KR20080099345A - Process for producing thermoplastic resin sheet with controlled warpage - Google Patents

Abstract

A process for producing a thermoplastic resin sheet with controlled warpage, characterized in that in the extrusion forming of a thermoplastic resin sheet, mechanically controlled warpage is applied to the sheet at the position where the temperature of extruded sheet is close to the glass transition temperature (Tg) of the thermoplastic resin constituting the sheet. In this process, preferably, mechanically controlled warpage is applied to the sheet by causing the sheet to pass through a gap of a vertical pair of warp controlling rolls at the above position and selecting the morphology of the warp controlling rolls and/or arranging the warp controlling rolls above or below the height for realizing a flat sheet. By this process, the thermoplastic resin sheet with controlled warpage can be efficiently produced in an easy manner.

Description

Manufacturing method of thermoplastic resin sheet having controlled warpage {PROCESS FOR PRODUCING THERMOPLASTIC RESIN SHEET WITH CONTROLLED WARPAGE}

The present invention relates to a method for producing a thermoplastic resin sheet having a controlled warpage.

The thermoplastic resin sheet is produced by, for example, an extrusion molding method. In this case, a thermoplastic resin sheet is obtained by heat-melting a resin composition, extruding from a die, rolling with a cooling roll, and cooling and solidifying by taking over with a takeover roll etc. via a guide roll. When manufacturing a thermoplastic resin sheet by the extrusion molding method, generally, the intention is to obtain the flat sheet | seat by suppressing curvature, and various research is performed.

For example, Japanese Laid-Open Patent Publication No. H06-344417 discloses a method of relieving internal stress by controlling the temperature of a cooling roll and heating the extruded sheet to increase the temperature and then slowly cooling the medium. Japanese Laid-Open Patent Publication No. H07-276471 discloses a method for relieving internal stress by making the sheet flexible between the final cooling roll and the first guide roll, and Japanese Laid-Open Patent Publication No. 2001-2001. 139705 and Japanese Unexamined Patent Publication No. 2005-81757 disclose a method of suppressing the generation of internal stress by adjusting the speed ratio of the second and third cooling rolls and setting the roll temperature relatively low. Japanese Patent Laid-Open No. 2004-126185 discloses an improved method using a method disclosed in Japanese Patent Laid-Open No. H07-276471 and Japanese Patent Laid-Open No. 2001-139705 in combination.

As described above, in the prior art, attention has been focused on suppressing warpage and obtaining a flat sheet by suppressing generation of internal stress or relieving internal stress.

By the way, depending on the use of a thermoplastic resin sheet, it may be necessary to provide curvature on purpose rather. For example, a light diffusing plate used for a backlight unit such as a liquid crystal display device or a medical monitor is flat during manufacturing, but after absorbing moisture in the air, the side facing the light is dried and contracted by the heat of the light. This causes a problem that the convex warp occurs toward the display surface side, which adversely affects the display performance when the backlight unit is used.

Moreover, in the case of construction materials, when applied to the R-shaped portion, the construction materials intentionally providing warpage are more favorable to the base material than the flat construction materials without warpage, and the stress applied to the construction materials is also reduced. In the case of manufacturing a thermoplastic resin sheet as a building material having warpage, a method of providing warpage by hot molding after extrusion of a flat sheet has been adopted.

However, this method requires a hot forming process separately from the extrusion molding process, resulting in an increase in the manufacturing cost of the building material.

Therefore, Japanese Laid-Open Patent Publication No. 2002-120249 uses a production line of thermoplastic resin sheets to heat or cool the sheet to control the temperature difference between the upper and lower surfaces of the sheet when the temperature of the sheet from the cooling roll is within a predetermined range. Thereby, the method of adjusting the curvature amount of a sheet | seat is proposed.

However, in this method, it is difficult to control the temperature difference on the upper and lower surfaces with high accuracy, and it is considered difficult to manufacture the thermoplastic resin sheet having the controlled warpage.

An object of the present invention is to provide a method for efficiently and simply manufacturing a thermoplastic resin sheet having a controlled warpage.

As a result of various studies, the inventors of the present invention have found that, in extruding a thermoplastic resin sheet, the extruded sheet is mechanically attached to the sheet at a position near the glass transition temperature (Tg) of the thermoplastic resin constituting the sheet. It has been found that the invention can provide a controlled warp (in some cases, also thermally) and the present invention has been completed.

That is, in the present invention, in the extrusion molding of a thermoplastic resin sheet, the mechanically controlled warpage is provided to the sheet at a position at which the temperature of the extruded sheet becomes near the glass transition temperature (Tg) of the thermoplastic resin constituting the sheet. The manufacturing method (henceforth a "manufacturing method of this invention") of the thermoplastic resin sheet which has the controlled curvature provided is provided.

In the manufacturing method of this invention, Preferably, the said sheet | seat passes between a pair of upper and lower deflection control rolls at the said position, and selects the shape of this deflection control roll, and / or the said deflection control roll Is arranged above or below at a height where a flat sheet can be obtained, thereby providing mechanically controlled warping to the sheet. Moreover, the temperature of the said sheet in the position of the said bending control roll becomes like this. Preferably it exists in the range of (Tg +/- 20 degreeC). In addition, by adjusting the temperature of the bending control roll up and down to generate a difference in the cooling rate of the upper and lower surfaces of the sheet, and / or by adjusting the temperature difference between the upper and lower surfaces of the sheet at or near the position of the bending control roll. By making a difference in the cooling rate of the upper and lower surfaces of the sheet, it is also possible to provide the sheet with thermally controlled warping.

In the production method of the present invention, the thermoplastic resin constituting the sheet is preferably selected from the group consisting of polycarbonate resins, (meth) acrylic resins, styrene resins, acrylic-styrene resins and norbornene resins. Moreover, in order to express light diffusivity, you may contain microparticles | fine-particles.

The present invention also provides a thermoplastic resin sheet having a controlled warpage, which is obtained by the above production method.

According to the present invention, a thermoplastic resin sheet having a controlled warpage can be efficiently and conveniently obtained. When the obtained thermoplastic resin sheet is used, for example, as a light diffusion plate in the backlight unit of a liquid crystal display device, if it is designed to provide a slight warp toward the light side in advance, and is designed to be almost flat by the heat of the light at the time of use, Since the warp toward the display surface side occurs and the liquid crystal display panel is not pressed, the display performance of the liquid crystal display device is not adversely affected. In the case of a backlight such as a medical monitor, if a slight deflection toward the light side is provided in advance and designed to be substantially flat due to the heat of the light during use, it does not adversely affect the display performance of the medical monitor or the like.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the structure of the typical sheet extruder which can be used for the manufacturing method of this invention.

FIG. 2: is a schematic diagram which shows the case where 1 set of upper and lower deflection control rolls are moved to the upper side, when manufacturing a thermoplastic resin sheet using the sheet extruder shown in FIG. 1, so that the upward convex curvature may be provided.

FIG. 3: is a schematic diagram which shows the case where 1 set of upper and lower deflection control rolls are moved to lower side, when manufacturing a thermoplastic resin sheet using the sheet extruder shown in FIG.

EMBODIMENT OF THE INVENTION Hereinafter, although this invention is demonstrated in detail, the scope of the present invention is not restrict | limited to these descriptions, It can change and implement suitably in the range which does not impair the meaning of this invention other than the following illustration.

`` Method for producing thermoplastic resin sheet having controlled warpage ''

The manufacturing method of the present invention, in extrusion molding a thermoplastic resin sheet, provides a mechanically controlled warp to the sheet at a position where the temperature of the extruded sheet is near the glass transition temperature (Tg) of the thermoplastic resin constituting the sheet. Characterized in that. "Bending" means the deviation from the case where the thermoplastic resin sheet is flat. Specifically, in the state where the thermoplastic resin sheet is embedded, the flow direction of the extrusion molding (hereinafter referred to as "the longitudinal direction") and the width direction of the extrusion molding (hereinafter referred to as the "lateral direction"). When the thread is unfolded at the center of each side to face, it means the distance from the center part of a sheet | seat to a thread. In addition, + when the sheet is bent to the front side (that is, when the curvature is convex upward) is indicated by +, and-when the sheet is bent to the back side (ie when the curvature is convex downward).

In the manufacturing method of this invention, the magnitude | size of a curvature can be suitably set according to a use, and is not specifically limited, Specifically, -100 mm or more, -5 mm or less, or +5 mm or more, +100 mm It is in the range of the following degree. Moreover, the curvature of a thermoplastic resin sheet is stuck along a longitudinal direction and / or a lateral direction. Here, that the warpage is stuck along the longitudinal direction means that the sheet appears to be convex upward or downward when the sheet is viewed in the transverse direction, and that the warpage is stuck along the transverse direction means that the sheet is longitudinally As seen from, it means that the sheet looks convex upwards or downwards, and that the warpage is stuck in the longitudinal and transverse directions means that the sheet is curved upward or downward toward the center at the periphery of the sheet. . Moreover, when a thermoplastic resin sheet has a curvature in a longitudinal direction and a transverse direction, it is preferable that the magnitude | size of curvature is about the same in a longitudinal direction and a transverse direction depending on a use.

In the manufacturing method of this invention, Preferably, the said sheet | seat passes between a pair of upper and lower deflection control rolls at the said position, and selects the shape of the deflection control roll, and / or of the said deflection control roll By arranging the height above or below the height where a flat sheet can be obtained, the sheet is mechanically controlled in warpage. Moreover, the temperature of the said sheet in the position of the said bending control roll becomes like this. Preferably it exists in the range of (Tg +/- 20 degreeC). When the temperature of the sheet is less than (Tg-20 ° C), since the temperature of the sheet is too low, it may be difficult to provide warpage to the sheet. On the contrary, when the temperature of the sheet exceeds (Tg + 20 ° C.), the temperature of the sheet is too high, so that the magnitude of the warpage provided in the sheet may change, and thus the desired warp may not be provided to the sheet.

Moreover, by adjusting the temperature of the said bending control roll up and down and generating a difference in the cooling rate of the said upper and lower surfaces, and / or adjusting the temperature difference of the upper and lower surfaces of the said sheet | seat at or near the position of the said bending control roll. By making a difference in the cooling rate of the upper and lower surfaces of the sheet, it is possible to provide the thermally controlled warpage to the sheet as well.

In the production method of the present invention, when the upper and lower sets of the warpage control rolls used in the extrusion molding are disposed above or below the height where a flat sheet can be obtained, warpage can be provided along the longitudinal direction of the sheet. In addition, when a roll having a shape such as crowning, reverse crowing, arch, or the like is used as a pair of upper and lower warp control rolls, warpage can be provided along the transverse direction of the sheet. In addition, by changing the temperature of a pair of up and down warpage control rolls up and down, warpage can be provided even if a difference in the cooling rate of the top and bottom sheets is generated by adjusting the temperature difference between the top and bottom sheets. In addition to the control of the warp by such a warpage control roll, by heating and / or cooling the sheet at a position downstream from the warpage control roll in the flow direction of the extrusion molding, the temperature difference between the top and bottom of the sheet is adjusted to control the top and bottom of the sheet. May cause a difference in cooling rate. Moreover, it is preferable that the position which adjusts the temperature difference of the upper and lower surfaces of a sheet | seat as close to a warpage control roll as possible by heating and / or cooling a sheet | seat.

As mentioned above, in addition to the control of the warpage by a warpage control roll, when using together adjusting the temperature difference of the upper and lower surfaces of a sheet | seat, a larger warpage can be provided. In order to provide a larger warp, for example, a reverse-crowning roll is used as the upper warpage control roll, a crowning roll is used as the lower warpage control roll, and / or the warpage control roll is flat. It is arranged on the upper side at a height where the sheet can be obtained, and the temperature of the upper bending control roll is set lower than the temperature of the lower bending control roll, and the surface of the sheet passing through the bending control roll is cooled, and / or Heating the back side of the sheet; Alternatively, a crowning roll is used as the upper bending control roll, an inverse crowning roll is used as the lower bending control roll, and / or the lower side is at a height where a flat sheet can be obtained. And the temperature of the upper bending control roll is set higher than the temperature of the lower bending control roll, and further, the surface of the sheet passing through the bending control roll is heated, and / or the back surface of the sheet is Can be cooled.

In the extrusion method of the thermoplastic resin sheet, the production method of the present invention is a method of providing a controlled warp to the extruded sheet according to the height, shape, and temperature of the warpage control roll. That is, by controlling the temperature difference between the upper and lower surfaces of the sheet by heating or cooling the sheet, it is easier and more reliable to control the warpage than in the method of adjusting the warp amount of the sheet, and efficiently and conveniently produce a thermoplastic resin sheet having a controlled warpage. can do.

As a material of a thermoplastic resin sheet, it is polycarbonate resin, for example; (Meth) acrylic resins such as polymethyl methacrylate; Styrene resins such as polystyrene; Acrylic-styrene resins; Norbornene-based resins; Etc. can be mentioned. Of these thermoplastic resins, polycarbonate resins are particularly preferred.

The thermoplastic resin sheet may be formed of a single material, may be formed of two or more kinds of materials, or may be composed of a single layer or a plurality of layers.

Additives, such as a stabilizer, antioxidant, an antistatic agent, a plasticizer, a dispersing agent, a fluorescent brightener, and a diffusing agent, can be mix | blended with the thermoplastic resin which comprises a sheet, for example. What is necessary is just to adjust suitably the compounding quantity of these additives according to the kind, etc., and it is not specifically limited.

Alternatively, a thin layer containing additives such as an antioxidant, an antistatic agent, an ultraviolet ray inhibitor, a fluorescent brightener, and a diffusing agent may be formed on at least one side of the thermoplastic resin sheet. All of these additives may be contained in a single thin layer, or may be contained in a plurality of thin layers, respectively, or in combination.

As a material which comprises a thin layer, (meth) acrylic-type resin, polyester-based resin, epoxy-type resin, silicone-type resin, etc. are mentioned, for example. These resins may be used independently or may use 2 or more types together. Among these resins, (meth) acrylic resins are preferable. In this case, instead of mix | blending an antistatic agent and an ultraviolet absorber, you may mix | blend and use the (meth) acrylic-type resin which has antistatic property, and the (meth) acrylic-type resin which has ultraviolet absorbency.

The thickness of the thin layer (the thickness of each thin layer in the case of a plurality of thin layers) is preferably 100 µm or less, more preferably 50 µm or less. When the thickness of the thin layer exceeds 100 µm, when a thermoplastic resin sheet and a different material are used, unintentional warping may occur due to a difference in heat shrinkage rate or a difference in water absorption rate. In addition, the thickness of a thin layer slices arbitrary ten points in the thermoplastic resin sheet which formed the thin layer to 15 micrometers in thickness with a microtome, observes the cross section with a microscope, actually measures the thickness of a thin layer, and makes it the 10-point average value. .

Additives, such as a stabilizer, antioxidant, a plasticizer, and a dispersing agent, can also be mix | blended with a thin layer, for example. What is necessary is just to adjust suitably the compounding quantity of these additives according to the kind, etc., and it is not specifically limited.

The thickness of the thermoplastic resin sheet (the thickness including the thin layer when the thin layer is formed) is preferably 0.5 mm or more and 15 mm or less, more preferably 1 mm or more and 10 mm or less. If the thickness is less than 0.5 mm, the mechanical strength of the thermoplastic resin sheet may decrease. On the contrary, when the thickness exceeds 15 mm, extrusion of the thermoplastic resin sheet becomes difficult, and the quality of the sheet may be deteriorated.

In the case of using the thermoplastic resin sheet as the light diffusion plate, for example, an appropriate amount of a fluorescent brightener and an antioxidant is added to the thermoplastic resin as described above, respectively, if necessary, but the thermoplastic resin sheet in this case Haze is preferably at least 70%, more preferably at least 80%, more preferably at least 90%, and / or the total light transmittance is preferably at least 40%, more preferably at least 50%, More preferably, it is 60% or more. In addition, haze and total light transmittance are the values measured by the measuring method based on JISK7105. In addition, the fine particles contained in the thermoplastic resin sheet are preferably dispersed substantially uniformly in order to diffuse the light from the light source uniformly and satisfactorily.

Examples of the material of the fine particles include (meth) acrylic resins, styrene resins, polyurethane resins, polyester resins, silicone resins, fluorine resins, synthetic resins such as copolymers thereof; Glass; Clay compounds such as smectite and kaolinite; Inorganic oxides such as silica and alumina; Etc. can be mentioned. Among these materials, silicone resins and silicas are particularly preferred.

The fine particles may be formed of a single material, may be formed of two or more kinds of materials, may be composed of one kind of fine particles of the same material, or may be composed of two or more kinds of fine particles of different materials.

As a shape of microparticles | fine-particles, spherical shape, flat shape, ellipsoid shape, polygonal shape, plate shape, etc. are mentioned, for example. The microparticles | fine-particles which have these shapes may be used independently, or may use 2 or more types together. Among the fine particles having these shapes, spherical particles are suitable, but in the form of flat, ellipsoidal, polygonal, plate, and the like, since spherical particles have stronger light diffusivity than spherical particles and high luminance is obtained by adding a small amount. Particles may be suitable.

The average particle diameter of the fine particles is preferably 0.1 µm or more, 30 µm or less, more preferably 0.5 µm or more, 25 µm or less, more preferably 1 µm or more and 20 µm or less. When the average particle diameter is less than 0.1 µm, light incident on the thermoplastic resin sheet may not be sufficiently diffused. On the contrary, when the average particle diameter exceeds 30 µm, the amount of light passing through the thermoplastic resin sheet may decrease, and the luminance may decrease. In addition, the average particle diameter of microparticles | fine-particles is the value which measured the particle diameter about 100 arbitrary microparticles | fine-particles observed with the microscope, and simply averaged it. In addition, when microparticles | fine-particles are mold release particle | grains, let average of a maximum diameter and a minimum diameter be a particle diameter.

The usage-amount of microparticles | fine-particles is 0.1 mass part or more, 20 mass parts or less, More preferably, it is 0.2 mass part or more and 10 mass parts or less with respect to 100 mass parts of the thermoplastic resin which comprises a sheet | seat. When the amount of use is less than 0.1 part by mass, the light incident on the thermoplastic resin sheet may not be sufficiently diffused. On the contrary, when the amount of use exceeds 20 parts by mass, extrusion of the thermoplastic resin sheet becomes difficult, and the amount of light passing through the thermoplastic resin sheet decreases, and the luminance may decrease.

As the thermoplastic resin constituting the sheet, a particularly preferred polycarbonate resin is obtained by, for example, reacting a dihydric phenol with a carbonate precursor by an interfacial polycondensation method or a melting method.

As the dihydric phenol, for example, 2,2-bis (4-hydroxyphenyl) propane [common name bisphenol A], 1,1-bis (4-hydroxyphenyl) ethane, 1,1-bis (4-hydroxy) Hydroxyphenyl) cyclohexane, 2,2-bis (3-methyl-4-hydroxyphenyl) propane, 2,2-bis (3,5-dimethyl-4-hydroxyphenyl) propane, bis (4-hydroxy Phenyl) sulfide, bis (4-hydroxyphenyl) sulfone, etc. are mentioned. These dihydric phenols may be used independently or may use 2 or more types together. Of these dihydric phenols, bisphenol A is particularly suitable.

Moreover, as a carbonate precursor, a carbonyl halide, a carbonate ester, haloformate, etc. are mentioned, for example, For example, phosgene, diphenyl carbonate, dihaloformate of a dihydric phenol, etc. can be used. .

When the above-mentioned dihydric phenol and the carbonate precursor are reacted by interfacial polycondensation or melting, a polycarbonate-based resin can be used, if necessary, a catalyst, an end terminator, an antioxidant of dihydric phenol and the like can be used.

The polycarbonate resin may be a branched polycarbonate resin obtained by copolymerizing a trifunctional or higher polyfunctional aromatic compound, or may be a polyester carbonate resin copolymerized with an aromatic or aliphatic bifunctional carboxylic acid. Moreover, the mixture which mixed 2 or more types of obtained polycarbonate resin may be sufficient.

The molecular weight of polycarbonate resin is represented by a viscosity average molecular weight, Preferably it is 15,000 or more, 40,000 or less, More preferably, it is 18,000 or more and 35,000 or less. In addition, a viscosity average molecular weight is the value computed by inserting the specific viscosity ((eta) sp) computed from the solution which melt | dissolved 0.7 g of polycarbonate resins in 20 ml of methylene chloride at 20 degreeC in following Formula.

(Where c = 0.7, [η] is the ultimate viscosity and M is the viscosity average molecular weight)

Examples of the polycarbonate resin include thermal stabilizers such as phosphorous acid, phosphoric acid, phosphorous acid ester, phosphate ester, and phosphonic acid ester, as necessary; Ultraviolet absorbers such as triazoles, acetophenones and salicylic acid esters; Antistatic agents such as anionic, cationic, amphoteric and nonionic surfactants and conductive resins; Bluing agents such as anthraquinone dyes; Flame retardants such as tetrabromobisphenol A, low molecular weight polycarbonate of tetrabromobisphenol A and decabromodiphenylene ether; Flame retardant aids such as antimony trioxide; Additives, such as these, can be mix | blended with the addition amount expressing the performance.

As described above, the manufacturing method of the present invention is a method of providing a controlled warp to the extruded sheet according to the height, shape, and temperature of the warpage control roll in the extruded thermoplastic resin sheet.

The conditions of extrusion molding in the manufacturing method of the present invention, for example, the amount of discharge from a die, the temperature and interval of the cooling roll, the takeover (takeover) speed of the takeover roll, and the like are the same as those of producing a flat thermoplastic resin sheet. Substantially the same conditions can be set and are not specifically limited. However, the glass transition temperature (Tg) of the thermoplastic resin in which the temperature of the sheet at the position of the bending control roll controls the amount of discharge from the die and / or uses heating means such as various heaters constitutes the sheet. It is necessary to be in the vicinity, preferably within the range of (Tg ± 20 ° C). In general, the position where the temperature of the extruded sheet becomes near the glass transition temperature (Tg) of the thermoplastic resin constituting the sheet moves to the downstream side in the flow direction of extrusion molding when the amount of discharge from the die is increased. On the contrary, when the discharge amount from the die is reduced, it moves to the upstream side in the flow direction of the extrusion molding.

The structure of the typical sheet extruder used for the manufacturing method of this invention is shown typically in FIG. The sheet extruder 10 includes an extrusion device (not shown), a die 11, a first cooling roll 12, a second cooling roll 13, a third cooling roll 14, a guide roll 15, and a take. It is a normal sheet extruder which consists of over rolls 16, and also 1 pair of upper and lower warpage control rolls 17 are arrange | positioned between the 3rd cooling roll 14 and the guide roll 15 further. Moreover, it moves to the bending control roll 17, upper side, or lower side, and can adjust the height.

When manufacturing a thermoplastic resin sheet using the sheet extruder shown in FIG. 1, in order to adjust the temperature difference of the upper and lower sides of a sheet in addition to the movement of the bending control roll 17, for example, the bending control roll 17 and the guide roll 15 Preferably, heating means for heating the sheet, cooling means for cooling the sheet, and if necessary, to insulate the sheet, immediately downstream of the bending control roll 17 in the flow direction of the extrusion molding. What is necessary is just to arrange a thermal insulation means. In order to make the upper surface of the sheet into the high temperature side and the lower surface of the sheet into the low temperature side, heating means and heat insulating means are disposed on the upper side of the sheet, and / or cooling means is disposed below the sheet, or In order to make the upper surface side of the substrate a low temperature side, and the lower surface of the sheet to the high temperature side, cooling means is arranged on the upper side of the sheet, and / or heating means and warming means are arranged below the sheet. Examples of the heating means include electric heaters, infrared heaters, hot air blowers, and the like. Examples of the cooling means include blowers and cold air blowers. Examples of the heating means include a heat insulating cover. It is not specifically limited.

The process of manufacturing the thermoplastic resin sheet of this invention is demonstrated below using the sheet extruder 10 shown in FIG. First, the thermoplastic resin which comprises a sheet, and various additives are supplied to an extrusion apparatus (not shown) as needed, and knead | mixed sufficiently, and is extruded from the dice | dies 11 into the sheet form of a molten state. The extruded sheet is introduced between the first cooling roll 12 and the second cooling roll 13 to advance on the main surface of the second cooling roll 13, followed by the second cooling roll 13 and the third. It is introduced between the cooling rolls 14, advances on the main surface of the 3rd cooling roll 14, separates it from the 3rd cooling roll 14 in the position of the peeling line 18, and sets of 1 and a set of bending control rolls 17 up and down. After passing through), it is picked up by the take-over roll 16 via the guide roll 15.

At this time, the position of the warpage control roll 17 is a position where the temperature of the extruded sheet is in the vicinity of the glass transition temperature (Tg) of the thermoplastic resin constituting the sheet, preferably in the range of (Tg ± 20 ° C). The thermoplastic resin sheet 20 by selecting the shape of the bending control roll 17 at the position, and / or arranging the bending control roll 17 on the upper side or the lower side at a height where a flat sheet can be obtained. Provides mechanically controlled bending.

In order to provide the curvature controlled according to the shape of the curvature control roll 17, the roll which has shapes, such as crowning, reverse crowing, arch, etc. can be used as the curvature control roll 17, for example. An upward or downward deflection is given along the transverse direction. In this case, the magnitude | size of curvature can be controlled according to the amount of crowning and the bow amount of the curvature control roll 17. FIG.

Moreover, in order to provide the curvature controlled according to the height of the curvature control roll 17, when the curvature control roll 17 is arrange | positioned upward, for example, as shown in FIG. On the contrary, as shown in FIG. 3, when the bending control roll 17 is arrange | positioned below, bending will be given downward along a longitudinal direction. In this case, the magnitude | size of curvature can be controlled with the height (moving distance from the height which can obtain a flat sheet) of the curvature control roll 17. Specifically, if the bending control roll 17 is arrange | positioned on the upper side or the lower side within the range of about 100 mm or less on the basis of the height which can obtain a flat sheet, respectively, it will be in the range of about 100 mm or less, respectively. The deflection is given upward or downward.

Moreover, thermally controlled warpage can also be provided by adjusting the temperature of the warpage control roll 17 up and down to generate a difference in the cooling rate of the top and bottom surfaces of the sheet. In this case, the magnitude | size of curvature can be controlled according to the temperature difference of the upper bending control roll 17 and the lower bending control roll 17. As shown in FIG.

In addition, the glass transition temperature (Tg) of the thermoplastic resin which comprises a sheet can be previously measured by DSC (differential scanning calorimetry). Moreover, since the surface temperature and back surface temperature of the sheet in the position of a bending control roll are substantially the same, the temperature of the extruded sheet means the surface temperature of a sheet | seat, and can be measured with a radiation thermometer.

The thermoplastic resin sheet obtained in this way has the curvature controlled according to the height, shape, and temperature of one set of upper and lower deflection control rolls used for extrusion formation. According to the production method of the present invention, a thermoplastic resin sheet having a controlled warpage can be produced efficiently and conveniently without forming a hot forming process separately from the extrusion molding process, which is industrially advantageous.

`` Thermoplastic sheet ''

The thermoplastic resin sheet of the present invention is a thermoplastic resin sheet produced by the above method. For example, it can be used as a light diffusing plate or building material for a backlight unit such as a liquid crystal display device or a medical monitor, but the display performance of the liquid crystal display device can be stabilized over a long period of time. A large liquid crystal display device that can be used for a liquid crystal display of a television or a desktop PC can be suitably used as a light diffusion plate of a backlight unit.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following Examples, and the present invention is not limited by the following Examples. It is also possible, and they are all included in the technical scope of the present invention.

First, the method of measuring the glass transition temperature (Tg) of the thermoplastic resin which comprises a sheet, the temperature of a sheet, and the magnitude of curvature is demonstrated.

Glass Transition Temperature (Tg)

The glass transition temperature (Tg) of the thermoplastic resin was measured in accordance with JIS K 7121 using a differential scanning calorimeter (trade name: Thermo Plus DSC 8230, Rigaku Co., Ltd.). Specifically, the sample was set in a differential scanning calorimeter, held at 180 ° C. for 10 minutes, then quenched to 80 ° C., at a stable time, heated up to 180 ° C. at a rate of 20 ° C./min, and free from the DSC curve obtained. The transition temperature (Tg) was calculated.

<Temperature of sheet>

The temperature of the extruded sheet was measured using a radiation thermometer (trade name: IR-TAF, Chino Co., Ltd.). Moreover, since the surface temperature and back surface temperature of the sheet in the position of a bending control roll are substantially the same, the surface temperature of the sheet was made into the temperature of a sheet | seat.

<Size of warpage>

The size of the warp is formed by forming a hole at a position where the thermoplastic resin sheet having a length of 1,000 mm × width 1,000 mm is divided into three equal parts at one end in the transverse direction, passing through the strings, and hanging the sheet. The yarn was unfolded at the center of each of the opposite sides in the longitudinal and transverse directions, and the distance from the center of the sheet to the yarn was measured with a steel ruler. In addition, + is the case where the bow is convex upward, and the case where the bow is convex downward is indicated by-.

≪ Reference Example ≫

A sheet extruder equipped with a T dice having a width of 1,200 mm, first, second and third cooling rolls having a diameter of 300 mm, a bending control roll having a diameter of 200 mm, a guide roll, and a takeover roll (the configuration is the sheet shown in FIG. 1). Polycarbonate-based resin sheet was prepared as follows, using the same method as the extruder).

T-Dib with a screw diameter of 120 mm was mounted on the sheet extruder as described above, and a polycarbonate-based resin (trade name: 302-6, Sumitomo Dow Co .; glass transition temperature (Tg): 153 ° C) was used as a thermoplastic resin. Continuously extruded to about 280 ° C. and a width of 1,100 mm, rolled with a first cooling roll and a second cooling roll (two-sided touch method), and a polycarbonate resin sheet was molded while cooling, for example, as shown in FIG. Similarly, one set of bending control rolls 17 (up and down roll temperature: 95 ° C.) is arranged so that the sheet becomes flat from the peeling line 18 to the guide roll 15, and the take-over roll 16 is taken over and flat. A polycarbonate resin sheet (20) was obtained. Moreover, the temperature of the sheet in the position of a bending control roll was (Tg + 5 degreeC). Both ends of the obtained sheet in the width direction were side trimmed by 50 mm to have a width of 1,000 mm and crosscut to a length of 1,000 mm to obtain a polycarbonate resin sheet having a thickness of 2 mm. Table 1 shows the results obtained by measuring the warpage of the obtained sheet.

≪ Example  1≫

For example, as shown in FIG. 2, up and down set of bending control roll 17 (upper and lower roll temperature: 95 degreeC) so that a sheet may be convex upward from the peeling line 18 to the guide roll 15. FIG. , And more specifically, the polycarbonate-based resin sheet was obtained in the same manner as in the reference example except that the height of the bending control roll was moved 2 cm upward on the basis of the height to obtain a flat sheet. . Table 1 shows the results obtained by measuring the warpage of the obtained sheet.

≪ Example  2≫

For example, as shown in FIG. 2, the bending control roll 17 (up-down roll temperature: 95 degreeC) is arrange | positioned so that the sheet | seat may be convex upward from the peeling line 18 to the guide roll 15. Using a reverse-crowning roll as the upper bending control roll, and using a crowning roll as the lower bending control roll, More specifically, the height of a pair of upper and lower bending control rolls each having a 2 cm crowning amount The polycarbonate-based resin sheet was obtained by the same method as the reference example except that 2 cm was moved upwards with respect to the height which can obtain the flat sheet | seat. Moreover, the temperature of the sheet in the position of a bending control roll was (Tg-10 degreeC). Table 1 shows the results obtained by measuring the warpage of the obtained sheet.

≪ Example  3≫

For example, as shown in FIG. 3, the up-and-down set of bending control roll 17 (up-down roll temperature: 95 degreeC) is carried out so that the sheet may be convex downward from the peeling line 18 to the guide roll 15. As shown in FIG. A polycarbonate-based resin sheet was obtained in the same manner as in Reference Example, except that the height of the bending control roll was moved 4 cm downward based on the height at which the flat sheet could be obtained. . Moreover, the temperature of the sheet in the position of a bending control roll was (Tg-5 degreeC). Table 1 shows the results obtained by measuring the warpage of the obtained sheet.

≪ Example  4≫

For example, as shown in FIG. 3, the upper and lower bending control rolls 17 are arranged so that the sheet is convex downward from the peeling line 18 to the guide roll 15, and the upper and lower bending control rolls Adjusting the temperature difference, more specifically, the height of the bending control roll (upper roll temperature: 100 ° C, lower roll temperature: 80 ° C) was moved 4 cm to the lower side on the basis of the height to obtain a flat sheet Obtained the polycarbonate-type resin sheet by the method similar to a reference example. Moreover, the temperature of the sheet in the position of a bending control roll was (Tg + 10 degreeC). Table 1 shows the results obtained by measuring the warpage of the obtained sheet.

≪ Example  5≫

Polystyrene resin (trade name: HH203, PS Japan Co., Ltd.) as the thermoplastic resin; Polystyrene-based resin sheet in the same manner as in Example 1 except that the glass transition temperature (Tg) was 108 ° C.) and the molding temperature was about 220 ° C. and the temperature of the warpage control roll 17 was set to 60 ° C .. Got. Table 1 shows the results obtained by measuring the warpage of the obtained sheet.

≪ Example  6≫

As a thermoplastic resin, methacryl-type resin (brand name: Sumipex EX Sumitomo Chemical Co., Ltd .; glass transition temperature (Tg): 97 degreeC) is used, the molding temperature is about 250 degreeC, and the temperature of the warpage control roll 17 is raised and lowered. A methacrylic resin sheet was obtained in the same manner as in Example 1 except that the temperature was set at 80 ° C. Table 1 shows the results obtained by measuring the warpage of the obtained sheet.

≪ Example  7≫

Polycarbonate resin (trade name: Eupyron E2000FN. Mitsubishi Engineering Plastics Co., Ltd .; glass transition temperature (Tg): 154 ° C) was used as the thermoplastic resin, and 100% by mass of this polycarbonate resin was used as the fine particles of silica spherical fine particles. A polycarbonate-based resin sheet was obtained in the same manner as in Example 1 except that 0.5 mass% of (trade name: Shihostar KE-P150, Nihon Shokubai Co., Ltd .; average particle size: 1.33 to 1.83 µm) was mixed. Table 1 shows the results obtained by measuring the warpage of the obtained sheet.

≪ Comparative example  1 to 3≫

Except having set the temperature of the sheet | seat in the position of a curvature control roll to (Tg + 30 degreeC), the polycarbonate-type resin sheet was obtained by the method similar to Examples 1-3, respectively. Table 1 shows the results obtained by measuring the warpage of the obtained sheet.

≪ Comparative example  4 to 6≫

Except having set the temperature of the sheet in the position of a bending control roll to (Tg-30 degreeC), the polycarbonate-type resin sheet was obtained by the method similar to Examples 1-3, respectively. Table 1 shows the results obtained by measuring the warpage of the obtained sheet.

As is apparent from Table 1, the bending control roll is raised at a height where a flat sheet can be obtained at a position where the temperature of the extruded sheet is within a range of (Tg-20 ° C) or more and (Tg + 20 ° C) or less. Or the thermoplastic resin sheet of Examples 1-7 arrange | positioned at the lower side is the thermoplastic resin sheet of the reference example which arrange | positioned the bending control roll at the height which can obtain a flat sheet at the position where the temperature of an extruded sheet becomes (Tg + 5 degreeC). In comparison, apparently mechanically controlled warpage is given. Further, in detail, the thermoplastic resin sheets of Examples 1, 3, 5, 6, and 7 using the warpage control roll having a planar shape are given upward or downward warpage along the longitudinal direction, respectively, and the magnitude of the warpage. Is controlled according to the movement distance of a bending control roll. In addition, the thermoplastic resin sheet of Example 2 using the roll having the shape selected as the warpage control roll is given the same degree of warpage along the longitudinal direction and the transverse direction, and the magnitude of the warpage is the movement distance and the crowning amount of the warpage control roll. It is controlled according to. Moreover, the thermoplastic resin sheet of Example 4 which made the difference of the cooling rate of the upper and lower sides of the sheet | seat by adjusting the temperature of a curvature control roll up and down is given larger curvature along a longitudinal direction and a lateral direction.

On the other hand, the thermoplastic resin sheet of Comparative Examples 1-6 which arrange | positioned the bending control roll at the upper side or lower side at the height which can obtain a flat sheet at the position where the temperature of an extruded sheet becomes (Tg +/- 30 degreeC) is an extruded sheet The temperature of the extruded sheet is (Tg + 5 ° C.) because the temperature of the substrate is too low or too high, so that the bending control roll is mechanically similar to the thermoplastic resin sheet of the reference example in which a flat sheet is obtained. Controlled warpage is not given.

From the above results, in the extrusion molding of the thermoplastic resin sheet, at a position where the temperature of the extruded sheet becomes near the glass transition temperature (Tg) of the thermoplastic resin constituting the sheet, preferably in the range of (Tg ± 20 ° C) It can be seen that in the in-place position, the sheet can be provided with mechanically controlled warpage, preferably controlled warpage according to the height, shape, and temperature of the warpage control roll.

Since the present invention can easily and efficiently provide a thermoplastic resin sheet having a controlled warpage, it is possible to use such a thermoplastic resin sheet as a building material for a light diffusion plate or a building used for a backlight unit such as a liquid crystal display device or a medical monitor. By doing this, we make a big contribution in wide field.

Claims (8)

In extrusion molding a thermoplastic resin sheet, control is provided to provide mechanically controlled warp to the sheet at a position at which the temperature of the extruded sheet is near the glass transition temperature (Tg) of the thermoplastic resin constituting the sheet. A method for producing a thermoplastic resin sheet having a warped bending. The method of claim 1, By passing the sheet between the upper and lower sets of bending control rolls at the position and selecting the shape of the bending control roll, and / or the upper and lower sides of the bending control roll at a height where a flat sheet can be obtained. By providing a mechanically controlled warp to the sheet. The method of claim 2, The manufacturing method in which the temperature of the said sheet in the position of the said bending control roll exists in (Tg +/- 20 degreeC). The method of claim 2, And adjusting the temperature of the bending control roll up and down to generate a difference in the cooling rate of the upper and lower surfaces of the sheet, thereby providing the thermally controlled bending to the sheet. The method of claim 2, A method for producing a thermally controlled warp in the sheet further by adjusting a temperature difference between the upper and lower surfaces of the sheet at a position of or near the warping control roll to generate a difference in the cooling rate of the upper and lower surfaces of the sheet. The method of claim 1, The manufacturing method in which the thermoplastic resin which comprises the said sheet contains microparticles | fine-particles. The method of claim 1, The thermoplastic resin constituting the sheet is selected from the group consisting of polycarbonate resins, (meth) acrylic resins, styrene resins, acrylic-styrene resins and norbornene resins. A thermoplastic resin sheet having a controlled warpage, which is obtained by the manufacturing method according to any one of claims 1 to 7.

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