TRIPLE STAGE EXTRUSION COATING  LAMINATING LINES FOR U.H.T. PACKAGING

Model: EXCOL-12/35 TRIPL-O-MATIC.

Forewords

The multi-stage extrusion lamination process is well known and available on the market since more than 30 years.

It is based on the principle to use polyolefinic resins for A healthy adhesion of 2 webs (no glues involved) of different kind/nature, and/or to coat with polyetilene (or polypropilene) one or two web’s sides, so as to permit a further thermo-welding.

It is a “flexible” process applicable to any web, it is “modular” and in the triple-stage case, makes a “complex laminate web” that is totally impermeable to liquids, vapours, aromas, greases, etc…

This web, properly formed and heat-sealed, can preserve the “sterility” on foods and liquids for months, without the necessity of the so called “cold-chains” and without any chemical preservation.

In December of 2009, in the Dolci Extrusion factory of Biassono, an open house was held showing in operation a modern triple-stage extrusion lamination line, that will start to produce complex-web-reels destined to be converted into aseptic UHT packaging for milk or fruit juice (bricks).

The Aseptic Stucture

The widely used web structure for this type of packaging is composed by a 250 gr/mq paper-board (primary web) sandwich, laminated by co-extrusion to a 7 μ thin alufoil and coated on both sides with co-extruded layers of polyolefines, of total thickness between 20 and 50 μ.

The final “complex-web” is a barrier structure of 350 – 450 gr/mq in form of reels.

This modular triple-stage process is made at line speed of 350 m/min, with possibility to arrive till 500 m/min.

The triple-stage line

Due to the complexity of the line (is almost 40 meters long), and due to the fact that it is fully automatic, it was decided to call it EXCOL-12/35 TRIPL-O-MATIC.

The two unwinders and the final rewinder are automatic.

The three dies are automatic, fitted with internal deckling and variable geometry feed block; each stage has a proper automatic gauge control system; the treatments included in the line have a power automatically synchronized with the line speed; the resins dosing and feeding are automatic in all the 3 stages; the temperature profiles of extruders/die in all the 3 stages are automatically set and recalled by the operation in accordance to the type of “complex” web to be produced (with or without Alufoil).

Unwinders and rewinders 

Differently of most of the standard execution of extrusion coating lines, the automatic primary unwinder is an uncommon “butt-splicer” for “non-overlapping” reel change over at line speed.

The junction of the 2 web’s ends (front of new roll and end of finishing roll) is done at zero speed, with upper/lower side typing, thanks to a Festoon compensator.

The secondary automatic unwinder (sandwich unwinder) is a classic turret dual-shaft unwinder with flying-splice at working speed, located on an elevate platform to minimize the alufoil distance from the laminating chill-roll.

The automatic rewinder is flying splice turret type, with 6” air shafts, max reel diameter 1800 mm. with contact roller moving on horizontal lines guides and is fitted with a lowering hydraulic platform to put on the floor the finished reels.

First stage

In this first section, the paper board (that was previously printed, punched, creased and flame or corona treated) passes through a pre-heating drum and then enters into the chill roll (3 cylinders type) where is sandwich laminated with the incoming alufoil via 2-layer of film, with E.A.A. on the alufoil side and PE on the paper side.

A combination of EAA resin and proper processing temperature maximizes the adhesion strength, without the necessity of ozonization (not an operator-friendly step).

Each extruder (of each stage) is fitted with a pressure valve providing good “back pressure control” and is driven by water cooled A.C. vector motor.

The total extrusion capacity is near to 1000 kg/hour and 2 extruders can produce a total film thickness of 25 – 60 micron.

The extruder’s cart is motorized, has a 3” axis adjustment possibility and is fitted with a slow-shifting device, particularly usefull (in case of non using of the automatic gauge control system) to randomize the film profile.

Second and third stages

In this second stage section, 3 extruders coat three layers of polyolefins on the free side of alufoil, with a total film thickness of 40 – 70 micron.

One of those extruders is fitted with a special reducer that permits the screw extraction from backside.

This outstanding features is particularly welcome when producing a barrier sandwich structure without alufoil, being EVOH responsible for the barrier effects, once using a specific screw profile for this resin.

The three layer feed block is fitted with a interchangeable “selector-plug technology” to move the EVOH layer in the appropriate layer sequence.

The third stage is similar to the previous one, but with two extruders only, of same size of the 2 fitted in the first stage.

Trims recovery

At each stage, a slitting/recovery unit for the film edge-beads is provided.

A specially featured compacting unit receives the 2 edge beads and delivers compacted and bricks-shaped pieces of pre-selectable length.

This “clean” recovered scrap can be off-line reprocessed or sold elsewhere.

Automatic dies and automatic gauge control

The three dies are automatic and made in the , with specific design of the manifold and the feed block, for the extrusion coating specific process.

The three feed blocks are “variable geometry type”, with possibility to modify the melt flow cross section on each layer.

The three stage automatic gauge control system is interlocked in the following way:

-         After the primary unwinder, a beta gauge scanner controls the profile of the paper board;

-         After the second stage chill roll a double-head scanner (beta and infrared) controls the overall web thickness and the film profile coated on the external side of alufoil;

-         After the third stage chill roll a beta-gauge scanner controls the overall profile of the third die.

The multistage gravimetric dosing and feeding group (mounted on each of the 7 extruders), grants a constant grammage of film (for square meter) even during the ramp-up and ramp-down phases.

Work station

The line operator has a work station with 3 videoscreens on which he can check in real time working parameters, temperature profiles, the 3 film gauge profiles and the recipe of the resins.

The “presence effect” in the production hall of our engineers, is granted by a modem service and by 3 webcams that will send us in real time the images of the line during the working phase.