12 Common Hot Melt Adhesive Problems and How to Solve Them

Hot melt adhesive problems rarely come from one cause alone.

A weak bond may be blamed on the adhesive, while the real problem is a cold substrate, insufficient compression, incorrect application temperature, contamination, or a bonding step that occurs outside the adhesive’s open time. Similarly, stringing may look like a formulation problem but actually come from a worn nozzle, unstable pressure, incorrect gun distance, or partially blocked filter.

Effective hot melt adhesive troubleshooting therefore requires more than increasing the temperature or applying more glue. The adhesive, substrate, equipment, production settings, storage conditions, and final service environment must be evaluated together.

This guide explains the most common hot melt adhesive problems, how to identify their likely causes, and how factories can correct adhesive bonding failure without creating new production issues.

Quick answer: Start by checking where the adhesive remains after the failed bond is opened. Then verify the adhesive grade, substrate condition, actual temperature, coating weight, open time, compression, line speed, equipment condition, and final service environment. Change only one variable at a time and stay within the adhesive supplier’s recommended processing range.

Why Do Hot Melt Adhesive Problems Occur?

A reliable hot melt bond depends on several variables working together:

1. Adhesive selection: The formulation must match the substrates, application method, production speed, and final performance requirements.
2. Substrate condition: Dust, oil, coatings, release agents, moisture, low surface energy, or low substrate temperature can reduce wetting.
3. Application temperature: The adhesive must reach the correct viscosity without being overheated.
4. Timing: The materials must be joined while the adhesive is still within its practical open time.
5. Compression: Adequate and uniform pressure must hold the substrates together while the bond develops initial strength.
6. Coating weight: Too little adhesive may not provide sufficient coverage, while too much may slow cooling or cause squeeze-out.
7. Equipment condition: Blocked filters, worn nozzles, damaged hoses, inaccurate sensors, and unstable pressure can change adhesive delivery.
8. Service environment: Heat, cold, moisture, chemicals, stress, vibration, and aging can cause a bond that initially looked acceptable to fail later.

Understanding hot melt adhesive viscosity, open time, and setting time is especially important because these properties directly affect wetting, bead formation, compression time, and line speed.

Hot Melt Adhesive Troubleshooting: Quick Diagnosis Table

This table should be used as a starting point. A visible symptom can have several causes, so production settings should not be changed before basic evidence is collected.

Diagnose Adhesive Bonding Failure by Looking at the Failure Surface

One of the fastest ways to investigate adhesive bonding failure is to carefully separate the failed joint and examine both surfaces.

Adhesive Remains Mainly on One Substrate

If most of the adhesive remains on only one side, the second surface may not have been properly wetted.

Possible causes include:

• The adhesive cooled before the second substrate made contact
• The substrate was too cold
• The application temperature was too low
• The practical open time was too short
• The materials did not make full contact
• The surface contained dust, oil, coating, moisture, or release agent
• The adhesive was not suitable for that substrate
• The coating weight was insufficient

The first correction should not automatically be a large temperature increase. Confirm the actual temperature, application-to-compression delay, substrate temperature, bead placement, and surface condition first.

Adhesive Appears on Both Substrates

Adhesive on both surfaces normally indicates that some transfer or wetting occurred. However, this does not prove that the final bond was strong enough.

Possible causes include:

• Movement while the adhesive was still setting
• Insufficient compression time
• Excess adhesive that cooled too slowly
• Cohesive failure inside the adhesive layer
• Heat softening or cold brittleness
• Excessive stress on the joint
• An adhesive grade that does not meet the final performance requirement

The Adhesive Surface Is Smooth or Glossy

A smooth, rounded, or glossy bead can indicate that the second substrate did not compress the adhesive properly.

Check:

• Compression pressure
• Compression alignment
• Bonding gap
• Warped or uneven substrates
• Nozzle position
• Bead height
• Timing between application and contact

The Substrate Tears Before the Bond Separates

For paperboard and corrugated packaging, visible fiber tear generally indicates that the adhesive bond is stronger than the local paper surface.

However, fiber tear should not be used as the only quality standard for plastic, film, foam, textile, metal, or coated substrates. These materials require suitable peel, shear, aging, heat, cold, or durability tests.

1. Poor Initial Adhesion or No Bond Formation

Poor initial adhesion occurs when the adhesive does not properly wet one or both substrates before cooling.

Common Causes

• Application temperature is below the recommended range
• Adhesive viscosity is too high for the equipment or substrate
• Substrate temperature is too low
• Adhesive cools before the materials are joined
• Coating weight is too low
• Compression is insufficient or uneven
• Substrate is dusty, oily, wet, coated, or contaminated
• Adhesive chemistry is incompatible with the substrate
• Nozzle is partially blocked, reducing the actual glue amount
• The adhesive has degraded during storage or heating

How to Solve It

1. Compare tank, hose, and nozzle settings with the current technical data sheet.
2. Measure actual temperature instead of relying only on the machine display.
3. Confirm that the adhesive reaches the second substrate within its practical open-time window.
4. Inspect the entire glue pattern for missing or thin areas.
5. Check substrate temperature and allow cold materials to reach suitable production conditions.
6. Clean or replace contaminated substrates where possible.
7. Verify compression pressure, contact area, and holding time.
8. Run a controlled trial with a slightly adjusted coating weight.
9. Test a different adhesive grade if the surface is coated, non-polar, or difficult to bond.

If the problem began after receiving a new shipment, compare the product code, lot number, packaging condition, storage history, and current hot melt adhesive TDS, SDS, and COA.

2. Bond Opens After Cooling or Handling

A bond may look acceptable when it leaves the compression section but open several seconds or minutes later. In packaging, this is often described as a pop-open.

Common Causes

• Compression is released before sufficient handling strength develops
• Adhesive set time is too slow for the line speed
• Carton flaps, foam, fabric, or other substrates create strong recovery force
• Too much adhesive retains heat and delays setting
• The adhesive remains soft because the factory or product is warm
• Bonded parts shift during cooling
• The compression mechanism is misaligned
• The adhesive has insufficient initial tack or green strength

How to Solve It

• Increase effective compression time where the process allows
• Check whether compression is uniform across the complete bond area
• Prevent the substrates from sliding during setting
• Compare the adhesive’s set speed with the real line speed
• Reduce excessive coating weight if the bond remains molten too long
• Evaluate a faster-setting formulation for high-speed production
• Use an adhesive with stronger initial tack for high-memory materials
• Check whether the substrate or product enters the bonding area unusually warm

For carton sealing, open a failed joint and compare bead compression, adhesive transfer, and fiber tear before changing the formula. A rounded bead usually points toward poor contact, while adhesive on both surfaces may indicate a later heat, cold, movement, or cohesive failure.

3. Bond Delamination, Creep, or Edge Lifting Under Heat

Application temperature and service temperature are not the same.

Application temperature controls how the adhesive melts and flows through the equipment. Service temperature describes the environment the finished bond must survive. A hot melt applied at a high temperature can still soften and fail at a much lower service temperature.

Common Causes

• Adhesive softens under the real service temperature
• The joint remains under continuous load
• Bond area is too small
• Adhesive layer is too thick
• Substrate expansion creates peel stress
• Adhesive chemistry lacks sufficient heat resistance
• Finished products were tested only at room temperature
• Heat, humidity, and mechanical load act together

How to Solve It

1. Record the highest expected temperature during storage, transport, installation, and use.
2. Test bonded samples under both temperature and load.
3. Evaluate heat creep, peel, shear, and edge-lifting performance.
4. Reduce peel stress through better joint design where possible.
5. Avoid approving an adhesive based only on softening point.
6. Test a more suitable heat-resistant formulation.
7. Consider PUR when strong, moisture-resistant, long-term bonding is required.
8. Consider a suitable polyolefin, APAO, or heat-resistant PSA when flexibility, substrate compatibility, or permanent tack is also needed.

For more demanding environments, review the high temperature resistant hot melt adhesive selection guide.

4. Brittle Bond Failure at Low Temperature

Some hot melt adhesives become harder and less flexible when exposed to cold conditions. The bond may pass a room-temperature test but crack during freezer storage, winter transport, impact, bending, or product movement.

Common Signs

• Fracture lines through the adhesive
• Clean, brittle separation
• Bond failure after dropping or flexing a cold product
• Packaging opens only after cold storage
• Foam or textile layers delaminate during winter handling
• Performance returns when tested at room temperature

How to Solve It

• Test complete bonded products at the lowest expected service temperature
• Include bending, impact, peel, or drop testing where relevant
• Allow test samples to remain at the target temperature before testing
• Evaluate a low-temperature or freezer-grade adhesive
• Use a more flexible formulation for foam, fabric, nonwoven, or moving joints
• Check whether excessive adhesive hardness or bond-line thickness increases stress

Increasing the application temperature will not correct an adhesive chemistry that becomes too brittle in service. The solution normally requires a formulation designed for the required low-temperature range.

5. Hot Melt Adhesive Stringing, Webbing, or Tailing

Stringing occurs when the adhesive does not separate cleanly from the nozzle, leaving thin strands between the applicator and substrate.

Common Causes

• Adhesive viscosity is too high
• Actual nozzle temperature is too low
• Substrate is cold
• Nozzle is too far from the surface
• Nozzle tip is dirty, worn, or partially blocked
• Valve or module closes too slowly
• Adhesive contains char or degraded material
• Pressure or timing is unstable
• Air movement pulls thin adhesive strands across the line
• Adhesive grade is too tacky for the application method

How to Solve It

1. Confirm the actual temperature at the nozzle.
2. Stay within the adhesive supplier’s recommended temperature range.
3. Reduce unnecessary distance between the applicator and substrate.
4. Inspect the nozzle, filter, valve seat, solenoid, and cutoff action.
5. Check the adhesive for char, contamination, or viscosity change.
6. Stabilize pressure and application timing.
7. Protect the application point from strong drafts where appropriate.
8. Allow cold substrates to reach suitable production temperature.
9. Test a cleaner-cutting adhesive with viscosity matched to the nozzle and line speed.

Do not assume that every stringing problem requires more heat. Excessive temperature may make the adhesive too fluid or tacky and can accelerate oxidation, odor, and charring.

6. Charring, Black Specks, Gels, or Severe Discoloration

Char forms when adhesive is exposed to excessive heat, oxygen, contamination, or prolonged thermal residence. It can accumulate on tank walls and later travel into filters, hoses, and nozzles.

Common Causes

• Temperature is above the recommended range
• Adhesive remains molten for too long
• Tank is repeatedly topped up without controlled cleaning
• Tank lid is left open
• Hot tank walls remain exposed to air
• Production stops while the system stays at full operating temperature
• Old and new adhesive grades are mixed
• Foreign material enters through open bags or dirty tools
• Temperature sensor or controller is inaccurate
• Adhesive has insufficient thermal stability for the process

How to Solve It

• Measure actual temperature with suitable calibrated equipment
• Compare all heating zones with the technical data sheet
• Use the equipment’s approved standby or setback mode during planned stops
• Keep the tank covered during normal operation
• Refill in a controlled way to reduce large temperature fluctuations
• Use clean, dedicated tools for each adhesive
• Follow the equipment and adhesive supplier’s approved cleaning procedure
• Replace blocked or damaged filters where necessary
• Avoid mixing unidentified, incompatible, or degraded adhesive
• Evaluate a more thermally stable formulation if the operating process cannot be changed

Fresh adhesive added on top of degraded adhesive does not restore the damaged material. If char repeatedly returns after cleaning, investigate temperature control, residence time, tank condition, contamination, and adhesive suitability.

7. Smoking, Fuming, or Abnormally Strong Odor

A small amount of normal process odor may be noticeable with some formulations, but visible smoke, sudden strong odor, or rapid discoloration can indicate overheating or degradation.

Common Causes

• Actual temperature is higher than the displayed temperature
• Thermostat, sensor, heater, or controller has failed
• Adhesive is held hot for an excessive time
• Contamination is reacting in the tank
• Wrong adhesive has been loaded
• Residual cleaning material remains in the system
• Adhesive has poor thermal stability
• PUR has been mishandled or contaminated with moisture

How to Solve It

1. Follow the site’s hot-material safety procedure.
2. Stop or isolate the affected equipment where required.
3. Verify the adhesive identity.
4. Measure actual tank, hose, and nozzle temperatures.
5. Check sensors, heaters, and controllers.
6. Inspect the adhesive for darkening, gel, skin, or contamination.
7. Review the SDS before handling, cleaning, or disposing of material.
8. Contact the adhesive or equipment supplier if the source is uncertain.

Do not solve smoke by simply increasing ventilation and continuing production. The cause of abnormal heat or material degradation must be identified.

For odor-sensitive packaging, hygiene, textile, furniture, and mattress applications, see the low odor hot melt adhesive guide.

8. Blocked Nozzle, Filter, or Hose and Uneven Adhesive Flow

Uneven flow can create missing beads, weak areas, overspray, incorrect coat weight, and inconsistent bond strength across the same product.

Common Causes

• Nozzle or filter contains char or contamination
• Adhesive viscosity is too high
• A hose or nozzle heating zone is too cold
• Pressure drops across multiple applicators
• Nozzle orifice is too small
• Pump is worn or operating inconsistently
• Hose is damaged or incorrectly installed
• Adhesive supply is interrupted
• Tank level changes are causing temperature instability
• Cured PUR particles have entered the system

How to Solve It

• Compare the flow from each nozzle
• Inspect and service filters according to the equipment schedule
• Confirm the actual temperature of every heating zone
• Check pressure under real production flow, not only while idle
• Inspect hoses for cold spots, damage, or incorrect routing
• Clean, repair, or replace blocked nozzles using the approved procedure
• Confirm nozzle size and adhesive viscosity compatibility
• Check pump output and adhesive supply
• Investigate char or gel before restarting the line

If only the most distant nozzle has low output, pressure loss or heat loss may be involved. If all nozzles show unstable flow, begin with the tank, pump, main filter, adhesive condition, and common temperature control.

9. Dripping, Drooling, or Adhesive After the Nozzle Closes

Dripping occurs when adhesive continues to leave the nozzle after the application signal has stopped.

Common Causes

• Nozzle needle or valve seat is worn
• Solenoid response is slow
• Air supply is unstable
• System pressure is too high
• Adhesive viscosity is too low
• Nozzle temperature is too high
• Residual pressure remains in the hose or module
• Nozzle contains contamination
• Incorrect timing makes normal flow appear as dripping

How to Solve It

1. Inspect and clean the nozzle and shutoff components.
2. Check valve, module, spring, seal, and solenoid condition.
3. Confirm stable air and hydraulic pressure.
4. Verify nozzle temperature and adhesive viscosity.
5. Review trigger timing against the real product position.
6. Reduce excessive pressure within the approved operating range.
7. Replace worn shutoff components.

Changing the adhesive may not solve a mechanically damaged valve. Confirm equipment condition before approving a different formulation.

10. Splashing, Spitting, Overspray, or Unstable Spray Pattern

Spray problems can reduce coverage, contaminate equipment, waste adhesive, and create weak areas in laminates, hygiene products, mattresses, packaging, and general assembly.

Common Causes

• Adhesive pressure is too high
• Adhesive viscosity is too low
• Temperature is too high
• Nozzle is too far from the substrate
• Nozzle type does not match viscosity or flow rate
• Air pressure is incorrect
• Adhesive contains moisture, air, contamination, or degraded particles
• Substrate speed and application timing do not match
• Spray head is partially blocked
• Coat weight is outside the stable operating range

How to Solve It

• Check the nozzle and spray head for partial blockage
• Verify adhesive and air pressure
• Confirm temperature and viscosity compatibility
• Reduce excessive applicator distance
• Match nozzle type, orifice, pattern, and flow rate to the process
• Inspect adhesive and packaging for moisture exposure
• Stabilize line speed and triggering
• Run a controlled pattern test before full production
• Measure actual coat weight across the full bonding width

For textile or film applications, pattern appearance alone is not enough. Bond strength, flexibility, coverage, strike-through, hand feel, and aging performance must also be checked.

11. Excessive Squeeze-Out, Penetration, or Bleed-Through

Too much penetration can leave an insufficient adhesive film at the interface, while excessive squeeze-out creates contamination, poor appearance, wasted material, or rigid edges.

Common Causes

• Coating weight is too high
• Adhesive viscosity is too low
• Application temperature is too high
• Compression pressure is excessive
• Substrate is highly porous
• Adhesive remains molten too long
• Bond gap is too small or inconsistent
• Adhesive grade is not suitable for thin fabric, foam, paper, or nonwoven

How to Solve It

• Measure and reduce excessive coat weight
• Confirm the recommended application temperature
• Reduce unnecessary compression without losing surface contact
• Use a higher-viscosity or faster-setting grade where appropriate
• Adjust the application pattern to improve distribution
• Test a formulation designed for porous or lightweight substrates
• Check whether the adhesive line remains thick enough after penetration
• Evaluate both appearance and final bond performance

The objective is not simply to use less adhesive. The goal is to create a continuous and effective bond line without excessive penetration or squeeze-out.

12. PUR Hot Melt Adhesive Gelling, Foaming, or Premature Curing

PUR hot melt adhesive requires a different troubleshooting approach from conventional thermoplastic hot melts.

After application, PUR reacts with moisture and develops a crosslinked final bond. However, moisture exposure before application can cause premature reaction inside the package, melter, hose, or nozzle.

Common PUR Problems

• Skin or hardened material in an opened package
• Gel or cured particles that do not remelt normally
• Blocked filters or nozzles
• Foaming, bubbles, or spitting
• Increasing viscosity during processing
• Weak initial handling strength
• Incomplete final cure
• Bond failure after moisture or heat exposure
• Shortened usable time after opening

Possible Causes

• Damaged moisture-barrier packaging
• Package left open in humid air
• Condensation on cold material or feeding equipment
• Incorrect melter or dispensing system
• Moisture-contaminated tools
• Excessive thermal residence
• Inadequate purge or shutdown procedure
• Insufficient curing time before testing
• Low available moisture in the bonding system
• Wrong PUR grade for the substrates or process

How to Solve It

• Inspect package seals before use
• Allow sealed cold packages to reach suitable room conditions before opening
• Minimize unnecessary exposure to humid air
• Use clean and dry feeding tools
• Follow the supplier’s approved startup, purge, and shutdown procedure
• Do not mix cured particles back into fresh PUR
• Confirm that equipment is designed and maintained for reactive hot melt
• Test initial strength and final strength separately
• Allow the specified curing period before final approval
• Review temperature, moisture, coating weight, and substrate compatibility with the supplier

For a broader comparison of reactive and thermoplastic systems, read PUR vs EVA hot melt adhesive.

Troubleshooting Differences Between Hot Melt Adhesive Chemistries

Different adhesive chemistries should not be evaluated by exactly the same criteria.

If the current chemistry repeatedly fails even after the process is controlled, compare the main types of hot melt adhesives instead of forcing one formula to work in every application.

A Practical Factory Troubleshooting Procedure

Random adjustments make it difficult to identify the real cause. Use a controlled procedure.

Step 1: Define the Failure

Record:

• What failed
• When it failed
• Where it failed
• Whether the issue is continuous or intermittent
• Whether it affects every product or only part of the line
• Whether the problem began after a material, equipment, or shift change

Step 2: Preserve Evidence

Keep:

• Failed samples
• Acceptable comparison samples
• Adhesive lot number
• Substrate lot number
• Photos of the glue pattern
• Temperature and pressure records
• Production time and machine identification

Step 3: Check the Failure Interface

Determine whether the adhesive is:

• Mainly on one substrate
• Present on both substrates
• Split within the adhesive layer
• Accompanied by substrate tear
• Brittle, oily, foamed, darkened, or contaminated

Step 4: Verify Actual Conditions

Check actual rather than assumed values:

• Tank temperature
• Hose temperature
• Nozzle temperature
• Substrate temperature
• Ambient temperature
• Line speed
• Application pressure
• Coat weight
• Open time
• Compression pressure and time

Step 5: Change One Variable at a Time

If temperature, pressure, coat weight, and line speed are changed together, the result will not show which adjustment solved the problem.

Make one controlled change, record the result, and then decide whether another change is necessary.

Step 6: Reproduce the Result

A successful bond on one sample is not enough. Repeat the test across normal production speed, startup, steady operation, material changes, shift changes, and planned environmental conditions.

Step 7: Validate Finished-Product Performance

Depending on the application, validation may include:

• Peel testing
• Shear testing
• Fiber tear
• Heat aging
• Cold storage
• Temperature cycling
• Humidity exposure
• Water resistance
• Drop or impact testing
• Flexing or fatigue
• Chemical exposure
• Finished-product storage

Before bulk purchase, use real materials and production conditions as described in this hot melt adhesive sample testing guide.

Hot Melt Adhesive Troubleshooting Record

Factories can use the following information for every investigation:

A complete record allows the adhesive supplier to provide a specific recommendation instead of guessing from a general description such as “the glue is not strong.”

How to Prevent Hot Melt Adhesive Problems

Preventive control is more effective than repeated emergency adjustments.

Follow the Current Technical Data Sheet

Make sure the product code on the package matches the TDS used by production. Do not rely on an old data sheet from another grade.

Control Storage and Lot Rotation

Heat, moisture, damaged packaging, contamination, and excessive storage time can change adhesive performance. Use controlled storage and appropriate lot rotation as described in this hot melt adhesive storage and shelf-life guide.

Keep the Tank Covered

A closed tank reduces dust, fibers, foreign material, and unnecessary oxygen exposure.

Use Standby Mode During Planned Stops

Do not leave adhesive at full processing temperature during long idle periods unless the supplier and equipment instructions specifically require it.

Keep Adhesive Grades Separated

Similar-looking pellets, blocks, or pillows may have completely different viscosity, open time, set speed, substrate compatibility, and heat resistance.

Calibrate Temperature Controls

The displayed temperature is not always the true adhesive temperature. Establish a suitable calibration and verification schedule.

Maintain Filters, Hoses, and Nozzles

Do not wait for complete blockage. Preventive inspection can identify char, wear, cold spots, leaks, and unstable shutoff before the line fails.

Test Every Important Material Change

A new paper coating, recycled-board content, plastic film, foam density, fabric treatment, release agent, or surface finish can change adhesion even when the adhesive remains the same.

When Should You Change the Adhesive Instead of the Process?

Changing production settings cannot solve every problem.

Consider testing a different adhesive when:

• The current adhesive does not bond the substrate within its approved processing range
• Required open time or set time cannot match the line
• Heat resistance is below the service requirement
• The bond becomes brittle in cold conditions
• PSA loses shear strength or transfers under heat
• The application requires more flexibility
• The adhesive repeatedly chars under unavoidable operating conditions
• Odor remains unacceptable under correct processing conditions
• PUR curing behavior does not fit the production cycle
• Required coating weight makes the process uneconomical
• Final aging, moisture, chemical, or durability tests repeatedly fail

The correct adhesive is not necessarily the product with the highest strength or highest application temperature. It is the formulation that provides stable processing and sufficient finished-product performance at a practical total cost.

What Information Should You Send to an Adhesive Supplier?

For faster troubleshooting, provide:

• Application and finished product
• Exact substrates and surface treatments
• Current adhesive product and chemistry
• Tank, hose, and nozzle temperatures
• Application method
• Nozzle or coating configuration
• Coat weight or glue amount
• Line speed
• Open time and compression time
• Ambient and substrate temperature
• Failure photos
• Failure-surface description
• Adhesive and substrate lot numbers
• Storage and opening history
• Required heat, cold, moisture, peel, shear, or aging performance
• Recent changes to materials, equipment, settings, or suppliers

KAISUN supplies industrial hot melt adhesive solutions for packaging, woodworking, furniture, textiles, mattresses, hygiene products, automotive interiors, labels, tapes, electronics, filters, and general assembly.

Frequently Asked Questions

Why Is My Hot Melt Adhesive Not Sticking?

The most common causes are insufficient wetting, low actual temperature, a cold or contaminated substrate, bonding outside the open-time window, insufficient compression, low coating weight, blocked application equipment, or the wrong adhesive chemistry.

Examine both failed surfaces before changing the settings.

Does Increasing Temperature Improve Hot Melt Adhesion?

Sometimes, but not always.

A controlled increase within the approved range may reduce viscosity and improve wetting. However, excessive temperature can cause slow setting, squeeze-out, oxidation, odor, smoke, viscosity changes, and char.

Always confirm the actual temperature and follow the grade-specific technical data sheet.

What Causes Hot Melt Adhesive Stringing?

Common causes include excessive viscosity, low nozzle temperature, cold substrates, excessive gun distance, poor nozzle shutoff, unstable pressure, incorrect timing, contamination, and degraded adhesive.

Stringing should be investigated as both an adhesive and equipment problem.

How Can Hot Melt Charring Be Prevented?

Use the correct temperature, reduce unnecessary thermal residence, keep the tank covered, use approved standby settings, prevent contamination, maintain a controlled refill procedure, and clean the equipment according to supplier instructions.

Can Different Hot Melt Adhesives Be Mixed?

Mixing should be avoided unless the adhesive supplier has confirmed compatibility.

Different products may have different polymers, tackifiers, additives, viscosities, and thermal behavior. Mixing can cause gelling, separation, unstable viscosity, poor bonding, char, or equipment blockage.

Why Does the Bond Work in the Morning but Fail Later?

Possible reasons include increasing tank residence time, adhesive degradation, changing ambient or substrate temperature, pressure drift, material-lot variation, contamination, nozzle buildup, or differences between startup and steady production.

Compare recorded conditions from the acceptable and failed periods.

How Do I Know Whether the Problem Is the Adhesive or the Machine?

Run a controlled comparison using:

• The same adhesive on verified equipment
• A retained approved adhesive lot
• Clean nozzles and filters
• Measured temperature and pressure
• Identical substrates and test conditions

If the failure follows the machine position, equipment is more likely involved. If it follows the adhesive lot or substrate lot across positions, the material should be investigated.

How Is PUR Hot Melt Troubleshooting Different?

PUR is moisture-reactive. Storage, package integrity, exposure time, condensation, dry feeding tools, equipment design, initial set, and final curing time must all be checked. Cured PUR particles cannot simply be remelted like normal thermoplastic adhesive.

Final Thoughts

Most hot melt adhesive problems can be traced to one or more of five areas:

• Incorrect adhesive selection
• Poor substrate condition
• Incorrect temperature or timing
• Insufficient application or compression control
• Equipment contamination, wear, or instability

The most effective troubleshooting method is to examine the failure surface, record actual production conditions, change one variable at a time, and validate the result under real service conditions.

Do not use temperature as the universal solution. A weak bond may require better compression, a cleaner substrate, a different open time, a more suitable coating weight, repaired equipment, or a completely different adhesive chemistry.

If you are experiencing stringing, charring, nozzle blockage, delamination, poor wetting, heat creep, cold failure, odor, or PUR gelling, contact KAISUN with your substrates, equipment settings, production speed, adhesive lot, and failure photos. A controlled application review can identify whether the correct solution is a process adjustment, equipment repair, or a better-matched hot melt adhesive.