Corrugating single-facer glue bonding
27 January 2010
Background
A 'B' flute corrugating plant had sporadic problems with brittle bonding at the single-facer ('zipper bonds)' when running certain combinations of linerboard and fluting medium.
Method
Smithers Pira had undertaken a multiclient project on the 'Gluability of densified corrugated case materials'. This had shown that brittle bonding was a result of premature gelatination of both the carrier phase and the starch granules. This leads to crystallization of the starch rather than formation of an adhesive paste at the interface between flute tip and liner. The problem arises due to a combination of too great a rate of heat input in relation to the conductivity of the papers and gelatination temperature of the starch.
Slowing down the corrugator would exacerbate the problem. The use of densified 'high performance' corrugated case materials would also cause problems due to their smoothness and density, both of which increase the rate of heat transfer.
Outcome
At our instigation, the corrugator supervisor increased the speed of the machine when moving from trouble-free to the troublesome grade combination. Rather to his surprise, brittle bonding was eliminated. Increasing the speed reduced the amount of heat transferred from pre-conditioner and corrugating rolls. This was an easier option than either re-formulating the adhesive, with the attendant stoppage to clean-up and re-charge the gluing system, idling the machine to reduce the temperature of the pre-conditioner and rolls. or adjusting the wrap on the pre-conditioner.
This instance underlines the rate-dependent nature of green bond formation, ie the rates of heat transfer, granule swelling, water absorbency, contact times and nip dwell time. Problems also arise from premature de-watering of the adhesive due to high paper absorbency, especially when running some recycled grades. This effect can rob the granules of the water needed to swell, so a brittle bond results but with white unswollen or semi -swollen starch granules visible in the glue lines.
Rapid-grade changes can cause problems if they involve moving between materials with sharply differing properties in terms of absorbency, compressibility, surface roughness and density.
See Also
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Nick Kernoghan Food Contact Regulatory Expert at Smithers Pira, talks to Packaging and Converting Intelligence Magazine's Philip Kleinfield about potentially harmful mineral oils entering food products, the possible threat to consumers and the dangers of a knee-jerk response.
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Join Nick Kernoghan's expert briefing and Q&A on Global food contact regulations beyond Europe and North America.
Understand how regulations vary from region to region and what is required for compliance. If you are you are looking to supply, specify or develop food contact materials or packaging to any of these regions - this is a must-attend. It's also opportunity to pose questions direct.
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Learn more about the behaviour of fillers. Listen to this expert briefing from Smithers Pira Consultant Nigel Jopson focusing on fillers for paper and the unexpected consequences they can have.