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The production process of 100% recyclable retort pouch is very difficult, mainly due to the high temperature resistance characteristics and the differences in lamination. At present, the standard retort pouch technology is mature. But the 100% recyclable retort pouch technology is new and difficult.
Longdapac had spent 3 years in developing 100% recyclable retort pouches, not the mono-material PP retort pouch is mature and good quality. It can be with high barrier, and the detail film structure is BOPP/High barrier PP/RCPP.
In this article, we mainly talk about 3 key factors of making 100% recyclable retort pouch.
Adhesive
When using solvent-free adhesives in composite cooking products, it is recommended to choose models that have good temperature resistance, medium resistance (acid, alkali, salt, oil, spicy, special additives, etc.), and are non-toxic, odorless, and hygienic.
Thin film
At present, when selecting a thin film for solvent-free high-temperature cooking composite (121 ℃), the following points should be noted:
(1) Surface tension of thin film
Generally, the surface tension of RCPP should be greater than 38 dynes, and the surface tension should be greater than 52 dynes. Insufficient surface tension of the film directly affects the final composite strength, and there may be delamination and poor peeling after steaming at 121 ℃.
(2) Cleanliness
High surface cleanliness and surface tension of 72mN/m or above should be selected for grinding. When using the machine, water brushing verification should be carried out. If the surface oil stains are severe, it will directly affect the final composite strength, and there will be delamination, poor peeling and other phenomena after steaming at 121 ℃.
(3) Corona discharge
During production, double corona film is selected and the original corona surface is left for the inner RCPP film.
Pay attention to the workshop environment humidity of 40%~60% (glue will not dry if it is too high), (curing speed will be affected if it is too low); Humidifiers and dehumidifiers can be used to control workshop humidity. When the humidity is too high and solvent-free composite is used, there is often a stretching of several meters at the joint when the material is stopped for feeding. There may be knife running during bag making and cutting, and there may be active wrinkles at the bottom of the composite winding or at the joint.
When the inner layer is compounded with RCPP, it is prone to wrinkling. This problem will exist regardless of the composite process used, and the key is how to control it within our acceptable range. The factors that can affect the generation of wrinkles when using solvent-free composite include: winding paper core, winding tension, tension taper, winding pressure roller, joint, raw material, etc. We can use 6 # paper core or printing plate roller; Set the matching winding tension and taper tension based on the width and thickness of the raw materials; Adjust the level and parallelism of the winding roller to be consistent with the paper core, with a pressure of 0.2MPa~0.3MPa; The raw material film should use a film with small thickness deviation. If the film has edge oscillation, reduce the machine speed to 80m/min for operation.
Pay attention to the workshop environment temperature (too high affects the lifespan of the disc), (too low affects the leveling of the glue); The workshop temperature can be controlled using air conditioning; When the winter temperature is below 15 ℃, the adhesive can be preheated.
During continuous production, the entire coating system must be cleaned every 6-12 hours. The glue can containing “NCO” must be inspected regularly to ensure good sealing and prevent the glue from curing or semi curing.
The type of ink (polyurethane, polypropylene, chlorinated polypropylene, etc.), solvent type and solvent residue of the ink, and fineness of the ink all have an impact on the composite strength, appearance, and adhesive ratio. Testing is required before use. If replacing the printing ink, it is necessary to conduct experiments first to verify whether the ink is suitable to avoid losses.
① Generally less than 15 minutes of shutdown: the measuring roller and the glue feeding roller rotate at low speed, and the mixed glue in the glue tank is cleared out. When used again, it can be mixed with fresh glue and reused;
② Shutdown for 20-25 minutes, and all mixed glue must be discarded;
③ If the shutdown lasts for more than 25 minutes, the entire system must be thoroughly cleaned because the mixed adhesive has already solidified and must be completely discarded.
① When using solvent-free production, follow the adhesive manufacturer’s instructions for curing;
② During production, if dry composite production is used for the outer layer, a partial curing process is used. After the surface layer is cured in a high-temperature curing chamber for 24-48 hours, the inner layer RCPP is then cured using solvent-free composite according to the solvent-free manufacturer’s instructions.
After maturation, let it cool naturally for 12 hours before cutting and bag making.
The reasons for the problems are different, and the solutions used are also different.
(1) Reason: Incorrect ratio setting. (Poor curing of the entire piece)
Countermeasure: Reset the ratio.
(2) Reason: Blockage of the glue mixer. (Poor curing of the entire piece)
Countermeasure: Clean the glue mixer again.
(3) Reason: The switch of the glue dispensing shut-off valve of the glue mixer is inconsistent. (Localized poor solidification)
Countermeasure: Replace the adhesive shut-off valve.
(4) Reason: Poor curing of the printing area.
Countermeasure: If the residual solvent is too high or the NCO is consumed by the ink, control the solvent residue or replace it with a suitable ink.
(5) Reason: The adhesive is sticky but cannot press out fingerprints.
Countermeasure: No defects, caused by the excessively smooth surface of the composite film.
(1) Reason: Improper control of winding tension or tension reduction.
Countermeasure: Set appropriate winding tension and decreasing tension.
(2) Reason: Poor quality of the winding paper tube.
Countermeasure: Replace the appropriate paper tube.
(3) Reason: The thickness deviation of the composite film is too large.
Countermeasure: Replace with a suitable composite film.
(4) Reason: Poor ink distribution.
Countermeasure: Redesign the printing pattern layout.
Reason: Ink (such as alcohol soluble ink or transparent ink) has poor compatibility with adhesives (such as low viscosity solvent-free adhesives and polyester solvent-free adhesives).
Countermeasure: Choose appropriate ink and adhesive. For full white ink, a certain amount of hardener can be added to the ink, and the amount of glue should not be too high. The winding needs to be cooled and matured at room temperature for 3-4 hours before entering the maturation room for maturation.
(1) Reason: Excessive amount of glue applied.
Countermeasure: Control the amount of glue applied.
(2) Reason: Uneven distribution of ink.
Countermeasure: Redesign the ink distribution.
(3) Reason: The composite speed is too fast.
Countermeasure: Control the correct composite speed.
(1) Reason: The composite high barrier composite film generates carbon dioxide gas that cannot be emitted.
Countermeasure: Stop using, use solvent glue or water-based glue composite, or control the composite site environment.
(2) Reason: Uneven distribution of ink causes local looseness of winding pressure and the presence of bubbles.
Countermeasure: Stop using and use solvent glue composite.
(3) Reason: There are particles on the surface of the material.
Countermeasure: Replace with suitable composite materials