Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-11-15
2001-11-13
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S096000
Reexamination Certificate
active
06316531
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to the field of dyeing of polyester films.
The energy crisis of the 1970's resulted in the development of many processes and products for energy conservation and many countries accorded priority to such efforts in parity with environmental protection. One of the means of saving energy successfully attempted by scientists has been through laminated films. U.S. Pat. Nos. 3,943,105, 4,047,889 and 4,115,054 of Julius Hermes and U.S. Pat. No. 4,399,265 of Garware et al were all directed towards this subject matter. More specifically, the Garware et al patent was directed to a new process for the manufacture of dyed film for sun control applications.
Dyed polyester films have numerous applications including solar controls films for window application, light filters in research laboratories and industrial applications, colored films for decorative applications, packaging applications and greenhouse applications.
U.S. Pat. No. 4,399,265 discloses a process for producing UV stabilized polyester films in which UV absorbers from the benzophenone and benzotriazole group are blended with polyester granules in the desired concentration, and extruded or co-extruded to obtain a UV stabilized film in various thicknesses.
U.S. Pat. No. 3,943,105 discloses a process for UV stabilization of dyed or undyed film by a solvent assisted treatment. The films are treated with UV stabilizer and carriers such as polyhydric glycols at 250 and 430° F. Subsequently, the treated film is washed with water to remove excess surface solvents.
In the case of colored polyethylene terephthalate (PET) films used for solar control applications/greenhouse applications, the films are exposed to electromagnetic radiation from the sun. A high energy UV component having a wave length ranging from 200 nm to 400 nm is responsible for decomposition of organic matter, and the films must therefore be UV stabilized to prevent the destructive effects of UV radiation. Another important function of UV stabilization is to prevent UV radiation from passing through the windows.
The PET window films are generally available in laminate form, which consist of a UV stabilized colored film coated with pressure sensitive adhesive which is protected with a release liner. One of the known methods of dyeing the film is to incorporate mixtures of blue, red and yellow dyes in the polyester matrix before extrusion. The concentration of dyes to be incorporated in the polymer matrix depends upon the required shade and transmission. The dyes are mixed in the polymer matrix during polymerization, and the polymer matrix is directly fed to the extruder followed by biaxial orientation.
These films have exceptional dimensional stability against thermal aging and outdoor exposure. It is not, however, practical to produce small quantities of colored films using this method, as colors cannot be changed in the production runs.
U.S. Pat. No. 4,047,889 describes a method of waterless dyeing or solvent-assisted dyeing, which involves swelling of polyester films with high boiling polyhydric alcohols and glycols. The swelling of the polyester matrix at high temperatures is followed by a dye treatment. The dyes in contact with the polymer matrix diffuses into the film; the rate of dye diffusion depends upon the concentration of individual dyes in the bath and swelling capability of the solvent.
These films are subsequently washed with low boiling solvents such as methanol, ethanol and chlorinated low boiling solvents, which are continuously recycled in the process. This method does not generate effluent but there is very high risk of explosion and a fire hazard.
U.S. Pat. No. 4,115,054 is a continuation-in-part of the above patent, which includes the non aqueous dyeing of woven polyamide, woven polyester fibers and polyamide knitted fabrics.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved method for dyeing of polyester films, with a reduced risk of fire and explosion.
It is a further object of the invention to provide dyed polyester films with reduced shrinkage in the machine direction and/or the transverse direction.
To achieve these and other objects, the invention is directed to dyeing of UV stabilized polyester films using disperse dyes and polyhydric alcohols at a temperature above the glass transition temperature of the film. The process dyeing of pre-UV stabilized polyester film with disperse dyes dissolved or suspended in polyhydric alcohols and polyhydric glycols, and requires polyhydric glycols/alcohols as a carrier medium when the additives are added in the solvent medium, followed by pinching, washing with high boiling solvents or water, scrubbing and finally drying the film in an oven at higher temperatures using the tenter process. The shrinkage properties are monitored in MD and TD directions.
This invention also provides a safe, explosion proof process. In the prior art, low boiling solvents were used for cleaning, which made the process hazardous. The washing step in the process of the invention includes cleaning of the films with high boiling solvents followed by a mechanical scrubbing operation, and removes undissolved particles on the films which include degraded dyes, polyester oligomers and excess undissolved colors.
This invention further provides a dyed polyester film having controlled shrinkage in MD and TD directions. The films have shrinkage values not more than 10% either in the machine direction or the transverse direction or in both directions after 30 minutes treatment in an air circulated oven at 150° C. The controlled shrinkage films of the invention have excellent shrinkage properties and are suitable for installation on curved window glasses of automobiles. A specially designed tenter is used for obtaining the controlled shrinkage property of the polymeric films.
The invention thus provides window film laminates for installation on the curved glasses of automobiles using a hot air gun at the time of the film installation.
The invention utilizes polyester films produced by extrusion, where the UV stabilizers are incorporated in the polymer matrix before the extrusion process.
REFERENCES:
patent: 5981076 (1999-11-01), Ojeda
patent: 6049419 (2000-04-01), Wheatley et al.
patent: 6113811 (2000-09-01), Kausch et al.
Garware Shashikant B
Modi Monika Garware
Cain Edward J.
Dennison, Scheiner Schultz & Wakeman
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