and the resin, the surface treatment agent should not simply be inserted into the space between the crystals, but the molecular weight should be increased in the space so as not to escape from the space between the crystals. It is also important to form a network structure better.

It is not only necessary that the surface treating agent fixed together with the surface treating agent penetrate deep into the intercrystalline gap. If the treating agent and the matrix resin have low adhesiveness, some of the treating agents may not be used. It is also important to be able to expose the fiber surface from the intercrystalline space through increasing the molecular weight and network structure.

It is presumed that through these measures, a force transmission path was actually provided between the aramid fiber, the surface treatment agent, and the resin, the interface strengthening was improved, and the physical properties of the composite material were also improved.

In addition, in the process of molding a composite material using the surface-treated fiber, molding pressure also has an effect on interface strengthening.
When the matrix resin has fluidity and low viscosity at the time of molding, the resin can be impregnated in accordance with the molding pressure immediately before the crystal of the fiber impregnated with the treatment agent, and can be hardened and solidified immediately before. In this case, the resin is filled just before many crystals constituting the circumference of the fiber, and as a result, the two phases are alternately erected alternately at the interface. Such a two-phase multiple alternating upright interface structure, for example, is equivalent to a state in which pages of a telephone directory are overlapped with each other, and the interface strength is extremely high.

Such a two-phase multi-alternating upright interface structure is not found in reinforcing fibers such as glass fibers and carbon fibers, but has a multi-crystal structure and reflects the characteristics of flexible organic fibers. I can say

Before the surface treatment, the silane coupling agent and the film former have a molecular weight of less than 1,000 or 10, respectively.
It has a molecular structure of less than 000, but will have a molecular structure comparable to high molecular weight in the course of processing. Therefore,
It is considered that such performance significantly contributes to the fixation to the aramid fiber after the intercalation.

It is easy to select a practical silane coupling agent as a surface treatment agent from film formers based on such basic considerations on interface strengthening. At this time, the knowledge obtained with other reinforcing fibers can be directly applied to suitability for different resins. For example,
Urethane-based binders have excellent impact resistance and fatigue resistance. Further, the epoxy binder has high reactivity with the high-performance matrix epoxy resin, and is excellent in interface strengthening and rigidity improvement. Thus, not only interface strengthening but also excellent properties can be imparted to the fiber.

The aramid fiber used in the present invention is not particularly limited as long as it is a fiber made of para-type wholly aromatic polyamide represented by polyparaphenylene terephthalamide, and any fiber can be used. .

At this time, the aramid fiber preferably satisfies at least one of the following conditions (1) and (2) before the surface treatment, and in this case, particularly excellent effects can be obtained.

(1) Crystal size of filament (11)
0) is less than 50 angstroms, (2)
Moisture content is 15 to 200% by weight.

The aramid fiber to be treated may be in any form such as filament, woven fabric, knitted fabric, short fiber, fabric and non-woven fabric.

The surface treatment agent for aramid fibers of the present invention is selected according to the above-mentioned interface strengthening mechanism. However, as long as the effects of the present invention are not impaired, other agents such as a pH adjuster, a surfactant and a smoothing agent are used. Can be contained.

The surface-treated aramid fiber thus obtained can be used not only as a reinforcing fiber for a composite material, but also as a treatment method for giving the aramid fiber a second property. Therefore, by selecting a film former for many practical matrix resins, good adhesion can be formed at the interface between the fiber and the matrix. It is expected to be widely applied.

[0048]

EXAMPLES The structure and effects of the present invention will be further described below with reference to examples. [Example 1] Improvement rate of interfacial shear strength exhibited by silane-urethane mixing treatment with supercritical fluid Aminopropyltriethoxysilane and urethane former (Bondick 1310F), which are used for commercially available glass fibers, were each distilled water. The solution was dissolved at a ratio of 0.5% by weight and 2.0% by weight, and the solution was further removed with a freeze dryer to prepare a surface treatment agent.

On the other hand, polyparaphenylene terephthalamide having an average molecular weight of about 20,000 obtained by polycondensation of terephthalic acid and paraphenylenediamine is dissolved in concentrated sulfuric acid, and the viscous liquid is extruded from a spinneret into a filament. After neutralization with an aqueous sodium hydroxide solution, the undensed aramid fiber and the densified aramid fiber were obtained by adjusting the drying and heat treatment conditions. Hereinafter, the non-densified aramid fiber is referred to as open aramid fiber, and the densified aramid fiber is referred to as normal aramid fiber.

This open aramid fiber has a fiber diameter of 12
mm, the crystal size of the filament (110 faces): about 40 Å, and the water content: 30% by weight. On the other hand, the normal aramid fiber had a fiber diameter of 12 mm, a crystal size of the filament (110 faces): about 60 angstroms, and a water content of less than 15% by weight. From this, the open aramid fiber has a wider intercrystalline space than the normal aramid fiber.

Using a supercritical apparatus, the above-mentioned surface treating agent is treated with the above-mentioned aramid fiber in a carbon dioxide fluid atmosphere, and stored at room temperature for two months. An aramid fiber surface-treated by heat treatment for 20 minutes and at 170 ° C. for 30 minutes was obtained.

Next, a single filament was taken out from the surface-treated open aramid fiber. After attaching a sol-like epoxy resin to a single filament aramid fiber, the epoxy resin was cured at a predetermined temperature to prepare a single fiber pull-out test sample.

For the single fiber pull-out test sample,
The adhesion between the aramid fiber and the matrix resin was evaluated by a single fiber pull-out test method using a composite material interface characteristic evaluation device manufactured by Toei Sangyo Co., Ltd. The value obtained is the interfacial shear strength representing the interfacial strength. From the interfacial shear strength (abbreviated as σ _s and σ ₀ ) of the normal aramid fiber measured simultaneously with the interfacial shear strength of the surface-treated aramid fiber as the improvement rate, r, the following equation (2) is obtained. Therefore, it was calculated.

R (%) = (σ _s / σ ₀ −1) × 100 (2) That is, the interface shear strength between the aramid fiber and the matrix resin is determined by the maximum pulling load obtained from the single fiber pulling test. I asked. The higher the interfacial shear strength, the better the adhesion between the aramid fiber and the matrix resin.

As a result, the interfacial shear strength of the open aramid fiber obtained in Example 1 showed a value of 24.56 ± 2.11 MPa, which was improved by 38% as compared with the case of the untreated normal aramid fiber. It was found that the adhesion between the resin and the matrix resin was extremely excellent.
On the other hand, the interfacial shear strength of normal aramid fiber is 19.46.
It showed a value of ± 1.43 MPa, showing an improvement of 9% as compared with the case of untreated normal aramid fiber, but was extremely inferior to that of open aramid fiber. [Comparative Example 1] The improvement rate of the interfacial shear strength exhibited by the silane-urethane mixed treatment treated by immersion.Aminopropyltriethoxysilane and urethane former were dissolved in distilled water at a ratio of 0.5% by weight and 2.0% by weight, respectively. The surface treatment agent was adjusted.

The normal aramid fiber and the open aramid fiber were immersed in the above-mentioned surface treating agent, pulled up, and then reduced at 100 ° C. for 20 minutes and at 170 ° C.
A heat treatment was performed for a minute to obtain a surface-treated aramid fiber.

Next, a single fiber pull-out test sample was prepared in the same manner as in Example 1, and the interfacial shear strength was determined. As a result, the interfacial shear strength of the open aramid fiber showed a value of 25.33 ± 3.82 MPa, and the improvement rate showed a value of 13% as compared with the case of untreated normal aramid fiber. The adhesion was very good. It was found that the interface was strengthened by using open aramid fibers even in the immersion method using an aqueous medium. However, it was inferior to the open aramid fiber of Example 1. The interfacial shear strength of the normal aramid fiber was 18.67 ± 1.40 MPa, which was not improved as compared with the case of the untreated normal aramid fiber, resulting in a 37% reduction. This showed that the adhesion between the aramid fiber and the matrix resin was extremely poor as compared with the open aramid fiber of Example 1.

As shown in Table 1, the interfacial shear strength obtained in Example 1 and Comparative Example 1 showed the maximum value when the open aramid fiber was surface-treated with a supercritical fluid. Showed that the adhesion was extremely excellent. It was also found that the normal aramid fiber did not improve the interfacial shear strength in any case. Hereinafter, the treatment for the open aramid fiber will be described.

[0059]

[Table 1] [Example 2] Improvement rate of interfacial shear strength showing aramid fiber treated with a silane coupling agent and a urethane former with a supercritical fluid An aminopropyltriethoxysilane stock solution was used as a surface treatment agent. Further, a urethane former was dissolved in distilled water at 2.0% by weight, and the solution was further removed with a freeze dryer to prepare a surface treating agent.

Using the above two surface treating agents,
The open aramid fiber of No. 1 was subjected to surface treatment in the same manner as in Example 1, and a single fiber pull-out test sample was prepared in the same manner as above, and the interfacial shear strength was determined. As a result, the interfacial shear strength of the open aramid fiber treated with aminopropyltriethoxysilane showed a value of 21.0 ± 2.3 MPa, and the improvement rate was 18% compared to the case of the untreated normal aramid fiber. However, the adhesion between the aramid fiber and the matrix resin was inferior to the open aramid fiber of Example 1. On the other hand, the interfacial shear strength of the open aramid fiber treated with a urethane former with a supercritical fluid shows a value of 20.0 ± 2.0 MPa, and the improvement rate is smaller than that of the untreated normal aramid fiber.
Although showing a high value of 12%, the adhesion between the aramid fiber and the matrix resin was inferior to that of the open aramid fiber of Example 1. Comparative Example 2 Aramid Fiber Treated with a Silane Coupling Agent and Urethane Former by Dipping Improving Interfacial Shear Strength 0.5% by weight of aminopropyltriethoxysilane in distilled water
The surface treatment agent was prepared by dissolving. Further, a surface treatment agent was prepared by dissolving a urethane former in distilled water at 2.0% by weight.

Using the above two surface treatment agents,
Surface treatment was performed on the open aramid fiber of No. 1 in the same manner as in Comparative Example 1, and a single fiber pull-out test sample was prepared in the same manner, and the interfacial shear strength was determined. As a result, the interfacial shear strength of the open aramid fiber treated with aminopropyltriethoxysilane showed a value of 25.3 ± 2.4 MPa, which was not improved as compared with the case of the untreated normal aramid fiber, resulting in a 15% reduction. . This showed that the adhesion between the aramid fiber and the matrix resin was extremely poor as compared with the open aramid fibers of Examples 1 and 2. On the other hand, the open aramid fiber treated with the urethane binder showed an interfacial shear strength of 29.9 ± 3.5 MPa, and showed a slight improvement of 1% as compared with the untreated normal aramid fiber. Although the adhesion between the resin and the matrix resin was slightly increased, it was extremely poor as compared with the open aramid fibers of Examples 1 and 2.

Table 2 summarizes the improvement rate of the interfacial shear strength exhibited by the surface treatment for the open aramid fibers obtained in Example 2, Comparative Example 2 and Example 1 above. The method that showed the most improvement in surface treatment was by a supercritical fluid. As a surface treatment agent, a mixture of aminopropyltriethoxysilane and urethane former showed a good value by any method. It is considered that the mixed treatment agent forms a network structure with aminopropyltriethoxysilane and urethane forma, and as a result, is stably fixed in the gap between the aramid fiber crystals. It can be inferred that this improves the interface strength. [Example 3] Improvement rate of interfacial shear strength exhibited by silane-urethane mixing treatment with a supercritical fluid on open aramid fibers with reduced moisture content A surface treatment agent was prepared in the same manner as in Example 1.

The open aramid fiber of Example 1 was air-dried to reduce the moisture contained in the aramid fiber. This open aramid fiber was subjected to a surface treatment in the same manner as in Example 1, and a single fiber pull-out test sample was prepared in the same manner, and the interfacial shear strength was determined. As a result, 22.6 ±
2.4 MPa, the improvement rate compared to the case of untreated normal aramid fiber was as high as 27%, indicating that although the adhesion between the aramid fiber and the matrix resin was excellent, the water content was high compared to Example 1. And showed a low improvement rate. This indicates that retention of the moisture content is an important factor in the present invention. Example 4 Heat Treatment Effect on Surface Treatment of Open Aramid Fiber Treated with Silane-Urethane Using Supercritical Fluid A surface treatment agent prepared in the same manner as in Example 1 was subjected to surface treatment on open aramid fiber. In this example, it was left for two months, but in this example, it was stored at room temperature for 15 days with a shorter storage period. Further, the heat treatment was adjusted in the same manner as in Example 1 to prepare a single fiber pull-out test sample, and the interfacial shear strength was determined. As a result, it shows a very high value of 32.4 ± 3.7 MPa, an improvement rate of 67% compared to the case of untreated normal aramid fiber, and shows a higher value if heat treatment is performed early after penetrating the surface treatment agent. I understand. Therefore, after the infiltration treatment, it is important to reduce the water content and to reduce the gap between the crystals. From this, the adhesiveness between the aramid fiber and the matrix resin is the same as in Examples 1 to 3.
It can be seen that Example 4 was most excellent than the sample for the single fiber pull-out test. From this, it is understood that in the present invention, the penetration of the surface treating agent and the heat treatment conditions are extremely important. [Example 5] Flexural strength and flexural modulus of unidirectional fiber reinforced composite material Twenty bundles (20,000 filaments) of the surface-treated open aramid fibers produced in Example 1 were prepared. After impregnating the open aramid fiber with a sol-like epoxy resin, it is drawn into a glass tube with an inner diameter of 2.5 mm, and the epoxy resin is further cured at a predetermined temperature to obtain a diameter of 2.5 m.
m, a unidirectional fiber reinforced composite material having an aramid fiber volume content of 46% was produced.

The adhesion between the aramid fiber and the matrix resin was evaluated for the unidirectional fiber reinforced composite material by a three-point bending test using an instron type universal testing machine manufactured by Shimadzu Corporation with a bending probe. .

The flexural strength and flexural modulus were determined from the three-point bending test. As a result, the unidirectional fiber reinforced composite material obtained in Example 5 exhibited a bending strength of 620 ± 33 MPa and a flexural modulus of 26.1 ± 1.7 GPa. As compared with the case of untreated normal aramid fiber, the improvement rate was improved by 14% in bending strength and 10% in bending elastic modulus, showing extremely high values. Since the adhesion between the aramid fiber and the matrix resin is excellent, even a practical composite material is considered to exhibit good mechanical properties. From this, the improvement of the interface strength shown in Example 1 was
It can be seen that the bending strength and the flexural modulus of the unidirectional fiber reinforced composite material were improved. [Example 6] Fiber strength of surface-treated fiber with supercritical fluid Using the surface-treating agent of Examples 1 and 2, surface treatment was performed on open aramid fiber of Example 1 in the same manner as Examples 1 and 2. . The fiber strength of the surface-treated aramid fiber was determined by a single fiber tensile test. As a result, the open aramid fiber treated by mixing aminopropyltriethoxysilane and urethane forma exhibited a value of 3.43 ± 0.47 GPa. The single fiber strength of the open aramid fiber treated with the supercritical fluid was not inferior to the single fiber strength of untreated normal aramid fiber of 3.48 ± 0.44 GPa. This indicates that the open aramid fiber surface-treated with the supercritical fluid improves the adhesion between the aramid fiber and the matrix resin without reducing the fiber strength. [Example 7] Improvement rate of interfacial shear strength exhibited by silane-urethane mixed treatment treated by effective immersion Aminopropyltriethoxysilane and urethane former were dissolved in distilled water at a ratio of 0.5% by weight and 2.5% by weight, respectively. Thereby, the surface treatment agent was adjusted.

The open aramid fiber is immersed in the above-mentioned surface treating agent by a few days after spinning, pulled up, and immediately reduced the intercrystal space at 100 ° C. for 20 minutes and at 170 ° C.
A heat treatment was performed for 30 minutes to obtain a surface-treated aramid fiber.

Next, a sample for a single fiber pull-out test was prepared in the same manner as in Example 1, and the interfacial shear strength was determined. As a result, the improvement rate of the interfacial shear strength of the open aramid fiber was 44%, and the adhesion between the aramid fiber and the matrix resin was extremely excellent. By adjusting the number of days from spinning aramid fibers to immersion and the number of days until heat treatment in a short time even in surface treatment using an aqueous medium in this way, although it is not better than the method using a supercritical fluid medium, aramid fibers and matrix The adhesion between the resin and the resin could be made quite good. Example 8 Effective Treatment Concentration in Surface Treatment of Open Aramid Fiber Treated with Silane-Urethane by Dipping In Example 7, the surface treatment agents were aminopropyltriethoxysilane and urethane forma in distilled water, respectively.
It was adjusted by dissolving at a ratio of 2.5% by weight. In this example, the surface treatment agent was prepared by dissolving aminopropyltriethoxysilane and urethane former in distilled water at a ratio of 0.1% by weight and 0.5% by weight, respectively, in order to know the effective treatment concentration.

The open aramid fiber was immersed in the above-mentioned surface treatment agent, pulled up, and immediately heat-treated at 100 ° C. for 20 minutes and 170 ° C. at 30 ° C. for 30 minutes to narrow the intercrystalline space. An aramid fiber was obtained.

Next, a single fiber pull-out test sample was prepared in the same manner as in Example 1, and the interfacial shear strength was determined. As a result, the interfacial shear strength did not decrease significantly as compared with the time of surface treatment using an aqueous medium having a high concentration. From this, the same effect was exhibited even when the concentration of the surface treatment agent in the aramid fiber was changed at least about 4 to 5 times. Therefore, it was found that the effective processing density in this processing has a wide range.

Since the effective treatment concentration of the surface treating agent in the aqueous medium is wide, it is considered that the effective concentration of the surface treating agent is wide even in the surface treatment using the supercritical fluid medium. [Example 9] Interfacial shear strength indicated by low-throughput treatment in silane-urethane mixing treatment by immersion method As in Examples 7 and 8, the concentrations of aminopropyltriethoxysilane and urethane former were 0.5% by weight and 2.
5% by weight of the surface treatment agent, the concentration of the aminopropyltriethoxysilane and the urethane former were 0.1% by weight and 0.5%, respectively.
A weight% surface treatment agent was prepared.

The open aramid fiber was different from Examples 7 and 8 in that the surface treating agent solution was added to the fiber while the treating agent was permeated. As a result, even when the treating solutions had the same concentration, only about 1/6 of the treating agent was applied to the fibers as compared with Examples 7 and 8. Thereafter, heat treatment was performed at 100 ° C. for 20 minutes and at 170 ° C. for 30 minutes in the same manner as in Examples 7 and 8, to obtain surface-treated aramid fibers.

Next, a single fiber pull-out test sample was prepared in the same manner as in Example 1, and the interfacial shear strength was determined. As a result, the interfacial shear strength of the surface-treated open aramid fiber was 22.8 ± 3.3 MP at a high treatment concentration.
The value of a was shown, showing a 10% improvement compared to the case of untreated normal aramid fiber. 1 when processing density is low
It showed a value of 8.3 ± 2.5 MPa, which was not improved as compared with the case of untreated normal aramid fiber, resulting in a decrease of 11%. Therefore, it was found that when the reasoning was extremely reduced, the adhesion between the aramid fiber and the matrix resin was reduced, and the interfacial shear strength was significantly reduced. Example 10 Flexural Strength and Flexural Modulus of Unidirectional Fiber-Reinforced Composite Material Shown by Dip-Method Silane-Urethane Mixing Treatment Example 5 Using Aramid Fiber Surface-Treated in Example 9
A unidirectional fiber reinforced composite material was produced in the same manner as in the above.

The bending strength and flexural modulus of this unidirectional fiber reinforced composite material were determined in the same manner as in Example 5.
As a result, the bending strength at high concentration is 582 ± 43 MPa
And the flexural modulus showed a value of 11.7 ± 0.4 GPa. As compared with the case of the untreated normal aramid fiber, the improvement rate was 4% in the bending strength and 0.2% in the bending elastic modulus. On the other hand, when the concentration is low, the bending strength is 618 ± 2
It showed a value of 8 MPa and a flexural modulus of 12.5 ± 0.5 GPa. Compared to untreated normal aramid fiber,
The improvement rate was improved by 12% in bending strength and 8% in bending elastic modulus, showing extremely high values.

The change in the characteristics due to the difference in density is shown in the embodiment.
The order was different from the result of interfacial shear strength at 9. That is, in the case of the composite material, the physical property value was improved as the treatment amount was smaller. This different result appears to be due to the molding pressure acting when molding as a composite material. It is considered that the smaller the treatment amount, the more the resin penetrates into the inter-crystal gap due to the molding pressure and hardens in the inter-crystal gap. As a result, as described in the embodiment, the two-phase multiple alternating upright interface It is considered that the structure was effectively formed. Since the molding pressure is not generated in the single fiber pull-out test sample used in the evaluation of the interface strength, it is considered that the adhesion to the resin does not appear unless the treatment amount is large. [Example 11] Improvement of interface strength indicated by silane-epoxy mixing treatment by immersion method In Examples 1 to 7, urethane former was used as the film former of the surface treatment agent. In this embodiment, an epoxy former was used as the film former. The surface treatment agent was prepared by dissolving aminopropyltriethoxysilane and epoxy former at a ratio of 0.5% by weight and 2.5% by weight, respectively, in distilled water.

The open aramid fiber was immersed in the above-mentioned surface treatment agent, pulled up, and immediately subjected to a heat treatment at 100 ° C. for 20 minutes and a heat treatment at 170 ° C. for 30 minutes to narrow the intercrystalline space. An aramid fiber was obtained.

Next, a single fiber pull-out test sample was prepared in the same manner as in Example 1, and the interfacial shear strength was determined.
As a result, the interfacial shear strength of the surface-treated open aramid fiber showed a value of 25.7 ± 3.9 MPa, and the improvement rate showed a value of 20% as compared with the case of the untreated normal aramid fiber. It was found that the used epoxy former was excellent in strengthening the interface between the aramid fiber and the matrix resin. From this, it was found that the surface treatment method of the present invention allows various film formers to be selected in the right material at the right place. [Example 12] Retention of fiber strength exhibited by silane-epoxy mixing treatment by dipping method A surface treatment agent was prepared in the same manner as in Example 11.

The open aramid fiber was immersed in the above-mentioned surface treatment agent, pulled up, and immediately subjected to a heat treatment at 100 ° C. for 20 minutes and a heat treatment at 170 ° C. for 30 minutes to narrow the intercrystalline space. An aramid fiber was obtained.

Next, the fiber strength was determined in the same manner as in Example 6. As a result, the fiber strength of the surface-treated aramid fiber showed a value of 3.41 ± 0.22 GPa, while the fiber strength of the untreated normal aramid fiber was 2.90 ± 0.04 GPa
The value of was shown. Therefore, it was found that the aramid fiber subjected to the silane-epoxy mixed treatment improved the interface strength as well as the fiber strength as in Example 11. Example 13 Flexural Strength and Flexural Elasticity of Unidirectional Fiber-Reinforced Composite Material Shown by Dip Method of Silane-Epoxy Mixed Treatment A surface treatment agent was prepared in the same manner as in Example 11.

The open aramid fiber was immersed in the above-mentioned surface treatment agent, pulled up, and immediately subjected to a heat treatment at 100 ° C. for 20 minutes and a heat treatment at 170 ° C. for 30 minutes to narrow the intercrystalline space. An aramid fiber was obtained.

Next, a unidirectional fiber reinforced composite material was prepared in the same manner as in Example 5, and its bending strength and bending elastic modulus were determined. As a result, the flexural strength of the surface-treated open aramid fiber showed a value of 676 ± 26.0 MPa, and the flexural modulus showed a value of 14.0 ± 0.5 GPa. Compared with the case of untreated normal aramid fiber, the improvement rate was improved by 27% in flexural strength and 24% in flexural modulus, showing extremely high values. Therefore, the bending characteristics of the unidirectional fiber reinforced composite material using aramid fiber were more excellent than those of Examples 5 and 9.
It turns out that 13 is the best.

Table 2 summarizes the main improvements in interfacial shear strength obtained in the above examples. The method that showed the most improvement in surface treatment was by a supercritical fluid. Also,
Even though the surface treatment by immersion in an aqueous medium was not as effective as the treatment with supercritical fluid, high interfacial reinforcement was achieved by adjusting the number of days from fiber spinning to immersion and the number of days to heat treatment in a short time. As the surface treatment agent, the silane-urethane mixing treatment showed a good value in either the supercritical fluid method or the immersion method. The mixing agent forms a network structure with aminopropyltriethoxysilane and urethane forma,
As a result, it is considered that the particles are stably fixed in the gaps between the aramid fiber crystals. It can be inferred that this improves the interface strength. Also, even if the urethane former was changed to an epoxy former, the interfacial shear strength was improved,
In this surface treatment method, it can be said that a surface treatment can be performed by selecting a film former for many practically used matrix resins.

[0082]

[Table 2] Table 3 summarizes the improvement rates of the bending strength and the bending elastic modulus of the unidirectional fiber reinforced composite material obtained in the above examples. The use of interfacial reinforced aramid fibers improved the composite material properties. On the other hand, the bending properties were further improved by the molding pressure of the fiber-reinforced composite material, which caused the resin to penetrate into the intercrystalline spaces of the fibers. When a highly reactive epoxy former was used as the film former, the bending characteristics were most improved.
It can be said that the aramid fibers reinforced by the surface treatment method improve the material properties of the unidirectional fiber reinforced composite material.

[0083]

[Table 3] [Example 14] Improvement of interfacial strength exhibited by silane-keratin mixing treatment by immersion method In this example, as shown below, a natural film former and a silane-based treating agent that were effective with glass fiber / resin were used. The fact that it is also effective as a surface treatment agent for aramid fibers will be described as an example.

As a natural film former, S-sulfonated keratin, a protein derivative extracted from wool, was used. In addition to this protein, mercaptopropyltrimethoxysilane was added to the surface treatment agent, and each was dissolved in distilled water at the same ratio of 1.0% by weight and used.

After the open aramid fiber is immersed in the above-mentioned surface treating agent and pulled up, the surface-treated aramid fiber is immediately subjected to heat treatment at 100 ° C. for 20 minutes and at 170 ° C. for 30 minutes to narrow the intercrystalline space. I got

A single filament was taken out from the surface-treated open aramid fiber, and a melted thermoplastic resin polycarbonate was applied thereto in order to determine the interfacial shear strength. A sample for a pull-out test was used. As a result, the interfacial shear strength of the surface-treated open aramid fiber was 30.0 ±
The value was 3.2 MPa, and the improvement rate was 25% compared to 24.0 ± 1.2 MPa in the case of untreated normal aramid fiber.

The case of glass fiber is described as a reference. The glass fibers were immersed in a treating solution having the same composition, and then heat-treated at 60 ° C. for 60 minutes. The interface shear strength for the polycarbonate resin was determined in the same manner as for the aramid fiber. As a result, the interfacial shear strength of the surface-treated glass fiber showed a value of 37.6 ± 2.5 MPa, and the improvement rate showed a value of 20% as compared with 31.3 ± 2.1 in the case of the untreated glass fiber.

From the above, it was confirmed as an actual example that the mixed treatment agent of a film former and a silane agent, which is effective as a surface treatment agent for glass fibers, is also effective for aramid fibers.

[0089]

According to the treatment method of the present invention, the surface treatment can be performed on the aramid fiber without impairing the physical properties of the aramid fiber, and an excellent composite material can be obtained without selecting a matrix resin.

Continued on the front page (72) Inventor Eiji Fujioka 1-5-6 Nihonbashi Honcho, Chuo-ku, Tokyo Toray Dupont Co., Ltd. (72) Inventor Kazuhiko Kosuge 1-5-6 Nihonbashi Honcho, Chuo-ku, Tokyo Toray・ D-Pont Co., Ltd. F-term (reference) 4L031 AA21 AB01 BA08 CA06 CA09 DA21 4L033 AA08 AC11 BA96 BA98 CA50 CA69

Claims (14)

[Claims] 1. A method for surface treating aramid fiber, comprising treating the aramid fiber with a film former in a supercritical fluid or an aqueous medium. 2. A method for treating the surface of aramid fiber, comprising treating the aramid fiber with a silane coupling agent in a supercritical fluid or an aqueous medium. 3. A method for surface treating aramid fiber, comprising treating the aramid fiber with a mixture of a film former and a silane coupling agent in a supercritical fluid or an aqueous medium. 4. The method for surface treating aramid fibers according to claim 1, wherein the treatment is a heat treatment at 80 to 200 ° C. after immersion. 5. A surface-treated aramid fiber treated by the treatment method according to claim 1. Description: 6. The crystal size of aramid fiber (110 planes)
6. The surface-treated aramid fiber according to claim 5, wherein is less than 50 angstroms. 7. The surface-treated aramid fiber according to claim 5, wherein the water content of the aramid fiber is 15 to 200% by weight. 8. The heat treatment of the surface-treated aramid fiber according to claim 6, whereby the fiber has a crystal size (1).
Aramid fiber with 50 angstrom or more on 10 sides). 9. An aramid fiber having a water content of less than 15% by weight by dehydrating the surface-treated aramid fiber according to claim 6 or 7. 10. After the aramid fiber is spun and neutralized with a sulfuric acid solution of para-based wholly aromatic polyamide, the water content is always adjusted to 15%.
The method for treating aramid fibers according to any one of claims 1 to 4, wherein the fibers are fibers held at not less than% by weight. 11. The surface treatment method for aramid fiber according to claim 11, wherein the aramid fiber is a fiber further cut to have an aspect ratio of 50 to 5,000. 12. An aramid fiber which has been surface-treated by the method according to any one of claims 8 to 10, further comprising 80 to 200.
A method for treating the surface of aramid fibers, which comprises heat-treating at a temperature of ° C. A matrix resin is applied to the surface-treated aramid fiber according to any one of claims 5 to 9 or the aramid fiber surface-treated by the method according to any one of claims 10 to 12. A fiber-reinforced composite material characterized by being impregnated. 14. The fiber-reinforced composite material according to claim 13, wherein the matrix resin is the same resin as a film former used for surface treatment.