Stock material or miscellaneous articles – Composite – Of polyester
Reexamination Certificate
2001-08-24
2004-01-13
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyester
C428S212000, C428S910000, C264S173110, C264S173160, C264S288400, C264S290200
Reexamination Certificate
active
06677049
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a multi-layered biaxially-oriented film, mainly made of a crystallizeable thermoplastic polyester. The film can be economically produced with a high surface quality and at speeds of more than 340 m/min. The invention also relates to a process for the production of this film.
During the production of multi-layered films with thicknesses lying within the range from 0.5 to 350 &mgr;m plastic granulates are initially melted in extruders, the extruded melts are then led through a multi-layer slot die. The prefilm emerging from the slot die is then placed on a take-off—and quenching roll and, after leaving the take-off roll, longitudinally and transversely stretched in relation to the machine direction.
For the benefit of a stabilized placement of the prefilm on the take-off roll the state-of-the-art technology requires the application of additional forces to the prefilm in the area between the point at which the film exits the flat-film die and the point at which it is placed on the take-off roll. These additionally applied forces can be generated by blowing a stream of air out of an air knife at the prefilm, by spraying water into the nip of the prefilm prior to the point of application on the take-off roll, by producing a water film on the take-off roll, or by generating an electrical field by means of an electrode under high tension, with the field lines of the electrical field being directed towards the surface of the take-off roll. The additionally applied forces serve the purpose of removing the air which is enclosed between the surface of the take-off roll and the bottom side of the prefilm, i.e. that side of the prefilm facing the take-off roll, and which is underneath the nip of the prefilm, prior to placing the prefilm on the take-off roll, in order to obtain a stabilized placing of the prefilm on the surface of the roll by means of a given wrap angle. If this cannot be acomplished, enclosures of air of a more or less voluminous nature, so-called pinning bubbles, may result, which can be found between the bottom side of the prefilm and the surface of the take-off roll, adversely affecting the smoothness of the surface and, thus, the quality of the prefilm previously cooled down on the take-off roll, and subsequently the quality of the biaxially-stretched film manufactured from it.
2. Description of the Related Art
It is known that as an electrode a high-grade steel blade can be parallelly arranged to the surface of the take-off roll. For this purpose a 10 mm-wide portion of the steel blade is usually punched out or cut out from a metal blade which has a thickness of about 20 &mgr;m.
The german utility model G 9402027 describes a device for the production of films, especially thin films or thinnest films by means of a rotating roll, with which a plastically formable film, previously fed into a slot die, is transported and stretched. Between the roll and a steel band parallely arranged to the roll at a short distance, electrical tension is applied by which the film is placed on the roll. The steel band in this known device has a sharp longitudinal edge which is arranged right next to the roll and pointed directly to it. This sharp edge is, similar to a cutting edge, arranged at the tapered area of the steel band, which is hereby arranged right next to the roll at a distance of less than 6 mm. The center line of this tapered area is directly pointed towards the center point of the roll. The use of such a steel band electrode helps to improve the quality of the film.
As the final speed during the film production is increased to a value of more than 340 m/min, an increased amount of pinning bubbles can be noticed. Increasing the electrical tension can counteract this development to a certain degree, but if the tensions applied are too high, electric arcing between the electrode and the quenching roll is the result. This leads to a severe defect within the film in the area affected by these arcings, namely an extremely thin area extending over the width of the film. As a result the film breaks within the machine, which is extremely unfavourable from an economical point of view. The procedural window for the production safety in the relation between pinning bubbles and electric arcing with film breaks gets smaller and smaller as the production speed is increased.
SUMMARY OF THE INVENTION
It was the object of this invention to produce a multi-layered, biaxially-oriented polyester film with a thickness lying within the range from 1 to 20 &mgr;m at speeds of 340 m/min or more assuring a procedural window of a sufficient size for the production stability during the manufacturing process.
This object is achieved by the using a kind of film as previously mentioned, wherein the average specific electrical melt resistance over the total thickness of the multi-layered polyester film lies within the range from 1.5×10
7
to 30×10
7
&OHgr;×cm, preferably from 2×10
7
to 10×10
7
&OHgr;×cm, especially preferred from 3×10
7
to 6×10
7
&OHgr;×cm.
The average specific melt resistance over the total thickness [&rgr;] (rho) is the arythmetical average of the specific electrical resistances of the individual layers based on the thicknesses of the individual layers.
For a three-layered ABC-film the following formula applies
ρ
=
ρ
A
·
d
A
d
g
e
s
+
ρ
B
·
d
B
d
g
e
s
+
ρ
C
·
d
C
d
g
e
s
d
A
, d
B
, d
C
: thickness of the individual layers
d
ges
=d
A
+d
B
+d
C
: total thickness
&rgr;
A
, &rgr;
B
, &rgr;
C
: specific electrical resistance of the individual layers
During the production of films with thicknesses of 1 to 20 &mgr;m at final speeds of 340 m/min or more under electrical tension, a dramatically high amount of pinning bubbles is the result every time polyester raw material with an average specific electrical melt resistance over its thickness of more than 30×10
7
&OHgr;×cm is used. Increasing the electrical tension slightly reduces, but does not eliminate the forming of pinning bubbles, since this in turn leads to an increased amount of electric arcing.
If, however, the average specific electrical melt resistance over the thickness is below 1.5×10
7
&OHgr;×cm, the previously described problems do reoccur whenever production speeds are high.
It was completely surprising that biaxially-oriented polyester films produced with a thickness of 1 to 20 &mgr;m at final speeds of 340 m/min or more could be manufactured without pinning bubbles and free of electric arcing if its average specific electrical melt resistance [&rgr;] over the total thickness of the film is within the range from 1.5×10
7
to 30×10
7
&OHgr;×cm according to the invention.
The manufactured films are multi-layered. They can have a symmetrical or an unsymmetrical structure, wherein differently composed polyesters, respectively composed or non-composed polyesters, or polyesters of the same chemical compound but with a different molecular weight and a different viscosity are combined by way of coextrusion.
The film according to the invention mainly consists of crystallizeable polyethylene terephthalates, of crystallizeable polyethylene naphthalates (PEN), or mixtures thereof.
Crystallizeable polyethylene terephthalate or crystallizeable polyethylene naphthalate means
crystallizeable homopolymers
crystallizeable copolymers
crystallizeable compounds
crystallizeable recycled material
other variations of crystallizeable polyester.
Polyesters can either be produced according to the ester interchange process, e.g. catalyzed by ester interchange catalysts such as Zn—, Mg—, Ca—, Mn—, Li—, or Ge—salts, or according to the direct ester process (PTA method), where antimone compounds are used as polycondensation catalysts and phosphorus compounds as stabilizers. The IV-value (intrinsic
Mueller Harald
Murschall Ursula
Chen Vivian
Mitsubishi Polyester Film GmbH
ProPat L.L.C.
LandOfFree
Multi-layered, biaxially-oriented polyester film with an... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multi-layered, biaxially-oriented polyester film with an..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multi-layered, biaxially-oriented polyester film with an... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3224428