Gum arabic for lithographic fountain solutions
Purified spray-dried gum arabic that desensitizes the non-image areas of an offset plate. Types 4880 and 4915 dissolve in cold water with no grinding step. Country of origin Germany.
Purified spray-dried gum arabic that desensitizes the non-image areas of an offset plate. Types 4880 and 4915 dissolve in cold water with no grinding step. Country of origin Germany.
Gum arabic desensitizes the non-image areas of a lithographic plate. Image and non-image areas sit on one surface at the same level, and the press separates them chemically: the image areas take ink and reject water, the open areas hold water and reject ink. Gum arabic is what makes the open areas hold water.
Gum arabic is an anionic polysaccharide, an arabinogalactan carrying acidic sugar residues and a small protein fraction. Those acidic groups adsorb onto the grained, anodized aluminum oxide of the plate surface. The rest of the molecule faces outward into the solution, where it is strongly hydrophilic and carries a water film with it. The adsorbed layer is thin, it is tenacious, and the dampening system renews it on every revolution of the plate cylinder.
The same chemistry does a second job off the press. A plate gummed at the end of a run keeps its desensitized surface through storage and comes back to the press ready to run, which is why gum arabic appears in plate finishers and preservers as well as in the fountain concentrate itself.
Both grades are purified, agglomerated, fast-soluble spray-dried gum arabic powders. The specification calls them coarse yellowish powders, fast soluble in cold water, forming a colloidal solution. Every value below is read off the current supplier specification.
| Property | Type 4880 | Type 4915 | Method |
|---|---|---|---|
| Form | Agglomerated spray-dried powder | Agglomerated spray-dried powder | Appearance |
| Color, 25% w/w on dry matter | 4 to 10 | 5 to 12 | Lovibond Tintometer, 1 inch cell |
| Viscosity, 25% w/w after 24 h | 60 to 100 mPa·s | 60 to 100 mPa·s | Brookfield LVT, spindle 2, 60 rpm, 20 °C |
| pH, 25% w/w in water | 4 to 5 | 4 to 5 | Internal method |
| Insoluble matter | 0.1% max | 0.1% max | FCC |
| Acid-insoluble ash | 0.5% max | 0.5% max | FCC |
| Total ash | 4.0% max | 4.0% max | USP |
| Loss on drying | 10.0% max | 10.0% max | Ph. Eur. |
| Specific optical rotation | Dextrorotatory | Dextrorotatory | Internal method |
| Country of origin | Germany | Germany | Documentation |
Type 4880 is the grade to open on. Type 4915 is the second grade, built the same way, with a wider color band.
The optical rotation row names the botanical species. Dextrorotatory means Acacia seyal. Levorotatory means Acacia senegal. Both grades here are seyal, and seyal builds less viscosity than senegal for the same weight of dissolved gum, which is why a 25 percent concentrate stays thin enough to pump and meter.
Kibbled gum arabic is raw material broken into lumps. A plant running it has to grind it and hydrate it before anything reaches a make-up tank, and the grinder is a piece of equipment with dust, wear parts, and a cleaning routine attached to it.
Types 4880 and 4915 are specified as fast soluble in cold water. There is no grinder, no heated hydration vessel, and no overnight stand. A plant that has taken its grinding step out can keep running gum arabic chemistry on the same formulations.
Purification happens upstream of the powder rather than in your tank. Insoluble matter is specified at 0.1 percent maximum and acid-insoluble ash at 0.5 percent maximum, which is what a tank screen and a metering pump see. Moving a fountain solution off kibbled gum arabic covers what changes on the line when a plant makes the switch.
At 25 percent solids the solution runs 60 to 100 mPa·s, measured on a Brookfield LVT with spindle 2 at 60 rpm and 20 °C after 24 hours. That is thin enough that a concentrate at working strength meters through the same hardware as the rest of the fountain chemistry.
Solution pH at that concentration is 4 to 5, which sits on the acid side where conventional fountain chemistry already runs, so the gum is not fighting the buffer.
Gum arabic is a natural polysaccharide, and a made-up aqueous solution supports microbial growth. Concentrate held in a tank needs preservation and a turnover plan, the same as any other water-based pressroom mix.
The desensitizing component of the dampening solution, renewed on the plate every revolution.
Applied at the end of a run so the non-image areas survive storage and the plate comes back ready.
Restores the hydrophilic layer where a plate has started to take ink in the open areas.
Gum in the rinse step returns the plate to a desensitized state after solvent contact.
Gum arabic is one of three things we ship into fountain chemistry. Sodium benzotriazole 40% solution protects the copper and brass a circulating solution touches, and citric acid holds the pH. All three are on pressroom and fountain solution chemistry.
Every grade ships with a product specification, a Safety Data Sheet, and a Certificate of Analysis for the lot. Country of origin is Germany. Additional statements, including allergen, GMO and heavy-metal declarations, are available on request.
Tell us the grade, the annual volume, and the pack size you run, and we will come back with availability and a sample. If you are working from a competitive specification rather than a type number, send it and we will tell you which grade matches and where it does not.
Type 4880. It is a purified spray-dried gum arabic powder in agglomerated form, so it goes into cold water without a grinding step, and its color band is the tighter of the two at 4 to 10 on the Lovibond scale. Type 4915 is the second grade, built the same way with a color band of 5 to 12. Tell us the volume and the make-up method and we will confirm which one to sample.
It desensitizes the non-image areas. Gum arabic is an anionic polysaccharide, and its acidic groups adsorb onto the grained aluminum oxide surface of the plate while the rest of the molecule faces outward and holds water. That adsorbed layer is what keeps the open areas water-receptive so they reject ink, and the dampening system renews it on every revolution.
No. Kibbled gum arabic arrives as lumps and has to be ground and hydrated before it reaches a make-up tank. Types 4880 and 4915 are supplied as agglomerated spray-dried powders specified as fast soluble in cold water, so a plant that has taken out its grinding step can still run gum arabic chemistry.
Yes. Gum arabic, gum acacia and acacia gum are the same material, CAS 9000-01-5, listed as E 414 in the EU additive numbering. Printing uses gum arabic, food formulation tends to use gum acacia, and the specification documents are the same either way.
The color number is on the specification because some applications set a limit on it. A dampening solution does not, so the choice between 4880 and 4915 comes down to what the rest of the formulation needs rather than to the Lovibond band.
Germany. Both grades are produced there, and the country of origin on the documentation reads Germany.