What are the methods for testing the peel strength of hot melt adhesive particles? Explain the operation steps and judgment criteria in one go

There are three commonly used testing methods for the peel strength of hot melt adhesive particles:180 ° peel off(Soft substrate to soft substrate, such as laminated paper, non-woven fabric)90 ° peeling(Soft substrate to hard substrate, such as cardboard bonding) andT-shaped peeling(Used when the flexibility of the substrate on both sides is similar). The most commonly used methods in the book binding and packaging sealing industry are 180 ° and T-shaped. During testing, the adhesive layer is made into a standard specimen with a width of 25mm, which is uniformly stretched at a speed of 300mm/min on a tensile testing machine. The average force value of the stable section is taken, and the unit is recorded as N/25mm or kN/m.

How to prepare standard samples without distortion

Many printing factories produce fluctuating data, and the problem lies not in the machines but in the sample preparation. There are four key points for sample preparation:

• Substrate homologyReal paper or corrugated paper used on the production line must be used, and white cardboard cannot be used instead of copperplate paper. Film coated paper must be sampled together with the film.
• Consistent thickness of adhesive layerUse a scraper or coating wheel to control the thickness between 0.15-0.3mm. Uneven thickness can cause jagged edges on the curve.
• Temperature and pressure are controllableThe three fixed parameters of melt adhesive temperature, pressing pressure, and pressing time should be recorded on the test sheet, otherwise there will be no comparability between different batches.
• State adjustmentAfter bonding, the data measured immediately after hot bonding in an environment of 23 ℃ and 50% RH for 24 hours has limited reference value.

Reference judgment values for different application scenarios

It should be noted that paper bonding is more importantFiber failure rateInstead of absolute values. If the paper surface is torn off and the fibers are transferred to the adhesive layer in large areas after peeling, it indicates that the cohesion of the adhesive has exceeded that of the paper itself, and this is a qualified bonding; On the contrary, even if the value is high but the interface is smooth and peeled off, it still belongs to unqualified.

How to make quick judgments without a tensile machine

Small and medium-sized graphic and text fast printing shops and small packaging factories may not necessarily be equipped with tensile testing machines. There are two simple alternative methods: one isHand tearing fiber destruction methodAfter cooling for 24 hours, tear it open at a constant speed by hand and observe the fiber transfer area; SecondHanging Load MethodFix one end of the 25mm wide sample and hang a 500g weight on the other end for 30 minutes. If there is no creep slip, it is considered qualified. Although these two methods cannot produce reports, they are sufficient for comparing the stability of incoming batches.

Frequently Asked Questions

Q: Is higher peel strength better?
Answer: No. The binding of books and magazines requires a balance between firmness and flexibility. If the peel strength is too high, it often accompanies a hard adhesive layer, which can easily lead to spine cracking when flipping pages. The selection of adhesive should be comprehensively judged based on softening point, opening time, and flexibility.

Q: Is it normal for the same batch of rubber particles to have lower values measured in winter than in summer?
Answer: Normal. The ambient temperature can affect the modulus of the adhesive layer, and at low temperatures, the adhesive layer becomes harder and the peeling curve becomes steeper. So the standard requires testing under constant temperature and humidity conditions, and daily comparisons should also indicate the ambient temperature.

Q: Can the supplier provide a peel strength report?
Answer: Sure. Guangzhou Sunlife Trading provides batch testing data for Sunlife’s hot melt adhesive book binding and packaging box sealing series, and also supports the issuance of bonding test conclusions based on actual paper samples from customers, avoiding the gap between “laboratory qualified and machine unqualified”.