Patent Application
20180024284
The invention relates to a method for manufacturing a retardation film by using a dual-axial stretching process (also called as a bi-axial stretching process), and more particularly to a method for manufacturing a PMMA (Polymethylmethacrylate) retardation film by using stretching and shrinking processes in the proceeding direction and the width direction simultaneously so as to obtain the PMMA retardation film with substantial high wider optical uniformity.
The retardation film is widely applied to an LCD or OLED display panel of the display device, so as to increase the contrast, viewing angle and optical uniformity. A well-known material for the retardation film of the LCD display panel is the TAC (Triacetate cellulose), a cellulose derivative, that has excellent water vapor permeability and thus is good to remove moisture on the polarizer. However, since a stricter rising demand for meeting a high-temperature and high-moisture environment currently in the panel industry, the TAC featured in high water absorption, dimensional stability and surface quality is no more a good choice for the retardation film. Hence, the PMMA gradually replaces the TAC in the marketplace for producing the retardation film.
Since the retardation film is generally asked to present some specific optical characteristics, the ordinary PMMA purchasable in the market can't meet the needs. Thus, a copolymerizing process is usually introduced to modify the PMMA. However, because of production difficulty and cost in synthesizing special polymeric segments, the PMMA does meet a technical barrier of application to the retardation film. Generally speaking, one of crucial topics in manufacturing the retardation film is to control the birefringence of the retardation film. In the art, two resorts are popular to control the birefringence of the retardation film.
1. Alignment birefringence: While at a temperature higher than the glass transition temperature, the molten material would produce an alignment difference which would lead to a difference of the birefringence at the material itself; and
2. Photoelastic birefringence: While the material is stressed to change its volume and so as further to vary the birefringence at all directions, the photoelastic coefficient of the material is usually used as an observation index.
Currently in the marketplace, the normal PMMA usually has a photoelastic coefficient of 6×10−12 Pa−1. While in meeting any stress change, the refractive index of the PMMA would vary. Namely, the birefringence of the PMMA can't be steadily controlled. In the art, a general improvement thereupon is to copolymerize a methyl methacrylate (MMA) with another monomer (such as 3FMA or BzMA) so as to decrease the photoelastic coefficient. However, as described above, such a copolymer usually includes special polymeric segments that are synthesized difficultly and thus costly, and so, in the art, the PMMA is not a popular material for producing the retardation film.
Accordingly, it is the primary object of the present invention to provide a method for manufacturing a retardation film by using a dual-axial stretching process that can produce a PMMA retardation film by using stretching and shrinking processes in the proceeding direction and the width direction simultaneously so as to obtain a product film with substantial high wider optical uniformity and without an involvement of copolymerization.
In the present invention, the method for manufacturing a retardation film by using a dual-axial stretching process includes the steps of:
Step (A): providing a cast film;
Step (B): in a preheating process, at a predetermined preheating temperature, preheating the cast film;
Step (C): in a stretching process, at a predetermined stretching temperature, performing simultaneously dual-axial stretching upon the cast film; wherein, in this stretching process, the cast film is stretched by a vertical stretching magnification factor (MD) and a horizontal stretching magnification factor (TD), and both the MD and the TD are within 1.0˜5.0 times;
Step (D): in an annealing process, at a predetermined annealing temperature, annealing the cast film so as to shrink the cast film simultaneously in both a vertical direction and a horizontal direction; and
Step (E): in a cooling process, at a predetermined cooling temperature, cooling the cast film, and then outputting an output retardation film.
In one embodiment of the present invention, the predetermined preheating temperature is within 100˜200° C., and, while in preheating, a preheating wind speed is within 5˜22 m/s; the predetermined stretching temperature is within 120˜200° C., and, while in stretching, a stretching wind speed is within 5˜16 m/s so as to control a temperature of the cast film in the stretching process to be within 120˜170° C.; the predetermined annealing temperature is within 80˜200° C., and, while in annealing, a annealing wind speed is within 5˜22 m/s; the predetermined cooling temperature is within 25˜120° C., and, while in cooling, a cooling wind speed is within 5˜16 m/s; and, in the annealing process, a shrinkage ratio for both the MD and the TD of the cast film is within 0˜18%.
In one embodiment of the present invention, the predetermined stretching temperature (Text), the MD, the TD and the predetermined annealing temperature (Tshrink) fulfill mathematical criteria as follows:
R0=α*ΔTe+β*ΔXe+γ*ΔTs+δ*ΔXs+C1;
Wherein: R0 R0 is an in-plane retardation value of the output retardation film and is within 0˜3 nm; ΔTe is a temperature difference value in the stretching process, and ΔTe=Text−Tg; ΔXe is a stretching magnification factor difference value in the stretching process, and ΔXe=MD−TD; ΔTs is a temperature difference value in the annealing process, and ΔTs=Tshrink−Tg; ΔXs is a shrinkage ratio value of the cast film in the annealing process, and ΔXs=[(1−MDshrink)*(1−TDshrink)−1], wherein the MDshrink is a shrinkage ration of the cast film in the vertical direction in the annealing process, wherein the TDshrink is a shrinkage ration of the cast film in the horizontal direction in the annealing process; and α, β, γ, δ and C1 are all machine parameters, and Tg is a material parameter. Also, according to different processing machines or different raw materials, the corresponding parameter values are different. Preferably, α=−0.0879, β=−6.24, γ=0.011, δ=−12.8, Tg=118 and C1=2.19.
In one embodiment of the present invention, the predetermined stretching temperature (Text), the MD, the TD, and the predetermined annealing temperature (Tshrink) fulfill mathematical criteria as follows:
Rth=a*ΔTe+b*ΔXe+c*ΔTs+d*ΔXs+C2;
wherein: Rth is an in-depth retardation value of the output retardation film and is within −40˜0 nm; ΔTe is a temperature difference value in the stretching process, and ΔTe=Text−Tg; ΔXe is a stretching magnification factor difference value in the stretching process, and ΔXe=MD−TD; ΔTs is a temperature difference value in the annealing process, and ΔTs=Tshrink−Tg; ΔXs is a shrinkage ratio value of the cast film in the annealing process, and ΔXs=[(1−MDshrink)*(1−TDshrink)−1], wherein the MDshrink is a shrinkage ration of the cast film in the vertical direction in the annealing process, wherein the TDshrink is a shrinkage ration of the cast film in the horizontal direction in the annealing process; and a, b, c, d and C2 are all machine parameters, and Tg is a material parameter. Also, according to different processing machines or different raw materials, the corresponding parameter values are different. Preferably, a=0.958, b=2.5, c=0.321, d=12.1, Tg=118 and C2=−39.4.
In one embodiment of the present invention, the cast film is made of a PMMA having a thickness within 250˜1200 μm and a width within 500˜980 μm.
In one embodiment of the present invention, an in-plane retardation value R0 of the output retardation film is within 0˜3 nm, an in-depth retardation value Rth of the output retardation film is within −40˜0 nm, a refractive index Nx of the cast film in an in-plane slow axis direction is within 1.499900˜1.499995, a refractive index Ny of the cast film in an in-plane fast axis direction is within 1.499900˜1.499955, a refractive index Nz of the cast film in a thickness direction is within 1.500001˜1.500045, and a thickness of the output retardation film is within 38˜250 μm.
Another object of the present invention is to provide a retardation film manufactured by using a dual-axial stretching process, wherein an in-plane retardation value R0 of the output retardation film is within 0˜3 nm, an in-depth retardation value Rth of the output retardation film is within −40˜0 nm, a refractive index Nx of the cast film in an in-plane slow axis direction is within 1.499900˜1.499995, a refractive index Ny of the cast film in an in-plane fast axis direction is within 1.499900˜1.499955, a refractive index Nz of the cast film in a thickness direction is within 1.500001˜1.500045, and a thickness of the output retardation film is within 38˜250 μm.
All these objects are achieved by the method for manufacturing a retardation film by using a dual-axial stretching process and the retardation film described below.
The present invention will now be specified with reference to its preferred embodiment illustrated in the drawings, in which:
The invention disclosed herein is directed to a method for manufacturing a retardation film by using a dual-axial stretching process and a retardation film. In the following description, numerous details are set forth in order to provide a thorough understanding of the present invention. It will be appreciated by one skilled in the art that variations of these specific details are possible while still achieving the results of the present invention. In other instance, well-known ingredients are not described in detail in order not to unnecessarily obscure the present invention.
Refer now to
Step 31: Provide a cast film. Referring to
Step 32: Perform preheating. In a preheating process, at a predetermined preheating temperature, the cast film is preheated. In this embodiment, the predetermined preheating temperature is ranged between 100° C. and 200° C., a preheating wind speed for the preheating process is ranged between 5 m/s and 22 m/s. Namely, in this preheating process, a 100° C.˜200° C. hot wind with a 5 m/s˜22 m/s preheating wind speed is provided to the cast film. Preferably, the predetermined preheating temperature is ranged between 145° C. and 155° C.
Step 33: Stretch dual-axially and simultaneously. In a stretching process, at a predetermined stretching temperature, simultaneous dual-axial stretching is applied to the cast film. In the stretching process, the cast film is stretched to have both a vertical stretching magnification factor (MD) and a horizontal stretching magnification factor (TD) to be ranged from 1.0 to 5.0 times. In this embodiment, the predetermined stretching temperature is ranged between 120° C. and 200° C., and a stretching wind speed is ranged between 5 m/s and 16 m/s. Namely, in this stretching process, a 120° C.˜200° C. hot wind with a 5 m/s˜16 m/s heating wind speed is provided to the cast film, such that a film temperature of the cast film (i.e. the temperature of the cast film itself) during the stretching process can be controlled within 120˜170° C. Preferably, the predetermined stretching temperature is ranged between 130° C. and 150° C.
Step 34: Perform annealing. In an annealing process, at a predetermined annealing temperature, the cast film is annealed so as to shrink the cast film simultaneously both in the vertical direction and in the horizontal direction. In this embodiment, the predetermined annealing temperature is ranged between 80° C. and 200° C., and an annealing wind speed is ranged between 5 m/s and 22 m/s. Namely, in this annealing process, a 80° C.˜200° C. hot wind with a 5 m/s˜22 m/s annealing wind speed is provided to the cast film. Also, in the annealing process, a shrinkage ratio of the cast film in either the vertical direction (i.e. the MD direction) or the horizontal direction (i.e. the TD direction) is ranged between 0% and 18%. Preferably, the predetermined annealing temperature is ranged between 120° C. and 150° C.
Step 35: Perform cooling. In a cooling process, at a predetermined cooling temperature, the cast film is cooled down, and then an output retardation film is outputted (Step 36). In this embodiment, the predetermined cooling temperature is ranged between 25° C. and 120° C., and a cooling wind speed is ranged between 5 m/s and 16 m/s. Namely, in this cooling process, a 25° C.˜120° C. hot wind with a 5 m/s˜16 m/s cooling wind speed is provided to the cast film. Preferably, the predetermined cooling temperature is ranged between 25° C. and 100° C.
In the present invention, through the aforesaid specific temperature and wind speed ranges for performing the preheating, the dual-axial stretching, the annealing and the cooling, the output retardation film would have an in-plane retardation value R0 within 0˜3 nm and an in-depth retardation value Rth within −40˜0 nm. A refractive index Nx of the cast film in an in-plane slow axis direction is within 1.499900˜1.499995, a refractive index Ny of the cast film in an in-plane fast axis direction is within 1.499900˜1.499955, a refractive index Nz of the cast film in a thickness direction is within 1.500001˜1.500045, and a thickness of the output retardation film is within 38 μm˜250 μm. Also, the output retardation film is featured in substantial high wider optical uniformity. Such an optical characteristic for the retardation film can meet client's need to some extent for the LCD or OLED display panels. More importantly, by using the aforesaid method, a copolymerizing process is no more needed, and thus the manufacturing of the retardation film is comparatively less complicated and less expensive.
In the preferred embodiment of the method for manufacturing a retardation film by using a dual-axial stretching process in accordance with the present invention, except for the aforesaid specific limitations of temperatures and wind speeds in the preheating, the dual-axial stretching, the annealing and the cooling, the predetermined stretching temperature (Text), the MD value, the TD value and the predetermined annealing temperature (Tshrink) shall fulfill the following mathematical criteria.
R0=α*ΔTe+β*ΔXe+γ*ΔTs+δ*ΔXs+C1;
wherein,
R0 is the in-plane retardation value of the output retardation film, and R0 is within 0˜3 nm;
ΔTe is the temperature difference value in the stretching process, and ΔTe=Text−Tg;
ΔXe is the stretching magnification factor difference value in the stretching process, and ΔXe=MD−TD;
ΔTs is the temperature difference value in the annealing process, and ΔTs=Tshrink−Tg;
ΔXs is the shrinkage ratio value of the cast film in the annealing process; and,
ΔXs=[(1−MDshrink)*(1−TDshrink)−1], in which the MDshrink is the shrinkage ratio of the cast film in the vertical direction in the annealing process, and TDshrink is the shrinkage ratio of the cast film in the horizontal direction in the annealing process.
Also, α, β, γ, δ and C1 are all machine parameters, Tg is the material parameter. Based on different processing machines or different raw materials, the corresponding parameter values would be different. In this embodiment, α=−0.0879, β=−6.24, γ=0.011, δ=−12.8, Tg=118 and C1=2.19.
Preferably, the predetermined stretching temperature (Text), the MD value, the TD value, and the predetermined annealing temperature (Tshrink) shall fulfill further the following mathematical criteria.
Rth=a*ΔTe+b*ΔXe+c*ΔTs+d*ΔXs+C2;
wherein,
Rth is the in-depth retardation value of the output retardation film, and Rth value is within −40˜0 nm;
ΔTe is the temperature difference value in the stretching process, and ΔTe=Text−Tg;
ΔXe is the difference value of the stretching magnification factor in the stretching process, and ΔXe=MD−TD;
ΔTs is the temperature difference value in the annealing process, and Ts=Tshrink−Tg;
ΔXs is the shrinkage ratio value of the cast film in the annealing process; and,
ΔXs=[(1−MDshrink)*(1−TDshrink)−1], in which the MDshrink is the shrinkage ratio of the cast film in the vertical direction in the annealing process, and TDshrink is the shrinkage ratio of the cast film in the horizontal direction in the annealing process.
Also, a, b, c, d and C2 are all machine parameters, Tg is the material parameter. Based on different processing machines or different raw materials, the corresponding parameter values would be different. In this embodiment, a=0.958, b=2.5, c=0.321, d=12.1, Tg=118 and C2=−39.4.
As shown in
As shown in
As follows, based on the aforesaid method for manufacturing the retardation film by using the dual-axial stretching process of the present invention, various exemplary embodiments with different testing conditions are provided to verify the aforesaid manufacturing parameters and the mathematical criteria. It would be confirmed from the testing results that the method for manufacturing the retardation film by using the dual-axial stretching process of the present invention can produce a satisfied retardation film for the LCD or OLED display panel that meets the demanded optical characteristics, and no synthesis of copolymers is required.
Firstly, for being applied to the method of
Then, according to Table 2, by varying the rotational speed of the take-off roller for different embodiments 1˜5 (i.e. changing the speed difference between the chill roller and the take-off roller), testing results of the optical axis value and the average retardation value of the cast film are shown in the following Table 2. It is found, from Table 2, that optical characteristics of Embodiments 1˜4 are satisfied, but only the R0 value of Embodiment 5 is less satisfied. It is thus concluded that, by controlling the difference of the rotational speeds of the chill roller and the take-off roller to be within ±1 m/min with the rotational speed of the take-off roller within 4˜6 m/min, the optical axis and the retardation value are not affected, and the optical characteristics of the cast film can be effectively controlled.
Then, by having the cast film of Embodiment 4 in Table 2 as a basic example, in the process of manufacture the retardation film by the dual-axial stretching process, by varying and controlling the stretching temperature (ST), the proceeding-directional magnification factor MD, the width-directional magnification factor TD, the anneal temperature (AT), the stretching wind speed (SWS), the annealing wind speed (AWS), the proceeding-directional shrinking percentage (PDSP) and the width-directional shrinking percentage (WDSP) so as to obtain different Embodiments 6˜15 from Embodiment 4 of Table 2, the testing results of the retardation values (R0 and Rth) of the output retardation films of Embodiments 6˜15 (Em 6˜15)are listed in the following Table 3.
Since parameter conditions of Table 3 include changes in the stretching temperature ST, the proceeding-directional magnification factor MD, the width-directional magnification factor TD, the stretching temperature ST, the anneal temperature AT, the proceeding-directional shrinking percentage PDSP, and the width-directional shrinking percentage WDSP, the effect of the individual parameter condition upon the retardation values of the output retardation film is not so easy to observe. Alternatively, it could be easier to observe the effect of the individual parameter condition upon the retardation values of the output retardation film by adopting some specific parameters, namely observing a simplified table from these adopted parameters. For example, if the columns for the adopted parameters include only the number, the stretching temperature, the stretching wind speed, the thickness and the retardation values, then the results are shown in Table 4. It is easy to find, from Table 4, that contributions of the retardation values R0 and Rth of the output retardation film can fulfill the following mathematical expressions:
R0=αΔTstretching temperature, and
Rth=aΔTstretching temperature.
Namely, R0=α(Stretching temperature−Tg), in which Tg=118 and α=−0.0879. Also, Rth=a(Stretching temperature−Tg), in which Tg=118 and a=0.958. In the present invention, the Tg value (material parameter) of the machine parameters is a variable dependent upon the raw material of the cast film, not upon the processing machine. For example, in the case of the code-T11 PMMA, the Tg value (material parameter) of the machine parameters is a constant, i.e. 118 as listed above.
In addition, it only the number, the proceeding-directional magnification factor, the width-directional magnification factor, the thickness and the retardation are adopted, the results are listed as Table 5. It is easily found, from Table 5, that contributions of the retardation values R0 and Rth of the output retardation film fulfill the following mathematical expressions, respectively.
R0=βΔXstretching magnification factor, and Rth=bΔXstretching magnification factor.
Namely, R0=β(MDmagnification factor−TDmagnification factor), where β=−6.24. Rth=+b(MDmagnification factor−TDmagnification factor))−1], where b=2.5.
Further, if only the number, the annealing temperature, the annealing wind speed, the thickness and the retardation are adopted, the results are listed as Table 6. It is easily found, from Table 6, that contributions of the retardation values R0 and Rth of the output retardation film fulfill the following mathematical expressions, respectively.
R0=γΔTannealing temperature, and Rth=cΔTannealing temperature.
Namely, R0=γ(Annealing temperature−Tg), where γ=0.011. Rth=c(Anneal temperature−Tg), where c=0.321.
Furthermore, if only the number, the proceeding-directional shrinking percentage, the width-directional shrinking percentage, the thickness and the retardation are adopted, the results are listed as Table 7. It is easily found, from Table 7, that contributions of the retardation values R0 and Rth of the output retardation film fulfill the following mathematical expressions, respectively.
R0=δ ΔXshrinking percentage, and Rth=dΔXshrinking percentage.
Namely, R0=δ [(1−MDshrinking percentage)*(1−TDshrinking percentage)−1], where δ=−12.8. Rth=d [(1−MDshrinking percentage)*(1−TDshrinking percentage)−1], where d=12.1.
Accordingly, after each verification of the foregoing mathematical criteria by the results listed from Table 4 through Table 7, two aforesaid mathematical criteria of the present invention can be then obtained. In particular, by plugging data of Table 3, these two mathematical criteria of the present invention, as follows, are still fulfilled.
R0=α*ΔTe+β*ΔXe+γ*ΔTs+δ*ΔXs+C1, and
Rth=a*ΔTe+b*ΔXe+c*ΔTs+d*ΔXs+C2.
Since these two mathematical criteria have been fully disclosed above, thus details thereabout are omitted herein. If the method of the present invention is applied to other machine, different embodiments having different given parameter conditions (i.e. via controlling and varying the stretching temperature, the proceeding-directional magnification factor MD, the width-directional magnification factor TD, the annealing temperature, the proceeding-directional shrinking percentage, the width-directional shrinking percentage and so on) can be provided in a manner similar to the aforesaid Table 3. Then, retardation values R0 and Rth of the output retardation films produced from the respective embodiments are measured to generate the parameters to be plugged into these two mathematical criteria. Thereupon, machine parameters such as α, β, γ, δ, C1, a, b, c, d and C2 can be calculated. Thereafter, according to these two mathematical criteria and the calculated machine parameters, optimal stretching temperature, proceeding-directional magnification factor MD, width-directional magnification factor TD, annealing temperature, proceeding-directional shrinking percentage, width-directional shrinking percentage and the other parameter can then be achieved so as to meet the industrial requirements upon specific optical characteristics of the retardation film. Therefore, according to steps shown in
While the present invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be without departing from the spirit and scope of the present invention.
