KR20180027158A - Thermal conductive adhesives having graphite and zinc oxide, and preparation method thereof - Google Patents

Abstract

The present invention relates to a thermal conductive adhesive having graphite and zinc oxide, and a manufacturing method thereof. According to the present invention, the thermal conductive adhesive uses a mixture of artificial graphite and zinc oxide at a specific mixing ratio, thereby having improved heat radiation (vertical thermal conductivity) characteristics. Furthermore, when the zinc oxide is replaced with tetragonal zinc oxide, the heat radiation (vertical thermal conductivity) characteristics are further improved.

Description

TECHNICAL FIELD [0001] The present invention relates to a thermally conductive adhesive containing graphite and zinc oxide and a method of manufacturing the same,

The present invention relates to a thermally conductive adhesive containing graphite and zinc oxide and a method of producing the same.

Recently, due to the high performance, miniaturization and high performance of electronic devices including LED lighting, the amount of heat generated by the electronic components circuit is increased. As a result, the internal temperature of the device rises and malfunctions of the semiconductor devices, characteristics of the resistor components, Problems are occurring. Accordingly, various technologies have been developed as heat dissipation measures for solving such problems.

Conventionally developed heat dissipation measures include a method of installing a heat sink or a heat sink and a method of inserting a heat transfer material such as a thermal grease, a heat radiation pad, a heat radiation tape or the like between a heat source and a heat sink have.

However, in the conventional heat dissipating method, only the heat generated from the heat source is transferred to the heat sink, and the heat accumulated in the heat sink is not discharged into the air. Furthermore, in order to protect the heat source, the heat sink, and the heat sink of the electronic product, the liquid coating material is coated on the surface thereof. In this case, the coating film interferes with the heat emission of the object, .

On the other hand, the thermal conductivity of general epoxy resin is very low (0.15 ~ 0.3 W / mK) compared to metal and ceramic. For this reason, gas has been combined (formed into a foam) in a polymer matrix and used as a heat insulating material in various fields. However, attention has been focused on high thermal conductivity characteristics of polymer composite materials, paying attention to materials having excellent heat conduction characteristics as well as electric insulation, moisture absorption, workability, corrosion resistance, and the like, .

The technology using epoxy resin is widely used in the field of electronic parts. The development of complex polymeric materials such as thermoconductive grease, thermally conductive adhesive, and thermally conductive sheet has been developed in order to lower the contact thermal resistance between the surface where the metal and the ceramic are in contact and the part where the electronic component is attached. The thermally conductive grease helps heat conduction of metal parts such as heat exchangers and the thermally conductive adhesive is mainly used for bonding the cooling fin to the metal as the main body. The heat conductive sheet is sandwiched between the power transistor and the substrate, . In recent years, electronic products such as notebook computers and mobile phones have become more highly integrated and have a tendency to have high output specifications. In addition, as the substrate is becoming smaller and smaller, a large amount of heat is generated during operation of the apparatus. Which is a significant influence on the performance. Therefore, the heat dissipation problem of advanced electronic devices is becoming an important issue in product development for increasing the stability and reliability of the device more and more.

Accordingly, the inventors of the present invention have been studying thermally conductive adhesives having excellent thermal conductivity, and it has been found that the use of artificial graphite and zinc oxide in a specific mixing ratio improves heat radiation (vertical thermal conductivity) characteristics, (Vertical thermal conductivity) property is further improved by replacing the tetrahedral zinc oxide with tetragonal zinc oxide. The present invention has been completed based on this finding.

Korean Patent No. 10-1447258

It is an object of the present invention to provide a thermally conductive adhesive containing graphite and zinc oxide.

Another object of the present invention is to provide a thermally conductive adhesive comprising zinc oxide in the form of graphite and tetrapod.

It is still another object of the present invention to provide a method for producing a thermally conductive adhesive containing graphite and zinc oxide.

Another object of the present invention is to provide a method for producing a thermally conductive adhesive containing graphite and tetrafluoride zinc oxide.

In order to achieve the above object,

The present invention relates to a resin composition comprising 17-18 parts by weight of a polymer resin;

2 to 3 parts by weight of a curing agent;

20 to 70 parts by weight of artificial graphite; And

10 to 60 parts by weight of zinc oxide;

And a thermally conductive adhesive.

Also, the present invention relates to a resin composition comprising 17-18 parts by weight of a polymer resin;

2 to 3 parts by weight of a curing agent;

20 to 70 parts by weight of artificial graphite; And

10 to 60 parts by weight of zinc oxide in the form of tetrapods;

And a thermally conductive adhesive.

Further, the present invention provides a method for producing a polyester resin composition, which comprises: (1) irradiating ultrasonic waves while mixing 17-18 parts by weight of a polymer resin, 20-70 parts by weight of artificial graphite and 10-60 parts by weight of zinc oxide for 10-14 hours;

Stirring the mixture of step 1 in an oil bath at 40-60 DEG C for 22-26 hours (step 2); And

Adding 2 to 3 parts by weight of a curing agent to the mixture of step 2, stirring and curing in an oven at 60 to 80 DEG C for 1 to 3 hours (step 3);

The present invention also provides a method for producing the thermally conductive adhesive.

In addition, the present invention provides a method for producing zinc oxide, comprising the steps of: (1) preparing zinc oxide in the form of tetrapods by heat treating the zinc powder in an oven at 950-1050 캜 for 60-120 minutes;

17 to 18 parts by weight of polymer resin, 20 to 70 parts by weight of artificial graphite and 10 to 60 parts by weight of tetrafluoro zinc oxide are mixed for 10 to 14 hours (step 2);

Stirring the mixture of step 2 in an oil bath at 40-60 DEG C for 22-26 hours (step 3); And

Adding 3 to 2 parts by weight of a curing agent to the mixture of step 3, stirring and curing in an oven at 60 to 80 DEG C for 1 to 3 hours (step 4);

The present invention also provides a method for producing a thermally conductive adhesive.

The thermally conductive adhesive according to the present invention has an effect of improving heat radiation (vertical thermal conductivity) characteristics by using artificial graphite and zinc oxide in a specific mixing ratio, and further, when zinc oxide is replaced with zinc oxide in the tetrapod form And the heat dissipation (vertical thermal conductivity) characteristics are further improved.

Fig. 1 is an SEM image of artificial graphite (a), ZnO (b), and T-ZnO (c).
2 is a graph showing the results of measurement of vertical thermal conductivity of the thermally conductive adhesive manufactured in Examples 1-1 to 1-6.
3 is a graph showing the results of measurement of vertical thermal conductivity of the thermally conductive adhesive prepared in Examples 2-1 to 2-6.

Unless defined otherwise, all technical terms used in the present invention have the following definitions and are consistent with the meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In addition, preferred methods or samples are described in this specification, but similar or equivalent ones are also included in the scope of the present invention. The contents of all publications referred to herein are incorporated herein by reference.

The term "about" is used herein to refer to a reference quantity, a level, a value, a number, a frequency, a percentage, a dimension, a size, a quantity, a weight or a length of 30, 25, 20, 25, 10, 9, 8, 7, Level, value, number, frequency, percentage, dimension, size, quantity, weight or length of a variable, such as 4, 3, 2 or 1%.

Throughout this specification, the words "comprises" and "comprising ", unless the context requires otherwise, include the steps or components, or groups of steps or elements, Steps, or groups of elements are not excluded.

Hereinafter, the present invention will be described in detail.

Artificial graphite ( pGr ) And zinc oxide ( ZnO ) include Thermal conductivity  glue

The present invention relates to a resin composition comprising 17-18 parts by weight of a polymer resin;

2 to 3 parts by weight of a curing agent;

20 to 70 parts by weight of artificial graphite; And

10 to 60 parts by weight of zinc oxide;

And a thermally conductive adhesive.

In the ZnO-containing adhesive according to the present invention, a small amount of a dispersion solvent may be further contained. As the dispersion solvent, toluene, methyl ethyl ketone (MEK), xylene, hexane, ethyl acetate, butanol, diethyl ether, ethyl cellulose and the like may be used singly or in combination. Preferably, MEK / toluene mixed solvent Can be used.

In the ZnO-containing adhesive according to the present invention, the mixing weight ratio of the zinc oxide and the artificial graphite to the thermally conductive filler is preferably 15-25: 55-65, more preferably 19-21: 59-61, Especially preferably 20:60 can be used. Here, the artificial graphite has an average particle size of 18-22 占 퐉 and the zinc oxide has an average particle size of 0.2-0.8 占 퐉.

In the ZnO-containing adhesive according to the present invention, the polymer resin may be an epoxy resin, an acrylic resin, a copolymer or a composite thereof, or the like.

Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolak type epoxy resin, cresol novolak type epoxy resin, alkylphenol novolak type epoxy resin, bisphenol type epoxy resin, Type epoxy resin, dicyclopentadiene type epoxy resin, triglycidyl isocyanate epoxy resin, and acyclic epoxy resin. In the present invention, bisphenol A epichlorohydrin epoxy is used as the bisphenol A type epoxy resin .

As the acrylic resin, an olefin resin, a polyurethane resin, a cyanoacrylate resin, an isocyanate resin, an acrylic copolymer, and methyl methacrylate can be used.

In the ZnO-containing adhesive according to the present invention, the curing agent is not particularly limited so long as it serves to facilitate rapid curing of the coating composition.

Examples of the curing agent suitable for the epoxy resin include an amine curing agent, an imidazole curing agent, an acid anhydride curing agent, or a mixture thereof.

Examples of the amine curing agent include linear amines, aliphatic amines, modified aliphatic amines, aromatic amines, secondary amines, and tertiary amines, and examples thereof include benzyldimethylamine, triethanolamine, triethylamine, Diethylenetriamine, triethylenamine, dimethylaminoethanol, tri (dimethylaminomethyl) phenol, and the like.

Examples of the imidazole-based curing agent include imidazole, isoimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2,4-dimethylimidazole, butylimidazole, 2- Undecenedimidazole, 1-vinyl-2-methylimidazole, 2-n-heptadecylimidazole, 2-undecylimidazole 2-methylimidazole, 1-cyanoethyl-2-methylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl- Methylimidazole, adduct of imidazole and methylimidazole, adduct of imidazole and trimellitic acid, 2-n-heptadecyl-4-methylimidazole, phenylimidazole, Benzylimidazole, 2-methyl-4,5-diphenylimidazole, 2,3,5-triphenylimidazole, 2-styrylimidazole, 1- (dodecylbenzyl) already 2- (2-methoxyphenyl) -4,5-diphenylimidazole, 2- (2-hydroxyphenyl) -4,5- (3-hydroxyphenyl) -4,5-diphenylimidazole, 2- (p-dimethyl-aminophenyl) -4,5-diphenylimidazole, 2- Diphenylimidazole, di (4,5-diphenyl-2-imidazole) -benzene-1,4,2-naphthyl-4,5-diphenylimidazole, 1-benzyl- -Methylimidazole and 2-p-methoxystyrylimidazole, and the like.

Examples of the acid anhydride-based curing agent include phthalic anhydride, maleic anhydride, trimellitic anhydride, pyromellitic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, methylnadic anhydride, nadic anhydride, And an anhydride-based curing agent. The acid anhydride-based curing agent is preferably used as a catalyst rather than being used alone.

Examples of the curing agent suitable for the acrylic resin include phenol-based, epoxy-based, cyanoacrylate, and polyester acrylate.

Artificial graphite ( pGr ) And Tetrapod  Shaped zinc oxide (T- ZnO ) include Thermal conductivity  glue

The present invention relates to a resin composition comprising 17-18 parts by weight of a polymer resin;

2 to 3 parts by weight of a curing agent;

20 to 70 parts by weight of artificial graphite; And

10 to 60 parts by weight of zinc oxide in the form of tetrapods;

And a thermally conductive adhesive.

In the T-ZnO-containing adhesive according to the present invention, the tetragonal zinc oxide may be obtained by heat treating the zinc powder in an oven at 950-1050 ° C for 60-120 minutes.

In the T-ZnO-containing adhesive according to the present invention, a small amount of a dispersion solvent may be further contained. Examples of the dispersion solvent are as described above.

In the T-ZnO-containing adhesive according to the present invention, the mixing weight ratio of the zinc oxide and the artificial graphite to the thermally conductive filler is preferably 15-25: 55-65, more preferably 19-21: 59- 61, particularly preferably 20:60. Here, the artificial graphite has an average particle size of 18-22 占 퐉, and the tetrade-shaped zinc oxide has an average particle size of 5-20 占 퐉.

In the adhesive containing T-ZnO according to the present invention, examples of the polymer resin are as described above.

In the T-ZnO-containing adhesive according to the present invention, examples of the curing agent are as described above.

ZnO  include Thermal conductivity  Method of manufacturing adhesive

The present invention relates to a method for producing a polyester resin composition, which comprises: (1) irradiating ultrasonic waves while mixing 17-18 parts by weight of a polymer resin, 20-70 parts by weight of artificial graphite and 10-60 parts by weight of zinc oxide for 10-14 hours;

Stirring the mixture of step 1 in an oil bath at 40-60 DEG C for 22-26 hours (step 2); And

Adding 2 to 3 parts by weight of a curing agent to the mixture of step 2, stirring and curing in an oven at 60 to 80 DEG C for 1 to 3 hours (step 3);

The present invention also provides a method for producing a thermally conductive adhesive.

In the manufacturing method according to the present invention, mixing of the components can be smoothly performed by irradiating ultrasonic waves in the step 1. In this step, at least one dispersion solvent selected from the group consisting of toluene, methyl ethyl ketone, xylene, hexane, ethyl acetate, butanol, diethyl ether and ethyl cellulose may be further added.

The thermally conductive adhesive according to the present invention can be manufactured in the form of an adhesive film on a release paper, but is not limited thereto.

T- ZnO  include Thermal conductivity  Method of manufacturing adhesive

The present invention provides a method for preparing zinc oxide, comprising the steps of: (1) preparing zinc oxide in the form of tetrapods by heat treating the zinc powder in an oven at 950-1050 캜 for 60-120 minutes;

17 to 18 parts by weight of polymer resin, 20 to 70 parts by weight of artificial graphite and 10 to 60 parts by weight of tetrafluoro zinc oxide are mixed for 10 to 14 hours (step 2);

Stirring the mixture of step 2 in an oil bath at 40-60 DEG C for 22-26 hours (step 3); And

Adding 3 to 2 parts by weight of a curing agent to the mixture of step 3, stirring and curing in an oven at 60 to 80 DEG C for 1 to 3 hours (step 4);

The present invention also provides a method for producing a thermally conductive adhesive.

In the manufacturing method according to the present invention, the step 1 is a step of preparing zinc tetrahedral zinc oxide by heat treating the zinc powder in an oven at 950-1050 ° C for 60-120 minutes. In the present invention, the thermal conductivity of tetragonal zinc oxide (T-ZnO) is more excellent than that of zinc oxide (ZnO).

In the manufacturing method according to the present invention, mixing of constituent components can be smoothly performed by irradiating ultrasonic waves in the step 2. In this step, at least one dispersing solvent selected from the group consisting of toluene, methyl ethyl ketone, xylene, hexane, ethyl acetate, butanol, diethyl ether and ethyl cellulose may be further added.

The thermally conductive adhesive according to the present invention can be manufactured in the form of an adhesive film on a release paper, but is not limited thereto.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are illustrative of the present invention, and the present invention is not limited by the following examples.

< Example  1-1 to 1-6> zinc oxide ( ZnO ) And artificial graphite ( pGr ) include Thermal conductivity  Manufacture of adhesives

Thermally conductive filler 1: zinc oxide (ZnO) (particle size 0.5 탆)

Thermally conductive filler 2: artificial graphite (pGr) (particle size size 20 탆)

Resin: bisphenol A epichlorohydrin epoxy resin (MW ≥ 700, manufacturer: Struers, model name: Epofix)

Hardener: triethyltetramine (TETA)

Dispersion solvent: MEK (methylethylketone) / Toluene (1/1 to 3/1 v / v )

The mixed content was mixed with 20 wt% of the total of the thermally conductive fillers 1 and 2 in an amount of 80 wt%, the resin (8 g) and the curing agent (1 g), and further X mL of the dispersion solvent was added.

The mixing procedure was conducted by irradiating ultrasonic waves while mixing the thermally conductive fillers 1 and 2 and the resin for 12 hours, followed by stirring in a 50 ° C oil bath for 24 hours via a mechanical stirrer. At this time, a small amount of a dispersion solvent was added to aid dispersion of the fillers. Next, triethyltetramine (TETA) was added to the mixture so as to prevent the formation of bubbles, followed by curing in an oven at 70 ° C for 2 hours to prepare a thermally conductive adhesive.

< Example  2-1 to 2-6> Tetrapod  Shaped zinc oxide (T- ZnO ) And artificial graphite (pGr) Thermal conductivity  Manufacture of adhesives

A thermally conductive adhesive was produced in the same manner as in Examples 1-1 to 1-6, except that tetragonal zinc oxide (T-ZnO) (particle size: 5-20 μm) was used as the thermally conductive filler 1 .

Here, the tetragonal zinc oxide (T-ZnO) was prepared and used as follows. Specifically, 1 g of zinc powder was placed in a crucible (200 mL) and heat treated in an oven at 1000 ° C for 60-120 minutes to prepare tetrapod-shaped zinc oxide (T-ZnO).

FIG. 1 shows an image of artificial graphite (a), ZnO (b), and T-ZnO (c) photographed by SEM.

< Experimental Example  1> Thermal conductivity filler  Evaluation of vertical (thickness direction) heat dissipation characteristics of each component

The vertical heat radiation characteristics of the thermally conductive adhesive prepared in the same manner as in Example 1 were evaluated, except that 80% by weight of the single composition shown in Table 1 below was used as the thermally conductive filler.

 filler 80% Cp
(J / g * K) Density
(g / cm ³⁾ out thermal diffusivity
(mm ² / s) out thermal conductivity
(W / m * K) pGr 0.903 1.541 1.411 1.964 ZnO 0.917 1.846 0.383 0.648 T-ZnO 0.917 1.685 0.696 1.075

As shown in Table 1, the thermal conductivity of T-ZnO was improved about 65% as compared with ZnO.

< Experimental Example  2> Thermal conductivity  Evaluation of vertical (thickness direction) heat dissipation characteristics of adhesive 1

The vertical heat dissipation characteristics of the thermally conductive adhesive prepared in Examples 1-1 to 1-6 prepared by using 80% by weight of the sum of the thermally conductive fillers 1 and 2 shown in the following Table 2 were evaluated. The results are shown in Table 2 below.

2 is a graph showing the results of measurement of vertical thermal conductivity of the thermally conductive adhesive manufactured in Examples 1-1 to 1-6.

Example ZnO / pGr
(weight%) Cp
(J / g * K) Density (g / cm ³ ) out thermal diffusivity
(mm ² / s) out thermal conductivity
(W / m * K) 1-1 10/70 0.9048 1.75 1.103 1.746 1-2 20/60 0.9066 1.71 1.433 2.221 1-3 30/50 0.9084 1.75 1.159 1.843 1-4 40/40 0.9102 1.76 1.047 1.678 1-5 50/30 0.912 1.78 0.941 1.527 1-6 60/20 0.9138 1.71 0.712 1.112

As shown in Table 2, the vertical thermal conductivity of Example 1-2 was higher than that of artificial graphite alone in Table 1. On the other hand, the thermal conductivity was greatly influenced by the mixing ratio of ZnO / pGr, and it was found that the vertical thermal conductivity was the best in the mixing ratio (ZnO / pGr = 20/60 wt%) of Example 1-2.

< Experimental Example  3> Thermal conductivity  Evaluation of vertical (thickness direction) heat dissipation characteristics of adhesive 2

The vertical heat radiation characteristics of the thermally conductive adhesives prepared in Examples 2-1 to 2-6 prepared by using 80% by weight of the sum of the thermally conductive fillers 1 and 2 shown in the following Table 3 were evaluated. Table 3 shows the results.

3 is a graph showing the results of measurement of vertical thermal conductivity of the thermally conductive adhesive prepared in Examples 2-1 to 2-6.

Example T-ZnO / pGr
(weight%) Cp
(J / g * K) Density (g / cm ³ ) out thermal diffusivity
(mm ² / s) out thermal conductivity
(W / m * K) 2-1 10/70 0.9048 1.812 1.223 2.005 2-2 20/60 0.9066 1.797 1.702 2.772 2-3 30/50 0.9084 1.809 1.404 2.307 2-4 40/40 0.9102 1.849 1.322 2.224 2-5 50/30 0.9120 1.841 1.178 1.977 2-6 60/20 0.9138 1.851 0.774 1.309

As shown in Table 3, the vertical thermal conductivities of Examples 2-1 to 2-6 using T-ZnO were higher than those of Examples 1-1 to 1-6 using ordinary ZnO. On the other hand, the thermal conductivity was greatly influenced by the mixing ratio of T-ZnO / pGr, and the vertical thermal conductivity was the best in the mixing ratio (T-ZnO / pGr = 20/60 wt%) of Example 2-2 Could know.

Claims (14)

17 to 18 parts by weight of a polymer resin;
2 to 3 parts by weight of a curing agent;
20 to 70 parts by weight of artificial graphite; And
10 to 60 parts by weight of zinc oxide;
And a thermally conductive adhesive.
17 to 18 parts by weight of a polymer resin;
2 to 3 parts by weight of a curing agent;
20 to 70 parts by weight of artificial graphite; And
10 to 60 parts by weight of zinc oxide in the form of tetrapods;
And a thermally conductive adhesive.
3. The method according to claim 1 or 2,
And at least one dispersing solvent selected from the group consisting of toluene, methyl ethyl ketone, xylene, hexane, ethyl acetate, butanol, diethyl ether and ethyl cellulose.
3. The method according to claim 1 or 2,
Wherein the polymer resin is any one selected from the group consisting of an epoxy resin, an acrylic resin, and a composite thereof.
3. The method according to claim 1 or 2,
The curing agent,
In the case of an epoxy resin, it is an amine-based curing agent, an imidazole-based curing agent or an acid anhydride-based curing agent,
In the case of an acrylic resin, a phenol-based, epoxy-based, cyanoacrylate or polyester acrylate.
3. The method of claim 2,
Wherein the tetragonal zinc oxide is obtained by heat treating the zinc powder in an oven at 950-1050 deg. C for 60-120 minutes.
The method according to claim 1,
The artificial graphite has an average particle size of 18-22 탆,
Wherein the zinc oxide has an average particle size of 0.2-0.8 占 퐉.
The method according to claim 1,
The artificial graphite has an average particle size of 18-22 탆,
Wherein the tetragonal zinc oxide has an average particle size of 5 to 20 占 퐉.
The method according to claim 1,
Wherein the mixing weight ratio of the zinc oxide and the artificial graphite is 15-25: 55-65.
3. The method of claim 2,
Wherein the mixing weight ratio of the tetragonal zinc oxide and the artificial graphite is 15-25: 55-65.
17 to 18 parts by weight of a polymer resin, 20 to 70 parts by weight of artificial graphite and 10 to 60 parts by weight of zinc oxide for 10 to 14 hours while irradiating ultrasound (step 1);
Stirring the mixture of step 1 in an oil bath at 40-60 DEG C for 22-26 hours (step 2); And
Adding 2 to 3 parts by weight of a curing agent to the mixture of step 2, stirring and curing in an oven at 60 to 80 DEG C for 1 to 3 hours (step 3);
The method of producing a thermally conductive adhesive according to claim 1,
Heat treating the zinc powder in an oven at 950-1050 캜 for 60-120 minutes to prepare tetrapod-shaped zinc oxide (step 1);
17 to 18 parts by weight of polymer resin, 20 to 70 parts by weight of artificial graphite, and 10 to 60 parts by weight of tetrafluoro zinc oxide are mixed for 10 to 14 hours to irradiate ultrasound (step 2);
Stirring the mixture of step 2 in an oil bath at 40-60 DEG C for 22-26 hours (step 3); And
Adding 2 to 3 parts by weight of a curing agent to the mixture of step 3, stirring and curing in an oven at 60-80 占 폚 for 1-3 hours (step 4);
The method of producing a thermally conductive adhesive according to claim 2,
12. The method of claim 11,
Wherein at least one dispersing solvent selected from the group consisting of toluene, methyl ethyl ketone, xylene, hexane, ethyl acetate, butanol, diethyl ether and ethyl cellulose is further added to step 1 above.
13. The method of claim 12,
Wherein at least one dispersing solvent selected from the group consisting of toluene, methyl ethyl ketone, xylene, hexane, ethyl acetate, butanol, diethyl ether and ethyl cellulose is further added to step 2 above.

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