WO2000007045A1

WO2000007045A1 - Microcreped optical films

Info

Publication number: WO2000007045A1
Application number: PCT/US1999/000533
Authority: WO
Inventors: Janet T. Keller
Original assignee: Minnesota Mining And Manufacturing Company
Priority date: 1998-07-31
Filing date: 1999-01-05
Publication date: 2000-02-10
Also published as: AU2315399A

Abstract

A decorative article such as a bow or ribbon is provided that includes a multilayer optical film. The film includes an optical stack having a plurality of layers. The layers include at least one birefringent polymer and at least one different polymer so that the optical stack comprises a strain induced index of refraction differential along at least a first in-plane axis. The optical stack has a creped configuration that imparts an unusual visual appearance to the film.

Description

Microcreped Optical Films

Technical Field of the Invention

The present invention relates generally to an article formed from multilayer optical films, and more particularly to an article formed from a creped multilayer optical film that may be configured into a decorative item having unusual visual characteristics.

Background of the Invention

Decorative items such as bows, ribbons and gift bags may be formed from materials such as foamed polypropylene or paper that may be further coated with thin layers of metal. These materials can be provided in different colors and may even be embossed or printed.

However, consumers are continuously demanding a greater variety of decorative items that are formed from new materials and which display different and unusual decorative effects. Besides being unduly familiar to consumers, most known decorative articles do not offer unusual decorative effects. Often, decorative items are desired that exhibit more interesting visual characteristics such as a brilliant appearance that may change as an observer views the item from different orientations.

Accordingly, there is need for a decorative item that is visually interesting and appealing and which can be made available with a wide variety of different visual characteristics so that consumers do not quickly become overly accustomed to their appearance.

Summary of the Invention

In one aspect of the present invention, an article is provided that includes a multilayer optical film. The film includes an optical stack having a plurality of layers. The layers include at least one birefringent polymer and at least one different polymer so that the optical stack comprises a strain-induced index of refraction differential along at least a first in-plane axis. The optical stack has a creped configuration that imparts an unusual visual appearance to the film.

In another aspect, the article of the present invention includes a creped optical stack that has at least one region having a specified compression ratio. In some embodiments of the invention the creped optical stack includes a plurality of regions having different compression ratios. The plurality of regions may be randomly distributed along the length of the article.

In yet another aspect of the invention, a region of the creped optical stack having a higher compression ratio has an overall appearance that is more white in color than a another region having a lower compression ratio.

In still another aspect, the article of the present invention is configured into a decorative item. Examples of such decorative items include ribbons, bows, wrapping paper, gift bags, garlands, streamers, centerpieces, and ornaments.

In another aspect, the creped configuration of the optical stack is determined by adjustment of select process parameters. The select process parameters may be applicable to a creping apparatus having at least one roller and a retarder element cooperating with the roller. The select process parameters may include the temperature and diameter of the roller, the position and configuration of the retarder element, and a line speed produced by the roller. One example of the creping apparatus includes first and second rollers arranged to form a nip therebetween and the retarder element includes a pair of blades that form a retarding cavity between them. In this apparatus the pair of blades are arranged adjacent to the nip.

In another aspect of the invention, a method of manufacturing an article that includes a multilayer optical film is provided. The multilayer optical film includes an optical stack that has a plurality of layers. The layers include at least one birefringent polymer and at least one different polymer. The optical stack includes a strain-induced index of refraction differential along at least a first in-plane axis. In accordance with the method, the optical stack is creped to cause a change in its visual appearance.

In yet another aspect of the invention, the creping step causes an increase in the observed brilliance of the article.

Brief Description of a Drawing

Figure 1(a) shows a schematic diagram of a portion of an exemplary creping apparatus that may be employed by the present invention and Figure 1(b) shows a portion of Figure 1(a) on an enlarged scale. Figure 2(a) shows a schematic diagram of a portion of another creping apparatus that may be employed by the present invention and Figure 2(b) shows a portion of Figure 2(a) on an enlarged scale.

Figure 3 shows an example of the creped surface of the multilayer optical film resulting from the present invention.

Description of the Preferred Embodiment(s)

Optical Films

Many multilayer optical films used in connection with the present invention and methods of manufacturing them are described in U.S. Patent Application Serial No. 08/402,041 (filed on March 10, 1995) and Serial Nos. 09/006,085; 09/006,118;

09/006,288; 09/006,455; 09/006,591 (all filed on January 13, 1998); as well as in various other patents referred to herein. While several optical films can be used in the present invention, the multilayer optical films described above are the preferred films.

Briefly, however, pre-creped multilayer optical films used in the methods and articles of the present invention include a multilayer stack having alternating layers of at least two diverse polymeric materials, at least one of which preferably exhibits birefringence, such that the index of refraction of the birefringent material is affected by stretching. The adjacent pairs of alternating layers preferably exhibit at least one strain- induced refractive index differential (Δx, Δy) along at least one of two perpendicular in- plane axes as discussed briefly below. By stretching the multilayer stack over a range of uniaxial to biaxial orientation, a multilayer optical film can be created with a range of reflectivities for differently oriented plane polarized incident light along reflective directions (typically corresponding to the stretch directions) based on the values of Δx and Δy. Preferably, those refractive index differentials are generally uniform throughout the film to provide uniform optical properties throughout the film. Variations in those refractive index differentials that fall below desired minimum values for the desired optical characteristics may cause undesirable variations in the optical properties of the films. Materials Selection

A variety of polymer materials suitable for use in the present invention have been taught for use in making coextruded multilayer optical films. For example, the polymer materials listed and described in U.S. Pat. Nos. 4,937,134, 5,103,337, 5,448,404, 5,540,978, and 5,568,316 to Schrenk et al., and in 5,122,905, 5,122,906, and 5,126,880 to

Wheatley and Schrenk are useful for making multilayer optical films according to the present invention. Of special interest are birefringent polymers such as those described in 5,486,949 and 5,612,820 to Schrenk et al, U.S. Application No. 08/402,041 to Jonza et al, and U.S. Application entitled "Modified Copolyesters and Improved Multilayer Reflective Films" filed on January 13, 1998 under Attorney Docket No. 53550USA6A. Regarding the preferred materials from which the films are to be made, there are several conditions which should be met to make the multilayer optical films of this invention. First, these films should consist of at least two distinguishable polymers; the number is not limited, and three or more polymers may be advantageously used in particular films. Second, at least one of the two required polymers, referred to below as the first polymer, preferably has a stress optical coefficient having a large absolute value. In other words, it preferably should be capable of developing a large birefringence when stretched. Depending on the application, the birefringence may be developed between two orthogonal directions in the plane of the film, between one or more in-plane directions and the direction perpendicular to the film plane, or a combination of these. In the special case that the isotropic indices are widely separated, the preference for large birefringence in the first polymer may be relaxed, although at least some birefringence is desired. Such special cases may arise in the selection of polymers for mirror films and for polarizer films formed using a biaxial process that draws the film in two orthogonal in-plane directions. Third, the first polymer should be capable of maintaining birefringence after stretching, so that the desired optical properties are imparted to the finished film. Fourth, the other required polymer, referred to as the "second polymer", should be chosen so that in the finished film, its refractive index, in at least one direction, differs significantly from the index of refraction of the first polymer in the same direction. Because polymeric materials are typically dispersive, that is, the refractive indices vary with wavelength, these conditions must be considered in terms of a particular spectral bandwidth of interest. Although many polymers may be chosen as the first polymer, certain of the polyesters have the capability for particularly large birefringence. Among these, polyethylene 2,6-naphthalate (PEN) is frequently chosen as a first polymer for films of the present invention. It has a very large positive stress optical coefficient, retains birefringence effectively after stretching, and has little or no absorbance within the visible range. It also has a large index of refraction in the isotropic state. Its refractive index for polarized incident light of 550 nm wavelength increases when the plane of polarization is parallel to the stretch direction from about 1.64 to as high as about 1.9. Its birefringence can be increased by increasing its molecular orientation which, in turn, may be increased by stretching to greater stretch ratios with other stretching conditions held fixed.

Other semicrystalline naphthalene dicarboxylic polyesters are also suitable as first polymers. Polybutylene 2,6-Naphthalate (PBN) is an example. These polymers may be homopolymers or copolymers, provided that the use of comonomers does not substantially impair the stress optical coefficient or retention of birefringence after stretching. The term "PEN' herein will be understood to include copolymers of PEN meeting these restrictions.

In practice, these restrictions impose an upper limit on the comonomer content, the exact value of which will vary with the choice of comonomer(s) employed. Some compromise in these properties may be accepted, however, if comonomer incorporation results in improvement of other properties. Such properties include but are not limited to improved interlayer adhesion, lower melting point (resulting in lower extrusion temperature), better rheological matching to other polymers in the film, and advantageous shifts in the process window for stretching due to change in the glass transition temperature.

Other optical films suitable for use in the microcreping process of the present invention include, for example, multilayer films and films comprised of a blend of immiscible materials having differing indices of refraction. Examples of suitable multilayer films include polarizers, visible and infrared mirrors, and color films such as those described in Patent Publications WO 95/17303, WO 96/19347, and WO 97/01440; filed applications having U.S. Serial Numbers 09/006086 and 09/006591; U.S. Pat. Nos. 5,103,337 (Schrenk), 5,122,905 (Wheatley et al), 5,122,906 (Wheatley), 5,126,880 (Wheatley), 5,217,794 (Schrenk), 5,233,465 (Schrenk), 5,262,894 (Wheatley), 5,278,694

(Wheatley)5,339,198 (Wheatley), 5,360,659 (Arends), 5,448,404 (Schrenk), 5,486,949 (Schrenk) 4,162,343 (Wilcox), 5,089,318 (Shetty), 5,154,765 (Armanini), 3,711,176 (Alfrey, Jr. et al.); and Reissued U.S. Patents RE 31,780 (Cooper) and RE 34,605 (Schrenk), the contents of which are incorporated herein by reference. Examples of optical films comprising immiscible blends of two or more polymeric materials include blend constructions wherein the reflective and transmissive properties are obtained from the presence of discontinuous polymeric regions, such as the blend mirrors and polarizers as described in Patent Publication WO 97/32224, the contents of which is incorporated herein by reference. Preferred films are multilayer films having alternating layers of a birefringent material and a different material such that there is a refractive differential between the alternating layers. Especially preferred are multilayer films wherein the birefringent material is capable of stress-induced birefringence, wherein the refractive index differential between the alternating layers is caused, at least in part, by drawing the film. The drawing or similar forming process causes the refractive index of the birefringent material to change, thereby causing the inter-layer refractive index differential to change. Those strain-induced refractive index differentials provide a number of desirable optical properties, including the ability to reflect light incident on the films from a wide range of angles, high reflectivity over broad ranges of wavelengths, the ability to control the reflected and transmitted wavelengths, etc.

Microcreping of Optical Films

The terms creping and microcreping will be used herein interchangeably. However, it should be noted that microcreping refers specifically to the formation of relatively small pleats in a thin film which cause a change in the optical properties of the film.

In a microcreping process lengthwise compressive forces are exerted on traveling lengths of film so that the film is shortened to a fraction of its original length. As detailed below, the dimensions of the crepe undulations can be tailored to produce different visual effects. For example, the crepe undulations may be extremely small so that successive crepe undulations are in substantial contact with one another.

The decorative items resulting from creping the previously mentioned optical films may be used as stand-alone articles or they may be incorporated into other articles including additional multilayers. Decorative items that may be formed from the creped films include ribbons, bows, wrapping paper, gift bags, garlands, streamers, centerpieces, and ornaments. The creped films may also be employed in a gift box or other decorative packaging (e.g., cosmetic or food packaging), yarns, or they may be arranged as a window in a gift bag. These examples of decorative items are presented for illustrative purposes only and should not be construed as a limitation on the variety of decorative items in which the creped films may be employed.

Figure 1 shows a simplified cross-sectional view of the treatment zone of a microcreping apparatus that may be employed in accordance with the method of the present invention. The area inside the dotted rectangle of FIG. 1(a) is shown on a more enlarged scale in FIG. 1(b). The apparatus has a driven rotary roll 1, a retarder blade 2 with blade edge 3 and retarding working surface 9, and a covering resilient spring blade 4 projecting from a blade assembly 6. The roll rotates in the direction of the arrow. The film to be micro-creped is pressed onto the roll by means of pressure plate 5 via the blade assembly 6 and exits at reference numeral 7 after going through cavity 8 and the region between blades 2 and 4. The film itself is not shown in this Figure. Figure 2(a) shows an example of another microcreping apparatus that may be employed by the present invention. This apparatus differs from that shown in Figure 1 primarily in that two independently driven rolls 21 and 22 are employed, which are supported by yoke assemblies 23 and 24, respectively. As seen in more detail in Figure 2(b), two blades 25 and 26 are positioned adjacent to roll nip 30. The blades 25 and 26 are supported by blade holders 27 and 28, respectively. As the film is fed through the nip by action of rolls 21 and 22 its forward movement (which is from left to right in Figure 2b) is restrained by an initial portion of a diverging cavity formed between blades 25 and 26. This initial portion of the cavity serves as a retarding passage that maintains the end of the film so that high resistance pressures are transmitted longitudinally through the film, thus forming a pleat (i.e., an undulation) in the film. As the film continues its forward movement the retarding passage continues to exert high pressure through the pleat onto the oncoming portions of film, in direct opposition to the driving forces produced by rolls 21 and 22. As a consequence, additional pleats or undulations are formed. The longitudinal pressures eventually force the creped film through the remainder of the diverging cavity, discharging it from the microcreping apparatus.

By adjustment of the process parameters, varying amounts of residual compaction or compression and crepe cross-section can be attained, depending upon the desired results and characteristics of the film being treated. These parameters include the pressure within the nip 30, the rotational speed of the rolls 21 and 22, the temperature of the rolls 21 and 22, and the thickness and lateral position of the blades 25 and 26 with respect to the center of the nip. As the examples presented below will illustrate, these parameters may be adjusted to produce different decorative effects.

It should be noted that the exemplary creping devices shown in Figures 1 and 2 are presented for illustrative purposes only. One of ordinary skill in the art will recognize that any apparatus may be employed providing it performs a creping process.

Figure 3 shows the structure that results from the creping process performed in accordance with the present invention. As shown, creping of the film produces pleats such as pleats 40, 41 and 42. The pleats need not all be uniform in shape or dimension. Moreover, the pleats need not be provided over the entire length of the film. Rather, they may be provided on one or more portions so that they form discontinuous regions along the film's length. The pleats also may be irregular along the film's length, varying in height or shape. Furthermore, the individual pleats need not extend along the width of the film. As an alternative, the pleats may be rotated by a few degrees with respect to the width of the film. The precise value of this small rotation may vary from pleat to pleat or region to region along the film length.

Optical Characteristics of Creped Multilayer Films The visual appearance of the treated films will depend at least in part on the degree of microcreping that is applied. In general, when minimal processing is applied, a coarse or large pleat is produced that gives the film a crinkled appearance. Such a treated film displays a range of colors since the multilayer optical films employed in the present invention exhibit a phenomenon known as color shifting. That is, these films reflect incident light in one wavelength range and transmit light in another wavelength range, with the wavelength ranges of reflection and transmission varying with changes in the angle of incidence of the light. Since the different portions of the creped film occupy different planes, the incident angle of light striking the different portions of the film will also vary, thus increasing the number of different colors that are observed. Surprisingly, it has also been observed that as the film is more highly creped so that there is an increase in pleat density (i.e., the number of pleats per linear inch along the film), the more white in appearance the resulting film appears. Moreover, in some instances variations in other visual characteristics such as luster have been observed. For example, in some cases the appearance of the film changes from its precreped, primarily transparent appearance to resembling a metallized film or textured fabric. Additionally, at higher pleat densities, the pleats are relatively small in dimension and the mechanical forces applied to the film by the creping process may cause it to undergo internal changes, possibly including delamination. These internal processes may further influence the appearance of the creped film.

This invention is further illustrated by the following examples that are not intended to limit the scope of the invention.

Examples

Example 1

A decorative article was prepared from an 8.5 inch wide roll of multilayer colored mirror film the microcreped process of the present invention. The pre-creped film was prepared from a coextruded film containing 224 layers made on a sequential flat-film making line by a coextrusion process. This multilayer polymer film was made from polyethylene naphthalate (PEN) (60 wt. % phenol 40 wt. dichlorobenzene) with an intrinsic viscosity of 0.48 dl/g available from Eastman Chemical Company and polymethyl methacrylate (PMMA) available from ICI Acrylics under the designation CP82. PETG 6763 provided the outer or "skin" layers. PETG 6763, believed to be a copolyester based on terephthalate as the dicarboxylate and 1,4-cyclohexane dimethanol and ethylene glycol as the diols, is commercially available from Eastman Chemicals Co., Rochester, NY. A feedblock method (such as that described by U.S. Patent No. 3,801,429) was used to generate about 224 layers which were coextruded onto a water chilled casting wheel and continuously oriented by conventional sequential length orienter

(LO) and tenter equipment. PEN was delivered to the feedblock by one extruder at a rate of 24.2 Kg/hr and the PMMA was delivered by another extruder at a rate of 19.3 Kg/hr. These melt streams were directed to the feedblock to create the PEN and PMMA optical layers. The feedblock created 224 alternating layers of PEN and PMMA with the two outside layers of PEN serving as the protective boundary layers through the feedblock.

The PMMA melt process equipment was maintained at about 274°C. The PEN melt process equipment, feedblock, skin-layer modules were maintained at about 274°C; and the die was maintained at about 285°C. A gradient in layer thickness was designed for the feedblock for each material with the ratio of thickest to thinnest layers being about 1.25.

After the feedblock, a third extruder delivered PETG as skin layers (same thickness on both sides of the optical layer stream) at about 25.8 Kg/hr. Then the material stream passed through a film die and onto a water cooled casting wheel using an inlet water temperature of about 24°C. A high voltage pinning system was used to pin the extrudate to the casting wheel at 3.1 meters/min. The pinning wire was about 0.17 mm thick and a voltage of about 4.9 kV was applied. The pinning wire was positioned manually by an operator about 3-5 mm from the web at the point of contact to the casting wheel to obtain a smooth appearance to the cast web.

The cast web was length oriented with a draw ratio of about 3.1 :1 at about 130°C. In the tenter, the film was preheated before drawing to about 135°C in about 30.9 seconds and then drawn in the transverse direction at about 140°C to a draw ratio of about 4.5: 1, at a rate of about 20% per second. The finished film had a final thickness of about 0.05 mm.

A two roll microcreping apparatus similar to that described in connection with Figure 2 was employed. The apparatus is commercially available from Micrex Corporation, of Walpole, Massachusetts. The process parameters were as follows:

Upper yoke pressure: 50 psi

Upper blade pressure: 42 psi

Lower yoke pressure: 42 psi

Lower blade pressure: 35 psi

Main nip pressure: 60 psi Temperature: 115 degree F

Input speed: 50 fpm

Output speed: 5-20 fpm

Top blade thickness: 20 mil

Bottom blade thickness: 20 mil Initial blade setting position: Top - 0.490 inches from nip center Bottom - 0.225 inches from nip center

The pre-creped multilayer colored mirror film, as observed in normal transmission under fluorescent room lighting, exhibited randomly distributed areas of clear, cyan and blue elongated in the crossweb direction. The resulting creped colored mirror film had significantly changed in its visual appearance. The creping process produced micropleats that caused the resulting film to appear brilliant. The brilliant appearance occurs because the different portions of the pleated film now occupy different planes so that these different locations return light back to the viewer. In other words, light was directed back to the viewer from an increased number of source locations, giving the film its unusually brilliant appearance.

The creped film was processed so that randomly selected portions along its length had pleats of different dimensions. The portions having larger dimensioned pleats had a compression ratio of approximately 2 to 1. That is, a 2 inch length of pre-creped film was compressed or compacted into a length of 1 inch. The portions of the film having smaller dimensioned pleats had a compression ratio as high as 3.5 to 1. The unique appearance of the film was accentuated by this provision of randomly dimensioned pleats. In addition, the creped film maintained its color shifting properties, which were especially apparent when the sample was viewed in transmission at a normal angle.

Example 2

A decorative multilayer colored mirror film a Vi inch in width was prepared in a manner similar to that described for Example 1 above. The pre-creped film was formed from a multilayer film containing about 418 layers made on a sequential flat-film making line via a coextrusion process. This multilayer polymer film was made from PET and

ECDEL 9967. ECDEL 9967, believed to be a copolyester based on 1,4 cyclohexane dicarboxylic acid, 1,4-cyclohexane dimethanol, and polytetramethylene ether glycol, is commercially available from Eastman Chemicals Co., Rochester, N.Y. A feedblock method (such as that described by U.S. Patent No. 3,801,429) was used to generate about 209 layers with an approximately linear layer thickness gradient from layer to layer through the extrudate. The PET, with an Intrinsic Viscosity (IV) of 0.6 dl/g was delivered to the feedblock by an extruder at a rate of about 34.5 kg/hr and the ECDEL at about 32.8 kg/hr. After the feedblock, the same PET extruder delivered PET as protective boundary layers to both sides of the extrudate at about 7.1 kg/hr total flow. The material stream then passed though an asymmetric two times multiplier (U.S. Patent Nos. 5,094,788 and

5,094,793) with a multiplier design ratio of about 1.40. The multiplier ratio is defined as the average layer thickness of layers produced in the major conduit divided by the average layer thickness of layers in the minor conduit. This multiplier ratio was chosen so as to leave a spectral gap between the two reflectance bands created by the two sets of 209 layers. Each set of 209 layers has the approximate layer thickness profile created by the feedblock, with overall thickness scale factors determined by the multiplier and film extrusion rates.

The ECDEL melt process equipment was maintained at about 265°C, the PET (optical layers) melt process equipment was maintained at about 265°C, and the feedblock, multiplier, skin-layer melt stream, and die were maintained at about 274°C.

The feedback used to make the film for this example was designed to give a linear layer thickness distribution with a 1 :3: 1 ratio of thickest to thinnest layers under isothermal conditions. To achieve a smaller ratio for this example, a thermal profile was applied to the feedblock. The portion of the feedblock making the thinnest layers was heated to 285°C, while the portion making the thickest layers was heated to 265°C. In this manner the thinnest layers are made thicker than with isothermal feedback operation, and thickest layers are made thinner under isothermal operation. Portions intermediate were set to follow a linear temperature profile between the two extremes. The overall effect is a narrower layer thickness distribution that results in a narrower reflectance spectrum. Some layer thickness errors are introduced by the multipliers, and account for the minor differences in the spectral features of each reflectance band. The casting wheel speed was adjusted for precise control of the final film thickness, and therefore, final color.

After the multiplier, thick PET skin layers were added at about 28.8 Kg/hour (total) that was fed from a third extruder. Then the material stream passed through a film die and onto a water cooled casting wheel. The inlet water temperature on the casting wheel was about 5°C. A high voltage pinning system was used to pin the extrudate to the casting wheel. The pinning wire was positioned manually by an operator about 3 to 5 mm from the web at the point of contact to the casting wheel to obtain a smooth appearance to the cast web. The cast web was continuously oriented by conventional sequential length orienter (LO) and tenter equipment. The web was length oriented to a draw ratio of about 3.5 at about 100°C. The film was preheated to about 110°C in about 21 seconds in the tenter and drawn in the transverse direction to a draw ratio of about 3.5 at a rate of about

10% per second. The finished pre-creped film had a final thickness of about 0.7 mm.

The pre-creped film appeared cyan in color when observed under fluorescent room lighting at normal transmission, and when viewed against an opaque white background from a normal angle. The creping process achieved a compression ratio of approximately 1.5 to 1 (e.g., a 1.5 inch length of film was compressed into a length of 1 inch).

The resulting microcreped film exhibited an overall white appearance with some cyan coloration and a gold luster when viewed normally against an opaque white background. Closer examination of the film revealed that a diamond pattern was also embossed on the film during the creping operation. The embossing was most likely a cold embossing process produced by the rolls of the creping apparatus. This conclusion is strongly supported by noting that the rolls have a knurled diamond pattern on their surface that matches the pattern observed on the film. The diamond pattern is visible on the film with the naked eye and under a microscope using a low magnification setting such as 7.5 times. Finally, the creped film exhibited brilliance since the creping process produced multiple source locations that direct light back to the viewer.

Example 3

A decorative multilayer colored mirror film was prepared by microcreping an 8 inch wide multilayer colored mirror film in a manner similar to that described for Example 1. The pre-creped film was prepared in a manner identical to the pre-creped film discussed in Example 2, except that the film was preheated to about 110°C in about 13 seconds in the tenter and drawn in the transverse direction to a draw ratio of about 3.5 at a rate of about 15% per second, and the finished pre-creped film had a final thickness of about 0.04 mm.

The pre-creped multilayer colored mirror film exhibited regions of yellow and magenta when observed in normal transmission under fluorescent room lighting and when observed against an opaque white background from a normal angle. The resultant microcreped film had different portions with compression ratios ranging from 2: 1 to 3:1. When the creped film was observed in normal transmission under fluorescent lighting, yellow, white and magenta colors were visible. When viewed from a normal angle against an opaque white background the film had an overall white appearance, although colors such as yellow and magenta were observed to come from the pleats due to the color shifting properties of the film. The different colors (other than white) were more apparent on the portions of the film having a compression ratio of 2: 1 than on those portions having a compression ratio of 3:1 ratio, when viewed at a normal angle against an opaque white background. The portion of the film having a compression ratio of 3: 1 appeared whiter than the less compressed portions, while still maintaining an opalescent violet sheen.

Scanning electron microscopy (SEM) indicated that some delamination had occurred in this film.

Example 4

The microcreped multilayer colored mirror film prepared in Example 2 was formed into a 4 7/8 inch diameter confetti bow comprising 31 loops. The bow was produced using a Cambarloc bow machine available from Cambarloc Engineering, Inc. Lebanon, MO. Example 5

The microcreped multilayer colored mirror film prepared in Example 3 was converted into a 1/2 wide roll of film using a conventional score roll slitting process (with minimal tension). The resulting film was used to produce a 4 7/8 inch diameter bow similar to the bow described in Example 4.

Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and principles of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth hereinabove. All publications and patents are incorporated herein by reference to the same extent as if each individual publication or patent was specifically and individually indicated to be incorporated by reference.

Claims

What is claimed:

1. An article including a multilayer optical film, comprising: an optical stack that includes a plurality of layers, the layers including at least one birefringent polymer and at least one different polymer, wherein the optical stack comprises a strain-induced index of refraction differential along at least a first in-plane axis, and further wherein the optical stack has a creped configuration.

2. The article of claim 1 wherein the creped optical stack has at least one region having a specified compression ratio.

3. The article of claim 1 wherein the creped optical stack includes a plurality of regions having different compression ratios.

4. The article of claim 3 wherein a region of the creped optical stack having a higher compression ratio has an overall appearance that is more white in color than a region having a lower compression ratio.

5. The article of claim 3 wherein the plurality of regions are randomly distributed along the length of the article.

6. The article of claim 1 wherein the multilayer optical stack is configured into a decorative item.

7. The article of claim 6 wherein the decorative item is selected from the group consisting of ribbons, bows, wrapping paper, gift bags, garlands, streamers, centerpieces, and ornaments.

8. The article of claim 13 wherein the creped configuration is determined by adjustment of select process parameters.

9. The article of claim 8 wherein the select process parameters are applicable to a creping apparatus having at least one roller and a retarder element cooperating therewith, and further wherein the select process parameters include: the temperature and diameter of the roller; the position and configuration of the retarder element; and a line speed produced by the roller.

10. The article of claim 9 wherein the creping apparatus includes first and second rollers arranged to form a nip therebetween and wherein the retarder element includes a pair of blades forming a retarding cavity therebetween, the pair of blades being arranged adjacent to the nip.

11. A method of manufacturing an article including a multilayer optical film, comprising: providing a multilayer optical film comprising an optical stack that includes a plurality of layers, the layers including at least one birefringent polymer and at least one different polymer, wherein the optical stack comprises a strain-induced index of refraction differential along at least a first in-plane axis; and creping the optical stack to cause a change in its visual appearance

12. The method of claim 11 wherein the creping step causes an increase in observed brilliance.

13. The method of claim 11 wherein the creping step produces a creped optical stack that has at least one region having a specified compression ratio.

14. The method of claim 11 wherein the creping step produces a creped optical stack that includes a plurality of regions having different compression ratios.

15. The method of claim 14 wherein a region of the creped optical stack having a higher compression ratio has an overall appearance that is more white in color than a region having a lower compression ratio.

16. The method of claim 14 wherein the plurality of regions are randomly distributed along the length of the article.

17. The method of claim 11 further comprising the step of configuring the multilayer optical stack into a decorative item.

18. The method of claim 17 wherein the decorative item is selected from the group consisting of ribbons, bows, wrapping paper, gift bags, garlands, streamers, centerpieces, and ornaments.

19. The method of claim 11 wherein the step of creping the optical stack includes the step of adjusting select process parameters to determine the creped configuration.

20. The method of claim 19 wherein the select process parameters are applicable to a creping apparatus having at least one roller and a retarder element cooperating therewith, and further wherein the select process parameters include: the temperature and diameter of the roller; the position and configuration of the retarder element;; and a line speed produced by the roller.

21. The method of claim 20 wherein the creping apparatus includes first and second rollers arranged to form a nip therebetween and wherein the retarder element includes a pair of blades forming a retarding cavity therebetween, the pair of blades being arranged adjacent to the nip.