The Specific Advantages Of The BMC In-mold Coating Process

The BMC in-mold coating process (full name: Bulk Molding Compound In-Mold Coating, abbreviated as IMC/PIMC) is an integrated process that simultaneously completes the injection molding of BMC substrate and the curing of surface coating. It differs from the traditional step-by-step mode of "injection molding → pretreatment → spraying → drying". Its advantages can be specifically analyzed based on specific process parameters, practical operation details, and industry application scenarios. Each point is supplemented with specific and implementable information for easy understanding and application reference:

 

1. Cost reduction and efficiency improvement: Complete process streamlining, quantification of cost savings, and adaptation to mass production

Compared with the cumbersome process of traditional spraying technology, BMC in-mold spraying achieves "one-step molding". The specific advantages lie in the quantitative improvement in three aspects: process, cost, and efficiency. The details are as follows:

Comparison dimension	Traditional spraying process	BMC In-Mold Spraying Process	Strengths and Highlights
Number of processes	9 steps (Injection molding → Grinding → Dust removal → Primer application → Drying → Topcoat application → Secondary drying → Inspection → Packaging)	3 steps (molding → in-mold spraying → synchronous curing → demolding → inspection and packaging)	The process has been reduced by 67%, eliminating time-consuming steps such as sanding and multiple drying processes.
equipment input	Approximately 800,000 - 1,200,000 yuan (annual production of 100,000 automotive interior components), and it is necessary to purchase grinding machines, spraying lines, etc.	Approximately 3 to 4 million yuan (same as production capacity), no need to purchase additional auxiliary equipment	The equipment investment has decreased by 60% to 70%.
man efficiency	It requires a team of workers, with each worker producing 200 to 300 pieces per day.	Only 1-2 operators are needed, and the average daily output per person is 1,500-2,000 pieces.	The demand for human resources has decreased by 70%, and the average monthly labor cost has dropped by 50% to 60%.
Coating utilization rate	40% - 60%, with issues of atomization and edge-corner wastage	Nearly 100%, no waste from atomization	The annual cost reduction in paint usage is approximately 100,000 to 150,000 yuan (for the same production capacity)
Energy consumption level	120 - 150 kWh per hour (requires continuous drying)	30 - 50 kWh per hour (synchronous curing, no additional heating required)	Energy consumption is reduced by 60% - 80%, and monthly electricity savings amount to 30,000 - 50,000 yuan.
process cycle	60 - 90 minutes per piece	8 - 15 minutes per piece	Efficiency has been increased by 6 to 8 times.
Time taken for color change	30 to 60 minutes (including time for cleaning the spray gun, spray booth, etc.)	5 to 10 minutes (only for changing the nozzle and adjusting the program)	Suitable for multi-color batch production scenarios

II. Environmental Protection and Low Carbon: Specific pollutants are under control, in line with industry environmental protection standards, and the cost of environmental protection operations is reduced.

This process reduces pollution from both material and process aspects. All environmental protection-related data are clearly traceable and comply with national environmental protection policies and the environmental protection requirements of various industries. The details are as follows:

Pollutant emissions are controllable: We use solvent-free or low-solvent-specific coating materials (main components are powder resins and curing agents, without volatile solvents such as benzene and toluene), with VOCs (volatile organic compounds) emissions ≤ 10mg/m³. Compared to traditional solvent-based spraying (VOCs emissions 200-500mg/m³), this reduces by over 95%. Some high-end solutions can achieve near-zero VOCs emissions, fully complying with the "Unorganized Emission Control Standard for Volatile Organic Compounds" (GB 37822-2019). No additional investment in large VOCs treatment equipment (such as activated carbon adsorption devices, catalytic combustion equipment) is required. Only a simple exhaust gas collection device is needed to meet the emission standards.

No secondary pollution: Traditional spraying requires the use of solvents and cleaning agents (for cleaning the spray gun and the surface of the workpiece), which will produce wastewater containing solvents and waste rags, and need to be treated separately; In-mold spraying does not require solvents or cleaning agents, only generating a small amount of coating waste (which can be recycled and reused), no wastewater or waste solvents are produced, no pollution to the soil or water body, the environmental treatment cost is reduced by more than 70%, and at the same time, it avoids the risks of fines (maximum single fine of 500,000 yuan) and production restrictions faced by enterprises due to non-compliance with environmental protection standards.

Green material compatibility: The coating material can be made of environmentally friendly and biodegradable resins, which have strong compatibility with the BMC substrate (glass fiber + resin). Waste products can be crushed and recycled to achieve resource recycling, conforming to the development trend of "low-carbon production and circular economy" in industries such as automotive and healthcare (such as the environmental requirements of new energy vehicles in the automotive industry).

III. Product Quality: Quantifiable parameters, superior appearance and performance, addressing the pain points of traditional manufacturing processes

In-mold spraying relies on precise control of the mold, ensuring stable product quality. The appearance, adhesion, durability and other key indicators are supported by clear parameters, and it can also solve common flaws of traditional spraying. The details are as follows:

 

(1) Appearance accuracy: No defects, capable of achieving complex designs, suitable for high-end demands

Controllable coating thickness: Through mold channel design and spraying pressure adjustment (0.3-0.5 MPa), the coating thickness can be precisely controlled within 0.15-0.25 mm, with an error of ≤ ±0.02 mm, far superior to traditional spraying (thickness error ±0.05 mm), avoiding problems such as excessive coating causing wrinkling or insufficient coating leading to exposure.

Appearance flawless: The coating is uniformly and simultaneously cured within the mold, resulting in a smooth and even surface. There are no common imperfections such as orange peel effect, bubbles, run-off, pinholes, or color differences found in traditional spraying. The surface gloss can be customized (60° gloss 20-90 GU), enabling the replication of nano-level fine textures (such as wood grain, leather texture), structural colors, matte/high gloss, etc., achieving complex appearance effects. It can effectively cover the glass fiber patterns and scratches of the BMC substrate, increasing the product's pass rate from 85%-90% in traditional spraying to over 99%.

·

Strong color consistency: Using an automated spraying system, the coating is evenly mixed and the spraying angle is fixed (adjustable from 15° to 90°). The color difference between products from the same batch and different batches is ≤ 1.5 (industry standard ≤ 3), without the color deviation of manual spraying. It is suitable for scenarios with high requirements for color consistency (such as automotive interior parts, home appliance shells).

 

(2) Adhesion and Durability: Far exceeding traditional processes, suitable for demanding usage scenarios

Extremely strong adhesion: The coating and the BMC substrate are simultaneously formed and co-cured (curing temperature 150-180℃, curing time 5-8 minutes). Their molecular structures are similar, and the interface bonding is tight. According to the GB/T 9286-1998 grid test standard, the adhesion can reach 0 level (no coating detachment after the grid test, only slight wear of the grid lines), while traditional spraying has an adhesion of only 1-2 levels (partial detachment occurs after the grid test). This completely solves the pain point of traditional coatings peeling and falling off.

Excellent durability: ① Scratch resistance: The pencil hardness can reach 2H-3H (while traditional spraying only reaches 1H). According to the GB/T 6739-2006 standard, when the scraping force is 500g, there is no obvious scratch, and it can withstand frequent daily contact and friction (such as the exterior of household appliances, car interior armrests); ② Weather resistance: After xenon lamp aging test (1000 hours, simulating outdoor exposure to sunlight and rain), the surface gloss retention rate is ≥85%, without fading, cracking, or powdering. The outdoor service life can reach over 10 years (while traditional spraying only lasts 5-6 years); ③ Chemical corrosion resistance: It can withstand common chemicals such as alcohol, acetone, dilute acid (pH ≥ 4), and dilute alkali (pH ≤ 10) wiping, without color change or paint peeling, suitable for medical, chemical, and other scenarios (such as medical equipment that needs to be frequently disinfected with alcohol).

Function customization: Functional additives can be added to the coating according to industry requirements to achieve exclusive functions: ① In the medical field: Adding silver ion antibacterial agents, the antibacterial rate against Staphylococcus aureus and Escherichia coli is up to 99.9%, it can withstand high-temperature and high-pressure steam sterilization (134℃, 30 minutes), ultraviolet sterilization, and meets the hygiene standards for medical equipment (GB 15980-1995); ② In fire-retardant scenarios: Adding fire-retardant agents (such as aluminum hydroxide, bromine-based fire-retardants), the fire-retardant grade of the coating can reach UL94 V-0 level, suitable for automotive, electrical equipment, etc. with fire-retardant requirements; ③ Self-repair function: Adding elastic resin, after a slight scratch (scratch depth ≤ 0.05mm), it can self-repair in a 60-80℃ environment, without the need for additional paint application.

 

III. Adaptability and Operability: Wide coverage of scenarios, high automation level, strong stability

This process does not require complex operations, is compatible with various BMC products, and is less affected by external factors, suitable for large-scale and standardized production. Specific details are as follows:

Wide application scope: It can be used for surface treatment of various BMC products, covering the automotive industry (dashboard, bumper, door interior panel, engine compartment components), medical industry (surgical instrument tray, disinfection box, medical equipment shell), home appliance industry (washing machine shell, air conditioner panel, oven inner liner), outdoor building materials (street lamp shell, manhole cover decorative part), electrical industry (distribution box shell, insulator), etc. It is particularly suitable for scenarios with high requirements for weather resistance, strength, and flame retardancy (such as outdoor building materials, automotive engine compartment components).

 

Automated operation with high stability: Utilizing a PLC automated control system, combined with a mechanical hand (spraying accuracy ±0.1mm), it completes processes such as spraying and demolding. It is less affected by factors such as the proficiency of manual operation,environmental humidity (traditional spraying requires a humidity range of 40%-60%, while in mold internal spraying there are no strict requirements), and temperature. The defect rate of the products can be controlled below 1%, while the traditional spraying has a defect rate of approximately 8%-12%. At the same time, the equipment can operate continuously for 24 hours, with a low failure rate (monthly failure rate ≤ 3%), reducing downtime losses.

 

Advantages of molds and demolding: The coating material contains a small amount of special demolding agents (no additional addition required), the demolding resistance is ≤ 500N, demolding is convenient, and it will not damage the coating surface; at the same time, internal spraying in the mold can reduce the friction between the BMC substrate and the mold, extending the mold service life by more than 3 times (the service life of traditional injection molds is approximately 100,000 mold cycles, while the internal spraying molds can reach more than 300,000 mold cycles), and reducing the mold replacement cost (the cost of a single set of molds is approximately 50,000 - 100,000 yuan).

 

IV. Space Saving: Adaptation to Workshop Layout and Enhancement of Space Utilization

The traditional spraying workshop requires separate divisions for injection molding area, grinding area, spraying area, and drying area, resulting in a large floor area (500-800㎡ are needed for an annual production of 100,000 products); the BMC in-mold spraying process integrates all processes into a single integrated equipment, with the equipment occupying only 100-200㎡ of floor space, saving over 70% of workshop space, and the equipment can be flexibly placed to adapt to different scale workshop layouts (such as compact workshops of small and medium-sized enterprises); at the same time, through the联动of mechanical hands, during the gap period (5-8 minutes) after coating solidification, the next BMC substrate can be fed in, further improving the space utilization and production continuity, especially suitable for workshop layouts of large-scale batch production such as in the automotive and home appliance industries.