In plastic product manufacturing, surface gloss is one of the core indicators for evaluating product quality. Many manufacturers frequently encounter defects such as dull surfaces, matte haze and uneven gloss on molded parts during production. These issues not only ruin the visual texture of finished products but also trigger large quantities of defective goods, driving up production costs and bringing risks to order delivery. To address this common injection molding imperfection, Ningbo Konger Machinery Co., Ltd. (hereinafter referred to as Konger) has developed a standardized Cause Analysis + Rectification Solution based on years of hands-on molding commissioning experience and equipment R&D expertise. This solution helps manufacturers rapidly resolve defects and raise the appearance yield rate of plastic molded parts.

I. Root Causes for Dull and Low-Gloss Injection Molded Products

Mass case studies conducted by Konger’s technical team prove that surface dullness and gloss loss stem from multiple factors, which mainly fall into three categories: raw material system, injection molding process, and mold hardware. Detailed causes are listed below:

(1) Improper Control Over Raw Materials & Additives (Source-Level Defects)

• Excessive moisture content in raw materials: Excess water inside pellets vaporizes during melting, forming a thin hazy layer on the molded part surface and resulting in permanent gloss loss. This ranks among the most prevalent causes.
• Misuse of auxiliary materials: Poor compatibility occurs when selected processing additives fail to match the base material formula. Excessively or unevenly sprayed mold release agent leaves residual films covering part surfaces, directly causing overall dullness and degraded surface finish.

(2) Improper Injection Molding Process Parameters (Inaccurate Equipment Control)

As a high-tech enterprise engaged in the R&D and manufacture of injection molding equipment, Konger fully recognizes the decisive impact of process parameters on product quality. All injection molding machines under Konger are equipped with high-precision temperature control and closed-loop pressure control systems. Numerous commissioning records verify that mismatched parameters constitute a major cause of poor surface gloss:

• Low holding pressure & insufficient holding time: The melt cannot cling tightly to the mold cavity surface, impairing replication of the mold’s smooth finish and leading to dullness and surface irregularities.
• Undersized temperature for barrel and nozzle: Incomplete plasticization reduces melt fluidity, yielding rough, dull molded surfaces after forming.
• Excessively long molding cycle: Molten plastic resides and cools inside the barrel for prolonged periods, destabilizing filling behavior and causing inconsistent surface gloss.
• Low plasticizing back pressure: Inadequate homogenization of raw material mixing leads to uneven melt composition, resulting in mottled gloss and dark patches on finished products.
• Low mold wall temperature: High-temperature melt cools abruptly upon contact with the mold surface, failing to fully replicate the mirror finish of the cavity and leaving dull marks on the part exterior.

(3) Structural & Machining Defects of Molds (Substandard Hardware Foundation)

• Undersized gates and runners: High melt flow resistance disturbs material flow, degrading surface molding quality and inducing dullness as well as flow marks.
• Poor surface finish of mold cavities: Scratches, corrosion and rough textures on cavity inner walls are directly reproduced on molded products and lower overall gloss.
• Poor venting at material flow convergence zones: Missing or undersized vents at weld lines and material merging areas trap air inside the cavity. Entrapped gas scorches and erodes part surfaces, triggering partial or full-surface dullness.

II. Targeted Rectification: Standardized Solutions from Konger

Corresponding actionable rectification measures are formulated by Konger’s technical team in accordance with equipment characteristics and actual production conditions. Manufacturers may troubleshoot and implement improvements item by item following the table below:

III. Long-Term Quality Assurance: Dual Empowerment via Konger Equipment & Professional Technology

Adjusting process parameters and repairing molds can only fix existing defects temporarily. Stable molding equipment serves as the fundamental guarantee to permanently eliminate appearance imperfections. Konger has over ten years of experience in injection molding equipment R&D and manufacturing and holds 19 patents related to injection molding technology. Supported by its full-spectrum machine lineup including the K-TEC servo general series, CMS two-color series and dedicated PET molding machines, Konger delivers comprehensive technical support for manufacturers:

• Precision hardware control: All Konger injection molding machines adopt imported temperature and pressure sensing components with minor temperature fluctuation and rapid pressure response. Critical parameters including back pressure, holding pressure, mold temperature and barrel temperature are stably and precisely controlled at the equipment end to prevent gloss defects caused by parameter drift. The self-developed non-drying machine drastically reduces appearance flaws derived from damp raw materials while cutting energy consumption for material drying.
• Full-scenario process support: Konger’s professional engineers provide one-on-one molding commissioning services for single-color, two-color, sandwich injection molding and gradient multi-color molded products. Custom parameter recipes are customized according to workpiece materials and mold conditions to meet the production requirements of appearance parts across automotive, electronics, daily consumer goods and other industries.
• Nationwide localized service network: Konger operates offline service offices in more than 20 domestic cities and partners with distributors in multiple overseas countries. 7×24 online technical support is available, with field engineers promptly dispatched for on-site inspections and matched mold & process debugging. We deliver one-stop solutions for all types of injection molding defects to help manufacturers continuously reduce reject rates and raise productivity and product quality.
• Patented process advantages: Leveraging patented two-color sandwich molding technology, Konger uses virgin resin for product outer layers to guarantee premium surface gloss, while qualified recycled material is applied for inner structures. This solution slashes comprehensive raw material costs by 15%~25% without compromising surface quality, balancing aesthetic requirements and cost control targets.

IV. Summary

Dull and low-gloss plastic parts are mostly the combined result of problematic raw materials, mismatched processes and defective molds. We recommend manufacturers conduct troubleshooting and rectification in the following order: raw material inspection → process parameter calibration → mold maintenance, polishing and vent improvement.

Moving forward, Konger will continuously optimize injection molding solutions based on accumulated technical expertise and equipment strengths. Beyond defect correction guidance for clients, Konger also provides customized injection molding equipment and overall molding plant layout solutions aligned with enterprises’ product planning, fully safeguarding the surface quality and mass production stability of plastic products.