WO2009022715A1

WO2009022715A1 - Manufacturing method and apparatus for uneven thickness resin sheet

Info

Publication number: WO2009022715A1
Application number: PCT/JP2008/064562
Authority: WO
Inventors: Takahiro Hayashi; Yoshihiko Sano; Hideo Nagano; Ryuichi Katsumoto
Original assignee: Fujifilm Corporation
Priority date: 2007-08-10
Filing date: 2008-08-07
Publication date: 2009-02-19
Also published as: JP2009040009A

Abstract

A manufacturing method for uneven thickness resin sheet with unevenness in sheet thickness in a width direction comprises a molding and cooling process (14) in which the extruded resin sheet is nipped between the molding roller (46) and a nip roller (48) and unevenly molded while being cooled and solidified. In the molding and cooling process (14), a heating device (47) is provided for partially heating only a surface part of the molding roller (46) corresponding to a thin part (A2). Therefore, during a period from when a resin sheet extruded from a die is nipped till when the sheet is peeled off from a molding roller, falling-off of a thin part of the resin sheet from the molding roller can be effectively restrained, and a thick part does not become difficult to be peeled off when the resin sheet is peeled off from the molding roller.

Description

MANUFACTURING METHOD AND APPARATUS FOR

UNEVEN THICKNESS RESIN SHEET

Technical Field

The present invention relates to a manufacturing method and an apparatus for uneven thickness resin sheet and particularly to a manufacturing method and an apparatus for uneven thickness resin sheet used as a light guide plate of a backlight for a liquid crystal display device and a light guide plate for various large-sized displays such as decorative display, sign display, illumination display and the like.

Background Art

Light guide plates of surface emission that guides light from a light source are used in a backlight of a liquid crystal display device and display devices for decoration, illumination and the like. In the liquid crystal display device, for example, a backlight that irradiates light from a rear face side of a liquid crystal panel (LCD) through the light guide plate for illuminating the liquid crystal panel is provided.

The light guide plate used in a liquid crystal panel of a relatively small screen such as a small-sized liquid crystal panel of a cellular phone and the like and a liquid crystal panel of a laptop computer is often manufactured by injection molding method in which a molten resin is injection-molded. However, the light guide plate of a liquid crystal panel of 20 inches or more, for example, such as a large-screen liquid crystal TV is not manufactured by the injection molding method due to molding facilities and forming technologies but manufactured by extrusion molding method in which the molten resin is extrusion-molded.

In general, in a liquid crystal panel with a relatively small screen such as a laptop computer, a wedge-shaped light guide plate having one thick end side and the other thin end side, as shown in a sectional view of Figure 13 A, is used, while in a liquid crystal panel with a large screen such as a large-screen liquid crystal TV, a light guide plate in a hog-backed shape with a thick center part and thin both ends, as shown in a sectional view of Figure 13B, is used. In order to manufacture the uneven resin sheet, as shown in Patent Document 1 , for example, a resin sheet extruded from a die is cooled and solidified while unevenly molding it by a molding roller so that an uneven thickness shape of the molding roller is transferred to the resin sheet, and the transferred resin sheet is peeled off from the molding roller by a peeling roller and then, slowly cooled.

In a molding and cooling process in which such resin sheet is unevenly molded by a molding roller, it is important that the nipped resin sheet is in close contact with the molding roller in a wrapped state till it is peeled off by the peeling roller.

Patent Document 1 : Japanese Patent Application Laid-Open No. 2006-297910

Disclosure of the Invention

Problems to be Solved by the Invention

However, when the resin sheet to be manufactured is an uneven thickness resin sheet, since a cooling speed is higher in the thin part than in the thick part in the molding and cooling process, the thin part loses its resin tackiness faster than the thick part.

Thus, there is a problem that, during the period from when the resin sheet extruded from the die is nipped between the molding roller and the nip roller till when it is peeled off from the molding roller, that is, while the resin sheet is wrapped around the molding roller, only the thin part of the resin sheet falls off (comes off) the molding roller. This falling-off causes a planar defect on the manufactured uneven thickness resin sheet and a transport defect (twist of the resin sheet and the like) during manufacture.

The present invention was made in view of the above circumstances, aims to effectively prevent from falling of the thin part of the resin sheet from the molding roller during a period from when the resin sheet extruded from the die is nipped till when the sheet is peeled off from the molding roller, and difficulty in peeling off a thick part when the resin sheet is peeled off from the molding roller, thereby providing a manufacturing method and an apparatus for uneven thickness resin sheet that can improve the planar defect on the manufactured uneven thickness resin sheet and the transport defect during manufacture.

Means for Solving the Problem To attain the object, according to a first aspect of the present invention, a manufacturing method for uneven thickness resin sheet which has unevenness in sheet thickness in a width direction, the manufacturing method comprises: an extrusion process of extruding a molten resin from a die in a sheet state; a molding and cooling process of cooling and solidifying the extruded resin sheet while nipping and unevenly molding the resin sheet between a molding roller and a nip roller; a partial heating process of partially heating, of a thin part and a thick part in the uneven thickness resin sheet, only a surface part on the molding roller corresponding to the thin part, immediately before a nip position; and a slow cooling process of slow cooling the resin sheet peeled off from the molding roller.

According to the manufacturing method according to the first aspect, in the molding and cooling process, among the thin part and the thick part of the uneven thickness resin sheet with unevenness in the sheet thickness, only the molding roller surface part corresponding to the thin part is partially heated immediately before the nip position. That is, not the molding roller surface part corresponding to the entire width of the resin-sheet width direction but only the molding roller surface part corresponding to the thin part in the resin-sheet width direction is partially heated. By this arrangement, during the period from when the sheet is nipped till when it is peeled off from the molding roller, the cooling speed only of the thin part of the resin sheet can be slowed. Thus, the problem that only the thin part of the resin sheet falls off the molding roller before the resin sheet is peeled off from the molding roller can be solved. In addition, since the thick part in the resin sheet is not heated, the cooling speed on the thick part is not slowed. Thereby the problem that the thick part becomes difficult to be peeled off at the peeling-off from the molding roller can be prevented. Thus, the problem of the planar defect on the uneven thickness resin sheet and a transport defect (twist of the resin sheet and the like) during the manufacture can be solved.

Here, the molding roller surface part corresponding to the thin part refers to the molding roll surface part that molds the thin part when the resin sheet is nipped between the rotating molding roller and the rotating nip roller. According to a second aspect of the present invention, in the manufacturing method according to the first aspect, when a maximum thickness in the width direction of the uneven thickness resin sheet is "a", a part in the uneven thickness resin sheet with a thickness of 2a/3 or less is distributed into the thin part.

The second aspect specifies a preferable condition when the thin part and the thick part are divided from each other. When the maximum thickness of the uneven thickness resin sheet is "a", the resin sheet part with the thickness of 2a/3 or less is preferably distributed into the thin part. By this arrangement, the problem of falling-off of the thin part during the period from when the sheet is nipped till when it is peeled off from the molding roller and the problem that the thick part is difficult to be peeled off at the peeling-off can be solved more effectively. If this condition is specified from the viewpoint of the molding roller, when a maximum machining depth of the molding roller is "a", a molding roller surface part with the machined depth of 2a/3 or less becomes a region subject to the partial heating.

The more preferable division between the thin part and the thick part is to distribute the resin sheet part with the thickness of 1A/3 or less into the thin part. According to a third aspect of the present invention, in the manufacturing method according to the first aspect or the second aspect, the molding roller surface is partially heated by heating device of a high frequency induction heating type.

The high frequency induction heating type heating device can heat only a region on the molding roller surface to be heated with high accuracy and can heat it rapidly to a desired temperature in a short time. Therefore, it is suitable as means for instantaneously heating only the roller surface corresponding to the thin part of the rotating molding roller.

According to a fourth aspect of the present invention, in the manufacturing method according to any one of the first to third aspects, a heating amount of the surface part of the molding roller in the partial heating process is adjusted so as to be in proportion with a degree of thinness of the thin part.

Since the uneven thickness resin sheet has a form in which the thickness is gradually increased or gradually decreased, there is also unevenness in the thickness in the thin part. Therefore, in the molding roller surface part corresponding to the thin part, by reducing the heating amount for a thinner part, while increasing the heating amount for a thicker part, temperature rise on the thin part can be made uniform. Thus, a better effect can be exerted. According to a fifth aspect of the present invention, in the manufacturing method according to any one of the first to fourth aspects, a temperature of the surface part of the molding roller corresponding to the thin part is raised by 5 to 20°C by the partial heating process. The fifth aspect specifies a preferable temperature to raise the surface temperature of the molding roller by the partial heating process, and the temperature rise of 5 to 20°C is preferable.

With the heating by less than 5°C, during the period from when the resin sheet is nipped till when it is peeled off from the molding roller, the effect to prevent the thin part from falling off the molding roller is small, while if the heating too much by exceeding 20°C, tackiness becomes too large and even the thin part can not be easily peeled off from the molding roller at the peeling-off.

To attain the object, according to a sixth aspect of the present invention, a manufacturing apparatus for uneven thickness resin sheet which has unevenness in sheet thickness in a width direction, the manufacturing apparatus comprises: an extruding device which extrudes a molten resin in a sheet state from a die; a molding and cooling processing device which cools and solidifies the extruded resin sheet while nipping and unevenly molding the resin sheet between a molding roller and a nip roller; a heating device disposed above the molding roller immediately before a nip position, the heating device partially heating only a surface part of the molding roller corresponding to a thin part of the resin sheet in a width direction of the molding roller; and a slow cooling processing device which slow cools the resin sheet peeled off from the molding roller.

The sixth aspect constitutes the manufacturing method according to the first aspect of present invention as an apparatus. According to the manufacturing method and apparatus for uneven thickness resin sheet of the aspects, during the period from when the resin sheet extruded from the die is nipped between the molding roller and the nip roller till when the sheet is peeled off from the molding roller, falling of only the thin part of the resin sheet from the molding roller can be effectively restrained, and the thick part does not become difficult to be peeled off when the resin sheet is peeled off from the molding roller. Therefore, the planar defect on the obtained uneven thickness resin sheet and transport defect during manufacture can be improved. Brief Description of the Drawings

Figure 1 is a process diagram for explaining a flow of a manufacturing method for uneven thickness resin sheet according to an embodiment of the present invention; Figure 2 is a conceptual diagram of an apparatus for embodying the manufacturing method for uneven thickness resin sheet according to the embodiment of the present invention;

Figure 3 is an explanatory diagram for explaining major configuration around a molding roller when an uneven thickness resin sheet in the hog-backed shape is to be molded;

Figure 4 is an explanatory diagram for explaining an arrangement relation between a molding roller and a heating device;

Figure 5 is an explanatory diagram for explaining major configuration around the molding roller when an uneven thickness resin sheet in which two hog-backed shapes are arranged continuously is molded;

Figure 6 is an explanatory diagram for explaining another mode of the arrangement relation between the molding roller and the heating device;

Figure 7 is an explanatory diagram for explaining an example of a shape maintaining device; Figure 8 is an explanatory diagram for explaining another mode of the shape maintaining device;

Figure 9 is an explanatory diagram for explaining still another mode of the shape maintaining device;

Figure 10 is an explanatory diagram for explaining warpage of a resin sheet; Figure 11 is an explanatory diagram for explaining a control system in a manufacturing apparatus for uneven thickness resin sheet;

Figure 12 is an explanatory diagram for explaining equipment driven by the control system in the manufacturing apparatus for uneven thickness resin sheet; and

Figures 13 A and 13B are explanatory diagrams for explaining examples of a shape of the uneven thickness resin sheet.

Description of Symbols 10 Mateπal process

12 Extrusion process

14 Molding and cooling process

16 Slow cooling process

18 Warpage measurement process

20 Control process

22 Laminate process

24 Cutting/trimming process

26 Loading process

28 Material silo

30 Additive silo

32 Automatic weighing machine

34 Mixer

36 Hopper

38 Extruding machine

40 Metering pump

42 Feed pipe

44 Die

46 Molding roller

47 Heating device

48 Nip roller

50 Peeling roller

52 Cooling control device

54 Slow cooling zone

55 Heating portion

56 Shape maintaining device

58 Concave roller

60 Straight roller

62 Short roller

64 Long roller

66 Bearing

68 Air cylinder 70 Beaπng

74 Air nozzle device

76 Feed roller

78 Warpage measuring instrument

79 Stacker

80 Measurement base

82 Reel

84 Protective film

86 Nip roller

88 Cutter

90 Trimmer

A Resin sheet

Al Thick part

A2 Thin part

Best Mode for Carrying Out the Invention

According to the attached drawings below, preferred embodiments of the manufacturing method and apparatus for uneven thickness resin sheet according to preferred embodiments of the present invention will be described. In the embodiments, a case where the sectional shape in the sheet width direction is the hog-backed shape will be described as the uneven thickness resin sheet.

Figure 1 shows an example of an entire process flow of manufacture of the uneven thickness resin sheet of the present invention, and Figure 2 is a conceptual diagram of a manufacturing apparatus of uneven thickness resin sheet provided with various types of equipment for executing each process.

As shown in Figure 1, the manufacturing method of the uneven thickness resin sheet of the present invention mainly includes a material process 10 in which a material is weighed, mixed or the like, an extrusion process 12 in which a molten resin is continuously extruded in a sheet state (band state), a molding and cooling process 14 in which the extruded resin sheet A is cooled and solidified while being unevenly molded, a slow cooling process 16 for slow cooling the solidified resin sheet A, a warpage measurement process 18 for measuring acceptance or rejection of the warpage of the slow cooled resin sheet with respect to a predetermined standard, a control process 20 for control such that a slow cooling speed in the resin-sheet width direction is made uniform by feedback to the slow cooling process 16 if the warpage exceeds the predetermined standard, a laminate process 22 for laminating a film for surface protection on the front and back faces of the resin sheet A, a cutting/trimming process 24 for cutting/trimming the resin sheet A to a predetermined size (length, width), and a loading process 26 for loading the cut resin sheet A.

Configuration of the manufacturing apparatus for uneven thickness resin sheet will be described for each of the processes 10 to 26 below. As shown in Figure 2, in the material process 10, a material resin and additives fed from a material silo 28 (or a material tank) and an additive silo 30 (or an additive tank) to an automatic weighing machine 32 are automatically weighed and mixed in a mixer 34 so that the material resin and the additives are mixed in a predetermined ratio. If scattering particles are added as the additive to the material resin, a master batch method in which a master pellet in which the scattering particles are added to the material resin in a concentration higher than a predetermined concentration is manufactured in advance by a granulating machine and the master pellet and a base pellet in which the scattering particles are not added are mixed by the mixer 34 in a predetermined ratio can be preferably employed. The same applies to a case where additives other than the scattering particles are added.

As the material resin used in the present invention, a thermoplastic resin can be used such as polymethylmethacrylate resin (PMMA), polycarbonate resin (PC), polystyrene resin (PS), MS resin, AS resin, polypropylene resin (PP), polyethylene resin (PE), polyethylene terephthalate resin (PET), polyvinylchloride resin (PVC), thermoplastic elastomer or their copolymer, cycloolefinpolymer and the like, for example. The material resin weighed and mixed appropriately in the material process 10 is fed to the extrusion process 12.

In the extrusion process 12, the material resin mixed by the mixer 34 is inputted in an extruding machine 38 through a hopper 36 and molten by the extruding machine 38 while being kneaded. The extruding machine 38 may be any one of a single-shaft extruder or a multi-shaft extruder and preferably has a vent function to vacuum the inside of the extruding machine 38. The material resin molten by the extruding machine 38 is fed to a die 44 (T-die, for example) through a feed pipe 42 by a metering pump 40 such as a screw pump or a gear pump and the like. Then, the resin sheet A extruded in a sheet state from the die 44 is next fed to the molding and cooling process 14.

In the molding and cooling process 14, the resin sheet A extruded from the die 44 is nipped between a molding roller 46 and a nip roller 48 and cooled and solidified while being unevenly molded, and the solidified resin sheet A is peeled off by a peeling roller 50. These rollers 46, 48, 50 are called molding and cooling rollers.

As shown in Figure 3, the molding roller 46 is formed in a concave shape with a thin center part and thick both end parts, while the nip roller 48 is formed in a flat state. That is, on a roller surface of the molding roller 46, a reversed shape for molding an uneven thickness resin sheet is formed. By this arrangement, the high-temperature resin sheet A extruded from the die 44 is nipped between the molding roller 46 and the nip roller 48 with a predetermined nip pressure so that the resin sheet is molded in the hog- backed shape. The molded uneven thickness resin sheet preferably has a difference in the thickness between the thickest part and the thinnest part in a range of 0.5 to 5 mm and more preferably in a range of 0.5 to 2 mm.

As the material of the molding roller 46, various steel members, stainless steel, copper, zinc, brass, those with these metal materials as a core metal and lined by rubber on the surface, those obtained by HCr plating, Cu plating, Ni plating and the like on these metal materials, ceramics and various complex materials can be employed.

For formation of the inverse hog-backed shape on the molding roller surface, though depending on the material of the roller surface, combination of cutting work by NC lathe and finishing buffing work can be preferably employed in general. Also, other known working methods (grinding work, ultrasonic work, discharge work and the like) can be employed. The surface roughness on the molding roller surface is preferably 0.5 μm or less by the centerline average roughness Ra and more preferably 0.2 μm or less. The molding roller 46 is rotated and driven in an arrow direction in Figure 3 at a predetermined circumferential speed by a driving device, not shown.

The nip roller 48 is a roller arranged opposite to the molding roller 46 for nipping the resin sheet A with the molding roller 46. As the material of the nip roller 48, various steel members, stainless steel, copper, zinc, brass, those with these metal materials as a core metal and lined by rubber on the surface, those obtained by HCr plating, Cu plating, Ni plating and the like on these metal materials, ceramics, and various complex materials can be employed.

The surface of the nip roller 48 is preferably worked in the mirror surface state and preferably has the centerline average roughness Ra at 0.5 μm or less or more preferably 0.2 μm or less. By having such smooth surface, the back face of the resin sheet A after being molded can be made favorable condition. Also, the nip roller 48 is rotated and driven in an arrow direction in Figure 3 by a driving device, not shown, at a predetermined circumferential speed. Configuration without the driving device at the nip roller 48 is possible, but provision of the driving device is preferable since the back face of the resin sheet A can be made favorable condition.

At the nip roller 48, a pressurizing device, not shown, is provided so that the resin sheet A between the nip roller and the molding roller 46 can be nipped with a predetermined pressure. The pressurizing device is so configured that a pressure is applied in a normal direction at a contact point between the nip roller 48 and the molding roller 46 in any case, and various known devices such as a motor driving device, an air cylinder, a hydraulic cylinder and the like can be employed.

For the nip roller 48, configuration such that deflection due to a reaction to a nip pressure hardly occurs can be also employed. For that purpose, configuration in which a backup roller, not shown, is provided on the rear face side of the nip roller 48 (on the side opposite the molding roller 46), configuration employing a crown shape (shape with a center convexed), configuration with a roller having intensity distribution such that rigidity at the center part in the axial direction of the roller is larger, configuration combining the above and the like can be employed.

The peeling roller 50 is arranged opposite to the molding roller 46 and is a roller for peeling the resin sheet A off from the molding roller 46 by winding the resin sheet A and is arranged on the downstream side of the molding roller 46 by 180 degrees. The surface of the peeling roller 50 is preferably worked in the mirror surface state. By having such surface, the back face of the resin sheet A after being molded can be made favorable condition. The surface roughness of the peeling roller surface is preferably 0.5 μm or less by the centerline average roughness Ra or more preferably 0.2 μm or less. As the material of the peeling roller 50, various steel members, stainless steel, copper, zinc, brass, those with these metal materials as a core metal and lined by rubber on the surface, those obtained by HCr plating, Cu plating, Ni plating and the like on these metal materials, ceramics, and various complex materials can be employed. The peeling roller 50 is rotated and driven in an arrow direction in Figure 3 by a driving device, not shown, at a predetermined circumferential speed. Configuration without the driving device at the peeling roller 50 is possible, but provision of the driving device is preferable since the back face of the resin sheet A can be made favorable.

And as shown in Figures 3 and 4, above the molding roller 46 immediately before the nip position, heating devices 47, 47 for partially heating only a surface part A2¹ of the molding roller 46 corresponding to a thin part A2 of the resin sheet A in the roller width direction (direction of axis) on the molding roller surface are provided. If the uneven thickness resin sheet in the hog-backed shape is to be manufactured, uneven molding is carried out so that a center part in the width direction of the resin sheet A becomes a thick part Al by the molding roller 46, while the both end parts in the width direction become the thin parts A2, and a pair of heating devices 47 are arranged at both end parts in the width direction of the molding roller surface.

The division between the thick part Al and the thin part A2 in the width direction of the resin sheet A is made, as shown in Figure 4, preferably such that when a maximum thickness of the uneven thickness resin sheet is "a", the resin sheet part with the thickness of 2a/3 or less is distributed (classified) into the thin part A2, while the resin sheet part exceeding 2a/3 is distributed (classified) into the thick part Al . More preferably, the resin sheet part with the thickness of la/3 or less is distributed (classified) into the thin part A2.

By this arrangement, the problem that the thin part A2 falls off the molding roller 46 during the period from when the resin sheet A is nipped between the molding roller 46 and the nip roller 48 till when the resin sheet is peeled off from the molding roller 46 by the peeling roller 50 and the problem that the thick part Al becomes difficult to be peeled off at the peeling-off can be solved more effectively. If this condition is specified from the viewpoint of the molding roller 46, when a maximum machining depth of the molding roller 46 is "a", the molding roller surface part A2' with the machining depth of 2a/3 or less is partially heated by the heating devices 47, while a molding roller surface part Al' with the machining depth exceeding 2a/3 is not heated. Figure 5 shows a case of manufacture of the uneven thickness resin sheet in which two hog-backed shapes are continuously arranged, and in this case, since the both end parts and the center parts of the resin sheet A become the thin parts A2, three units in total of the heating devices 47 are provided at both end parts and the center part in the width direction on the molding roller surface. Though not shown, in case of manufacture of the uneven thickness resin sheet in which three hog-backed shapes are continuously arranged, four units of the heating devices 47 in total are arranged.

As the heating devices 47, a radiation heating method (an infrared heater, for example) or a high frequency induction heating method (high frequency induction heating coil, for example) can be preferably used. Particularly, the high frequency induction heating coil can heat only a region on the molding roller surface to be heated with high accuracy by selecting arrangement and frequency of the coil and can raise the temperature to a desired one in a short time, which is preferable. If the high frequency induction heating coils are used as the heating devices 47, the material of the molding roller 46 should be a dielectric body such as iron, cobalt, nickel, and alloys with them as their main component, carbon steels represented by S45C and the like, and it is possible to apply nickel plating or chromium plating on their surfaces.

With regard to a heating temperature on the molding roller surface corresponding to the thin part by the heating devices 47, the higher the temperature is, the larger the tackiness of the thin part A2 becomes, and the effect to restrain falling-off is better, but when the sheet is peeled off from the molding roller 46 by the peeling roller 50, the resin sheet A should be cooled to a softening point temperature Ta or below.

In order to satisfy such condition, a temperature rise of the molding roller surface A2' corresponding to the thin part A2 is preferably in a range of 5 to 20°C. With the heating by less than 5°C, the effect to restrain falling of the thin part A2 off the molding roller 46 is small during the period from when the resin sheet A is nipped till when it is peeled off from the molding roller 46, while with heating too much by exceeding 20°C, the tackiness becomes so large that even the thin part A2 can not be easily peeled off from the molding roller 46 at the peeling-off. However, in order to control the surface temperature of the molding roller 46 corresponding to the thin part A2 more finely, a roller-temperature measuring device (not shown) for monitoring the surface temperature of the molding roller 46 is preferably provided close to the heating device 47, and a film-surface temperature measuring device (not shown) for monitoring the surface temperature of the thin part A2 at the peeling off is also provided. As the measuring devices for measuring the surface temperature of the molding roller 46 and the resin sheet A, known various measuring devices such as an infrared thermometer, radiation thermometer and the like can be employed.

Based on a monitoring result of the molding-roller surface temperature heated by the heating devices 47 and a monitoring result obtained by measurement of the surface temperature of the thin part A2 at the peeling-off, the heating amount of the heating devices 47 is preferably controlled such that the temperature of the thin part A2 becomes the softening point temperature Ta or below immediately before the peeling-off and a temperature raise of the molding roller 46 becomes as high as possible.

Figure 6 shows adjustment of the heating amount on the surface in the width direction of the molding roller 46 corresponding to the thin part A2 so that it is in proportion with a degree of thinness. That is, the heating devices are arranged with inclination with respect to an axis 49 of the molding roller 46 so that the molding roller surface part corresponding to the thinnest part in the thin part A2 is far from the heating devices, while the molding roller surface part corresponding to the thickest part in the thin part A2 is close to the heating devices. By this arrangement, since temperature rise on the molding roller surface corresponding to the thin part A2 can be made uniform, prevention of falling-off of the thin part and improvement of peel property (detachability) at the peeling-off can be realized more finely.

The resin sheet A having gone through the molding and cooling process 14 is taken up by take-up rollers 51, 53 (See Figures 3, 5) and fed to the slow cooling process 16. The slow cooling process (or annealing process) 16 is provided, as shown in

Figure 2, in order to prevent rapid temperature change of the resin sheet A on the downstream side of the peeling roller 50. If the rapid temperature change occurs in the resin sheet A, though the vicinity of the surface on the resin sheet A is in a plastic state, inside of the resin sheet A is still in an elastic state, and contraction due to hardening of this part deteriorates the surface shape of the resin sheet A, for example. Also, a temperature difference occurs between front and back faces of the resin sheet A, and warpage of the resin sheet A can easily happen. Particularly if there is thickness distribution in the resin-sheet width direction as in the uneven thickness resin sheet, the warpage can easily occur.

In the slow cooling process 16, a slow cooling zone 54 (or annealing zone) in a tunnel state having an inlet and an outlet is provided, in which at the first half part of the slow cooling zone 54, the resin sheet A is heated by a heating portion 55 for gradual natural cooling, while at the second half part of the slow cooling zone 54, a cool air is blown to the resin sheet A for forced cooling.

For the heating portion 55 provided at the first half part of the slow cooling zone 54, known various devices can be employed such as configuration in which a temperature-controlled air (hot air) is injected from a plurality of nozzles toward the resin sheet A, configuration for heating the resin sheet A by a nichrome-wire heater, infrared heater, dielectric heating device and the like.

At the first half part of the slow cooling zone 54, a shape maintaining device 56 is provided for maintaining of the resin sheet A in the essential hog-backed shape without warpage at slow cooling and transporting the resin sheet A by applying an external force to the resin sheet so as not to prevent transport of the resin sheet A. As the shape maintaining device 56, those shown in Figures 7 to 9, for example, can be preferably used.

In the shape maintaining device 56 in Figure 7, a single concave roller 58 (uneven thickness shape roller) is arranged on the face of a projecting side of the hog- backed resin sheet A, while a single straight roller 60 with a flat straight roller face is arranged on the opposite flat face so that the resin sheet A is nipped with a predetermined pressure. For the above-mentioned take-up rollers 51, 53, the shape maintaining device 56 in Figure 7 is also preferably employed. In the shape maintaining device 56 in Figure 8, on the face of a projecting side of the hog-backed resin sheet A, a plurality of short rollers 62 with flat roller faces are dividedly arranged in the resin-sheet width direction (in Figure 8, constituted by two pieces of the short rollers 62), while a single straight long roller 64 with a flat roller face is arranged on the opposite flat face so that the resin sheet A is nipped with a predetermined pressure. Both ends of a rotating shaft of the short rollers 62 are rotatably supported by bearings 66, and air cylinders 68 (external-force adjusting device) are provided at the bearings 66. The nipping pressure is adjusted by a stroke expanding a piston of the air cylinders 68. Reference numerals 70 are bearings of the long roller 64, and the bearings 70 of the long roller 64 and the air cylinders 68 of the short rollers 62 are supported by a slow cooling device body, not shown.

The shape maintaining device 56 in Figure 9 has a basic structure similar to Figure 8, in which a length of the short rollers 62 arranged in the resin-sheet width direction are made shorter than that in Figure 8 (constituted by four pieces of the short rollers 62) so that they can precisely nip the resin sheet A following the hog-backed shape thereof. The shape maintaining device 56 is not limited to the structures in Figures 7 to 9 but that may be any devices in essential as long as the resin sheet A is maintained in the hog-backed shape without warpage so as not to prevent transport of the slow cooled and transported resin sheet A. For example, it is possible to form the shape maintaining device by closely arranging a pressing device provided with wheels formed by further reducing the length of the short roller 62 in the width direction of the resin sheet A. Among the above rollers constituting the shape maintaining device 56, at least the roller arranged on the face on the projecting side of the resin sheet A is preferably an elastic roller. The material of the elastic roller includes, for example, silicon rubber (SR), styrene butadiene rubber (SBR), chloroprene rubber (CR), chlorosulfonated polyethylene (CSM), acrylonitrilebutadiene rubber (NBR), urethane rubber (U), ethylenepropylene rubber (EPT), chlorinated polyethylene rubber (CPE), fluoro rubber (FPM), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), Hypalon rubber (CMS) and the like, but they are not limiting.

In the shape maintaining devices 56 in Figures 7 to 9, a slow cooling control device (not shown) for applying slow cooling temperature distribution (See temperature distribution curve in Figure 11) is preferably provided in the resin-sheet width direction so as to substantially match the hog-backed shape of the molding roller.

By constituting the slow cooling process 16 as above, even if an internal stress (internal force) that would generate warpage occurs inside the resin sheet A during the slow cooling process 16, since the resin sheet A is maintained in the essential hog- backed shape without warpage by the pressure (external force) by the shape maintaining device 56, the sheet is slowly cooled without generating warpage and the internal stress is also gradually eased. If warpage should occur in the resin sheet A in the molding and cooling process 14, since the slow cooling is performed in a state where the warpage is forcedly corrected by the pressure of the shape maintaining device 56 in the slow cooling process 16, the internal stress having caused the warpage is gradually eased.

In this case, since the shape maintaining device 56 is constituted so that the roller arranged on the side of the hog-backed shaped face in the resin sheet A follows the hog-backed shaped face, even if the pressure is applied, the hog-backed shape of the resin sheet A is not broken. Also, since a gap hardly occurs between the hog-backed shaped face and the roller face, the resin sheet A can be maintained in the essential hog- backed shape without warpage with high accuracy. Also, since the slow cooling speed in the resin-sheet width direction is made uniform by the slow cooling control device, slow cooling can be realized without generating warpage in the slow cooling process 16. Even if warpage occurs in the resin sheet A in the molding and cooling process 14 before the slow cooling process 16, the warpage can be corrected while the internal stress is eased. In this case, a surface temperature of the resin sheet A in contact with the first shape maintaining device 56 provided at the inlet of the slow cooling zone 54 is preferably set at a glass transition temperature Tg⁰C of the resin or below and Tg-30°C or above, and the surface temperature of the resin sheet A at the outlet of the first half part of the slow cooling zone 54, that is, at a point when retention by the shape maintaining device 56 ends is preferably Tg-20°C or below and Tg-80°C or above, or more preferably Tg-50°C or below and Tg-60°C or above.

An interval between the shape maintaining device 56 arranged in the slow cooling zone 54 is preferably 1000 mm or less in a transport direction of the resin sheet A, or more preferably 500 mm or less. A pressure for nipping the resin sheet A by the shape maintaining device 56 is preferably 200 kgf/cm or less and 10 kgf/cm or more in linear pressure, or more preferably 50 kgf/cm or less and 30 kgf/cm or more.

At the second half part of the slow cooling zone 54, a plurality of air nozzle devices 74 for floating and transporting the resin sheet A by injecting a cool air are provided on an upper side and a lower side with the resin sheet A between them. As the air nozzle device 74, a known device used for floating and transporting a web-like transported article can be used. By this arrangement, the resin sheet A is cooled to approximately a normal temperature in a non-contact state not in contact with the rollers. Next, as shown in Figure 2, the resin sheet A cooled in the slow cooling process 16 is taken up by a feed roller 76 of a nip type and fed to a warpage measurement process 18.

In the warpage measurement process 18, acceptance or rejection of the warpage in the resin sheet A with respect to a predetermined standard is measured by a warpage measuring instrument 78. Explaining by an example of the hog-backed shape resin sheet A, as shown in Figure 10, when the back face (flat face side) of the resin sheet A cut into a longitudinal size of 600 mm and a lateral size of 1100 mm is mounted on an upper face of a flat measurement base 80, a maximum distance H between the resin sheet A and the measurement base 80 is referred to as a warpage amount. A predetermined standard of the warpage amount (standard value) is set by intended use of the resin sheet A and a standard on a user side, and the warpage measuring instrument 78 measures the warpage for acceptance or rejection with respect to the predetermined standard. As the warpage measuring instrument 78, such a method can be employed that a surface (outer periphery) of the reins sheet A is scanned by an electrostatic sensor and the like so as to measure a distance between the resin sheet A and the electrostatic sensor (shape) and the warpage amount is acquired from a relation prepared in advance between the measured value and the warpage amount. If the warpage amount measured by the warpage measuring instrument 78 exceeds the predetermined standard, it is fed back to the molding and cooling process 14 and the slow cooling process 16 so as to control such that the cooling speed and the slow cooling speed in the resin-sheet width direction become uniform. That is, in the above-mentioned molding and cooling process 14 by a cooling control device 52 and in the slow cooling process 16 by the slow cooling control device, a temperature distribution substantially in the same hog-backed shape as the molding roller 46 is formed in the resin-sheet width direction, by which the cooling speed and the slow cooling speed in the resin-sheet width direction is made uniform.

In this case, in the hog-backed shape resin sheet A, since a warpage might occur or might not occur depending on a type of the hog-backed shape, a degree of uneven thickness distribution and the like, feedback is made only if the warpage exceeds the predetermined standard. If the cooling speed and the slow cooling speed in the resin- sheet width direction are uniformly controlled even when warpage does not occur, that can rather cause a bad result. As shown in Figure 2, on the downstream side of the warpage measurement process 18, the laminate process 22, the cutting/trimming process 24, and the loading process 26 provided with a stocker 79 are provided in this order. Among them, the laminate process 22 is a process for affixing a protective film (film of polyethylene and the like) on the front and back faces of the resin sheet A, in which protective films 84 wound back from a pair of reels 82 are merged so as to sandwich the resin sheet A between them and make it pass through a nip roller 86 for lamination.

The cutting/trimming process 24 is a process to cut off both end parts (lug portion) in the width direction of the resin sheet A and to cut the resin sheet A into a predetermined length. As a cutter 88, as shown in Figure 2, a guillotine type cutter including a receiving blade 88A and a pressing blade 88B can be suitably used, but not limited to that. Also, as a trimmer 90, as shown in Figure 2, a laser cutter 9OA or an electronic beam cutting can be suitably used, but not limited to that.

According to a manufacturing apparatus for uneven thickness resin sheet configured as above, the sheet-like resin sheet A extruded from the die 44 is nipped between the molding roller 46 and the nip roller 48 so as to mold the resin sheet A in the hog-backed shape and to cool and solidify it and then, the sheet is peeled off from the molding roller 46 by the peeling roller 50. The resin sheet A peeled off from the molding roller 46 is transported in the horizontal direction and made to pass through the slow cooling zone 54 so as to slowly cool it and in a state where distortion is removed, and then it is cut to a predetermined length at a product picking portion on the downstream side and stored as a product of the resin sheet A. In this case, as an extrusion speed to extrude the resin sheet A from the die 44, a value of 0.1 to 50 m/minute or preferably 0.3 to 30 m/minute can be employed. Therefore, a circumferential speed of the molding roller 46 is made to substantially match it. Speed variation among the molding roller 46, the nip roller 48, and the peeling roller 50 is preferably controlled to stay within 1% to a set value.

In the embodiments of the present invention, in such molding and cooling process 14, only the surface part of the molding roller 46 corresponding to the divided thin part A2 in the molding roller surface in the roller width direction immediately before the nip position is partially heated. By this arrangement, during the period from when the resin sheet A is nipped till when the sheet is peeled off from the molding roller 46 by the peeling roller 50, that is, while the resin sheet A is wrapped around the molding roller 46, the cooling speed only of the thin part A2 of the resin sheet A can be slowed. Therefore, the problem that only the thin part A2 of the resin sheet A falls off the molding roller 46 before the resin sheet A is peeled off by the peeling roller 50 can be solved, and the problem that the thick part Al is not peeled off at the peeling-off is prevented. Thus, planar defect of the molded uneven thickness resin sheet or twisting of the resin sheet A caused by defective transport of the resin sheet A during manufacture does not occur, either.

Figures 11 and 12 show a control system of the manufacturing apparatus for uneven thickness resin sheet. Measuring devices in Figures 11 and 12 includes various measuring instruments such as a thickness measuring instrument for measuring the thickness of the resin sheet A, a transmittance measuring instrument for measuring optical transmittance of the resin sheet A, a roughness measuring instrument for measuring surface roughness of the resin sheet A, and a retardation measuring instrument for measuring retardation of the resin sheet A in addition to the above-mentioned measuring instruments such as the warpage measuring instrument 78.

As shown in Figure 11 , various measurement data measured by the measuring devices such as 78, 78 A to 78E are inputted to a DCS 102 (Distributed Control System) including a PLC (Programmable Logic Controller: sequencer). Also, operation data from each device is inputted to the DCS 102. The DCS 102 stores the measurement data and operation data and performs calculation for properly controlling each of the devices based on the measurement data and operation data. And a control signal obtained by the calculation is outputted to each of the devices such as the automatic weighing machine, the mixer 32 and 34, the hopper 36, the extruding machine 38, the die 44, the molding and cooling rollers 46, 48 and 50, the slow cooling machine 104, and the sorting device 108. Here, the sorting device 108 is a device for rejecting defective resin sheets from a manufacturing line to a disposal box 110, and resin sheets out-of- specification in evaluation items such as warpage, thickness, transmittance, surface roughness, retardation and the like are removed as defectives. A specific control for each of the devices by the DCS 102 is, as shown in Figure

12, mixing amount control (232) of the automatic weighing machine 32 in the material process and extruding amount control (238) of molten resin from the extruding machine 38 to the die 44 by controlling the metering pump such as a screw pump or a gear pump. In the material process, flow-rate distribution control (244) of the resin sheet in the die width direction is performed. In the molding and cooling process, control of each rotary driving units 246A of the molding and cooling rollers (molding roller 46, nip roller 48, peeling roller 50), control of a gap driving unit 246B for adjusting a gap between the rollers, and control of each temperature control unit 246C and the heating devices 47 are performed. At the first half part of the slow cooling process, control (204) of the temperature control unit and a pressure control unit of the shape maintaining device are performed, while in the floating transport at the second half part, the pneumatic conveyance driving unit 205 is controlled. Also, a feed roller (take-up roller) driving unit 207, a laminator driving unit 206, a trimmer driving unit 290, a cutter driving unit 288, an end-face finishing driving unit 289 and the like are controlled.

In the embodiment of the present invention, manufacture of the uneven thickness resin sheet in the hog-backed shape is used as an example of explanation, but not limited to that, and the present invention can be applied to any uneven thickness resin sheet having thickness distribution in the resin width direction such as a wedge-shaped uneven thickness resin sheet. The wedge-shaped uneven thickness resin sheet can be manufactured by making the uneven thickness resin sheet in the hog-backed shape and cutting it into halves. Examples (Example 1)

PMMA (80NH by Asahi Kasei Corporation, glass transition temperature at HO⁰C) is extruded from the die 44 set at the temperature of 260⁰C at 100 kg/hr and made to pass through the nip roller 48, the molding roller 46, the peeling roller 50, and the slow cooling zone 54 so as to make the uneven thickness resin sheet whose sectional shape in the sheet width direction is the hog-backed shape as in Figure 13B. The uneven thickness resin sheet has a width of 545 mm, the thinnest part of 2 mm, and the thickest part of 3.5 mm.

And above the molding roller 46 immediately before the nip position as in Figure 3, a pair of high frequency induction heating coils (heating devices 47) are provided for partially heating only the surface part of the molding roller 46 corresponding to the thin part A2 of the resin sheet A in the roller width direction on the molding roller surface. That is, the pair of high frequency induction heating coils are arranged so as to be parallel with the axis 49 of the molding roller 46 (See Figure 6) at the roller both end parts (corresponding to the thin part of the resin sheet A) with a small machining depth in the molding roller 46 so that the end parts of the resin sheet A are aligned with the end parts of the high frequency induction coil. The high frequency induction heating coils with the size of the length in the molding-roller axial direction at 200 mm and the length in the molding-roller circumferential direction at 100 mm are used. Also, a distance between the molding roller surface part corresponding to the thinnest part in the thin part A2 and the high frequency induction coil is set at 28 mm. The material of the molding roller 46 is S54C and chromium plating is applied to its surface.

A voltage of 200 V and a current of 100 A is made to flow through the high frequency induction heating coil at a frequency of 25 kHz so as to raise the surface temperature of the molding roller 46 by 10°C. The surface temperatures of the nip roller 48, the molding roller 46, and the peeling roller 50 while the high frequency induction heating coil is not electrified are set at 70°C, 90°C, and 95°C, respectively.

As a result, during the period from when the resin sheet A is nipped between the molding roller 46 and the nip roller 48 till when the resin sheet A is peeled off from the molding roller 46 by the peeling roller 50, the thin part A2 of the resin sheet A does not fall off the molding roller. Also, the thick part Al of the resin sheet A does not become difficult to be peeled off at the peeling-off. When the resin sheet A falls off the molding roller 46, an air layer is formed between the resin sheet A and the molding roller 46 and the color of the resin sheet becomes darker than the resin sheet in close contact with the molding roller 46, which enables to visually evaluate whether the resin sheet falls off or not. (Example 2)

Under the conditions of Example 1, the current flown through the high frequency induction coil is set at 130 A (the surface temperature of the molding roller is raised by 15°C), and a result similar to Example 1 can be obtained. (Example 3)

Under the conditions of Example 1, as shown in Figure 6, the high frequency induction heating coil is installed with inclination (5° inclination) with respect to the axis 49 of the molding roller 46 so that the thicker part in the thin part A2, that is, the more deeply hollowed part in the molding roller 46, the closer the molding roller surface and the high frequency induction heating coil are brought to each other so as to increase the heating amount. As a result, as compared with Example 1 , close contact of the thin part to the molding roller 46 is improved. In addition, when the resin sheet A is to be peeled off, detachability (peel propensity) of the thin part from the molding roll is made more favorable than Examples 1 and 2. (Example 4) Under the condition of Example 1 , an uneven thickness resin sheet with the sectional shape in the resin-sheet width direction in which two hog-backed shapes are arranged continuously as shown in Figure 5 is manufactured. This uneven thickness resin sheet has a width of 545 mm, the thinnest part of 2 mm, and the thickest part of 3.5 mm, and since the thin part is formed on the both end parts and the center part of the resin sheet A, three high frequency induction coils are arranged at the both end parts and the center part in the width direction of the molding roller 46 as in Figure 5.

As a result, during the period from when the resin sheet A is nipped between the molding roller 46 and the nip roller 48 till when the sheet is peeled off from the molding roller 46 by the peeling roller 50, none of the three thin parts fall off the molding roller 46. Also, the thick part Al in the resin sheet A does not become difficult to be peeled off at the peeling-off. (Comparative Example 1)

When the high frequency induction coil is not electrified, the thin part A2 of the resin sheet A falls off the molding roller 46 immediately after a nip position between the nip roller 48 and the molding roller 46. (Example 5)

The current flown through the high frequency induction coil is set at 6OA so that rise of the surface temperature of the molding roller corresponding to the thin part does not reach 5°C. In this case, close contact of the thin part A2 to the molding roller 46 is improved as compared with Comparative Example 1, but the color of the thin part tends to be slightly darker in the second half part of wrapping around the molding roller 46, and close contact between the thin part and the molding roller is found to be worsened.

Claims

1. A manufacturing method for uneven thickness resin sheet which has unevenness in sheet thickness in a width direction, the manufacturing method comprising: an extrusion process of extruding a molten resin from a die in a sheet state; a molding and cooling process of cooling and solidifying the extruded resin sheet while nipping and unevenly molding the resin sheet between a molding roller and a nip roller; a partial heating process of partially heating, of a thin part and a thick part in the uneven thickness resin sheet, only a surface part on the molding roller corresponding to the thin part, immediately before a nip position; and a slow cooling process of slow cooling the resin sheet peeled off from the molding roller.

2. The manufacturing method for uneven thickness resin sheet according to claim 1, wherein when a maximum thickness in the width direction of the uneven thickness resin sheet is "a", a part in the uneven thickness resin sheet with a thickness of 2a/3 or less is distributed into the thin part.

3. The manufacturing method for uneven thickness resin sheet according to claim 1 or 2, wherein the molding roller surface is partially heated by a heating device of a high frequency induction heating type.

4. The manufacturing method for uneven thickness resin sheet according to any one of claims 1 to 3, wherein a heating amount of the surface part of the molding roller in the partial heating process is adjusted so as to be in proportion with a degree of thinness of the thin part.

5. The manufacturing method for uneven thickness resin sheet according to any one of claims 1 to 4, wherein a temperature of the surface part of the molding roller corresponding to the thin part is raised by 5 to 20⁰C by the partial heating process.

6. A manufacturing apparatus for uneven thickness resin sheet which has unevenness in sheet thickness in a width direction, the manufacturing apparatus comprising: an extruding device which extrudes a molten resin in a sheet state from a die; a molding and cooling processing device which cools and solidifies the extruded resin sheet while nipping and unevenly molding the resin sheet between a molding roller and a nip roller; a heating device disposed above the molding roller immediately before a nip position, the heating device partially heating only a surface part of the molding roller corresponding to a thin part of the resin sheet in a width direction of molding roller; and a slow cooling processing device which slow cools the resin sheet peeled off from the molding roller.