JPS633642B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for recovering pigment from waste ink. Inks used for various types of printing, such as convex, concave, offset, and gravure, generally contain pigments, resins,
It consists of additives such as a solvent and a plasticizer, and as schematically shown in FIG. 1, it is thought that pigment particles 1 are uniformly dispersed in a solvent 3 with a resin 2 interposed therebetween. These pigment particles are broadly classified into extender pigments, inorganic pigments, and organic pigments, each of which has physical properties as shown in Table 1.

【table】

[Table] It goes without saying that appropriate additives such as solvents, resins, and plasticizers are used depending on the type of pigment mentioned above. The hues of new inks are broadly classified into red, blue, yellow, white, and black, and depending on the purpose, they are used alone or in combination of two or more colors. By the way, ink that has become black and dull and can no longer be used, as well as waste liquid after cleaning printing machines, etc.
A large amount of waste ink is discharged from ink manufacturing processes, printing factories, etc., and each waste ink is a mixture of inks of various hues, and the dull colored waste ink includes black ink made of carbon black, Contains blue ink consisting of phthalocyanine blue. It is difficult to recover valuable materials such as pigments and solvents from the above waste ink, and conventionally, most of it has been incinerated or dumped, and in rare cases, hot air, steam, etc. have been injected into the waste ink to dissipate the solvent. , recovery using a condenser or the like was possible, but sufficient recovery could not be achieved. The present inventors recovered valuable materials such as pigments and solvents from waste ink, and in order to increase the degree of reuse of the recovered pigments, we removed carbon black and blue pigments (phthalocyanine blue) that cause dull colors. As a result of repeated research on methods for recovering pigments with vivid hues such as red, yellow, and brown, the following findings were obtained. First, the pigment particles used in the inks shown in Table 1 show different dispersibility depending on the type of solvent, as shown in Table 2.

[Table] △ Slightly good dispersibility × Poor dispersibility Next, as mentioned above, when pigment particles are used in ink, a resin (2 in Figure 1) is used, but depending on the type of resin, , the dispersion properties in Table 2 differ as follows. (1) Aromatic hydrocarbons such as toluene and xylene are
As shown in Table 2, none of the pigments is dispersed and tends to settle, and this tendency does not change regardless of the type of intervening resin. (2) As shown in Table 2, ethers such as methyl cellosolve and ketones such as cyclohexanone disperse well in all pigments, and this tendency does not change regardless of the type of intervening resin. (3) As shown in Table 2, esters such as ethyl acetate, alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol exhibit selectivity in dispersibility depending on the type of pigment, and also depending on the type of intervening resin. Even so, for example, methyl alcohol, ethyl alcohol: When the intervening resin is an alkyd resin, these alcohols have no effect of dissolving the alkyd resin, so the dispersibility is poor regardless of the type of pigment. If the intervening resin is nitrocellulose,
Since these alcohols have the effect of dissolving nitrocellulose, they exhibit the same dispersibility as shown in Table 2. Isopropyl alcohol: Regardless of whether the intervening resin is alkyd resin or nitrocellulose,
Isopropyl alcohol has no effect of dissolving these resins, so it has poor dispersibility regardless of the type of pigment. Ethyl acetate: Ethyl acetate dissolves these resins, whether the intervening resin is alkyd resin or nitrocellulose. Because of this effect, it shows dispersibility similar to that shown in Table 2, and shows selectivity in dispersion as shown in Table 2. (4) Blue pigments (phthalocyanine blue) and carbon black tend to be somewhat easily dispersed in any solvent. Based on the above findings, the present inventors first added to the waste ink a solvent with poor pigment dispersibility, or a mixture of the solvent with a solvent with good pigment dispersibility, alcohol, etc. to form pigment particles. We proposed a method to recover the pigment and the solvent through coagulation and sedimentation separation. The inventors of the present invention further considered that the pigment could be recovered even if treated only with a solvent with good pigment dispersibility, and as a result of further investigation, the dispersibility of the pigment in the solvent shown in Table 2 was found. It was confirmed that in a solvent with good pigment dispersibility, the results are as shown in Table 2', that is, it shows very good pigment dispersibility against phthalocyanine blue and carbon black, which cause dull colors. This is because a solvent with good pigment dispersibility exhibits solubility in the intervening resin mentioned above and transfers the resin to the solvent side, and the above-mentioned phthalocyanine blue and carbon black have a strong bond with this resin. This is thought to be due to the dispersion to the solvent side.

[Table] Therefore, if waste ink is treated only with a solvent that has good pigment dispersibility, phthalocyanine blue and carbon black, which cause dull colors, will not coagulate and settle but will remain in the solvent, and other vivid hues will remain. It was confirmed that as the pigment coagulated and precipitated, the intervening resin and additives were also dissolved and transferred to the solvent side, making it possible to recover pigments with fairly high purity and vivid hues. The present invention has been completed based on this point, and relates to a method for recovering pigment from waste ink, which is characterized by adding a solvent with good pigment dispersibility to waste ink and then centrifuging it. FIG. 2 is a flow sheet showing an embodiment of the method of the present invention. In FIG. 2, a solvent 2 with good pigment dispersibility is added to waste ink 1 and mixed 3 and then vigorously stirred 4. Next, this liquid is centrifuged 5 to separate solid and liquid. Decantation can also be carried out before this centrifugation. The pigment is recovered in the solid phase 6 and the solvent is recovered in the liquid phase 7. Here, as the solvent 2 having good pigment dispersibility, as mentioned above, ketones such as cyclohexanone and methyl isobutyl ketone, and ethers such as methyl cellosolve are used. In addition, the mixing ratio of waste ink 1 and solvent 2 with good pigment dispersibility is determined by The ink ratio (capacity ratio) is preferably 2 to 3 or more. Hereinafter, the method of the present invention will be explained in more detail with reference to Examples. Example 1 100 ml of cyclohexanone was added to 20 ml of waste ink, set in a centrifugal separator, and operated at a rotation speed of 6000 rpm for 10 minutes to separate the pigment from the liquid phase. As a result, 3.1 g of pigment with a purity of 90 to 99% could be obtained. Example 2 100 ml of methyl cellosolve was added to 20 ml of waste ink, the centrifugal separator was set, and the centrifugal separator was operated at a rotation speed of 6000 rpm for 10 minutes to separate the pigment from the liquid phase. As a result, 3.2 g of pigment with a purity of 85 to 90% could be obtained. In addition, as a result of conducting the same test as above using a solvent other than the above-mentioned solvent with good pigment dispersibility, almost the same results as above were obtained.

[Brief explanation of the drawing]

Fig. 1 is a diagram schematically showing the dispersion state of pigment particles in ink, Fig. 2 is a flow sheet showing an embodiment of the method of the present invention, and Fig. 3 is a diagram showing the pigment separation rate and solvent/waste ink during pigment recovery. It is a figure showing the relationship with ratio (capacity ratio).

Claims (1)

[Claims] 1. A method for recovering pigments from waste ink, which comprises adding a solvent with good pigment dispersibility to waste ink and then centrifuging the mixture.