What Are the Quality Inspection Items for Plastic Products?

Based on over a decade of experience in cooperating with domestic and international customers and manufacturing various plastic products, Kingsjeng Technology believes that the quality inspection of plastic products needs to cover core dimensions such as safety, functionality, stability, and appearance compliance. Specific inspection items vary in focus depending on the product’s application (e.g., food contact, electronic components, automotive parts, daily necessities), but they can generally be divided into the following seven categories, with each category including clear inspection content, standards, or tools:

1. Appearance Quality Inspection (The Most Basic and Intuitive Preliminary Inspection)  

Appearance is the first impression of a product and a key basis for judging surface defects. The main focus is to check for "defects" and "compliance with design specifications"**:  

- Surface Defect Inspection:  

  - No cracks, bubbles, pinholes, dents, protrusions, scratches, scrapes, or impurities (e.g., black spots, foreign objects);  

  - No flash (excess plastic at the mold joint), material shortage (local incomplete filling), or sink marks (surface depressions caused by uneven wall thickness);  

  - No discoloration, color spots, or color deviation (compared with the design color card, usually quantified by a color difference meter; for example, the ΔE value must meet requirements, typically ΔE ≤ 1.5).  

- Texture and Gloss:  

  - Surface texture (e.g., matte, leather texture, smooth finish) must be uniform, with no local blurring or misalignment;  

  - Gloss (especially for smooth-surfaced products) must meet standards (tested with a gloss meter, unit: GU; for example, home appliance casings usually require 60° gloss ≥ 80 GU).  

- Markings and Printing:  

  - Content of silk screen printing/pad printing/hot stamping (e.g., logos, parameters, warning labels) must be clear, without blurring or peeling (tested by adhering 3M tape and peeling it off to check for ink peeling);  

  - The position of markings must align with the design drawings, with no offset.  

2. Dimensional and Geometric Accuracy Inspection (Ensuring Assemblability and Compliance)  

Plastic is prone to dimensional deviations due to shrinkage (e.g., PP has a shrinkage rate of 1.5%-2.5%, and ABS has a shrinkage rate of 0.5%-1.0%). Tools are required to verify compliance with design drawings (e.g., CAD annotations):  

- Common Tools:  

  - Basic dimensions: Calipers (accuracy of 0.01mm, for measuring length, width, and thickness), micrometers (accuracy of 0.001mm, for measuring thin walls and diameters);  

  - Complex dimensions/geometric tolerances: Coordinate Measuring Machine (CMM, for measuring 3D spatial dimensions, positional tolerance, coaxiality, parallelism, perpendicularity, etc.; for example, the positional tolerance of screw holes in electronic casings must be ≤ 0.1mm);  

  - Hole/slot width: Plug gauges (go gauge should pass, no-go gauge should not pass), pin gauges;  

  - Curvature/radius: Profilers (for measuring curved surface accuracy, e.g., curved automotive interior parts).  

- Core Inspection Items:  

  - Critical dimensions (e.g., assembly positions, interface dimensions): Deviations must be within the tolerance range specified in the drawings (e.g., ±0.05mm);  

  - Geometric tolerances: Such as flatness (tested with a dial indicator on a flat plate, requiring ≤ 0.1mm/m), roundness (for shaft-like products), and coaxiality (e.g., plastic pipes);  

  - Wall thickness uniformity: Tested with an ultrasonic thickness gauge (especially for thick-walled products such as barrels; the wall thickness difference must be ≤ 0.5mm to avoid cracking due to uneven shrinkage).  

3. Physical Performance Inspection (Judging Mechanical Strength and Durability)  

Plastic products need to withstand external forces during use (e.g., extrusion, stretching, impact, friction), and physical performance directly determines their service life:  

4. Chemical and Environmental Performance Inspection (Core of Safety, Especially for Contact Products)  

The key is to check for the **release/migration of harmful substances** to avoid endangering humans or the environment. Products for different purposes must comply with specific regulations:  

- 1. Harmful Substance Content (Heavy Metals, Toxic Substances):  

  - General requirements: Comply with RoHS 2.0 (EU) and GB/T 26572 (China), which restrict lead (Pb), cadmium (Cd), mercury (Hg), hexavalent chromium (Cr⁶⁺), polybrominated biphenyls (PBBs), polybrominated diphenyl ethers (PBDEs), etc. The limit is usually ≤ 1000mg/kg (cadmium ≤ 100mg/kg);  

  - Children’s products: Stricter requirements apply, e.g., EU EN 71-3 requires lead migration ≤ 13.5mg/kg and cadmium ≤ 0.07mg/kg.  

- 2. Food Contact Safety (e.g., Plastic Tableware, Baby Bottles, Food Packaging)**:  

  - Compliance standards: China GB 4806.7, EU No 10/2011, US FDA 21 CFR;  

  - Inspection items:  

    - Migration amount: In 4% acetic acid (simulating acidic food) and 50% ethanol (simulating oily food), the migration of heavy metals (lead, cadmium) must be ≤ 0.01mg/dm², and the total migration amount ≤ 60mg/dm²;  

    - Volatile substances: Content of volatile substances after heating ≤ 10mg/dm² (to avoid odors).  

- 3. Odor and VOCs (Volatile Organic Compounds):  

  - Odor: Tested by olfaction in a sealed container after heating (e.g., 70℃ × 2h), with no irritating odor (usually requiring ≤ Grade 3; Grade 1 = odorless, Grade 5 = strong odor);  

  - VOCs: Tested with Gas Chromatography-Mass Spectrometry (GC-MS). For example, indoor plastic products (furniture, flooring) must comply with GB/T 35456, with total VOCs ≤ 100μg/m³.  

- 4. Chemical Resistance:  

  - Test the stability of the product in common liquids (e.g., sweat, detergent, alcohol, engine oil). After immersion (e.g., 24h × 25℃), there should be no discoloration, cracking, or swelling (weight/size change rate ≤ 5%).  

5. Thermal Performance Inspection (Adapting to High/Low Temperature Environments to Avoid Deformation/Failure)  

The thermal stability of plastic directly affects its use in high-temperature (e.g., automotive interiors, kitchenware) or low-temperature (e.g., outdoor products, refrigerated environments) conditions:  

- Heat Distortion Temperature (HDT):  

  - Definition: The temperature at which a product deforms to a specified value under a certain pressure (usually 1.82MPa) (to judge whether it softens at high temperatures);  

  - Standard: GB/T 1634. For example, automotive plastic parts require HDT ≥ 80℃ (to avoid deformation under summer exposure).  

- Vicat Softening Temperature (VST):  

  - Definition: The temperature at which a standard indentor (10N force) penetrates the product to a depth of 1mm (more in line with actual softening conditions);  

  - Example: Plastic casings of electric kettles require VST ≥ 100℃.  

- Low-Temperature Brittleness:  

  - After being placed in a low-temperature environment (e.g., -40℃, -20℃) for a certain period (e.g., 2h), the product is subjected to an impact test with no cracking (outdoor plastic pipes must pass this test).  

- Thermal Aging Performance:  

  - After aging in a high-temperature oven (e.g., 120℃ × 1000h), the retention rate of tensile strength and impact strength is tested (usually requiring ≥ 80% to judge whether it becomes brittle under long-term high temperatures).  

6. Functional Inspection (Aligned with Actual Product Usage Scenarios)  

Customized according to product purposes, the core is to verify "whether the designed function can be achieved":  

- Sealing Products: Such as plastic gaskets and waterproof boxes. Tested with an air tightness tester, with no air/water leakage after pressurization (e.g., 0.2MPa);  

- **Connecting Products**: Such as plastic buckles and plugs. Test the insertion/extraction force (e.g., USB plastic housings require an insertion/extraction force of 5-30N) and connection stability (still functional after 5000 repeated insertions/extractions);  

- Light-Transmitting Products: Such as plastic lamp shades and lenses. Tested with a light transmittance meter (e.g., PC lamp shades require light transmittance ≥ 85%) with no haze (haze ≤ 5%);  

- Elastic Products: Such as silicone buttons and plastic buffers. Test the compression set (deformation rate ≤ 10% after compression at 70℃ × 22h) to ensure rebound performance.  

7. Reliability and Service Life Inspection (Stability in Long-Term Use)  

Simulate the product’s full-life-cycle usage environment to verify durability:  

- Weather Resistance: Outdoor products (e.g., plastic flower pots, outdoor furniture) require xenon lamp aging tests (simulating sun exposure and rain). After 1000h, there should be no obvious discoloration or cracking, and the physical performance retention rate ≥ 70%;  

- Fatigue Test: For products subjected to repeated forces (e.g., plastic hinges, buttons), no cracking or functional failure after 100,000 repeated openings/closings or presses;  

- Thermal Cycle Test: Alternately place the product in high-temperature (e.g., 80℃) and low-temperature (e.g., -40℃) environments. After 50 cycles, there should be no cracking or excessive dimensional deviation;  

- Drop Test: For portable products (e.g., plastic toys, electronic casings), drop from a standard height (e.g., 1.2m) onto a hardwood board. No damage or functional failure is allowed (complying with GB/T 2423.8).  

Summary: The "Priority Principle" for Inspection Items  

- Food/Medical Contact Products: Prioritize **chemical and environmental performance (migration amount, harmful substances) + functionality (e.g., sealing);  

- Electronic/Automotive Products: Prioritize dimensional accuracy (assemblability) + physical performance (impact, heat distortion) + reliability (thermal cycle);  

- Daily Necessities/Outdoor Products: Prioritize appearance + physical performance (abrasion resistance, weather resistance) + functionality (e.g., elasticity, light transmittance).  

All inspections must be based on clear standards ([GB], [ISO], and industry standards such as IATF 16949 for the automotive industry), and inspection records must be retained to ensure traceability.