Zinc Etching Plates

12 STEPS ZINC ETCHING PROCEDURE 

1)- STORAGE:  

Store zinc photoplates in a cool, dry place.

2)-ARTWORK:

Inspect negative carefully and opaque pinholes in the black areas. Pinholes result in pimply etching if not opaqued.

3)-EXPOSURE:

Expose using a Stouffer 21-Step Sensitivity Guide to a solid step 8-10. Overexposure causes excessive shadow-dot plugging and does not increase etching resistance of coating. Underexposure causes wash-off in development and etching failure.

4)-DEVELOPING:

Mix one part of Heated or Cold Hydro-Coat Developer with five parts water. Heated Hydro-Coat Developer should be used at 105°-115°F (41°-46°C). Cold Hydro-Coat Developer can be used at room temperature 70°-85°F (21°-29°C). In case of evaporation loss when using Hydro-Coat Developer, water alone should be added back to developer solution. DO NOT add back concentrate  Hydro-Coat  Developer to compensate for evaporation loss. Heated Hydro-Coat Developer should be changed when developing times exceed 90 seconds. Cold Hydro-Coat Developer used in trays should be changed daily.

5)-TOUCH UP:

Examine plate for flaws in the image areas retained on the plate and touch up as needed with Retouch Solution.

6)-WEIGH

Record initial plate weight on your etching log prior to etching. Scale must be capable of weighing to the nearest 1/4 ounce.

7)-DESCUM:

Descum Hydro-Coat zinc plates using a solution of sulfuric and nitric acid. Refer to descum formulas on next page. Wipe the descum solution across the plate both horizontally and vertically. For best results apply solution n°1 followed by solution n°2, with a final repeat application of solution n°1. Use separate descum pads for each solution. Rinse between solution applications.

8)-RINSE:

Rinse plates thoroughly with water after descumming.

9)-PLATE PROTECTOR:

An application of Express Guard Plate Protector is recommended prior to etching to enhance performance of etching bath by preventing oxidation which can cause pimples.

10)-ETCH:

Etch plates according to recommendations of etching machine manufacturers and additive technical data sheets.

11)-REPLENISH BATH:

Record plate weight after etching to determine proper acid replenishment. Refer to acid addition chart on last page. Use the following formula to calculate replenishment (where 1:1 represents 30 milliliters of acid per ounce of zinc dissolved into bath):

Initial plate weight – Post etching plate weight = amount of zinc dissolved

Rate of replenishment (1:1 or 1.5:1) will depend upon how much zinc is in the bath. Refer to recommendations of equipment manufacturer.

Example: 38.2 – 31.7 = 6.5 ozs. of zinc dissolved at a rate of 1:1 replenishment, 195 mls of acid are added to bath at a rate of 1.5:1 replenishment, 292,5 mls of acid are added to bath.

Check dip gauge and restore proper level in bath by adding water or draining excess.

12)-TOP REMOVAL (optional)

Use Hydro-Coat Top Remover II according to directions on label.

BASIC ZINC ETCHING BATH FORMULA:

• NITRIC ACID (42 Bé)……………….12%.
• SUPER ETCH or VELV-ETCH………………….3%.
• WATER………………………85%.

STANDARD ZINC ETCHING BATH SHOULD BE MAINTAINED AT 78° – 82°F (26° -28°C). IDEAL TEMPERATURE MAY VARY BASED ON APPLICATIONS.

ZINC DESCUM:

SOLUTION N°1: H2SO4 / HNO3

• 3.42 L WATER
• 350 ML CONCENTRATE SULFURIC ACID*
• 30 ML NITRIC ACID* (42 Bé)

(FORMULA MAKES 3.8 L OR 1 GAL. OF DESCUM SOLUTION).

SOLUTION N°2: HNO3

• 3.04 L WATER
• 760 ML NITRIC ACID* (42 Bé) 20% HNO3

(FORMULA MAKES 3.8 L OR 1 GAL. OF DESCUM SOLUTION).

* CAUTION: DO NOT ADD WATER TO ACID.

ALWAYS ADD ACID SLOWLY TO WATER TO AVOID A HAZARDOUS EXPLOSION.

RECOMMENDED BATH MAKEUP for SELECTED STANDARD INDUSTRY ETCHING MACHINES:

ACID ADDITION CHART