How to distinguish hot melt adhesive particles mixed with recycled materials? The experience of a cardboard box factory identifying low-priced materials in three steps

Direct answer: DistinguishHot melt adhesive pelletsThe most practical steps to determine whether the recycled material has been added are three: checking the appearance (whether the particle color is uniform, whether there are black spots or impurities), smelling the heating odor (the irritating burnt smell of the recycled material is more obvious), and comparing the melt (the viscosity fluctuates greatly at the same temperature, and there is more residue at the bottom of the pot). Combined with a third-party testing report, it can basically be qualitative.

The experience of a packaging factory

A medium-sized cardboard box factory in Dongguan, in order to reduce costs last year, obtained sealing rubber particles from a new supplier that were more than 2000 yuan per ton lower than the regular quotation. I used it well in the first two weeks, but started to have problems in the third week: the nozzle clogged twice a day, the black residue at the bottom of the pot formed hard lumps, and the sealed boxes started to curl after being piled up in the warehouse for a few days in the summer. After calculation, the losses from downtime cleaning and rework are several times the price difference saved.

Three-step identification method

Why do low-priced materials always reveal their filling

• After repeated high-temperature processing, the molecular chains of the recycled material have broken, and the initial adhesion may still be good, but the adhesion and heat resistance have significantly decreased.
• The sources of the returned materials are mixed, and the composition is inconsistent between batches. The most obvious manifestation is that “this bag is good to use, but the next bag is not good to use”.
• There are many impurities, which increase the burden on the nozzle and filter, and the frequency of blockage increases.
• Antioxidants are consumed, and prolonged insulation makes them more prone to carbonization and coking.

The Four Lines of Defense in the Procurement Process

• Sample retention systemEach batch of goods should be sealed with 500 grams for comparison in case of any issues.
• Batch consistency verificationConduct melt viscosity or softening point sampling for three consecutive batches and observe the fluctuation range.
• Need information instead of promises：MSDS、 The detection report and batch number can be traced, which is more useful than verbal assurance.
• Calculate comprehensive costCalculate the shutdown cleaning, rework, and adhesive consumption together, and then compare the price per ton.

subsequent processing

This cardboard box factory eventually switched back to Sunlife hot melt adhesive from Guangzhou Sunlife Trading, and retained the methods of sample retention and sampling testing. After two months of use, the nozzle blockage decreased from twice a day to almost no blockage, and the cleaning cycle for the pot bottom was extended from one week to one month. The factory director later summed up with a sentence: for things like glue, cheap places must be hidden elsewhere.

Frequently Asked Questions

Does a yellow color necessarily indicate material return?

not always. Some formulas are naturally yellowish or have been stored for a long time, resulting in slight oxidation. The judgment should be based on a comprehensive consideration of odor, melt state, and batch consistency.

How to do simple testing without a laboratory?

You can use the same glue pot, the same temperature, and the same time to melt equal amounts of samples, observe the smoothness of the glue, the drawing situation, and the residue at the bottom of the pot, and compare horizontally to see the differences.

Can the adhesive mixed with recycled materials continue to be used up?

Suggest conducting small-scale validation first. If there is only a slight decrease in performance, it can be used for internal packaging with low requirements; If there is blockage or glue opening, stop using it immediately and clean the glue pot.