In-Mold Decoration (IMD) is an advanced surface decoration process that places pre-printed films into injection molds and forms integrally through injection molding, allowing plastic and films to bond firmly. Finished products feature wear resistance, color fastness, delicate patterns, environmental friendliness and high efficiency, and are widely used in household appliance panels, automotive interiors, 3C housings, instrument panels and other fields. The IMD process has extremely high requirements for molds, equipment, materials, environment and operation. Improper operation may lead to defects such as film displacement, bubbles, wrinkles, ink washout, whitening and deformation. Based on workshop practical experience, this article provides a set of directly applicable IMD process control guidelines for stable production and defect reduction.
Basic Principle and Classification of IMD ProcessThe core of IMD is to place the film into the mold first, inject plastic later, and achieve a permanent bond between plastic and film. It is divided into two categories: IMS (only the ink layer of the film is retained) and IML (the surface layer of the film is retained), among which IML is the most common in daily production. The complete process includes film printing, drying, forming and cutting, in-mold positioning, mold-closing injection, product removal and post-inspection. During injection molding, high-temperature and high-pressure plastic presses the film tightly against the mold cavity surface, allowing the ink layer to fuse with plastic molecules. After molding, the pattern is sealed inside, making it fade-resistant, scratch-resistant and chemical corrosion-resistant. Since the film is a flexible material, it is extremely sensitive to temperature, pressure, speed, positioning, venting and mold temperature, requiring full-process standardized control.
Film Preparation and Pre-Molding ControlThe film is the core of IMD, and early-stage control directly determines the yield rate. Printed films must be fully dried to avoid solvent residues that cause bubbles or ink detachment during injection. Generally, films are dried at 50–80°C for 30 minutes to 2 hours according to ink requirements, and then left to cool before production. The cutting size of the film must be precise, with the gap between the positioning hole and the mold positioning pin controlled at 0.05–0.15 mm. Excessively large gaps easily cause displacement, while excessively small gaps may jam the film and cause wrinkles. Before mold loading, the film appearance must be inspected: no scratches, dirt, creases, color deviation or missing printing. Defective films are strictly prohibited from production. Films should be stored in a dust-proof, moisture-proof and anti-static environment. The workshop humidity is controlled at 40%–60% and temperature at 22–28°C to prevent moisture absorption and deformation of the film. During mold loading, ensure the film is flat and close to the cavity without arching, displacement or twisting. The positioning pin must fully pass through the positioning hole, which is the basis for avoiding ink washout and displacement.
Mold and Equipment RequirementsIMD molds must adopt a dedicated structural design: the cavity needs polishing but not excessive gloss to prevent film adsorption and rebound; reasonable venting must be provided, especially at film edges, corners and rib positions, to prevent air traps and bubbles. Molds should be equipped with positioning pins, positioning grooves and anti-eccentric ejection structures. Some products require vacuum adsorption devices to fix the film, greatly reducing displacement defects. Injection machines should be selected with stable injection performance and good linear pressure response. Tonnage is calculated based on the projected area of the product, and sufficient clamping force is required to prevent flash at the parting line and damage to the film. The barrel, nozzle and hot runner must be clean, free of foreign materials, black spots and carbonization. Thorough cleaning is required during material changes to avoid color contamination. Mold temperature control is critical. IMD molds generally require a mold temperature controller, with a conventional mold temperature of 30–60°C for IML, which can be increased appropriately for high-gloss products to ensure good bonding between the film and plastic without film scorching.
Key Points of Injection Process Parameter OperationThe principle of IMD parameter setting is medium and low-speed injection, medium-pressure holding, smooth transition and impact avoidance. Temperature is set based on the plastic material, slightly 5–10°C lower than conventional injection to prevent high temperature from damaging the ink, causing yellowing or ink washout of the film. Injection is controlled in stages: the first stage uses low speed to allow plastic to contact the film edge and advance steadily, preventing the film from being pushed askew; the second stage uses medium speed for filling to ensure stable flow; the third stage switches from low speed to holding pressure to avoid whitening caused by excessive pressure on the film edge. Holding pressure should not be too high, and shall be subject to no shrinkage and stable product size. Excessive pressure will wrinkle or deform the film. Sufficient cooling time is required to ensure the product is solidified before mold opening, avoiding stretching and deformation of the film during ejection. Speed control is the core. Deceleration is required at any position that may impact the film, especially where the gate directly faces the film, where ink washout, film rupture and white spots are most likely to occur.
Common Defect Causes and On-Site SolutionsFilm displacement is mainly caused by inaccurate positioning, insufficient clamping force, excessive injection speed and vacuum adsorption failure. Solutions include correcting positioning, increasing clamping force, reducing the first-stage injection speed and checking the vacuum system. Bubbles and streaks are mostly caused by poor venting, film arching, excessive injection speed and low mold temperature. Solutions include deepening vents, cleaning vent channels, reducing injection speed, increasing mold temperature and ensuring the film is fully attached to the mold. Ink washout or peeling is caused by high temperature, excessive speed, direct gate impact on the film and poor ink adhesion. Solutions include lowering material temperature and injection speed, optimizing gate position and using qualified ink. Film wrinkles are caused by film deformation, poor positioning, uneven mold clamping and excessive local pressure. Solutions include rearranging the film, correcting positioning, adjusting mold balance and optimizing injection direction. Product whitening or fogging is mostly caused by excessive film pressure, high holding pressure and insufficient cooling. Solutions include reducing holding pressure, extending cooling time and ensuring stable injection. All defects should be addressed in the order of checking the film first, then positioning, then speed, and finally optimizing temperature and pressure for quick troubleshooting.
Production Operation and Quality Control StandardsIMD production must implement strict operating standards: confirm film direction, front and back sides and positioning before production; check whether the film is placed correctly and free of wrinkles for each cycle; direct hand contact with the printed surface of the film is strictly prohibited to prevent oil stains and fingerprints; ensure no foreign matter, plastic filaments or scratches in the cavity before mold closing. A first-piece, in-process and last-piece inspection system shall be established, focusing on pattern position, appearance, adhesion, wear resistance and dimensions. Operators must receive training before taking up posts, be familiar with film characteristics, defect judgment and parameter adjustment logic, and are prohibited from adjusting parameters without authorization. Molds should be regularly cleaned of cavities, positioning pins and vent channels to keep them clean and smooth, preventing carbon deposits and plastic debris from damaging the film.
Safety and Maintenance PrecautionsDuring production, attention should be paid to anti-scalding at high temperatures, anti-leakage at the nozzle and anti-clamping of the film by the manipulator. During shutdown, lower the temperature first, then clean the barrel and mold. For long-term shutdown, molds should be protected against rust and films should be stored in sealed packages. Avoid impact and scratches on the mold cavity. Bent positioning pins should be corrected in a timely manner, otherwise batch defects will occur. Inks, cleaning agents and plastic materials should be stored separately in compliance with anti-static and fire protection regulations.
ConclusionThe core of stable IMD process lies in stable film, accurate positioning, low speed, stable pressure, good venting and uniform mold temperature. Standardizing early-stage preparation, mold conditions, injection parameters and operating procedures can greatly reduce defects and achieve efficient mass production. IMD not only improves the appearance grade of products, but also simplifies post-processing procedures, making it a mainstream process for high value-added products in modern injection molding. Strict implementation of this practical guide can quickly achieve a leap from trial production to stable mass production.
