Bleaching and dyeing; fluid treatment and chemical modification – Diffusion transfer dyeing process – transfer sheet and product – Dry heat treatment for penetration
Reexamination Certificate
1998-11-02
2001-04-24
Liott, Caroline D. (Department: 1751)
Bleaching and dyeing; fluid treatment and chemical modification
Diffusion transfer dyeing process, transfer sheet and product
Dry heat treatment for penetration
C008S467000, C008S495000, C008S512000, C008S552000, C008S562000, C008S933000
Reexamination Certificate
active
06221112
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods of colouring polyester film and to the coloured polyester films so produced.
BACKGROUND TO THE INVENTION
Coloured polyester films have numerous uses, for example as light filters, particularly in industrial applications, and in solar control applications such as window films for automobile, domestic and office windows. Polyester films are commonly coloured by dyeing with disperse dyes. A disperse dye may be defined generally as a substantially water-insoluble dye having substantivity for one or more hydrophobic polymers such as polyesters, for example poly(ethylene terephthalate).
One known method of dyeing a polyester film with a disperse dye relies upon swelling the film with an organic solvent. The dye is generally applied to the film in solution in the solvent, either at the same time as or subsequently to the swelling treatment. The former of these techniques is the one more commonly used. The dye diffuses into the swollen polyester film, which is then washed to remove the solvent and dried. The process of diffusion may be assisted by heating. This technique can be referred to as solvent dyeing. Solvent dyeing has the disadvantage that organic solvents capable of swelling polyester film and therefore suitable for the purpose are in general not environmentally friendly. The organic solvent may furthermore be difficult or expensive to remove from the film and to reclaim or to dispose of. The presence of residual solvent in the dyed film may affect subsequent processes such as metallisation.
Another known method of dyeing a polyester film utilises a suspension of disperse dye in a mixture of water and an organic solvent which swells the film. This method may be called solvent-assisted dyeing, and is otherwise similar to solvent dyeing.
Another known method of dyeing a polyester film with a disperse dye relies upon thermal diffusion of the dye into the film. The dye is brought into contact with the film which is then heated to cause migration of the dye into the film. The dye may be coated onto the film and the coated film dried and heated, or the dye may be provided on a separate sheet which is brought into contact with the film and the sheet and film are then heated. The former process may be referred to as theremofixation or thermosol fixation dyeing and the latter process as transfer printing. The heating step is generally carried out at or around the sublimation temperature of the dye. The process of transfer of dye into the film may be referred to as fixation.
DESCRIPTION OF THE PRIOR ART
U.S. Pat. No. 2,833,613 describes a process for dyeing polyester fibres in which the fibres are treated with disperse dyes in aqueous systems at about 100° C. using as carrier a mixture of dimethyl terephthalate and benzanilide, in a ratio of from 1:3 to 3:1 by weight.
U.S. Pat. No. 2,938,811 describes a process for improving the dyeability of a synthetic polyester textile material. The material is impregnated with a water-soluble high-boiling organic liquid, for example a polyhydroxy compound, preferably diethylene glycol, by heating at a temperature in excess of 120° C. or 175° C. The treated material is more rapidly dyed by disperse dyestuffs than untreated material is. The liquid may easily be removed or substantially completely removed from the dyed material by washing with water.
U.S. Pat. No. 3,034,847 describes a process for colouring polyethylene terephthalate film. The surface of the film is coated with a homogeneous composition comprising essentially a disperse type dye uniformly distributed in an organic liquid which uniformly (evenly) wets the surface of the film. The coated film is then heated to a temperature of 150-200° C. for a period of time sufficient to set the dye, i.e. to cause the dye to penetrate the surface of the film and hence become affixed in the film. The composition may contain 1-6% by weight dyestuff suspended or dissolved in the composition. The organic solvent must wet the surface of the film, and may for example be methyl ethyl ketone, benzyl alcohol, toluene, methyl isobutyl ketone, anisole, ethyl acetate, cyclohexanone, or a mixture of dimethyl acetamide and methyl ethyl ketone. The dyestuff may be applied to the film in the form of a uniform layer by any convenient coating or printing expedient, for example a gravure roll.
U.S. Pat. No. 3,058,798 describes a process for dyeing hydrophobic fibres, for example polyester fibres, in tow form. The tow is first padded with an aqueous dispersion of the disperse dye and then placed in a conventional raw stock dyeing machine, after which water is circulated through the padded tow at a temperature of 200-300° F. (93-149° C.) to fix the dye on the fibre. The aqueous dispersion contains 1-4% dye, 0.1% sodium alginate and 0.003% of a sodium aryl sulfonate wetting agent.
U.S. Pat. No. 3,512,913 describes a process for the continuous dyeing of polyethylene terephthalate film. A pre-treatment liquid containing dye-carrier is applied to the traveling web of the film and thereafter a hot aqueous dye-bath containing a disperse dye is applied to the web. Examples of suitable dye-carriers are phenol, ortho- and paraphenylphenol, diphenyl, chlorinated benzenes and diphenyls, methyl salicylate, benzoic acid and benzyl alcohol. Other examples include simple solvents such as the chlorinated hydrocarbons, for example methylene chloride, tetrachloroethane, chloroform or trichloroethylene. The dye-carrier is a material which has a noticeable swelling action on the film and consequently accelerates dyeing so that, for example, dyeing can satisfactorily be carried out at a temperature in the range 80-100° C. with a dyeing time of about 1-3 hours.
U.S. Pat. No. 3,958,934 describes a process in which an organic disperse dye is first applied by conventional means to a synthetic polymer, which may be a polyester film, by spraying, padding or printing, and the dye-treated polymer, optionally dried, is then passed through a fluorocarbon fluid at a temperature greater than the glass transition temperature of the polymer.
U.S. Pat. No. 4,065,259 describes a process for exhaust dyeing of disperse dyeable synthetic polymers, for example polyester, for example in the form of film, fibre or fabric, utilising a dye dispersion which comprises a disperse dye and a normally liquid fluorocarbon, for example poly(perfluoropropylene glycol).
C. J. Hawkyard, in a paper entitled ‘The Release of Disperse Dyes from Thickener Films during Thermal Processes’, Journal of the Society of Dyers and Colourists, Volume 97 (1981), pages 213-219, describes thermofixation dyeing of polyester films. A dye paste consists of a disperse dye (for example C. I. Disperse Red 60), 2.5-8% of a high molecular weight thickener (for example sodium alginate, sodium carboxymethyl starch, or hydroxylated guar gum), and water. The viscous dye paste is applied as a layer at least 24 micron thick to the surface of a polyester film using a stainless steel wire-wrapped rod. The layer is then dried, and the film heated to 200° C. to cause diffusion of the disperse dye from the dye paste into the film. The highest degree of fixation (that is, the proportion of the dye which diffuses from the layer of paste into the film) is obtained when a heterogeneous dye paste is used, for example by using sodium carboxymethyl starch as thickener or by emulsifying a low boiling point hydrocarbon, for example white spirit, into the dye paste.
SUMMARY OF THE INVENTION
The invention provides a process for producing a coloured polyester film including the steps of:
(1) providing a dye mixture which has a viscosity of no more than 500 centipoise at ambient temperature and which is a suspension of at least one disperse dyestuff in a solution of a thickener in water;
(2) coating said dye mixture onto a polyester film to form a layer; and
(3) heating said film to cause said dyestuff to migrate from said layer into said film.
The polyester film is commonly poly(ethylene terephthalate), although other polyesters including polycarbonates may be used.
CP Films, Inc.
Howson and Howson
Liott Caroline D.
LandOfFree
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