KR100679327B1 - Resist Composition For Forming Column Spacer of LCD - Google Patents

Abstract

The present invention relates to a resist composition for forming a column spacer of a liquid crystal display device comprising a binder resin, a polyfunctional monomer having an ethylenically unsaturated bond, a photoinitiator and a solvent, and a resin represented by the following general formula (1) is used as the binder resin. According to the present invention, the resist composition including the binder resin represented by the general formula (1) can not only form a column spacer excellent in elasticity and ductility, but also can form a pattern having good residual film rate and stability even at a low exposure amount, thereby increasing productivity. Is improved.

<Formula 1>

LCD, column spacer, resist composition, binder resin, elastic

Description

Resist Composition For Forming Column Spacer of LCD

The present invention relates to a resist composition for forming a column spacer of a liquid crystal display device, and more particularly, to form a column spacer excellent in elasticity and ductility, and to form a pattern having good residual film rate and stability even at a low exposure amount. It relates to a resist composition.

Typically, a liquid crystal display (LCD) is composed of two opposing top and bottom panels, a spacer inserted between the panels and a liquid crystal, and the spacer functions to maintain a cell gap, that is, the thickness of the liquid crystal layer, that is, the gap between the panels. Only when the cell gap is kept constant can the performance of liquid crystal display devices such as high-speed response, high contrast, and wide viewing angle be implemented.

The most widely used spacer forming method is the dispersing and coating of transparent spherical or cylindrical polymethyl methacrylate or silica particles having a diameter slightly larger than the cell gap in the case of notebook panels. Fixed column spacers are used for large panels. The method of applying the particles not only partially aggregates spherical or cylindrical particles when the liquid crystal is injected, but also disperses the particles due to the movement, vibration, or impact of the liquid crystal panel. It is difficult for a constant cell gap to be maintained due to a deviation of the cell gap. Accordingly, the thickness of the liquid crystal layer is uneven, so that the color of the liquid crystal display element changes and the image is distorted. In addition, the alignment film may be scratched to damage the alignment film, and the electrode may be damaged when the upper and lower panel substrates are pressed and sealed. These problems become more serious as the size of liquid crystal display devices such as TFT LCDs increases, or as the use of information terminals such as mobile phones and pagers, mobile communication devices, and vehicle navigation systems increases.

As a method for solving this problem, a method of forming a fixed column spacer using a photocurable composition is used. For example, Korean Patent Publication No. 10-2002-76924 discloses a resist composition for forming a column spacer of a liquid crystal display device, the resist composition comprising a binder resin, a polyfunctional monomer having an ethylenically unsaturated bond, a photoinitiator and a solvent. Is disclosed. Using such a resist composition, it is possible to form a fixed spacer having a constant thickness at regular intervals, there is an advantage that can maintain a uniform cell gap regardless of the external environment.

However, as the number of factories using glass of the fifth generation increases, new problems such as poor gravity when producing a monitor or TV panel requiring a large screen and high image quality are generated. Gravity failure is a phenomenon in which the column spacer deformed by the pressure applied outside the panel does not recover to its initial shape when the panel is manufactured, and thus the liquid crystal in the panel has an uneven distribution due to the influence of gravity. The gravity failure is increasing in severity as the production of large fixed LCDs such as monitors and TVs increases.

On the other hand, as the glass is enlarged, an exposure time is increased when manufacturing the column spacer using the photocurable resist composition, thereby causing another problem of lowering productivity.

Since it is difficult to solve the above-mentioned problem with the resist composition containing the conventional binder resin, the resist composition for liquid crystal display element column spacer formation which can solve the problem of poor gravity and productivity fall is calculated | required.

Accordingly, the technical problem to be achieved by the present invention is to provide a resist composition capable of forming a column spacer having excellent elasticity and ductility, as well as a pattern having a good residual film ratio and stability with a small exposure amount.

In order to achieve the above technical problem, the present invention, in the resist composition for forming a column spacer of a liquid crystal display device comprising a binder resin, a polyfunctional monomer having an ethylenically unsaturated bond, a photoinitiator and a solvent, represented by the general formula 1 as a binder resin The resist composition used provides a resist composition.

<Formula 1>

In the general formula 1, a, b, c, d, e is a mole ratio (mole ratio) of each monomer 0≤a <1, 0≤b <1, 0≤c <1, 0 <d <1, 0 <e <1, where 0 <a + b <1, a + b + c + d + e = 1, and X is independently of each other a hydrogen atom or an alkyl group having 1 to 5 carbon atoms (methyl group, ethyl group, n-propyl group) , Isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, etc.), Y ¹ and Y ² are each independently an alkyl group having 1 to 12 carbon atoms, Cyclic alkyl group, hydroxy alkyl group, benzene group, phenylethyl group, amine, amide, carbamate or alkyl group including urea, Y ³ is an aromatic hydrocarbon (phenyl group, naphthyl group, etc.), Z is 1 carbon It is an alkyl group, a cyclic alkyl group, or an aromatic hydrocarbon (benzene group, a phenylethyl group etc.) which are -24, l, m, and n are the integers of 1-12, respectively, and k is an integer of 0-6.

The resist composition for forming a column spacer of the liquid crystal display device of the present invention may further include a silicon-based compound including an epoxy group or an amine group.

Hereinafter, the resist composition for forming column spacers of the liquid crystal display device of the present invention will be described in detail.

As described above, a resist composition in which a binder resin, a polyfunctional monomer having an ethylenically unsaturated bond, and a photoinitiator is added to a solvent is commonly used to form a column spacer (see Korean Patent Publication No. 10-2002-76924). The present inventors use the resin represented by the general formula (1) as the binder resin used in the resist composition for forming the column spacer, thereby improving the elasticity and ductility when forming the column spacer to reduce the gravity failure, even with a small exposure amount The resist composition which can form the pattern with good stability and greatly improved productivity was developed.

Resin of the general formula 1 is a copolymer of a monomer containing a carboxylic acid and a monomer having a double bond, in formula 1, Y ¹ and Y ² are each independently an alkyl group having 1 to 12 carbon atoms, cyclic As the alkyl group, the hydroxy alkyl group, the benzene group, the phenylethyl group, etc., not only the chemical resistance can be improved, but also the model of the pattern can be controlled and the adhesion can be improved. In addition, unlike conventional binder resins made of acrylic copolymer resins containing an aromatic group, Y ³ can not only increase the residual film ratio by including a bulky substituted group structure, but also increase the glass transition temperature, thereby increasing heat resistance and resistance to heat. It improves chemistry and transparency. On the other hand, the acrylate containing carbamate (carbamate) is introduced into the main chain of the binder resin, the elasticity and ductility is significantly increased. In addition, since a carboxylic acid in the form of a chain including a carboxylic ester is present in the main chain, the degree of curing is increased and developability is improved. The functional group contained in the resin represented by the general formula (1) supplements the multifunctionality in the composition, thereby increasing the degree of curing, improving the elasticity and ductility, and increasing the compatibility with the polyfunctional monomer in the composition, thereby increasing the compatibility with the glass surface. It improves the adhesion of and improves the fracture resistance of the pattern as well as disappears whitening.

The average molecular weight of the resin represented by the general formula (1) is preferably 2,000 to 50,000, the dispersity is 1.0 to 5.0 and the acidity is 30 to 400 KOHmg / g, the average molecular weight is 5,000 to 40,000 and the dispersity is 1.6 to Most preferably, the pH is 3.0 and the acidity is 50 to 150 KOHmg / g.

In the resist composition for forming a column spacer of the liquid crystal display device of the present invention, a preferred amount of binder resin is 5 to 30% by weight based on the total weight of the composition.

 A silicon compound containing an epoxy group or an amine group may be further added to the resist composition for forming a column spacer of the liquid crystal display device of the present invention. When the silicone-based additive having an epoxy group or an amine group is added, the adhesion between the ITO electrode and the resist composition is further improved, and the heat resistance property after curing is also improved. Such silicone compounds include (3-glycidoxypropyl) trimethoxy (ethoxy) silane (3-glycidoxypropyl) methyldimethoxy (ethoxy) silane, (3-glycidoxypropyl) dimethyldimethyl Oxy (ethoxy) silane, 3,4-epoxybutyltrimethoxy (ethoxy) silane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxy (ethoxy) silane, N- (2 -Aminoethyl) -3-aminopropyldimethoxymethylsilane, (3-aminopropyl) trimethoxysilane, (3-aminopropyl) triethoxysilane, (3-mercaptopropyl) trimethoxysilane Phosphorus, (N, N-diethyl-3-aminopropyl) trimethoxysilane, N-beta (aminoethyl) gamma-aminopropyltrimethoxysilane, and the like, each of which can be used alone or in combination thereof. Can be used. The preferred content for the addition of silicone-based additives having epoxy or amine groups is 0.001 to 0.1% by weight, based on the total weight of the composition.

The above-mentioned binder resin is formed by adding a solvent together with a polyfunctional monomer having an ethylenically unsaturated bond and a photoinitiator to form a resist composition, spin coating the substrate onto the substrate, irradiating ultraviolet rays with a mask, and developing with an alkaline developer. To form a spacer.

As the polyfunctional monomer having an ethylenically unsaturated bond contained in the resist composition of the present invention, a polymerizable compound having an ethylenically unsaturated bond used in a conventional photosensitive composition can be used. For example, ethylene glycol di (meth) acryl Polyethylene glycol di (meth) acrylate, trimethylolpropanedi (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, penta, wherein the number of ethylene oxide groups is 2 to 14; Polyhydric alcohols such as erythritol tetra (meth) acrylate, propylene glycol di (meth) acrylate having a number of propylene oxide groups of 2 to 14, dipentaerythritol penta (meth) acrylate and dipentaerythritol hexa (meth) acrylate; compounds obtained by esterifying α, β-unsaturated carboxylic acids; Compounds obtained by adding (meth) acrylic acid to glycidyl group-containing compounds such as trimethylolpropanetriglycidyl ether acrylic acid adduct and bisphenol A diglycidyl ether acrylic acid adduct; ester compounds of a compound having a hydroxyl group and an ethylenically unsaturated bond, such as a phthalic acid diester of β-hydroxyethyl (meth) acrylate, a toluene diisocyanate adduct of β-hydroxyethyl (meth) acrylate, or a polyhydric carboxylic acid, or Adducts with polyisocyanates; (Meth) acrylic-acid alkylesters, such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate, etc. are mentioned, In addition, ditrimethylol propane Tetraacrylate, tris (2-acryloxyethyl) isocyanurate, ethoxylated pendaerythritol tetraacrylate (EO 4 mol), pendaerythritol tetraacrylate (EO 35 mol), ethoxylated trimethylolpropane Triacrylate (9 moles of EO), ethoxylated trimethylolpropane triacrylate (3 moles of EO), proticated pentaerythritol tetraacrylate (PO 4 moles), nonaethylene glycol diacrylate, dipentaerythritol hexa Acrylate modified caprolactone, trimethylolpropane propoxylate triacrylate, and the like. Of course, these can be used individually or in mixture of 2 or more types of these, of course. The preferred amount of the polyfunctional monomer having an ethylenically unsaturated bond is 5 to 35% by weight based on the total weight of the composition.

In addition, as a photoinitiator, a photoinitiator which is commonly used may be used, and acetophenone-based or benzophenone-based photoinitiators are usually used. When the photoinitiator itself has a color, the transparency is lowered. Therefore, high transparency can be achieved by using an appropriate sensitivity in the wavelength band used during exposure and having no color in the photoinitiator itself. In general, the photoinitiator of the crosslinking reaction using an acrylic multifunctional monomer is used according to the wavelength of the ultraviolet ray used. The mercury lamp, which is the most widely used ultraviolet ray, has a wavelength in the range of 310 to 420 nm, and generates radicals in this wavelength range. Use photoinitiators.

Such photoinitiators include benzophenone-based and triazine-based photoinitiators such as Irgacure 369, Irgacure 907, CGI 124, and CGI 242 EPD / BMS mixed systems. For example, benzophenone, phenylbiphenylketone, 1-hydroxy-1- Benzoylcyclohexane, benzyl, benzyldimethyl ketal, 1-benzyl-1-dimethylamino-1- (4-morpholino-benzoyl) propane, 2-morpholinyl-2- (4-methylmercapto) benzoylpropane, cheo Xanthone, 1-chloro-4- hydroxythioxanthone, isopropylthioxanthone, diethyl thioxanthone, ethyl anthraquinone, 4-benzoyl-4-methyldiphenylsulfide, benzoin butyl ether, 2-hydroxy- 2-benzoylpropane, 2-hydroxy-2- (4-isopropyl) benzoylpropane, 4-butylbenzoyltrichloromethane, 4-phenoxybenzoyldichloromethane, methyl benzoyl formate, 1,7-bis (9-arc Ridinyl) heptane, 9-n-butyl-3,6-bis (2-morpholino-isobutyloyl) carbazole, diphenyl (2,4,6-trimethylbenzoyl) -phosphine oxide, 10- Butyl-2-chloro Loacridone, 4,4′-bis (diethylamino) -benzophenone, 2- [2- (4-methoxy-phenyl) -vinyl] -4,6-bis-trichloromethyl- [1,3, 5] triazine, 2- (4-methoxy-naphthalen-1-yl) -4,6-bis-trichloromethyl- [1,3,5] triazine, 2-benzo [1,3] di Oxol-5-yl-4,6-bis-trichloromethyl- [1,3,5] triazine, 2-methyl-4,6-bis (trichloromethyl) -s-triazine, 2-phenyl- 4,6-bis (trichloromethyl) -s-triazine, 2-naphthyl-4,6-bis (trichloromethyl) -s-triazine, etc. are used alone or in combination of two or more thereof. It is preferable. The preferred addition amount of photoinitiator is 0.1 to 10% by weight, based on the total weight of the composition.

On the other hand, the solvent added to the resist composition of the present invention may also be used a solvent commonly used, considering the compatibility with binder resins, polyfunctional monomers having ethylenically unsaturated bonds, photoinitiators and other compounds, diethylene glycol dimethyl Ether (DMC), diethylene glycol methyl ethyl ether (MEC), methyl methoxy propionate, ethyl ethoxy propionate (EEP), ethyl lactate, propylene glycol methyl ether acetate (PGMEA), propylene glycol methyl ether , Propylene glycol propyl ether, methyl cellosolve acetate, ethyl cellosolve acetate, diethylene glycol methyl acetate, diethylene glycol ethyl acetate, methyl isobutyl ketone, cyclohexanone, dimethyl formamide (DMF), N, N- Dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), gamma-butyrolactone, diglyme, methylcellosolve, Cellosolve tilsel to, diethylene glycol methyl ether, diethylene glycol ethyl ether, dipropylene glycol methyl ether and the like it is preferred to use them alone or in a mixture of two or more of the. The solvent is preferably added so that the viscosity of the resist composition is in the range of 3 to 35 cps, and more preferably, adjusting the viscosity to be 5 to 25 cps results in no pin hole of the thin film after coating and the thickness of the cell gap. It is more advantageous to produce a coating layer that can be maintained at a thickness of 2 to 10 μm.

 In the resist composition for forming a column spacer of the liquid crystal display device of the present invention, any other known solvent having a compatibility such as a photosensitizer, a thermal polymerization inhibitor, an antifoaming agent, a leveling agent, etc. within the range not impairing the object of the present invention as necessary. Of course, additives can be added.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

<Preparation of resin represented by General formula 1>

Table 1 shows the resin compounds corresponding to the general formula (1). The average molecular weights of the resin compounds listed in Table 1 were about 17,000 to 24,000, the dispersity was about 2.0 to 2.5, and the acidity was about 103 to 116.

Resin of the general formula 1 was synthesized as follows.

Synthesis of Formula 1c

125.5 g of monomer benzyl methacrylate, 121.5 g of glycidyl methacrylate, 55.6 g of 2-hydroxyethyl methacrylate, and 73.6 g of methacrylic acid were 14 g of azobis isobutyronitrile (AIBN) and di 610 g of ethylelglycol dimethyl ether was added to a polymerization tank, and stirred at 80 ° C. for 5 hours to obtain a solution of 1000 g of a raw material polymer.

100 g of the solution was added, 6.63 g of 2-methacryloyloxyethyl isocyanate (MOI) and 0.9 g of dibutyl tin dilaurate were added and stirred at room temperature for 3 hours, followed by 10 minutes of 0.01 g of hydroquinone. Was stirred again to obtain a resin of the general formula 1c.

Obtained resin had an average molecular weight of 21,000, a distribution degree of 2.3, and an acidity of 104.

Synthesis of General Formula 1g

13 g of azobisisobutyronitrile (AIBN) 146.6 g of monomeric dicyclopentanyl methacrylate, 117.3 g of glycidyl methacrylate, 34.7 g of 2-hydroxyethyl methacrylate and 77.9 g of metaalcrylic acid And 610 g of diethyleleglycol dimethyl ether were charged, and the mixture was stirred at 80 ° C for 5 hours to obtain a solution of 1000 g of a raw material polymer.

100 g of the solution was added, 4.13 g of 2-methacryloyloxyethyl isocyanate (MOI) and 0.54 g of dibutyl tin dilaurate were added and stirred at room temperature for 3 hours, followed by 10 minutes of 0.01 g of hydroquinone. Was stirred again to obtain a resin of the general formula 1g.

Obtained resin had an average molecular weight of 18,000, a distribution degree of 2.1 and an acidity of 115.

Synthesis of General Formula 1h

109 g of monomeric dicyclopentanyl methacrylate, 123.1 g of glycidyl methacrylate, and 144.9 g of 2-hydroxyethyl methacrylate are 13 g of azobisisobutyronitrile (AIBN) and 610.1 g of diethylell glycol dimethyl ether. It put in this superposition | polymerization tank, it stirred at 80 degreeC for 5 hours, and obtained the solution of 1000 g of raw material polymer.

100 g of the solution was added, 10.8 g of 2-methacryloyloxyethyl isocyanate (MOI) and 1.4 g of dibutyl tin dilaurate were added and stirred at room temperature for 3 hours, followed by 10 minutes of 0.01 g of hydroquinone. Then, the mixture was stirred again, and then 7.76 g of trimellitic anhydride was added, 0.06 g of dimethylaminopyridine and 0.03 g of triethylamine were added, followed by stirring at room temperature for 24 hours to obtain a resin of the general formula 1h.

The average molecular weight of the obtained resin was 22,000, the degree of distribution was 2.4, and the acidity was 110.5.

Since the resin synthesis method of another general formula 1 can be easily derived from the above-mentioned synthesis method, description is abbreviate | omitted.

<Examples 1 to 17>

A resist composition was prepared according to the composition and content shown in Table 2 below in a reaction mixing tank equipped with a UV blocking film and a stirrer, and stirred at room temperature, and a solvent was added to the composition to form a column spacer of a liquid crystal display device having a viscosity of about 16 cps. A resist composition was prepared.

In Table 2 above,

DPHA: dipentaerythritol hexaacrylate

UA-4:

A-187: (3-glycidoxypropyl) trimethoxysilane

A-1120: N- (2-aminoethyl) -3-aminopropyldimethoxymethylsilane

I-907: Irgacure 907

CGI-124: Ciba Products

DETX: Diethylthioxanthone

Leveling agent: R-08 from DIC Corporation was used.

<Comparative Examples 1 to 4>

Examples 1 to 4 (Comparative Example 1-Example 1, Comparative Example 2-Example 2, except that binder resin (average molecular weight 30,000) represented by the following formula (2) instead of the binder resin of Example 1 was used ...) and a resist composition for forming a column spacer of the liquid crystal display device with the same components and content.

<Formula 2>

In Formula 2, o is 0.52, p is 0.3, q is 0.08, r is 0.1.

In the above Examples and Comparative Examples, the evaluation of the resist composition was carried out on a substrate such as a silicon wafer or a glass plate to evaluate the performance, and the results are shown in Table 3 below.

(1) flatness

The resist composition was applied onto the substrate using a spin coater at a speed of 600 rpm for 13 seconds, then prebaked at 90 ° C. for 3 minutes and exposed at 100 mJ, followed by postbake at 220 ° C. for 30 minutes. A resist film was formed. The thickness of the resist film formed on the silicon wafer or the glass plate was measured at 25 different locations using a thickness measuring device to determine the difference between the maximum thickness and the minimum thickness.

(2) residual film rate

The resist composition for the column spacer was spin-coated on a substrate, and the thickness after pre-baking and post-baking to remove the solvent to measure the thickness ratio (%) of the formed film.

(3) limit exposure dose measurement

The resist composition was applied onto a silicon wafer for 13 seconds at a speed of 600 rpm using a spin coater, then prebaked at 90 ° C. for 3 minutes, exposed using a step mask, and then developed with KOH developer and developed at 220 ° C. Postbake was carried out for 30 minutes to form a resist film. The exposure amount in which the pattern in which the pattern CD did not increase by 15% or more without remaining film remaining on the wafer surface and the film not being reduced was determined as the threshold exposure amount.

(4) pattern stability

The silicon wafer in which the resist pattern was formed was cut from the vertical direction of the line pattern, and the result observed by the electron microscope in the cross-sectional direction of the pattern was shown. It was determined that the film was not reduced as 'good', and that the reduction of the film was recognized as 'film'.

(5) elastic recovery rate and ductility

After pressing the resist pattern with the indenter for 5 seconds with a force of 40mN, measure the depth (A) with the indenter, and measure the depth (B) when the force was removed. ) / A) was calculated as elastic recovery rate, initial depth (A).

In Table 3 above, "not measurable" means that a limit exposure amount cannot be measured because no residual film remains on the wafer surface and a pattern is not formed in which the pattern CD does not increase by 15% or more without decreasing the film.

As described above, the resist composition including the binder resin represented by Formula 1 according to the present invention can not only form a column spacer excellent in elasticity and ductility, but also form a pattern with a uniform and proper thickness even with a small exposure amount. The remaining film ratio and pattern stability are good. Therefore, when the column spacer is formed using the resist composition of the present invention, it is possible to prevent the change of the cell gap due to the movement, vibration, impact, gravity, etc. of the liquid crystal panel, and to reduce the exposure time, thereby greatly improving the productivity.

Claims (6)

A resist composition for forming a column spacer of a liquid crystal display device comprising a binder resin, a polyfunctional monomer having an ethylenically unsaturated bond, a photoinitiator, and a solvent, wherein the binder resin is a resin represented by the following general formula (1): A resist composition for forming column spacers of the device; <Formula 1>

In the general formula 1, a, b, c, d, e is a mole ratio (mole ratio) of each monomer 0≤a <1, 0≤b <1, 0≤c <1, 0 <d <1, 0 <e <1, where 0 <a + b <1, a + b + c + d + e = 1, X is independently of each other a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and Y ¹ and Y ² are each Independently selected from the group consisting of an alkyl group having 1 to 12 carbon atoms, a cyclic alkyl group, a hydroxy alkyl group, a benzene group, a phenylethyl group, an amine, an amide, a carbamate or an urea, or an alkenyl group; ³ is an aromatic hydrocarbon, Z is any one selected from the group consisting of an alkyl group having 1 to 24 carbon atoms, a cyclic alkyl group and an aromatic hydrocarbon, l, m and n are each an integer of 1 to 12, k is 0 to 6 Integer of. The column spacer of claim 1, wherein the average molecular weight of the resin represented by Formula 1 is 2,000 to 50,000, the dispersity is 1.0 to 5.0, and the acidity is 30 to 400 KOHmg / g. Formation resist composition. The resist composition for forming a column spacer of a liquid crystal display device according to claim 1, further comprising a silicon compound containing an epoxy group or an amine group. The content of the binder resin is 5 to 30% by weight based on the total weight of the composition, the content of the polyfunctional monomer having an ethylenically unsaturated bond is 5 to 35% by weight, the content of the photoinitiator is 0.1 to 10 A resist composition for forming a column spacer of a liquid crystal display device, characterized in that the weight%. The resist composition for forming a column spacer of a liquid crystal display device according to claim 4, further comprising 0.001 to 0.1% by weight of a silicon compound containing an epoxy group or an amine group. The resist composition for forming a column spacer of a liquid crystal display device according to claim 4, wherein the solvent is added so that the viscosity of the composition is 3 to 35 cps.