How to deal with hot melt adhesive in printing waste paper? The relationship between hot melt adhesive and paper recycling and ink removal

#How to deal with hot melt adhesive in printing waste paper? The relationship between hot melt adhesive and paper recycling and ink removal

After printing books, brochures, and paper boxes, there are always waste paper such as cut edges, discarded pages, and box scraps. Nowadays, most printing factories recycle waste paper and then make paper, which is a good thing; But many customers have found that:Waste paper with hot melt adhesive is prone to “sticky lumps, tangled nets, and paper spots” during recyclingWhere is the problem, is it related to the glue used, and can we avoid it in advance when selecting? Below, we will explain the relationship between hot melt adhesive and paper recycling and ink removal.

1、 First of all, let’s answer directly: Hot melt adhesive itself is insoluble in water, and the difficulty in recycling lies in the “adhesive material”

The mainstream methods used for book binding, paper box pasting, and other packaging are EVA hot melt adhesiveSunlife book and magazine adhesive 292/296/295/298, flat adhesive 391, graphic store adhesive 393/395, pearl cotton adhesive 39B/399, etc. all belong to this category. It is a solid particle at room temperature, melted and coated at 160-180 ℃, and solidified into a polymer film after cooling to firmly bond the paper.

The general process of recycling waste paper is:Crushing (breaking paper into fiber suspension) → Deinking (separating printing ink from fibers) → Impurity screening → Regenerated pulpHot melt adhesive in the pulping stageInsoluble in water and not reabsorbed by fibersIt will remain in the system in the form of “stickers” – this is the source of trouble.

2、 The specific impact of hot melt adhesive residue on recycling

1. Block the screen mesh and stick the formed mesh

Adhesive materials are soft and sticky, making them easy to hang on pressure screens, forming nets, and blankets. For light cases, they can be cleaned at a reduced speed, while for heavy cases, they can break paper and shut down. This is the most troublesome type of “sticky impurities” for paper mills.

2. Spots and holes appear on the paper surface

Unclean adhesive spots will transfer to the finished paper, forming transparent/semi transparent spots. In severe cases, holes, powder loss, degradation, or even scrap may occur during subsequent printing and film coating.

3. Lower the cleanliness of recycled pulp

The more adhesive there is, the stronger the “impurity feeling” in the pulp, and the whiteness and strength will be affected. High end paper types (food cards, high-end cultural paper) are particularly sensitive.

3、 Is it related to ‘what glue is used’? Yes, and it can be selected in advance

Although waste paper recycling is a secondary process in paper millsThe formula characteristics of the adhesive will directly affect the difficulty of residual treatmentWhen purchasing hot melt adhesive, you can take a step forward:

• Easy to disperse, low viscosity adhesiveIt is more easily dispersed into small particles in the pulp and can be removed by screening, which is more friendly to “hard, tough, and clumpy” glue.
• Low additive, clean materialLess impurities bring in less foreign matter.
• Match with paper and avoid excessive coatingReasonable control of adhesive layer (refer to the book core adhesive layer in the training materials: thin book ≈ 0.4mm, thick book ≈ 0.8-1.0mm), which not only adheres firmly but also does not accumulate excessively, resulting in less residue in the later stage.

Sunlife has corresponding models for books, graphic printing, and packaging (including pearl cotton) scenes, which can be recommended based on the balance of “bonding strength requirements+whether the subsequent process enters the recycling process”——Not all scenarios require the strongest adhesive strength, which can be achieved with lower residual glue to meet process requirements and is more recycling friendly。

4、 3 things that printing/packaging factories can do now

1. Classify and collect waste paperSeparate the edges of pure paper, adhesive waste pages, and box scraps appropriately, which is easier to handle than mixing them together.
2. Control the amount of glue appliedControl the adhesive layer within a reasonable range according to the thickness of the book core to avoid excessive residue caused by “thick coating for firmness”.
3. When choosing a product, ask more about “recyclability”If the finished product needs to go through waste paper recycling, clarify this demand to the supplier and ensure that the selection is both adhesive and ink friendly.

5、 Relationship with Sunlife’s real business

Sunlife hot melt adhesive is used for book binding, quick printing of graphics and text, packaging, and pearl cotton bonding. It covers paper scenes such as copperplate paper/adhesive paper/double adhesive paper/thin paper, with different types of adhesive such as backing adhesive (292/296/295/298, 396/397/398), flat adhesive (391), test paper adhesive (39D), and graphic store adhesive (393/395). The customer is concerned about whether the glue will cause chaos during the recycling of waste paper. Essentially, it isCan bonding quality and sustainable post-treatment be balanced——This type of problem can be balanced by Sunlife according to the application scenario during the selection stage, rather than waiting for problems to occur at the recycling end before rework.

Explanation: This article describes the general characteristics of EVA hot melt adhesive in the waste paper recycling system; There are significant differences in the tolerance of adhesive materials among different paper types and paper machine processes. The specific selection and “easy to de ink” indicators are based on Sunlife’s accompanying “Instructions/Process Card” and actual sample conclusions. This article does not provide specific de ink rate and other data.