Double-sided reflector films

Details Double-sided reflector films Double-sided reflector films

1995-01-17

2001-12-25

Chen, Vivian (Department: 1773)

Stock material or miscellaneous articles

Light transmissive sheets, with gas space therebetween and...

C428S457000, C428S458000, C428S480000, C428S622000, C428S626000, C428S672000, C428S673000, C428S141000, C427S533000, C427S535000, C427S536000, C204S192100, C204S192120, C204S192220, C204S192260, C204S192270

Reexamination Certificate

active

06333084

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to plastic films which carry metal-containing reflector layers on both sides. More particularly, it concerns such double-metal layer-carrying plastic films which are light transmissive and which exhibit long-term stability.
DESCRIPTION OF BACKGROUND MATERIALS
It is common practice to employ partially reflective—partially transmissive metal layer-bearing films in glazing structures. These films may, be applied to the surface of glass window glazing materials. They may be laminated into glazing structures. They may be suspended alone or in combination with other sheets of glazing. These products are characterized by transmitting substantial proportions, such as at least 20% to as much as 90% or more of visible light while substantially reflecting heat and near infrared wave length radiation. These products typically have a plastic film substrate which carries the reflector metal layer adherent to it.
As will be described in more detail, plastic films are often marketed with a coating, known in the art as a slip coating, on one side to facilitate handling during production and fabrication. The side of the film having the slip coating is called (not unexpectedly) the “slip” side. The other side is the “nonslip” side. Slip coatings generally work by texturing the surface of the film. Two representative approaches to this involve surface texturizing by adding small particles to the plastic film as shown in U.S. Pat. No. 3,884,870 (American Hoechst) and applying and cracking an organic coating on the film as shown in U.S. Pat. No. 4,302,506 (also American Hoechst).
These reflector products, as a general class, may be prepared by applying the reflective layer to the film with a wide range of chemical mirroring methods, vapor deposition processes and sputter deposition techniques. In sputtering, a plasma is created between two electrodes in a high vacuum chamber. This plasma causes atoms of one electrode (the target), which is either metal or a metal compound, to be dislodged and drawn toward the other electrode. The plastic film substrate is placed between the electrodes and the material dislodged from the target is deposited upon the substrate.
Sputtering processes are often accompanied by a pretreatment step called preglow. Preglow also employs a plasma that is generated under conditions such that little or no material is deposited upon the substrate. As the name implies, “preglowing” commonly takes place immediately prior to the sputtering steps which involve actual material deposition on the substrate.
One simple format for these films used heretofore involves a single partially transparent metal reflector layer adherent to one side of the plastic film. Another widely employed format has a partially transparent, partially reflective sequence of dielectric and metal layers on one side of the film. Often these layers are in a dielectric-metal-dielectric sequence. In other cases more than one metal layer can be present with the several metal layers bounded by and optionally separated by dielectric layers.
Also in the past it has been proposed to place reflective layers on both sides of a plastic film. This has not found acceptance because the products do not have UV acceptable stability. This has been a vexing problem since double-sided materials do possess certain theoretical performance advantages. The most widely used plastic substrates are polyester materials, most commonly poly(ethyleneteryshthalate) or “PET”. We observed that when double-sided polyester products, that is polyester-based materials having metal-layer-containing, heat-reflective structures on both sides, were prepared using art-taught coating methods the products degraded and yellowed prematurely.
STATEMENT OF THE INVENTION
We have now discovered a way to make stable, durable, double-sided, double-metal-layer-containing, heat-reflective, light-transmissive plastic (e.g. polyester) films using sputter-depositing.
We have discovered that the life and durability of light-transmissive, heat and near infrared reflectors based on polyester films with metal-layer-containing reflectors on each side of the polyester film is improved by providing oxygen accessibility to the polyester film. This is accomplished by achieving at least a minimum level of oxygen permeability, that is 0.035 cc/(100 in
2
×24 hours), in at least one of the metal-layer-containing reflectors.
We have also found that the oxygen permeability can be attained by assuring that at least one of the surfaces of the polyester film has a mean surface roughness (R
a
) of at least about 8 nm at the time that the metal containing reflectors are sputter-deposited upon it. The desired level of oxygen permeability is achieved if this sputter-depositing is carried out in ways which preserve the surface roughness to a mean level of about 8 nm or greater. Although not required, this level of surface roughness is typically achieved on the slip side of slip-treated polyester films.
In accord with our invention we have found that a particular regimen of preglow treatment of the plastic (polyester) substrate leads to stable, durable double-sided reflective films. More particularly, we have discovered that when the slip-coated side of the plastic substrate has a mean surface roughness that is greater than about 8 nm, preglowing this surface can smooth and degrade the needed roughness. Thus, if the nonslip side of the plastic (polyester) film is preglowed and the slip side is not preglowed prior to depositing their respective reflective metal-layer-containing, heat-reflective coatings, the resulting product is durable and more stable (less prone to yellow prematurely) and more acceptable for commercial application. If the slip side is preglowed the desired product is not attained.
Thus, in one embodiment this invention provides a method for producing a reflective composite film. This method applies to plastic (polyester) film having a slip side and a nonslip side. It involves applying, by sputtering, a reflector structure including at least one metal layer to each side of the plastic film but preglowing only the nonslip side of the film. This method yields a coated film product which is significantly and unexpectedly more durable and long-lived than similar double-sided products made with the same plastic films preglowed on both sides.
In other aspects this invention is embodied as the product of this process or as a double-sided reflective film product per se. This film product has a plastic (polyester) film support. This plastic film has a nonslip side which has been modified by a preglow treatment and which carries a sputter-deposited metal-containing reflective layer adhered to it. It also has a slip side which has not been significantly modified by a preglow treatment and which also carries a sputter-deposited metal-layer-containing reflector layer.
In yet an additional aspect, this invention provides a plastic (polyester) film product which is light transmissive and which has metal-layer-containing heat and near infrared-reflective coatings on its slip side and on its nonslip side with these reflective coatings being such as to permit a plastic film-stabilizing quantity of oxygen to permeate to the film.
In yet an additional aspect, this invention provides an improvement in multipane window glazing structures in which a light transmissive, heat and near infrared-reflecting plastic film as suspended in a gas-filled dead space defined by two perimeter-sealed panes of glazing. This improvement involves using one of the double-sided polyester film based products of this invention and employing an oxygen-containing gas (e.g. from 1 to 20% O
2
by volume) as the gas filling the dead space.


REFERENCES:
patent: 4337990 (1982-07-01), Fan et al.
patent: 4414254 (1983-11-01), Iwata et al.
patent: 4510190 (1985-04-01), Glaser
patent: 4769261 (1988-09-01), Belkind et al.
patent: 5156894 (1992-10-01), Hood et al.
patent: 5306547 (1994-04-01), Hood et al.
patent: 5840161 (1998-11-01), Woodard et al.
Grant & Hackh's Chemical

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