Plastic Bottle Color Fading Testing: Standards, Methods, and Evaluation Criteria

Plastic bottle color fading testing evaluates the ability of plastic bottles and their printed or decorated surfaces to retain color when exposed to light, rubbing, moisture, and environmental stress. This testing is essential for manufacturers in the cosmetics, pharmaceutical, food, and household chemical industries to verify product quality, ensure shelf-life appearance, and comply with ISO, ASTM, and GB standards. This article explains the testing samples, testing items, methods, evaluation criteria, and practical applications of color fading assessment for plastic bottles.

Technical Overview

Color fading in plastic bottles refers to the loss, alteration, or deterioration of color on the bottle body, closures, or decorated surfaces caused by ultraviolet radiation, visible light, heat, humidity, oxygen, friction, or contact with chemicals. The color of a plastic bottle originates from colorants (pigments or dyes) incorporated into the resin, printing inks applied by silk-screen or offset processes, hot-stamping foils, spray coatings, and in-mold labels. Each of these color sources has a different resistance profile, and fading can appear as lightening, yellowing, discoloration, chalking, or ink transfer loss.

Color fading testing, often described as colorfastness testing, is a laboratory procedure that exposes bottle samples to accelerated or simulated degradation conditions and then quantifies the degree of color change. Evaluation is typically performed by visual comparison against a grey scale (rating 1 to 5) or by instrumental colorimetry using the CIELAB color space to calculate color difference values such as ΔE*ab. International standards organizations, including ISO, ASTM, and the Chinese national standardization body (GB), have published widely accepted test methods for this purpose, and accredited third-party laboratories routinely conduct these tests for manufacturers, brand owners, and exporters.

Testing Samples

Bottle Body Materials

Test samples can include bottles manufactured from common packaging resins such as PET (polyethylene terephthalate), HDPE (high-density polyethylene), LDPE (low-density polyethylene), PP (polypropylene), PVC (polyvinyl chloride), and PS (polystyrene). Both unpigmented natural bottles and fully pigmented colored bottles can be evaluated for yellowing, whitening, or hue shift after exposure.

Printed and Decorated Surfaces

Decorated samples include silk-screen printed logos, flexographic or offset printed artwork, hot-stamped foil decoration, heat-transfer labels, pressure-sensitive labels, spray-coated finishes, and electroplated or metallized layers. Fading tests on these samples focus on ink colorfastness, coating integrity, and adhesion retention.

Closures and Auxiliary Components

Colored caps, pump heads, sprayers, and dropper components are frequently tested together with the bottle, since differential fading between the bottle and closure is highly visible to consumers and considered a quality defect.

Sample Preparation Requirements

• Samples should be representative of actual production and free from surface contamination, scratches, or molding defects.
• Typical submission quantities range from 5 to 20 pieces per test condition, depending on the selected standard and laboratory protocol.
• Samples should be conditioned at standard laboratory atmosphere (usually 23 ± 2 °C and 50 ± 5% relative humidity) before testing.
• Reference or retained control samples should be kept in dark storage for comparison after exposure.

Testing Items

Depending on the product's end use and the buyer's specification, common testing items for plastic bottle fading assessment include:

• Colorfastness to artificial light (xenon arc) — resistance to fading under simulated sunlight.
• Colorfastness to UV fluorescent lamp exposure — accelerated photo-degradation screening.
• Weathering resistance — combined light, heat, and moisture cycling.
• Colorfastness to rubbing (dry and wet crocking) — resistance of color or ink to abrasion transfer.
• Colorfastness to water immersion — color stability after contact with water.
• Colorfastness to perspiration or salt solution — relevant for personal care packaging.
• Resistance to alcohol and cosmetic ingredients — rubbing with ethanol, sanitizer, or lotion simulants.
• Detergent and chemical resistance — contact with surfactants, bleach, or cleaning agents.
• Thermal aging and humidity resistance — color stability under elevated temperature and humidity.
• Ink adhesion (cross-cut or tape test) — often performed alongside fading tests for printed surfaces.
• Quantitative color difference (ΔE*ab, ΔL*, Δa*, Δb*) — instrumental measurement of total color change.

Testing Methods

Light Fastness Testing (Xenon Arc Method)

The most widely used method for evaluating fading resistance is xenon arc lamp exposure, performed according to ISO 4892-2, ASTM G155, or the Chinese national standard GB/T 16422.2. Samples are mounted in a xenon weathering chamber equipped with daylight-filtered lamps, controlled irradiance (commonly 0.35 to 0.55 W/m² at 340 nm), black panel temperature (typically 55 to 65 °C), and humidity or water-spray cycling. Exposure duration is defined in hours (for example, 100 h, 300 h, or 500 h) or by radiant energy dose, and blue wool reference materials may be exposed simultaneously as a calibration control.

UV Fluorescent Lamp Exposure

For screening UV sensitivity, samples are exposed in fluorescent UV condensation apparatus following ISO 4892-3, ASTM G154, or GB/T 16422.3. This method uses UVA-340 or UVB-313 lamps to reproduce the shorter-wavelength portion of sunlight, which is often the dominant driver of polymer and pigment photodegradation.

Rubbing and Abrasion Fastness Testing

Colorfastness to rubbing is evaluated with a crockmeter in accordance with ISO 105-X12 or GB/T 3920. A standard rubbing finger covered with dry or wet white cotton cloth moves across the bottle surface a defined number of strokes; color transferred to the cloth is rated against the grey scale for staining. For printed plastic surfaces, alcohol rub tests (for example, 50 rubs with a specified ethanol concentration using a fixed load) are commonly specified by brand owners to verify ink durability.

Water, Perspiration, and Chemical Contact Tests

Specimens are immersed in or spotted with the specified liquid — distilled water, artificial perspiration solution, detergent solution, or alcohol — for a defined time and temperature, then dried and assessed for color change, bleeding, and staining of adjacent materials. These procedures reference ISO 105 series principles adapted for plastic packaging.

Color Difference Measurement

Instrumental evaluation uses a spectrophotometer or colorimeter to measure L*, a*, b* values before and after testing. The total color difference ΔE*ab is calculated and reported alongside the visual grey scale rating. Visual assessment is conducted in a standard light booth (typically D65 illumination) by trained observers, with ratings assigned on the grey scale for change in color (ISO 105-A02 / GB/T 250), where grade 5 means no change and grade 1 means severe change.

Applications

Plastic bottle fading tests support quality control and compliance across many industries:

• Cosmetics and personal care packaging — ensuring bottles, caps, and printed decorations retain color under retail display lighting and product contact.
• Pharmaceutical packaging — verifying that colored bottles and printed dosing information remain legible and stable throughout the product shelf life.
• Food and beverage packaging — confirming pigment and label stability under storage, transport, and display conditions.
• Household chemicals and detergents — validating resistance to bleach, surfactants, and UV exposure on store shelves and windowsills.
• Automotive and industrial chemical containers — assessing weathering resistance for products used outdoors.
• Export compliance — providing third-party test reports that demonstrate conformity to buyer specifications and relevant ISO, ASTM, EN, JIS, or GB standards.
• Material development — comparing colorant formulations, UV absorbers, hindered amine light stabilizers (HALS), and ink systems during R&D.

FAQ

What fading rating is considered acceptable for plastic bottles?

Acceptance criteria depend on the buyer and application, but a grey scale rating of 4 or higher (corresponding to very slight color change) after the specified exposure is the most common commercial requirement. Some premium cosmetics specifications require a rating of 4–5, and ΔE*ab limits of 2.0 or less are frequently used as instrumental acceptance thresholds.

How long does xenon arc fading testing take?

The exposure itself typically ranges from 100 to 500 hours depending on the specification, which translates to several days to several weeks of chamber time. Including conditioning, evaluation, and reporting, total turnaround at an accredited third-party laboratory is usually one to four weeks.

Can a fading test predict real shelf life?

Accelerated tests provide comparative rather than absolute predictions. By correlating xenon arc exposure hours with indoor retail lighting conditions, laboratories can estimate relative lightfastness; however, actual shelf-life claims should be supported by real-time storage studies in parallel.

Which standard should be selected: ISO, ASTM, or GB?

The choice depends on the target market and buyer requirements. ISO 4892-2 and GB/T 16422.2 are technically equivalent xenon arc methods common in international trade and the Chinese market, while ASTM G155 is frequently requested for North American clients. An accredited laboratory can help match the correct method, exposure cycle, and evaluation criteria to the intended use.

Is sample preparation by the laboratory possible?

Yes. Laboratories can cut bottle panels into standard specimen sizes, mask areas for defined exposure windows, and prepare printed coupon samples, but final-product testing on intact bottles is generally preferred because curved surfaces and full assembly reflect real-world fading behavior.