Optical brighteners are widely used in papermaking to improve paper whiteness and brightness.
However, selecting a suitable optical brightener is not simply a matter of choosing the product with the highest whitening strength.
One of the most important questions is:
Where will the optical brightener be added?
In papermaking, optical brighteners may be applied through different stages, including:
Pulp or stock application
Wet-end addition
Size press
Surface sizing
Coating formulations
Different application points require different performance characteristics.
The correct optical brightener should therefore be selected according to the papermaking process, fiber system, required whiteness, chemical environment, application efficiency and overall cost.
1. Why Does the Application Point Matter?
An optical brightener added directly to pulp does not experience the same conditions as one applied at the paper surface.
In stock application, the optical brightener must interact effectively with fibers and remain sufficiently retained during sheet formation.
At the size press, the product needs to perform well in starch or other surface-sizing systems.
In coating applications, compatibility with binders, pigments and other coating ingredients becomes particularly important.
For this reason:
Pulp application ≠ Size press application ≠ Coating application
Even when two products are both described as paper optical brighteners, they may not provide the same performance at every application point.
2. Pulp and Wet-End Application: Fiber Affinity Is Critical
When an optical brightener is added to the pulp or wet end, it needs sufficient affinity for the cellulose fibers.
A suitable product should provide:
Good fiber substantivity
Effective retention
Uniform distribution
Stable whitening performance
Compatibility with wet-end chemistry
If fiber affinity is too low, part of the optical brightener may remain in the water phase rather than being retained effectively on the sheet.
This can reduce application efficiency and increase the amount of product required.
Commercial paper OBAs designed for stock application therefore often emphasize high substantivity and wet-end efficiency.
3. Retention Should Be Considered Together with Whiteness
In wet-end application, maximum fluorescence alone does not determine the best product.
A more useful question is:
How much of the optical brightener actually contributes to the finished paper?
If a product provides strong fluorescence but poor fiber retention, the real application efficiency may be lower than expected.
For pulp application, papermakers should consider:
Whitening effect + Fiber affinity + Retention + Required dosage + Cost
together.
The most economical grade is not necessarily the product with the lowest price per kilogram.
It is the one that provides the required whiteness at an efficient retained dosage.
4. Wet-End Chemicals Can Affect Optical Brightener Performance
The paper stock contains more than fibers and optical brightener.
Depending on the paper grade and production process, the wet end may also contain:
Sizing agents
Retention aids
Strength additives
Fillers
Dyes
Fixing agents
Aluminum salts
Cationic polymers
Other process chemicals
These chemicals can influence optical brightener behavior.
Many paper optical brighteners are anionic, so compatibility with strongly cationic additives should be evaluated carefully.
This does not mean cationic chemicals can never be used in the same papermaking system. However, incorrect addition sequence or excessive interaction may affect:
Solubility
Retention
Fluorescence
Bath stability
Final paper shade
For this reason, the complete wet-end chemical system should be considered during product selection and production trials.
5. When Is Size Press Application Attractive?
The size press is another important application point for paper optical brighteners.
Instead of adding the OBA into the pulp, the optical brightener is applied closer to the paper surface together with the sizing formulation.
This approach can be particularly useful when:
High surface whiteness is required
Brightness needs to be adjusted efficiently
The paper grade uses surface starch
The mill wants greater control of final appearance
Additional whiteness is needed after sheet formation
Commercial paper OBA technologies specifically designed for size-press use demonstrate that this application route can achieve very high brightness levels.
6. Compatibility with Starch Is Important at the Size Press
Size-press formulations commonly contain starch and may also contain other functional additives.
The optical brightener should therefore be evaluated for:
Solubility
Compatibility with starch
Application uniformity
Viscosity effects
Stability in the sizing formulation
Final surface whiteness
An optical brightener that performs well in stock application may not automatically provide the best performance in a concentrated surface-sizing formulation.
The actual starch type, solids level, pH and other additives should be included in the evaluation.
7. Why Can Surface Application Give Strong Whiteness?
Optical brighteners work by interacting with light.
When a larger proportion of the optical brightener is located near the paper surface, its fluorescent contribution to the visual appearance can be very effective.
This is one reason size-press and other surface applications can be useful for achieving high-brightness printing and writing papers.
However, this does not mean that surface application is always more economical than wet-end addition.
The best process depends on:
Base-sheet whiteness
Required final whiteness
Paper grade
Existing production equipment
Surface-sizing formulation
OBA efficiency
Production cost
8. Coating Application Requires Good Formulation Compatibility
For coated paper and board, an optical brightener may be incorporated into the coating formulation.
In this system, the OBA needs to perform in the presence of materials such as:
Mineral pigments
Binders
Starch
PVOH
CMC
Latex
Other coating additives
Compatibility is therefore critical.
Commercial paper OBAs exist that are specifically suited for coating formulations containing binders such as PVOH, CMC or casein, illustrating the importance of matching the optical brightener to the coating system.
A good coating OBA should contribute to whiteness without negatively affecting the stability or application behavior of the coating formulation.
9. Pigments and Binders Can Affect the Whitening Result
Coated paper formulations can be complex.
The final optical brightening performance may be influenced by:
Calcium carbonate
Clay
TiO₂
Binder chemistry
Binder concentration
Coating solids
pH
Drying conditions
Other dyes or shading agents
This is why the same optical brightener can give different results in two coating formulations.
The OBA should therefore be evaluated in the actual coating formulation, not only in water or a simplified laboratory solution.
10. More Optical Brightener Does Not Always Mean More Whiteness
One of the most important formulation principles in papermaking is that optical brightener dosage should be optimized.
At low to moderate levels, increasing dosage may significantly increase whiteness.
However, beyond a certain point, the improvement can become progressively smaller.
The customer may then experience:
Limited additional whiteness
Increased chemical cost
Unwanted shade shift
Lower cost efficiency
Therefore, the objective should not be:
Maximum OBA dosage
but rather:
Target whiteness at the most efficient dosage
This is particularly important for high-whiteness paper grades, where the last few whiteness points may become increasingly expensive.
11. Do Not Evaluate OBA Cost Only by Price per Kilogram
Two paper optical brighteners may have different:
Concentrations
Affinity
Sulfonation levels
Application efficiencies
Recommended dosage
Suitability for stock or surface application
Therefore, comparing only the purchase price can be misleading.
A more useful calculation is:
Product price + required dosage + retention/application efficiency + achieved whiteness
For example, a higher-priced product may still provide a lower actual whitening cost if it achieves the required result at a lower effective dosage.
12. Whiteness and Brightness Are Not Exactly the Same
Papermakers should also distinguish between:
Brightness
and
Whiteness
These measurements describe different optical characteristics of paper.
A sheet can have high brightness while its visual white shade still does not match the customer’s preferred appearance.
Optical brighteners may also be used together with shading dyes or pigments to adjust the final white tone.
Industry whiteness systems therefore commonly combine optical brightening agents with shading colorants when a specific paper shade is required.
The final product should be evaluated according to the customer’s actual specification rather than relying on only one optical measurement.
13. Base Pulp Quality Has a Major Influence
The starting quality of the pulp affects how much optical brightening is required.
Important factors can include:
Initial pulp brightness
Fiber source
Bleaching quality
Recycled-fiber content
Residual color
Contaminants
A clean, well-bleached pulp may require a different optical brightener strategy from a lower-brightness or recycled-fiber furnish.
If the starting pulp has strong intrinsic coloration, simply increasing OBA dosage may become inefficient.
Improving the base sheet and optimizing the optical brightener should therefore be considered together.
14. Recycled Fiber Can Require Additional Evaluation
Recycled paper furnish can present greater variability than virgin pulp.
Possible factors include:
Mixed fiber sources
Previous dyes
Printing ink residues
Fillers
Previous optical brighteners
Different chemical histories
Variable starting brightness
For recycled-fiber paper, the same OBA dosage may not produce identical results from batch to batch.
Papermakers should therefore evaluate:
Incoming furnish brightness
Base-paper shade
Retention
OBA dosage
Final whiteness consistency
before fixing a standard formulation.
15. Pulp, Size Press or Coating: Which One Should You Choose?
There is no universal answer.
Consider Pulp / Wet-End Application When:
The OBA needs to be incorporated throughout the sheet
Good cellulose affinity and retention are available
The process is designed for stock addition
Base-sheet whiteness needs improvement
Consider Size Press Application When:
High surface whiteness is required
Surface starch is already being applied
Final whiteness needs more flexible adjustment
Efficient surface brightening is desired
Consider Coating Application When:
The product is coated paper or coated board
Whiteness needs to be adjusted through the coating layer
The OBA is compatible with the coating binder and pigment system
In many mills, more than one application point may also be used.
The final strategy should depend on the paper grade and production economics.
16. Can Optical Brighteners Be Used at More Than One Stage?
Yes.
In some high-whiteness paper grades, manufacturers may use a combination such as:
Wet-end OBA + Size Press OBA
or
Wet-end OBA + Coating OBA
The purpose is not simply to add more optical brightener.
Instead, different application stages can be used to balance:
Base-sheet brightness
Surface whiteness
Application efficiency
Shade
Production cost
The optimum distribution should be determined through production trials.
17. A Practical Selection Process
A practical approach can follow these steps.
Step 1 — Identify the Paper Grade
Determine whether the product is:
Printing and writing paper
Coated paper
Paperboard
Packaging paper
Specialty paper
Another grade
Step 2 — Check the Fiber Furnish
Confirm:
Virgin or recycled fiber
Starting brightness
Fillers
Existing wet-end chemistry
Step 3 — Determine the Application Point
Decide whether the optical brightener will be used in:
Pulp / stock
Wet end
Size press
Coating
Multiple stages
Step 4 — Review Chemical Compatibility
Consider:
Retention aids
Sizing chemicals
Starch
Binders
Pigments
Cationic additives
pH
Step 5 — Define the Target
Determine the required:
Brightness
Whiteness
White shade
Paper appearance
Step 6 — Test Several Dosages
Keep the main process conditions constant while comparing different OBA levels.
Step 7 — Evaluate Application Efficiency
Compare:
Whiteness gain
Required dosage
Retention
Surface appearance
Process stability
Overall chemical cost
18. How Should Different Paper Optical Brighteners Be Compared?
When comparing two products, avoid comparing only their liquid color, concentration or purchase price.
Use the same:
Pulp batch
Paper furnish
Wet-end chemistry
Starch or coating formulation
pH
Application point
Drying conditions
Then evaluate:
Whiteness Gain
How much improvement is achieved?
Shade
Does the finished paper have the desired white tone?
Application Efficiency
How much OBA is required?
Compatibility
Does the product remain stable in the pulp, starch or coating system?
Retention
For wet-end application, how efficiently is the product retained?
Process Stability
Does it perform consistently during production?
Cost
What is the chemical cost per ton of finished paper at the required whiteness?
What Is the Best Optical Brightener for Paper?
There is no single optical brightener that is best for every paper application.
The correct choice depends on:
Paper Grade + Fiber Furnish + Application Point + Affinity + Chemical Compatibility + Required Whiteness + Shade + Dosage + Cost
For pulp application, fiber affinity and retention are important.
For size-press application, surface whitening efficiency and compatibility with the sizing system become more important.
For coating application, compatibility with pigments, binders and the complete coating formulation should be carefully evaluated.
The best product is the one that achieves the required paper whiteness and appearance with stable processing performance and efficient overall application cost.
Need Help Choosing an Optical Brightener for Paper?
If you are selecting an optical brightener for papermaking, tell us your paper grade, fiber furnish, application point, current OBA, target whiteness and production process.
Blue Dolphin can help you evaluate suitable optical brightener grades for pulp, size press and coating applications according to your papermaking requirements.
Post time: Aug-13-2026