JP2002292731A - Plant and method for producing transpiration film of polyolefin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a transpiration film of a polyolefin which can at least partially solve the problems of the formation of micro holes and the nonuniformity of a vaporization/dispersion capacity and an apparatus for the method. SOLUTION: The method for producing the transpiration film of the polyolefin by means for extruding bubbles of a charged LLDPE mixture, for flattening an extruded pipe to obtain a flat film, and for stretching the flat film in the cross direction and/or in the longitudinal direction and a plant therefor are disclosed.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an apparatus and method for producing a vaporized polyolefin film that is permeable to vapor and air but impermeable to liquids.

[0002] Patents EP 0,2 for an overview of the prior art
83, 200B1, low density linear polyethylene (LLDP) charged with CaCO ₃
E) extruding the extruded film by first hot stamping to give an imprint of reduced thickness, and then stretching to obtain an evaporative film having a specific increased transpiration capacity in the area of reduced thickness. A method for producing is described.

[0003] Evaporative films according to the prior art also have various problems and disadvantages. One of the problems facing known polyolefin vaporized films is that micropores can be formed in the elongation phase of the film due to the presence of impurities, especially oxidized and carbonized particles.

[0004] Such impurities may already be present in the extruded mixture or may be formed during the polyethylene extrusion process.

[0005] Micropores with an average diameter of 0.2 to 2 mm can reduce the properties of liquid impermeability, and this risk is increased by increasing the speed of the stretching process and the degree of stretching of the film.

[0006] Another problem facing polyolefin evaporation films is the non-uniformity of the evaporation ability. It is a primary object of the present invention to provide a method and apparatus for producing a polyolefin vaporized film that can at least partially overcome the aforementioned problems. Such a goal is obtained by a method according to claim 1 and a plant according to claim 3.

A further embodiment of the method may be performed according to dependent claim 2, and a further embodiment of the plant may be performed according to dependent claim 4.

The method and the device according to the invention, together with the drawing, schematically show a production plant according to the invention.
The following description of one of the possible embodiments provided in a purely exemplary manner will appear in a clear manner.

This process involves low density linear polyethylene (LLDP) charged with a base of CaCO _3.
Provided is the use of a mixture, which is preferably E).

Alternatively, low density linear polyethylene (LLDPE) or medium density polyethylene (MDP)
It is also possible to use E).

Also, α- having 4 to 10 carbon atoms
Olefin (1 butene, 1 pentene, 1 esene (esen)
e) 1 eptene, 1 ottene,
It is also possible to use a copolymer of polyethylene having 4-methyl (1 pentene).

It is of course possible to use other types of charges, organic or inorganic, having dimensions of 0.6 to 6 μm and whose surface has been treated to make them hydrophobic. In particular, clay, kaolin, zeolite, Zn, A
1, Ca, CaSO ₄ , BaSO ₄ , MgO, Mg (O
H) ₂ and TiO ₂ can be used.

The quality of the charge applied also depends on the degree of transpiration desired, and usually the charge is 30% of the weight of the mixture.
From 70%.

The mixture is subjected to bubble extrusion (so-called blow molding) by an extruder 1 having a circular head, and
0 is obtained.

The temperature of the tube coming out of the extruder 1 is 150-
230 ° C, preferably 170-190 ° C.

The expansion ratio of tube 10 may vary between 1: 2 and 1: 4, and is preferably 1: 3. One of the features of the method of the present invention is the fact that the extruded and expanded tube 10 undergoes a calendering operation.

More specifically, tube 10 is at about 80-100 ° C.
At the temperature of the first calender 2 where it is compressed and stretched to form a sheet 11 composed of two stacked layers of width equal to half the circumference of the tube and twice the thickness of the tube In the form of

Such a feature has the advantage of overcoming the problem of insufficient liquid impermeability due to micropores that can form in the film in the stretching phase. That is, it is very unlikely that both layers of the film will be damaged at the same point. The calender 2 used to flatten the tube 10 includes a pair of smoothly connected rollers,
The first roller is chrome steel and the second roller is 6
Rubber having a hardness of 0-80 Shore. The pressure applied to the tube 10 flattened by the calender 2 is 5
To 10 kg / cm ² .

A second feature of the method according to the invention lies in the fact that the film 11 is heated to the softening temperature after being flattened.

These temperatures depend on the type of mixture to be extruded, and in the case of LLDPE-based mixtures are
It can vary between 0 and 130 ° C., usually it is about 1
00 ° C.

In the heating performed in this manner, it is preferred to remove the low boiling additives present in the humidity or mixture.

Furthermore, in the heating carried out in this manner, it is preferable to eliminate the small stresses present in the film due to the preceding phase of the method, and to homogenize the internal structure of the film.

To obtain this heating, the film 11 first travels on a heated roller 3 having a temperature of about 60-70 ° C., and then passes near an infrared lamp 4 which raises the temperature further to the softening point.

In fact, using only rollers which are usually heated by water or oil, the softening temperature cannot be reached, or at least very difficult.

In addition, infrared lamps also strongly heat the layer of air near film 11 (typically 300-400).
C.) offers the advantage that residual humidity still present on the film 11 can be completely eliminated.

A third feature of the method according to the invention lies in the fact that the film heated in this manner is further calendered by a calender 5 and subsequently cooled to a temperature of from 8 to 30 ° C.

[0027] Such cooling is preferably effected through contact by one of the rollers of the calender 5 maintained at a constant temperature of 8 to 30 ° C.

This further calendering allows the first two layers to coalesce directly through the compression provided by the rollers, preventing the risk of delamination of the film produced in this manner, Can hinder the stabilization process.

In this phase, it is also possible to perform a film embossing operation for purely aesthetic purposes without changing the weight of the film.

It has been found that the thermal shock experienced by the film results in improved transpiration in successive stretching operations.

The compression of the film is performed by using a rubber roller (having a hardness of 60).
-80 shore) obtained by combining a chrome steel roller combined with a chrome steel roller.

Following the sterilization process, the film 11 undergoes transverse and / or longitudinal stretching.

For this purpose, there are suitable means 6 adapted to perform a lateral extension and suitable means 8 adapted to perform a longitudinal extension.

[0034] In the illustrated example, the film 11 first undergoes transverse stretching and then longitudinal stretching, although of course these phases may be reversed.

[0035] Between the transverse stretching means 6 and the longitudinal stretching means 8 there is preferably provided a tentering means 7 for eliminating the folds created by the first process of stretching.

Normally, the longitudinal stretching ratio varies between 1: 1.5 and 1: 2.5. Also in this embodiment, the longitudinal extension ratio usually varies between 1: 1.5 and 1: 2.5. However, if necessary, the stretch ratio may reach a ratio of 1: 4.

At the end of the stretching phase, the film 11 may undergo further working steps or may be wound up by a suitable winding machine 9.

[Brief description of the drawings]

FIG. 1 schematically shows a manufacturing plant according to the invention.

[Explanation of symbols]

1 extruder, 2 calenders, 3 rollers, 4 infrared lamps, 5 calenders, 6 lateral stretching means, 8
Longitudinal stretching means, 10 tubes, 11 films.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Graziano Boletto, Italy-31059 Zero Branco (Treviso), Via Pietro Micca, 5F term (reference) 4F210 AA08 AG01 AR06 QC02 QC03 QC05 QG01 QG18

Claims (4)

[Claims] 1. A method for producing a polyolefin vaporized film, comprising: bubble extruding a charged mixture of LLDPE; flattening a tube (10) to obtain a flat film (11); Heating the flat film (11) to a softening temperature; compressing the flat film (11); cooling the flat film to a temperature of 8-30 ° C .; Stretching laterally and / or longitudinally. 2. The method according to claim 1, wherein the flat film is heated first by conduction and subsequently by radiation. 3. A plant for producing a stretched polyolefin film, comprising: a bubble extruder (1); a first calender (2) adapted to flatten an extruded tube; Means (3, 4) adapted to heat the heated film to a softening temperature; a second calender (5) adapted to compress the heated film; Means (5) adapted to cool quickly to temperature, and means (6) adapted to stretch the film in the transverse direction.
And / or a means (8) adapted to stretch the film longitudinally. 4. The means adapted to heat the flat film (11) comprises: first heating means adapted to heat the film by conduction; and first means adapted to heat the film by radiation. 4. The plant according to claim 3, comprising continuously two heating means.