Patent Application
20110171440
1. Field of the Invention
The present invention relates to a decorative film and an In Mode Decoration/Forming (IMD) process, and more particularly, to an IMD process that enables colors to change associated with viewing angles by virtue of a difference in refractive indices of different layers within a plurality of optical film layers and a decorative film thereof.
2. Description of Related Art
The In Mold Decoration/Forming (IMD) technology has now been developed and widely applied in projects of modifying plastic surfaces. Nowadays, the IMD technology has found wide application in exterior parts of electronic products, household appliances, automobiles and the like. The IMD technology may be subdivided into IMR, IML, IMF and etc., and mainly comprises three processes, i.e., printing, forming and molding. However, when the conventional IMD technology is employed to fabricate a mirror with a sparkling enclosure or to deliver a color conversion effect, one or more layers of metallic or pigment coatings must be coated on a surface of a substrate. If an effect of changing colors associated with viewing angles is desired, multi-layer vapor deposition will be further needed. Unfortunately, such a process is costly and the metallic coatings exhibit poor ductibility, which leads to a low yield rate of the IMD process and makes it impossible to improve quality of the overall product.
A conventional multi-layer optical film is an optical component which allows light of a certain wavelength band to transmit therethrough but reflects light of other wavelength bands. U.S. Pat. No. 3,610,729 proposed a multi-layer optical film formed by laminating two kinds of optical layers together, where the two kinds of optical layers are made of polymers of different refractive indices. Difference in refractive indices of the two different polymers can lead to constructive interference of incident light. Thereby, the multi-layer optical film can allow light of a specific wavelength to transmit therethrough but reflect light of other wavelengths.
Generally speaking, optical layers of a multi-layer optical film are in form of a quarter wave stack. By the quarter wave stack, it means that, each of the optical layers is of a thickness equal to a quarter of a wavelength to which the optical layer corresponds. Here, the optical thickness is a product of a thickness of the optical layer and a refractive index thereof.
U.S. Pat. No. 5,976,424 proposed a method of producing a multi-layer optical film, the production process of which is as follows: firstly, a first resin and a second resin are provided; then, the first resin and the second resin are extruded into a resin stream, which comprises a plurality of layers and has a first major surface and a second major surface, wherein at least some of the plurality of layers comprises the first resin while at least some other of the plurality of layers comprises the second resin, and wherein the number of layers having a thickness of less than k microns (μm) and disposed within 400 μm in depth of the first major surface is m, and the number of layers having a thickness of less than k μm and disposed within 400 μm in depth of the second major surface is n, where m>n, k≦10; further, the resin stream is casted against a casting surface so that the first major surface is in contact with the casting surface.
Accordingly, in view of the shortcomings of the aforesaid multi-layer vapor deposition process and the metallic coating films, the present inventor has made great efforts to impart a sparkling appearance and an effect of changing colors associated with viewing angles to an IMD product through applications of the design principles of multi-layer optical films.
A primary objective of the present invention is to provide a decorative film and an In Mode Decoration/Forming (IMD) process. With superior formability, the decorative film is very suitable for use in an IMD process without the problem of cracking; on the other hand, a difference in refractive indices exists in at least one direction between the film layers made of different materials of the decorative film, which imparts a particular quality to a final product with sparkling colors in appearance in accordance with an effect of changing colors associated with different viewing angles.
To achieve the above-mentioned objectives, the present invention provides a decorative film, comprising: a plastic substrate, comprising a surface; a plurality of optical film layers, formed by laminating optical film layers of at least two different materials onto the surface, wherein each of the optical film layers and another optical film layer are stretched in at least one direction to create a difference in refractive indices of no less than 0.1 between the optical film layers.
To achieve the above-mentioned objectives, the present invention also provides an In Mode Decoration/Forming (IMD) process, comprising the following steps of: step 1: providing a plastic substrate having an upper surface and a lower surface, a plurality of optical film layers made of at least two different materials, a skin layer and a plastic material; step 2: laminating the plurality of optical film layers made of the at least two different materials onto the upper surface, wherein each of the optical film layers and another optical film layer are stretched in at least one direction to create a difference in refractive indices of no less than 0.1 between the optical film layers; step 3: attaching the skin layer onto the upper surface of the plurality of optical film layers to form a decorative film; step 4: forming the decorative film into a predetermined shape; and step 5: injection molding the plastic material onto the lower surface of the decorative film of the predetermined shape.
Referring now to
Step 1: a plastic substrate 10 having an upper surface and a lower surface, a plurality of optical film layers made of at least two different materials (i.e., the first resin film layers 110 and the second resin film layers 111), a skin layer 12 and a plastic material 20 are provided. The plastic substrate 10 is primarily an optical film with good formability, and is made of, for example but not limited to, polyethylene terephthalate (PET), polycarbonate (PC), tri-acetyl cellulose (TAC), polymethylmethacrylate (PMMA), methylmethacrylate styrene (MS) or cyclic olefin copolymer (COC). Additionally, in embodiments of the present invention, thickness of the plastic substrate 10 may be adjusted depending on different applications.
Step 2: the plurality of optical film layers is laminated onto the upper surface of the plastic substrate 10. The plurality of optical film layers are formed by laminating two or more kinds of materials together (e.g., the first resin film layers 110 and the second resin film layers 111 shown in
The plurality of optical film layers are fabricated through the following steps.
Step A: the aforesaid two or more kinds of polyester materials are coextruded into a plurality of polyester film layers that are alternately arranged; and step B: the plurality of polyester film layers are axially (uniaxially or biaxially) stretched to create a predetermined difference in refractive indices in at least one direction between the optical film layers made of different polyester materials. The difference in refractive indices is no less than 0.1, and most preferably is 0.29, and this can lead to constructive interference of incident light. Thereby, the plurality of optical film layers can allow light of a specific wavelength to transmit therethrough but reflect light of other wavelengths. As a result, by means of these optical film layers, a sparkling appearance and an effect of changing colors with different viewing angles can be obtained.
However, to impart formability to the plurality of optical film layers to make them more suitable for the IMD process, the plurality of optical film layers may, upon being stretched, be introduced into a cooling zone to be cooled at a cooling temperature of 60° C. to 120° C. for 1 second (s) to 5 s and then subjected to a heat setting treatment to impart good formability to the plurality of optical film layers. It shows properties and formability of the plurality of optical film layers after being stretched using different stretching process parameters, wherein the plurality of optical film layers are characterized in that:
1. After being subjected to a heat setting treatment at a temperature of 150° C. for 30 min, the plurality of optical film layers exhibit a ratio of machine direction (MD) shrinkage to transverse direction (TD) shrinkage of 0.8 to 1.2. This characteristic of the plurality of optical film layers is an important indicator of formability. By using the process of the present invention, the ratio of MD shrinkage to TD shrinkage of the plurality of optical film layers may be controlled to be from 0.8 to 1.2, i.e., shrinkages in the two directions are very close to each other. As a result, after the thermal forming step (e.g., injection molding at a high temperature and under a high pressure), dimensions of the plurality of optical film layers will not vary greatly in the two directions; in other words, after the injection molding, dimensions of the plurality of optical film layers in the MD direction and the TD direction are very close to each other, which helps to improve formability of the plurality of optical film layers greatly.
2. The plurality of optical film layers has a bowing region of no greater than 1.5%. The bowing region is calculated according to Equation 1 as follows:
Bowing region=(B/W)×100%, Equation 1
where W is a width in the transverse direction, and B is a maximum depression depth. Referring to
Step 3: a skin layer 12 is attached onto the upper surface of the plurality of optical film layers to form a decorative film 100 with formability (as shown in
Step 4: the decorative film 100 with formability is formed into a predetermined shape, as shown in
Step (5): a plastic material 20 is formed and attached onto the lower surface of the plastic substrate 10 of the decorative film 100, which has been formed into the predetermined shape, to produce an IMD product 1, as shown in
According to the above embodiment, the plurality of optical film layers with superior formability and having difference in refractive indices between different film layers is applied, through attachment, to the IMD process to produce a product that has an effect of changing colors with different viewing angles; and the plastic substrate 10, the plurality of optical film layers and the skin layer 12 are attached together to produce the decorative film 100.
Additionally, the present invention further provides another embodiment of the IMD process that uses the decorative film 100. The IMD process of the second embodiment differs from the first embodiment in that, the aforesaid attachment step is replaced by a coextrusion process in the second embodiment. This IMD process comprises the following steps of (referring back to
Step 1: a plastic substrate 10, a plurality of polyester films made of two or more kinds of polyester materials and a skin layer 12 are laminated, through coextrusion, into an extruded multi-layer film. In this step, instead of the attachment step in the above embodiment, materials of the individual film layers are coextruded into one piece, wherein the plastic substrate 10 has good formability.
Step 2: the coextruded multi-layer film is then axially (uniaxially or biaxially) stretched to form a decorative film 100 with formability (as shown in
Step 3: the decorative film 100 with formability is formed into a predetermined shape, as shown in
Step 4: forming and attaching a plastic material 20 onto the lower surface of the plastic substrate 10 of the decorative film 100 with the predetermined shape, as shown in
Steps 3 and 4 described herein are the same as steps 4 and 5 of the first embodiment and, thus, will not be further described herein.
Next, the present invention will utilize the two embodiments described above to fabricate an IMD product 1.
First Experiment Group:
Initially, the present invention can utilize the first embodiment to fabricate an enclosure having a mirror effect (i.e., a first product).
Step 1: a plastic substrate 10 made of polycarbonate is provided.
Step 2: a plurality of optical film layers are attached onto an upper surface of the plastic substrate 10. In this step, a UV curable adhesive is used to attach the plurality of optical film layers onto the plastic substrate 10 made of polycarbonate. Here, with a total thickness of 260 micrometers (μm), the plurality of optical film layers includes 302 layers of PEN (i.e., the first film layers 110) and PMMA (i.e., the second film layers 111) that are formed through coextrusion and laminated alternately. Then the plurality of optical film layers is biaxially stretched, either being stretched in the machine direction (MD) and the transverse direction (TD) by 2.8 times and 3.5 times individually or being stretched in both directions by 3.0 times simultaneously. After being stretched, the PEN film layers and the PMMA film layers exhibit therebetween a difference in refractive indices of approximately 0.26 and a ratio of extruded thickness of 1/1.165, which represents a gradient variation in thickness.
Step 3: the skin layer 12 made of PMMA is attached onto an upper surface of the plurality of optical film layers. The skin layer 12 made of PMMA is of a high hardness to provide a satisfactory protection capability. Then, subsequent forming and molding processes are performed to complete the enclosure of the electronic product.
Next, the second embodiment is utilized to fabricate an enclosure having a mirror effect as follows. A 1050 μm thick decorative film having 304 layers is produced, through coextrusion, from a plastic substrate 10 made of polycarbonate, PEN materials and PMMA materials, and a skin layer 12 made of PMMA, in which the skin layer 12 made of PMMA is 40 μm in thickness and the plastic substrate 10 made of polycarbonate is 750 μm in thickness. The skin layer 12 used in this experiment group is made of a modified PMMA material which, through the aforesaid stretching and orientation, may get a hardness of at least 2H to effectively improve the protection capability.
Second Experiment Group:
The present invention can utilize the first embodiment to produce an enclosure having a color-changing effect (i.e., a second product). In this experiment group, 218 layers of PMMA (i.e., the first film layers 110) and COPEN (i.e., the second film layers 111) that are laminated alternately are coextruded to form a plurality of optical film layers of 220 μm in thickness. The plurality of optical film layers is further biaxially stretched, either being stretched in the machine direction (MD) and the transverse direction (TD) by 3.0 times and 3.7 times individually or being stretched in both directions by 3.2 times simultaneously. Then the plurality of optical film layers is attached onto the plastic substrate 10 and, meanwhile, the skin layer 12 is attached onto the plurality of optical film layers for purpose of protection.
For this experiment group, the second embodiment may also be utilized to co-extrude the plastic substrate 10, the COPEN material and the PMMA material, and the skin layer 12 into a decorative film 100 comprising 220 layers, and then subsequent steps such as axial stretching, forming and molding are performed to produce the IMD product 1 having a color-changing effect.
Third Experiment Group:
The present invention can utilize the first embodiment to produce an enclosure having a color-changing effect (i.e., a third product). In this experiment group, 247 layers of PMMA (i.e., the first resin film layers 110) and COPEN (i.e., the second resin film layers 111) that are laminated alternately are coextruded to form a plurality of optical film layers of 230 μm in thickness. The plurality of optical film layers is further biaxially stretched, either being stretched in the machine direction (MD) and the transverse direction (TD) by 3.0 times and 3.7 times individually or being stretched in both directions by 3.2 times simultaneously. Then the plurality of optical film layers is attached onto the plastic substrate 10 and, meanwhile, the skin layer 12 is attached onto the plurality of optical film layers for purpose of protection.
For this experiment group, the second embodiment may also be utilized to co-extrude the plastic substrate 10, the plurality of optical film layers made of COPEN and PMMA, and the skin layer 12 into a decorative film 100 comprising 249 layers, and then subsequent steps such as axial stretching, forming and molding are performed to fabricate the final product.
The present invention further discloses an IMD product 1, comprising: a plastic material 20; and a decorative film 100 with formability disposed on the plastic material 20. The decorative film 100 comprises: a plastic substrate 10; a plurality of optical film layers disposed on the plastic substrate 10, being formed by laminating two or more kinds of polyester materials together, wherein a predetermined difference in refractive indices exists between the film layers of different polyester materials; and a skin layer 12 disposed on the plurality of optical film layers. Properties of the plurality of optical film layers have already been described in the aforesaid process steps and, thus, will not be further described herein.
