Multi-layer iridescent films

Details Multi-layer iridescent films Multi-layer iridescent films

1998-11-16

2002-11-05

Chen, Vivian (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S480000, C359S577000, C359S580000, C359S584000, C359S586000, C359S588000, C359S589000

Reexamination Certificate

active

06475608

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to multilayer coextruded light-reflecting films which have a narrow reflection band because of light interference and contain a layer of naphthalate-based polyester.
BACKGROUND OF THE INVENTION
Iridescent multilayer films are composed of a plurality of generally parallel layers of transparent thermoplastic resinous material in which the contiguous adjacent layers are of diverse resinous material whose index of refraction differs by at least about 0.03. The film contains at least 10 layers and more usually at least 35 layers and, preferably, at least about 70 layers.
The individual layers of the film are very thin, usually in the range of about 30 to 500 nm, preferably about 50-400 nm, which causes constructive interference in light waves reflected from the many interfaces. Depending on the layer thickness and the refractive index of the polymers, one dominant wavelength band is reflected and the remaining light is transmitted through the film. The reflected wavelength is determined by the sum of the optical thickness of a pair of layers.
The quantity of the reflected light (reflectance) and the color intensity depend on the difference the two refractive indices, on the ratio of optical thicknesses of the layers, on the number of layers and on the uniformity of the thickness. If the refractive indices are the same, there is no reflection at all from the interfaces between the layers. In multilayer iridescent films, the refractive indices of contiguous adjacent layers differ by at least 0.03 and preferably by at least 0.06 or more. For first order reflections, reflectance is highest when the optical thicknesses of the layers are equal, although suitably high reflectances can be achieved when the ratio of the two optical thicknesses falls between 5:95 and 95:5. Distinct color reflections are obtained with as few as 10 layers. However, for maximum color intensity, it is desirable to have between 35 and 1000 or more layers. High color intensity is associated with a reflection band which is relatively narrow and which has high reflectance at its peak. It should be recognized that although the term “color intensity” has been used here for convenience, the same considerations apply for the invisible reflection in the ultraviolet and infrared ranges.
The multilayer films can be made by a chill-roll casting technique using a conventional single manifold flat film die in combination with a feedblock which collects the melts from each of two or more extruders and arranges then into the desired layer pattern. Feedblocks are described for instance in U.S. Pat. Nos. 3,565,985 and 3,773,882. The feedblocks can be used to form alternating layers of either two components or more (e.g. ABABAB . . . , ABCABC . . . or ACBCACBC . . . ). The very narrow multilayer stream flows through a single manifold flat film die where the layers are simultaneously spread to the width of the die and thinned to the final die exit thickness. The number of layers and their thickness distribution can be changed in inserting a different feedblock module. Usually, the outermost layer or layers on each side of the sheet are thicker than the other layers. This thicker skin may consist of one of the components which makes up the optical core, may be a different polymer which is utilized to impart desirable mechanical, heat sealing, or other properties, or may be a combination of these.
Examination of iridescent films of desirable optical properties revealed deficiencies in certain mechanical properties. For example, the adhesion between individual layers of the multilayer structure may be insufficient, and the film may suffer from internal delamination or separation of layers during use. The iridescent film is often adhered to paper or board for its decorative effect, and is then used for greeting cards, cartons, wrapping paper and the like. Delamination of the film is unsightly and may even lead to separation of the glued joints if carton. In addition, the solvent resistance and heat stability of such films are not as great as desired for widespread utilization.
In U.S. Pat. No. 4,310,584, these deficiencies are significantly overcome by using a thermoplastic terephthalate polyester or copolyester resin as the high refractive index component of the system in which two or more resinous material form a plurality of layers. While a substantial improvement was realized, it also required the use of two polymers from significantly different polymer families. That fact, in turn, means that there are inherent significant differences between the two polymers and their relative adhesion to each other, chemical resistance, toughness, etc. As a result, the film itself is generally no better with regard to a particular characteristic than the weaker or poorer of the polymers employed. If two polymers closely related were employed in order to maximize relative adhesion to one each other, or toughness, or chemical resistance, etc., the polymers involved did not have a sufficient difference in refractive index so as to create the desired iridescent color.
Schrenk and Wheatly (Co-extruded Elastomeric Optical Interference Film, Antec '88, 1703-1707) have reported the preparation of a multilayer light reflecting film co-extruded from two thermoplastic elastomers. The film which had one thermoplastic elastomer based on nylon and the other based on urethane, exhibited reversible changes in reflection spectra when deformed and relaxed. That is, this very specific combination had the ability of stretching without losing appearance characteristics. This type of films has been described in more detail in U.S. Pat. No. 4,937,134.
U.S. Pat. No. 5,089,318 discloses that further improvements in adhesion, solvent resistance and the like can be obtained by employing a thermoplastic elastomer (TPE) as one of the resinous materials. Such materials are copolymers of a thermoplastic hard segment such as polybutyl terephthalate, polyethylene terephthalate, polycarbonate, etc., and a soft elastomeric segment such as polyether glycols, silicone rubbers, polyetherimide and the like.
While prior art structures represented significant improvement in the areas of delamination resistance and better solvent stability, there were still some limitations with regard to these properties. In addition, iridescent films of the prior art still had deficiencies relative to their temperature stability, tensile strength and UV stability. The present invention surprisingly provides significant improvements over current known structures with regard to these properties.
SUMMARY OF THE INVENTION
It is, therefore an object of the invention to provide a transparent thermoplastic resinous laminate having good heat and solvent stability, good tensile strength, good delamination resistance, and good UV stability.
In one embodiment, the present invention provides a transparent thermoplastic resinous laminate film of at least 10 very thin layers of substantially uniform thickness, said layers being generally parallel, the contiguous adjacent layers being of different transparent thermoplastic resinous materials of which one is a naphthalate-based polyester or copolyester resin, the contiguous adjacent layers differing in refractive index by at least about 0.03.
In another embodiment, the present invention provides a transparent thermoplastic resinous laminate film of at least about 70 very thin layers of substantially uniform thickness, said layers being generally parallel, the contiguous adjacent layers being of different transparent thermoplastic resinous materials of which one is a polyethylene naphthalate polyester or copolyester, and the other is a polybutylene terephthalate polyester or copolyester, wherein the outermost layers are polybutylene terephthalate polyester.
Other objects and advantages of the present invention will become apparent from the following description and appended claims.
DETAILED DESCRIPTION OF THE INVENTION
It has now been found that the objectives of this invention are realized by employing a naph

Affiliated with

Also associated with

Rating

Multi-layer iridescent films 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-layer iridescent films, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multi-layer iridescent films will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2964690