Section
| HS Code | 150694 |
| Product Name | Acid Ink Blue G |
| Synonyms | Methyl Blue; Cotton Blue; Ink Blue G; C.I. Acid Blue 93 |
| Colour Index Name | C.I. Acid Blue 93 |
| Colour Index Number | 42780 |
| Cas Registry Number | 28983-56-4 |
| Einecs Number | 249-352-9 |
| Chemical Class | Triphenylmethane acid dye |
| Molecular Formula | C37H27N3Na2O9S3 |
| Molecular Weight | 799.8 g/mol |
| Appearance | Dark blue powder or granules |
| Solubility | Soluble in water; slightly soluble in ethanol |
| Dye Type | Anionic acid dye |
| Principal Use | Writing inks, biological staining, and dyeing of wool, silk, and paper |
As an accredited Acid Ink Blue G factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Acid Ink Blue G is supplied in 25 kg net weight, moisture-resistant, double-lined woven bags with sealed inner polyethylene liners. |
| Container Loading (20′ FCL) | Acid Ink Blue G packed in sealed drums, palletized, moisture-protected, evenly distributed, and secured inside a 20′ FCL container for safe transport. |
| Shipping | Acid Ink Blue G is generally shipped as a non-hazardous dyestuff in sealed, moisture-resistant containers. Protect from heat, sunlight, and contamination. Follow the SDS and applicable transport regulations; if classified as dangerous goods, use appropriate UN packaging, labels, and documentation. |
| Storage | Store Acid Ink Blue G in a cool, dry, well-ventilated area, away from direct sunlight and heat sources. Keep containers tightly closed and protected from moisture. Avoid dust generation, and separate from oxidizers and incompatible chemicals. Use appropriate personal protective equipment. Keep away from food, drink, and animal feed. Follow the manufacturer’s safety data sheet and local regulations. |
| Shelf Life | Typically 24 months when stored sealed in a cool, dry, dark place, away from moisture, heat, and incompatible substances. |
Writing ink concentrate manufacture using Acid Ink Blue G (C.I. Acid Blue 93, C.I. 42780, CAS 28983-56-4) begins with powder addition into deionized water heated to 60–70 °C in a jacketed 304L stainless steel vessel equipped with an anchor stirrer and a rotor-stator high-shear head. Finished dye-based writing ink is formulated at 1.5–4.0 wt%; masterbatch concentrates for remote dilution are compounded at 10–15 wt% active dye, above which ambient storage can produce aggregate settling and viscosity instability. pH is adjusted to 7.5 ± 0.3 with a phosphate buffer after visible-spectrum absorbance stabilizes at the supplier-specified λmax; excursions below this band increase dye aggregation on final filter media and can generate shade drift in piston-fill ink delivery systems. The liquid passes through a 5 µm polypropylene depth prefilter and a 0.8 µm absolute-rated polypropylene membrane capsule before vacuum deaeration at −0.08 to −0.095 MPa for 30 min. Inline differential pressure transmitters across the membrane capsule are mandatory; an upward pressure trend during a batch signals incomplete dissolution and requires recirculation through the rotor-stator head before packaging. Finished ink viscosity is checked with a Brookfield UL adapter at 25 °C; typical values are 1.5–3.5 mPa·s, and deviations outside this range alter capillary flow in piston-fill and cartridge-fed writing systems. Colorimetric release testing uses a sphere-based spectrophotometer with D65 illuminant and 10° observer; batch acceptance is ΔE*ab ≤ 0.5 against a frozen reference standard. Compliance for stationery ink is checked against EN 71-3:2019+A1:2021 soluble-element migration limits, ASTM F963-23 where children’s writing sets are possible, ISO 12757-2 for ballpoint/rollerball refill documentary use, and REACH Regulation (EC) No 1907/2006 Annex XVII entry 43 aromatic amine absence; although the chromophore is triphenylmethane rather than azo, certificate-of-analysis runs include aniline and benzidine residuals as process markers. Downstream terminal product types include bottled fountain pen ink, international standard cartridges, disposable writing pens, and drafting ink concentrates. Operational limitation: Acid Ink Blue G typically shows Blue Wool Scale 1–2 under ISO 105-B02:2014, disqualifying it for archival documents requiring lightfastness higher than level 2; compatibility with cationic antimicrobials, especially quaternary ammonium compounds, must be evaluated because localized precipitation has been observed in low-pH ink bases.
Stamp pad and self-inking stamp fluids differ from bottled writing ink because the fluid must remain mobile in open-cell foam or felt wicks without crusting at the stamp surface during intermittent use. Acid Ink Blue G is charged at 2.0–6.0 wt% of finished ink; below 2.0 wt%, stamped image density on porous paper requires densitometric verification against a customer-specified minimum reflection optical density, and above 6.0 wt%, cold-storage crystallization risk rises, particularly in high-glycerol formulations stored at 5 °C. The dye is pre-dissolved in a heated 60 °C water-glycerol phase containing 10–20 wt% glycerol or sorbitol humectant, then blended with triethylene glycol monobutyl ether or a propylene glycol ether to a Brookfield LVT viscosity of 25–50 mPa·s at 25 °C, spindle 1 at 60 rpm. Filtration trains use a 5 µm depth prefilter followed by a 0.8 µm absolute-rated polypropylene capsule; the final absolute rating is not optional because foamed stamp pads retain particles and convert them into surface defects during repeated stamping. Production equipment includes a vacuum deaeration vessel and an inline differential pressure monitor across the membrane capsule; batches are held for 72 h at 5 °C and inspected for sediment before release. Compliance documentation includes EN 71-3:2019+A1:2021 heavy-metal migration limits, ASTM F963-23 for craft stamp sets, and REACH Annex XVII entry 43 aromatic amine documentation. Downstream terminal product types include pre-inked self-inking stamp cartridges, replacement stamp pad refill bottles, industrial date-stamp pads, and textile marking pads; textile marking applications require separate wet-rub and washfastness testing because the dye, unless fixed with a cationic aftertreatment, redissolves from woven cotton after aqueous laundering.
In drum dyeing of chrome-tanned shaved crust for stationery and bookbinding leather, Acid Ink Blue G is applied at 0.5–2.0% of shaved wet-blue weight after neutralization with sodium formate and sodium bicarbonate to a cut pH of 5.0–5.5. The dyebath float is maintained at 200–300% on shaved weight and heated to 55–65 °C in a stainless steel drum with baffle mixing; drum speed is set between 6–10 rpm for large hides but is adjusted to prevent grain damage on thin splits. The dye is pre-dissolved at 1:20 in hot water and added through the drum axle in three equal feeds at 10–15 min intervals to avoid localized uptake and grain-side streaking. Exhaustion is monitored by visible-spectrum absorbance on the spent float; when absorbance plateaus across two consecutive readings, fixation proceeds with 85% formic acid diluted 1:10 and fed in two portions until float pH reaches 3.8–4.2. Low-pH fixation protonates collagen carboxyl groups and draws the anionic triphenylmethane dye toward the fibre surface, increasing wet-rub fastness but raising grain darkening risk on full-grain aniline articles. Spent float residual dye concentration after fixation is used to calculate exhaustion; values below 90% trigger process review because residual dye loads downstream effluent treatment and can unevenly redeposit on subsequent batches. Compliance for leather shipped to EU and North American stationery or footwear customers requires ISO 11640:2018 rub fastness evaluation with grey scale, ISO 105-B02:2014 lightfastness evaluation on the finished article, and REACH Annex XVII entry 43 documentation for restricted aromatic amines. ZDHC MRSL v3.1 screening includes aniline and benzidine residuals from triphenylmethane synthesis even though the chromophore is not azo; low-salt grade selection avoids dyebath electrolyte shifts that can cause dye precipitation on drum walls. Downstream terminal product types include drum-dyed full-grain aniline bookbinding leather, embossed split leather for stationery covers, and unlined leather goods. Operational boundary: the Blue Wool Scale rating is typically 1–2, so Acid Ink Blue G is excluded from leather components requiring level 4 or better under ISO 105-B02; interior low-UV uses or UV-absorber topcoats require qualification testing because retained tanning agents can shift shade in rub fastness trials.
In bleached kraft and cotton linter stock intended for stationery board and index card, Acid Ink Blue G is introduced at the fan pump inlet rather than during pulping because the triphenylmethane dye is poorly retained on unmodified cellulose at neutral pH. Addition levels on oven-dry fiber are 0.05–0.3 wt% for pastel to medium blue board; saturated cover and folder stock require 0.5–1.0 wt%, but higher loading increases white-water colour load unless a cationic poly-DADMAC or alum retention aid is metered at 0.05–0.2 wt% on dry fibre after the dye has equilibrated with the stock. Stock pH is controlled at 4.5–5.5 with aluminium sulphate upstream of the dye feed; headbox and tray water absorbance are monitored in the visible band to calculate first-pass retention. The dosing skid includes a 0.5–1.0% dye solution makeup tank and magnetic flow meters at the fan pump suction; shade drift occurs when broke containing residual dye returns to the furnish without colour compensation, so the control loop must include broke ratio. Compliance documentation for finished stationery paper and board includes EN 71-3:2019+A1:2021 soluble-element migration, ISO 2144:2019 ash determination where filler content affects shade, and REACH Annex XVII entry 43 aromatic amine absence. Acid Ink Blue G is not claimed for direct food-contact paper or board under FDA 21 CFR 176.170 unless a specific regulatory clearance letter for the batch composition is obtained. Downstream terminal product types include colored writing paper, index cards, file folders, pressboard dividers, and kraft envelopes. The product is not recommended for exterior packaging subjected to prolonged retail window light because ISO 105-B02:2014 Blue Wool Scale remains at 1–2, and visible shade change can occur before normal shelf rotation.
Histology laboratories substituting Acid Ink Blue G in connective tissue stains prepare a stock solution at 2.5% w/v in 2% v/v acetic acid and filter it through 0.45 µm low-protein-binding polyethersulfone membrane to remove insoluble particles that would otherwise deposit on slides as artefactual precipitate. Working dilutions are prepared at 0.1–1.0% w/v in aqueous acetic acid and applied after phosphomolybdic acid/phosphotungstic acid mordanting in modified Masson trichrome sequences; differentiation with 1% acetic acid controls background staining intensity. Products sold to EU clinical laboratories fall under Regulation (EU) 2017/746 (IVDR) only when marketed as an in vitro diagnostic reagent; research-use-only sales remain outside IVDR scope but require REACH registration and safety data sheets. Laboratories operating under ISO 15189:2022 must verify lot-to-lot dye purity and staining specificity before diagnostic use. Downstream terminal product types include research-use-only histology staining kits, in-house working solutions for collagen visualization, and quality control reagents for pathology training sets. The operational boundary is purity: commercial Acid Ink Blue G is not automatically biological stain grade; certificates of analysis must specify dye content, insoluble matter, and heavy metals before a batch is approved for slide stainer use.
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Acid Ink Blue G is the commercial designation for the water-soluble triarylmethane acid dye C.I. Acid Blue 93, C.I. 42780, CAS 28983-56-4. The colorant is supplied as a dark blue powder and is reported as the disodium salt of a sulfonated triphenylmethane derivative with molecular formula C37H27N3Na2O9S3 and molecular weight 799.80 g/mol. The product is used primarily in water-based flexographic and gravure printing inks for absorbent substrates, paper and board stock dyeing, tissue shading, and selected leather finishing operations in which a transparent, non-pigment blue is required. Because the chromophore is not an azo structure, the dye falls outside the aromatic amine screening scope of EN 14362-1:2012, a distinction that reduces the regulatory testing package relative to many acid and direct azo dyes used in the same shade area.
Lot acceptance is normally controlled by colour strength relative to a type standard rather than by absolute dye content. The release criteria below are representative of dyehouse quality agreements and should be confirmed against the supplier’s certificate of analysis for the specific batch. Deviations outside these bands are typically caused by incomplete desalting, excessive moisture uptake, or cross-contamination from other water-soluble dyes.
| Parameter | Test method | Typical specification |
|---|---|---|
| Appearance | Visual inspection | Dark blue powder |
| Colour strength | UV-Vis spectrophotometry at λmax | 100 ± 3% relative to type standard |
| Absorption maximum | UV-Vis, 0.02 g/L in deionized water, 10 mm cell | 598–602 nm |
| Moisture | ISO 787-2 | ≤ 5.0% |
| Water-insoluble matter | ISO 787-3 | ≤ 0.3% |
| pH of 1% aqueous solution | ISO 787-9 | 5.5–7.5 |
| Solubility in deionized water at 25 °C | Supplier equilibrium method | ≥ 50 g/L |
For colour strength measurement, a 0.02 g/L solution is prepared in deionized water buffered to pH 6.5, and absorbance is read at the absorption maximum in a 10 mm quartz cell. The strength is calculated against a reference lot of C.I. Acid Blue 93 using the ratio of absorbance at λmax. The method avoids the matrix effects of ink resins and is used only for incoming dye acceptance; final ink strength is verified by drawdown on the target substrate.
Dissolution of Acid Ink Blue G at production scale is carried out in a jacketed stainless-steel vessel fitted with a high-torque, low-shear propeller agitator operating at 500–800 rpm. Water is preheated to 50–60 °C before powder addition. Adding the powder directly to cold tap water is not recommended because the resulting lumps can blind a 10 µm filter. A typical stock solution is 10 wt% dye in demineralized water. The solution is cooled to below 30 °C before letdown into acrylic or styrene-acrylic varnishes to avoid thermal shock that can destabilize polymer emulsions. On production flexographic lines, stock solution is metered through a mass-flow meter and an in-line 10 µm polypropylene bag filter, with pressure differential across the filter recorded at the start and end of the batch. A rising differential above 0.8 bar under constant flow indicates incomplete dissolution, hard-water precipitation, or filtration bypass.
Divalent cations in tap water reduce the solubility of Acid Ink Blue G by forming insoluble calcium and magnesium sulfonate salts. This is the main field failure mode observed when a dye stock is diluted directly with untreated process water. At total hardness above 150 mg/L CaCO3, haze may appear within 30 min at 25 °C. The correction is not higher shear; it is chelation or demineralization. Tetrasodium EDTA at 0.1–0.3 wt% of dye, or sodium hexametaphosphate at comparable dosage, is added to the dissolution water before the dye powder. pH is maintained between 7.0 and 9.0. Below pH 5.0, some triarylmethane sulfonates undergo protonation and shade drift; above pH 10.0, acrylic resin systems in typical water-based inks may saponify. The dye solution pH is therefore checked after 20 min of mixing and adjusted with dilute sodium hydroxide or acetic acid only if the target window is exceeded. Make-up water with conductivity below 10 µS/cm and total hardness below 50 mg/L CaCO3 is used where consistent shade stability is required.
At paper and board mills, Acid Ink Blue G is applied either at the wet end or at the size press. Wet-end application uses the anionic dye with a cationic retention aid; without a retention aid, dye loss to white water is high and shade control is poor. Typical wet-end dose ranges from 0.05 kg to 0.5 kg per metric ton of dry fiber; higher doses produce diminishing gain and increase white-water colour. The dye injection point is separated from cationic starch, wet-strength resins, and polyDADMAC retention aid by at least 30 s of flow travel to avoid insoluble polyelectrolyte complexes. Shade is monitored by reflectance spectrophotometry at the reel. In closed white-water systems, dissolved dye can accumulate and shift shade without a corresponding increase in fresh dye addition; a controlled bleed or white-water treatment is therefore part of the process control strategy.
Substitution of Acid Ink Blue G for C.I. Acid Blue 9 is not drop-in. The two dyes belong to the same triarylmethane class but differ in absorption maximum, molecular mass, and visual chroma. On uncoated woodfree paper, Acid Ink Blue G produces a duller, red-shifted blue, while C.I. Acid Blue 9 produces a brighter greenish blue. The shift in absorption maximum from approximately 598–602 nm for Acid Ink Blue G to approximately 628–632 nm for C.I. Acid Blue 9 requires a full rebalance of the yellow and magenta components in a formulation, not a simple one-to-one replacement. The difference is measurable by UV-Vis spectrophotometry and by comparative drawdown.
| Property | Acid Ink Blue G | C.I. Acid Blue 9 | Pigment Blue 15:3 dispersion |
|---|---|---|---|
| Chromophore class | Triarylmethane | Triarylmethane | Copper phthalocyanine |
| Molecular weight | 799.80 g/mol | 792.85 g/mol | Not applicable |
| Absorption maximum in water | 598–602 nm | 628–632 nm | Not applicable |
| Application form | True solution | True solution | Colloidal dispersion |
| Aromatic amine screening under EN 14362-1:2012 | Not triggered | Not triggered | Not triggered |
Accelerated xenon-arc testing of printed drawdowns under ISO 12040 shows the triarylmethane chromophore fades faster than a β-phthalocyanine pigment dispersion; the dye-based print is generally below grade 4, while the pigment-based print retains grade 7–8. This limits Acid Ink Blue G to interior or disposable applications unless a UV absorber and hindered amine stabilizer package is formulated into the ink. Compared with C.I. Acid Blue 9, Acid Ink Blue G has lower visual brilliance but can be easier to meter in pastel shading because its lower tinctorial strength per unit mass reduces the effect of weighing error. Compared with pigment dispersions, Acid Ink Blue G contributes no specking, no grinding, and no grind gauge value; it is selected where transparency and low viscosity are more important than outdoor durability.
The non-azo structure of Acid Ink Blue G removes the need for reductive aromatic amine analysis under EN 14362-1:2012. For food-contact-adjacent paper and board, the dye by itself does not provide food-contact compliance; migration testing under EU Regulation 1935/2004 or US 21 CFR 176.170 is required on the finished print. Dust from the powder should be controlled under national occupational exposure limits; local exhaust ventilation and EN 149 FFP2 respiratory protection are used during weighing.
On production gravure lines, most rejects associated with Acid Ink Blue G are not viscosity shifts but filtration plugging and anilox contamination from undissolved or precipitated material. The dye is a true solution; it does not contribute to grind gauge readings and does not raise high-shear viscosity. In a typical water-based gravure set-up, the stock solution is prepared at 10 wt%, cooled below 30 °C, and passed through a 10 µm absolute polypropylene bag filter before being metered into the press ink. If the filter pressure differential rises above 0.8 bar under constant flow, the batch is quarantined and reworked. Published data for the specific viscosity contribution of Acid Ink Blue G in high-solids flexographic formulations is limited; formulators treat the dye as a non-film-forming solute that replaces water volume, not as a rheology modifier. The primary operational boundary is therefore solution preparation: demineralized water, controlled temperature, chelation where needed, and post-cooling filtration.
In chrome-tanned leather drum dyeing, Acid Ink Blue G is applied in an anionic float after neutralization, with penetration controlled by temperature and ammonium sulfate or formic acid fixation. Typical use levels range from 0.5% to 2.0% on shaved weight; spent float is exhausted before discharge. Cationic retanning agents and cationic fixatives should not be introduced before dye fixation because insoluble lakes form and shade becomes unlevel. The use is limited to interior linings and non-visible components because the triarylmethane chromophore has lower lightfastness under ISO 105-B02 than metal-complex or selected azo acid dyes. For automotive leather, published data for this specific configuration is limited; accelerated weathering to SAE J2412 is required before any acceptance.
