JP2000211949A - Sizing agent for glass fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject sizing agent by designing its composition to comprise a film-forming agent and a nitrogen-contg. compound having amino group and/or imino group with the amount of the nitrogen atoms per molecule of the compound at a specified level or greater so as to suppress aldehyde gas emission in the incineration and deoiling process for the glass textile fabrics sized with this agent. SOLUTION: This sizing agent is obtained by designing its composition to comprise a film-forming agent and pref. 0.1-10 wt.% of a nitrogen-contg. compound having amino group and/or imino group with the amount of the nitrogen atoms per molecule of the compound at >=10 wt.%; wherein the film-forming agent is pref. starch or polyvinyl alcohol when this sizing agent is used as a primary sizing agent, or pref. starch, polyvinyl alcohol or a water-soluble urethane in the case of a secondary sizing agent; and the nitrogen-contg. compound is pref. a primary amine, secondary amine, primary amide or secondary amide (esp. pref. urea, melamine, dicyandiamide, or a derivative thereof), with a molecular weight of pref. <=350.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sizing agent for glass fibers, and more particularly to a sizing agent for glass fibers capable of suppressing the generation of aldehyde gas in the incineration and deoiling step of a glass fiber fabric.

[0002]

2. Description of the Related Art A sizing agent used for a glass fiber fabric is used to prevent fuzzing, thread breakage, breakage, etc. of the glass fiber due to friction, bending, impact, etc. from the drawing process of the glass fiber to the weaving process. The glass fiber is generally coated with an aqueous material containing an organic substance as a main component and containing a water-soluble polymer such as starch, polyvinyl alcohol or water-soluble urethane.

[0003] Here, the glass fiber sizing agent includes a primary sizing agent and a secondary sizing agent. The primary sizing agent is a size to be coated immediately after the molten glass is drawn and formed as glass fiber. Agent. In addition, the secondary sizing agent,
Prior to weaving glass fiber into glass fiber fabric,
It is a sizing agent that is coated only on the warp when necessary.

On the other hand, a glass fiber woven fabric made of glass fibers is used as a reinforcing material for printed wiring boards and other reinforced plastic products. At this time, in order to strengthen the adhesive force between the glass fiber fabric and the resin, the glass fiber fabric is subjected to a surface treatment with a silane coupling agent. At this time, if an organic substance derived from the sizing agent is attached to the surface of the glass fiber fabric, the adhesive force between the glass fiber fabric and the resin by the silane coupling agent is extremely reduced. Therefore, prior to the surface treatment of the glass fiber fabric with the silane coupling agent, generally, the glass fiber fabric is incinerated and deoiled at 350 to 400 ° C. to thermally decompose the organic substance which is the sizing component covering the glass fiber surface. And a removing step is provided.

There are a continuous incineration method and a batch incineration method for incineration and deoiling of glass fiber fabrics. The continuous incineration method is a method in which a glass fiber fabric is continuously incinerated and deoiled for several tens of seconds through a heating furnace, but the amount that can be incinerated and removed is limited, so that it is not implemented alone. The batch incineration method is a method in which a glass fiber fabric is wound into a roll and incinerated and deoiled for several tens to several hundreds of hours. In the batch incineration method, the inside of the roll becomes a reducing atmosphere, and a long time is required for incineration deoiling for removing organic substances, which is not only inefficient but also causes a significant decrease in the tensile strength of the glass fiber. Therefore, as de-oiling incineration of glass fiber fabric,
Although the direct batch incineration method, in which incineration and deoiling is performed only by the batch incineration method, is partially adopted, a two-stage incineration method in which organic substances are continuously incinerated and reduced by the continuous incineration method and then incinerated and removed by the batch incineration method A method called oil is common.

However, the process conditions such as the incineration temperature and the incineration time in the incineration and deoiling of glass fiber fabrics are more related to the relationship between the state of removal of organic substances from the glass fibers and the cost in the incineration and deoiling process than to suppress the generation of odor. Is determined by For this reason, although the combustion method is generally adopted as an odor countermeasure in the incineration deoiling process, further suppression of the amount of odor is desired, and in particular, the continuous incineration deoiling process and the direct batch incineration method are required. Odor control in the oil process is not yet sufficient.

[0007] The reason why such an odor problem arises is that organic substances derived from the sizing agent, when completely burned, become carbon dioxide, water and nitrogen oxides having a weak odor. It has been speculated that oxidation products may become irritants and that the irritants may worsen the odor. In addition, the components of the gas discharged from the incinerator used in the incineration and deoiling process of the glass fiber fabric are generally represented by carbon monoxide, carboxylic acid, and formaldehyde, in addition to steam, carbon dioxide, and nitrogen oxide. It is considered that carbonyl compounds such as aldehydes are contained.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in order to eliminate the above-mentioned disadvantages of the prior art, and an object of the present invention is to provide a method for coating a glass fiber using a specific sizing agent. By doing so, it is to suppress the generation of irritating substances contained in the gas components discharged in the incineration and deoiling step of the glass fiber fabric, that is, the amount of aldehyde gas such as formaldehyde.

[0009]

Means for Solving the Problems The inventors of the present invention have studied various sizing agents for coating a glass fiber in order to achieve the above object, and have found that a sizing agent containing a specific nitrogen-containing compound having a certain amount of nitrogen is contained. The inventors have found that the use of a sizing agent can significantly suppress the amount of aldehyde gas generated in the deoiling step, and have completed the present invention.

That is, the present invention comprises a nitrogen-containing compound having at least one nitrogen-containing group selected from the group consisting of an amino group and an imino group, and a film-forming agent, and the amount of nitrogen atoms per molecule of the nitrogen-containing compound. Is 10% by weight or more.

When the sizing agent is a primary sizing agent, the film forming agent is preferably starch, polyvinyl alcohol or a mixture thereof. Means that the film forming agent is starch,
It is preferably polyvinyl alcohol, water-soluble urethane or a mixture thereof.

Further, the molecular weight of the nitrogen-containing compound in the sizing agent is preferably 350 or less.
The nitrogen-containing compound is preferably at least one selected from the group consisting of urea, melamine, dicyandiamide and derivatives thereof.

Furthermore, the amount of the nitrogen-containing compound is preferably 0.1 to 10% by weight based on the whole sizing agent.

Further, the glass fiber of the present invention is a glass fiber obtained by coating any one of the above-mentioned sizing agents.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the sizing agent for glass fibers of the present invention is characterized by containing a film forming agent and a specific nitrogen-containing compound.

Film-forming agent The film-forming agent in the present invention is not particularly limited as long as it is a compound capable of protecting the glass fiber from any bending or friction derived from equipment and machinery used in the glass fiber production process. It is preferable to use starch or polyvinyl alcohol as the primary sizing agent,
It is preferable to use starch, polyvinyl alcohol or water-soluble urethane as the secondary sizing agent.

Examples of the starch in the film-forming agent include ordinary raw starch such as corn starch, high amylose type starch,
Enzymatically modified starch, starch degradation products subjected to acid treatment, wet heat treatment, or oxidation treatment, or starch derivatives chemically modified such as cross-linking, esterification, etherification, or grafting can be used.

The polyvinyl alcohol is not particularly restricted but may be either partially saponified or completely saponified. For example, those having a degree of polymerization of 500 to 2400 can be exemplified.

Further, examples of the water-soluble urethane include a reaction product obtained by reacting a polyhydric alcohol (a) with a polyisocyanate (b) having a molecular weight of about 20,000 to 400,000 as shown below. (A) Molecular weight 50 such as polyethylene glycol or polyhydroxyethylene hydroxypropylene glycol
(B) Polyisocyanate or 2 such as hexamethylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, ethylene diisocyanate, tetraalkyldiphenylmethane diisocyanate, etc.
Polyisocyanate having at least two isocyanate groups

Nitrogen-Containing Compound The nitrogen-containing compound used in the sizing agent for glass fibers of the present invention has at least one nitrogen atom-containing group selected from the group consisting of amino groups and imino groups. I do. The -NH ₂ is an amino group in the present invention means a = NH and imino group, the nitrogen atom in an amino group and imino groups are respectively bonded to a carbon atom. In the case of an imino group, a nitrogen atom is bonded to the same carbon atom by a double bond (C = NH), and a nitrogen atom is bonded to two separate carbon atoms (C-NH- C). The nitrogen-containing compound of the present invention includes those having both an amino group and an imino group in addition to those having only an amino group and those having only an imino group in the molecule.

In general, the sizing agent for glass fiber provided to the glass fiber fabric has the highest content of starch, polyvinyl alcohol or water-soluble urethane as a film forming agent. Therefore, it is considered that most of the exhaust gas in the incineration and deoiling step of the glass fiber fabric is generated from starch, polyvinyl alcohol, water-soluble urethane, or the like contained in the glass fiber sizing agent. That is, when the amino group and / or imino group contained in the sizing agent (primary sizing agent, secondary sizing agent) used for the coating treatment of the glass fiber is incinerated and deoiled in the glass fiber fabric, the organic component of the sizing agent It is presumed that by reacting with the carbonyl group of the carbonyl compound generated from the above, the generation amount of aldehyde gas represented by formaldehyde is suppressed.

In order to efficiently collect an aldehyde gas as a carbonyl compound, the effect is higher as the ratio of the amino group or imino group to the amount of the generated carbonyl group is higher. Therefore, the nitrogen-containing compound used in the present invention needs to have 10% by weight or more, preferably 20% by weight or more, more preferably 40% by weight or more of nitrogen atoms in one molecule. Further, the upper limit of the nitrogen atomic weight is preferably 70% by weight or less based on one molecule of the nitrogen-containing compound.

Preferred examples of the nitrogen-containing compound in the present invention include primary amines, secondary amines, primary amides, and secondary amides (imides). It is preferable that the molecular weight of the nitrogen-containing compound is 350 or less, since the property is improved and the film property is deteriorated.

<Primary amine> The primary amine in the present invention refers to a compound represented by the general formula RNH ₂ (R is a hydrocarbon group), and is an aliphatic (chain) amine (where the hydrocarbon group is an aliphatic group). (Chain-type) amines that are compounds only, and the hydrocarbon group may contain a multiple bond such as a double bond), an aromatic amine (an amine containing at least one aromatic compound as a hydrocarbon group) ) And alicyclic amines (amines containing at least one alicyclic compound as a hydrocarbon group). The hydrocarbon group in the primary amine may be substituted, and examples of the hydrocarbon group include a heterocyclic compound such as triazine. In addition,
If the number of nitrogen atoms is 10% by weight or more based on one molecule of the nitrogen-containing compound, the number of nitrogen atoms derived from the primary amine may be one (monoamine) or plural (polyamine).
May be.

Here, examples of the aliphatic primary amine of the present invention include compounds in which R is a lower alkyl group, an allyl group, a propenyl group or the like. Specifically, propylamine, isopropylamine, butylamine Pentylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, allylamine and the like. Examples of the aromatic primary amine include aniline, methylaniline, ethylaniline, toluidine,
Benzylamine and the like, as an example of an alicyclic primary amine,
Cyclopropylamine, cyclobutylamine, cyclopentylamine, cyclohexylamine and the like can be mentioned.
Further, since the hydrocarbon group R also includes a heterocyclic compound such as triazine, a compound such as melamine can be exemplified.

<Secondary amine> The secondary amine in the present invention is represented by the general formula R ₂ NH (R is a hydrocarbon group), and like the primary amine, aliphatic amine, aromatic amine and alicyclic amine. Either may be used. Further, the hydrocarbon group may be substituted, and the number of nitrogen atoms derived from the secondary amine may be one or more. Examples of secondary amines include diethylamine, dipropylamine, diisopropylamine, dibutylamine, diamylamine, diallylamine, and the like.

Further, compounds containing both an amino group and an imino group such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, dicyandiamide and the like are also included in the nitrogen-containing compound of the present invention.

<Primary amide> The primary amide in the present invention is a compound represented by the general formula RCO-NH ₂ ,
For example, acid amide of carboxylic acid, acid amide of carbamic acid and the like can be mentioned. That is, R in the above formula includes an amino group in addition to the same hydrocarbon group as the primary amine. Specific examples of the primary amide compound include acylamine and urea.

<Second amide> The second amide in the present invention is a compound represented by the general formula RCO-NH-COR. Also includes an amino group and the like. Examples of the second amide include phthalamide.

Among the above nitrogen-containing compounds, urea (acid amide of carbamic acid), melamine, dicyandiamide and derivatives thereof are particularly preferable as the nitrogen-containing compound of the present invention. Here, as the urea derivative, methylol urea, methylol methylene diurea, dimethyl urea and the like, and as the melamine derivative, monomethylol melamine, dimethylol melamine, trimethylol melamine,
Tetramethylolmelamine, pentamethylolmelamine and the like are preferable, and dicyandiamide derivatives are preferably dicyandiamidine and the like.

Other Ingredients The glass fiber sizing agent of the present invention includes a smoothing agent, a softening agent, an emulsifier, an antiseptic, etc., which are generally used as a glass fiber sizing agent for a glass fiber fabric. It may be.

The smoothing agent is used to impart smoothness to the glass fiber,
A component that is added to reduce friction on the machine and protect glass fibers, and is used as a synthetic oil such as a hydrogenated hardened oil, paraffin wax or a condensate of a higher saturated fatty acid and a higher saturated alcohol in animal and vegetable oils. Can be

Softeners are used to soften hard glass fibers and reduce friction between the glass fibers, and are selectively adsorbed on the glass surface and exhibit some lubricity, for example, tetraethylene pentane. Examples thereof include amides obtained by reacting a mine with stearic acid, imidazolines that have undergone a further reaction, and amides obtained by reacting a fatty acid having 8 to 18 carbon atoms with polyethyleneimine having a molecular weight of about 600 to 1800.

The emulsifier is a component mainly added for emulsifying a lubricating oil, and includes alkyl ethers such as polyoxyethylene polyalkyl ethers, alkyl esters, alkyl phenyl ethers, copolymers of polyethylene oxide and polypropylene oxide, sorbitan A surfactant such as an ester is used. In addition, as a preservative,
Formalin is mainly used.

The amount of each component in the glass fiber sizing agent The amount of each component in the glass fiber sizing agent of the present invention is as follows:
What is necessary is just to determine suitably according to the kind, use, etc. of glass fiber, and it does not specifically limit. However, the amount of the nitrogen-containing compound of the present invention is preferably 0.1 to 10% by weight, more preferably 1 to 8% by weight, based on the total amount of the sizing agent.
If it is less than 0.1% by weight, there is no effect of suppressing the generation of aldehyde gas during deoiling by incineration, and if it exceeds 10% by weight, the fluff of the glass fiber fabric increases and the flight property of the glass fiber during woven fabric decreases. Sometimes. Here, the “size for glass fiber” is in a liquid state, and each component such as a film forming agent, a nitrogen-containing compound, a smoothing agent, and a lubricant is dispersed and dissolved in water, an organic solvent, and the like. I have. Therefore, the term “total amount of the sizing agent” as used herein means the amount of the solvent in which these components are dispersed and dissolved in addition to the contents of the components such as the film forming agent, the nitrogen-containing compound, the smoothing agent, and the lubricant. The total amount of the dispersion (solution) forming the sizing agent is included. The content of the above-mentioned smoothing agent, softening agent, surfactant and preservative may be appropriately selected depending on the use of the glass fiber.

Glass fiber Usually, the glass composition of the glass fiber is an alkali-free glass belonging to alumina borosilicate glass called E glass, and its main composition is, for example, SiO ₂ ; 52 to 56% by weight, A
l ₂ O _3; 12~16 wt%, CaO; 16 to 25 wt%, MgO; Less than six percent by weight, B ₂ O; 5 to 10 wt%,
M ₂ O (M is Na or K); a 0-3% by weight. The glass composition used for the glass fiber is D in addition to the above E glass.
There are glass compositions called glass, silica glass, and quartz glass. In the present invention, the glass composition of the glass fiber is not particularly limited as long as it is selected according to the application. Furthermore, the structure (plain weave, twill weave, satin weave, etc.) and weave density of the glass fiber fabric, the count and twist of the glass fiber, and the shape and thickness of the glass filament constituting the glass fiber may be selected according to the application. There is no particular limitation.

Method for Coating Glass Fiber with Sizing Agent Prior to preparing a treatment solution for a glass fiber sizing agent used in the present invention, it is desirable that the nitrogen-containing compound be neutralized with an organic acid or an inorganic acid. This is for preventing precipitation by reacting with a surfactant as a softener. The method for attaching the primary sizing agent and the secondary sizing agent to the glass fiber is not particularly limited. For example, the primary sizing agent is rotated while dipping a rubber roller in a size tank, and the rubber with the sizing agent is attached. For the method of applying the glass fiber by directly contacting the roller with the roller, for the secondary sizing agent, once pass the glass fiber sheet through the size tank,
For example, a method of squeezing with a mangle (rubber roller) to take an extra size agent can be used. Also, the amounts of the primary sizing agent and the secondary sizing agent may be appropriately selected and adjusted depending on the type and use of the glass fiber. Specifically, the amount of the primary sizing agent is about 0 to the weight of the glass fiber. .
Preferably, the secondary sizing agent is applied in the range of about 0.5 to about 2% by weight based on the weight of the glass fiber, in the range of 5 to about 2% by weight.

Further, when a primary sizing agent and a secondary sizing agent are used in combination in the coating treatment, the nitrogen-containing compound of the present invention is contained in either the primary sizing agent or the secondary sizing agent. May be included in both the primary sizing agent and the secondary sizing agent, but if it is desired to more effectively suppress the generation of aldehyde gas, the sizing agent may be included in both the primary sizing agent and the secondary sizing agent. It is desirable.

In order to achieve the object of the present invention, the glass fiber fabric may be incinerated and deoiled under the same conditions as usual, and the conditions may be appropriately selected depending on the type of the coated glass fiber fabric. That is, the incineration temperature is 350 to 450
C. is preferable, and the incineration time is preferably one hundred and several hours in the case of the direct batch incineration method, and several tens of seconds in the continuous incineration method and several tens of hours in the case of the two-stage incineration deoiling method. Combustion method (direct combustion method using afterburner or contact combustion method), gas absorption method, adsorption method, masking method, neutralization method, chemical treatment method, microbial treatment method etc. However, the present invention does not prevent the combination use of odor control by these deodorizing methods.

[0040]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples. Further, as the glass fiber, a glass fiber fabric of IPC standard 7628 was used.

Example 1 A coating treatment was carried out with the primary sizing agent shown in Formulation 1 of Table 1 and glass fibers having the primary sizing agent adhered at 0.9% by weight with respect to the glass fiber weight were used as weft yarns. The glass fibers coated with the primary sizing agent are coated with the secondary sizing agent shown in Formulation 1 of Example 1, and the glass fibers having the secondary sizing agent attached thereto at 1.5% by weight with respect to the glass fiber weight are referred to as warps. did. Next, the weft and the warp were woven by a high-speed air jet loom to obtain a glass fiber fabric of Example 1 having 44 warps / 25 mm and 32 wefts / 25 mm.

[Examples 2 to 5] Glass fibers were coated and woven in the same manner as in Example 1 using the primary sizing agents and secondary sizes shown in Formulations 2 to 5 in Table 1, and woven.
The glass fiber fabrics of Examples 2 to 5 were used.

Examples 6 to 10 Glass fibers were coated and woven in the same manner as in Example 1 using the primary sizing agents and the secondary sizing agents shown in Formulations 6 to 10 in Table 2. And the glass fiber fabrics of Examples 6 to 10, respectively.

Example 11 Glass fibers were coated and woven in the same manner as in Example 1 using the primary sizing agent and the secondary sizing agent shown in Formulation 11 of Table 3, and woven. Glass fiber fabric.

Comparative Examples 1 to 3 Glass fibers were coated and woven in the same manner as in Example 1 using the primary sizing agent and the secondary sizing agent shown in Formulations 12 to 14 in Table 3. And the glass fiber fabrics of Comparative Examples 1 to 3, respectively.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

Various physical properties of the fiber woven fabrics of the above Examples and Comparative Examples were measured by the following evaluation methods. [Evaluation method] a) Amount of aldehyde gas generated: glass fiber fabric 1 m ² (2
09g) was heated from normal temperature to a maximum temperature of 400 ° C. at a rate of 3 ° C./min, incinerated and deoiled, and the generated formaldehyde gas was collected in 10.0 ml of a sodium bisulfite solution. Next, 8.0 ml of a chromotropic acid solution (sodium chromotropic acid [C ₁₀ H ₄ (O
H) ₂ (SO ₂ Na) ₂ .2H ₂ 0] aqueous solution and sulfuric acid) to obtain a test solution. The absorbance at 570 μm was measured according to the chromotropic acid method, and the amount of aldehyde gas generated (concentration: ppm) ).

B) Weaving property b-1) Evaluation of fluffing property: glass fiber 1000 after weaving
The number of fluffs per m was measured by a fluff counter manufactured by Toray Industries, Inc., and evaluated according to the five grades according to the procedure in Table 4.

[Table 4]

B-2) Flyability (weaving) evaluation: Glass fibers were drawn from a yarn bobbin on which glass fibers were continuously wound, and passed through an air nozzle. After measuring the weight of the yarn bobbin in this state, 1 k is inserted into the air nozzle.
Air pressure of gf / cm ² was applied to fly the glass fiber by air (blowing), and the weight of the yarn bobbin after one minute was measured again. From the difference between the weights of the yarn bobbin before and after the air pressure treatment, the weight of the glass fiber which flew in one minute was calculated, and evaluated according to the five grades according to the procedure shown in Table 5.

[Table 5]

[Results] Table 6 shows the evaluation results of the glass fiber fabrics of the respective Examples and Comparative Examples. In addition, here, the grade of fluff and the grade of flight performance (weaving property) indicate that the smaller the grade value, the better the result was obtained. If the grade is 3 or less, the workability under normal conditions is obtained. It doesn't matter at all.

[0053]

[Table 6]

As shown in Table 6, when the glass fiber was coated with the primary sizing agent and the secondary sizing agent containing the nitrogen-containing compound of the present invention, the glass fiber fabric was fluffed or the glass was woven. The amount of generation of aldehyde gas represented by formaldehyde contained in the exhaust gas in the incineration deoiling process was significantly suppressed without affecting the flight properties of the fibers.

Here, the relationship between the concentration of the aldehyde gas, which is an odor component, and the intensity of the odor is determined in accordance with Weber-Fechner's law.
It is known that the intensity of the odor depends on the concentration of the odor component. Therefore, the reduction in the concentration of the odor component is effective for odor control.

[0056]

The coating treatment of glass fibers with the sizing agent for glass fibers of the present invention does not cause problems such as fuzzing and deterioration of weaving in the process, and incineration and deoiling of glass fiber fabrics made of the glass fibers. There is an effect that the generation amount of aldehyde gas typified by formaldehyde contained in the exhaust gas in the process can be significantly suppressed.

As described above, when the glass fiber sizing agent of the present invention is used, efficient deodorization can be performed without making any changes or additions to the equipment used in the incineration deoiling process currently used. As a result, it is possible to produce glass fibers efficiently and at low cost under a favorable working environment.

Claims (7)

[Claims] 1. A nitrogen-containing compound having at least one nitrogen atom-containing group selected from the group consisting of an amino group and an imino group, and a film-forming agent, wherein the amount of nitrogen atoms per molecule of the nitrogen-containing compound is 10% by weight. % For glass fiber. 2. The sizing agent according to claim 1, wherein the sizing agent for glass fibers is a primary sizing agent, and the film forming agent is starch, polyvinyl alcohol or a mixture thereof. 3. The sizing agent for glass fiber is a secondary sizing agent, and the film forming agent is starch, polyvinyl alcohol,
The sizing agent according to claim 1, which is a water-soluble urethane or a mixture thereof. 4. The sizing agent according to claim 1, wherein the molecular weight of the nitrogen-containing compound is 350 or less. 5. The sizing agent according to claim 4, wherein the nitrogen-containing compound is at least one compound selected from the group consisting of urea, melamine, dicyandiamide and derivatives thereof. 6. The method according to claim 1, wherein the amount of the nitrogen-containing compound is 0.1 to 10% by weight based on the total amount of the sizing agent.
The sizing agent according to item. 7. A glass fiber coated with the sizing agent according to any one of claims 1 to 6.