JP5619392B2 - Front plate for image display device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a front plate for an image display device arranged to protect an image display unit from contact or collision of an external foreign object in an image display device such as a liquid crystal display device, and a method for manufacturing the same.

  In an image display device such as a liquid crystal display device, a front plate is often disposed in order to protect the image display unit from contact or collision of external foreign matter. The front plate can be arranged at an arbitrary position outside the image display unit in the image display device (external side with respect to the image display surface), but is generally arranged on the outermost layer of the image display device. The front plate is required to have impact resistance that is not easily destroyed by contact or collision of external foreign matter. Further, even if the surface of the front plate is not destroyed, the quality of the image visually recognized by the user is deteriorated by scratching the surface of the front plate. Therefore, a characteristic that the surface is not scratched as much as possible, specifically, high surface hardness is required. That is, the front plate is required to have both high impact resistance and surface hardness.

  When the front plate is arranged, in order for the user to view the image displayed on the image display unit through the front plate, the front plate needs to be made of an optically transparent material. A transparent polymer such as acrylic, polystyrene, and polycarbonate, or glass is considered as a material used for the front plate. However, in recent years, the level of impact resistance and surface hardness required for the front plate is high, and it has become difficult to satisfy the required level with a single material. For example, glass has a very high surface hardness, but is inferior in impact resistance and is often difficult to adopt due to weight problems. Acrylic resins have high surface hardness but are inferior in impact resistance. Contrary to this, polycarbonate has high impact resistance but is inferior in surface hardness. Polystyrene does not meet the level required in recent years for any properties.

  For this reason, a front plate combining a plurality of materials has been developed. JP-A-2006-103169 and JP-A-2007-237700 disclose a front plate in which an acrylic layer is laminated by coextrusion on the surface of a base layer made of polycarbonate, and has high impact resistance derived from polycarbonate. Both the characteristics of high surface hardness derived from acrylic are achieved.

JP 2006-103169 A JP 2007-237700 A

  However, in a front plate having a multilayer structure composed of a plurality of layers made of different materials, optical defects such as wave patterns and streak patterns may occur at the interface between the layers. In addition, the front plate having such a multilayer structure is usually formed by coextrusion, but the resin flow path in the coextrusion molding apparatus is more complicated than that of a normal extrusion molding apparatus. The occurrence of optical defects due to thermal degradation of the resin produced by the retention is often observed. Optical defects and defects lead to a reduction in image quality viewed by the user. In addition, from the standpoint of manufacturing cost, a front panel for an image display device that can achieve a single layer structure that can be molded by a simple extrusion molding device, while achieving both impact resistance and surface hardness characteristics. Is desired.

The front plate for an image display device according to the present invention is a front plate for an image display device that protects the image display unit while transmitting an image displayed on the image display unit of the image display device to the outside. And / or a polymer having a methyl methacrylate unit as a constituent unit as a main component, and the total proportion of constituent units including a methyl methacrylate unit and a ring structure that is a derivative of the unit in all the constituent units of the polymer is 45% by weight or more, or the proportion of styrene units is 45% by weight or more, and the polymer has at least one ring structure selected from a lactone ring structure and an N-substituted maleimide structure in the main chain. and, wherein the polymer glass transition temperature heat shrinkage at 30 ° C. higher temperature than the is 70% or less than 20% conform to the provisions of JIS K7361-1 The measured total light transmittance is 90% or more, the thickness is 0.5 mm or more and 3 mm or less, and it is a stretched resin sheet.

The manufacturing method of the present invention is a method for manufacturing a front plate for an image display device that protects the image display unit while transmitting an image displayed on the image display unit of the image display device to the outside. A resin sheet having a thickness of 6 mm or more and 10 mm or less is stretched to form the front panel for an image display device composed of a stretched resin sheet having a thickness of 0.5 mm or more and 3 mm or less. The resin sheet is composed of styrene units and / or methyl methacrylate. A polymer having a unit as a constituent unit as a main component, and the total proportion of constituent units including a methyl methacrylate unit and a ring structure that is a derivative of the unit in all the constituent units of the polymer is 45% by weight or more. the proportion of certain or styrene units is 45 wt% or more, the polymer is at least 1 selected from a lactone ring structure and N- substituted maleimide structure It has a ring structure is the backbone, the sheet temperature at the time of stretching the resin sheet, the polymer glass transition temperature (Tg) as a reference (Tg + 5) is ℃ ~ (Tg + 20) ℃ , to form The front plate for the image display device has a heat shrinkage of 20% to 70% at a temperature 30 ° C. higher than the Tg of the polymer, and the total light transmittance measured in accordance with the provisions of JIS K7361-1. Is 90% or more.

  The heat shrinkage rate is a value indicating the degree to which the resin sheet shrinks when the resin sheet is heated from room temperature to a predetermined temperature. Whether the resin sheet is stretched (whether it is a stretched resin sheet) or not It becomes the standard of judgment. In an unstretched resin sheet, the shrinkage hardly occurs, and the heat shrinkage rate is −1% or more and 1% or less. The larger the heat shrinkage rate, the larger the shrinkage due to heating, and it can be determined that the stretched resin sheet is formed through strong stretching. The front plate for an image display device of the present invention is composed of a stretched resin sheet stretched to such an extent that the heat shrinkage rate is 20% or more and 70% or less.

  The main component means a component having the maximum content in the front plate for an image display device or the resin sheet. Usually, the content is 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more. It is.

  According to the present invention, by using a stretched resin sheet whose main component is a polymer having a specific constituent unit with a specific content, both the impact resistance and the surface hardness can be obtained while being able to take a single layer structure. Thus, a front plate for an image display device in which the above characteristics are compatible can be obtained.

  The thickness of the front plate for an image display device of the present invention is 0.5 mm or more and 3 mm or less. In the production method of the present invention, a resin sheet having a thickness of 0.6 mm to 10 mm is stretched to obtain a front plate (stretched resin sheet) for an image display device having a thickness of 0.5 m to 3 mm. Conventionally, the thin resin film has been stretched widely, but such a thick resin sheet has not been stretched. In the case of (I) a resin film, thinning the film is one of the important purposes of stretching, while in the case of a resin sheet, the sheet thickness can be reduced during molding without changing the sheet thickness by stretching. It can be easily controlled, that is, there is no motive for stretching a thick resin sheet by those skilled in the art. (II) Stretching requires preheating of the object to be stretched and cooling after stretching. Unlike a film that can be preheated or cooled simply by being conveyed, a thick resin sheet is very difficult to follow along the roll due to its high rigidity, and the film stretching device can be used to stretch the resin sheet. (III) In the field of optical members, it is widely used to obtain a retardation film by stretching a film. However, a thick resin sheet is stretched to form an optical member. It is contrary to those skilled in the art of the technical problem to be trying to obtain as much as possible thin phase difference film, that nobody and did not attempt, due to reasons such as that. The present invention has been made by carrying out a process that has never been envisaged in the past, in which a thick resin sheet is stretched to obtain a front plate for an image display device which is a kind of optical member.

  The front plate for an image display device of the present invention contains a polymer (A) having a styrene unit and / or a methyl methacrylate unit as a constituent unit as a main component. However, the total of the proportion of methyl methacrylate units and the proportion of structural units containing a ring structure which is a derivative of the units in all the structural units of the polymer (A) is 45% by weight or more, The proportion of styrene units is 45% by weight or more.

  As long as the polymer (A) satisfies these conditions regarding the structural unit and can form a front plate for an image display device having a total light transmittance of 90% or more measured in accordance with the provisions of JIS 7361-1, It is not limited.

  The styrene unit is a structural unit of a polymer that conventionally constitutes a front plate for an image display device, as can be seen from the fact that polystyrene, which is a homopolymer of the unit, is inferior in both properties of impact resistance and surface hardness. It was not preferable as. On the other hand, in the front plate for an image display device of the present invention, even when the content of styrene units is 45% by weight or more, both the impact resistance and the surface hardness can be obtained while being able to take a single layer structure. It is possible to balance properties. This is also advantageous from the viewpoint of the manufacturing cost of the front plate for an image display device.

  When the polymer (A) has a methyl methacrylate unit as a structural unit, the proportion of the methyl methacrylate unit in the total structural unit of the polymer (A) and the structural unit containing a ring structure that is a derivative of the unit. The total ratio is preferably 50% by weight or more.

  The polymer (A) may have both styrene units and methyl methacrylate units as constituent units. An example of such a polymer (A) is a styrene-methyl methacrylate copolymer.

  The polymer (A) satisfies the above-mentioned condition regarding the structural unit, and has a structural unit other than the styrene unit and the methyl methacrylate unit as long as it can form a front plate for an image display device that satisfies the above-mentioned condition regarding the total light transmittance. It may be. Such a structural unit is, for example, a (meth) acrylic acid ester unit other than a methyl methacrylate unit.

  The polymer (A) may have a ring structure in the main chain. By having a ring structure in the main chain, the glass transition temperature (Tg) of the polymer (A) is increased, and a front plate for an image display device having excellent heat resistance is obtained. Depending on the type of the ring structure and the content of the ring structure in the polymer (A), the Tg of the polymer (A) having a ring structure in the main chain is, for example, 110 ° C. or higher, 115 ° C. or higher, 120 ° C. or higher, Furthermore, it becomes 130 degreeC or more. The Tg of the polymer (A) can be measured by the midpoint method in accordance with the provisions of JIS K7121.

  Moreover, when the polymer (A) has a ring structure in the main chain, it becomes a front plate for an image display device having higher surface hardness.

  Specific examples of the ring structure that the polymer (A) may have in the main chain are at least one selected from a lactone ring structure, a maleic anhydride structure, and an N-substituted maleimide structure. These ring structures hardly reduce the transparency (total light transmittance) of the polymer (A), and are easy to copolymerize with methyl methacrylate units and styrene units. Depending on the type of ring structure, methyl methacrylate units and / or styrene units, and (meth) acrylic acid ester units and / or (meth) acrylic acid units that can be easily copolymerized with these structural units are included in the structural units. The polymer (A) can be formed relatively easily by causing the dealcoholization cyclocondensation reaction to proceed on the copolymer.

  The lactone ring structure is not particularly limited, but for example, is a structure represented by the following formula (1).

R ¹ , R ² and R ³ in the formula (1) are each independently a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom. The organic residue is, for example, an alkyl group such as a methyl group, an ethyl group, or a propyl group; an unsaturated aliphatic hydrocarbon group such as an ethenyl group or a propenyl group; an aromatic hydrocarbon group such as a phenyl group or a naphthyl group; A group, one or more of hydrogen atoms in the unsaturated aliphatic hydrocarbon group or the aromatic hydrocarbon group substituted by at least one group selected from a hydroxy group, a carboxyl group, an ether group and an ester group ;

The lactone ring structure represented by the formula (1), for example, proceeds a dealcoholization cyclocondensation reaction on a copolymer having a structural unit having an ester group (carboxylic acid ester group) and a structural unit having a hydroxyl group. Can be formed. Such a copolymer is, for example, a copolymer of (meth) acrylic acid ester units and (meth) acrylic acid ester units having a hydroxyl group. An example of such a copolymer is a copolymer having methyl methacrylate (MMA) units and 2- (hydroxy) methyl acrylate (RHMA) units. At this time, R ^{1 of the} lactone ring structure shown in Formula (1) is H, R ² is CH ₃ , and R ³ is CH ₃ .

  When the copolymer is subjected to a dealcoholization cyclocondensation reaction on the copolymer to obtain a polymer (A), the content of methyl methacrylate units can be easily set to 45% by weight or more. It is preferable that the structural unit having a MMA unit. When the structural unit having an ester group is an MMA unit, the ring structure formed by the dealcoholization cyclocondensation reaction between the structural unit having a hydroxyl group and the MMA unit is a derivative of the MMA unit.

  Examples of the structural unit having a hydroxyl group include methyl 2- (hydroxymethyl) acrylate, ethyl 2- (hydroxymethyl) acrylate, isopropyl 2- (hydroxymethyl) acrylate, and n-butyl 2- (hydroxymethyl) acrylate. , T-butyl 2- (hydroxymethyl) acrylate, 2- (hydroxymethyl) methyl methacrylate, 2- (hydroxymethyl) ethyl methacrylate, 2- (hydroxymethyl) isopropyl methacrylate, 2- (hydroxymethyl) methacryl It is a structural unit formed by polymerization of each monomer of n-butyl acid and t-butyl 2- (hydroxymethyl) methacrylate.

  The following formula (2) shows an N-substituted maleimide structure and a maleic anhydride structure.

In the above formula (2), R ⁴ and R ⁵ are each independently a hydrogen atom or a methyl group, and X ¹ is an oxygen atom or a nitrogen atom. When X ¹ is an oxygen atom, R ⁶ does not exist, and when X ¹ is a nitrogen atom, R ⁶ is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms, a cyclopentyl group, a cyclohexyl group, or a phenyl group. .

When X ¹ is a nitrogen atom, the ring structure shown in Formula (2) is an N-substituted maleimide structure. The polymer (A) having an N-substituted maleimide structure in the main chain can be formed, for example, by copolymerizing an N-substituted maleimide and methyl methacrylate and / or styrene.

When X ¹ is an oxygen atom, the ring structure shown in Formula (2) is a maleic anhydride structure. The polymer (A) having a maleic anhydride structure in the main chain can be formed, for example, by copolymerizing maleic anhydride with methyl methacrylate and / or styrene.

  When the polymer (A) has a ring structure in the main chain, the content of the ring structure in the polymer (A) may be adjusted according to the desired properties as the front plate for an image display device. More than 80% by weight, preferably 10% by weight or more and less than 60% by weight.

The content of the ring structure in the polymer (A) can be determined by a known method such as ¹ H nuclear magnetic resonance ( ¹ H-NMR) or infrared spectroscopic analysis (IR). It can also be obtained by the method described in JP-A-2008-133462.

  The front plate for an image display device of the present invention has a heat shrinkage rate of 20% to 70%. If it is less than 20%, the degree of stretching as a stretched resin sheet is insufficient, making it difficult to achieve both impact resistance and surface hardness. When it exceeds 70%, the degree of stretching as a stretched resin sheet becomes excessive, and there are few merits obtained for such difficult stretching.

  The thickness of the front plate for an image display device of the present invention is 0.5 mm or more and 3 mm or less.

  The turbidity (haze) of the front plate for an image display device according to the present invention is preferably 1% or less as a value measured in accordance with JIS K7136.

  The surface roughness of the front plate for an image display device according to the present invention is Ra (arithmetic mean roughness) defined in JIS B0601, although it varies depending on the presence or absence of surface treatment and the type of surface treatment. 0.1 μm or less, and depending on conditions, it may be 0.05 μm or less.

  As long as the polymer (A) is a main component and the total light transmittance measured in accordance with JIS 7361-1 is 90% or more, the front plate for an image display device of the present invention is a polymer ( A material other than A) may be included. Such a material is, for example, elastic organic fine particles.

  By containing elastic organic fine particles, the impact resistance of the front plate for an image display device of the present invention is further improved. Elastic organic fine particles are, for example, structural units formed by polymerization of conjugated diene monomers (for example, butadiene units and isoprene units) and structural units formed by polymerization of (meth) acrylate monomers (for example, , Butyl acrylate unit, ethyl acrylate unit). As the elastic organic fine particles, the elastic organic fine particles disclosed in JP 2008-242421 A can be used. The method for producing elastic organic fine particles is disclosed in the publication.

  When the front plate for an image display device of the present invention contains elastic organic fine particles, the content of elastic organic fine particles in the front plate is preferably 5 to 30% by weight. When the content of elastic organic fine particles is excessively large, the turbidity (haze) of the front plate increases due to the scattering of incident light to the front plate caused by the elastic organic fine particles, rather than the merit of improving impact resistance. The demerit that the light transmittance decreases or the surface hardness decreases increases.

  The front plate for an image display device of the present invention may be subjected to surface treatment such as hard coat treatment on the surface thereof. By the hard coat treatment, the surface hardness of the front plate is further improved. The surface treatment includes anti-glare treatment, antistatic treatment, antireflection treatment and the like in addition to the hard coat treatment. A specific surface treatment method may follow a known method.

  The front plate for an image display device of the present invention typically has a single-layer structure of a resin composition mainly composed of the polymer (A) and, in some cases, composed of the polymer (A). As long as an effect is acquired, you may have arbitrary layers other than the layer which consists of the said resin composition.

  The front plate for an image display device of the present invention can be used for any image display device such as a liquid crystal display device. By disposing the front plate for the image display device of the present invention outside the image display unit (outside of the image display surface) in the image display device, the image displayed on the image display unit is transmitted to the outside, and the image is displayed. The part can be protected from contact or collision of external foreign matter. In addition, since the front plate for an image display device of the present invention can have a single layer structure, it can cause optical defects such as wave patterns and streak patterns at the interface of the layers as compared with a conventional front plate having a multilayer structure. There is no occurrence of interference patterns, and there are few optical defects due to the incorporation of thermally deteriorated products during production. Moreover, it is more advantageous than the front plate having a multilayer structure in terms of manufacturing cost.

  The front plate for an image display device of the present invention can be manufactured, for example, by the method for manufacturing the front plate for an image display device of the present invention.

  In the manufacturing method of the present invention, a resin sheet having a thickness of 0.6 mm or more and 10 mm or less is stretched to form a front panel for an image display device comprising a stretched resin sheet having a thickness of 0.5 mm or more and 3 mm or less. Here, the extending | stretching resin sheet is a sheet | seat which has a polymer (A) which has a styrene unit and / or a methyl methacrylate unit as a structural unit as a main component. The total of the proportion of methyl methacrylate units and the proportion of structural units containing a ring structure which is a derivative of the units in all the structural units of the polymer (A) is 45% by weight or more, or The proportion is 45% by weight or more. Further, the total light transmittance (total light transmittance measured in accordance with JIS 7361-1) of the front panel for an image display device formed by stretching is 90% or more. The total light transmittance of the front plate for an image display device can be adjusted by selecting the composition of the polymer (A), the content of the polymer (A) in the resin sheet, and components other than the polymer (A).

  For stretching the resin sheet, a general stretching method can be applied except for the preheating method. For example, the front plate for an image display device may be formed by stretching a resin sheet by uniaxial stretching or biaxial stretching. Since both higher impact resistance and surface hardness are possible, it is preferable to biaxially stretch the resin sheet to form a front panel for an image display device made of the stretched resin sheet. A known stretching method can be applied to the uniaxial stretching and the biaxial stretching except for the preheating method.

  For specific stretching, for example, a method in which a resin sheet is introduced in the order of a low-speed roll and a high-speed roll, and a method of using a difference in conveyance speed between the low-speed side and the high-speed side, or a method of gripping and pulling the end of the resin sheet By using these alone or in combination, uniaxial stretching and biaxial stretching of the resin sheet can be realized. Although a method of spreading the film by applying a compressive force to the main surface of the resin film is also conceivable, it is difficult to control the direction in which the film spreads, and the shrinkage rate may vary depending on the part of the sheet Is not preferable. Further, the shape of the obtained sheet is also rounded, which is not preferable as a method for obtaining a generally preferred rectangular product. Further, in this method, continuous stretching of the extruded strip-shaped unstretched sheet is impossible.

  Further, in this method, a compression force is usually applied to the sheet by pressing the compression die against the main surface of the resin sheet. However, the unevenness present on the surface of the compression die is transferred to the sheet, or the die is pressed with a large pressure. In this state, the unevenness caused by the lubricant used to move the sheet horizontally relative to the die is transferred to the sheet, so that a stretched resin sheet having a smooth surface cannot be obtained. On the other hand, in uniaxial stretching or biaxial stretching, a stretched resin sheet having an Ra (arithmetic mean roughness) specified in JIS B0601 of 0.1 μm or less and 0.05 μm or less depending on conditions is obtained.

  The sheet | seat temperature at the time of extending | stretching is (Tg + 30) degree C or less on the basis of Tg of a polymer (A), for example, (Tg + 5)-(Tg + 20) degreeC are preferable. The draw ratio is, for example, 1.2 to 4 times, and preferably 1.2 to 3 times.

  When stretching the resin sheet, it is necessary to preheat the resin sheet to the stretching temperature. In conventional stretching of a thin film, it was possible to perform preheating when the film passed through a heating roll, but when using a thick resin sheet as in the present invention, the heat capacity is larger than the film. In addition, since it is impossible in the first place to place the resin sheet on the heating roll, it is impossible to perform such preheating. For this reason, it is preferable to use other means for preheating the resin sheet, for example, introduction of hot air or irradiation with infrared rays. When irradiating infrared rays, it is preferable to irradiate both main surfaces of the resin sheet with infrared rays. Similarly, for cooling the stretched sheet, it is impossible to place the sheet on a cooling roll, and therefore it is preferable to use other means, for example, introduction of cold air.

  The resin sheet to be stretched can be formed by a known molding method such as extrusion molding of a resin composition containing the polymer (A) as a main component.

  In the manufacturing method of this invention, as long as the front plate for image display apparatuses of this invention is obtained, arbitrary processes other than extending | stretching a resin sheet and setting it as a resin stretched sheet can be implemented at arbitrary time points.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the examples shown below.

  Initially, the evaluation method of the polymer produced in a present Example and the front plate for image display apparatuses is shown.

[Polymerization reaction rate, polymer composition analysis]
The polymerization reaction rate in producing the polymer was calculated from the amount of unreacted monomer remaining in the obtained polymerization solution. The amount of unreacted monomer was measured by gas chromatography (manufactured by Shimadzu Corporation, GC17A). The composition of the polymer was determined from the amount of unreacted monomer and the amount of monomer initially added to the polymerization system.

[Weight average molecular weight]
The weight average molecular weight of the polymer was determined in terms of polystyrene using gel permeation chromatography (GPC). The equipment and measurement conditions used for the measurement are:
System: manufactured by Tosoh Column: TSK-GEL SuperHZM-M 6.0 × 150 2 in series Guard column: TSK-GEL SuperHZ-L 4.6 × 35 1 Reference column: TSK-GEL SuperH-RC 6.0 × 150 2 in series Eluent: Chloroform Flow rate 0.6 mL / min Column temperature: 40 ° C
It is.

[Glass-transition temperature]
The glass transition temperature (Tg) of the polymer was determined according to JIS K7121. Specifically, a differential scanning calorimeter (manufactured by Rigaku, DSC-8230) was used, and a temperature of about 10 mg of the sample was raised from room temperature to 200 ° C. in a nitrogen flow (50 mL / min) atmosphere (temperature increase rate 10 ° C./min). ) Was evaluated by the midpoint method from the DSC curve obtained. Α-alumina was used as a reference.

[Total light transmittance]
The total light transmittance of the front plate was determined using a haze meter (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7361-1.

[Surface roughness]
As the surface roughness of the front plate, Ra (arithmetic mean roughness) defined in JIS B0601: 2001 was obtained by extending it to a plane. The measurement was performed using a laser microscope (manufactured by Keyence, VK-9700) with a measurement area of 95 μm × 70 μm. In addition, the measurement site | part of the surface roughness in a front plate selected at random the site | part which does not have the damage | wound and dirt which can be visually recognized in a front plate.

[Heating shrinkage]
The heat shrinkage rate of the front plate was determined as follows.

  A test piece having a size of 80 mm × 80 mm was cut out from the produced front plate, and a circle having a diameter of about 50 mm was drawn with a magic on the surface of the test piece. The diameter of the circle at this time was Φ1. Next, a test piece was placed on a tray in which talc powder was evenly spread, and talc powder was also spread on the test piece, and a stainless steel plate (150 mm × 150 mm, weight 180 g) was placed thereon. This stainless steel plate was used for the purpose of suppressing the test piece from curling or waving when the test piece was heated. Next, the tray was accommodated together with the test piece in a hot air oven maintained at a temperature 30 ° C. higher than the Tg of the polymer constituting the front plate, and the test piece was heat-treated for 1 hour. After the heat treatment, the tray was taken out of the oven and cooled to room temperature, and the maximum value (Φ2a) and the minimum value (Φ2b) of the diameter of the circle drawn on the surface of the cooled specimen were measured with a caliper. The value of the formula [Φ1- (Φ2a + Φ2b) / 2] / Φ1 × 100 (%) was taken as the heat shrinkage rate, and the average value of the heat shrinkage rates obtained for the three test pieces was taken as the measurement result.

[Shock resistance]
The impact resistance of the front plate was evaluated according to the free-fall dart method (JIS K7124, method A). The test was carried out on three test pieces cut out from the same front plate using a 50 g weight warhead. Judgment of impact resistance was defined as acceptable (◯) when the warhead did not penetrate through all three test pieces, and rejected (×) when the warhead penetrated through even one test piece.

[Abrasion resistance]
The scratch resistance of the front plate was evaluated according to JIS K5600-5-4. The evaluation was performed using a pencil with hardness H, and the case where the surface of the front plate was not damaged was accepted (O), and the case where the surface was damaged was rejected (X).

(Production Example 1)
Into a reaction vessel having an internal volume of 30 L equipped with a stirrer, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe, 8 kg of methyl methacrylate (MMA), 2 kg of methyl 2- (hydroxymethyl) methyl acrylate (RHMA), polymerization 10 kg of methyl isobutyl ketone as a solvent and 5 g of n-dodecyl mercaptan as a regulator were charged, and the temperature was raised to 105 ° C. while passing nitrogen through this. When refluxing with increasing temperature started, 5 g of t-amyl-3,5,5-trimethylhexanoate was added as a polymerization initiator, and t-amyl-3,5,5 was added to 230 g of methyl isobutyl ketone. -While a solution in which 10 g of trimethylhexanoate was dissolved was dropped over 2 hours, solution polymerization was allowed to proceed under reflux at about 105 to 120 ° C, and further aging was performed for 4 hours.

  Next, 30 g of stearyl phosphate / distearyl phosphate mixture (Phoslex A-18, manufactured by Sakai Chemical Industry Co., Ltd.) was added to the resulting polymerization solution as a catalyst for the cyclization condensation reaction (cyclization catalyst). A dealcoholization cyclocondensation reaction for forming a lactone ring structure was allowed to proceed for 5 hours under reflux at ˜120 ° C.

  Next, the polymerization solution thus obtained was converted into a vent type screw having a barrel temperature of 260 ° C., a rotation speed of 100 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), a rear vent number of 1, and a forevent number of 4. Introduced into a shaft extruder (Φ = 29.75 mm, L / D = 30) at a processing rate of 2.0 kg / hour in terms of resin amount, and further cyclized condensation reaction and devolatilization were carried out in the extruder. Thus, a polymer (1) having an MMA unit and a structural unit containing a lactone ring structure which is a derivative of the unit was obtained. The weight average molecular weight of the obtained polymer (1) was 150,000, and the glass transition temperature (Tg) was 131 ° C. Moreover, the total of the content rate of the MMA unit in the obtained polymer (1) and the structural unit containing the lactone ring structure which is a derivative | guide_body of the said unit was 100 weight%.

  Next, the produced polymer (1) was made into a sheet (1A) having a thickness of 4 mm and a sheet (1B) having a thickness of 5 mm by an extrusion molding method. For extrusion molding, an apparatus in which a single-screw extrusion unit (cylinder diameter: 20 mm) and a coat hanger type die (width: 150 mm) were attached to a lab plast mill manufactured by Toyo Seiki Seisakusho. The heat shrinkage ratios of the obtained sheets (1A) and (1B) were between -1% and 1%, and it was confirmed that each was substantially unstretched.

Example 1
The unstretched sheet (1A) produced in Production Example 1 was cut into a 97 mm square and set in a stretching machine (manufactured by Toyo Seiki Seisakusho, corner stretch type biaxial stretching test apparatus X6-S). This stretching machine has a function of stretching the sheet by holding each of the four sides of the set sheet with ten chucks. Each chuck moves in conjunction with each other and can stretch the sheet in two orthogonal directions simultaneously or sequentially.

  Next, the set sheet was preheated at 150 ° C. for 3 minutes (that is, the stretching temperature was 150 ° C.) and then stretched in the first stage so that the magnification was 1.5 times in 20 seconds. One second after the completion of the first stage stretching, the second stage stretching was performed in a direction orthogonal to the first stage so that the magnification was 1.5 times in 20 seconds. After maintaining the state after completion of the second stage of stretching for 20 seconds, the heating furnace was opened and the stretched sheet was cooled to obtain a stretched sheet (1), which was used as a front plate. In addition, a 50 mm square was drawn by magic at the center of the unstretched sheet (1A), and it was confirmed how this square changed with stretching. It was a 75 mm square, and was approximately 75 mm × 75 mm square at the end of the second stage of stretching.

(Example 2)
A stretched sheet (2) was obtained in the same manner as in Example 1 except that the stretch ratio was 2.0 times in both the first and second stages, and this was used as a front plate.

Example 3
A stretched sheet (3) is obtained in the same manner as in Example 1 except that the unstretched sheet (1B) produced in Production Example 1 is used and the stretch ratio is 3.0 times in both the first and second stages. This was the front plate.

(Production Example 2)
A lactone which is a derivative of an St unit, an MMA unit, and an MMA unit, in the same manner as in Production Example 1, except that 7 kg of MMA, 2 kg of MHMA, and 1 kg of styrene (St) were used as the monomers to be polymerized. A polymer (2) having a structural unit containing a ring structure was obtained. The obtained polymer (2) had a weight average molecular weight of 145,000 and a glass transition temperature (Tg) of 127 ° C. Further, the total content of the MMA unit in the obtained polymer (2) and the structural unit containing a lactone ring structure which is a derivative of the unit was 89% by weight.

  Next, an unstretched sheet (2) having a thickness of 4 mm was obtained from the produced polymer (2) in the same manner as in Production Example 1.

Example 4
Stretching in the same manner as in Example 1 except that the unstretched sheet (2) prepared in Production Example 2 was used, the stretching temperature was 145 ° C., and the stretching ratio was 2.0 times in both the first and second stages. A sheet (4) was obtained and used as a front plate.

(Production Example 3)
A reaction vessel having an internal volume of 30 L equipped with a stirrer, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe was charged with 9 kg of MMA, 1 kg of N-phenylmaleimide (PMI), and 10 kg of toluene as a polymerization solvent. The temperature was raised to 105 ° C. while passing nitrogen through. When refluxing with the temperature increase started, 12 g of t-amylperoxyisonononanoate was added as a polymerization initiator, and a solution of 24 g of t-amylperoxyisonononanoate dissolved in 136 g of toluene was added for 2 hours. The solution polymerization was allowed to proceed under reflux at about 105 to 110 ° C. while dropping, and aging was further performed for 4 hours.

  Next, the polymerization solution thus obtained was converted into a bent type screw having a barrel temperature of 240 ° C., a rotation speed of 120 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), a rear vent number of 1 and a forevent number of 4 pieces. Introduced into a shaft extruder (Φ = 29.75 mm, L / D = 30) at a processing rate of 2.0 kg / hour in terms of resin amount, devolatilized in the extruder, MMA units, N− A polymer (3) having phenylmaleimide units was obtained. The weight average molecular weight of the obtained polymer (3) was 170,000, and the glass transition temperature (Tg) was 127 ° C. Moreover, the content rate of the MMA unit in the obtained polymer (3) was 90 weight%.

  Next, an unstretched sheet (3) having a thickness of 4 mm was obtained from the produced polymer (3) in the same manner as in Production Example 1.

(Example 5)
Stretching in the same manner as in Example 1 except that the unstretched sheet (3) produced in Production Example 3 was used, the stretching temperature was 145 ° C., and the stretching ratio was 1.3 times in both the first and second stages. A sheet (5) was obtained and used as a front plate.

(Production Example 4)
A polymer (4) having MMA units and MA units was prepared in the same manner as in Production Example 3 except that 9.5 kg of MMA and 0.5 kg of methacrylic acid (MA) were used as the monomers to be polymerized. Obtained. The resulting polymer (4) had a weight average molecular weight of 1580,000 and a glass transition temperature (Tg) of 106 ° C. Moreover, the content rate of the MMA unit in the obtained polymer (4) was 95 weight%.

  Next, an unstretched sheet (4) having a thickness of 4 mm was obtained from the produced polymer (4).

( Reference Example 1 )
Stretching in the same manner as in Example 1 except that the unstretched sheet (4) produced in Production Example 4 was used, the stretching temperature was 125 ° C., and the stretching ratio was 2.0 times in both the first and second stages. A sheet (6) was obtained and used as a front plate.

(Production Example 5)
A polymer having MMA units, MA units and St units in the same manner as in Production Example 3 except that 8.8 kg of MMA, 1 kg of PMI, and 0.2 kg of St are used as the monomers to be polymerized ( 5) was obtained. The weight average molecular weight of the obtained polymer (5) was 160,000, and the glass transition temperature (Tg) was 126 ° C. Moreover, the content rate of the MMA unit in the obtained polymer (5) was 88 weight%.

  Next, an unstretched sheet (5) having a thickness of 4 mm was obtained from the produced polymer (5) in the same manner as in Production Example 1.

(Example 7)
Stretching in the same manner as in Example 1 except that the unstretched sheet (5) produced in Production Example 5 was used, the stretching temperature was 145 ° C., and the stretching ratio was 2.0 times in both the first and second stages. A sheet (7) was obtained and used as a front plate.

(Production Example 6)
Into a reaction vessel having an internal volume of 30 L equipped with a condenser, a stirrer, and two dropping funnels, 1.8 kg of St and 9.1 kg of toluene were charged, and the temperature was raised to 114 ° C. while passing nitrogen through the reactor. When the temperature reached 114 ° C., 2.5 g of t-butylperoxyisopropyl carbonate was added as a polymerization initiator, and a preliminarily prepared dropping solution comprising 5.8 kg of PMI and 3.8 kg of toluene. (I), and 4.4 kg of St and 5.0 g of t-butylperoxyisopropyl carbonate, respectively, are reacted at a uniform rate over a period of 3.5 hours from different routes. While dropping into the kettle, the polymerization was allowed to proceed in a reflux state. After completion of the dropwise addition, the inside of the reaction kettle was kept warm for an additional 1.5 hours to obtain a composition comprising 52% by weight of toluene, 5.1% by weight of styrene, and 42.9% by weight of maleimide copolymer. The content of N-phenylmaleimide units in the maleimide copolymer was 54.3% by weight, the content of styrene units was 45.7% by weight, and the Tg was 206 ° C.

  Next, the composition obtained was heated to 240 ° C. by passing it through a static mixer type heat exchanger using a gear pump, and then a vent type twin-shaft co-directional extruder (screw diameter (D) was 65 mm, Cylinder length (L) was continuously supplied to 2600 mm, L / D = 40, 1 rear vent, 3 fore vents), and devolatilization was performed in the extruder. At this time, the composition supply rate was 110 kg / hour, the barrel temperature was 270 ° C., and the screw rotation speed was 120 rpm. The pressure of each vent was set to 700 mmHg for the rear vent, 250 mmHg for the first forevent, 20 mmHg for the second forevent, and 20 mmHg for the third forevent. Furthermore, water was injected at a supply rate of 7 kg / hour in the previous stage of the second and third forvents. The thus obtained maleimide copolymer (6) had a weight average molecular weight of 230,000.

  Next, an unstretched sheet (6) having a thickness of 5 mm was obtained from the produced polymer (6) in the same manner as in Production Example 1.

(Example 8)
Stretching in the same manner as in Example 1 except that the unstretched sheet (6) prepared in Production Example 6 was used, the stretching temperature was 220 ° C., and the stretching ratio was 1.8 times in both the first and second stages. A sheet (8) was obtained and used as a front plate.

(Production Example 7)
Using a commercially available copolymer of MMA and St (manufactured by Nippon Steel Chemical Co., Ltd., MS-600, copolymerization ratio of MMA and St is 6: 4 by weight), in the same manner as in Production Example 1, An unstretched sheet (7) having a thickness of 5 mm was obtained. The Tg of the copolymer used was 100 ° C.

( Reference Example 2 )
Stretching in the same manner as in Example 1 except that the unstretched sheet (7) produced in Production Example 7 was used, the stretching temperature was 120 ° C., and the stretching ratio was 2.5 times in both the first and second stages. A sheet (9) was obtained and used as a front plate.

(Production Example 8)
Using a commercially available copolymer of MMA and St (manufactured by Nippon Steel Chemical Co., Ltd., MS-300, copolymerization ratio of MMA and St is 3: 7 by weight), in the same manner as in Production Example 1, An unstretched sheet (8) having a thickness of 6 mm was obtained. The Tg of the copolymer used was 92 ° C.

( Reference Example 3 )
Stretching in the same manner as in Example 1 except that the unstretched sheet (8) produced in Production Example 8 was used, the stretching temperature was 110 ° C., and the stretching ratio was 1.5 times in both the first and second stages. A sheet (10) was obtained and used as a front plate.

(Comparative Example 1)
The unstretched sheet (4) produced in Production Example 4 was used as a front plate without being stretched as it was.

(Comparative Example 2)
A commercially available polycarbonate sheet (manufactured by Sumitomo Bakelite, Polycarbonate ACK100, thickness 2.0 mm) was used as it was as the front plate.

Examples 1 to 5, 7 to 8, Reference Examples 1 to 3 and Comparative Examples 1 to 2 The polymers constituting the front plate, the monomer composition before polymerization and the glass transition temperature (Tg), and before the production Table 1 below shows the results of the characteristics evaluation of the face plate.

As shown in Table 1, each front plate produced in Examples 1 to 5, 7 to 8 and Reference Examples 1 to 3 had a high surface hardness and impact resistance while having a single layer structure.

  The image display front plate of the present invention can be used as a front plate regardless of the type of image display device.

Claims (7)

A front plate for an image display device that protects the image display unit while allowing the image displayed on the image display unit of the image display device to pass outside,
The main component is a polymer having styrene units and / or methyl methacrylate units as constituent units,
The total of the proportion of structural units containing a methyl methacrylate unit and a ring structure which is a derivative of the unit in all the structural units of the polymer is 45% by weight or more, or the proportion of styrene units is 45% by weight or more. And
The polymer has in its main chain a ring structure that is at least one selected from a lactone ring structure and an N-substituted maleimide structure,
The heat shrinkage at a temperature 30 ° C. higher than the glass transition temperature of the polymer is 20% or more and 70% or less,
The total light transmittance measured in accordance with JIS K7361-1 is 90% or more,
The thickness is 0.5 mm or more and 3 mm or less,
A front plate for an image display device, which is a stretched resin sheet.   The front plate for an image display device according to claim 1, wherein the polymer has both styrene units and methyl methacrylate units as constituent units.   The front plate for an image display device according to claim 1, wherein the polymer has a glass transition temperature of 110 ° C. or higher.   2. The front plate for an image display device according to claim 1, wherein the surface roughness is 0.1 μm or less in terms of Ra (arithmetic mean roughness) defined in JIS B0601. A method of manufacturing a front plate for an image display device that protects the image display unit while transmitting an image displayed on the image display unit of the image display device to the outside,
Stretching a resin sheet having a thickness of 0.6 mm or more and 10 mm or less to form the front panel for an image display device comprising a stretched resin sheet having a thickness of 0.5 mm or more and 3 mm or less,
The resin sheet is mainly composed of a polymer having styrene units and / or methyl methacrylate units as constituent units,
The total of the proportion of structural units containing a methyl methacrylate unit and a ring structure which is a derivative of the unit in all the structural units of the polymer is 45% by weight or more, or the proportion of styrene units is 45% by weight or more. And
The polymer has in its main chain a ring structure that is at least one selected from a lactone ring structure and an N-substituted maleimide structure,
The sheet temperature when stretching the resin sheet is (Tg + 5) ° C. to (Tg + 20) ° C. based on the glass transition temperature (Tg) of the polymer,
The total light ray measured according to JIS K7361-1 has a heat shrinkage rate of 20% to 70% at a temperature 30 ° C. higher than Tg of the polymer of the formed front plate for an image display device. A method for manufacturing a front plate for an image display device, wherein the transmittance is 90% or more.   The method for producing a front plate for an image display device according to claim 5, wherein the resin sheet is uniaxially or biaxially stretched to form a front plate for an image display device comprising the stretched resin sheet.   The front surface of an image display device according to claim 5, wherein the surface roughness of the stretched resin sheet formed by stretching the resin sheet is 0.1 μm or less in terms of Ra (arithmetic mean roughness) defined in JIS B0601. Manufacturing method of face plate.