NO131174B - - Google Patents

Description

In addition to the metal-free phthalocyanine with a structure stated above, several metal derivatives of phthalocyanine are known in which the two hydrogen atoms in the middle of the molecule are replaced by metals from any group in the periodic table. It is also known that from two to sixteen of the peripheral hydrogen atoms in the four benzene rings in the phthalocyanine molecule can be replaced by halogen atoms and by numerous organic and inorganic groups.

Phthalocyanine is known to exist in at least three polymorphic forms which can be easily distinguished by comparison of their X-ray diagrams and/or infrared spectra. The color of the pigment also varies according to the polymorphic form, the beta form being greener than the alpha or gamma forms. As indicated in more detail below, there is some doubt as to whether the gamma form is really a distinct polymorphic form or is a less crystalline form of alpha-phthalocyanine. In addition to these three known forms that exist in both metalline-containing and metal-free phthalocyanine, further polymorphic forms of metalline-containing phthalocyanine are known, namely an "R" form as indicated in US Patent 3,051,721, a "delta" form as described in US Patent 3,160,635 and another "delta" form as described in US Patent 3,150,150.

It has now been found that metal-free phthalocyanine exists in a further form, hereinafter referred to as "X" form phthalocyanine. As pointed out more fully below, the X-ray and infrared spectra of this form differ significantly from the corresponding spectra of the previously known forms. As described in Norwegian patent document 124,709, the "X"-form phthalocyanine has utility as a photoconductive material in electrophotography when it is mixed with a binder and coated on a substrate. The resulting electrophotographic plate has surprisingly high photosensitivity when the phthalocyanine is either entirely "X" form or a mixture of "X" form and alpha-form phthalocyanine.

According to the invention, a metal-free phthalocyanine in the "X" form has been produced, which is characterized by having an X-ray diagram showing strong lines at Bragg angles 7.5, 9.1,

16.7, 17.3 and 22.3.

Metal-free phthalocyanine in "X" form, is prepared by the following steps: Obtaining a phthalocyanine, removing impurities and any metal atom from the phthalocyanine, and grinding the phthalocyanine until its X-ray pattern exhibits strong lines at Bragg angles 7.5, 9.1, 16, 7, 17.3 and 22.3.

The differences between the new "X" form of metal-free phthalocyanine and the previously known alpha, beta and gamma forms will be further clarified by reference to the drawing showing comparative X-ray diagrams of the various polymorphic forms of metal-free phthalocyanine.

The drawing shows X-ray diagrams of alpha, beta and X-form polymorphic forms of samples prepared in the laboratory.

The drawing shows a set of curves comparing the alpha, beta and gamma forms of metal-free phthalocyanine, arranged vertically in line for easy comparison. The samples of each form of phthalocyanine tested with X-ray radiation were prepared in the laboratory and analyzed with the same equipment by the same operator in order to be sure of conformity between the samples. The sample used to generate the curve for the alpha form was prepared from commercial "Monolite Fast Blue GS", a mixture of alpha and beta metal-free phthalocyanine. This pigment was completely converted to the alpha form prior to testing by solvent extraction with dichlorobenzene, washing with acetone and precipitation from sulfuric acid in ice water. The sample of the beta form which gave the curve shown in the drawing was prepared by suspending commercial "Monolite East Blue G-S" in triethylenetetramine at a concentration of 1 part by weight of pigment to 5 parts by weight of triethylenetetramine for four days at 23°C. The pigment was then washed with methanol and dried. The "X" form phthalocyanine which gave the curve shown in the drawing was prepared as follows: Commercial "Monolite Fast Blue G-S" was solvent extracted with dichlorobenzene, then washed with acetone and dried. The pigment was then dissolved in sulfuric acid and precipitated in ice water. The precipitate was washed with methanol and dried. The pigment was then carefully milled in a ball mill for seven days, washed with dimethylformamide and then with methanol.

The X-ray diagrams for alpha- and beta-phthalocyanine, prepared in the laboratory, agree, as shown in the drawing, with the diagrams referred to in the literature.

As can be seen in the drawing, the "X" form of phthalocyanine deviates strikingly from the alpha and beta forms. The spectrum for the "X" form has peaks at Bragg angles 17.5 and 22.3 which do not exist for the alpha and beta polymorphic forms. The "X" form also shows a peak at 9.1 which is not present for the alpha form and which is of lower intensity than the corresponding peak for the beta form.

Furthermore, the beta form peaks at around 26.2, 18.0, 14.1 and

7.0, and the alpha form has peaks at about 26.7, 13.6 and 6.8 which do not appear in the "X" form. In addition, the "X" shape has peaks at 7.5 and 16.7.

Special methods of preparation for the alpha, beta and X forms of phthalocyanine are as follows:

Preparation of alpha metal-free phthalocyanine.

86.7 g of lithium phthalocyanine was added to a 600 ml well

stirred concentrated sulfuric acid at 0°C. The mixture was then stirred at this temperature for two hours. The resulting solution was then filtered through a coarse, sintered glass funnel and emptied slowly and with stirring into 4 liters of ice water. After setting for several hours, the mixture was filtered and the filter cake washed until neutral with water. The filter cake was finally rinsed with methanol several times and dried in air The resulting powder was then extracted with acetone in a continuous extractor for twenty-four hours and allowed to air dry to form a blue powder.

To ensure against residual lithium salt, the precipitation was repeated. There was obtained 55.4 g of a blue powder whose X-ray pattern corresponded to the known published pattern for alpha metal-free phthalocyanine.

Preparation of beta metal-free phthalocyanine.

10 g of commercial "Monolite Fast Blue GS" was placed in a "Vycor" dish which was inserted into a 50 mm glass tube suitable for heating in an incinerator. The temperature in the oven was slowly raised to 350°C during the first one-hour hour to avoid spoiling the sample and finally held at 350-430°C for the next four hours. A stream of dry nitrogen was passed through the tube during the heat treatment. The treated sample was transferred to a drying apparatus for cooling. The result was 9.45 g of blue-black powder which gave an X-ray pattern corresponding to that of the beta form. Preparation of "X"-form metal-free phthalocyanine.

A 9-gram sample of alpha metal-free phthalocyanine, prepared by precipitation from sulfuric acid, and 90 g of sodium chloride were placed

served in an approx. 1 liter porcelain ball mill and ground for 72 hours at 70 revolutions per minute.

The ground powder was removed manually from the mill and extracted with 1500 ml of 1 percent hydrochloric acid at 70-80°C for one hour.

The resulting sludge was filtered and the filter cake washed repeatedly with distilled water to remove residual sodium chloride. The filter cake was finally rinsed with methanol several times and dried in air. The result was 8.8 g of blue powder. The X-ray diagram of this material cannot be reconciled with any of the published structures for various polymorphic forms of metal-free phthalocyanines, but is consistent with the established diagrams for the "X" form as shown in the accompanying drawing, and therefore, the material must be considered to be the "X" form of metal-free phthalocyanine.

Although the most effective electrophotographic plates are made by mixing the "X" form of metal-free pigment in resin binder, very good plates can also be made with the alpha metal-free form, especially if this is converted to the beta form by solvent recrystallization or to "X" -the form in a coating, which will be described later. In order to determine the crystal form of the phthalocyanine pigment as it actually exists in the photoconductive layer after it has been dried and cured, the layer is scraped off from its substrate and pulverized without any attempt to remove the surrounding resin (the latter does not significantly affect the measurement). The powder is then filled into a capillary and various tests are carried out with compressed powder pellets. The results of these tests are reproduced as indicated above (on the alpha, beta, gamma and "X" forms of metal-free phthalocyanine pigments).

To all Bragg angles mentioned in the description of

this invention, radiation corresponding to the copper K wavelength, 1.54050 Å, was used. If desired, values measured in Bragg angles can be converted to absolute distances (d) by the following equation: N-A. = 2 d sin 0, where N is the degree of diffraction (here 2). X is the wavelength of the X-ray radiation (here 1.54050 A), d is the distance that causes the interference phenomenon and 0 is the Bragg scattering angle.

Claims (1)

Metal-free phthalocyanine in "X" form used as photoconductive material together with binder in electrophotography, characterized in that it has an X-ray diagram showing strong lines at Bragg angles 7.5, 9.1, 16.7 and 22.3.