JPS631884B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for recovering pigment from waste ink. Inks used in various types of printing, such as letterpress, intaglio, 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. For example, methyl alcohol, ethyl alcohol: If the intervening resin is an alkyd resin, these alcohols have no effect of dissolving the alkyd resin, so regardless of the type of pigment, the dispersibility is poor. In the case of cellulose, these alcohols dissolve nitrocellulose, so they show the same dispersibility as shown in Table 2. Isopropyl alcohol: Regardless of whether the intervening resin is an alkyd resin or nitrocellulose, isopropyl alcohol dissolves these resins. Ethyl acetate: Regardless of whether the intervening resin is an alkyd resin or nitrocellulose, ethyl acetate has the effect of dissolving these resins, so the dispersibility is poor regardless of the type of pigment. Shows similar dispersibility, and shows selectivity in dispersion. (4) Blue pigments (phthalocyanine blue) and carbon black tend to be somewhat easily dispersed in any solvent. Based on the above knowledge, the present inventors first added a solvent with poor pigment dispersibility, or a mixture of the solvent with a solvent with good pigment dispersibility, alcohol, etc. to the waste ink to form pigment particles. We proposed a method to recover the pigment and the solvent by coagulation and sedimentation separation. The present inventors further investigated solvents that exhibit selectivity in pigment dispersibility depending on the type of pigment and the type of intervening resin, and found that among these solvents, esters do not interfere with the intervening resin as described above. Knowledge that phthalocyanine blue and carbon black, which exhibit good solubility in resins and cause dullness of color, have a strong bond with this intervening resin, and are therefore dispersed into the solvent as the resin dissolves. I got it. Therefore, if waste ink is treated with esters,
Phthalocyanine blue and carbon black migrate to the solvent side together with the resin in the waste ink, and as shown in Table 2, pigments with bright hues have poor dispersibility with respect to esters, so they settle, and can be separated and recovered. The present invention has been completed based on this point, and relates to a method for recovering pigments from waste ink, which is characterized by adding esters to waste ink and then centrifuging the mixture. FIG. 2 is a flow sheet showing an embodiment of the method of the present invention. In FIG. 2, esters 2 are added to waste ink 1 and mixed 3, followed by vigorous stirring 4. Next, this liquid is centrifuged 5 to separate solid and liquid. Incidentally, decantation can also be performed prior to this centrifugation. The pigment is recovered in the solid phase 6 and the solvent is recovered in the liquid phase 7. Here, as the esters 2, as mentioned above, methyl acetate, ethyl acetate, butyl acetate, etc. can be used. Furthermore, the mixing ratio of waste ink 1 and esters 2 is determined by the solvent/waste ink ratio (volume ratio), as is clear from the relationship between the pigment separation rate and the solvent/waste ink ratio (volume ratio) during pigment recovery shown in Figure 3. 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 100 ml of ethyl acetate was added to 20 ml of waste ink, the centrifuge 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 85-90% could be obtained. When the same test as above was conducted using methyl acetate or butyl acetate instead of ethyl acetate, 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 in pigment recovery. It is a figure showing the relationship with ink ratio (capacity ratio).

Claims (1)

[Claims] 1. A method for recovering pigments from waste ink, which is characterized by adding esters to waste ink and then centrifuging it.