JP2008015442A - Extruded polymer plate for anisotropic light scattering having high dimensional stability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical diffuser which has improved scattering behavior, furthermore has an excellent mechanical characteristic and accordingly has no problem in processing. <P>SOLUTION: The optical diffuser is constituted of a transparent polymer and glass fiber and is obtained by an extrusion method, wherein the inorganic glass fiber and the polymer are mixed with a mass ratio between 1:10 and 1:10000 and an obtained mixture is extruded. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a transparent plastic (transparent polymer) material extruded in the form of a semi-finished product after the introduction of a diffuser and / or glass fiber. The plastic molded body has excellent mechanical properties as well as excellent light diffusion characteristics in a preferable diffusion direction.

Various principles have already been used to achieve anisotropic light diffusion. The most important aspects of the present invention are as follows:
1. Mechanically uniaxially stretching a polymer substrate containing spherical diffusion beads of a different polymer material,
2. The glass fibers are oriented parallel to each other in the polymer substrate.

  A configuration was investigated and proposed, primarily by 3M, in which spherical diffusing particles were formulated in a polymer substrate, and these diffusing particles had a different refractive index than the substrate. Subsequent uniaxial stretching of the entire polymer plate simultaneously results in stretching of the spherical particles, thus making the particles elliptical. This shape thus leads to anisotropic diffusion behavior throughout the material.

  WO 02/057384 (3M) describes a polymer composition consisting of an adhesive and a longitudinal structure embedded therein. The adhesive is optically isotropic and the refractive indices of the two materials differ by at least 0.01. The longitudinal structure is made of plastic.

  WO 02/071148 (3M) describes a screen provided with an adhesive in which longitudinal structures are dispersed. Its longitudinal structure is the same as in WO 02/057384.

  WO 2004/106989 (Eastman Kodak) describes polymer films from two polymers with anisotropic optical properties. In addition to weighted refraction by a longitudinal member (longitudinale Teil), the photorefractive effect is enhanced by a three-dimensional structure on the film surface.

  US-OS 2005/0036199 (3M) describes a screen in which an adhesive is present on the screen and some longitudinal structures are present in the adhesive. The refractive index of the adhesive and the vertically long structure differ by at least 0.01. In some cases, a polarizer, a Fresnel lens or a reflector may be present.

  US-PS 5,940,211 (US Philips Corp.) describes an optical system that polarizes light passing through and thus achieves an anisotropic distribution of light intensity.

  US-PS 6,123,877 (Nashua Corporation) describes a method for directing anisotropic light with polymer substrates having different refractive indices in generating anisotropic light. The difference in refractive index is caused by spherical particles.

  US-OS 2003/0175466 (Suggle Mion) describes a film with anisotropic light diffusion achieved by aligning a cage structure in a polymer substrate. The rod is oriented in one direction, and the refractive index in the axial direction of the rod and the refractive index in the corresponding direction of the substrate are different. The rod has a diameter less than 200 μm and a length longer than 800 μm. The rod-shaped body is made of a liquid crystal aromatic polyester. Improvements in the mechanical properties of anisotropic plastic moldings are not discussed in the prior art.

  European Polymer Journal 41 (2005) 1729-1737. Kim describes the effect of thermophysical properties, humidity and stiffness on a diffuser plate made of substrate PMMA modified with glass fibers.

  Kim found that the addition of glass fiber dramatically reduces warpage (deflection) under the action of the ambient conditions described above. In addition, it can be confirmed that the influence on the optical characteristics is negligible, and no anisotropic diffusion characteristics are observed.

The following properties are found:
1. The storage modulus increases as the proportion of glass fibers increases (2.2 → 3.2 GPa at T = 25 ° C.).

2. The glass transition temperature goes upward (T _g 111.7 → 113.3 ° C. (20% glass fiber ratio)).

  3. Water absorption is greatly reduced (24 hours: 0.4% → 0.2%).

4). Warpage decreases.
WO02 / 057384 WO02 / 071148 WO2004 / 106989 US-OS2005 / 0036199 US-PS 5,940,211 US-PS 6,123,877 US-OS 2003/0175466 European Polymer Journal 41 (2005) 1729-1737. Kim

  In view of the prior art, the object of the present invention is to provide a further optical diffuser which has an improved diffusion behavior and still has good mechanical properties and thus has no processing problems. Met. A further problem was to provide a simple and inexpensive method for producing anisotropic plastic moldings.

  The subject is a diffuser composed of the transparent polymer and glass fiber according to claim 1, wherein the inorganic glass fiber and the polymer are mixed at a mass ratio of 1:10 to 1: 10000 and extruded. This is solved by a light diffuser obtained by the extrusion method according to claim 10.

  Transparent plastics include polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate (PET), cycloolefin copolymer (COC), polystyrene (PS), polyester, polyolefin, and copolymers that combine the above monomers. To do. In some cases, the plastic molding material may also have impact strength. In particular, the use of a transparent PMMA molding material is preferred.

  The glass fibers used consist of A-glass, C-glass, D-glass, E-glass, AR-glass, ECR-glass and R-glass, which are in terms of composition and thus in refractive index. Different from each other. Commercially available products differ further in terms of fiber length and diameter, and in particular coatings (coating) that ensure compatibility with various polymer substrates. These glass fibers are available from, for example, PPG Industries Glass & Fiber GmbH or Saint Gobain.

  According to the invention, the difference in refractive index between the polymer and the inorganic glass fiber may be at least 0.01, preferably at least 0.05.

  The diameter of the inorganic glass fiber used in the present invention may be 1.0 to 100 μm. Furthermore, the average aspect ratio of the inorganic glass fibers may be 1-10, preferably 1-20, in particular 1-50.

  A possible production method for anisotropic plastic moldings is to mix a certain amount of glass fibers with the respective plastic molding material, and using commercial extruders, the conditions adapted to the respective plastic There is to push down. Here, the inorganic glass fibers and the polymer can be mixed in a mass ratio of 1:10 to 1: 10000 and extruded.

  Other possible manufacturing methods for anisotropic plastic moldings are the two-stage process, in which a predetermined amount of glass fiber and a portion of the plastic material are individually blended to produce a masterbatch and the second stage In mixing a predetermined amount of the masterbatch with the respective plastic molding material and extruding it using a customary extruder under conditions adapted to the respective plastic. In that case, mass ratio of an inorganic glass fiber and a polymer in a masterbatch may be 1: 5-1: 500.

  In one advantageous embodiment, in the production of the masterbatch, glass fibers are metered into the hot plastic melt via a side filler (Seitenstopfwerk), which is particularly suitable for gentle processing. .

  The anisotropic light diffusing plastic mixture can also be applied on at least one side on the plastic molding as a coextrudate in the extrusion process.

  The main usefulness of the anisotropic light diffusing plate is to improve energy efficiency.

  In the following applications, how energy efficiency is increased by this anisotropic light diffusion will be described as an example.

1. Backlight unit for large-screen display applications (large-screen flat displays such as television receivers)
Large backlight units are usually backlit in a direct manner. This is because edge lights do not combine with the required brightness over a large surface. Direct backlighting is often composed of a so-called CCFL (cold cathode fluorescent lamp). This is because CCFL is inexpensive and relatively robust. The fluorescent lamp itself has a cylindrical structure (long structure, for example, 30 cm long and 2 mm diameter), and is installed in the backlight unit parallel to each other and perpendicular to the viewing surface. Therefore, in order to obtain a uniformly lit image, the diffuser plate must be installed in front of the CCFL light source device. The distance from the light source (on the other hand from the original display) must be kept small. This is because flat displays provide only a very limited mounting space. Similarly, it is desirable to make the diffuser thin (usually 2 mm thick). Due to the small spacing between the light source and the diffuser, the required “uniformity” of the adjusted brightness profile can only be achieved with a very thick diffuser. However, it is a disadvantage that the total light transmittance is only 40-60% (HWW = 70-86 °), that is, high losses are produced. To date, in this case, only isotropic diffusers that diffuse light in all spatial directions have been used. Here, the anisotropic diffuser plate has the advantage that it diffuses light advantageously on the face of the viewer, ie perpendicular to the direction of the fluorescent lamp. Strictly speaking, this is the diffusion direction necessary for the uniformity of the light irradiation field. Downward or upward diffusion (which the viewer does not confirm in any case) is not necessary at all in this case. This is because the light source emits uniformly over its length (over a wide range). Therefore, high light diffusion must be effective only for one main axis (perpendicular to the direction of the fluorescent lamp device) and in another main axis direction (parallel to the direction of extension of the light source), an isotropic diffuser Clearly less light diffusion than “less waste”. Therefore, in order to achieve the same brightness on the viewer side, in the case of an anisotropic diffuser, less light energy is required for input coupling as compared to a device having a brightness enhancement film (BEF). .

2. Rear Projection Plate that Diffuses Anisotropically In the case of rear projection, an image is projected onto the screen from behind (ie, on the side facing the viewer) by a beamer. Therefore, rear projection is based on light transmission, as opposed to front projection. In the case of such a screen, it is important that the images have as much brightness as possible at various viewing angles. For this purpose, the light has to be diffused into the space accordingly. Due to the size of the screen, again no light diffusion is needed above or below, while diffusion in the horizontal plane is highly desired. In the range of rear projection, the effect is achieved by the use of lenticular lenses on the viewer side surface. Since light is concentrated and diffused on the viewer's surface, higher output power can be obtained and uniformity on the viewer's surface can be achieved for the same input coupling output.

The temperature in the heating zone of the extruder is T = 180 ° C. and T = 230 ° C., for example in the case of PLEXIGLAS® 7N (PMMA—molding material available from Roehm GmbH), the melt from the nozzle The outlet temperature is approximately T = 240 ° C. The flow rate selection should not be too high (about 10 kg / hour) and the screw speed is 175 min- ¹ .

  Of importance is an extruder manufactured by Breyer with a degassing screw having a diameter D = 60 mm, a pitch 60 mm and a length 33D = 1980 mm, and a fluted bush (Nutbuchse) attached to the feed.

  The flow field produced by the flow of the plastic melt orients the glass fibers substantially parallel in the polymer substrate. The flow field exhibits a parabolic velocity profile within the extruder nozzle, which further leads to a linear shear field, whereby the glass fibers rotate and align parallel to the extruder nozzle wall.

  In particular, two types of glass fibers differing in diameter were used.

  The average aspect ratio of the inorganic glass fiber is 1 to 10, preferably 1 to 20, particularly preferably 1 to 50.

Efforts are made to ensure that the glass fibers have a high orientation: for this the following process conditions:
• High shear rate • Narrow lip spacing • Higher melt viscosity is required in extrusion.

  The orientation of the glass fibers in the polymer is usually specified by an orientation distribution function. In this case, for each orientation direction, plot the number of glass fibers around the principal axis direction (in principle the arbitrarily chosen principal axis direction); a reasonable choice of principal axis is in the extrusion direction, which direction is flow It is the main axis of orientation due to the profile. These Gaussian distribution curves become narrower as the degree of orientation of the glass fiber increases, that is, its half-value width decreases. In the case of an ideal distribution, i.e. all glass fibers are strictly in a direction parallel to the extrusion. In the case of an ideal distribution (ie all glass fibers are strictly parallel to the extrusion direction), the Gaussian distribution curve is very narrow. The average deviation between the glass fiber and the removal direction (Vorzugsrichtung) may be between 0 ° and 45 °.

  However, the orientation distribution function cannot be defined directly or requires considerable labor. However, a very good measure for the degree of orientation is the measured optical anisotropy of the diffuser. For this purpose, BTDF (bidirectional transmission distribution function) with corresponding measurement settings. For characterization of the substantial effect of orientation, it is sufficient to determine a two-dimensional diffusion distribution curve along both orientation principal axes. The half-value angle as well as the diffusion properties of both curves are different, which allows for adoption as a good measure for orientation anisotropy. The anisotropy ratio is at least 1.1.

  In general, a gentle treatment of the plastic mixture is selected, so that the glass fibers are not shear broken, thus resulting in a high fine component.

  Mild treatment means that the glass fibers are not exposed to high loads due to shearing, thereby preventing the glass fibers from breaking down into too small parts. This is achieved by blending the glass fibers with the heated liquid polymer via a so-called side filler (side feeder), just before the extrusion nozzle during compounding. Thus, the glass fibers are not subjected to shear throughout the entire screw process during heating of the polymer.

  The diffuser according to the invention can also be used as a cover for the illumination means.

Example 1: PLEXIGLAS® 7N (PMMA) containing chopped strand EC14 4.5 mm-914 as glass fiber
In the extrusion test, various weight percentages of glass fibers (10%, 20%, 30% and 40%) were mixed with PMMA-molding material: PLEXIGLAS® 7N and extruded into 2 mm thick plates. The optical characterization results are summarized in Table 1:

  An important aspect of optical characterization is the measurement of light diffusion properties by goniometric light density measurements.

  The diffusion characteristics and intensity half-value angle were measured according to DIN 5036 using a measuring instrument LMT-goniometer measuring board GO-T-1500 (manufactured by LMT).

  These measurements were performed on the test specimen in the extrusion direction and across the extrusion direction, respectively, thereby confirming the anisotropy of the diffusion characteristics.

  1-4 show the anisotropy with increasing glass fiber ratio.

  1-4 confirm that the strongest diffusion anisotropy is brought about at a glass fiber ratio of 20%. At a limit area of 10% as well as a glass fiber proportion of 40%, the curves approach each other.

The following figure shows the results:
FIG. 5 shows the increase in half-value angle with increasing glass fiber proportion. In this case, the half-value angle across the extrusion direction increases far more significantly than the half-value angle along the extrusion direction between 10% by weight glass fiber proportion and 20% by weight glass fiber proportion.

  This is also apparent from FIG. 6 by the anisotropy coefficient A = HWW (q): HWW (l), that is, the quotient of the half-value angle having a maximum at about 20% by mass.

From the above results, it can be concluded that:
a. A glass fiber proportion of 10% to 20% by weight results in a significant increase in light diffusion.

  b. The increase in the average orientation of the glass fibers is significantly increased in the above range, with the uniaxial orientation at higher glass fiber proportions no longer improving drastically.

  FIG. 7 shows a decrease in light transmittance with increasing glass fiber ratio.

Transmittance tau _{D65 / 10 °} / reflective [rho _{D65 / 10 °,} using the DIN (manufactured by Perkin Elmer Co.) measuring instrument Lambda19 according (German Industrial Standard) 5036 (or a Varian Cary 5000 (Varian Inc. Co.)) measured did. In this case, an irradiation source of photo species D65 (sodium light) was used.

  In the range of 10% by weight glass fiber to 40% by weight glass fiber, the light transmittance decreased from 75% to 39%, and the course was almost linear.

  FIG. 8 shows the increase in yellow value with increasing glass fiber proportion. A possible explanation is a glass fiber additive (coating), which dissolves / decomposes throughout the treatment process, thus producing a low molecular weight component in the material that correspondingly produces a yellowing effect.

The yellow value [τ _{D65 / 10 °} or ρ _{D65 / 10 °} ] was measured according to DIN 6167 using a measuring instrument Lambda19 (manufactured by Perkin Elmer) (or Varian Cary 5000 (manufactured by Varian Inc.)).

  Summing up from all the measurement results, the optimum value occurs at a glass fiber proportion of about 20% by weight. This is because here the loss of light transmission and the yellow value (undesirable effect) are still not too high, and on the other hand the light diffusion and its anisotropy are already very pronounced.

FIG. 1 shows anisotropy at 10% glass fiber ratio. FIG. 2 shows anisotropy at 20% glass fiber proportion. FIG. 3 shows anisotropy at 30% glass fiber proportion. FIG. 4 shows the anisotropy at 40% glass fiber proportion. FIG. 5 shows the increase in half-value angle with increasing glass fiber proportion. FIG. 6 shows a function of anisotropy coefficient (HWW) and glass fiber ratio. FIG. 7 shows a decrease in light transmittance with increasing glass fiber ratio. FIG. 8 shows the increase in yellow value with glass fiber proportion.

Claims (15)

  A diffuser composed of transparent polymer and glass fiber.   The diffuser according to claim 1, wherein polymethyl methacrylate, polycarbonate, polyester or polyolefin is used as the transparent polymer.   The diffuser according to claim 1, wherein the difference in refractive index between the polymer and the inorganic glass fiber is at least 0.01.   4. A diffuser according to claim 3, wherein the difference in refractive index between the polymer and the inorganic glass fiber is at least 0.05.   The diffuser according to any one of claims 1 to 4, wherein the inorganic glass fiber has a diameter of 1.0 to 100 µm.   The diffuser according to any one of claims 1 to 5, wherein the inorganic glass fiber has an average aspect ratio of 1 to 10.   The diffuser according to any one of claims 1 to 5, wherein the inorganic glass fiber has an average aspect ratio of 1 to 20.   The diffuser according to any one of claims 1 to 5, wherein the inorganic glass fiber has an average aspect ratio of 1 to 50.   The diffuser according to any one of claims 1 to 8, wherein an average deviation between the glass fiber and the take-out direction is 0 ° to 45 °.   A method for producing a diffuser according to any one of claims 1 to 9, wherein the inorganic glass fibers and the polymer are mixed in a mass ratio of 1:10 to 1: 10000 and extruded. .   The method of claim 10, wherein the inorganic glass fibers are added to the polymer in the form of a masterbatch.   A master batch, wherein the mass ratio of the inorganic glass to the polymer is 1: 5 to 1: 500.   The diffuser according to claim 1, wherein the anisotropy ratio is at least 1.1.   Use of a diffuser according to any one of claims 1 to 9 or claim 13 as a cover for a lighting means.   Use of a diffuser according to any one of claims 1 to 9 or claim 13 as a component for a flat display.

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