NJTAP Pollution Prevention Case Study -- Constant Services

Summary

Constant Services Inc. (CSI), a midsized company based in Fairfield, New Jersey, prints and laminates vinyl web, primarily for use as wallpaper. Up until 1994, it cleaned, ran its presses, and formulated its inks with solvents listed under the EPA's Toxic Release Inventory (TRI). The New Jersey Technical Assistance Program for Industrial Pollution Prevention (NJTAP), located at the New Jersey Institute of Technology, helped the company switch to non-TRI solvents.

Work Practices, Modifications, and Cost Savings

Between production runs CSI washed down its ink trays and doctor blades with a 1:1 mixture of methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK), which it then recaptured in pails for use in ink. The company also cleaned its equipment with rags soaked with the MEK/MIBK mix.

The new procedure uses dry rags to wipe down the press parts, which are cleaned solely by the solvent content in the ink residues. This eliminates the washdown with solvents, and reduces total solvent consumption and emissions.

Under the old system, approximately 10,800 pounds of solvents per year were used to clean the print stations, 10 percent of which is estimated to have escaped as fugitive emissions during washdown. Eliminating the washdown, therefore, results in the reduction of 1,100 pounds of the 1:1 MEK/MIBK consumed per year and (based on a mixture price of $0.40 per pound) an annual savings of $440.

The quantity of solvents lost by evaporation from rags was estimated by comparing the weight of solvent-laden rags immediately after discard to their weight after they had fully dried. Multiplying the resulting average to reflect the 50 four-day workweeks CSI logs each year, the annual solvent loss was calculated to have been 3,600 pounds. The savings for using dry rags is therefore $1,440.

Cleaning with dry rags also reduces overall cycle time. Shutdowns that used to take 90 minutes now take only 10 to 20 minutes. The resultant reduction in labor hours is estimated to be 2,300 per year. Given average hourly labor costs of $10.25, that translates into an extra $23,575 that the new approach saves CSI each year.

Table 1: Overall Cost Savings

Solvent Changes Reduce Hazards

CSI has a one-cylinder proofing (or "strike-off") press. The ink formerly used on this press included cyclohexanone and MIBK. The company's initial search for substitutes led to the introduction of PMA, a glycol ether acetate (1-methoxy-2-propyl acetate). CSI then began using ISP Printsolve® solvent both in the ink formulation and to clean the press. Printsolve is a combination of two high-boiling solvents, N-methyl 2-pyrrolidone and dipropylene glycol methyl ether, and cleans well without emitting dangerous vapors or creating a fire hazard (Table 2).

Printsolve provided better than expected printing results. Its viscosity, which is higher than MIBK’s, improved print image quality. The company went on to reformulate its solvent into a 2:1 mixture of Printsolve and PMA before experimenting with DBE, a DuPont-manufactured dibasic ester mixture of dimethyl glutarate, dimethyl adipate, and dimethyl succinate. CSI gradually replaced the PMA in the ink with DBE.

Today, CSI's ink contains a 4:1 mixture of Printsolve and DBE. MIBK and cyclohexanone were eliminated from the proofing pressroom. Printsolve and DBE are used for both inkmaking and press cleaning. Because both alternative solvents have low evaporation rates, ink drying time has increased. Small amounts of PMA are sometimes mixed with Printsolve for jobs that require faster drying.

Table 2 shows some properties of the aforementioned chemicals. Both Printsolve and DBE have far lower vapor pressures and higher flash points than the others, earning them safer ratings under the hazard codes. Although Printsolve's threshold limit value (TLV) is half that of MEK, its vapor pressure is 258 times lower, greatly reducing vapor inhalation rates.

Based on these successes, CSI decided to try using DBE and Printsolve as substitutes in the formulation of its pigments, which had been MIBK solutions. Trials were very successful, and the company soon replaced the MIBK in the pigment formulation with a Printsolve/DBE blend. This reduced the plant's hazardous air pollutant (HAP) totals and fugitive emissions. The estimated quantity of MIBK replaced with the Printsolve/DBE blend is approximately an additional 10,000 pounds per year.

Table 2: Physical Properties of Solvents

New Jersey Technical Assistance Program for Industrial Pollution Prevention (NJTAP)
138 Warren Street
University Heights
Newark, NJ 07102-1982
973-596-5864
Reprinted November 1998