Complete Application Guide of Fluorescent Whitening Agents in PVC Profiles

I. Basic Whitening Mechanism

II. Comparison of Mainstream Fluorescent Whitening Agent Grades for PVC Profiles

1. OB-1 (Universal First Choice for Plastic-Steel Profiles)

• Chemical Structure: Distyryl bisbenzoxazole; Melting point: 353–359℃; High temperature resistance without sublimation
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• Advantages: Powerful whitening capacity, excellent dispersibility, pure blue-white tint; suitable for door & window profiles, PVC pipes and wall panels
• Dosage: 0.01%–0.05% (10–50 g per 100 kg of raw materials)
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• Application Scope: Standard new-material plastic-steel profiles and high-whiteness outdoor profiles; Use with caution in flexible PVC as precipitation may easily occur

2. KCB (Special Grade for High Weather-Resistant Outdoor Profiles)

• Melting point: 210–212℃; Lightfast, migration-resistant, anti-precipitation; superior weather resistance to OB-1
• Advantages: Resistant to yellowing under long-term outdoor exposure; applicable to exterior wall cladding panels, outdoor PVC decorative profiles and high-calcium-filled profiles
• Dosage: 0.01%–0.04%

3. OB (Economical Grade for Low-End Profiles / Recycled Materials)

• Melting point: 196–203℃; Average heat resistance with slight sublimation at high temperatures
• Advantages: Low unit price; fit for non-standard products, low-filler indoor wall panels and recycled-material profiles
• Disadvantages: Prone to aging and whitening loss under long-term outdoor exposure; not recommended for main door & window profiles

4. PF (Low-Cost Domestic Alternative for Low-End Pipes)

• Low decomposition temperature, easy to decompose above 200℃; lower whitening efficiency than OB-1
• Only applicable to indoor PVC threading pipes and ordinary decorative strips

5. Special Profile Whitening Agent (LD-X01 / RQT-B-1)
    
   Modified composite formula developed for high-calcium and high-recycled-material profiles; stronger dispersibility and anti-yellowing performance

• Dosage: 0.01%–0.06%

III. Standard Formula Matching (Reference for Rigid PVC Door & Window Profiles)

• Titanium Dioxide (Rutile Type R): 4–6 parts (Basic hiding power & weather resistance)
• Calcium Carbonate Filler: 20–40 parts (Cost reduction, tends to cause greying of profiles)
• Fluorescent Whitening Agent OB-1: 0.01–0.04 parts (Core brightening & whitening additive)
• Ultramarine Blue: 0.001–0.003 parts (Fine-tune base color to offset slight yellow tint)
• Standard supporting materials: PVC stabilizer, CPE, processing aids and lubricants

Matching Principles

• Low titanium dioxide content, high calcium carbonate content or high recycled material proportion: Appropriately increase OB-1 dosage to 0.04%–0.05%
• Outdoor door & window profiles: Combine OB-1 with a small amount of UV absorber, or directly replace with KCB for improved weather resistance
• Strictly prohibit overdosage: Dosage exceeding 0.06% easily causes blooming, blue surface discoloration and late-stage yellowing during storage

IV. Production Feeding Processes (Two Main Methods)

1. Direct Powder Mixing (Adopted by Most Profile Manufacturers)

1. Add PVC resin, calcium carbonate, stabilizer and CPE into a high-speed thermal mixer for preliminary mixing
2. After uniform dispersion of lubricant system, add titanium dioxide, ultramarine blue and fluorescent whitening agent
3. Fully stir at 80–110℃ for 5–8 minutes, then transfer to cold mixer and cool down to below 40℃ before discharging

2. Masterbatch Feeding (Accurate Dosing & Dust-Free Workshop)
    
   OB-1 masterbatch with a concentration of 5%–10% is mixed in small quantities before extrusion. It is suitable for automatic production lines with less dust and more uniform dispersion.
    
   Dosage Conversion: Adding 0.2%–0.5% masterbatch can achieve an effective whitening agent content of 0.01%–0.05%.

V. Core Application Advantages

1. Reduce titanium dioxide cost: A small amount of whitening agent can eliminate grey discoloration caused by reduced titanium dioxide dosage, cutting the consumption cost of titanium dioxide per ton of raw materials.
2. Improve surface gloss: Unlike pure blue pigments, it increases total reflected light, delivering brighter and higher-grade profiles.
3. Optimize appearance of recycled-material products: Profiles mixed with crushed recycled materials tend to be dull and yellow; whitening agents can rapidly restore whiteness.
4. Fine-tune color tint: Cooperate with ultramarine blue to precisely control blue-white base color and avoid defective products with cyan or yellow bias.
5. Auxiliary mild weather resistance: Absorb partial short-wave ultraviolet light to slightly delay aging and yellowing of PVC.

VI. Common Problems & Solutions

1. Blue haze and blooming precipitation on profile surface

• Causes: Excessive whitening agent dosage, excessive lubricant, low processing temperature
• Solutions: Reduce dosage, raise extrusion temperature and decrease paraffin-based external lubricants

2. White right after extrusion but rapid yellowing after storage / sun exposure

• Causes: OB/PF with poor heat and weather resistance, no UV additives added
• Solutions: Replace with OB-1 or KCB, and compound with UV absorbers UV531 and UV327

3. Local white spots and uneven whiteness on profiles

• Causes: Poor dispersion of whitening agent, insufficient mixing time
• Solutions: Adopt high-fineness powder, extend thermal mixing time or switch to whitening masterbatch

4. Grey and dull surface of high-calcium-filled profiles

• Solution: Raise the maximum OB-1 dosage to 0.05% and moderately increase titanium dioxide addition

VII. Grade Selection Suggestions

1. Standard plastic-steel doors & windows and high-end outdoor profiles: OB-1 as the first choice; KCB for exterior wall panels under long-term sunlight exposure
2. Indoor wall panels, threading pipes and low-end non-standard products: OB or PF to lower costs
3. Profiles with large proportion of recycled materials and high calcium carbonate filling: Special composite whitening agents for profiles
4. Unified control of dosage range: 0.01%–0.05%. Conduct gradient color matching small trials before mass production