Patent Application
20170204295
The present invention is generally related to micro-structured thin films. In particular, the present invention relates to micro-structured thin films that provide improved dampening performance.
As electronic devices (e.g., mobile phones and tablets) become increasing thinner, the dampening layers that provide drop and shock absorption must typically be less than about 20 millimeters in thickness. In applications requiring sound, vibration and shock absorption the dampening layers can be made of foams based on different chemistries, such as polyurethanes, polyolefins and acrylics. The dampening performance of these foams is strongly dependent on the chemistry as well as the size and type of cell structures of the foam. With the increasing demand for thinner display devices and thinner bond lines, the foams are required to offer similar or better cushioning characteristics at lower thickness values.
Current dampening layers are based on either open or closed cell foams of acrylic, polyolefin, natural or synthetic elastomers or polyurethanes. The gas in the foam cell structures helps in absorbing the stress generated during different mechanical processes. However, large cell volumes (typically around 30-40 vol %) are required to offer the required levels of stress absorption. With increasing emphasis on reducing display thickness, the thickness of damping layers has been reduced to less than 200 μm. Foams at these thickness values can suffer from multiple disadvantages in process handling and reworkability, due to poor cohesive strength.
In one embodiment, the present invention is a dampening structure including a polymer layer having a first surface and a second surface. The first surface includes a plurality of micro-structures, wherein each of the micro-structures has a width of less than about 400 microns. An elastic modulus of the polymer layer is greater than about 0.1 MPa and less than 5 GPa at 25 C. The polymer layer is non-tacky.
In another embodiment, the present invention is a dampening structure including a polymer layer and a sealing layer. The polymer layer has a first and a second surface. At least one of the surfaces includes a plurality of topographical features having discrete cavities. The sealing layer is positioned adjacent to the surface comprising the plurality of topographical features. The sealing layer seals at least a portion of the cavities, entrapping gas therein.
These figures are not drawn to scale and are intended merely for illustrative purposes.
The dampening structure of the present invention improves the dampening performance or shock absorbance of thin layers, such as films and/or foams. The dampening structure includes a polymer layer having a first surface and a second, opposing surface. Micro-structured cavities, e.g. channels or pockets, and/or protrusions (collectively micro-structures) are incorporated on at least one of the first and second surfaces of the polymer layer and function to improve product handling due to their dampening effect. The micro-structures provide a topographical surface and are an alternate route to foaming to increase the air volume in the polymer layer without significantly affecting the mechanical properties of the polymer layer. In addition to improved shock absorbance, the microstructures, i.e. dampening structures, of the present invention have improved repositionability, surface wetting, layer application and handling. Also, the shape and dimensions of the micro-structured polymer layer offers the ability to modify the amount local pressure in the micro-structured elements during lamination.
The polymer layer 12 may be any non-tacky polymer layer that is substantially free of inorganic particles that have a Mohs hardness of less than about 5, and particularly less than about 3. Substantially free of inorganic particles means less than about 5%, particularly less than about 3% and more particularly less than about 1% inorganic particles. In some embodiments, the polymer layer 12 does not include inorganic particles. The polymer layer 12 has a peak in the Tan delta of at least about 0.3, particularly at least about 0.5 and more particularly at least about 0.7, when measured by dynamical mechanical thermal analysis (DMTA). The DMTA tests may be conducted using any conventional DMTA methods. The DMTA may be conducted using a tensile mode configuration. The frequency employed can be from 0.1 to 1,000 Hz, 1 Hz being typical. The DMTA scan may be conducted over a temperature range of about at least 40° C. above and 40° C. below the peak in Tan delta, wherein the temperature increase during the DMTA may be selected in a range of from about 0.1 degrees C./min to about 10 degrees C./min. The thickness of the polymer layer 12 for testing may be in the range of about 50 microns to about 5 mm. The width of the sample may be in the range of about 1 mm to about 10 mm. The gauge length may be in the range of about 10 mm to 30 mm. The strain of the sample during testing may be in the range of about 0.01 to 2 times of the gauge length.
In one embodiment, the polymer layer 12 has an elastic modulus at 25° C. of about of about 0.01 MPa, or greater, 0.1 MPa or greater, 0.5 MPa or greater or even 1 MPa or greater. The elastic modulus may be about 5 GPa or less, about 1 GPa or less or even about 0.5 GPa or less. The polymer layer 12 may be a film or a foam. Examples of suitable polymers include, but are not limited to: acrylics, polyolefins, natural or synthetic elastomers and polyurethanes. Polyurethanes are particularly suitable as the polymer layer. The polymer layer 12 may optionally contain materials with functionality to improve electrical conductivity, thermal conductivity, electromagnetic interference (EMI) shielding, EMI absorption, or a combination thereof. In some embodiments, the polymer layer 12 and/or adhesive layer(s), when present, may include at least one of electrically conductive particles and an electrically conductive interconnected layer. In some embodiments, the polymer layer 12 and/or adhesive layer(s), when present, may include at least one of thermally conductive particles or a thermally conductive interconnected layer. In some embodiments, the polymer layer 12 and/or adhesive layer(s), when present, may include at least one of EMI absorbing particles, EMI shielding particles, an EMI absorbing interconnected layer and an EMI shielding interconnected layer. The cavities and/or protrusions formed on the surface of the polymer layer 12 dissipate stress by allowing air to bleed through the layer. The shape and dimensions of the cavities and/or protrusions are controlled by varying the topographical surface of the micro-structured liner 14. The topography of the first surface 18 of the polymer layer 12 will have the inverse topography of the micro-structured liner 14.
The second surface 24 of the micro-structured liner 14 includes topography created by a plurality of features 30 having shapes and dimensions which correspondingly create the cavities and/or protrusions (microstructures 32) in the polymer layer 12. The topography may include features such as protrusions and/or cavities interconnected in at least one dimension in the x, y plane of at least one of its major surfaces, and preferably, in at least two dimensions. In this case, the corresponding formed microstructures 32 of the polymer layer 12, having the inverse microstructure 30 of the micro-structured liner 14, may be channels allowing for air bleed. If the micro-structured liner 14 includes topography that includes only discrete protrusions, the corresponding formed microstructures 32 of the polymer layer 12 may be discrete cavities or pockets that allow for the entrapment of a fluid, e.g. a gas. The shape and size of these protrusions and/or cavities can be regular or irregular across the topographical surface of the structured liner. Likewise, the interconnection can follow a regular or irregular pattern in at least one dimension in the x, y plane of least one of the major surfaces of the structured liner. All of the key dimensions, e.g. height, width, shape and spacing, of the micro-structured features 30 of the micro-structured liner 14 are selected based on the final topography desired in the surface of the polymer layer. In one embodiment, each of the features 30 has a height of between about 5 and 200 microns and particularly between about 5 and 25 microns and a width of between about 15 and about 400 microns particularly between about 50 and about 300 microns. In another embodiment, each of the features 30 has a height/depth of between about 10 and about 200 microns particularly between about 25 microns and about 75 microns. In one embodiment, the center distance between the respective protrusions or the respective cavities is between about 20 and about 500 microns particularly between about 20 and about 100 microns. In one embodiment, for a 100 micron thick polymer layer, the features have a height of between 20 and 50 microns. In another embodiment, for a 100 micron thick polymer layer, the features have a height of between 30 and 45 microns.
The topographical surface of the micro-structured liner 14 may include any shaped features known to those of skill in the art without departing from the intended scope of the present invention. For example, the micro-structured features 30 of the micro-structured liner 14 may include, but are not limited to: posts, pyramids, trapezoids, channels, etc. In addition, the micro-structures do not have to be arranged in a regular or repeating pattern, such as lines or a cross pattern. The micro-structures 30 may also be in a random pattern. In one embodiment, the micro-structures 30 create channels, pockets, or combinations thereof.
In the embodiments of the present invention, a micro-structured polymer layer, i.e. a micro-structured polymer layer, is produced. In a first embodiment shown in
A fourth embodiment of a dampening structure 300 of the present invention is similar to the third embodiment of the micro-replicated structure except that in the fourth embodiment, as shown in cross-sectional views in
The pockets 420 allow air to be trapped within the micro-structured polymer layer 402a when a sealing layer 422, shown in
In one embodiment, the micro-structured surfaces of the dampening structures of the present invention are formed by preparing a curable polymeric precursor and coating the precursor between release liners. At least one of the release liners includes a micro-structured surface having the inverse surface of the desired surface on the polymer layer. After coating, the precursor is cured via heat or actinic radiation (e.g. UV radiation), to form the polymer layer. However, if a soft thermoplastic polymer or thermoplastic elastomer is used, a heat (above the glass transition temperature or softening temperature) and pressure (greater than 1 pound per lineal inch (PLI) embossing process may be used to form the micro-structured surface of the polymer layer. Additionally, if the pressure-sensitive adhesive is cast out of a solvent solution which is subsequently dried in a thermal oven, the dried pressure-sensitive adhesive will take on the micro-structured image.
The present invention is more particularly described in the following examples that are intended as illustrations only, since numerous modifications and variations within the scope of the present invention will be apparent to those skilled in the art. Unless otherwise noted, all parts, percentages, and ratios reported in the following example are on a weight basis.
MSL1 was prepared by a conventional micro-embossing technique, see for example U.S. Pat. No. 6,524,675 (Mikami, et. al.) and U.S. Pat. No. 6,759,110 (Flemming, et. al.) which are incorporate herein in their entirety by reference. The release liner was embossed to form patterns of protruding ridges on the front side surface. The liners generally had about 125 micron thick paper core, about a 25 micron thick polyethylene with a matte finish on the back side, about a 25 micron thick polyethylene with a glossy finish on the front side, and a commercial silicone coating on the glossy polyethylene side. The pattern was formed under heat and pressure using an engraved embossing tool. The final pattern embossed in the liner was an array of two sets of intersecting parallel ridges forming a square grid array of cavities oriented 45 degrees from the axis of the tool. The ridges had a trapezoidal cross-section shape. The base of the trapezoid was about 130 microns in length and the top of the trapezoid was about 26 microns in length. The angles between the two interior sidewalls of the trapezoid and the base were both about 30°. The height of the trapezoid was about 30 microns. The lineal density of the trapezoidal cross-section shaped ridges was about 15 lines per inch, yielding a repeat pitch (center to center distance between ridges) of about 1693 microns. The embossing tool used to create this liner pattern had the inverse of this pattern.
MSL2 was prepared similar to MSL1, except the feature dimensions were different. MSL2 had a square grid array of truncated, square pyramid shaped cavities oriented 45 degrees from the axis of the embossing tool. These cavities created a corresponding array of intersecting linear ridges, the linear ridges being perpendicular to one another. The pyramid top, which protruded into the liner and represented the bottom of the cavity, was about 2 microns in length. The pyramid base was about 286 microns and the pyramid height (depth) was about 25 microns. The lineal density of the truncated, square pyramid shaped cavities was about 87 per inch, yielding a repeat pitch (center to center distance between cavities) of about 292 microns and a corresponding space between cavities of about 6 microns. The embossing tool used to create this liner pattern had the inverse of this pattern.
MSL3 was a commercially available liner available under the trade designation 83703BE available from 3M Korea, LTD., Seoul, South Korea. 83703BE was a double side pressure sensitive adhesive (psa) transfer tape having black PET as the core substrate and dual release liners adjacent the psas. One of the psa's major surfaces had a micro-structured surface, corresponding to the inverse micro-structure of the adjacent release liner. The other Acrylic psa had a substantially flat major surface corresponding to the substantially flat major surface of the adjacent release liner.
A polyol premix was prepared by mixing 75 parts by weight (pbw) Carpol GP-1000, 25 pbw Carpol GP-700, 9.5 pbw Fyrol HF-5, 2.0 pbw REPI 90332 Black, 0.1 pbw Bicat 8210 and 0.2 pbw Bicat Z. The components were placed in a DAC cup, available from FlackTek Inc., Landrum, S.C., and mixed using a Hauschiid SPEEDMIXER DAC 400 FVZ, available from FlackTek Inc., operating at 2100 rpm for 2 minutes.
An isocyanate premix was made prepared from 90 pbw Rubinate 1670 and 10.5 pbw Fyrol HF-5. The components of the isocyanate premix were mixed as described above.
The two premix solutions were combined by using 2 parts by volume of the polyol premix and 1 part by volume of the isocyanante premix into a syringe having a static mixer. The liquid was dispensed from the syringe through the mixer forming a reactive polyurethane precursor solution.
Polyurethane thin films were made by knife coating the polyurethane precursor between the appropriate release liners (see Table 1). In all the examples and the comparative example, the polyurethane precursor was coated at a 5 mil (127 micron) thickness. The polyurethane precursor was then cured at 170° F. for 2 minutes, yielding a tack free polyurethane film. All the Examples, except Comparative Example 5, had at least one major surface having a micro-structured surface, produced via the coating process and corresponding adjacent micro-structured liner surface. The micro-structured surface of the polyurethane film was the inverse structure of that of the micro-structured release liner. When MSRL3 was used as the top liner, the release liner (of the as received double sided tape) adjacent micro-structured psa surface was removed, prior to coating. The polyurethane precursor was then coated such that it was adjacent to the micro-structured psa surface of MSRL3.
Example 4 was prepared similarly to Examples 1-3, except the bottom release liner was MSRL3 and the top release liner was MSRL1. In this case, the release liner (of the as received double sided tape MSRL3) adjacent the substantially flat surface was removed from MSRL3. When coated, the polyurethane precursor was coated adjacent the substantially flat surface of the psa of MSRL3 and the micro-structured surface of MSRL1. After curing the polyurethane precursor, the polyurethane film consisted of a laminate construction including one major surface of the micro-structured polyurethane (the surface that was adjacent to micro-structured surface of MSRL1) and the other major surface was the micro-structured surface of the psa of MSRL3. The construction still includes release liners that are in contact with the two outer major surfaces of the laminate (micro-structured polyurethane and micro-structured psa), the release liners can be removed prior to use.
Examples 1 and 2 produced polyurethane films that included one major surface being micro-structured. Examples 3 and 4 produced polyurethane films that included both major surfaces being micro-structured. Comparative Example 5 had no micro-structured surfaces. The constructions still includes release liners that are in contact with the two outer major surfaces of the polyurethane film, the release liners can be removed prior to use.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2015/041595 | 7/22/2015 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62028859 | Jul 2014 | US |
