Self-Bonding LSR to PC: Adhesion Methods & Design Rules - Kunshan Fuhongying Electronic Materials Co., Ltd.

Self-bonding liquid silicone rubber overmolded onto polycarbonate can combine a rigid structural component with a flexible sealing, cushioning, gripping, or insulating surface in one integrated part.

This hard-soft combination is widely considered for medical devices, respiratory products, electronics, wearable devices, waterproof housings, optical components, automotive sensors, connectors, and fluid-handling assemblies. Polycarbonate provides the rigid supporting structure, while LSR provides elasticity, sealing performance, and a soft interface.

However, successful adhesion between LSR and PC should never be assumed.

The term “self-bonding” does not mean that every self-bonding LSR will adhere to every polycarbonate grade under all molding conditions. Adhesion depends on the exact LSR formulation, PC resin grade, additives, surface condition, mold temperature, cure time, insert temperature, joint geometry, contamination control, and post-molding environment.

Material suppliers specifically recommend testing each LSR and substrate combination before mass production because different plastic grades can have different surface properties.

This guide explains the main adhesion methods, material-selection requirements, mold-design principles, process controls, testing procedures, and common failure modes involved in self-bonding LSR-to-PC overmolding.

What Is Self-Bonding LSR?

Self-bonding LSR is a specially formulated liquid silicone rubber designed to develop adhesion to selected thermoplastics or metals during the molding and curing process.

Standard LSR generally does not create reliable chemical adhesion to untreated polycarbonate. A conventional assembly may therefore require:

Mekaaninen lukitus
A separate primer
Plasma treatment
An adhesive
Secondary assembly
Additional sealing components

Self-bonding or primerless LSR can eliminate some of these operations by bonding directly to a compatible substrate during overmolding.

Momentive defines self-bonding LSR as a material formulated to bond directly to specific substrates during molding without a primer or secondary bonding step.

The word “specific” is important. The buyer must verify that the selected LSR grade is designed and tested for the exact PC resin used in the final product.

Why Combine LSR With Polycarbonate?

Polycarbonate is commonly selected for rigid medical, electronic, industrial, and optical components. Depending on its formulation, it can offer:

High impact resistance
Dimensional stability
Moldability
Avoimuus
Structural rigidity
Availability in healthcare grades
Availability in sterilization-compatible grades
Integration of clips, ribs, bosses, channels, and optical features

Healthcare polycarbonate grades are available with biocompatibility assessments and controlled change-management programs, but the exact grade and regional availability must be confirmed with the resin supplier.

LSR can add:

Waterproof sealing
Joustavat venttiilit
Soft-touch surfaces
Vibration isolation
Electrical insulation
Cushioning
Flexible membranes
Skin-contact interfaces
Integrated gaskets
Pölysuojaus
Pressure-responsive features

Overmolding the two materials can reduce component count and eliminate a separately installed gasket.

Common LSR-to-PC Applications

Typical two-component applications include:

Respiratory mask frames and face seals
Medical-device housings
Diagnostic equipment seals
Drug-delivery components
Fluid-control valves
Wearable-device housings
Electronic buttons and membranes
Waterproof connector bodies
Anturikotelot
Lighting components
Battery and electronics enclosures
Optical assemblies
Automotive radar and camera seals
Handheld-device grips
Reusable healthcare products

Polycarbonate overmolding with LSR is used in medical products such as respiratory masks and other devices requiring molded-in sealing features.

Main Adhesion Methods

There are four primary strategies for joining LSR to PC:

Primerless self-bonding LSR
Alustan avulla tapahtuva liimaus
Surface activation or treatment
Mekaaninen lukitus

A robust design may use more than one method.

Method 1: Primerless Self-Bonding LSR

Primerless self-bonding LSR is often the preferred method for high-volume two-component molding.

The PC insert or first-shot component is positioned in the LSR mold, and the self-bonding silicone is injected directly onto the exposed bonding surface. During curing, the LSR develops adhesion to the compatible polycarbonate.

Mahdollisia etuja ovat muun muassa:

Fewer manufacturing steps
No manual primer application
Lower contamination risk
Reduced solvent handling
Improved automation
Shorter production flow
Lower assembly labor
More consistent adhesive coverage
Better suitability for two-shot molding
Reduced work-in-process inventory

WACKER reports that certain self-adhesive LSR grades can bond to PC without substrate pretreatment and can support automated multicomponent production.

Momentive also offers self-bonding LSR families developed for primerless adhesion to PC and other selected thermoplastics.

Limitations of Primerless Bonding

Primerless bonding can fail when:

The PC grade is incompatible
The resin contains unsuitable additives
The surface is contaminated
The insert is too cold
Cure time is insufficient
The interface receives inadequate pressure
The LSR is molded onto the wrong side of a film or coated component
The PC has aged or absorbed contamination during storage
The interface is subjected to peeling stress
The mold surface becomes contaminated
The material combination has not been validated

A successful trial with one PC grade does not prove compatibility with another grade from the same resin family.

Method 2: Primer-Assisted Bonding

A primer can be applied to the PC bonding surface before LSR molding.

The primer acts as an adhesion-promoting layer between the silicone and thermoplastic substrate.

A primer may be considered when:

The selected LSR is not self-bonding
Primerless adhesion is inconsistent
The PC surface is difficult to bond
The application requires additional adhesion margin
The project uses an existing LSR grade
Production volume does not justify a new material system
Mechanical locking is limited

Silicone primers are commercially available to improve adhesion to plastics and other substrates, but compatibility must be confirmed for the selected PC and LSR system.

Primer Process Risks

Primer application introduces additional controls:

Pintojen puhdistus
Application thickness
Coverage consistency
Drying time
Primer shelf life
Solvent handling
Operator training
Environmental controls
Masking of nonbonding areas
Erän jäljitettävyys
Regulatory evaluation
Potential cosmetic marks
Increased cycle and labor cost

Too much primer may create deposits, visible marks, weak boundary layers, or dimensional variation.

Too little primer may leave unbonded areas.

For medical or food-contact products, every primer and solvent must be included in the material and regulatory assessment.

Method 3: Surface Activation

Surface treatment can increase surface energy and improve adhesion in selected systems.

Potential methods include:

Atmospheric plasma
Low-pressure plasma
Koronaviruksen hoito
Flame treatment
UV-ozone treatment
Chemical surface treatment

Plasma treatment is used in some silicone bonding systems to improve adhesion where untreated substrate bonding is insufficient.

However, surface activation is time-sensitive. The treated surface may gradually lose its activated condition before overmolding.

A validated process should define:

Treatment method
Power
Gas
Distance
Treatment speed
Number of passes
Maximum delay before molding
Storage environment
Surface-cleanliness requirements
Inspection or monitoring method

Surface treatment should not be added without a controlled validation plan.

Method 4: Mechanical Interlocking

Mechanical interlocking uses the shape of the PC component to physically retain the cured silicone.

Common features include:

Läpivientireiät
Kolikkopelit
Alaleikkaukset
Grooves
Windows
Rei'itykset
Kiinnitysrivat
Dovetail features
Wraparound edges
Captured flanges
Enlarged anchor pockets

The LSR flows through or around these features and becomes mechanically locked after curing.

Mechanical interlocking is useful when:

Chemical adhesion is uncertain
The application experiences peel stress
The bond is safety-critical
The product undergoes repeated flexing
The interface contacts water or chemicals
Long-term aging may reduce adhesion
The design requires a redundant retention method

Mechanical locking can support the chemical bond, but it should not compensate for an uncontrolled molding process.

Material Pairing Is the First Design Decision

The LSR and PC grades should be selected as a tested material pair.

Do not choose the PC based only on its mechanical properties and choose the LSR separately at a later stage.

The evaluation should include:

Exact LSR trade name and grade
Exact PC trade name and grade
PC color
LSR color
PC additives
Flame-retardant system
UV stabilizers
Internal mold-release additives
Glass reinforcement
Medical or food-contact status
Sterilization requirements
Transparency requirements
Processing-temperature compatibility
Change-control requirements

WACKER states that even when an LSR series is designed to adhere to PC and other high-performance plastics, each substrate should be tested before mass production because surface properties differ.

Do Not Treat All PC Grades as Equivalent

Two polycarbonate grades may differ in:

Molecular weight
Melt-flow rate
Lämmönkestävyys
Mold-release package
Colorants
Flame retardants
Reinforcement
UV additives
Impact modifiers
Healthcare documentation
Sterilization compatibility

These differences may influence molding behavior and interface adhesion.

A natural PC grade and a black flame-retardant PC grade should be treated as two separate substrates during adhesion qualification.

A change of resin supplier, grade, pigment, recycled content, or additive package should trigger a technical review.

Temperature Compatibility

LSR requires heat to cure, while PC can soften, deform, discolor, or accumulate internal stress if exposed to unsuitable molding conditions.

The selected PC must withstand:

LSR mold temperature
Insert preheating
Ruiskutuspaine
Kovettumisaika
Repeated molding cycles
Local heating at the interface
Post-curing, when required
Sterilization
Thermal aging

When standard PC cannot tolerate the required LSR curing conditions, a higher-heat polycarbonate or lower-temperature-curing LSR may be considered.

Special high-heat polycarbonate grades have been developed for LSR-overmolding applications where standard thermal resistance may be insufficient.

Dow also offers lower-temperature-curing LSR options intended for thermally sensitive substrates and thick overmolded sections.

Drying and Handling the PC Insert

PC is moisture-sensitive during its own molding process, so the thermoplastic supplier’s drying and processing recommendations must be followed when producing the rigid insert.

After molding, the insert should be protected from:

Oil
Pöly
Sormenjäljet
Mold-release sprays
Cleaning residues
Packaging contamination
Condensation
Excessive storage time
Contact with incompatible gloves
Silicone oils from unrelated operations

The bonding area should remain clean and dry before LSR overmolding.

The approved cleaning process should define:

Cleaning agent
Concentration
Application method
Drying method
Maximum holding time
Pakkaus
Handling gloves
Acceptance criteria

Avoid introducing an aggressive cleaner without checking its effect on PC stress cracking and surface chemistry.

One-Shot, Insert and Two-Shot Molding

Insert Overmolding

The PC component is molded in a separate operation, inspected, stored, and later loaded into the LSR mold.

Etuihin kuuluvat:

Separate optimization of each molding process
Flexible production scheduling
Lower multicomponent-equipment investment
Easier initial development

Disadvantages may include:

Additional handling
Surface contamination
Insert cooling
Inventory
Manuaalinen lataus
Positioning errors
Longer time between molding stages

Two-Shot Molding

The PC is molded as the first shot and transferred directly to another cavity for LSR overmolding.

Mahdollisia etuja ovat muun muassa:

Warm, freshly molded PC surface
Reduced contamination
Short delay between molding stages
Improved automation
Lower handling
Higher production consistency
Reduced work-in-process inventory

WACKER describes self-adhesive LSR as suitable for large-series overmolded parts produced through multicomponent or shuttle-mold processes.

Rotary or Shuttle Mold

A rotary mold, index plate, or shuttle system transfers the PC component from the thermoplastic cavity to the LSR cavity.

The design must account for:

Different mold temperatures
PC cooling and shrinkage
LSR curing temperature
Insert positioning
Cavity alignment
Cycle balancing
Robot access
Mold-surface isolation
Differential thermal expansion

Design the Interface for Shear, Not Peel

Adhesive joints usually perform better when loads act in shear or compression rather than peeling the silicone away from the PC edge.

Avoid designs where:

A thin silicone lip can be lifted easily
The bond line terminates at a sharp exposed edge
Repeated user contact pulls directly on the interface
Assembly force peels the silicone backward
Fluid pressure opens the bond line
A cable pulls perpendicular to the interface

Prefer designs where:

The LSR wraps around the PC edge
The interface has adequate overlap
Loads are distributed over a wide area
Mechanical anchors support the bond
The bond edge is protected
Sealing pressure pushes the LSR toward the PC

Increase Bonding Area Carefully

A larger bonding area can improve total retention, but more area does not automatically solve poor adhesion.

The interface should be:

Wide enough for stable bonding
Accessible to LSR flow
Properly vented
Free of sharp changes in thickness
Protected from trapped air
Designed for uniform heating
Easy to inspect

Long narrow bonding paths can trap air or create incomplete filling.

Add Mechanical Anchors in Critical Areas

Mechanical locking features should be considered near:

Pull tabs
Hinges
User-contact edges
Cable exits
Valve regions
Ohutkalvot
Corners
High-pressure sealing areas
Areas exposed to repeated bending

Through-holes allow the LSR on one side of the PC to connect with silicone on the opposite side, creating a strong physical lock.

The hole diameter and spacing must allow complete filling without weakening the plastic structure.

Vältä teräviä kulmia

Sharp PC corners can:

Restrict LSR flow
Create air traps
Concentrate stress
Cut or tear the silicone
Reduce effective bonding area
Create thin sections
Encourage crack initiation

Use appropriate radii at the interface.

The radius must be large enough to improve flow and stress distribution while still meeting the functional geometry.

Control LSR Thickness

Very thin LSR sections may:

Cure too quickly at the surface
Fill incompletely
Tear during demolding
Provide insufficient peel-test width
Create inconsistent bond strength
Be damaged during use

Very thick sections may:

Require longer curing
Increase cycle time
Create temperature gradients
Increase shrinkage effects
Distort the PC insert
Trap air

The thickness should be consistent where possible.

Gradual transitions are preferable to sudden changes.

Gate Location

The LSR gate should be positioned to promote complete and uniform filling of the bonding interface.

A poor gate location can cause:

Air entrapment
Flow hesitation
Uneven interface pressure
Premature curing
Weak weld lines
Incomplete encapsulation
Excessive pressure on the PC insert
Insert displacement

The gate should not direct a high-velocity material stream against a fragile PC wall.

The gate vestige should also be positioned away from:

Sealing surfaces
Cosmetic surfaces
Ohutkalvot
User-contact areas
Critical bond edges

Venting and Vacuum

LSR can flow into very small gaps, but trapped air can still prevent full contact with the PC surface.

Air traps may create:

Local unbonded spots
Bubbles
Surface burns
Short filling
Weak bond initiation points
Leak paths

Vacuum-assisted molding and properly located vents can improve filling consistency.

Vents must be designed carefully because low-viscosity uncured LSR can create flash.

Protect the Nonbonding Areas

Self-bonding LSR should bond to the PC component but release cleanly from the mold.

The mold may require:

Appropriate tool steel
Surface coating
Controlled polish
Defined texture
Temperature balance
Selective release treatment
Protected shutoff areas

WACKER reports that its PC-bonding LSR technology is designed to adhere to the hard component without bonding to the mold, supporting automated production.

However, actual release performance must be proven with the production tool.

Shutoff Design

The boundary between exposed PC and overmolded LSR requires precise shutoff geometry.

Poor shutoffs may cause:

Silicone flash on the PC surface
Cosmetic defects
Leakage paths
Difficult trimming
Damage to optical areas
Uncontrolled bond edges
PC deformation

The shutoff should:

Support the PC insert
Prevent insert movement
Avoid excessive clamping stress
Limit flash
Protect finished surfaces
Account for PC dimensional tolerance
Remain maintainable throughout tool life

PC Insert Temperature

A warm PC insert can improve bonding in some systems because the interface reaches the required reaction temperature more quickly.

An insert that is too cold may:

Delay adhesion development
Increase cure-time requirements
Create weak areas
Cause condensation in humid environments
Produce inconsistent bonding between cycles

An insert that is too hot may:

Deform
Accumulate stress
Lose dimensional accuracy
Increase sticking
Affect optical quality

The validated process should define the acceptable insert-temperature range at the time of overmolding.

Mold Temperature and Cure Time

Self-bonding LSR requires enough time and temperature to cure and develop adhesion.

Insufficient cure can lead to:

Adhesive failure
Soft or tacky silicone
Poor mechanical properties
Unstable dimensions
Weak peel strength

Excessive heat exposure can:

Deform PC
Increase cycle time
Discolor the plastic
Affect additives
Increase internal stress
Reduce production efficiency

Use the material supplier’s recommended processing window as the starting point and develop a validated production window through trials.

Pressure at the Interface

The LSR must contact the PC surface continuously before curing.

Insufficient interface pressure may create:

Dry spots
Air pockets
Partial adhesion
Weak edges
Leak paths

Excessive injection pressure may:

Move the insert
Deform thin PC walls
Open shutoffs
Create flash
Damage optical surfaces

Balanced filling is usually more important than maximum injection pressure.

Cure Inhibition and Contamination

Platinum-cured LSR can be affected by certain contaminants.

Potential sources include:

Rikkiä sisältävät materiaalit
Aamiinit
Phosphorus compounds
Joitakin liimoja
Some pigments
Rubber gloves
Lubricants
Cleaning products
Residues from other elastomers
Packaging materials

WACKER warns that amines, sulfur, and phosphorus compounds can interfere with platinum-catalyzed LSR systems.

The production area should control contact materials and cross-contamination.

Adhesion Failure Modes

Adhesive Failure

The silicone separates cleanly from the PC surface.

This usually indicates that the interface bond is weaker than the silicone itself.

Potential causes include:

Incompatible material pair
Surface contamination
Insufficient temperature
Short cure time
Incorrect LSR mixing
Aged or unsuitable PC surface
Inadequate treatment
Incorrect primer
Poor primer application

Cohesive Failure

The silicone tears while a layer remains attached to the PC.

This indicates that the interface bond is stronger than the local silicone strength.

Cohesive failure is often the preferred result during peel testing.

WACKER reports cohesive failure in peel testing for selected PC and self-bonding LSR combinations, with the silicone tearing while the interface remained intact.

Mixed Failure

Part of the interface separates cleanly while another area tears through the silicone.

Mixed failure may indicate:

Uneven surface condition
Temperature variation
Partial contamination
Air entrapment
Uneven primer
Inconsistent interface pressure
Variable cure

PC Substrate Failure

The PC cracks or breaks before the silicone bond separates.

This may indicate strong adhesion, but it can also reveal:

Excessive stress concentration
Weak PC geometry
Internal molding stress
Chemical attack
Poor mechanical design

Peel Testing

A 90-degree or 180-degree peel test is commonly used to compare adhesion between material combinations and process conditions.

A controlled test should define:

Specimen geometry
Bonding width
LSR thickness
PC thickness
Peel angle
Pull speed
Conditioning time
Test temperature
Sample quantity
Failure mode
Minimum peel strength

Report both the force and failure mode.

A high force followed by clean adhesive separation may indicate a different risk than a lower force with consistent cohesive tearing.

WACKER reports peel-test results for selected self-adhesive LSR and PC combinations, but those supplier values should not be used as automatic acceptance criteria for a different product geometry or resin grade.

Tensile Pull Testing

For buttons, inserts, connectors, and circular seals, a tensile pull or push-out test may better represent the actual load.

The test fixture should reproduce the expected service direction.

Possible measurements include:

Maximum pull force
Force at first separation
Displacement at failure
Failure location
Percentage of cohesive failure

Leak Testing

When the LSR functions as a waterproof seal, bond testing alone is not enough.

The assembly may also require:

Air-pressure decay testing
Vacuum decay testing
Water spray testing
Immersion testing
Bubble testing
Burst-pressure testing
Fluid-pressure testing

Leak testing should be repeated after environmental conditioning.

Environmental Validation

The LSR-to-PC bond should be evaluated after relevant exposures, such as:

Lämpösyklit
High-temperature aging
Low-temperature exposure
Korkea ilmankosteus
Water immersion
Detergents
Disinfectants
Skin oils
Automotive fluids
UV exposure
Tärinä
Mechanical shock
Repeated flexing
Sterilization
Accelerated aging

A bond that performs well immediately after molding may weaken after aging or chemical exposure.

Sterilization Considerations

For healthcare products, evaluate the complete PC-LSR assembly after the intended sterilization process.

Possible methods include:

Etyleenioksidi
Steam
Gammasäteily
Electron beam
X-ray
Höyrystetty vetyperoksidi

The sterilization process can affect:

PC transparency
PC stress cracking
Silikonin kovuus
Silicone elongation
Sidoksen lujuus
Väri
Mitat
Sealing force
Extractables
Long-term aging

Certain self-bonding LSR and PC systems have demonstrated compatibility with repeated steam sterilization, but this performance is material-grade-specific and does not apply automatically to all combinations.

Quality-Control Plan

A production control plan may include:

PC resin verification
LSR batch verification
Pigment verification
Insert dimensions
Insert cleanliness
Insert temperature
Muotin lämpötila
Ruiskutuspaine
Kovettumisaika
Silmämääräinen tarkastus
Flash inspection
Bond-edge inspection
Peel or pull testing
Leak testing
Toiminnallinen testaus
Erän jäljitettävyys

For medical, automotive, or safety-critical products, define the testing frequency and acceptance criteria before mass production.

Change Control

Adhesion is sensitive to material and process changes.

Require notification before changing:

PC grade
PC supplier
PC manufacturing site
PC color
Additive package
Mold-release package
Recycled content
LSR-laatu
LSR supplier
LSR pigment
Primer
Cleaning agent
Surface treatment
Mold coating
Muotin lämpötila
Cure conditions
Production site
Sterilointimenetelmä

SABIC notes that its healthcare polycarbonate portfolio uses formula-lock and management-of-change controls, illustrating why controlled resin sourcing matters in regulated applications.

Recommended Development Process

Phase 1: Define the Application

Document:

Product function
Bonding purpose
Sealing requirement
Expected load
Lämpötila
Kemikaaleille altistuminen
Sterilization
Service life
Regulatory market
Annual volume

Phase 2: Screen Material Pairs

Select several candidate combinations of:

Self-bonding LSR grade
PC grade
Väri
Kovuus
Lämmönkestävyys
Regulatory status

Request supplier adhesion tables or technical support where available.

Phase 3: Produce Test Plaques

Mold standardized plaques using representative:

PC processing conditions
LSR processing conditions
Surface conditions
Interface thickness
Kovettumisaika
Insert temperature

Compare peel strength and failure mode.

Phase 4: Prototype the Real Geometry

Test actual components because plaque results may not represent:

Corner flow
Thin sections
Gate location
Insert movement
Bond-edge geometry
Mechanical stresses
Sealing pressure

Phase 5: Establish the Process Window

Test combinations of:

Low and high mold temperature
Short and long cure time
Low and high insert temperature
Minimum and maximum holding time
Material-lot variation
PC color variation
LSR pigment variation

Phase 6: Complete Environmental Testing

Evaluate bonded samples after the required aging, fluid, thermal, mechanical, and sterilization conditions.

Phase 7: Validate Production

Validate:

Material handling
PC molding
Insert storage
Pintojen puhdistus
Insert transfer
LSR metering and mixing
Molding parameters
Demolding
Inspection
Pakkaus
Traceability

Information to Include in an RFQ

Provide the molding supplier with:

PC trade name and exact grade
LSR trade name and exact grade, when selected
Two-dimensional drawing
Three-dimensional model
Bonding-area dimensions
Required LSR hardness
PC and LSR colors
Mechanical load direction
Required peel or pull strength
Waterproof or leak requirement
Käyttölämpötila
Kemikaaleille altistuminen
Sterilointimenetelmä
Regulatory requirements
Annual quantity
Prototype quantity
Cosmetic requirements
Acceptable flash
Test requirements
Packaging and cleanliness requirements
Jäljitettävyysvaatimukset
Change-notification requirements

When the materials have not yet been selected, ask the supplier to propose and test at least two compatible LSR-to-PC combinations.

Supplier Qualification Questions

Ask the LSR overmolding supplier:

Which self-bonding LSR grades have you molded onto PC?
Which exact PC grades have been validated?
Can you provide peel-test samples?
Do you use insert molding or two-shot molding?
How do you control insert temperature?
How do you prevent PC surface contamination?
Is primer required?
Is plasma treatment required?
How do you monitor LSR mixing ratio?
How do you control cure inhibition?
What mold coatings are used?
How do you inspect the bond line?
Can you conduct peel, pull, and leak testing?
How do you manage material changes?
Can production lots be traced to both raw-material batches?

Johtopäätös

Successful self-bonding of LSR to polycarbonate depends on the complete material and process system.

The most important rules are:

Select the LSR and PC as a tested pair.
Do not assume that all PC grades behave the same.
Keep the bonding surface clean and controlled.
Design the joint to resist shear rather than peel.
Add mechanical locking for critical applications.
Protect bond edges from user handling and fluid pressure.
Balance mold temperature, insert temperature, cure time, and PC heat resistance.
Test actual production geometry, not only material plaques.
Validate the bond after aging, chemicals, thermal cycling, and sterilization.
Control every material and process change.

Primerless self-bonding LSR can reduce assembly steps and support automated production, but reliable adhesion must be demonstrated with the exact materials, tooling, process window, and service conditions intended for the final product.

Usein kysyttyjä kysymyksiä

Does every self-bonding LSR adhere to polycarbonate?

No. Self-bonding LSR grades are developed for selected substrates. The exact LSR and PC combination must be tested before mass production.

Is primer required when overmolding LSR onto PC?

Not always. A compatible self-bonding LSR may adhere to PC without primer. Primer may be required when the material pair does not provide sufficient primerless adhesion.

Can plasma treatment improve LSR-to-PC adhesion?

It may improve adhesion in selected systems, but the treatment parameters and maximum delay before molding must be validated.

What is the strongest LSR-to-PC joint design?

A wide interface loaded mainly in shear, combined with protected edges and mechanical interlocking, generally provides a more robust design than a thin exposed edge loaded in peel.

Why does the silicone peel away cleanly from the PC?

Clean separation indicates adhesive failure. Common causes include incompatible materials, contamination, insufficient heat, short cure time, low insert temperature, or inadequate surface treatment.

What is cohesive failure?

Cohesive failure occurs when the silicone tears while some silicone remains attached to the PC. It indicates that the interface is stronger than the silicone at the failure location.

Can a PC-LSR assembly be steam sterilized?

Some material combinations are suitable for repeated steam sterilization, but compatibility is grade-specific. The complete molded assembly must be tested after the intended number of cycles.

Should mechanical locks be added when using self-bonding LSR?

Mechanical locks are recommended for critical areas exposed to peel, pressure, repeated flexing, or safety-related loads. They provide additional retention if chemical adhesion weakens.

Can an internal mold-release additive in PC affect adhesion?

Potentially. Additives can change the surface characteristics of the plastic. The exact resin grade, color, and additive package should therefore be tested as part of the approved material combination.

How should adhesion be tested?

Use a defined peel, tensile pull, push-out, or functional test that represents the real product load. Record both maximum force and failure mode.

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