JP2019194369A - Extra fine short fiber and composite comprising extra short fibers dispersed in resin composition - Google Patents

Abstract

To provide the extra fine short fiber and the composite comprising the extra short fibers dispersed in the resin composition with excellent mechanical strength, wherein the extra fine short fiber can realize composites that cannot be realized with a conventional technology, and can provide the composites with excellent mechanical strength.SOLUTION: The extra fine short fiber of the present invention has an average fiber diameter of 3 μm or less and an aspect ratio of 200 or less, and is suitable for preparing the composite by being added to the resin composition because both the average fiber diameter and an average fiber length are small. Furthermore, the extra fine short fiber of the present invention can realize the composite in which the extra fine short fiber is dispersed in the resin composition because the extra fine short fiber comprises an organic resin that has been insolubilized, even when producing the composite using the organic resin constituting the extra fine short fiber before insolubilization and a resin that is soluble in a same solvent. The composite of the present invention is the composite having the excellent mechanical strength because the extra fine short fiber according to the present invention is dispersed in the resin composition.SELECTED DRAWING: None

Description

  The present invention relates to an ultrafine short fiber composed of an organic resin subjected to insolubilization treatment, and a composite in which the ultrafine short fiber is dispersed in a resin composition.

  Conventionally, thin and short extra-fine short fibers have been used in a wide range of applications such as filter materials, addition to cosmetics such as foundations, and addition to resin compositions. In particular, in order to provide a resin composition with improved mechanical strength, it has been practiced to produce a composite by adding ultrafine short fibers to the resin composition.

  As such ultrafine short fibers, for example, in JP 2009-114560 A (Patent Document 1), an average fiber diameter of 1000 nm or less and an average fiber length of 20 μm or less manufactured by an electrostatic spinning method are used. Further, a resin-made ultrafine short fiber having a CV value of fiber length of 55% or less is disclosed. Patent Document 1 discloses resin-made ultrafine short fibers having an aspect ratio of 200 as examples, and the performance of the film can be improved by adding these resin-made ultrafine short fibers to the film. It is disclosed. In addition, the applicant of the present application has obtained knowledge that thin fibers having an average fiber diameter of 3 μm or less can be produced by an electrospinning method.

  Based on the conventional knowledge in Patent Document 1 and the electrospinning method, the present applicant uses a resin ultrafine fiber having an average fiber diameter of 3 μm or less and an aspect ratio of 200 or less, and a resin composition and a resin ultrafine fiber. Attempts were made to prepare a fiber composite, which could cause the following problems. For example, when the resin constituting the resin composition and the resin constituting the ultrafine short fiber made of resin is soluble in the same solvent, an attempt to produce a composite by adding the ultrafine short fiber made of resin to the resin composition dissolved in the solvent, Resin-made ultrafine short fibers may also dissolve in the solvent. Therefore, it is not possible to realize a composite in which resin ultrafine fibers are dispersed in the resin composition, or the shape of the resin ultrafine fibers is broken by melting a part of the resin ultrafine fibers and the mechanical strength is improved. There was a problem that the complex could not be provided.

JP 2009-114560 A

  The present invention has been made in view of such circumstances, and is capable of providing a composite that cannot be realized by the prior art, and that can provide a composite having excellent mechanical strength, and the ultrafine short fiber. It aims at providing the composite_body | complex excellent in the mechanical strength formed by disperse | distributing a fiber to a resin composition.

  The invention according to claim 1 of the present invention is “an ultrafine short fiber characterized by comprising an organic resin having an average fiber diameter of 3 μm or less and an aspect ratio of 200 or less and subjected to insolubilization treatment” . "

  The invention according to claim 2 of the present invention is a “composite characterized in that the ultrafine short fibers according to claim 1 are dispersed in a resin composition”.

  The ultrafine short fiber according to claim 1 of the present invention has an average fiber diameter of 3 μm or less, an aspect ratio of 200 or less, an average fiber diameter, and an average fiber length that are both small. It is suitable for preparing a complex.

In addition, the ultrafine short fiber according to the present invention is composed of an organic resin that is insolubilized. Therefore, even if the resin composition and the organic resin constituting the ultrafine short fiber before insolubilization treatment are both made using a soluble solvent, the ultrafine short fiber according to the present invention is subjected to insolubilization treatment. Insoluble in the solvent. That is, since it is possible to prevent the ultrafine short fiber from being dissolved in the solvent and the shape of the ultrafine short fiber from collapsing, it is possible to realize a composite in which the ultrafine short fiber is dispersed in the resin composition.
Therefore, the ultrafine fiber according to the present invention can realize a composite that cannot be realized by the prior art.

  The composite according to claim 2 of the present invention is a composite excellent in mechanical strength since the ultrafine short fibers according to the present invention are dispersed in the resin composition.

  When used as a filler to reinforce and add to the resin composition such as a film, the ultrafine short fibers composed of the organic resin subjected to the insolubilization treatment of the present invention, so that the ultrafine short fibers are less likely to aggregate. The average fiber diameter is 3 μm or less and the aspect ratio is 200 or less.

  The average fiber diameter of the ultrafine short fibers may be 3 μm or less. However, the smaller the average fiber diameter, the better the dispersibility in the resin composition, so 2 μm or less is more preferable, and 1 μm or less is even more preferable. The lower limit of the average fiber diameter can be appropriately selected, but 0.05 μm or more is suitable so that the strength of the ultrafine short fiber is excellent.

  The “average fiber diameter” in the present invention refers to the arithmetic average value of the fiber diameters of 50 ultrafine short fibers, and the “fiber diameter” is based on a 5000 × electron micrograph of the ultrashort fibers. The diameter of the circle in the direction orthogonal to the major axis direction of the ultrafine short fiber measured in the above. When the cross section of the ultrafine short fiber is a non-circular cross section, the cross sectional area of the cross section is measured, and the diameter of the circle having the cross section is regarded as the fiber diameter.

  The aspect ratio of the ultrafine short fiber is 200 or less so that the ultrafine short fiber hardly aggregates in the resin composition and is excellent in dispersibility. The aspect ratio is more preferably 150 or less, and even more preferably 120 or less, because as the aspect ratio of the ultrafine short fibers becomes smaller, the ultrafine short fibers are less likely to aggregate in the resin composition and have excellent dispersibility. The lower limit of the aspect ratio is suitably 5 or more so that the composite formed by dispersing ultrafine short fibers in the resin composition has excellent mechanical strength.

  The “aspect ratio” in the present invention is a value obtained by dividing the average fiber length (μm) of the ultrafine short fibers by the average fiber diameter (μm).

  The average fiber length of the ultrafine short fibers is not particularly limited as long as the aspect ratio is satisfied. The “average fiber length” in the present invention refers to the arithmetic average value of each fiber length in 50 ultrafine short fibers, and the “fiber length” is based on an electron micrograph of 50 to 5000 times taken of the ultrashort fibers. The length in the major axis direction of the ultrafine short fiber measured in the above.

  Although the CV value of the fiber length of the ultrafine short fiber is not particularly limited, it means that the smaller the CV value is, the more uniform the fiber length is. Therefore, 0.5 or less is preferable, 0.4 or less is more preferable, 0.3 or less is more preferable, and 0 is ideal. The CV value of the fiber length is a value obtained by dividing the standard deviation of the fiber length by the average fiber length, that is, (standard deviation of fiber length / average fiber length). The “standard deviation of the fiber length” is a value calculated from the fiber lengths of the 50 ultrafine short fibers selected at the time of measuring the average fiber length.

  The type of the organic resin constituting the ultrafine short fiber of the present invention is not particularly limited as long as it is an organic resin that can be insolubilized as described below. For example, polyacrylonitrile resin, polyvinyl alcohol resin, maleic acid Copolymer resins (styrene-maleic anhydride copolymer, methyl vinyl ether-maleic anhydride copolymer, etc.), acrylic resins, polybenzimidazole resins, polyether resins (polyetheretherketone, polyacetal, modified polyphenylene) Ether, aromatic polyether ketone, etc.), polysulfone resin, polyester resin (polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polycarbonate, polyethylene Arylates, polylactic acid, wholly aromatic polyester resins, etc.), resins having a nitrile group (eg, polyacrylonitrile, etc.), fluororesins (polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, perfluoroalkoxyalkanes, etc.), cellulose Resins, thermoplastic polyimide resins, polyether resins (phenolic resins, melamine resins, urea resins, epoxy resins), polyester resins (such as unsaturated polyester resins), urethane resins, thermosetting polyimides Based resins and the like. In addition, the organic resin which comprises an ultrafine short fiber does not need to be 1 type, and may contain and comprise 2 or more types.

  The organic resin constituting the ultrafine short fiber may be either a linear polymer or a branched polymer, and the polymer may be a block copolymer or a random copolymer. The presence or absence of crystallinity is not particularly limited. And these ultrafine short fibers may contain organic resin other than the illustration. The molecular weight of the organic resin constituting the ultrafine short fiber is not particularly limited and can be appropriately selected because an appropriate molecular weight varies depending on the resin used.

  In the present invention, the “organic resin formed by insolubilization treatment” means that the organic resin before insolubilization treatment is treated with “soluble” solvent so that the organic resin after insolubilization treatment becomes “insoluble”. The applied organic resin.

In the present invention, whether an organic resin is “soluble” or “insoluble” in a solvent can be determined by subjecting the measurement object to the following <insolubilization test>.

<Insolubilization test>
(1) Prepare an ultrafine short fiber, and when an organic resin constituting the ultrafine short fiber to be measured is known, select a solvent known to be able to completely dissolve the organic resin, Use as test solvent. If the organic resin constituting the ultrafine short fiber to be measured is not known, the ultrafine fiber is subjected to a well-known analysis method such as IR, DSC, NMR, MS, Raman spectroscopy, elemental analysis, combustion test, etc. The organic resin constituting the short fiber is specified. A solvent known to be able to completely dissolve the organic resin is selected as a test solvent.
(2) Prepare 3 g of the ultrafine short fiber and prepare 300 g of a test solvent capable of completely dissolving the organic resin. And the said ultra-short fiber is put into the said test solvent, and a liquid mixture is produced.
(3) A stirrer is placed in the mixed solution, and the mixed solution is stirred under the following conditions.
Mixture temperature: 25 ° C
Stirrer rotation speed: 100 rpm
Time: 30 minutes (4) The mixture after the treatment of (3) is filtered. The ultrafine short fibers separated by filtration are dried to remove the test solvent, and then the weight of the ultrafine short fibers subjected to the treatment is measured.
(5) The weight change rate of the ultrafine short fiber after the processing of (4) is obtained by the following formula.
[Weight change rate]
t = | (3-m) / 3 | × 100
t: Weight change rate (%)
m: Weight of the ultrafine short fiber after the treatment of (4) (g)

  When the rate of weight change is 5% or less, the ultrafine short fiber that was the object of measurement was determined to be “insoluble” in the test solvent, and to be an ultrafine short fiber composed of an organic resin that was insolubilized. To do. Further, when the weight change rate exceeds 5%, it is determined that the ultrafine short fiber to be measured is “soluble” in the test solvent. In addition, when the ultrafine short fiber is completely dissolved in the test solvent or when the ultrafine short fiber does not remain when the mixed solution is filtered, the weight change rate of the ultrafine short fiber is set to 100%.

  Examples of test solvents that can be used for the insolubilization test include organic resins constituting ultrafine short fibers such as polyacrylonitrile resin, polysulfone resin, polyether resin, fluorine resin, thermoplastic polyimide resin, polybenzo In the case of an imidazole resin, N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone, methyl ethyl ketone can be used, and the type of organic resin constituting the ultrafine fiber is polyvinyl alcohol resin, maleic acid In the case of a copolymer resin, water, alcohol, N, N-dimethylformamide, or N, N-dimethylacetamide can be used.

  Even if all the organic resins constituting the ultrashort fibers of the present invention are composites prepared using a soluble solvent together with the resin composition and the organic resin constituting the ultrafine fibers before insolubilization treatment. The organic resin is required to be insolubilized so that a composite formed by dispersing ultrafine short fibers in the resin composition can be realized.

  In the present invention, as a method of preparing the “organic resin formed by insolubilization treatment”, the organic resin after the insolubilization treatment is described above with respect to the “soluble” solvent before the insolubilization treatment. Thus, a method of subjecting the organic resin before the insolubilization treatment to a treatment such as a heat treatment can be employed. Specifically, although it can be appropriately selected, heat treatment, electron beam irradiation, gamma ray irradiation, addition of a crosslinking agent that crosslinks an organic resin, and the like can be given, and heat treatment that is simple in production is preferable. The treatment temperature in the heat treatment is appropriately adjusted, but the heat treatment can be performed at 120 to 450 ° C. Specifically, it can be insolubilized by heat treatment at 210 to 270 ° C. in the case of polyacrylonitrile resin, 120 to 210 ° C. in the case of polyvinyl alcohol resin, and 350 to 450 ° C. in the case of polybenzimidazole resin.

  The reason why the organic resin constituting the ultra-short fiber according to the present invention is insolubilized by subjecting it to insolubilization treatment is that it undergoes structural change due to cross-linking, functional group substitution, etc. due to subjecting it to insolubilization treatment, and is soluble in solvents. It seems to have changed.

  The ultra-short fiber of the present invention may be composed only of the above-mentioned organic resin, but when the ultra-short fiber is put in a solvent, the additive dissolves in the solvent and the shape of the ultra-short fiber collapses. Various known properties may be imparted by adding conventionally known additives to the extent that unintentional strength reduction does not occur in the composite in which the ultrafine short fibers are dispersed in the resin composition. Specific examples of the additive include an antioxidant, a stabilizer, inorganic particles, a pigment, and a dye.

  As described above, the ultrafine short fibers of the present invention are dispersed in the resin composition and are suitable for reinforcing the resin composition. Therefore, the composite of the resin composition and the ultrafine short fibers is reinforced by the ultrafine short fibers and has excellent mechanical strength.

  The ultrafine short fiber of the present invention can be produced, for example, as follows.

  First, an organic resin constituting the ultrafine short fiber before insolubilization treatment and a solvent capable of dissolving the organic resin are prepared. The solvent is not particularly limited because it varies depending on the type of the organic resin, and can be appropriately selected.

Next, a spinning solution is prepared by dissolving the organic resin in a solvent. The solid content concentration of the organic resin in the spinning solution is not particularly limited as long as the organic resin can be dissolved, and the optimum value varies depending on the organic resin used, and can be adjusted as appropriate. Also, the viscosity of the spinning solution varies depending on the organic resin used, and can be adjusted as appropriate. The “viscosity” in the present invention refers to a value at a shear rate of 100 s ⁻¹ using a viscosity measuring device (manufactured by Thermo Scientific).

  Next, the spinning solution is spun to form fibers, and the fibers are accumulated to form a fiber assembly. As this spinning method, a conventionally known spinning method can be employed. For example, a wet spinning method, a dry spinning method, a flash spinning method, a centrifugal spinning method, an electrostatic spinning method, a method of spinning by gas shearing action as disclosed in JP 2009-287138 A, or JP Spinning is performed by a method of spinning by applying a shearing force of a gas in addition to the action of an electric field, as disclosed in 2011-32593, and the spun fibers are directly accumulated on a drum or a net to obtain fibers. Aggregates can be formed. Among these, the electrospinning method is preferable because it is easy to spin a fiber having a small fiber diameter.

  In addition, when spinning by an electrostatic spinning method, if the spinning solution is insufficiently conductive, the spinning property may be inferior and fiberization may be difficult. An appropriate amount of salt can be added to adjust the conductivity.

  Thereafter, the formed fiber assembly is subjected to insolubilization treatment. Examples of the insolubilization method include heat treatment, electron beam irradiation, gamma ray irradiation, addition of a crosslinking agent, and the like, and heat treatment that is simple in production is preferable. The treatment temperature in the heat treatment is adjusted as appropriate, but the heat treatment is preferably performed at the above treatment temperature.

  Furthermore, by pulverizing the fiber assembly, ultrafine short fibers having an aspect ratio of 200 or less can be obtained. Although it does not specifically limit as a grinding | pulverization method, For example, the method of using a stone mill and a pin mill is mentioned. Further, the fiber aggregate before insolubilization treatment may be pulverized to obtain ultrafine short fibers, and the obtained fibers may be subjected to insolubilization treatment to produce the ultrafine short fibers according to the present invention. The obtained ultrafine short fibers can be widely used for fillers added to resin compositions such as films, fillers added to cosmetics such as foundations, filter materials, and the like.

  The complex of the present invention can be produced by a conventional method. For example, after adding an ultrafine short fiber to a solution obtained by dissolving a resin composition to prepare an ultrafine short fiber dispersion, the ultrafine short fiber dispersion is applied, dried to remove the dispersion medium, and the composite The body can be manufactured.

  The kind of resin which comprises the resin composition in this invention is not specifically limited, It can select suitably. In particular, when the resin composition and the organic resin constituting the ultrafine fiber before insolubilization treatment are a composite made of the same resin, the interface between the resin composition and the ultrafine short fiber is difficult to separate in the composite. Therefore, it is preferable to provide a composite having excellent mechanical strength such as excellent strength and elongation. Furthermore, since the content of the resin composition and the ultrashort fiber in the composite and the ratio thereof vary depending on the application, they are not particularly limited and can be adjusted as appropriate.

  The form of the composite differs depending on the application and is not particularly limited. For example, the composite can be a sheet, a rectangular parallelepiped, a cylinder, a prism, a pyramid, or the like.

  Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to these specific examples.

(Production method of fiber assembly a)
Polyacrylonitrile (weight average molecular weight 370,000, hereinafter PAN) was dissolved in N, N-dimethylformamide to prepare a spinning solution having a concentration of 13.0 wt%. The spinning solution had a viscosity of 1000 mPa · s (23 ° C.).

  Next, using the spinning solution, spinning was performed under the following electrostatic spinning conditions, and the sheet-like fiber aggregate a (average fiber diameter: 0.30 μm) was produced by accumulating on a stainless drum collector.

<Spinning conditions>
・ Electrode: Metal nozzle (inner diameter: 0.33 mm)
・ Collector: grounded stainless steel drum ・ Discharge rate from nozzle: 1 g / hour ・ Distance between nozzle tip and stainless steel drum collector: 9 cm
・ Temperature and humidity in spinning container: 25 ℃ / 18% RH
・ Applied voltage to the nozzle: 20 kV

Example 1
The fiber assembly a was heat-treated at 265 ° C. for 2 minutes under normal pressure.
Next, the fiber assembly a subjected to the heat treatment was mixed with 3 times the amount of water with respect to its weight to prepare a mixed solution. Then, the mixed solution was supplied to a pulverizer (Mass Colloidal (registered trademark), manufactured by Masuko Sangyo Co., Ltd.), and the heat-treated fiber assembly a was pulverized under the following pulverization conditions.

<Crushing conditions>
・ Clearance: -200μm
・ Rotation speed: 1500rpm
Treatment time: 30 seconds Thereafter, the pulverized product was filtered off and dried at 110 ° C. for 30 minutes to remove water to produce ultrafine short fibers A.

(Comparative Example 1)
An ultrafine short fiber B was produced in the same manner as in Example 1 except that the heat treatment conditions were changed to 170 ° C. and 30 minutes under normal pressure.

(Comparative Example 2)
Ultrafine short fibers C were produced in the same manner as in Example 1 except that the heat treatment conditions were changed to 200 ° C. and 30 minutes under normal pressure.

(Comparative Example 3)
Ultrafine short fibers D were produced in the same manner as in Example 1 except that no heat treatment was performed on the fiber aggregate a.

(Method for producing fiber assembly b)
Polyvinyl alcohol (weight average molecular weight 45,000, hereinafter referred to as PVA) and a crosslinking agent (methyl vinyl ether-maleic anhydride copolymer) are dissolved in water at a mass ratio of 4: 1, and the concentration is 12.5 wt%. A solution was made. The spinning solution had a viscosity of 500 mPa · s (23 ° C.).

  Next, using the above spinning solution, spinning was performed under the following electrostatic spinning conditions, and the sheet-like fiber aggregate b (average fiber diameter: 0.20 μm) was produced by accumulating it on a stainless drum collector.

<Spinning conditions>
・ Electrode: Metal nozzle (inner diameter: 0.33 mm)
・ Collector: Grounded stainless steel drum ・ Discharge rate from nozzle: 1 g / hour ・ Distance between nozzle tip and stainless steel drum collector: 10 cm
・ Temperature and humidity in spinning container: 25 ℃ / 40% RH
・ Applied voltage to the nozzle: 20 kV

(Example 2)
The fiber assembly b was heat-treated at 160 ° C. for 3 minutes under normal pressure.
Next, the heat-treated fiber assembly b was mixed into N, N-dimethylformamide in an amount 3 times the weight to prepare a mixed solution. Then, the mixed solution is supplied to a pulverizer (Mass Colloider (registered trademark), manufactured by Masuko Sangyo Co., Ltd.), the heat-treated fiber assembly b is pulverized in the same manner as in Example 1, and the pulverized product is filtered to 160. N, N-dimethylformamide was removed by drying at 60 ° C. for 60 minutes to produce ultrafine short fibers E.

(Comparative Example 4)
An ultra-short fiber F was produced in the same manner as in Example 2 except that the fiber aggregate b was not heat-treated.

(Production method of fiber assembly c)
Polybenzimidazole (weight average molecular weight 260,000, hereinafter PBI) was dissolved in N, N-dimethylacetamide to prepare a spinning solution having a concentration of 18.0 wt%. The spinning solution had a viscosity of 7000 mPa · s (23 ° C.).

  Next, using the spinning solution, spinning was performed under the following electrostatic spinning conditions, and the sheet-like fiber aggregate c (average fiber diameter: 0.25 μm) was produced by accumulating it on a stainless drum collector.

<Spinning conditions>
・ Electrode: Metal nozzle (inner diameter: 0.33 mm)
・ Collector: grounded stainless steel drum ・ Discharge rate from nozzle: 1 g / hour ・ Distance between nozzle tip and stainless steel drum collector: 8 cm
・ Temperature and humidity in spinning container: 25 ℃ / 40% RH
・ Applied voltage to the nozzle: 15 kV

(Example 3)
The fiber assembly c was heat-treated at 400 ° C. for 30 minutes under normal pressure.
Next, the heat-treated fiber aggregate c was pulverized in the same manner as in Example 1, and the pulverized product was filtered off and dried at 110 ° C. for 60 minutes to remove water, thereby producing ultrafine short fibers G. .

  The average fiber diameters, average fiber lengths, aspect ratios, and CV values of the fiber lengths of the produced ultrafine short fibers of Examples 1 to 3 and Comparative Examples 1 to 4 were measured and summarized in Table 1.

  The produced ultrafine short fibers of Examples 1 to 3 and Comparative Examples 1 to 4 were evaluated by the above-described <insolubilization test>. Example 1 and Comparative Examples 1 to 3 used N, N-dimethylformamide, Example 2 and Comparative Example 4 used water, and Example 3 used N, N-dimethylacetamide as a test solvent for the insolubilization test. Moreover, after filtering and taking out the liquid mixture, the conditions for drying the filtered ultrafine short fibers are 160 ° C. and 60 minutes in Examples 1 and 3 and Comparative Examples 1 to 3, and Example 2 and Comparative Example 4 are The temperature was 110 ° C. for 60 minutes.

It was evaluated whether or not the ultrafine short fibers were insolubilized according to the evaluation criteria of the following insolubilization test.
[Evaluation criteria for insolubilization tests]
○: The weight change rate of the ultra-fine short fibers was 5% or less, and thus was insolubilized.
X: The weight change rate of the ultrafine short fibers was greater than 5%, or the ultrafine short fibers were completely dissolved in the test solvent, and thus were not insolubilized.

  Table 2 summarizes the results of insolubilization treatment methods and insolubilization tests in Examples 1 to 3 and Comparative Examples 1 to 4.

  From comparison between Examples 1 to 3 and Comparative Examples 1 to 4, an ultrafine short fiber made of an organic resin having an average fiber diameter of 3 μm or less and an aspect ratio of 200 or less and subjected to insolubilization treatment is produced. did it.

<Production of composite film or film>
Example 4
PAN solution (solvent: N) so that the solid content weight ratio when PAN is adopted as the resin composition to form a composite film in which ultrafine short fibers A are dispersed is PAN: extra fine fibers A = 95: 5 , N-dimethylformamide, solid content concentration: 10.0 wt%, manufactured by Sigma-Aldrich) and ultra-short fiber A were mixed and stirred at 2000 rpm for 10 minutes to prepare a mixed solution. The prepared mixed solution was coated on glass with a bar coater, dried at 180 ° C. for 30 minutes to remove N, N-dimethylformamide, and then peeled off from the glass to prepare a composite film having a thickness of 100 μm.

(Comparative Example 5)
A composite film having a thickness of 100 μm was produced in the same manner as in Example 4 except that the ultrafine fiber B was used instead of the ultrafine fiber A.

(Comparative Example 6)
A composite film having a thickness of 100 μm was prepared in the same manner as in Example 4 except that the ultrafine fiber C was used instead of the ultrafine fiber A.

(Comparative Example 7)
A PAN solution (solvent: N, N-dimethylformamide, solid content concentration: 10.0 wt%, manufactured by Sigma-Aldrich) was coated on a glass with a bar coater, dried at 180 ° C. for 30 minutes, and N, N-dimethyl After removing formamide, a film having a thickness of 100 μm was prepared by peeling from the glass.

(Example 5)
PBI solution (solvent: N) so that the solid content weight ratio when PBI is adopted as the resin composition and a composite film in which ultrafine short fibers E are dispersed is PBI: extra fine fibers E = 70: 30. , N-dimethylacetamide, solid content concentration: 20.0 wt%) and ultrafine fiber E were mixed and stirred for 10 minutes at a rotational speed of 2000 rpm to prepare a mixed solution. The prepared mixed solution is coated on glass with a bar coater, dried at 180 ° C. for 30 minutes to remove N, N-dimethylacetamide, then peeled off from the glass, and subjected to heat treatment (insolubilization treatment) at 400 ° C. for 30 minutes. Thus, a composite film having a thickness of 100 μm was produced.

(Example 6)
Except for having changed so that solid content weight ratio may be set to PBI: extra fine short fiber E = 80: 20 when it was set as the composite film which employ | adopted PBI as a resin composition and disperse | distributed extra fine short fiber E Produced a 100 μm-thick composite film in the same manner as in Example 5.

(Example 7)
Except for having changed so that solid content weight ratio may be set to PBI: extra-fine short fiber E = 90: 10 when it is set as the composite film which employ | adopts PBI as a resin composition and disperse | distributes the extra-short fiber E Produced a 100 μm-thick composite film in the same manner as in Example 5.

(Comparative Example 8)
A PBI solution (solvent: N, N-dimethylacetamide, solid content concentration: 20.0 wt%) was coated on glass with a bar coater and dried at 180 ° C. for 30 minutes to remove N, N-dimethylacetamide. The film was peeled from the glass and heat treated (insolubilized) at 400 ° C. for 30 minutes to produce a film having a thickness of 100 μm.

<Tensile test>
(1) A rectangular sample (width: 5 mm, length: 70 mm) was taken from the composite film or film. When measuring the strength and elongation of the composite film or film in the longitudinal direction (application direction by a bar coater), the length of the composite film or film in the horizontal direction (direction perpendicular to the application direction by a bar coater) is When a sample (longitudinal sample) having a length of 5 mm and a length of 70 mm is taken and the strength and elongation in the transverse direction of the composite film or film are measured, the length in the longitudinal direction is 5 mm and the length in the transverse direction. A sample (lateral sample) having a length of 70 mm was collected.
(2) After that, using a constant speed extension type tensile tester (Orientec, product number: UCT-100), the chuck when the sample was ruptured and the maximum load measured until the sample was broken under the following measurement conditions The distance was measured.
[Measurement condition]
Distance between chucks: 50mm
Tensile speed: 50 mm / min

Then, 5 samples each of the vertical sample and the horizontal sample were subjected to the above measurement, and the arithmetic average value of the maximum load of each of the 5 vertical samples and the horizontal sample was defined as the strength (N / μm thickness).
In addition, the arithmetic average value of the distance between chucks when each of the five vertical samples and the horizontal sample broke was substituted into the following formula to determine the elongation (%) of each of the vertical sample and the horizontal sample.

[Elongation]
s = {(x ₂ −x ₁ ) / x ₁ } × 100
s: elongation (%)
x ₁ : Distance between chucks (50 mm)
x ₂ : Distance between chucks when the sample broke in the tensile test (arithmetic average value of five samples) (mm)

  The physical properties of the composite films of Examples 4 to 7 and Comparative Examples 5 to 6 and the films of Comparative Examples 7 to 8 are shown in Table 3 below.

  As a result of comparing the composite film of Example 4 and the composite films of Comparative Examples 5-6, the composite film of Example 4 was improved in strength and elongation as compared with the composite films of Comparative Examples 5-6. The reason for this was thought to be that the ultra-short fibers composed of the organic resin formed by the insolubilization treatment did not dissolve in the solvent during the production process of the composite film and effectively reinforce the film.

  Moreover, as a result of comparing the composite film of Example 4 and the film of Comparative Example 7 not containing ultrafine short fibers, the composite film of Examples 5 to 7 and the film of Comparative Example 8 not containing ultrafine short fibers were also compared. From the comparison results, it was found that a composite with improved strength and elongation can be provided by dispersing ultrafine short fibers in the resin composition.

  As described above, the ultrafine short fiber having the configuration of the present invention can realize a composite having excellent mechanical strength such as strength and elongation. And it turned out that the composite_body | complex which the ultra-short fiber of this invention disperse | distributes to a resin composition is excellent in mechanical strength, such as intensity | strength and elongation.

  The ultra-short fibers of the present invention can be suitably used for fillers added to resin compositions such as films, fillers added to cosmetics such as foundations, filter materials, and the like. Moreover, since the composite of this invention is excellent in mechanical strength, such as tensile strength and elongation, it can be used suitably for various industrial uses.

Claims (2)

An ultra-fine short fiber characterized by comprising an organic resin having an average fiber diameter of 3 μm or less and an aspect ratio of 200 or less and subjected to insolubilization treatment. A composite comprising the ultrafine short fiber according to claim 1 dispersed in a resin composition.