Ningbo Runhe High-tech Materials Technology Co., Ltd. Release Agent for Composite and Plastic Molding

Release agents for composite and plastic molding are classified by active chemistry, carrier fluid, transfer tendency, and thermal endurance. The product supplied by Ningbo Runhe High-tech Materials Technology Co., Ltd. is intended for external and internal release applications in thermoset compression molding, thermoplastic injection molding, polyurethane reaction injection molding, and bulk molding compound processing. Surface energy modification is the primary mechanism. A low-energy release film with a water contact angle above 90° reduces demolding force and prevents micro-tearing of the resin-rich surface. However, contact angle alone does not predict transfer. Semi-permanent films crosslinked at 150–180 °C for 15–30 min produce a solvent-resistant layer that withstands multiple molding cycles, but incomplete crosslinking yields oligomeric species that migrate to the molded part and compromise subsequent bonding. The release film must therefore be validated by measuring the water contact angle on the molded face with ASTM D7334-08(2022) and by cross-cut adhesion after application of a two-component acrylic paint with ASTM D3359-23 method B.

In carbon fiber epoxy compression molding, the release boundary operates at the interface between a 120–180 °C tool surface and a curing matrix with a gel point between 80 °C and 130 °C depending on the amine curative. The mold surface should be prepared by stripping existing release film with a methylene chloride-free alkaline cleaner that satisfies low-VOC requirements under European Union Directive 2010/75/EU, followed by dry ice blasting to an arithmetic mean roughness Ra of 0.4–0.8 µm as measured by a contact stylus profilometer in accordance with ISO 21920-2:2021. A wiped semi-permanent release agent is then applied in 3–5 thin passes with a lint-free cotton pad and allowed to flash between passes for 5–10 min at 22–25 °C. The final film is cured in the closed press at the production mold temperature for 15–30 min. Release performance is not absolute; it depends on resin viscosity, molding pressure, and local shear stress at the tool surface. In a typical autoclave cycle at 0.6 MPa and 180 °C, the shear stress at a vertical wall can exceed 0.2 MPa when the cured laminate shrinks onto the core. A release film with low cohesive strength fails cohesively rather than adhesively, leaving visible residue on the part. The failure mode is distinguished by solvent wiping after demolding: adhesive failure leaves the tool wetting reagent unchanged, whereas cohesive failure produces a visible haze that reduces the water contact angle below 70°. Published data for the specific Ningbo Runhe formulation under autoclave conditions is limited, so qualification on a 300 mm × 300 mm flat plaque tool with a 5° draft angle is recommended before production use. The mold release system must not contain silicone species above 0.1% when the part will undergo subsequent bonding, because silicone transfer is known to reduce adhesive bond strength. The release agent must not be combined with amine-based additives in the same application line because residual amine vapors can neutralize acid-functional emulsifiers in water-based films and cause premature film loss. When relative humidity exceeds 60%, the mold surface should be pre-dried with forced air at 60 °C for 10 min before applying a water-based release.

Does Release Agent Composition Shift Integral Skin Urethane Surface Tear Strength?

The water-based release agent evaluated for integral skin polyurethane foam is applied to a cast aluminum mold maintained at 45–70 °C with a high-volume low-pressure spray gun having a nozzle diameter of 1.0–1.4 mm and a fluid pressure of 0.1–0.2 MPa. The foam system consists of a polyether polyol, a polymeric MDI with an isocyanate index of 100–105, and a water-blown cell structure. Release failure in this application appears as skin delamination or raised surface porosity because the release film, if not fully dried, reacts with isocyanate and forms urea-rich domains that adhere to the mold. Drying is therefore carried out at a mold surface temperature above the dew point, with relative humidity below 50%, for at least 2 min before pouring or injection. The active release chemistry must not contain amine-neutralized fatty acids at levels above 0.5 wt% because the amine can co-react with the isocyanate and create a high-friction boundary layer. The surface tear strength of the molded skin is measured with ASTM D624-00(2020) die C and should remain within 10% of the control molded without release. Water contact angle on the molded skin after demolding should be below 80° if the part is to receive waterborne paint; values above 95° indicate release agent transfer and require an alkaline wash before bonding with a polyurethane adhesive. The mold release agent is not recommended for use with tin-free bismuth-neodecanoate catalysts at concentrations above 0.1 wt% if the carrier contains ethylene glycol monobutyl ether, because phase separation has been observed in a 25 L pressure pot at 1.5 MPa with a 15 min circulation period. Migration kinetics in polymer matrices are governed by diffusion coefficients that depend on crystallinity and temperature; for flexible urethane skins, low-molecular-weight release additives must therefore be selected to remain below the surface and not affect the coefficient of friction of the final part after post-curing at 80 °C for 24 h.

Thermoplastic injection molding at melt temperatures above 240 °C exposes the mold release compound to thermal decomposition products and volatiles that condense on the cavity surface. For polyamide 6 with 30 wt% glass fiber, a 100 t clamp force machine with a 35 mm screw and an L/D ratio of 20:1 is typical for evaluation. The external release agent is applied as a one-second spray cycle every 10–15 shots when molding at a short cycle time below 30 s, but extension of the spray interval beyond 30 shots produces an increase in demolding force and surface stress whitening in the gate region. Demolding force is monitored indirectly by the ejector force curve in the machine controller; an increase above 15% of the baseline value indicates the release film has been depleted or that carbonized residues from the polymer have embedded into the film. The material should not be applied onto a mold at a temperature below 60 °C for water-based systems, because rapid evaporation causes non-uniform film thickness and raised film edges visible under white light at 10× magnification. The molded plaques are conditioned at 23 ± 2 °C and 50 ± 10% relative humidity for 40 h according to ISO 291:2008 before mechanical testing. Tensile modulus is measured with ISO 527-2:2012 using a type 1A specimen. Melt flow rate of the polyamide compound is determined at 275 °C with a 5 kg load using ISO 1133-1:2022. The release agent presence on the part is detected by Fourier transform infrared spectroscopy; carbonyl and silicon bands in the demolded sample should not exceed the spectral intensity of the unmolded pellet by more than 2%.

Table 1. Release Agent Class and Process Boundary for Molding Compounds

Surface Energy Management in Post-Mold Painting and Structural Adhesive Bonding

Post-mold painting and structural bonding require the release agent to remain on the tool and not transfer to the part. Release agents based on polydimethylsiloxane produce water contact angles above 95° on the molded surface and cannot be removed by conventional alkaline degreasing; they require plasma or corona treatment before painting. A mold release compound containing siloxane oligomers above 0.2 wt% is therefore incompatible with acrylic paints that have a wetting surface tension of 30–32 mN/m. The adhesion of a two-component polyurethane paint to a polycarbonate blend part is tested with ASTM D3359-23 method B after the painted panel is immersed in deionized water at 40 °C for 240 h. Any loss of coating adhesion greater than one classification step after water immersion indicates residual release film. For structural bonding of epoxy to polyamide, the lap shear specimen is prepared according to ASTM D1002-10(2019) with a bondline thickness of 0.2 mm and a bonded area of 25 mm × 12.5 mm. The control specimen without release agent should fail cohesively or with a lap shear strength above 20 MPa, whereas a release-contaminated surface may drop below 5 MPa. If the failure mode is adhesive at the substrate interface, the surface is analyzed by water contact angle using ASTM D7334-08(2022) and by optically stimulated electron emission to determine contamination layer thickness. The operational boundary is that the release agent should not be applied by airless spray without an extraction system, because overspray droplets smaller than 10 µm remain airborne for more than 10 min and redeposit on mold cavities and adjacent equipment.

When Mold Release Agents Are Required to Survive 180 °C Tooling Without Reapplication

Semi-permanent release films must maintain a low-surface-energy boundary layer over multiple cycles at 180 °C without mechanical removal. The crosslinked siloxane film is built in layers, with each layer cured at 150–180 °C for 15–20 min until the film reaches a dry film thickness of 0.5–2.0 µm measured by eddy current thickness gauge. The upper use temperature is limited by thermo-oxidative chain scission of the siloxane network; at 200 °C continuous exposure, the contact angle of the film decreases at a rate of approximately 1–2° per 100 h under circulating air. Reapplication intervals in production are determined by the maximum ejector force and by the number of consecutive releases before gloss loss on the part exceeds 10% from the starting value measured with ASTM D523-14(2018). For a 180 °C epoxy prepreg compression cycle, the release agent is expected to survive 50–100 cycles on a flat tool with no undercuts; however, on a tool with 1 mm undercuts and the same mold temperature, reapplication may be required every 10–20 cycles because local shear stresses exceed the cohesive strength of the film. The film should be removed and rebuilt when the water contact angle on the tool drops below 75° or when visual inspection under 365 nm UV-A shows transfer patches larger than 5 mm². The formulation should not be used on silicone rubber molds, because the solvent carrier swells the mold surface and changes cavity dimensions by more than 0.5% after 24 h immersion.

Bulk molding compound injection molding at 140–160 °C uses a polyester resin filled with 25–35 wt% calcium carbonate and 5–10 wt% magnesium oxide thickener. The compound releases styrene during plastication, and the mold release agent must withstand aromatic monomer exposure without dissolving. A water-based mold release containing high-molecular-weight silicone emulsified in water is applied to the tool surface every 5–8 shots when molding at 75 bar injection pressure and a clamp force of 150 t. The process limitation is styrene vaporization, which generates a tacky surface layer on the tool; the release agent must be removed with a hydrocarbon cleaner every 50 cycles to prevent carbon build-up. Dimensional stability of the molded BMC part is checked after 24 h conditioning at 23 ± 2 °C with a coordinate measuring machine. The release agent does not contribute to shrinkage measurement because shrinkage is controlled by the low-profile additive and is evaluated according to ISO 2577:2007. No measurable effect on flammability was observed when the release agent was used at a mold coverage of 0.5 g/m² dry film weight, as tested by UL 94 vertical burn on 3.0 mm specimens. The operation should be conducted with local exhaust ventilation, as the carrier evaporates at 40–50 °C and may form flammable mixtures above 2 vol% in air.

Table 2. Verification Matrix for Release Agent Acceptance in Composite and Plastic Molding

Continuous pultrusion of vinyl ester profiles at line speeds of 0.4–0.8 m/min places a different demand on release performance because the cured profile exits through a heated stationary die. The release agent must function as a continuous film on chromium-plated die steel at 120–160 °C while resisting methyl ethyl ketone peroxide decomposition products. Application is performed by flooding the upstream guide plate or by metering through a felt wick at a rate calibrated to 2–4 g/min. Film deficiency appears as chatter marks on the profile surface with a periodicity corresponding to the puller clamp interval, while excessive film thickness creates a haze that reduces the Barcol hardness reading by more than 5 points when tested with ASTM D2583-13a. The release agent should not be mistaken for a resin shrinkage control agent; profile dimensional tolerance is governed by ISO 1268-7:2016 and must be confirmed independently with a laser micrometer after the puller exit. Published data for the specific Ningbo Runhe formulation under pultrusion line conditions is limited, and a production trial on a 50 mm × 50 mm box profile die is required to establish reapplication frequency before full-scale commitment.