Description

An Efficient Process for Preparation of Copper Phthalocyanine Particles Exhibiting

Epsilon Crystallographic Form

Technical field

[0001] The present disclosure is directed to a new efficient and economical process for preparing epsilon-crystallographic type copper phthalocyanine (e-CuPc) particles having a small particle size and narrow particle size distribution.

Background art

[0002] Liquid crystal color display devices comprise color filter substrates having a glass substrate with red (R), green (G) and blue (B) picture elements regularly arranged on the substrate. In general, the color filter further comprises a shade pattern named black matrix, which is arranged to fill up the spaces formed between picture elements. This improves the contrast ratio of displayed images from the background.

[0003] A phthalocyanine based organic pigment is excellent in fastness and performance. It is also employed as a blue colorant for paints or plastics. Among all pigments, copper phthalocyanine is especially stable and is excellent in terms of having a variety of fastness. Further, the copper phthalocyanine has many crystal forms. Of these crystal forms, those known to have already found their actual use include alpha, beta and epsilon crystal forms of copper phthalocyanine. It is common practice to use the beta crystal form to impart a greenish blue color and the alpha crystal form to impart a reddish blue color. However, the epsilon crystal form is employed when a blue color, which is more reddish than that available from the use of the alpha crystal form, is required (BASF Corporation, Kirck Othmer Encylopedia ; Journal of Solid State Chemistry 177, p1987-1993 (2004)).

[0004] The epsilon crystal form copper phthalocyanine has a reddish hue, a high clearness and a high tinting strength compared to the alpha crystal form. In addition, their solvent resistance against the crystal growth of primary crystals is higher than that of the beta crystal form. Further, their solvent resistance against the crystal transformation into the beta crystal form is higher than that of other polymorph copper phthalocyanines. Therefore, the epsilon crystal form copper phthalocyanine is a molecular aggregate having a crystal form, which has remarkably excellent properties with less apprehension about a change of hue and a decrease in tinting strength and clearness. Also, the thermodynamic stability of the epsilon crystal form is next to that of the beta crystal form, which is the most stable crystal form among polymorph crystals.

[0005] It is known in the art that copper phthalocyanine (crystallographically crude or in the pure alpha crystallographic phase) is easily convertible into its epsilon crystal form, e.g., by salt grinding with a solvent, dry grinding in the presence or absence of a salt followed by solvent treatment, dry grinding with a solid binder in an inert atmosphere, or dry or aqueous grinding followed by conditioning. During the conversion process, crystals other than the epsilon crystal form are milled in an organic solvent in the presence of beads by means of a strong mechanical force for a long period of time.

[0006] Great Britain Patent Publication No. GB1411880 describes production of phthalocyanine pigments of the epsilon-crystallographic form. Specifically, copper phthalocyanine exhibiting alpha-form is converted to a 1:1 mixture of copper phthalocyanine particles having the alpha- and epsilon-crystallographic forms by ball milling. Then the 1:1 mixture is heated in ethanol for 8 hours to convert the remaining 50 % alpha-copper phthalocyanine particles to epsilon form. The resultant particles of epsilon form is washed with water, dried and then ground. Japan Patent Laid-Open Publication No. (Hei)4-252273 and Chinese Patent No. CN1827703 disclose similar processes as above.

[0007] Japan Patent Laid-Open Publication No. 2000-258620 discloses a process for manufacturing e-CuPc fine pigment which involves milling crude s-CuPc and semi-crude E-CUPC, in the presence of an organic solvent and a mineral salt. It also discloses manufacturing epsilon-type copper-phthalocyanine fine pigment by milling epsilon-type copper-phthalocyanine crude and semi-crude epsilon-type copper-phthalocyanine containing alpha-type copper-phthalocyanine or epsilon-type copper-phthalocyanine pigment having BET specific surface area of 95-150 m2/g or less in a nitrogen absorption process. Then using solvent and 8-20 weight parts of mineral salt per weight part of crude, semi-crude or pigment. Afterwards, organic solvent and mineral salt are removed.

[0008] US Patent Publication No. US 2005215780 describes a process for the production of epsilon crystal form copper phthalocyanine. Such a process comprises heat-treating copper phthalocyanine in a solvent at a temperature ranging from 80°C to 250°C in the presence of a Lewis acid.

[0009] However, the foregoing methods of preparing epsilon crystal form copper hthalocyanine require too much time for crystal phase conversion and particle size reduction. It has thus been desired to develop a method of effectively preparing epsilon crystal form copper phthalocyanine with less time for crystal phase conversion and particle size reduction.

Disclosure of the invention

[0010] It is thus an object of the present invention to provide a process of preparing epsilon crystal form copper phthalocyanine which requires less time to obtain epsilon crystal form copper phthalocyanine with high crystallographic purity and smaller particle size.

[0011] Another object of the present disclosure is to provide epsilon crystal form copper phthalocyanine primary particles of small size and narrow particle size distribution obtainable according to said process. Still yet another object of the present disclosure is to use said epsilon crystal form copper phthalocyanine particles in the preparation of color filter pigments and in the fabrication of liquid crystal display (LCD) devices.

[0012] The inventors of the invention found that when the pigment is handled during the conversion process (beta to alpha, or alpha to epsilon) in the state prior to drying (currently called wet cake) the resultant pigment particles have smaller particle size and the entire processing time can be shortened. Even though some references such as France Patent No. 2417531, Japan Patent Laid-Open Publication No. (Hei) 8 176457, etc., disclose use of such wet cake for increasing crystallinity, they do not teach or suggest use of wet cake for reducing the processing time in preparing copper phthalocyanine having epsilon crystal form.

Brief description of drawings

[0013] Fig. 1 is an image from a Transmission Electron Microscope (TEM) for the copper phthalocyanine particles exhibiting epsilon crystallographic phase prepared by the method according to Example 2. [0014] Fig. 2 is an image from a Transmission Electron Microscope (TEM) for the copper phthalocyanine particles exhibiting epsilon crystallographic phase
prepared by the method according to Comparative Example 1.

Detailed Description

[0015] Hereinafter, the present invention is described in detail.

[0016] As used herein, the term "wet cake" is defined as a solid-liquid mixture in the form of a suspension, comprising a liquid in an amount of at least about 30 percent by weight. In another embodiment, the wet cake can comprise preferably at least about 50 percent, more preferably at least about 70 percent, and most preferably at least about 80 percent of a liquid.

[0017] In one embodiment, copper phthalocyanine (CuPc) is developed for effective use as a blue pigment of color filters for LCDs. Such filters (e.g., phthalocyanine) must be highly transparent, homogeneous and be prepared in a layer with uniform thickness. These features are decided by chemical purity, crystallographic purity, primary particle size and particle size distribution of copper phthalocyanine. In this regard, the disclosure teaches a new and more efficient process of preparing copper phthalocyanine.

[0018] Copper phthalocyanine (CuPc) particles exhibiting a £ crystallographic form from CuPc particles with at least 50 wt % of the particles exhibiting an a crystallographic form is used as a starting material. The starting material has a water content of at least 30 percent by weight, preferably at least 50 percent by weight, more preferably at least 70 percent by weight, and most preferably at least 80 percent by weight.

[0019] The copper phthalocyanine particles exhibiting an a crystallographic form used in the process of the invention can be prepared by any process. It is preferred that they are prepared from copper phthalocyanine particles exhibiting a β crystallographic form by using an acid paste method. The beta crystal form copper phthalocyanine is commercially available from various companies such as Toyo Ink (Japan), Dainippon Ink & Chemicals Co. (Japan), etc. The beta crystal form copper phthalocyanine is subjected to crystal phase conversion into alpha crystal form by acid pasting. Acid pasting refers to the dissolution and precipitation of the pigment in a suitable acid. Preference is given to using acids such as sulfuric acid, chlorosulfonic acid and polyphosphoric acid. The precipitation medium generally comprises water, organic solvents or mixtures thereof. Precipitation takes place preferably under turbulent flow conditions. Such a treatment is described for instance in Ullmann's Encyclopedia of Industrial Chemistry, Fifth Completely Revised Edition, 1992, Volume A20, pp. 225-226.

[0020] In a first embodiment, copper phthalocyanine particles exhibiting
a E crystallographic form is prepared by heating the starting material at a temperature higher than or equal to 50°C in the presence of a first organic liquid and optionally milling in the presence of beads. Milling, as defined herein, means a process by which the solids are subjected to attrition, grinding, etc. to achieve particle size reduction. Dry milling, as defined herein, means a process by which the solids are subjected to attrition, grinding etc. to achieve particle size reduction while substantially free of liquid. However, a low level of solvent may be added.

[0021] In this embodiment, the alpha crystal form copper phthalocyanine is
treated at a temperature higher than or equal to 50°C, preferably higher than or equal to 60°C, more preferably higher than or equal to 70°C, and most preferably higher than or equal to 80°C. The temperature of the heating step is generally lower than or equal to 210°C, preferably lower than or equal to 150°C, more preferably lower than or equal to 120°C, and most preferably lower than or equal to 100°C.

[0022] During the process of this embodiment, the duration of the heating step is generally higher than or equal to 0.5 h, more preferably higher than or equal to 1 h, yet more preferably higher than or equal to 2 h, and most preferably higher than or equal to 3 h. That duration is generally lower than or equal to 12 h, preferably lower than or equal to 10 h, more preferably lower than or equal to 8 h, yet more preferably lower than or equal to 6 h, and most preferably lower than or equal to 4 h.

[0023] In this embodiment, the heating step is carried out in the presence of a first organic liquid. The first organic liquid suitable for the use in the present invention may include, but is not limited to, N-methyl-2-pyrrolidone, sulfolane, N,N-dimethyl formamide, glycols and glycols derivatives such as propylene glycol monomethyl ether acetate, diethylene glycol, alcohols such as diacetone alcohol, acetonitrile, monochlorobenzene, ethylene glycol butyl ether, ketones and quinolines, preferably N-methyl-2-pyrrolidone and any mixture of at least two of them. The first organic liquid may further comprise water.

[0024] The proportion of the first organic liquid to the alpha crystal form copper phthalocyanine by weight ratio is generally higher than or equal to 0.033 and preferably higher than or equal to 0.05. That ratio is usually lower than or equal to 0.2 and more preferably lower than or equal to 0.1.

[0025] The beads suitable for use as a milling media may include, but are not limited to, metallic beads, plastic beads, inorganic oxide beads such as zirconia and glass beads, preferably zirconia beads. The proportion of the beads used to the alpha crystal form copper phthalocyanine by weight ratio is generally higher than or equal to 0.01 and preferably higher than or equal to 0.166. That proportion is usually lower than or equal to 0.5 and more preferably lower than or equal to 0.333.

[0026] Through the heating treatment described above, the alpha crystal form copper phthalocyanine can be effectively converted into the epsilon crystal form having a narrow particle size distribution, which was determined from D10 and D90 percentiles measured by a Particle Size Analyzer.

[0027] In another embodiment, the process may comprise the following steps : a) separating the copper phthalocyanine particles exhibiting a E crystallographic form from the first organic liquid and optionally from the beads; and

b) kneading the copper phthalocyanine particles separated at step a) with at least one inorganic salt and a second organic liquid to obtain particles with an average particle size of less than 30nm.

[0028] The separation step can be carried out by filtration means known in the art including the use of any appropriate filter, decantation, centrifugation, etc. Preferably, filtration can be used to separate the copper phthalocyanine particles exhibiting a ε crystallographic form. In a preferred embodiment, after filtration, the copper phthalocyanines particles exhibiting a e crystallographic form are further washed with water. After further filtration, the resultant phthalocyanines particles exhibiting a ε crystallographic form may be used in the subsequent kneading step immediately, as a wet cake, or may be first dried. The resultant phthalocyanine particles exhibiting a e crystallographic form are preferably used in the subsequent kneading step in the form of a wet cake.

[0029] In order to reduce the primary particle size of the epsilon crystal form copper phthalocyanine converted above, the step of kneading the same with salt is conducted in the presence of at least a second organic liquid. For the preferred salt kneading process, it is possible to use a typical continuous kneading unit well known in the art including a single kneading-screw type and a twin kneading-screw type. Further, a salt-kneading system is employed.

[0030] The kneading step is carried out for a duration which is generally higher than or equal to 2 h, preferably higher than or equal to 3 h, more preferably higher than or equal to 5 h and most preferably higher than or equal to 6 h. That duration is generally lower than or equal to 36 h, preferably lower than or equal to 18 h, more preferably lower than or equal to 12 h and most preferably lower than or equal to 8 h.

[0031] The kneading step is carried out at a temperature which is generally higher than or equal to 0°C and preferably higher than or equal to 10°C and most preferably higher than or equal to 50°C. That temperature is generally lower than or equal to 130°C, preferably lower than or equal to 80°C and more preferably lower than or equal to 60°C.

[0032] The second organic liquid suitable for the kneading step may include, but is not limited to, N-methyl-2-pyrrolidone, sulfolane, N,N-dimethyl formamide, diethylene glycol, N-methyl formamide, diacetone alcohol, glycerin, ethylene glycol, propylene glycol, polypropylene glycol, 2-butoxy ethanol, triethylene glycol, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, 1-methoxy-2-propanol,1-ethoxy-2-propanol, ketones, quinolines, and any mixture of at least two of them, and the second organic liquid is preferably N-methyl-2-pyrrolidone. The second organic liquid may further comprise water.

[0033] In the kneading step, the proportion of the second organic liquid to the epsilon crystal form copper phthalocyanine by weight ratio is generally higher than or equal to 0.033 and more preferably higher than or equal to 0.050. That proportion is generally lower than or equal to 1.0 and more preferably lower than or equal to 0.666.

[0034] Moreover, the inorganic salt suitable for the salt kneading process may include, but is not limited to, aluminum sulfate, sodium sulfate, calcium chloride, potassium chloride or sodium chloride, and preferably sodium chloride which may if desired and available contain water of crystallization. The proportion of the inorganic salt to the epsilon crystal form copper phthalocyanine by weight ratio is generally higher than or equal to 0.067 and preferably higher than or equal to 0.1. That proportion is generally lower than or equal to 1.0 and more preferably lower than or equal to 0.2.

[0035] The inorganic salt has an average particle size which is generally higher than or equal to 0.3 urn. That average particle size is generally lower than or equal to 200 urn, preferably lower than or equal to 50 urn, which was measured by a Particle Size Analyzer. The inorganic salt is generally soluble in water, preferably to the extent of at least 10 g/100 ml of water.

[0036] In the kneading step, the proportion (by weight ratio) of solid products, i.e. the inorganic salt and the epsilon crystal form copper phthalocyanines, to the liquid products, i.e. the second organic liquid and the optional water, is usually at least 3.5, preferably at least 4, more preferably at least 4.5, especially at least 5, in particular at least 5.5, for example about 6. The optional water may come from the use of a wet cake of phthalocyanines particles, may be present in the second organic liquid or may be added to the mixture as an additional liquid.

[0037] The rotary speed of the salt kneading system used in the present invention should be adjusted, taking into account the cooling if necessary, in such a way that the kneaded composition is moved homogeneously under uniform share. It is preferable to maintain the rotary speed during the salt kneading in the range of 30 to 150 rpm, more preferably from 50 to 120 rpm.

[0038] In still another embodiment, the crystal phase conversion and size reduction take place simultaneously. In other words, kneading is conducted to convert alpha crystallographic phase into epsilon as well as to reduce primary particle size of the copper phthalocyanine.

[0039] In another embodiment, kneading is conducted in the presence of at least one liquid and at least one inorganic salt. Preferably, kneading is conducted under temperature conditions such that the temperature profile as a function of time exhibits at least two derivatives of temperature with respect to time (dT/dt) being equal to 0. The two temperatures are associated with the derivatives equal to 0 differing by at least 10°C. In another embodiment, kneading is conducted under a constantly changing temperature profile, or at least one time (stepwise). Preferably, kneading is conducted at the first temperature and then at the second temperature, wherein the first temperature is 80-150°C (preferably 100-120°C) and the second temperature is 30-70°C (preferably 50-60°C). This embodiment provides modification of the temperature during the kneading step by which CuPc particles exhibiting a-crystallographic form is converted to e crystallographic form and their particle size is significantly reduced. Further, the process reduces the time for crystal phase conversion and particle size reduction.

[0040] In this embodiment, the liquid is usually at least one selected from the group consisting of N-methyl-2-pyrrolidone, diethylene glycol, diacetone alcohol, glycerin, ethylene glycol, propylene glycol, polypropylene glycol, 2-butoxy ethanol, triethylene glycol, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, quinolines, and water.

[0041] In this embodiment, the proportion (by weight ratio) of solid products, i.e. the inorganic salt and the copper phthalocyanines, to the liquid products, i.e. the water comprised in the wet cake and the optional other liquids which were added, is usually at least 3.5, preferably at least 4, more preferably at least 4.5, especially at least 5, in particular at least 5.5, for example about 6.

[0042] Other conditions during kneading are identical to those of the kneading step of the previous embodiments in which the heating step (for crystal phase conversion) and the kneading step (particle size reduction) are conducted separately.

[0043] For all the embodiments disclosed above, the process may further comprise the following step :

a recovery step by recovering the copper phthalocyanine particles by removing the organic liquid and the inorganic salt.

[0044] After the last step, the copper phthalocyanine particles are recovered by removing the inorganic salt and the liquid. The removal can be done by any means, for instance filtration using any appropriate filter, decantation, centrifugation, etc. Preferably, filtration can be used to separate the copper phthalocyanine particles exhibiting a e crystallographic form. It is preferred that it is done by washing the inorganic salt and the liquid away with water, especially with demineralized water.

[0045] The process according to the invention may comprise a further drying step after the recovery step. The drying step is conducted preferably at a temperature higher than or equal to -20°C and lower than or equal to 250°C under pressure higher than or equal to 101 Pa and lower than or equal to 105 Pa, with very particular preference for a temperature around 80°C and for a pressure around 104 Pa.

[0046] In order to increase dispersibility of the resultant copper phthalocyanine particles exhibiting a t crystallographic form, particles of copper phthalocyanine substituted by a functional group (dispersion aid) may be further added during the acid pasting step and/or the heating step optionally in the presence of beads and/or during the kneading step b) of the process according to the invention. In addition, the process may further comprise the step of dry-blending, wherein particles of copper phthalocyanine substituted by a functional group are further blended after the recovery step.

[0047] The particles of copper phthalocyanine used as a dispersion aid may be substituted by at least one functional group selected from -SO3M, -SO2NR1R2 and -R3-NR4R5, wherein : R1 and R2 are independent of one another and can be selected from the group consisting of hydrogen, alkyl, alkenyl, aryl or cycloalkyl; M can be a proton, ammonium cation or metal cation ; R3 can be a single bond, alkylene, arylene, and wherein said alkylene and arylene may be substituted by at least one substituent; and R4 and R5 are independent of one another and can be a hydrogen, alkyl, alkenyl, aryl, cycloalkyl, or collectively form a condensed structure containing at least one of -CO-, -SO2- or -N=N-.

[0048] More preferably, the particles of copper phthalocyanine may be substituted by the functional group of-S03H, -SO2NHR1, wherein R1 is a hydrogen, alkyl, alkenyl, aryl, cycloalkyl of

[0049] In spite of reducing the kneading time compared to the existing method in the art, the process of the present invention can obtain epsilon crystal form copper phthalocyanine having a smaller averaged primary particle size, a narrower size distribution and a better primary particle shape.

[0050] The average primary particle size of copper phthalocyanine finally obtained by the process described is generally lower than or equal to 30 nm, preferably lower than or equal to 20 nm, which is smaller than those of commercially available products. Since having a smaller particle size for the epsilon crystal form copper phthalocyanine leads to better contrast of the color filter, they can be effectively used as blue filters for LCD devices. The average primary particle size can be determined by selecting at least 50 primary particles in the transmission electron microscope (TEM) image which form aggregates and then obtaining an average value of the longitudinal diameters.

[0051] One embodiment is directed to epsilon crystal form copper phthalocyanine particles obtainable according to the process of the present invention.

Another embodiment is directed to the use of the same in the preparation of color filter pigments.

[0052] Further, another embodiment is directed to color filter pigments comprising the epsilon crystal form copper phthalocyanine particles prepared according to the process disclosed herein. Also, the present invention is directed to the use of the same in the fabrication of liquid crystal display devices.

Examples
[0053] Hereinafter, the present invention will be explained in detail with reference to examples and comparative examples. These examples, however, should not in any sense be interpreted as limiting the scope of the present invention. Further, units are expressed by weight unless otherwise described.

Example 1. Crystal phase conversion of copper phthalocyanine from beta crystal form to alpha crystal form

[0054] 80 parts by weight of the crude copper phthalocyanine are added to 800 parts by weight of 95 wt % sulfuric acid. Further, the resultant mixture is stirred for 3 hours to prepare a suspension or solution of sulfate in the sulfuric acid. The suspension or the solution is poured two times into 8L of water to obtain an alpha crystal form copper phthalocyanine. After removing the solvent by filtration, wet cake of the alpha crystal form copper phthalocyanine containing 80 percent by weight of water is directly subjected to the following conversion process to epsilon crystal form.

Example 2. Crystal phase conversion of copper phthalocyanine from alpha crystal form to epsilon crystal form

[0055] 300 parts by weight of the obtained wet cake (containing 80 wt % of water thus corresponding to 60 parts by weight of the alpha crystal form copper phthalocyanine) and 12 parts by weight of a dry epsilon crystal form copper phthalocyanine are treated at 130°C for 2 hours in 750 parts by weight of N-methyl-2-pyrrolidone (NMP). After filtration of the phase converted copper phthalocyanine particles to remove NMP and subsequent washing with water 2 to 3 times, the wet cake of the resultant CuPc particles (including about 70 % of water) was subjected to the kneading process outlined below without drying. Upon analyzing a dried sample of some of the resultant copper phthalocyanine particles with a transmission electron microscope (TEM), copper phthalocyanine particles exhibiting a pure £ crystallographic form (confirmed by a XRD study showing no existence of p crystallographic form) and having a mean particle size of about 100 μm are obtained.

Comparative Example 1
[0056] Copper phthalocyanine particles exhibiting epsilon crystallographic form were obtained in an identical manner to that of Example 2, except that the copper phthalocyanine having alpha-form as a starting material was first dried and pulverized. Upon analyzing some dried samples of the resultant copper phthalocyanine particles exhibiting epsilon crystallographic form with a transmission electron microscope (TEM), they were shown to have a mean particle size of 300 to 500 \xm (Figure 2).

Example 3. Primary particle size reduction of epsilon crystal form copper phthalocyanine

[0057] 170 parts by weight of the obtained wet cake (containing 70 wt % of water thus corresponding to about 50 parts by weight of the obtained copper phthalocyanine) exhibiting a ε crystallographic form are added with 80 parts by weight of diethylene glycol and 800 parts by weight of sodium chloride to a lab scale kneader. The mixture is kneaded for 12 hours at 80°C at a rotation speed of 45 rpm. After kneading, the resultant particles are purified by filtration and dried at a temperature of 80°C under pressure of 104 Pa. Upon analyzing the particles with a TEM, the obtained copper phthalocyanine particles have smaller primary particle size and better particle shape compared to those of commercially available copper phthalocyanine particles.

Comparative Example 2
[0058] Kneading is conducted in an identical manner to that of Example 3, except that copper phthalocyanine particles exhibiting epsilon crystallographic form obtained in Comparative Example 1 were used and the kneading time was adjusted in order to obtain particles having a primary particle size and a particle shape comparable to those of Example 3. The kneading time had to be adjusted to 24 to 36 hours. The entire processing time to obtain particles having the desired size was thus from 12 to 24 hours longer than that of the Examples according to the present invention.

[0059] It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

1. A process of preparing copper phthalocyanine (CuPc) particles exhibiting a ε crystallographic form from CuPc particles with more than 50 wt % of the particles exhibiting an a crystallographic form as a starting material, wherein said starting material has a water content of at least 30 percent by weight.

2. The process of Claim 1, wherein the starting material has a water content of at least 50 percent by weight, preferably at least 70 percent by weight, more preferably at least 80 percent by weight.

3. The process of Claim 1 or 2, comprising a heating step by heating the starting material at a temperature higher than or equal to 50°C in the presence of a first liquid, and optionally milling in the presence of beads.

4. The process of Claim 3, further comprising :

a) separating the copper phthalocyanine particles exhibiting a £ crystallographic form from at least part of the first liquid and the beads, if used;

b) kneading the copper phthalocyanine particles separated at step a) in the presence of at least one inorganic salt and at least one second liquid to obtain the copper phthalocyanine particles having an average particle size of less than 30 nm ; and

c) recovering the copper phthalocyanine particles by removing at least part of the second liquid and the inorganic salt.

5. The process of Claim 3 or 4, wherein the heating step is conducted at a temperature lower than or equal to 210°C.

6. The process of Claim 1 or 2, comprising kneading the starting material under temperature conditions such that the temperature profile as a function of time exhibits at least two derivatives of temperature with respect to time (dT/dt) being equal to 0, the at least two temperatures associated with the at least two derivatives equal to 0 differing by at least 10°C, in presence of at least one liquid compound and of at least one inorganic salt.

7. The process of Claim 6, further comprising a recovery step by recovering the copper phthalocyanine particles by removing at least part of the liquid and the inorganic salt.

8. The process of Claim 6 or 7, wherein kneading is conducted at a first temperature and then at a second temperature, and wherein the first temperature is 80-150°C, preferably 100-120°C, and the second temperature is 30-70°C, preferably 50-60°C.

9. The process of any one of Claims 1 to 8, wherein the copper phthalocyanine particles exhibiting an a crystallographic form are prepared from copper phthalocyanine particles exhibiting a B crystallographic form by using an acid paste method.

10. The process of any one of Claims 3 to 5 and 9, wherein the first liquid is at least one selected from the group consisting of N-methyl-2-pyrrolidone, sulfolane, N,N-dimethyl formamide, glycols such as propylene glycol monomethyl ether acetate, diethylene glycol, alcohols such as diacetone alcohol, acetonitrile, monochlorobenzene, ethylene glycol butyl ether, ketones, quinolines, and water.

11.The process of any one of Claims 4, 5, 9 and 10, wherein the second liquid is at least one selected from the group consisting of N-methyl-2-pyrrolidone, diethylene glycol, diacetone alcohol, glycerin, ethylene glycol, propylene glycol, polypropylene glycol, 2-butoxy ethanol, triethylene glycol, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, quinolines, and water.

12. The process of any one of Claims 6 to 9, wherein the liquid is at least one selected from the group consisting of N-methyl-2-pyrrolidone, diethylene glycol, diacetone alcohol, glycerin, ethylene glycol, propylene glycol, polypropylene glycol, 2-butoxy ethanol, triethylene glycol, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, quinolines, and water.

13. The process of any one of Claims 4 to 12, wherein the inorganic salt is at least one selected from the group consisting of aluminum sulfate, sodium sulfate, calcium chloride, potassium chloride and sodium chloride.

14. The process of any one of Claims 4 to 13, wherein particles of copper phthalocyanine substituted by at least one functional group selected from the group consisting of -SO3M, -SO2NR1R2 and -R3-NR4R5,

wherein R1 and R2 are independent of one another and are hydrogen, alkyl, alkenyl, aryl or cycloalkyl; M is a proton, ammonium cation or metal cation ; R3 is a single bond, alkylene, arylene, wherein said alkylene and arylene may be substituted by at least one substituent; and R4 and R5 are independent of one another and are hydrogen, alkyl, alkenyl, aryl or cycloalkyl, or collectively form a condensed structure containing at least one of -CO-, -SO2- and -N=N-, are further added during the acid paste step or the kneading step.

15. The process of any one of Claims 4, 5 and 7 to 13, further comprising a step of dry-blending wherein particles of copper phthalocyanine substituted by at least one functional group selected from the group consisting of -SO3M, -SO2NR1R2 and -R3-NR4R5,

wherein R1 and R2 are independent of one another and are hydrogen, alkyl, alkenyl, aryl or cycloalkyl; M is a proton, ammonium cation or metal cation ; R3 is a single bond, alkylene, arylene, said alkylene and arylene may be substituted by at least one substituent; and R4 and R5 are independent of one another and are hydrogen, alkyl, alkenyl, aryl or cycloalkyl, or collectively form a condensed structure containing at least one of -CO-, -SO2- and -N=N-,

are further added to the phthalocyanine particles recovered after the recovery step.