R940

R940 belongs to the halogen-free flame retardant category (official English category name: Halogen-Free FR); product type, verbatim: "halogen-free reactive liquid flame retardant, suitable for UV unsaturated acrylic and polyurethane systems". Category and naming conventions: official Chinese name "R940 Unsaturated Acrylic-Polyurethane Reactive Flame Retardant", official website catalog page name "Unsaturated Acrylic-Polyurethane Reactive Flame Retardant", navigation short name "Acrylic-Polyurethane Reactive Flame Retardant", each level reproduced as-is. (Data source: product handbook / official product data)

The key difference from other flame retardants in the same family lies in the "mode of engagement": R940 is the only reactive + liquid grade on the flame retardant side — it does not rely on melt blending, but participates in polymerization through its double bonds and hydroxyl groups and chemically bonds the flame-retardant structure into the resin network. Mechanism sentence, verbatim: "contains methacrylic double bonds, can participate in UV/free-radical polymerization, is chemically bonded into the resin network, no migration, no exudation, no blooming; compared with additive flame retardants, it has less effect on transparency and mechanical properties." Usage definition, verbatim: "it is a reactive flame retardant, needs to participate in polymerization and crosslinking; simple physical blending without participating in the reaction is not recommended." (Data source: product handbook / official product data)

Halogen positioning: the product type line reads "halogen-free reactive liquid flame retardant"; the product composition section records "total phosphorus content approx. 10.5%; no halogen, meets RoHS and REACH requirements"; the official category field is halogen-free flame retardant. This product is a halogen-free grade, and the page's compliance wording is written in the halogen-free direction. (Data source: product handbook / official product data)

Masterbatch route check: no masterbatch grade corresponding to this product was found on the official website or in the masterbatch materials — this page states truthfully that "no masterbatch route is provided" and makes no inference of a corresponding relationship. (Data source: official product data)

• Reactive anchoring — contains methacrylic double bonds and participates in UV / free-radical polymerization; "no migration, no exudation, no blooming".
• Less effect on transparency and mechanical properties — "compared with additive flame retardants, it has less effect on transparency and mechanical properties"; it can be used in transparent systems and "does not noticeably affect the light transmittance of the article" (qualitative statement).
• Phosphorus-phosphorus-nitrogen synergy — DOPO provides highly efficient gas-phase flame retardancy; hexaphenoxycyclotriphosphazene (HPCTP) strengthens condensed-phase char formation and reduces smoke density, balancing flame retardancy and smoke suppression.
• Result target path — "it is recommended to control the total phosphorus content of the system at 1.5-3.0%, which can achieve the UL94 V-0 flame retardancy rating".
• Formulation variable note (PU line) — "pay attention to controlling the NCO/OH ratio; R940 contains hydroxyl groups that will consume -NCO groups, so the formulation needs to adjust the isocyanate dosage."
• Three hard usage notes — temperature should not exceed 120℃ for prolonged heating (to prevent self-polymerization); strongly alkaline substances should be avoided as far as possible in the formulation (to prevent gelation from inhibitor failure); if a higher flame retardancy rating is required, it can be compounded with a small amount of aluminum hydroxide and phosphate ester.

Product composition (mass fraction, verbatim): DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) 49% — the main phosphaphenanthrene flame-retardant body, gas-phase + condensed-phase flame retardancy; hexaphenoxycyclotriphosphazene (HPCTP) 10% — phosphorus-nitrogen synergistic flame retardancy, improving char formation and smoke suppression; HEMA (hydroxyethyl methacrylate) 40% — active double bonds, participating in copolymerization and providing compatibility; triphenylphosphine 0.8% — catalytic auxiliary; MEHQ (p-methoxyphenol) 0.2% — polymerization inhibitor, suppressing self-polymerization during storage. The five items sum to the total. (Data source: product handbook / official product data)

Two flame-retardant mechanisms: (1) reactive anchoring — methacrylic double bonds participate in UV / free-radical polymerization and are chemically bonded into the resin network, "no migration, no exudation, no blooming"; (2) phosphorus-phosphorus-nitrogen synergy — DOPO provides highly efficient gas-phase flame retardancy, and HPCTP strengthens condensed-phase char formation and reduces smoke density. Note that this product is described as "phosphorus-phosphorus-nitrogen" synergy (two phosphorus sources: DOPO and HPCTP), which differs from the wording for other grades; each grade is written according to its own data and is not transposed between grades. (Data source: product handbook / official product data)

Reactive aspects and formulation variables: in PU systems the hydroxyl groups of this product participate in the reaction — verbatim: "pay attention to controlling the NCO/OH ratio; R940 contains hydroxyl groups that will consume -NCO groups, so the formulation needs to adjust the isocyanate dosage." Storage protection uses a dual mechanism: the MEHQ polymerization inhibitor + "store in a cool, dark place, avoid high temperatures, and prevent self-polymerization". (Data source: product handbook / official product data)

Illustrative mechanism diagram on the page (qualitative comparison, not measured values): "Reactive flame retardant: bonded into the network vs. free migration out" — a comparison of the fate of reactive and additive types in the network. The materials do not provide experimental comparison data on migration amount, so this page does not cite it as measured data. (Data source: official product data)

1. Mixing — stirring at room temperatureUV line: "at room temperature, stir and mix directly and uniformly with acrylic monomers, prepolymers, and photoinitiators, then degas before UV curing"; PU line: "it can be mixed directly with polyols and then reacted with isocyanate".
2. Polymerization — double bonds / hydroxyl groups participate in the reactionMethacrylic double bonds participate in UV / free-radical polymerization; hydroxyl groups participate in the polyurethane reaction — the flame-retardant structure is chemically bonded into the resin network.
3. Char formation and smoke suppression — phosphorus-phosphorus-nitrogen synergyDOPO gas-phase flame retardancy + HPCTP strengthens condensed-phase char formation and reduces smoke density; controlling the total phosphorus of the system at 1.5-3.0% can achieve UL94 V-0.
4. Formulation correction — NCO/OH and storage disciplineThe PU line requires adjusting the isocyanate dosage (hydroxyl groups consume -NCO); avoid strongly alkaline substances; do not exceed 120℃ for prolonged heating; use up as soon as possible after opening to prevent self-polymerization from air contact.

The product physical/technical specification table (verbatim) is as follows, and it cross-confirms the spec box on the page. The data are typical ex-factory values; the page notes that a COA test report accompanies each batch; a small-scale trial is recommended for confirmation before bulk use.

Reading notes: (1) The viscosity range 800–2000 mPa·s (25℃) is wide, and the source gives no typical value; (2) Density, moisture, color, thermal decomposition temperature, test method for phosphorus content, and hydroxyl value (OH value) — not listed in the source materials, and not drafted in their place on this page; (3) Handling and protection items (mask / gloves / eye flushing, etc.) are not listed on this model's page. (Data source: product handbook / official product data)

There are two dosage lines, each with its denominator stated separately, and they must not be mixed in calculation: UV acrylic system (UV-curable) at 15-30% based on total resin mass; polyurethane system (PU/PUA) at 12-25% based on the polyol component. The resulting target is that a system total phosphorus of 1.5-3.0% can achieve UL94 V-0.

Dosage is taken separately for the two major systems; the two lines have different denominators (total resin mass / polyol component) and must not be converted into each other or mixed. Order-of-magnitude reference (engineering reading): the total phosphorus of this product is about 10.5%; added at 15%–30% on the UV line, its phosphorus contribution to the resin is on the order of 1.6%–3.2%, the same order of magnitude as, and in the same direction as, the "system total phosphorus 1.5%–3.0%" window — the source gives no conversion model; this serves only as an order-of-magnitude reference, and acceptance is based on measured values.

To be verified: (1) The application test points (system × addition level × target rating) are not given in the source; transparency and non-blooming are both qualitative statements; (2) The specific adjustment equivalent data for hydroxyl value (OH value) and NCO/OH are not given in the source; (3) For UL94 V-0, the specimen bar, thickness, testing organization and report number, and LOI and smoke density values are not given in the source; (4) All the above are values recorded in the source materials; determine the actual formulation through a small-scale trial.

The applicable systems are the two major systems of UV unsaturated acrylic and polyurethane; the compatibility list and application fields are given item by item below.

UV-curable acrylic resin / polyurethane acrylate / PU prepolymer

Listed in the source compatibility list; on the UV line, mix at room temperature and UV-cure after defoaming.

UV photocurable coatings, inks

Original text of the application fields: UV photocurable coatings, inks, wood / plastic UV coatings; the official application field is coatings and inks.

Polyurethane adhesives, sealants, PU potting compounds

Listed in the original text of the application fields; on the PU line it can be mixed directly with the polyol and then reacted with the isocyanate.

Composite matrix resins, electronic component encapsulation, glass fiber reinforced resins

Listed in the original text of the application fields.

Transparent flame retardant adhesives, 3D printing photocurable resins

Listed in the original text of the application fields; "can be used in transparent systems without noticeably affecting the light transmittance of the product; can be used together with photoinitiators and reactive diluents" (qualitative statement).

Scope and hard-constraint reminders

The source lists only the two major systems of UV acrylic / polyurethane — other systems should not be extrapolated on the basis of "also being a halogen-free flame retardant"; before entering a new system, first screen two hard constraints: avoid strongly alkaline substances, and do not use in addition-cure silicone (platinum-catalyzed) systems.

Field issues & application examples (as recorded in the source material)

The five flame retardant items are divided by system route (not ranked by strength); this table gives this model's position and the differences from adjacent routes, and the comparison columns are each source's original text.

Reading notes: (1) The five items are divided by system route — this model is the only reactive type + liquid route; (2) the two types of dosage have different denominators (of total resin mass / of total inorganic system mass, etc.), so the values cannot be compared directly with each other; (3) this model does not provide a masterbatch route (other models may have separate masterbatch paths); (4) the comparison columns are each source's original text. (Data source: product handbook / official product data)

The following points come item by item from the documented records (including three hard usage cautions and storage and transport clauses).

The data on this page comes from two types of sources, each item traceable:

• Product handbook: this model's complete technical data page (product type / product composition, five items / physical technical indicators, six items / features, four items / process and addition amount / application fields, four groups / storage and packaging / prohibited-use warnings); table of contents line; the identical-text page in the flame retardant series booklet (verbatim cross-verification across multiple booklets).
• Official product data: all fields of this model (name, category, description, mechanism, application, parameters, main components, dosage); the flame retardant series entry; page-level copy (product composition stack, curing mechanism comparison, physical indicators, process and addition amount, application fields, storage and packaging, and prohibited-use warnings).

Not covered by the source material (not written on this page — to be added later)

• Density, moisture, color, thermal decomposition temperature, phosphorus content test method, hydroxyl value (OH value) and NCO/OH adjustment amount — not listed in the sources.
• UL94 V-0 test bar / thickness / testing organization / report number, LOI and smoke density values, halogen content threshold and test report — not provided in the sources.
• Prohibited-use mechanism (details of the toxicity risk of incompatibility with addition-cure silicone) — the sources only have a brief statement.
• Typical viscosity range values and batch variation; how the shelf life is counted and the post-opening validity period; handling protection items — not provided in the sources.
• Actual application test points (system × addition amount × target rating) — not provided in the sources.