Composite polyester films as final coating supports

Details Composite polyester films as final coating supports Composite polyester films as final coating supports

1990-11-01

1992-07-07

Thibodeau, Paul J.

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Physical dimension specified

4274125, 428483, 428694, 428900, 428910, 525 64, 525445, 525446, B32B 2708, B32B 2736

Patent

active

051282062

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to composite polyester films having improved slip which are intended for use as support for varied final application coatings and in particular for magnetic coatings.
Because of their excellent mechanical and chemical properties, the polyester films are a material of choice as support for varied film-forming coatings leading to composite materials which find numerous applications: packaging, photographic coatings, films or sheets for graphic art, metallized films, and magnetic tapes for recording sound, images or other information. However, the polyester films lack slip, which causes difficulties in use and in particular in winding, this being a consequence of a high coefficient of friction of the films slipping on themselves or on fixed or moving smooth metallic surfaces, such as those present in film production equipment (rollers, cylinders) or conversion equipment or in application equipment, in particular equipment for the reproduction of recorded signals. The means most frequently used to resolve the problem posed by the lack of slip on the part of polyester films consists in conferring surface roughness to said films by incorporation of inert particles of metal salts or oxides which generate unevenness on the surface of the films. In certain cases, this solution is not always sufficient in itself to confer the desired slip to the polyester films and for some types of applications it proves detrimental to the properties of the final coating, in particular when magnetic coatings are concerned.
In fact, the irregularities in the surface of the support film are reflected by irregularities in the surface of the magnetic coating and even by a discontinuity in this coating, which are accompanied by a loss of information on recording and/or on reading the information. Moreover, the abrasion of this unevenness during repeated use of the magnetic films also contributes to their deterioration.
To mitigate these various drawbacks it has been proposed to provide the polyester films with coatings intended to improve their slip properties and consequently their machinability and their windability. In particular, slip coatings based on film-forming polymers which are very particularly suitable for polyester films of low roughness used as supports for magnetic layers have been described. Thus, in U.S. Pat. No. 4,233,352 it has been proposed to provide at least one of the faces of a polyester support film with a vermiculated coating intended to improve the slip properties of the film, consisting of a water-soluble polymer (polyvinyl alcohol, methylcellulose, hydroxyethylcellulose, carboxyethylcellulose or natural rubbers) and of a polysiloxane having a molecular weight of between 30,000 and 300,000, optionally containing functional groups (epoxy, amino or hydroxyl), and/or of a styrene-butadiene rubber. In European Patent Applications Nos. 74,750, 88,635 and 108,593 slip coatings have been described which are analogous to the above but also contain coupling agents intended to improve the bond between the surface of the polyester film and the coating. These coupling agents consist of silanes containing functional groups: on the one hand methoxy, ethoxy and silanol OH groups and on the other hand vinyl, epoxy, amino and mercaptan groups. These coatings are of limited industrial value because of their complex composition due essentially to the poor compatibility of the water-soluble polymers with the highly hydrophobic polyester film. The problem therefore arose of finding a coating which confers good slip properties to polyester films and which has a good compatibility with, and consequently a good adherence to, the polyester, without resorting to complex compositions. The present invention proposes to find a solution to this problem.
More specifically, the present invention relates to composite polyester films having improved slip, consisting of an orientated polyester film in which at least one of the faces carries a coating intended to confer upon it a good slip, characterized in that th

REFERENCES:
patent: 4605591 (1986-08-01), Nose et al.
patent: 4880700 (1989-11-01), Charmot et al.
patent: 4908277 (1990-03-01), Tsunashima et al.
Considered to the extent of English translation provided.

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