JPS6256763B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for recovering valuables such as pigments and solvents 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】

[Table] 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 dispersibility in Table 2 is as follows. to come in different ways. (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) With ethers such as methyl cellosolve and ketones such as cyclohexanone, all pigments are well dispersed as shown in Table 2, 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 have the effect of dissolving 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 has the effect of dissolving nitrocellulose. Ethyl acetate: Ethyl acetate has the effect of dissolving these resins, regardless of whether the intervening resin is alkyd resin or nitrocellulose. Shows dispersibility similar to 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. Furthermore, when collecting pigments from waste ink and reusing them by remaking them into ink, if the recovered pigments contain a large amount of resins such as the above-mentioned nitrocelluloses and alkyd resins, printing problems will occur. It is necessary to separate these resins in the process of recovering them. On the other hand, from the perspective of separation of pigment particles,
As pigment aggregation is promoted and the particle size becomes larger, separation becomes easier. In order to satisfy these requirements at the same time, it is sufficient to use a mixture of a solvent with good pigment dispersibility and a solvent with poor pigment dispersibility. That is, as a result of experiments, it was confirmed that there is a relationship as shown in FIG. 2 between the dispersion/coagulation properties of ink pigments in a solvent and the above-mentioned resins (mainly nitrocellulose). As is clear from Figure 2,
Solvents with poor pigment dispersibility have poor solubility of nitrocellulose, and therefore, a large amount of resin remains in the pigment recovered with this solvent, which is a problem in reusing the pigment. However, in this case, as is clear from the figure, the pigment has good cohesiveness, so it is easy to separate the pigment from the solvent. On the other hand, as is clear from the figure, solvents with good pigment dispersibility have good solubility of nitrocellulose, so resins such as nitrocellulose in waste ink migrate to the solvent side, and the pigments recovered with this solvent It does not contain resins. However, although this solvent has good pigment dispersibility, it has poor aggregation properties, so the pigment becomes fine particles and disperses, making it difficult to separate the pigment from the solvent. Therefore, if a mixture of a solvent with good pigment dispersibility and a solvent with poor pigment dispersibility is used, the aggregation of the pigment will be promoted.
Separation from the solvent becomes easy, and the pigment can be recovered from which a considerable amount of resin has been removed. The present invention has been made based on the above findings, and furthermore, in order to facilitate processing and downsize the device, the present invention removes impurities from waste ink and concentrates the waste ink beforehand. This is done as a treatment and also to recover the solvent from the liquid after pigment separation. That is, the present invention provides a method for recovering valuables from waste ink, which includes the following steps: (a) passing the waste ink through a filter consisting of 50 meshes or more to remove impurities; A process of concentrating the ink in a vacuum evaporator; (c) A process of cooling the concentrated waste ink and then mixing and dispersing it with a solvent that is a mixture of a solvent with poor pigment dispersibility and a solvent with good pigment dispersibility; (d) A process of mixing with the above solvent. A method for recovering valuables from waste ink, comprising the following steps: separating the dispersed waste ink into solid and liquid using a centrifugal separator, and then recovering the pigment from the solid matter while recovering the solvent from the separated liquid. It is related to. Hereinafter, the method of the present invention will be explained in detail with reference to the accompanying drawings. FIG. 3 is a flow sheet showing an embodiment of the method of the present invention. In FIG. 3, waste ink generated from a printing machine is temporarily put into a waste ink storage tank 1 because it is generated intermittently based on the printing process. Next, it is sent to a filter 2 in order to over-separate impurities such as sand, paper waste, rust, etc. that cause a loss of printing suitability. As a result of the following experiment, it has been confirmed that the filter 2 only needs to be composed of a filter having 50 meshes or more. That is, when the effect of removing impurities was investigated using wire mesh filters made of SUS304 with different meshes, the results shown in FIG. 4 were obtained. As is clear from the figure, in order to remove impurities from waste ink,
It has been found that it is better to use a filter with a mesh size of 50 or more, preferably in the range of 100 to 200 meshes. The filter material is based on the pH of the waste ink.
Since it is on the acidic side at 5 to 7, it is better to use SUS in consideration of corrosion. The waste ink leaving the filter 2 is sent to a waste ink concentrator 4 by a pump 3. Here, the low boiling point solvent is mainly evaporated, and the volume is usually reduced to 1/2 to 1/5. This waste ink concentrator 4 is intended to reduce the size of the device by reducing its volume, and is a step in the preparation operation for replacing the solvent components with a range that can be blended to achieve the optimum solvent composition in the next process (pigment dispersion process). It is. Note that as waste ink is concentrated, the viscosity of the ink increases, making subsequent handling difficult. Therefore, it has been confirmed that the viscosity of concentrated waste ink is 150 to 200 (centipoise) as the upper limit of the operable viscosity, considering transportation, handling, etc. Fifth
The figure is a chart showing an example of the relationship between the pigment concentration in waste ink and the viscosity of waste ink. The concentration level of waste ink can be determined by referring to the figure. In addition, the waste ink concentrator 4 uses a reduced pressure evaporation method to prevent large thermal changes and temperature differences, in order to prevent the pigment from changing due to heating and the mixed additives and resin from solidifying on the inner wall. , the liquid is transferred between the reboiler 5 and the waste ink concentrator 4. Further, the reboiler 5 is heated by hot water from the line 5' in order to reduce the temperature difference between the heating element, the wall surface, and the liquid in order to prevent the above-mentioned deterioration and solidification on the inner wall. By flowing the waste ink between the reboiler 5 and the waste ink concentrator 4 of the reduced-pressure evaporation method, good results are achieved in terms of uniformity of the waste ink, mixing effect, and prevention of caking and clogging. The waste ink leaving the waste ink concentrator 4 passes through a flow rate control device 6 and is once cooled down to near room temperature in a cooler 7, and then enters a dispersion tank 8. In the dispersion tank 8, a certain amount of the optimal dispersion solvent composition, that is, a solvent with good pigment dispersibility and a solvent with poor pigment dispersibility and a flocculating effect, is supplied from the solvent tank 9 and the solvent tank 10, respectively, depending on the properties of the waste ink. After supplying the ink at a constant rate and thoroughly mixing it in the mixing tank 11, the ink is added and thoroughly mixed and brought into contact with the waste ink by stirring or liquid circulation to improve the separation of the pigment particles and prevent adsorption to the pigment particles. dissociates and elutes resins, additives, etc. At this time, carbon black and blue pigments, which cause dullness of color, remain on the solvent side because they do not lose much of their dispersibility in either solvents with poor pigment dispersibility or solvents with good pigment dispersibility, as described above. As is clear from the above findings, aromatic hydrocarbons such as toluene and xylene are used as solvents with poor pigment dispersibility, while ketones such as cyclohexanone and methyl isobutyl ketone are used as solvents with good pigment dispersibility. esters, methyl cellosolve, and other ethers are used. The mixing ratio of these solvents with poor pigment dispersibility and solvents with good pigment dispersibility is preferably about 70/30 to 0/100 in terms of volume ratio. The reason is as follows. The mixing ratio of a solvent with good pigment dispersibility and a solvent with poor pigment dispersibility is a factor that affects the purity of the recovered pigment. FIG. 6 shows the relationship between the composition ratio of this mixed solvent and the purity of the recovered pigment. As is clear from the figure, when the purity of the recovered pigment is 95% or more, the composition ratio of solvent with poor pigment dispersibility/solvent with good pigment dispersibility is approximately 70/30 to 0/100 in terms of volume ratio. Preferably
It turns out that it is 70/30 to 10/90. The addition ratio of the mixed solvent to the waste ink can be determined from the example of the relationship between the pigment separation efficiency from the waste ink and the mixed solvent/waste ink ratio (volume ratio) shown in FIG. It turns out that 2 to 3 (capacity ratio) is preferable. The mixture of waste ink and the above solvent that has come out of the dispersion tank 8 is then sent to a centrifugal separator 12, where a separation operation is performed at 1000 G or more for 30 seconds or more. FIG. 8 shows an example of the relationship between the pigment separation rate and the centrifugal efficiency of the centrifugal separator. As is clear from the figure, in order to efficiently separate and recover pigments from waste ink, the centrifugal force of the centrifugal separator is 1000 G or more, preferably 2000 G or more. It goes without saying that prior to centrifugation, it is preferable to allow the mixture to stand and decant in order to remove pigments that cause dullness of color. The solid content separated by the centrifugal separator 12 is transferred to the dryer 1
After removing a certain amount of the solvent in step 3, it is taken out as a recovered pigment through line 19 and reused. On the other hand, the separated liquid enters the separated liquid tank 14, passes through the preheater 15, and is sent to the evaporator 16. Evaporator 16
Now, while heating the separated liquid in the reboiler 17,
The vacuum pump 18 reduces the pressure inside the evaporator 16 to promote evaporation of the solvent in the separated liquid, and the solvent is transferred to the line 20.
Collect from and reuse. Of the ink components remaining in the separated liquid, resins, additives, etc. are removed from the evaporator 1.
Since it is concentrated at the bottom of the tank, it is either disposed of or mixed with fuel oil and burned, and a portion is recovered as heat. The method of the present invention can be applied not only to the recovery of pigments from waste ink but also to the separation and recovery of dyes having similar properties to pigments. Example Waste ink 1 having the properties shown in Table 3 was
After passing through a mesh wire mesh filter to remove sand, paper scraps, iron rust, etc., the system internal pressure is 100 mmHg at 70℃.
After evaporating under reduced pressure for 2 hours, the pigment in the ink was reduced to 15wt.
%, and then add a dilution solvent consisting of toluene/ethyl acetate in a volume ratio of 50/50 in an amount three times the volume of the concentrated waste ink, and stir vigorously. Thereafter, this mixed solution was applied to a centrifuge and rotated for 5 minutes under a centrifugal effect of 2200 G to separate the pigment solids from the liquid phase, and about 60 g of pigment was recovered. It was found that the pigment recovered in this way had a bright hue and could be reused as ink by remaking it into ink. Table-3 Waste ink properties Color Phase: Dark brown Specific gravity: 0.94 Viscosity: 33cs (Cat 20℃) Pigment content: 7wt% Solvent content: 88.5wt% Solvent composition: Methanol 1.1wt% Ethyl acetate 18.4 Isopropanol 16.2 Toluene 48.1 Acetic acid Butyl 0.6 Xylene 5.7 Methyl cellosolve 6.2 Cyclohexanone 3.8

[Brief explanation of the drawing]

Figure 1 is a diagram schematically showing the dispersion status of pigment particles in ink, and Figure 2 is the relationship between the dispersibility and aggregation of pigments and the solubility of nitrocellulose in solvents with good and poor pigment dispersibility. 3 is a flow sheet showing an embodiment of the method of the present invention,
Figure 4 is a chart showing the relationship between filter mesh and the removal rate of impurities in waste ink, Figure 5 is a chart showing the relationship between pigment concentration in waste ink and viscosity of waste ink when waste ink is concentrated, The figure shows the relationship between the composition of a mixed solvent of a solvent with good pigment dispersibility and a solvent with bad pigment dispersibility and the purity of the recovered pigment. Figure 7 shows the relationship between the mixed solvent/waste ink ratio and the efficiency of pigment separation from waste ink. The chart shown in FIG. 8 is a chart showing the relationship between the pigment separation rate and the centrifugal force when waste ink to which a mixed solvent of a solvent with good pigment dispersibility and a solvent with poor pigment dispersibility is added is centrifuged.

Claims (1)

[Claims] 1. A method for recovering valuables from waste ink, including (a) passing the waste ink through a filter consisting of a filter of 50 or more meshes to remove impurities; (b) removing impurities. (c) the process of cooling the concentrated waste ink and then mixing and dispersing it with a mixture of a solvent with poor pigment dispersibility and a solvent with good pigment dispersibility; (d) the above solvent A process of separating solid-liquid waste ink mixed and dispersed with a centrifuge using a centrifugal separator, and then recovering pigment from the solid matter and recovering a solvent from the separated liquid. Collection method.