KR20180018129A - A dispersion composition for haptic display film, a haptic display film and the manufacturing method thereby - Google Patents

Abstract

The present invention relates to a dispersion solution for a haptic display film, comprising a PVDF terpolymer, a piezoelectric inorganic particle, a solvent, and a fluorine-based dispersant; a haptic display film comprising a PVDF terpolymer and a piezoelectric inorganic particle; and a manufacturing method of the haptic display film. A PVDF terpolymer with electrostrictive properties which cannot be subjected to poling is used in the present invention to produce films with high transparency and high dielectric constant without a poling process.

Description

TECHNICAL FIELD The present invention relates to a dispersion for a haptic display film, a haptic display film, and a method for manufacturing the haptic display film.

The present invention relates to a dispersion for a haptic display film, a haptic display film and a method for manufacturing the same, and more specifically, to a dispersion for a haptic display film having a high dielectric constant and a high modulus characteristic, a haptic display film and a method for manufacturing the same.

In recent years, a touch screen has been widely used for user's intuitive use of a display. In recent years, a touch screen has been used to touch a screen, A haptic function that gives haptic feedback to the screen has developed.

Here, haptic is a technology that makes the user feel tactile force, force, and sense of motion. In general, haptic technology can be realized by converting an electrical signal into a mechanical energy such as a vibration to a touch-enabled display, so that development of a transparent haptic film having excellent electro-activity is required.

Various electroactive polymers can be used as the material of the electroactive film. For example, there is a polymer such as PVDF using a piezoelectric method using a volume change through a phase transition by a voltage, or a polymer such as a urethane using a dielectric method which shrinks and expands in a vertical direction by charging of a dielectric.

Since the film for haptic display is a display, the transparency should be basically high. In the case of the PVDF film using the piezoelectric method, transparency due to crystallinity is lowered after poling.

Korean Patent Publication No. 10-2015-0069410

Therefore, PVDF terpolymer with electrostrictive property which does not poling process can produce high transparency film with high dielectric constant without poling process. However, PVDF terpolymer alone can not transmit vibrations because its modulus is low.

Therefore, in order to solve the above problems,

The present invention aims to provide a PVDF terpolymer-piezoelectric inorganic particle film for display which can maximize electric activity through improvement of dielectric constant and modulus characteristic.

To solve this problem,

The present invention provides a dispersion for a haptic display film comprising a PVDF terpolymer, a piezoelectric inorganic particle, a solvent, and a fluorine-based dispersant.

The present invention also provides a haptic display film comprising a PVDF terpolymer and piezoelectric inorganic particles.

The present invention also provides a process for producing a piezoelectric ceramic composition, comprising the steps of: a) mixing a piezoelectric inorganic particle and a fluorine-based dispersant in a solvent, and then subjecting the piezoelectric inorganic particle to a particle size of 1 to 100 nm at a temperature of 10 to 30 ° C at 1,000 to 5,000 rpm Distributing b) dispersing the PVDF terpolymer in a solvent; And c) mixing the dispersion prepared in the step a) with the dispersion prepared in the step b), coating on the substrate, and then performing heat treatment at a temperature of 80 to 150 ° C for 1 to 5 hours to produce a film The method comprising the steps of: preparing a film for a haptic display;

The haptic display film according to the present invention improves haptic performance by maximizing electroactivity by improving the dielectric constant and modulus of the film, and has an advantage of being excellent in transmittance characteristics and being applicable to displays.

Hereinafter, the present invention will be described in detail.

The dispersion for a haptic display film according to the present invention is characterized by containing a PVDF terpolymer, a piezoelectric inorganic particle, a solvent, and a fluorine-based dispersant.

First, PVDF terpolymer has electrostrictive properties different from PVDF polymer and PVDF copolymer.

For example, unlike other polymers, PVDF polymers have high piezoelectric properties. For example, at 25 ° C and 1 KHz, the dielectric constant is less than 10 and the dielectric constant is improved to 14 after poling.

The PVDF copolymer has an effect of increasing the crystallinity of PVDF to improve piezoelectric performance. Specific examples thereof include P (VDF-TFE (trifluoroethylene)), P (VDFTrFE (tetrafluoroethylene) (hexafluoropropylene)). Here, P (VDF-TrFE) has a crystallinity of 75% or more and a dielectric constant of 10 or more, and P (VDF-HFP) has a dielectric constant of 12 when the content of HFP is 20%.

As the PVDF terpolymer used in the present invention, P (VDF-TrFECFE (chlorofluoroethylene)) and P (VDF-TrFE-CTFE (chlorotrifluoroethylene) ) Is 32, and P (VDF-TrFE-CTFE) is 24. PVDF terpolymer has a lower crystallinity than film made of PVDF or PVDF copolymer due to bulky monomer such as CFE and CTF when the film is formed. Unlike the PVDF and PVDF copolymers, the bulky monomer such as CFE and CTF interfere with the formation of the polar phase to form a nano-polar domain, which acts as an electrostrictor to exhibit haptic performance without poling.

The PVDF terpolymer is a polymer having a molecular weight of 500,000 to 1,000,000 containing 50 to 70% of PVDF, 20 to 40% of PTrFE, and 10% or less of CFE or CTFE. The PVDF terpolymer (Terpolymer) is Ferroelectric characteristics Ps (saturation polarization) is ^{50 ~ 70 Mc / m 2,} Pr (remnant polarization) is ^{5 ~ 15Mc / m 2, (} coercive field) Ec is 10 ~ 15 (V / Mu m).

The piezoelectric inorganic particles used in the present invention may be a single crystal material selected from the group consisting of α-AlPO ₄ (berylite), α-SiO ₂ (Quartz), LiTaO ₃ , LiNbO ₃ , Sr _x Ba _y Nb ₂ O ₈ range 1), PGO (Pb5Ge3O11), Tb (MoO 4) 3, Li 2 B 4 O 7, CdS, ZnO, Bi 12 SiO 20, Bi 12 G 2 O 20, PZT (Lead zirconate titanate), PT (Lead titano, perovskite, and BaTiO _3. The piezoelectric inorganic particles are not limited to the above-described contents, and may be used singly or in combination of two or more kinds of inorganic particles having all the piezoelectric properties have.

The piezoelectric inorganic particles used in the present invention may be those having a particle size of 1 to 100 nm, preferably particles of 5 to 50 nm. When the particle size of the piezoelectric inorganic particles satisfies the above range, even when a display film produced using the dispersion is made to have a thickness of 10 μm or more, it can have a transmittance of 80% or more.

The piezoelectric inorganic particles used in the present invention preferably include 10 to 50 wt% based on the total weight of the dispersion.

When the content of the piezoelectric inorganic particles is less than 10% by weight, an increase in the dielectric constant of the film as a final product can not be expected, and the viscosity of the coating liquid is as low as 100 cPs or less. On the other hand, if it exceeds 50% by weight, the content of the particles in the solvent increases and aggregation tends to occur. Therefore, it is difficult to disperse the particles to 100 nm or less, the viscosity of the coating solution increases, There is a problem that the film is difficult to form such as cracking.

The solvent used in the present invention is a solvent capable of dissolving the PVDF terpolymer as a solvent such as tetrahydrofuran, methyl ethyl ketone, dimethyl formamide, dimethylacetamide, tetramethyl urea, dimethyl sulfoxide, N-methyl-2-pyrrolidone, , One or more of Methyl Isobutyl Ketone, N-Butyl Acetate, Cyclohexanone, Diaceton Alcool, Ethyl Aceto Acetate, Diisobutyl Ketone, Isophorone, Triethyl Phosphate, Carbitol Acetate, Propylene Carbonate, Glyceryl Triacetate and Glyceryl Triacetate.

As the dispersing agent used for dispersing the piezoelectric inorganic particles in the solvent in the present invention, a fluorine-based dispersant may be used. For the transparency of the film finally produced in the present invention, since the piezoelectric inorganic particles must be dispersed in the solvent to 100 nm or less, the fluorine-based dispersing agent that can be used to disperse the piezoelectric inorganic particles in 100 nm or less in the solvent is specifically A silane-based dispersing agent or a polymeric ester-based dispersing agent containing a fluoride ion may be used. More specifically, 3,3,3-trifluoropropyltrimethoxysilane or a fluoroaliphatic polymeric ester may be used .

When a phosphorus dispersant is used as a dispersant, even if the piezoelectric inorganic particles are dispersed below 100 nm, there is a problem that the dielectric constant of the phosphate system is lowered when the film is mixed with PVDF terpolymer. Therefore, in the present invention, fluorine ) System dispersing agent. Commercially available fluorine-based dispersants used in the present invention include 3M FC4430, FC4432, FC4434, and Dupont FS3100.

The fluorine-based dispersant used in the present invention is preferably contained in an amount of 3 to 10 parts by weight based on 100 parts by weight of the piezoelectric inorganic particles. When the content of the fluorine-based dispersant is less than 3 parts by weight, the particles are not reduced to 100 nm or less, and when the particles are stored at room temperature after being reduced, the particles are not stabilized, And if the dispersant content exceeds 10 parts, the dispersant may surround the particles thickly or the remaining dispersant may remain. Also, the dielectric constant is lowered due to the residual dispersing agent. Due to the above reasons, the particles may not be lowered to 100 nm or less or aggregation may occur, and when the final film is formed, the dielectric constant may be lowered.

The haptic display film according to the present invention is characterized by including a PVDF terpolymer and piezoelectric inorganic particles.

The PVDF terpolymer may be P (VDF-TrFECFE (chlorofluoroethylene)) or P (VDF-TrFE-CTFE (chlorotrifluoroethylene)).

The piezoelectric inorganic particles may be selected from the group consisting of α-AlPO ₄ (Berlinite), α-SiO ₂ (Quartz), LiTaO ₃ , LiNbO ₃ , Sr _x Ba _y Nb ₂ O ₈ (Lead zirconate titanate), lead titanate (PZT), perovskite and BaTiO ₃ (Pb 5 Ge ₃ O ₁₁ ), Tb (MoO ₄ ) ₃ , Li ₂ B ₄ O ₇ , CdS, ZnO, Bi ₁₂ SiO ₂₀ , Bi ₁₂ G ₂ O ₂₀ , May be used.

The piezoelectric inorganic particles may have a particle size of 1 to 100 nm.

The content of the piezoelectric inorganic particles may be 20 to 80% by volume based on the total volume of the haptic display film. When the volume ratio of the piezoelectric inorganic particles is less than 20 vol%, the increase of the dielectric constant can not be expected. If it exceeds 80 vol%, the content of the PVDF terpolymer is too low to coat the film, There is a problem that the film is not easily formed due to problems such as cracking.

The haptic display film according to the present invention may have a dielectric constant of 40 to 400 due to the above-described structural features. In order to exhibit haptic performance, it is advantageous that the dielectric constant is 40 or more. When the haptic performance is 40 or less, the vibration characteristics are not shown well.

The haptic display film according to the present invention may have a modulus value of 0.5 to 5.0 kg / mm 2 due to the above-described structural features. If the modulus is less than 0.5kg / mm, even if the dielectric constant is more than 40, the film absorbs the vibration and the vibration is not transmitted well. When the modulus is more than 0.5kg / mm,

The haptic display film according to the present invention may have a film transmittance of 80% or more based on a thickness of 10 m due to the above-described structural features. Since the film of the present invention is for display, the transmittance at a thickness of 10 m or more should be 80% or more.

In addition, the content of the PVDF terpolymer and the piezoelectric inorganic particles is the same as the dispersion for the haptic display film described above.

A method for manufacturing a film for a haptic display of the present invention includes the following steps.

First, in step a), the piezoelectric inorganic particles and the fluorine-based dispersant are mixed in a solvent, and the piezoelectric inorganic particles are dispersed in the solvent at a temperature of 10 to 30 ° C at 1,000 to 5,000 rpm to have a particle size of 1 to 100 nm .

In the step a), the contents of the piezoelectric inorganic particles, the solvent and the fluorine-based dispersant are the same as those described above for the dispersion for a haptic display film and the film for a haptic display.

Next, in step b), the PVDF terpolymer is dispersed in a solvent.

In the step b), the contents of the PVDF terpolymer and the solvent are the same as those described above for the dispersion for the haptic display film and the film for the haptic display.

It is also obvious that the order of steps a) and b) may be changed.

Finally, in the step c), the dispersion prepared in the step a) and the dispersion prepared in the step b) are mixed, coated on the substrate, and then heat-treated at a temperature of 80 to 150 ° C for 1 to 5 hours , And a film is produced.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the embodiments of the present invention described below are illustrative only and the scope of the present invention is not limited to these embodiments. The scope of the present invention is indicated in the claims, and moreover, includes all changes within the meaning and range of equivalency of the claims. In the following Examples and Comparative Examples, "%" and "part" representing the content are on a mass basis unless otherwise specified.

Example

Haptic  Preparation of Dispersion for Display Film

[Example 1]

DMF as a solvent, BaTiO ₃ (primary size 10 nm) as an inorganic particle and Fluroaliphatic polymeric ester (3M FC4434, solid content 25%) as a dispersant were mixed in the contents shown in the following Table 1 and then mixed with beads mill (NETZSCH) zirconia beads were dispersed at a temperature of 20 ° C at 2,500 rpm until the BaTiO ₃ particle size reached the particle size shown in Table 1 to obtain a BaTiO ₃ dispersion.

Thereafter, 35 g of dispersion containing P (VDF-TrFE-CTFE) as a polymer and well dispersed in DMF in an amount of 30% by weight and 30 g of the BaTiO ₃ dispersion were uniformly mixed to prepare a dispersion for a haptic display film.

 [Examples 2 to 7]

A dispersion was prepared in the same manner as in Example 1 except that the content was as shown in Table 1 below.

[Comparative Example 1]

P (VDF-TrFE-CTFE) was well dispersed in DMF at 30% by weight.

[Comparative Examples 2 to 4]

A dispersion was prepared in the same manner as in Example 1 except that the content was as shown in Table 1 below.

Polymer
Type and content DMF content Inorganic particle
Type and content Dispersant
Type and content Inorganic particle Granularity Example 1 A: 100 g 430 g BaTiO ₃ : 85 g FC4434: 2.55 g 58 nm Example 2 A: 100 g 575 g BaTiO ₃ : 147 g FC4434: 4.4 g 58 nm Example 3 A: 100 g 770 g BaTiO ₃ : 230 g FC4434: 11.5 g 70 nm Example 4 A: 100 g 770 g BaTiO ₃ : 230 g FC4434: 23 g 70 nm Example 5 A: 100 g 770 g BaTiO ₃ : 230 g FC4434: 11.5 g 99 nm Example 6 A: 100 g 770 g BaTiO ₃ : 230 g FC4434: 46 g 70 nm Example 7 A: 100 g 770 g BaTiO ₃ : 230 g (3,3,3-Trifluoropropyl) trimethoxysilane: 11.5 g 100 nm Comparative Example 1 A - - - Comparative Example 2 A: 100 g 770 g BaTiO ₃ : 230 g FC4430: 46 g 180 nm Comparative Example 3 A: 100 g 770 g BaTiO ₃ : 230 g FC4432: 46 g 200 nm Comparative Example 4 A: 100 g 770 g BaTiO ₃ : 230 g Ethyl phosphate (TCI): 11.5 g 84 nm Comparative Example 5 B: 100 g 770 g BaTiO ₃ : 230 g FC4434: 11.5 g 58 nm

Polymer A: P (VDF-TrFE-CTFE) (arkema)

Polymer B: Copolymer (Arkema, Kynar 2500)

Haptic  Manufacture of Display Film

The dispersion for haptic display films prepared in Examples 1 to 7 and Comparative Examples 1 to 5 was coated on a glass substrate by a bar coating method and treated at 120 ° C for 3 hours or longer to obtain a film.

Experimental Example

The obtained films were measured for dielectric constant, modulus, optical characteristics and vibration acceleration under the following conditions, and are shown in Table 2 below.

1. Permittivity

Capacitance was measured at 1 kHz after deposition of Pt on both sides of the film with an area of 2 cm * 2 cm, and the permittivity was determined using thickness and area.

2. Modulus

The film was made into a 15 mm x 15 mm dog bone type using a texture analyzer, and then the tensile strength was measured at 0.05 mm / s to measure the stress / strain.

3. Optical properties

The transmittance was measured using a haze meter HM-150 (Murakami Color Research Laboratory).

4. Vibration acceleration

After the film was formed on the ITO glass, Pt deposition was performed and the vibration acceleration was measured at 100 Hz and 100 V conditions.

(O: vibration is good, X: weak vibration, X: not vibration)

thickness Volume ratio of piezoelectric inorganic particles ^* Permittivity (no unit) Modulus (kg / mm) Permeability (%) Vibration acceleration Example 1 12 20 42 0.56 83 O Example 2 11 30 48 0.93 84 O Example 3 14 40 46 1.43 81 O Example 4 19 40 44 1.23 80 O Example 5 16 40 40 1.32 81 O Example 6 19 40 36 0.98 80 △ Example 7 19 40 40 1.02 80 O Comparative Example 1 20 - 39 0.26 95 X Comparative Example 2 - - - - - - Comparative Example 3 - - - - - - Comparative Example 4  19 40 37 1.59 78 X Comparative Example 5 12 40 19 1.59 67 X

* Piezoelectric inorganic particle volume: ratio of piezoelectric inorganic particle volume to total film volume

Comparing Examples 1 to 7 and Comparative Examples 1 to 5,

In the case of Comparative Examples 2 and 3, even when coated with a particle size of 100 nm or more, the film was not formed because the permeability was low.

In Examples 1 to 7, the permittivity was about 40 or more, or about 40 in order to exhibit the haptic performance, and the modulus values were all 0.5 kg / mm or more, and the vibration acceleration was also excellent there was.

In the case of Comparative Example 1, the modulus value was 0.5 kg / mm or less, and accordingly, the vibration acceleration did not appear sufficiently to exhibit the haptic performance.

In the case of Comparative Example 4 using a phosphate-based dispersant, the modulus value was high, but the permeability was low and the dielectric constant was lower than 40, so that the vibration acceleration performance was not obtained.

In the case of Comparative Example 5 using the copolymer, the dielectric constant was low and the vibration acceleration and the performance were not achieved. Also, the permeability was not better than that of the terpolymer.

Claims (25)

Dispersion for haptic display film comprising PVDF terpolymer, piezoelectric inorganic particles, solvent and fluorine-based dispersant. The method according to claim 1,
Wherein the PVDF terpolymer is P (VDF-TrFECFE (chlorofluoroethylene)) or P (VDF-TrFE-CTFE (chlorotrifluoroethylene)). The method according to claim 1,
The piezoelectric inorganic particles may be selected from the group consisting of α-AlPO ₄ (Berlinite), α-SiO ₂ (Quartz), LiTaO ₃ , LiNbO ₃ , Sr _x Ba _y Nb ₂ O ₈ (Lead zirconate titanate), lead titanate (PZT), perovskite and BaTiO ₃ (Pb 5 Ge ₃ O ₁₁ ), Tb (MoO ₄ ) ₃ , Li ₂ B ₄ O ₇ , CdS, ZnO, Bi ₁₂ SiO ₂₀ , Bi ₁₂ G ₂ O ₂₀ , , And a dispersion liquid for a haptic display film. The method according to claim 1,
Wherein the piezoelectric inorganic particles have a particle size of 1 to 100 nm. The method according to claim 1,
The solvent is selected from the group consisting of Tetrahydrofuran, Methyl Ethyl Ketone, Dimethyl formamide, Dimethyl acetamide, Tetramethyl urea, Dimethyl Sulfoxide, N-Methyl-2-Pyrrolidone, Trimethyl phosphate, Acetone, Methyl Isobutyl Ketone, Methyl Isobutyl Ketone, N-Butyl Acetate, Cyclohexanone, Wherein the dispersion liquid is at least one selected from the group consisting of Alcool, Ethyl Aceto Acetate, Diisobutyl Ketone, Isophorone, Triethyl Phosphate, Carbitol Acetate, Propylene Carbonate, Glyceryl triacetate and Glyceryl triacetate. The method according to claim 1,
Wherein the fluorine-based dispersant is a silane-based dispersant or a polymeric ester-based dispersant containing a fluoride ion. The method according to claim 1,
Wherein the fluorine-based dispersant is 3,3,3-trifluoropropyltrimethoxysilane or a fluoroaliphatic polymeric ester. The method according to claim 1,
Wherein the fluorine-based dispersant is contained in an amount of 3 to 10 parts by weight based on 100 parts by weight of the piezoelectric inorganic particles. The method according to claim 1,
Wherein the piezoelectric inorganic particles are contained in an amount of 10 to 50% by weight based on the total weight of the dispersion liquid. A haptic display film comprising PVDF terpolymer and piezoelectric inorganic particles. The method of claim 10,
Wherein the PVDF terpolymer is P (VDF-TrFECFE (chlorofluoroethylene)) or P (VDF-TrFE-CTFE (chlorotrifluoroethylene)). The method of claim 10,
The piezoelectric inorganic particles may be selected from the group consisting of α-AlPO ₄ (Berlinite), α-SiO ₂ (Quartz), LiTaO ₃ , LiNbO ₃ , Sr _x Ba _y Nb ₂ O ₈ (Lead zirconate titanate), lead titanate (PZT), perovskite and BaTiO ₃ (Pb 5 Ge ₃ O ₁₁ ), Tb (MoO ₄ ) ₃ , Li ₂ B ₄ O ₇ , CdS, ZnO, Bi ₁₂ SiO ₂₀ , Bi ₁₂ G ₂ O ₂₀ , Wherein the haptic display film is formed of a transparent material. The method of claim 10,
Wherein the piezoelectric inorganic particles have a particle size of 1 to 100 nm. The method of claim 10,
Wherein the piezoelectric inorganic particles are contained in an amount of 20 to 80% by volume based on the total volume of the film. The method of claim 10,
Wherein the film has a modulus value of 0.5 to 5.0 kg / mm. The method of claim 10,
Wherein the film has a dielectric constant of 40 to 400. The method of claim 10,
Wherein the film has a transmittance of 80% or more based on a thickness of 10 mu m. a) dispersing the piezoelectric inorganic particles so as to have a particle size of 1 to 100 nm at a temperature of 10 to 30 DEG C at 1,000 to 5,000 rpm after mixing the piezoelectric inorganic particles and the fluorine- ;
b) dispersing the PVDF terpolymer in a solvent; And
c) mixing the dispersion prepared in the step a) with the dispersion prepared in the step b), coating on the substrate, and then heat-treating the coated film at a temperature of 80 to 150 ° C for 1 to 5 hours to prepare a film step;
Wherein the film has a thickness of at least 100 nm. 19. The method of claim 18,
Wherein the PVDF terpolymer is P (VDF-TrFECFE (chlorofluoroethylene)) or P (VDF-TrFE-CTFE (chlorotrifluoroethylene)). 19. The method of claim 18,
The piezoelectric inorganic particles may be selected from the group consisting of α-AlPO ₄ (Berlinite), α-SiO ₂ (Quartz), LiTaO ₃ , LiNbO ₃ , Sr _x Ba _y Nb ₂ O ₈ (Lead zirconate titanate), lead titanate (PZT), perovskite and BaTiO ₃ (Pb 5 Ge ₃ O ₁₁ ), Tb (MoO ₄ ) ₃ , Li ₂ B ₄ O ₇ , CdS, ZnO, Bi ₁₂ SiO ₂₀ , Bi ₁₂ G ₂ O ₂₀ , Wherein the film is formed of a material selected from the group consisting of polyethylene terephthalate (PET), polyethylene terephthalate (PET), and polypropylene. 19. The method of claim 18,
The solvent is selected from the group consisting of Tetrahydrofuran, Methyl Ethyl Ketone, Dimethyl formamide, Dimethyl acetamide, Tetramethyl urea, Dimethyl Sulfoxide, N-Methyl-2-Pyrrolidone, Trimethyl phosphate, Acetone, Methyl Isobutyl Ketone, Methyl Isobutyl Ketone, N-Butyl Acetate, Cyclohexanone, Wherein the film is at least one selected from the group consisting of Alcool, Ethyl Aceto Acetate, Diisobutyl Ketone, Isophorone, Triethyl Phosphate, Carbitol Acetate, Propylene Carbonate, Glyceryl triacetate and Glyceryl triacetate. 19. The method of claim 18,
Wherein the fluorine-based dispersant is a silane-based dispersant or a polymeric ester-based dispersant containing a fluoride ion. 19. The method of claim 18,
Wherein the fluorine-based dispersant is 3,3,3-trifluoropropyltrimethoxysilane or a fluoroaliphatic polymeric ester. 19. The method of claim 18,
Wherein the fluorine-based dispersant is contained in an amount of 3 to 10 parts by weight based on 100 parts by weight of the piezoelectric inorganic particles. 19. The method of claim 18,
Wherein the piezoelectric inorganic particles are contained in an amount of 10 to 50 wt% based on the total weight of the dispersion.