JP6983566B2 - Aramid fiber cord for rubber reinforcement - Google Patents

Description

The present invention relates to an aramid fiber cord for rubber reinforcement. More specifically, the present invention relates to an aramid fiber cord for rubber reinforcement having excellent heat-resistant adhesiveness.

Reinforcing fiber cords are embedded in rubber products such as transmission belts, conveyor belts, and tires. Aramid fiber cords, which have high strength and low elongation, are widely known as reinforcing fiber cords. Aramid fiber cords have high strength, high elastic modulus, high heat resistance, flame retardancy, chemical resistance, and the like. It has excellent properties.

However, since the surface of the aramid fiber is relatively inert, the adhesiveness to the rubber is poor. In order to improve the adhesiveness between the aramid fiber and the rubber, a two-bath treatment is generally performed in which the fiber surface is activated and then treated with resorcin formalin latex (hereinafter referred to as RFL). For example, in the case of obtaining an aramid fiber cord for rubber reinforcement, a method of arranging a plurality of raw yarns to form a twisted yarn is subjected to epoxy treatment or isocyanate treatment to activate the fiber surface and then treated with an RFL treatment liquid. It is known (see Patent Document 1, Patent Document 2, etc.).

Patent Document 1 discloses a method in which an aqueous dispersion of a polyepoxide compound and a blocked polyisocyanate compound is used as a treatment agent for activating the fiber surface, and then the treatment is performed twice with an RFL treatment liquid containing a chlorophenol compound. .. Patent Document 2 discloses a method in which an aramid fiber is treated with an epoxy compound, then treated with a treatment liquid containing a polyurethane resin as a main component, and then treated with an RFL treatment liquid containing a chlorophenol compound.

However, the above method has a problem that the RFL treatment liquid does not uniformly adhere to the fiber surface.

Patent Document 3 discloses a method of treating a cord made of an aramid fiber composite in which a curable epoxy compound is impregnated into an aramid fiber skeleton with an RFL adhesive, even in a high load and high temperature environment. It does not mention the property that the fiber cord does not peel off from the rubber and the heat-resistant adhesiveness.

Japanese Unexamined Patent Publication No. 2005-171431 Japanese Unexamined Patent Publication No. 2010-09514 Japanese Unexamined Patent Publication No. 2012-207326

An object of the present invention is to provide an aramid fiber cord for rubber reinforcement, which is superior in adhesiveness (heat-resistant adhesiveness) between a fiber cord and rubber at a high temperature as compared with a conventional fiber cord.

As a result of diligent studies to achieve the above problems, the present inventors have treated the fiber cord with the first treatment liquid and the second treatment liquid having different compositions, and as a material for the fiber cord. We have found that the heat-resistant adhesiveness between the aramid fiber cord and the rubber is dramatically improved by using the aramid fiber composite in which the curable epoxy compound is infiltrated into the fiber skeleton, and the present invention is completed. I arrived.

That is, the present invention is as follows.

(1) A rubber reinforcing aramid fiber cord formed by sequentially applying a first treatment liquid and a second treatment liquid having different compositions to form a plurality of adhesive layers.
The aramid fiber is an aramid fiber composite in which a curable epoxy compound is infiltrated into the fiber skeleton .
The first treatment liquid comprises a curable epoxy compound and a blocked isocyanate compound.
The second treatment liquid contains resorcin formaldehyde latex (RFL), blocked isocyanate compound and triazine compound.
Aramid fiber cord for rubber reinforcement with excellent heat resistance and adhesiveness.
(2) The above-mentioned (1), wherein the permeation amount of the curable epoxy compound is 0.1 to 2.0% by mass with respect to the fiber mass when the water content of the aramid fiber is converted to 0%. Aramid fiber cord for rubber reinforcement.
(3) The aramid fiber cord for rubber reinforcement according to (1) or (2) above, wherein the epoxy compound permeated into the fiber skeleton and the epoxy compound used in the first treatment liquid are the same compound.
(4) The aramid fiber cord for rubber reinforcement according to any one of claims (1) to (3), wherein the blocked isocyanate compound used in the first treatment liquid and the second treatment liquid is the same compound.

According to the present invention, by forming a plurality of adhesive layers on a fiber cord made of an aramid fiber composite in which a curable epoxy compound is infiltrated into a fiber skeleton, it can be peeled off even in a high load and high temperature environment. It is possible to provide an aramid fiber cord for rubber reinforcement, which is difficult and has excellent heat-resistant adhesiveness.

In the present invention, the aramid fiber is a fiber having at least one divalent aromatic group which may be usually substituted in the repeating unit of the polymer forming the fiber, and is a fiber having at least one amide bond. However, there is no particular limitation, and it may be a known one called a total aromatic polyamide fiber or an aramid fiber. In the above, the "optionally substituted divalent aromatic group" means a divalent aromatic group which may have one or more identical or different substituents.

The aramid fiber includes a para-based aramid fiber and a meta-based aramid fiber, and the present invention is particularly effective and preferable for the para-based aramid fiber having excellent tensile strength. Examples of the para-aramid fiber include polyparaphenylene terephthalamide fiber (DuPont, USA, manufactured by Toray DuPont Co., Ltd., trade name "Kevlar" (registered trademark)), copolyparaphenylene-3,4'-oxydi. Examples thereof include phenylene terephthalamide fiber (manufactured by Teijin Limited, trade name "Technora" (registered trademark)).

In the present invention, the best form in which the curable epoxy compound is infiltrated into the fiber skeleton is that in the step of producing the aramid fiber, the spinning solution is discharged from the mouthpiece, coagulated in the spinning bath, and subjected to a washing neutralization treatment. After that, an oil agent containing a curable epoxy compound was applied to the aramid fiber in a state of water content of 15 to 100% by mass, which was adjusted by low-temperature drying at 100 to 150 ° C., and the fiber was impregnated and infiltrated. be. In particular, aramid fibers having a moisture content of 15 to 100% by mass, which has no history of being dried to a moisture content of less than 15% by mass after spinning, are preferable.

The application temperature is not particularly limited, and may be applied in a temperature range of about 5 to 90 ° C. If the amount of water during impregnation / permeation is too small, it becomes difficult to uniformly impregnate / permeate the curable epoxy compound into the fiber skeleton. On the other hand, if the amount of water is too large, the curable epoxy compound may fall off together with the water after impregnation / permeation and before the winding process. The more preferable moisture content of the aramid fiber impregnated with the curable epoxy compound is 25 to 70% by mass, and 25 to 50% by mass is particularly preferable.

The amount of impregnation / permeation of the curable epoxy compound to be infiltrated into the aramid fiber skeleton is preferably 0.1 to 2.0% by mass, more preferably 0.1 to 2.0% by mass, based on the fiber mass in which the water content of the aramid fiber is converted to 0%. It is 0.2 to 1.0% by mass.

As the curable epoxy compound, one or more or a mixture of two or more selected from glycidyl ethers of polyhydric alcohols such as glycerol, sorbitol, and polyglycerol is preferable. For example, glycerol diglycidyl ether, glycerol triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether and the like can be mentioned.

In addition to the curable epoxy compound, a curing agent may be impregnated / permeated. Examples of the curing agent include dimethyloctylamine, dimethyldecylamine, dimethyllaurylamine, and long-chain alkylpolyoxyethylene type tertiary amines obtained by adding ethylene oxide to an aliphatic primary amine. The curing agent can be impregnated and permeated simultaneously with or separately from the curable epoxy compound.

Examples of the oil agent include general oil agents used for aramid fibers, for example, low molecular weight fatty acid esters having 18 or less carbon atoms, polyethers, mineral oils, and the like.

It is desirable that the curable epoxy compound is used in the above oil in an amount of about 20 to 60% by mass, preferably 30 to 50% by mass. The curing agent is preferably used in the above oil in an amount of about 3 to 20% by mass, preferably 5 to 10% by mass.

The oil agent containing the curable epoxy compound is applied by a known method such as an immersion lubrication method, a spray lubrication method, a roller lubrication method, and a guide lubrication method using a measuring pump.

An oil agent containing a curable epoxy compound is infiltrated into the aramid fiber skeleton to form an aramid fiber composite, and then the aramid fiber composite is wound around a bobbin in a winding step. The wound aramid fiber complex is unwound from the bobbin and under tension, at 80 to 300 ° C. By heat-treating at 100 to 250 ° C. to a moisture content of less than 15% by mass, more preferably less than 10% by mass, an aramid fiber complex impregnated with a curable epoxy compound can be obtained.

The aramid fiber cord for rubber reinforcement of the present invention has a different composition from that of the cord after coding the aramid fiber in which a curable epoxy compound is impregnated into the fiber skeleton in a twisting step by a conventional method. It is obtained by applying the two treatment liquids in the order of the first treatment liquid and the second treatment liquid.

As the first treatment liquid, an aqueous solution or a solvent-based solution containing a curable epoxy compound or a dispersion liquid can be used, but in order to further exhibit the reactivity of the curable epoxy compound, an aqueous solution or an aqueous dispersion liquid can be used. Is preferable. An aramid fiber cord is prepared by using an aramid fiber composite in which a curable epoxy compound is infiltrated into the fiber skeleton, and the first treatment liquid containing the curable epoxy compound is applied to the aramid fiber cord. Since the treatment liquid penetrates and is retained in the twisted yarn cord, high surface activity can be imparted to the aramid fiber. The curable epoxy compound may be the same as or different from the one permeated into the fiber skeleton, but it can enhance the affinity with the aramid fiber composite and form a uniform film by heat curing described later. More preferably, the same compound.

The curable epoxy compound is more preferably applied as a mixture with blocked isocyanate. As for the blending ratio in the first treatment liquid, 1 to 50 parts by mass of blocked polyisocyanate is preferably used, and more preferably 5 to 15 parts by mass is used with respect to 100 parts by mass of the curable epoxy compound.

Blocked isocyanate is an adduct of a polyisocyanate compound and a blocking agent, and is a compound in which the blocking agent component is liberated by heating to produce an active polyisocyanate compound.
Examples of the polyisocyanate compound include polyisocyanates such as tolylene diisocyanate, metaphenylenedi isocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, polymethylene polyphenyl isocyanate, and triphenylmethane triisocyanate, or these polyisocyanates and two active hydrogen atoms. A polyol adduct polyisocyanate containing a terminal isocyanate group obtained by reacting a compound having the above, for example, trimethylolpropane, pentaerythritol, etc. with a molar ratio of isocyanate group (-NCO) to hydroxyl group (-OH) exceeding 1. And so on. In particular, aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate and polymethylene polyphenyl isocyanate give good results.
Examples of the blocking agent include phenols such as phenol, cresol and resorcin, lactams such as ε-caprolactam and valerolactam, oximes such as acetoxime, methylethylketone oxime and cyclohexanone oxime, and ethyleneimine. In addition, a compound such as a 2,4-toluene diisocyanate dimer in which the polyisocyanate compound itself also serves as a blocking agent can be mentioned.

The solid content concentration of the first treatment liquid is preferably about 0.1 to 30% by mass, which prevents aggregation of solute components in the liquid and is preferable from the viewpoint of long-term stability. Further, for the purpose of further enhancing the reactivity of the curable epoxy compound, a small amount of the alkaline compound can be added to the first treatment liquid. Examples of the alkaline compound include sodium hydrogen carbonate, sodium carbonate, sodium hydroxide, ammonia and the like. In order to exert the catalytic effect of the curable epoxy compound while suppressing the strong decrease due to the hydrolysis of the aramid fiber, the first The concentration of the alkaline compound in the treatment liquid is preferably in the range of 0.001 to 1% by mass.
The first treatment liquid is given, for example, by immersing the aramid fiber cord in the treatment liquid. The aramid fiber cord to which the first treatment liquid is applied is usually dried at 100 to 150 ° C. and then heat-treated at 200 to 260 ° C. to be cured. The amount of the first treatment liquid to be applied is preferably about 0.1 to 5.0% by mass with respect to the aramid fiber cord in terms of dry mass ratio.

As the second treatment liquid, an aqueous solution or a solvent-based solution or a dispersion liquid containing resorcin formaldehyde latex (RFL) and further containing a triazine compound can be used, but an aqueous solution or an aqueous dispersion liquid is preferable. In addition, it is more preferable to contain blocked isocyanate, chlorophenol compound and the like. The blocked isocyanate may be the same as or different from the compound used in the first treatment liquid, but it enhances the affinity with the first treatment liquid and forms a more uniform film of the second treatment liquid. The same compound is preferable because it can be formed.

The solid content concentration of the second treatment liquid is preferably about 0.1 to 30% by mass, which prevents aggregation of solute components in the liquid and is preferable from the viewpoint of long-term stability.

Further, for the purpose of further enhancing the reactivity of the blocked isocyanate and the chlorophenol compound, a small amount of the alkaline compound can be added to the second treatment liquid. Examples of the alkaline compound include sodium hydrogen carbonate, sodium carbonate, sodium hydroxide, ammonia and the like. In order to increase the reactivity of the blocked isocyanate and the chlorophenol compound while suppressing the strong decrease due to the hydrolysis of the aramid fiber, the first method is used. The concentration of the alkaline compound in the treatment liquid of No. 2 is preferably in the range of 0.001 to 1% by mass.

The blending ratio of the above components is not particularly limited, but RFL and the triazine compound are used in a ratio of 10/90 to 10/90, and the blocked isocyanate and the chlorophenol compound are added to the total amount of the second treatment liquid by 1, respectively. It is preferable to use ~ 20 parts by mass.

RFL is a mixture of latex and resorcin-formaldehyde initial condensate and aged. For example, 100 parts by mass of resorcin-formaldehyde initial condensate is mixed with 40 to 900 parts by mass of latex to prepare a mixed solution. Can be mentioned.
Examples of the latex include vinylpyridine-styrene-butadiene copolymer latex, styrene-butadiene latex, acrylonitrile-butadiene latex, chloroprene latex, chlorosulfonated polyethylene latex, acrylate latex and natural rubber latex.
Examples of the resorcin-formaldehyde initial condensate include a novolak-type condensate obtained by condensing resorcin-formaldehyde under an acid catalyst or an alkali catalyst.

Examples of the triazine compound include di or triol triazine, di or trithiol-s-triazine. Specific examples include 1,3,5-triazine-2,4,6-triol (cyanuric acid), isocyanuric acid, trihydroxyethylisocyanurate, 1,3,5-triazine-2,4,6-trithiol, Examples thereof include 6-dibutylamino-1,3,5-triazine-2,4-dithiol and the like. Of these, trioltriazine is preferred.
Since the triazine compound contributes to the vulcanization adhesiveness of rubber, if the addition amount is small, the vulcanization adhesiveness becomes insufficient, and if the addition amount is too large, the rubber may scorch.

The chlorophenol compound is a cocondensate of parachlorophenol, resorcin and formaldehyde, and specific examples thereof include 2,6-bis (2', 4-dihydroxy-phenylmethyl) 4-chlorophenol and the like.

The second treatment liquid is usually prepared by aging RFL at a temperature of 20 to 30 ° C. for 24 hours or more, and then adding and mixing a blocked isocyanate, a chlorophenol compound, and a triazine compound.

The second treatment liquid is applied to the aramid fiber cord in the same manner as the first treatment liquid. The aramid fiber cord to which the second treatment liquid is applied is usually dried at 100 to 150 ° C. and then heat-treated at 200 to 260 ° C. to be cured. The amount of the second treatment liquid to be applied is preferably about 3.0 to 15.0% by mass as a mixture with respect to the aramid fiber cord in terms of dry mass ratio.

As rubber using aramid fiber for rubber reinforcement, acrylic rubber, acrylonitrile-butadiene rubber, hydride acrylonitrile-butadiene rubber, isoprene rubber, urethane rubber, ethylene-propylene rubber, chloroprene rubber, silicone rubber, styrene-butadiene rubber, polysulfide Examples thereof include rubber, natural rubber, butadiene rubber, and fluororubber.

The rubber reinforcing aramid fiber of the present invention has high heat-resistant adhesiveness, and can be applied to, for example, a tire cord, a power transmission belt, a transport belt, a core wire reinforcing cord of a rubber hose, and the like.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Further, in the following examples and the like, unless otherwise specified, "% by mass" is abbreviated as "%" and "parts by mass" is abbreviated as "parts". Each measured value followed the following method.

[T-adhesive strength and T-heat resistant adhesive strength]
Adhesive strength according to JIS L 1017: 2002-A method, the treated code is embedded in unvulcanized rubber, and under pressure, the initial adhesive strength is 150 ° C x 30 minutes and the heat resistant adhesive strength is 170 ° C x 16 hours. After press vulcanization and allowing to cool, the cord was pulled out from the rubber block at a speed of 300 mm / min, and the load required for the pulling out was displayed in N / cm.
As the rubber compound in the adhesion evaluation, unvulcanized rubber containing natural rubber and SBR rubber as main components and containing carcass was used.

[45 degree cross peeling]
Adhesive strength according to JIS L 1017: 2002-A method, the treated code is crossed 45 degrees and embedded in unvulcanized rubber, and under pressure, the initial adhesive strength is 150 ° C. x 30 minutes, and the heat resistant adhesive strength is After press vulcanization at 150 ° C for 30 minutes and heating at 80 ° C for 30 minutes, the cord is pulled out from the rubber block at a speed of 300 mm / min in an atmosphere of 80 ° C, and the load required for the pulling is N / inch. displayed.
As the rubber compound in the adhesion evaluation, unvulcanized rubber containing natural rubber and SBR rubber as main components and containing carcass was used.

(Example 1)
Polyparaphenylene terephthalamide obtained in the usual way (PPTA) (molecular weight about 20,000) 1 kg was dissolved in concentrated sulfuric acid 4 kg, shear rate 30,000sec from a die having a plurality of holes of diameter 0.1 mm ^{- It was} discharged so as to be No. 1, spun into water at 4 ° C., and then neutralized with a 10% aqueous sodium hydroxide solution under the conditions of 10 ° C. × 15 seconds. Then, it was dehydrated and dried at a low temperature at 110 ° C. to adjust the moisture content to 35%.
This PPTA fiber is impregnated with an oil agent (a mixture of diisostearyl adipate / diorail adipate / hardened castor oil ethylene oxide / mineral oil) containing 50% of triglycerol triglycidyl ether as a curable epoxy compound to impregnate the curable epoxy compound. After the oil agent containing the above was impregnated into the PPTA fiber, it was wound around the bobbin in the winding step.
After that, the PPTA fiber is unwound from the bobbin, heat-treated under tension using a calculator processing machine (manufactured by Ritzler), and wound up. A curable epoxy compound having a moisture content of 6.9% is placed in the fiber skeleton. A PPTA fiber composite was obtained. The amount of the curable epoxy compound impregnated (in terms of% to absolute dry fiber mass) was 0.5%.

Using two multifilaments (fineness: 1,100 dtex) of the above-mentioned PPTA fiber complex, the PPTA fiber cord was twisted with a twist number of 35 times / 10 cm for lower twist and 35 times / 10 cm for upper twist to obtain a PPTA fiber cord.

Subsequently, the above PPTA fiber cord was subjected to triglycerol triglycidyl ether as a curable epoxy compound and diphenylmethane-bis-4, 4'-methylethylketone oxime carbamate as a blocked isocyanate using a calculator processing machine (manufactured by Ritzler). Was immersed in the first treatment liquid blended at a mass ratio of 10: 1, dried at 140 ° C. for 150 seconds, and then heat-treated at 245 ° C. for 60 seconds to prepare a dip cord. The amount of the first treatment liquid applied was 1.5% by mass with respect to the aramid fiber cord in terms of dry mass ratio.

Subsequently, the above dip cord was immersed in a second treatment liquid using a computer processor (manufactured by Ritzler), dried at 140 ° C. for 150 seconds, and then heat-treated at 245 ° C. for 60 seconds. An RFL dip code was made. The amount of the second treatment liquid applied was 8.8% by mass with respect to the aramid fiber cord in terms of dry mass ratio.

The second treatment liquid is prepared in the presence of sodium hydroxide under an acidic catalyst in a molar ratio of resorcin / formaldehyde = 1 / 0.65 to 100 parts of vinylpyridine-styrene-butadiene latex. 10 parts of a novolak-type precondensate (“Sumicanol 700S” manufactured by Sumitomo Chemical Co., Ltd.) precondensed in (1) was mixed and aged for 24 hours, and 30 parts of the same blocked isocyanate as the first treatment liquid was added. It was prepared by mixing 37 parts of a chlorophenol compound and 23 parts of a triazine compound.

(Example 2)
In Example 1, diphenylmethane-bis-4, 4'-carbamoyl-ε-caprolactam was used instead of diphenylmethane-bis-4, 4'-methylethylketone oxime carbamate only for the blocked isocyanate to be blended in the first treatment liquid. An RFL dip code was prepared in the same manner as in Example 1 except that the above was performed. The amount of the first treatment liquid applied was 1.3% with respect to the aramid fiber cord in terms of dry mass ratio. The amount of the second treatment liquid applied was 8.8% with respect to the aramid fiber cord in terms of dry mass ratio.

(Comparative Example 1)
In Example 1, the cord made of the PPTA fiber complex is treated only with the second treatment liquid without being treated with the first treatment liquid, and the RFL dip code is carried out by the same method as in Example 1. Was produced. The amount of the second treatment liquid applied was 9.5% with respect to the aramid fiber cord in terms of dry mass ratio.

(Comparative Example 2)
In Example 1, instead of the PPTA fiber composite, a polyparaphenylene terephthalamide fiber filament yarn (“Kevlar® 29”, tensile strength 20.3 cN / dtex, tensile modulus) manufactured by Toray DuPont Co., Ltd. An RFL dip code was obtained in the same manner as in Example 1 except that a rate of 490 cN / dtex, a single yarn fineness of 1.65 dtex, and a total fineness of 1,110 dtex) were used. The amount of the first treatment liquid applied was 1.3% with respect to the aramid fiber cord in terms of dry mass ratio. The amount of the second treatment liquid applied was 8.0% with respect to the aramid fiber cord in terms of dry mass ratio.

(Comparative Example 3)
In Comparative Example 2, the treatment with the second treatment liquid was carried out without the treatment with the first treatment liquid, and the RFL dip code was prepared by the same method as in Example 1. The amount of the second treatment liquid applied was 8.8% with respect to the aramid fiber cord in terms of dry mass ratio.

Table 1 shows the evaluation results of the aramid fiber cords obtained in Examples and Comparative Examples.

From Table 1, the raw yarn is heat-resistant bonded by using an aramid fiber composite in which a curable epoxy compound is impregnated into the aramid fiber skeleton and subjecting it to two-component treatment with a first treatment liquid and a second treatment liquid. It can be seen that a remarkable improvement effect is observed in the force and the heat-resistant cloth peeling strength.

Even when the same two-component treatment was applied, the initial adhesive strength and the initial cross peel strength were significantly improved by using the aramid fiber composite for the raw yarn (comparison between Example 1 and Comparative Example 2). Recognize. Further, in order to improve the heat-resistant adhesive strength of the aramid fiber complex (that is, to prevent the rubber and the fiber from peeling off even when exposed to a high temperature), the first method is compared with Example 1 and Comparative Example 1. It can be seen that the treatment liquid contributes.
Compared with the conventional RFL treatment liquid treatment code (Comparative Example 3), the processing code of the present invention is improved in all of the initial adhesive strength, heat-resistant adhesive strength, initial cloth peeling strength, and heat-resistant cloth peeling strength as compared with the conventional product. You can see that there is.

The rubber reinforcing aramid fiber cord of the present invention is useful for reinforcing rubber products that require heat-resistant adhesiveness.

Claims (4)

A rubber reinforcing aramid fiber cord formed by sequentially applying a first treatment liquid and a second treatment liquid having different compositions to form a plurality of adhesive layers.
The aramid fiber is an aramid fiber composite in which a curable epoxy compound is infiltrated into the fiber skeleton .
The first treatment liquid comprises a curable epoxy compound and a blocked isocyanate compound.
The second treatment liquid contains resorcin formaldehyde latex (RFL), blocked isocyanate compound and triazine compound.
Aramid fiber cord for rubber reinforcement with excellent heat resistance and adhesiveness. The rubber reinforcing aramid according to claim 1, wherein the permeation amount of the curable epoxy compound is 0.1 to 2.0% by mass with respect to the fiber mass when the water content of the aramid fiber is converted to 0%. Fiber cord. The aramid fiber cord for rubber reinforcement according to claim 1 or 2 , wherein the epoxy compound permeated into the fiber skeleton and the epoxy compound used in the first treatment liquid are the same compound. The rubber reinforcing aramid fiber cord according to any one of claims 1 to 3, wherein the blocked isocyanate compound used in the first treatment liquid and the second treatment liquid is the same compound.