A hot melt PSA can produce an impressive hand pull and still fail after coating, die cutting, storage, or use. The reason is straightforward: “sticky” is not one property. A pressure-sensitive bond must make contact quickly, resist peeling, and carry a sustained load without creeping.
That is why a useful hot melt PSA testing plan needs three separate measurements:
- a PSA peel test for resistance to removal at a defined angle and speed;
- a PSA loop tack test for immediate grab after brief contact;
- a PSA shear holding power test for resistance to sliding or cohesive creep under constant load.
These results only become comparable when the coated construction, substrate, coat weight, application pressure, dwell time, conditioning, test speed, temperature, and failure mode are also reported. A supplier’s three headline numbers are not enough.
Quick answer: Approve a hot melt PSA as a coated, finished construction. Test a current approved control and each candidate under the same conditions. Use standard stainless steel for repeatable quality control, actual production surfaces for application approval, and aged or temperature-conditioned samples for service validation. Set the pass limits before reviewing the results.
What peel, tack and shear each tell the buyer
The three tests answer different questions. One result cannot stand in for the other two.
| Test | Question it answers | Common result format | What it does not prove |
|---|---|---|---|
| Peel adhesion | How much force is required to remove the pressure-sensitive article at a defined angle and speed? | Force per specimen width, plus failure mode | Instant pickup or resistance to long-term sliding |
| Loop tack | How strongly does the exposed adhesive grab after short, low-pressure contact? | Maximum separation force, plus failure mode | Peel after a long dwell or holding power under sustained load |
| Shear holding power | How long can the bond resist a constant load applied parallel to the bonded surface? | Time to failure, displacement, or pass at a defined cutoff | Easy application, peel behavior, or clean removal |
The balance depends on the product. A permanent logistics label, removable protective film, foam tape, self-seal mailer, and hygiene construction should not share one generic approval target.
If the adhesive category is still unclear, start with the difference between a PSA, a conventional hot melt, and a hot melt pressure-sensitive adhesive. For a grade recommendation, the PSA hot melt adhesive product page describes the main coating methods and application directions.
Approve the coated construction, not the adhesive block alone
Peel, tack and shear are properties of the tested pressure-sensitive article. The result can change when any part of that article changes:
- HMPSA batch and thermal history;
- adhesive coat weight and coat uniformity;
- film, paper, nonwoven, foil, foam, or transfer-tape carrier;
- backing stiffness, thickness, elongation, and surface treatment;
- release liner and release level;
- coating and lamination conditions;
- test substrate, surface finish, cleanliness, and surface energy;
- time between coating, lamination, conversion, and testing.
A raw adhesive supplier may prepare a standard PET-backed specimen for early screening. That specimen is useful for comparing formulation directions. It does not automatically predict the result on the buyer’s paper face stock, flexible PE film, foam carrier, nonwoven, or finished tape construction.
The buyer should therefore use two connected test levels:
| Test level | Main purpose | Recommended construction |
|---|---|---|
| Standard laboratory comparison | Formulation screening and routine lot consistency | Controlled backing, coat weight, preparation method, and standard panel |
| Application qualification | Approval for the actual product and use surface | Production backing or face stock, actual coat weight, real liner, real target substrate, and representative converting history |
Standard panels help isolate variation. Actual substrates expose application risk. A sound approval uses both when the end-use surface differs materially from the standard panel.
PSA peel test: measure removal under defined conditions
ASTM D3330/D3330M-04(2025) covers several peel configurations for pressure-sensitive tape, including 180-degree and 90-degree procedures for selected constructions. The procedure must be named in the report. A value obtained at 90 degrees cannot be ranked directly against a value obtained at 180 degrees.
Peel results also depend on backing stiffness and adhesive rheology. ASTM’s own significance statement cautions that the method supports quality assurance for a defined tape and acceptance requirement, but may not provide a direct functional design value. That distinction matters during supplier comparison. Two suppliers can use the same standard name yet test different coated constructions.
Conditions to record for every peel result
A usable PSA peel test report should include:
- standard, edition, and selected procedure;
- adhesive grade, batch, and sample preparation date;
- backing or face-stock material, thickness, and direction;
- adhesive coat weight or dry thickness and the measurement method;
- test substrate, surface finish, cleaning method, and lot where relevant;
- specimen width and bonded length;
- application roller, number of passes, pressure, or other application method;
- dwell time before testing;
- conditioning time, temperature, and relative humidity;
- peel angle and crosshead speed;
- individual results, average, and variation;
- failure mode and visible residue;
- any deviation from the selected method.
Do not reduce this list to “180-degree peel on steel.” That phrase leaves out enough variables to make a supplier comparison unreliable.
Standard steel and the real application surface serve different jobs
| Surface | What it is good for | Main limitation |
|---|---|---|
| Standard stainless-steel panel | Repeatable formulation or lot comparison | May not represent coated board, PE, PP, textured plastic, glass treatment, painted metal, or a contaminated field surface |
| Buyer-supplied production substrate | Application fit and failure investigation | More variable, so the material grade, treatment, supplier, lot, and cleaning condition must be controlled |
| Finished customer part | Final-use confirmation | Geometry and process variation can make laboratory comparison harder |
For a label applied to HDPE, a strong result on steel is a screening result. Approval still requires the actual HDPE grade, molding condition, surface texture, and expected cleanliness. The same rule applies to coated paper, recycled board, powder-coated metal, and treated film.
Dwell time and peel speed belong with the number
Many PSAs continue to wet the surface after application. Peel may rise between an immediate test and a test after a longer dwell. Temperature, pressure, adhesive softness, coat weight, and substrate surface all affect that development.
Peel speed changes the deformation rate of the adhesive and backing. A supplier result at one speed should not be compared with a buyer result at another. If the product must be removed slowly by hand but converted rapidly on a machine, the approval plan may need more than one relevant rate.
Record how the specimen failed
| Observation | Reported failure direction | What to investigate |
|---|---|---|
| Adhesive remains mainly on the pressure-sensitive article | Adhesive or interfacial failure at the test surface | Surface energy, contamination, treatment, wet-out, pressure, dwell, and temperature |
| Adhesive splits and remains on both sides | Cohesive failure | Internal strength, coat weight, temperature, aging, oil migration, and load rate |
| Adhesive transfers substantially to the test surface | Transfer or residue | Cohesion, service temperature, dwell, aging, and removability target |
| Paper, foam, coating, or backing tears | Substrate or backing failure | The measured force may be limited by the construction rather than the adhesive interface |
| Peel trace jumps or chatters | Unstable peel | Backing stiffness, panel texture, test speed, alignment, coating uniformity, or stick-slip behavior |
A high peel number with heavy residue may be unacceptable for a removable label. A lower, stable peel with clean removal may be the correct result. Pass criteria should include both force and failure mode.
PSA loop tack test: measure immediate grab
ASTM D6195-22 provides two loop tack methods, one using a tensile tester and one using a dedicated loop tack tester. It measures the force required to separate a looped pressure-sensitive specimen shortly after contact. The method is useful for quality control and research, but backing stiffness affects the value. A stiffer backing can produce a higher result even when the adhesive formula is unchanged.
The test is relevant when the product must make fast contact with limited pressure, such as a label on a moving line or a self-seal strip. It should still be paired with an application test. A laboratory loop contacting a clean, flat panel does not reproduce a curved bottle, dusty carton, cold container, textured pouch, or short pressure zone.
What a loop tack report must disclose
Record:
- ASTM D6195 edition and Method A or Method B;
- tensile tester or loop tack tester model and fixture;
- specimen length, width, and loop preparation;
- backing material, thickness, stiffness direction, and splice method where relevant;
- adhesive coat weight or thickness;
- test panel material, finish, cleaning, and preparation;
- contact area and contact procedure;
- approach and withdrawal speed;
- conditioning temperature and relative humidity;
- maximum force, individual results, variation, and failure mode.
Comparing loop tack values from different backings is risky. A paper label stock and a thin PET film create different loop mechanics. If the buyer needs to compare adhesive formulas, coat each candidate on the same controlled backing at the same measured coat weight.
Higher loop tack is not automatically better
Very aggressive initial tack can create handling problems:
- poor repositionability during label placement;
- premature contact before alignment;
- blocking or edge pickup during conversion;
- difficult release from the liner;
- damage to a delicate surface during removal;
- contamination pickup on exposed adhesive.
The approval target should reflect the available application pressure, substrate geometry, line speed, and permitted repositioning. The strongest loop tack result may be the wrong grade for the finished product.
PSA shear holding power: measure creep under sustained load
ASTM D3654/D3654M-06(2024) covers procedures for measuring the ability of pressure-sensitive tapes and labels to remain adhered under a constant load applied parallel to the bonded surface. Its procedures include standard steel, specified fiberboards, buyer-seller agreed surfaces, and a high-temperature option for selected comparisons.
ASTM D6463/D6463M-06(2020) is another sustained-shear time-to-failure method for pressure-sensitive articles. Its stated uses include evaluating cohesive behavior connected with edge ooze, converting quality, tape telescoping, package sealing, and vertical holding power.
Select one controlled method that fits the construction and purchasing purpose. Do not merge conditions from several standards and report the result under only one method name.
Conditions to record for shear holding power
The report should state:
- standard, edition, and procedure;
- test surface and its preparation;
- specimen backing, dimensions, and bonded area;
- coat weight or adhesive thickness;
- application method and dwell before loading;
- applied mass or stress;
- panel orientation and load direction;
- test temperature and relative humidity;
- maximum test duration or timer cutoff;
- time to failure or measured displacement;
- failure mode and position;
- whether the result is an exact failure time or a right-censored pass.
If a specimen is removed after 10,000 minutes without failure, the report should state “>10,000 minutes under the defined test conditions” or “pass at 10,000 minutes.” It should not present 10,000 minutes as the exact failure time.
Room-temperature holding power does not prove heat resistance
A hot melt PSA may carry a load at room temperature and creep rapidly when warm. The approval matrix should include the highest relevant service condition, using the selected standard or an agreed application method. Record the actual bond-line or chamber condition and the time allowed for temperature equilibrium.
Cold exposure needs its own check. A colder PSA may become firmer and show strong static shear while losing tack or peel on the application surface. The low-temperature hot melt adhesive guide explains why cold application and cold service are separate questions. For the warm end of the service route, use the high-temperature resistant hot melt adhesive guide to define heat aging, creep, and temperature cycling.
Why the three results may point in different directions
PSAs are viscoelastic. They must deform enough to wet a surface, then retain enough internal strength to resist peel and creep. A formulation, coat-weight, or process change can shift that balance, but the result should be diagnosed from controlled tests rather than assumed from one number.
| Result pattern | Possible direction to investigate | Do not conclude yet |
|---|---|---|
| High loop tack, acceptable peel, weak shear | Adhesive may be too soft at the test temperature; coat weight, oil migration, or thermal history may also contribute | The formula alone is defective |
| Low loop tack, peel rises after dwell, strong shear | Slower wet-out, firm adhesive, low application pressure, stiff backing, or cold substrate | The adhesive cannot work in production |
| Good steel peel, weak peel on the actual substrate | Surface-energy mismatch, contamination, treatment variation, texture, or inadequate pressure | More coat weight will solve it |
| Strong shear, weak tack and peel on both surfaces | Insufficient wet-out, excessive firmness, low coat weight, or preparation error | The highest shear grade is the best grade |
| High peel with cohesive split or residue | Cohesion may be below the removal requirement, especially after heat or aging | High peel means a clean, durable bond |
| Large variation within one test set | Coat-weight variation, panel preparation, backing direction, operator technique, temperature, or specimen defects | The average alone describes the product |
These patterns are investigation prompts. Confirm the cause by changing one variable at a time and repeating the test against the approved control.
Build a hot melt PSA testing matrix before samples arrive
The test plan should be written before the supplier sends candidate grades. This prevents the team from changing the pass rules after seeing a preferred result.
| Test stage | Construction and surface | Condition | Main decision |
|---|---|---|---|
| Laboratory screen | Same controlled backing, coat weight, and standard panel | Standard conditioning | Remove clearly unsuitable candidates |
| Actual-surface screen | Production backing and real target substrate | Standard conditioning | Confirm substrate fit |
| Process-window trial | Production-made samples at nominal and expected limit settings | After defined conversion dwell | Check coat uniformity, wet-out, liner behavior, and repeatability |
| Environmental qualification | Actual construction | Defined heat, cold, humidity, or cycling | Check retention and failure mode after service exposure |
| Aged-product check | Packaged finished construction | Agreed accelerated or real-time aging points | Check peel drift, tack loss, shear creep, residue, blocking, and liner release |
| Incoming quality control | Approved standard construction or agreed routine specimen | Controlled laboratory condition | Compare commercial lots with the approved baseline |
Coat weight must be measured, not copied from the coater setting. The hot melt adhesive consumption and coating-weight guide explains how to calculate g/m² and verify actual deposited mass.
A copy-ready approval scorecard
| Test item | Method and condition | Control result | Candidate result | Acceptance rule | Failure mode | Decision |
|---|---|---|---|---|---|---|
| Initial peel | [method, angle, speed, dwell, surface] | [min/max/window] | ||||
| Peel after dwell | [dwell and condition] | [min/max/window] | ||||
| Loop tack | [D6195 method, backing, surface, speed] | [minimum or target window] | ||||
| Room-temperature shear | [method, area, load, cutoff] | [minimum time or displacement] | ||||
| High-temperature shear | [temperature, load, cutoff] | [minimum time or displacement] | ||||
| Peel after environmental exposure | [cycle and recovery condition] | [min/max/window] | ||||
| Clean removal | [surface, dwell, aging] | [residue and damage limit] | ||||
| Liner release | [method, speed, aged condition] | [target window] | ||||
| Production trial | [line, speed, coat weight, temperatures] | [process and finished-product criteria] |
Use the current approved material as the control whenever possible. A candidate does not need to copy every control number. It needs to remain inside the application’s approved performance window without introducing a new failure mode.
An eight-step hot melt PSA approval workflow
Step 1: define the use case
Record the complete construction, target surface, application pressure, dwell before loading, service temperature, load direction, removal requirement, expected life, and conversion process. State whether the bond is permanent, removable, repositionable, or resealable.
Step 2: obtain traceable candidate samples
Each sample should identify the manufacturer, grade, batch or sample code, preparation date, recommended application range, storage condition, and contact person. Keep enough material for confirmation work and a retained reference.
Step 3: prepare comparable coated specimens
Use the same backing, measured coat weight, liner, coating temperature, line speed, and lamination pressure for the control and candidates. If a candidate needs a different setting, record that setting and prepare a second controlled comparison. Do not hide a process change inside an adhesive comparison.
Step 4: run peel, tack and shear under controlled conditions
Follow the current controlled copy of each selected standard. Use the method’s required specimen count and conditioning. Add replicates when the data vary enough to affect the decision. Do not approve a grade from one visually good strip.
Step 5: test the actual target surface
Repeat the relevant tests on production surfaces from representative lots. Include the lowest surface-energy material, highest recycled content, roughest texture, tightest curvature, or other known limit that the finished product may encounter.
Step 6: condition and age the finished construction
Test at defined time points and after the relevant temperature, humidity, or cycle exposure. For removable products, inspect residue and surface damage after aging. For permanent products, inspect edge lift, adhesive transfer, creep, and substrate failure.
Step 7: run a production trial
Confirm melt delivery, coating uniformity, web handling, liner release, slitting, die cutting, edge cleanliness, blocking, odor, thermal stability, and finished-product performance. A laboratory pass does not prove that the adhesive will coat cleanly for a full shift.
The broader hot melt adhesive sample testing guide can be used to add equipment settings, trial duration, retained samples, and production observations.
Step 8: freeze the specification and change-control rules
Approve the exact grade, construction, test methods, conditions, limits, failure modes, packaging, shelf life, and document revision. State which properties appear on every batch certificate and what triggers revalidation. Typical TDS values should not become contractual limits without written agreement. The TDS, SDS and COA buyer’s guide explains how to separate typical data, specifications, and batch results.
Test the molten adhesive and the finished PSA separately
Peel, tack and shear qualify the coated pressure-sensitive construction. The molten adhesive also needs process controls.
Common raw-material or in-process checks include:
- apparent viscosity at a defined temperature, spindle, and speed;
- appearance, color, contamination, and gel content where applicable;
- softening or thermal behavior under an agreed method;
- heat stability during the expected residence time;
- coating response at the required line speed;
- package condition, blocking, and traceability.
Viscosity affects pumping and coat uniformity, but matching viscosity does not prove matching adhesion. Use the ASTM D3236 hot melt viscosity buyer guide to specify the temperature, instrument, spindle, speed, torque, sample identity, and result status.
Application-specific approval priorities
| Application | Peel priority | Tack priority | Shear priority | Other checks |
|---|---|---|---|---|
| Permanent label | Minimum adhesion after defined dwell and aging | Pickup at the available application pressure | Edge lift and creep on vertical or curved surfaces | Die cutting, liner release, cold application, moisture, and label stock stiffness |
| Removable label or protective film | Controlled minimum and maximum peel | Enough grab for placement without premature lock-in | No edge movement during service | Residue, staining, ghosting, surface damage, and peel drift after aging |
| Industrial tape | Peel on both standard and actual surfaces | Assembly pickup where relevant | Holding power under the real load and temperature | Backing stretch, foam split, liner release, slitting, and telescoping |
| Self-seal bag or mailer | Seal opening resistance after closure dwell | Fast closure under the available nip pressure | Resistance to seal creep during storage and transport | Film treatment, contamination, tamper behavior, temperature, and seal geometry |
| Hygiene or nonwoven construction | Peel or bond test matched to the layer | Pickup on porous or low-mass webs | Creep under body heat and use load | Spray pattern, strike-through, odor, softness, and material safety requirements |
No standard steel value can replace the finished-product check in the final column.
Red flags in a supplier PSA test report
Pause the comparison if the report:
- gives one generic “adhesion strength” value;
- names ASTM but omits the edition, method, or procedure;
- reports peel without angle, speed, dwell, width, or surface;
- reports loop tack without backing and method;
- reports shear without bonded area, load, temperature, and timer cutoff;
- omits coat weight or coated construction;
- compares results produced on different backings or surfaces;
- lists only averages and hides individual results or variation;
- does not record cohesive split, residue, substrate tear, or other failure mode;
- uses a typical TDS value as though it were the tested batch result;
- provides a pass statement without a written acceptance limit;
- presents a no-failure timer cutoff as an exact failure time;
- cannot connect the specimen to a grade, batch, and preparation record.
A complete hot melt adhesive RFQ checklist should request the substrate, coating method, coat weight, service condition, target test methods, acceptance windows, and sample quantity before quotations are compared.
Frequently asked questions
What is a good peel value for hot melt PSA?
There is no universal good value. The acceptable range depends on the construction, peel angle, speed, dwell, test surface, temperature, and whether the product is permanent or removable. Set the range from the finished product’s job, current control, customer specification, and validated trial data.
Can a PSA peel test replace a loop tack test?
No. Peel measures resistance to removal under a defined geometry after a defined dwell. Loop tack measures rapid grab after brief contact. A PSA can perform well in one and poorly in the other.
Why does peel increase after dwell?
The adhesive may continue to wet the surface and develop more intimate contact. The amount of change depends on the PSA, pressure, coat weight, backing, surface, temperature, and time.
Why can a label have high tack but lift later?
Initial contact may be strong while shear resistance is too low for the label stiffness, curvature, heat, or sustained stress. Contamination, poor surface treatment, insufficient application pressure, and dimensional movement can also cause edge lift.
Is loop tack the same as rolling-ball tack?
No. They use different mechanics and report different responses. Do not convert one into the other or compare the numbers directly. Specify one method for qualification and keep it consistent for routine control.
How should a removable PSA be approved?
Use a peel window with both minimum and maximum limits. Add residue, staining, substrate damage, edge lift, and aging criteria. Test removal at the expected rate and temperature on every important surface.
How many specimens should be tested?
Use the specimen count required by the selected standard and the buyer’s sampling plan. Add specimens if lot variation, multiple substrate lots, or inconsistent failure modes could change the decision. One strip is a demonstration, not an approval.
Is the supplier’s TDS enough for approval?
No. A TDS can identify typical properties and recommended processing. Approval requires traceable samples, agreed methods, controlled test conditions, actual-substrate results, a production trial, and written acceptance criteria.
Approve the test conditions before approving the grade
The most useful hot melt PSA testing report does more than list three numbers. It identifies the exact coated construction, preparation method, standard and procedure, test surface, coat weight, dwell, speed, load, environment, individual results, variation, and failure mode.
Send the supplier your production backing, release liner, target surfaces, coating method, nominal and limit coat weights, application pressure, line speed, service temperature, aging profile, and current control sample. Ask for a proposed PSA peel test, PSA loop tack test, and PSA shear holding power matrix before coating begins. Once the trial passes, place those methods and acceptance windows in the approved specification used for incoming inspection and repeat orders.
