KR20160015395A - Polycarbonate resin pellet for thin optical members and method for manufacturing same - Google Patents

Abstract

There is provided a polycarbonate resin pellet for a thin optical member having excellent mechanical properties, thermal properties and electrical properties, and excellent weather resistance, and exhibiting a high transmittance and a good color, and a method for producing the polycarbonate resin pellet is also provided. Which is an elliptic columnar pellet made of a polycarbonate resin having a viscosity average molecular weight of 10,000 to 15,500 and a length of 2.0 to 5.0 mm and whose elliptical cross section has a long diameter / short diameter ratio of 1.5 to 4 and a short diameter of 1.0 to 3.0 mm, A polycarbonate resin pellet for a thin optical member is provided.

Description

TECHNICAL FIELD [0001] The present invention relates to a polycarbonate resin pellet for a thin optical member, and a method for manufacturing the same. [0002]

The present invention relates to a polycarbonate resin pellet for a thin optical member and a method for producing the same. In particular, the present invention relates to a polycarbonate resin pellet for a thin optical member exhibiting excellent mechanical properties, thermal properties, electrical properties, and excellent weather resistance, and exhibiting high transmittance and good color, and a method for producing the same.

2. Description of the Related Art A liquid crystal display device used in a personal computer, a mobile phone, a tablet PC, and a smart phone incorporates a planar light source device in order to respond to a demand for thinning, lightening, cutting and high definition. The planar light source device is also provided with a light guide plate having a uniform cross section and a flat light guide plate having a uniform inclined plane for the purpose of uniformly and efficiently guiding the incident light to the liquid crystal display. In some cases, a concave-convex pattern is also formed on the surface of the light guide plate to give a light scattering function.

Such a light guide plate is obtained by injection molding of a thermoplastic resin, and the concavo-convex pattern is generated by transferring convex-concave portions formed on the surface of the insertion portion. Conventionally, the light guide plate has been molded from a resin material such as polymethylmethacrylate (PMMA); In recent years, a display device for illuminating a clearer image is required, and the temperature in the device tends to increase due to heat generated in the vicinity of the light source, so that conversion to a polycarbonate optical molding material having a higher heat resistance is achieved.

In the case of a polycarbonate resin for a light guide, since molding is performed at a temperature higher than the molding temperature for a conventional polycarbonate resin, a higher fluidity is required by decreasing the viscosity average molecular weight even at the sacrifice of mechanical strength . Therefore, the polycarbonate resin for a thin optical member typified by the light guide as described above is a material having a lower mechanical strength than the conventional polycarbonate resin, and as a result, the extruded polycarbonate There is a problem that the resin strand is easily split during cooling and it is difficult to stably produce the resin strand.

In addition, factory-manufactured pellets are transported in an envelope or a flexible container, for example, for delivery, and part of the pellets are undifferentiated due to contact between the pellets during transportation. When such a pellet containing the fine powder is used, for example, in the molding of a light guide, yellowing and optical fluctuations of the molded product tend to occur.

As means for solving the problems caused by the fine particles, it is possible to eliminate them by removing the fine particles through the fine particle eliminator during the molding process. However, this has the desire to avoid, and possibly avoid, the risk of contamination due to the introduction of excessive steps.

Patent Document 1 discloses a polycarbonate for optical disc having an average pellet length of 2.5 to 3.5 mm and an average value of at least 70% of the pellet length in the range of ± 0.1 mm in length for preventing the occurrence of silver strike of the optical disc Resin pellets have been proposed. In the above-mentioned same document, it is mentioned that when the pellet having such a small amount of fine particles is subjected to plasticization, there is no air entrainment and no optical stripe is produced, but the shape of such a pellet is not described .

Patent Document 2 discloses that the average value of the pellet length is in the range of 2.5 to 3.5 mm, the average value of the long diameter of the elliptical section is in the range of 2.60 to 3.2 mm, and more than 70% 0.08 mm and the average value of the long diameter is within ± 0.12 mm. In the same document, by setting the length and the long diameter of the pellet to the above-mentioned range, a three-dimensional shape in which the ratio of the length to the long diameter is balanced to about 0.7 to 1.5 is obtained, its distribution is specified and falls within a narrow range, . This also results in that the shape becomes more suitable for the structure of the cylinders and shafts of the injection molding machine for optical discs, the melting efficiency during plasticization is increased, the plasticizing time is shortened and the molding cycle is short, so-called high- it is possible to manufacture an optical disk substrate by molding. Another characteristic feature in Patent Document 2 is that the pellet mass has a uniform shape, but details of the shape of the ellipse of the individual pellet are not described. Further, as a concrete manufacturing method of such pellets, And only those that are manufactured by the above method are described.

In addition, as in the inventions described in Patent Documents 1 and 2, minimizing the fine particles in the pellet mass is also very important for a thin optical member such as a light guide, but only by that, occurrence of yellowing and optical fluctuation is suppressed It is not sufficient as a polycarbonate resin pellet for a thin optical member.

Japanese Patent Application Laid-Open No. H07-52272 Japanese Patent Laid-open No. H11-035692

The present invention has been made in view of the above-described circumstances, and it is an object of the present invention to provide a method of molding a light guide body using a low molecular weight polycarbonate resin processed to a low mechanical strength and a shape in which a relatively small amount of micro- And has the object to provide a light guide body in which occurrence of yellowing and optical fluctuation of the molded article is suppressed. A further object is to provide a method for stably producing such pellets.

The present inventors have conducted extensive investigations to solve the above problems. As a result of extensive research, it has been found that, in the production of pellets from such polycarbonate resin, the strand cross-sectional shape at the time of extrusion is flattened and thereby elasticity is imparted to the strands, , Pellets for a thin optical member can be stably produced.

Further, it has been found that the micronization due to contact between the pellets can be suppressed by making the shape of the pellet after pelletization into a specific flat shape, and as a result, it is possible to suppress the occurrence of yellowing and optical fluctuation in the molding, It has been found that excellent pellets are provided for the members. Based on these findings, the present invention has been accomplished.

The present invention provides a polycarbonate resin pellet for a thin optical member described below, a method for producing the same, a thin optical member and a light guide.

[1] Polycarboxylic acids having a viscosity average molecular weight of 10,000 to 15,500, a length of 2.0 to 5.0 mm, a major diameter / minor diameter ratio of 1.5 to 4 in the elliptical section thereof, and a minor diameter of 1.0 to 3.0 mm A polycarbonate resin pellet for a thin optical element, comprising an elliptical columnar pellet made of a boronate resin.

[2] The polycarbonate resin pellet for a thin optical member according to [1], wherein the viscosity average molecular weight is 11,500 to 15,000.

[3] A method for producing a polycarbonate resin pellet according to [1] or [2], wherein 500 g of a polycarbonate resin pellet is filled in a 2-liter polyethylene sealed container having an outer diameter of 125 mm and a total height of 233 mm and the container is fixed in a 50- , The polycarbonate resin pellets for a thin optical member having an amount of fine powder of 1 mm or less in particle size generated by the polycarbonate resin pellets after being rotated at a rotation speed of 30 rpm for 20 minutes is 50 ppm or less.

[4] The thin polycarbonate resin pellet for an optical member according to any one of [1] to [3], wherein the major axis / minor axis ratio of the elliptical cross section of the pellet is 1.8 to 4.

[5] A process for producing a polycarbonate resin pellet for a thin optical member according to any one of [1] to [4], wherein the process for producing a polycarbonate resin pellet comprises:

A polycarbonate resin having a viscosity average molecular weight of 10,000 to 15,500 is extruded as a strand from an extrusion nozzle having an elliptical die orifice disposed at the distal end of the extruder,

Cooling and solidifying such polycarbonate in a cooling water bath;

Polycarbonate is cut with a strand cutter.

[6] In the case where the strand acquisition speed is 100 mm / sec and the difference in height between the supports supporting the strands is 290 mm, in the case where strand breakage does not occur during one hour or more continuous operation, Is not more than 300 mm. The polycarbonate resin pellets according to claim 1,

[7] A thin optical member molded from a polycarbonate resin pellet for a thin optical member according to any one of [1] to [4].

[8] A light guide formed from a polycarbonate resin pellet for a thin optical member according to any one of [1] to [4].

The polycarbonate resin pellets of the present invention have a low viscosity average molecular weight of 10,000 to 15,500 and are difficult to be pulverized due to contact between the pellets. As a result, thin polycarbonate resin pellets, such as light guides, Is excellent as a member pellet. In addition, pellets for thin optical members can be stably produced by flattening the cross-sectional shape of the strands during extrusion during pelletization, thereby imparting elasticity to the strands and suppressing breakage during cooling.

1 is a schematic view of a polycarbonate resin pellet for a thin optical member of the present invention.
2 is a conceptual diagram of a process for producing a polycarbonate resin pellet by extruding a strand from an extruder and a method for evaluating a critical strength.
3 is a conceptual diagram showing the details of the method of evaluating the limiting strength of strands.

Hereinafter, the present invention will be described in detail with reference to embodiments and examples, but the present invention should not be construed as being limited to the corresponding embodiments and examples.

In this specification, "to" is used to mean that the numerical values described before and after "to" are included as lower limit and upper limit unless otherwise specified.

The polycarbonate resin pellets for a thin optical member of the present invention have a viscosity average molecular weight of 10,000 to 15,500, a length of 2.0 to 5.0 mm, a elliptical cross section of which has a long diameter / short diameter ratio of 1.5 to 4, Lt; RTI ID = 0.0 > mm, < / RTI >

[Polycarbonate resin]

Examples of polycarbonate resins to be used in the present invention include aromatic polycarbonate resins, aliphatic polycarbonate resins, and aromatic-aliphatic polycarbonate resins. Aromatic polycarbonate resins are preferred, and thermoplastic aromatic polycarbonate polymers or copolymers obtained by reacting aromatic dihydroxy compounds with phosgene or carbonate diesters are particularly used.

Examples of the aromatic dihydroxy compound include 2,2-bis (4-hydroxyphenyl) propane (i.e., bisphenol A), tetramethyl bisphenol A,?,? ' Propylbenzene, hydroquinone, resorcinol, and 4,4'-dihydroxydiphenyl. A compound in which at least one tetraalkylphosphonium sulfonate is bonded to an aromatic dihydroxy compound as described above or a compound in which a polymer or oligomer having a siloxane structure and containing a phenolic OH group at both terminals is used as a part of a dihydroxy compound , A polycarbonate resin having high flame retardancy can be obtained.

Preferable examples of the polycarbonate resin used in the present invention include 2,2-bis (4-hydroxyphenyl) propane as the dihydroxy compound or 2,2-bis (4-hydroxyphenyl) Is a polycarbonate resin used in combination with an aromatic dihydroxy compound.

The production method of the polycarbonate resin is not particularly limited, but is usually produced by an interfacial polymerization method (phosgene method) or a melting method (ester exchange method).

In the polymerization reaction in the interfacial polymerization method, phosgene is reacted with an aromatic dihydroxy compound and, if necessary, a molecular weight regulator (terminal terminator) in the presence of a reaction-inert organic solvent and an aqueous alkali solution, And an antioxidant for preventing oxidation of the aromatic dihydroxy compound; Adding a polymerization catalyst such as a tertiary amine or a quaternary ammonium salt or the like; Interfacial polymerization is carried out to obtain a polycarbonate resin. The addition of the molecular weight modifier is not particularly limited as long as it is added between the time of phosgenation and the initiation of the polymerization reaction. The reaction temperature is, for example, 0 to 40 ° C, and the reaction time is, for example, several minutes (for example, 10 minutes) to several hours (for example, 6 hours).

Examples of the reaction-inert organic solvent include chlorinated hydrocarbons such as dichloromethane, 1,2-dichloroethane, chloroform, monochlorobenzene and dichlorobenzene. Examples of the alkali compound used in the aqueous alkali solution include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide.

Examples of the molecular weight regulator include a monohydroxyl compound having a phenolic hydroxyl group, and preferred examples thereof include m-methylphenol, p-methylphenol, m-propylphenol, p-propylphenol, p- And p- (long chain alkyl) -substituted phenols. The amount of the molecular weight regulator expressed per 100 moles of the aromatic dihydroxy compound is preferably 50.0 to 0.5 mole, more preferably 30 to 1 mole.

Examples of the polymerization catalyst include tertiary amines such as trimethylamine, triethylamine, tributylamine, tripropylamine, trihexylamine and pyridine, and quaternary ammonium salts such as trimethylbenzylammonium chloride, tetramethylammonium chloride and triethylbenzyl Ammonium chloride is exemplified.

With respect to the melting method, the polymerization reaction in this production method is, for example, an ester exchange reaction between a carbonate diester and an aromatic dihydroxy compound. The carbonate diesters include dialkyl carbonate compounds such as dimethyl carbonate, diethyl carbonate and di-tert-butyl carbonate; Diphenyl carbonate; And substituted diphenyl carbonates such as ditolyl carbonate. The carbonate diester is preferably diphenyl carbonate or substituted diphenyl carbonate, and diphenyl carbonate is more preferable.

In general, the mixing ratio of the carbonate diester and the aromatic dihydroxy compound is adjusted, the degree of decompression during the transesterification reaction is adjusted, and the amount of the aromatic polycarbonate resin Can be obtained in a melt transesterification reaction. The carbonate diester is used in the melt transesterification reaction in an amount of usually not less than equimolar amount, preferably 1.001 to 1.3 mol, particularly preferably 1.01 to 1.2 mol, per 1 mol of the aromatic dihydroxy compound. Further, in a more aggressive adjustment method, a terminal terminator may be added separately during the reaction, and examples of the terminal regulator include 1 hydroxyl phenol, a monobasic carboxylic acid, and a carbonate diester.

The polycarbonate resin used in the present invention can be produced by an interfacial polymerization method as described above or a melt polymerization method as described above.

The polycarbonate resin used in the present invention relates to a polycarbonate resin having a viscosity average molecular weight [Mv] of 10,000 to 15,500. This is preferable for a thin optical member since a molded article having good flowability and low residual stress is obtained in the viscosity average molecular weight [Mv] within this range. When the viscosity average molecular weight [Mv] is less than 10,000, the strength of the molded article is significantly lowered. If it exceeds 15,500, the fluidity becomes insufficient and molding of the thin optical member becomes difficult. The viscosity average molecular weight [Mv] is preferably 10,500 or more, more preferably 11,000 or more, even more preferably 11,500 or more, and preferably 15,000 or less.

Here, the viscosity average molecular weight [Mv] means a value calculated using Schnell's viscosity formula, i.e., ŋ = 1.23 x 10 ^-4 Mv ^0.83 , wherein the intrinsic viscosity [ŋ] Unit: dl / g) is measured using a Ubbelohde viscometer using methylene chloride as a solvent. The intrinsic viscosity [ŋ] is the value calculated using the following equation and the specific viscosity [ _{sp sp} ] measured at each solution concentration [C] (g / dl).

[Equation 1]

Two or more polycarbonate resins may be used in combination as the polycarbonate resin, and a combination having a polycarbonate resin having a viscosity average molecular weight [Mv] outside the range of 10,000 to 15,500 may be used Adjusted to a molecular weight of 15,500).

The polycarbonate resin may contain additives such as heat stabilizers, antioxidants, mold release agents, ultraviolet absorbers, fluorescent brighteners, pigments, dyes, other polymers, flame retardants, impact modifiers, antistatic agents, plasticizers, compatibilizers and the like. One of these additives may be incorporated, or two or more may be incorporated. Among the above-mentioned, it is particularly preferable to use heat stabilizers and antioxidants.

There is no particular limitation on the heat stabilizer, but for example, a phosphorus compound is preferable. Any known phosphorus compound may be used as the phosphorus compound. Specific examples are phosphorous oxo acids such as phosphoric acid, phosphonic acid, phosphorous acid, phosphinic acid and polyphosphoric acid; Metal acid pyrophosphates such as sodium acid pyrophosphate, potassium acid pyrophosphate and calcium acid pyrophosphate; Phosphate salts of Group 1 or Group 10 metals such as potassium phosphate, sodium phosphate, cesium phosphate and zinc phosphate; Organophosphate compounds; Organophosphite compounds; And organophosphonite compounds.

Among the above, preferred are organophosphites such as triphenyl phosphite, tris (monononylphenyl) phosphite, tris (monononyl / dinonyl-phenyl) phosphite, tris (2,4-di- ) Phosphite, monoctyldiphenyl phosphite, dioctyl monophenyl phosphite, monodecyl diphenyl phosphite, didecyl monophenyl phosphite, tridecyl phosphite, triruryl phosphite, tristearyl phosphite, and 2 , 2-methylenebis (4,6-di-tert-butylphenyl) octylphosphite.

The content of the heat stabilizer represented by 100 parts by weight of the polycarbonate resin is generally 0.001 parts by mass or more, preferably 0.01 parts by mass or more, more preferably 0.03 parts by mass or more, and generally 1 part by mass or less Preferably 0.7 parts by mass or less, and more preferably 0.5 parts by mass or less. If the heat stabilizer is too small, the heat stabilizing effect may be insufficient, while if the heat stabilizer is excessively large, the effect may become saturated and may be uneconomical.

As an example of the antioxidant, a hindered phenolic antioxidant is preferable. Specific examples are pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octadecyl 3- (3,5- Hydroxyphenyl) propionate, thiodiethylene bis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], N, N'-hexane-1,6-diylbis Diethyl [[3,5-bis (4-hydroxyphenyl) propionamide] (1, 1-dimethylethyl) -4-hydroxyphenyl] methyl] phosphonate, 3,3 ', 3 ", 5,5' - (mesitylene-2,4,6-triyl) tri-p-cresol, 4,6-bis (octylthiomethyl) -ocresol, ethylene bis (oxyethylene) (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 1,3,5- Tris (3,5-di-tert-butyl-4-hydroxybenzyl) -1,3,5-triazine-2,4,6 (1H, 3H, 5H) trione and 2,6- -Butyl-4- (4,6-bis (Octylthio) -1,3,5-triazin-2-ylamino) phenol.

Among these, pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] and octadecyl 3- (3,5-di- -Hydroxyphenyl) propionate is preferable. Examples of such phenolic antioxidants include "Irganox 1010" (registered trademark, hereinafter the same) and "Irganox 1076" manufactured by BASF, and "Adeka Stab AO-50" and "Adeka Stab AO-60" manufactured by ADEKA Corporation have.

One type of antioxidant may be incorporated or two or more types may be incorporated in any proportion.

The content of the antioxidant shown per 100 parts by mass of the polycarbonate resin is generally 0.001 parts by mass or more, preferably 0.01 parts by mass or more, and generally 1 part by mass or less, and preferably 0.5 parts by mass or less. If the content of the antioxidant is lower than the lower limit of the indicated range, the effect as an antioxidant may not be satisfactory. If the content of antioxidant is above the upper limit for the indicated range, the effect may be saturated and uneconomical.

Regarding the polycarbonate resin in the present invention, it is possible to use a polycarbonate resin regenerated from a consumed product, that is, a material-regenerated polycarbonate resin as well as natural raw materials. In addition, it is also possible to use, for example, a pulverized product obtained from a defect product, a sprue, a runner or the like, and a fine particle obtained by melting it. The regenerated polycarbonate resin is preferably used in combination with a particulate polycarbonate resin which is not a regenerated product, and it is preferably used in an amount of 80 mass% or less, more preferably 50 mass% or less, Or less, particularly 30 mass% or less.

[Polycarbonate resin pellets]

The polycarbonate resin pellets of the present invention have an elliptical columnar shape. 1 is a schematic view of a polycarbonate resin pellet for a thin optical member of the present invention.

The polycarbonate resin pellets of the present invention have a length L in the range of 2.0 to 5.0 mm, a ratio (d / a) between the long diameter d and the short diameter a of the elliptical cross section of the pellets in the range of 1.5 to 4, To 3.0 mm.

If the length L is not within the range of 2.0 to 5.0 mm, the pellet is prone to fracture and a large amount of differentiation will occur. When the ratio (d / a) between the long diameter d and the short diameter a is out of the range of 1.5 to 4, the strength of the resin strand is lowered and the pellet production by extrusion becomes unstable. If the elliptical short axis a is not within the range of 1.0 to 3.0 mm, the pellet is likely to break and a large amount of differentiation will occur.

The ratio (d / a) between the long diameter d and the short axis a is preferably 1.6 or more, more preferably 1.7 or more, even more preferably 1.8 or more, preferably 3.5 or less, more preferably 3.0 or less.

By having such a shape, the polycarbonate resin pellets of the present invention have a unique characteristic that the pellets are loaded on, for example, envelopes or flexible containers and that the generation of fine particles is suppressed even when subjected to vibrations and loads during transportation and delivery . The longitudinal direction of the elliptical cross section of the pellet becomes horizontal and receives a load, so that it is considered that generation of the fine powder is suppressed.

With respect to the amount of occurrence of the fine powder from the polycarbonate resin pellets of the present invention, 500 g of the resin pellets were placed in a 2-liter polyethylene sealed container having an outer diameter of 125 mm and a total height of 233 mm and fixed in a 50- When rotated at a rotational speed of rpm for 20 minutes, the amount of the fine powder having a particle diameter of 1 mm or less is preferably 50 ppm or less.

[Production of polycarbonate resin pellets]

As a method of producing the polycarbonate resin pellets of the present invention, various methods can be used, and preferred embodiments are described below.

The polycarbonate resin having the above-mentioned viscosity average molecular weight is supplied to the extruder from a hopper which is stored in a raw material feeder and therefrom by a quantitative feeder, from a hopper installed on the extruder. The polycarbonate resin may take the form of pellets or powder.

When other components than the polycarbonate resin are mixed, the blending thereof can be carried out at any stage before introduction into the extruder. For example, all components may be blended with a tumbler, Henschel mixer or blender, and then introduced into a hopper chute, optionally through a feeder, and fed to the extruder. A single screw extruder or twin screw extruder can be used as the extruder. Also, feeding the hopper chute can be carried out by a separate path from the polycarbonate resin.

The extruder may be a single screw extruder or a twin screw extruder, preferably a twin screw extruder. The L / D of the axis of the extruder is preferably from 10 to 80, more preferably from 15 to 70, even more preferably from 20 to 60. When the shaft is too short, the degassing tends to be insufficient. On the other hand, when the shaft is too long, the color tends to deteriorate.

The polycarbonate resin is then extruded in the form of strands from the extrusion nozzle at the end of the extruder. A die having an elliptical die orifice is preferred for a die of an extrusion nozzle. The ellipticity of the pellet can be changed by changing the ellipticity of the elliptic die orifice of the extrusion nozzle.

The extrusion is preferably carried out using a die in an extrusion nozzle which is fixed so that the long diameter of the elliptical die orifice is substantially horizontal and the long diameter of the extruded strand of the elliptical cross section is approximately horizontal. The temperature of the polycarbonate resin immediately after extrusion is generally about 300 ° C.

A strand having an elliptical cross-section is taken by a take-up roller whose horizontal length is roughly horizontal and is conveyed and cooled in a water bath in a cooling water tank. In order to minimize deterioration of the resin, the time from when the strand is extruded from the die to entering the water is short. It is generally desirable to enter the water within one second after extrusion from the die.

The cooled strand is conveyed to a pelletizer by a take-up roller and cut to a pellet length of 2.0 to 5.0 mm to provide pellets.

FIG. 2 is a conceptual view showing a process of manufacturing a polycarbonate resin pellet by extruding a strand from an extruder, and FIG. 3 is a conceptual diagram showing details of a method of evaluating a critical strength.

The polycarbonate resin pellets are extruded from the extrusion nozzle 2 of the extruder, and the strands 1 are introduced into the cooling water tank 3, cooled and then taken up while being supported by the support rollers C, B and A of the take- Lt; / RTI > At this time, at a strand acquisition speed (Vx) of 100 mm / sec, when the difference in height between the support CA supporting the strand 1 and the support B between the supports C and A at the same height is 290 mm, (Xmm, hereinafter also referred to as "limit interval") defined as the interval between the support C and the support A where strand breakage does not occur is 300 mm or less.

[Thin optical member]

The polycarbonate resin pellets obtained by the present invention are molded into arbitrary shapes and used as thin optical members.

Means that the thickness of the thin portion is generally not more than 1 mm, preferably not more than 0.8 mm, more preferably not more than 0.6 mm, especially not more than 0.5 mm, while the lower limit is generally not less than 0.1 mm, preferably not more than 0.2 mm or more. The molded article having a thin part should have such a thin part at least on a part thereof, but its shape, dimensions and the like are not limited.

The shape, pattern, color, dimensions, etc. of the thin optical member are not limited and can be freely established depending on the use thereof.

The method of producing the thin optical member is not particularly limited, and any molding method generally used for the polycarbonate resin composition may be employed. Examples thereof include a blow molding method such as an injection molding method, an ultra high speed injection molding method, an injection compression molding method, a two-color molding method, a gas assist molding, a molding method using a heat insulating mold, a molding method using a rapid heating mold, Molding, insert molding, IMC (in-mold coating molding) molding, extrusion molding, sheet molding, thermoforming, rotary molding, lamination molding and press molding. Molding methods using a hot runner technique can also be used.

A light guide such as a light guide plate is a typical example of a thin optical member. A light guide plate is for transmitting light from a light source such as an LED in a liquid crystal backlight unit, various display devices, and lighting equipment. Generally, the light guide plate diffuses light introduced from a side or a rear surface and forms uniform light . The shape is generally flat, and may or may not have irregularities on the surface.

The molding of the light guide plate is generally carried out preferably by, for example, an injection molding method, an ultra-high speed injection molding method and an injection compression molding method.

The thin molded article molded by using the resin pellet of the present invention has no problem of occurrence of yellowing, white spot defect and vacuum void, and most preferably, it can be preferably used as various thin optical members including a light guide plate.

Examples of the thin optical member include a portable terminal such as a mobile phone, a mobile notebook, a netbook, a slate PC, a tablet PC, a smart phone and a tablet-type terminal, and also a camera, a wrist watch and a wall clock, And various thin optical members used in apparatuses and the like.

Example

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

(Example 1)

An aromatic polycarbonate resin (trade name: "Iupilon" (registered trademark), manufactured by Mitsubishi Engineering-Plastics Corporation) having bisphenol A as a starting material and having a viscosity average molecular weight (Mv) of 13,000 was extruded from a twin- Extruded under the following extrusion conditions: cylinder temperature = 240 占 폚, extrusion speed = 150 kg / hr, and shaft rotation speed = 150 占 폚 / 250 rpm. Extrusion was carried out from an extrusion nozzle equipped with a die having an elliptic die orifice as described in Table 1, in which the long diameter thereof was horizontal, and extrusion was performed in a strand shape such that the elliptical cross section of the elliptical cross section was substantially horizontal. And introduced into the cooling water tank. The strand thus obtained was cut in a pelletizer at a strand acquisition speed and a cutter blade rotation speed shown in Table 1 to obtain polycarbonate resin pellets.

(1) Long diameter / short diameter ratio of the pellet ellipse section

The long diameter, the short diameter and the length of the obtained polycarbonate resin pellets were measured, and an average value was obtained for each of 100 pieces. The average value of the long diameter / short diameter ratio was used as the pellet ellipticity.

(2) Strand stability

To prevent the extrusion direction of the strand discharged from the die from unexpectedly crumbling, the strand is produced so that the strand is extruded straightly by pressing the support against the strand and applying a constant load.

Using these conditions, the number of strands separated per hour was counted to evaluate the stability of extrusion.

(3) Limit strength of strand

The limiting strength of the strand was evaluated by the following method.

As shown in FIG. 2, the strands provided by extrusion of the polycarbonate resin pellets obtained from the extruder are conveyed from the support C to the pelletizer while being supported by the support B and the support A. As shown in detail in Figure 3, at a strand acquisition speed (Vx) of 100 mm / sec, when the difference in height between the support B at the same height and the supports C and A at the same height is 290 mm, The limit strength of the strand was evaluated as the distance (X mm) between the support C and the support A where no breakage occurred. The threshold strength is preferably 300 mm or less.

(4) Measurement of the amount of differential generation by vibration test

500 g of the obtained polycarbonate resin pellets were placed in a 2 liter capacity polyethylene hermetically sealed container having an outer diameter of 125 mm and a total height of 233 mm; This was fixed in a 50 liter tumbler ("SKD-50 ", manufactured by Seiwa Ironworks Co., Ltd.); And rotated at a rotation speed of 30 rpm for 20 minutes to make a situation in which the pellets were rubbed with each other to cause differentiation.

The amount of the fine powder was measured as follows: After the vibration test, 500 g of the pellet was mixed with 1: 1 of water and ethyl alcohol and introduced into 1 liter of the provided liquid. The supernatant containing the fine particles from the pellet was filtered using a filter paper, the filter paper was then dried in an oven at 120 ° C for 2 hours and the mass was measured; From the net increase in mass of the filter paper, the amount (mass-ppm) attached was calculated, which was used as the amount of the fine powder. The particle size of the fine powder in this measurement is 1 mm or less. If the particle size exceeds 1 mm, the particles are precipitated with the pellets due to their mass and are not present in the supernatant, so the fraction remaining in the filter paper is considered to be less than 1 mm.

(5) YI (yellow degree)

The obtained polycarbonate resin pellets were molded into a long optical path length molded article (300 mm x 7 mm x (manufactured by Toshiba Machine Co., Ltd.) molded at 340 DEG C by using an injection molding machine ("EC100SX- 4 mm) was used to measure YI at a path length of 300 mm. YI was measured using a long path length transmission spectrophotometer ("ASA1 ", manufactured by Nippon Denshoku Industries Co., Ltd.).

(6) White spot defect

A thin flat plate of 100 mm x 100 mm x 0.4 mm thick was molded at 340 DEG C using the obtained polycarbonate resin pellets and an injection molding machine ("EC100SX-2A ", manufactured by Toshiba Machine Co., Ltd.) The number of plates with white spot defects per 10 plates was counted.

(7) Vacuum voiding

100 obtained polycarbonate resin pellets were visually inspected and the number of pellets in which vacuum voids were present was counted.

The results of these evaluations are shown in Table 1.

(Examples 2 and 3)

A polycarbonate resin pellet was obtained by proceeding as in Example 1, except that the die was changed to a die having a long diameter and a short diameter relative to the die orifice as shown in Table 1.

The results are shown in Table 1.

(Example 4)

Except that the polycarbonate resin was changed to an aromatic polycarbonate resin (trade name: "Iupilon (registered trademark)" manufactured by Mitsubishi Engineering-Plastics Corporation) having bisphenol A as a starting material and having a viscosity average molecular weight (Mv) , The procedure proceeded as in Example 1 to obtain polycarbonate resin pellets.

(Example 5)

Except that the polycarbonate resin was changed to an aromatic polycarbonate resin (trade name: "Iupilon (registered trademark)" manufactured by Mitsubishi Engineering-Plastics Corporation) having a viscosity average molecular weight (Mv) of 14,500 as a starting material for bisphenol A , The procedure proceeded as in Example 1 to obtain polycarbonate resin pellets.

The results are shown in Table 1.

(Comparative Examples 1 to 4)

A polycarbonate resin pellet was obtained by proceeding as in Example 1 except that the die was changed to a die having a long diameter and a short diameter relative to the die orifice as shown in Table 2. [

The results are shown in Table 2.

(Comparative Examples 5 and 6)

Except that the rotation speed of the cutter blade was changed as shown in Table 2 and the pellet length was changed while maintaining the dimensions of the long and short diameters of the pellets and the long and short diameters / short axes ratio, the polycarbonate resin A pellet was obtained.

The results are shown in Table 2.

[Table 1]

[Table 2]

The polycarbonate resin pellets for a thin optical member of the present invention can provide a thin molded article having excellent mechanical properties, thermal properties and electrical properties and excellent weather resistance and exhibiting high transmittance and good color, And has very high industrial applicability.

Claims (8)

A polycarbonate resin having a viscosity average molecular weight of 10,000 to 15,500, a length of 2.0 to 5.0 mm, a major diameter / minor diameter ratio of the elliptical cross section of 1.5 to 4 and a minor diameter of 1.0 to 3.0 mm And an elliptical pillar-shaped pellet formed from the polycarbonate resin pellet. The polycarbonate resin pellet for a thin optical member according to claim 1, having a viscosity average molecular weight of 11,500 to 15,000. 3. The method according to claim 1 or 2, wherein 500 g of polycarbonate resin pellets are filled in a 2-liter polyethylene sealed container having an outer diameter of 125 mm and a total height of 233 mm and the container is fixed and rotated in a 50-liter tumbler, Wherein the polycarbonate resin pellets are rotated at a rotation speed of 30 rpm for 20 minutes and the amount of the fine particles having a particle diameter of 1 mm or less generated by the polycarbonate resin pellets is 50 ppm or less. The thin polycarbonate resin pellet for an optical member according to any one of claims 1 to 3, wherein the elliptical cross section of the pellet has a major axis / minor axis ratio of 1.8 to 4. A process for producing a polycarbonate resin pellet for a thin optical member according to any one of claims 1 to 4, comprising the steps of:
A polycarbonate resin having a viscosity average molecular weight of 10,000 to 15,500 is extruded as a strand from an extrusion nozzle having an elliptical die orifice disposed at a distal end of the extruder,
Cooling and solidifying the polycarbonate resin in a cooling water bath;
The polycarbonate resin is cut with a strand cutter. 6. A method according to claim 5, wherein when the strand acquisition speed is 100 mm / sec and the height difference between the supports supporting the strands is 290 mm, the spacing between supports at the same height, Wherein the thickness of the polycarbonate resin pellets is not more than 300 mm. A thin optical element molded from a polycarbonate resin pellet for a thin optical element according to any one of claims 1 to 4. A light guide molded from a polycarbonate resin pellet for a thin optical member according to any one of claims 1 to 4.

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