KR102668742B1 - Manufacturing method of Window cover for display device and window cover - Google Patents

Abstract

In the method of manufacturing a window cover for a display device of the present invention, a window cover is manufactured by injection compression molding, and a window cover with a reduced retardation value can be manufactured by adjusting the compression factor.
The flat side retardation value of the window cover manufactured by the manufacturing method of the present invention is 50 nm or less, and the 45° side retardation value is 270 nm or less.
The present invention can reduce retardation by controlling the temperatures of the upper and lower molds, compression core, and gate when manufacturing a window cover.

Description

{Manufacturing method of Window cover for display device and window cover}

The present invention relates to a method of manufacturing a window cover for a display device and a window cover for a display device.

Various display devices are used in vehicles to deliver necessary information while driving or to deliver content that provides convenience within the vehicle. Among them, CID (Center Information Display) is placed at the front of the vehicle and delivers necessary information to the driver.

Meanwhile, a window cover for a display device serves to protect the display panel of the display device. Previously, glass was used as a material for window covers, but it is being replaced by plastic materials due to demands for weight reduction and impact resistance. The window cover for the display device is located on the upper layer of the display panel, and requires optical characteristics to prevent information displayed on the display from being distorted to drivers or passengers.

Window covers made of plastic are generally manufactured by injection molding. However, injection molding applies high pressure to the cavity and causes large temperature changes, so large residual stress remains in the molded product, which leads to deterioration of optical properties such as increased birefringence. In addition, there was a problem that the physical properties became non-uniform because the pressure distribution was different depending on the location within the cavity.

Accordingly, there is a demand for the development of a window cover that can prevent information displayed on a display device from being distorted or visibility deteriorated by improving optical characteristics. In particular, there is a need for the development of a window cover manufacturing method that can manufacture a window cover for a display device with improved birefringence performance. In addition, from the viewpoint of manufacturing efficiency, there is a need to develop a manufacturing method that can manufacture a window cover for a display device with an optimized birefringence value so that visibility is not impaired.

Publication Patent No. 10-2007-0059073 (Name: Display device with birefringent substrate)

The purpose of the present invention is to provide a manufacturing method for manufacturing a window cover for a display device with improved birefringence properties and good visibility.

The purpose of the present invention is to provide a manufacturing method for manufacturing a window cover for a display device that can minimize residual stress during molding by controlling the mold temperature in the injection compression process.

A method of manufacturing a window cover for a display device according to an embodiment of the present invention includes the steps of placing an insert film on an upper mold, positioning the lower mold at a predetermined distance from the upper mold, injecting an injection material into the mold, and compressing. and pressurizing the core. The temperature of the upper mold and lower mold may be 70 to 95°C.

The method of manufacturing a window cover for a display device according to an embodiment of the present invention may further include the step of preforming the insert film before mounting the insert film on the upper mold.

In the method of manufacturing a window cover for a display device according to an embodiment of the present invention, the temperature of the gate into which the injection material is injected may be 20 to 40°C.

In the method of manufacturing a window cover for a display device according to an embodiment of the present invention, the temperature of the compression core may be 80 to 105 ° C.

In the method of manufacturing a window cover for a display device according to an embodiment of the present invention, the temperature difference between the upper mold and the compression core may be 10°C or more.

In the method of manufacturing a window cover for a display device according to an embodiment of the present invention, the temperature of the injection material may be 270 to 320 ° C.

In the method of manufacturing a window cover for a display device according to an embodiment of the present invention, the compression maintenance time in the step of pressurizing the compression core may be 8 to 10 seconds.

The method of manufacturing a window cover for a display device according to an embodiment of the present invention may have a clamping force of 250 to 600 tons in the step of pressing the compression core.

In the method of manufacturing a window cover for a display device according to an embodiment of the present invention, in the step of pressurizing the compression core, the compression speed may be controlled in two stages. The section from the initial position of the compression core to 1/2 the compression gap can be defined as section 1, and the section from 1/2 the compression gap to the final position of the compression core can be defined as section 2. The compression speed can be controlled to have a constant speed in section 1 and a constant acceleration in section 2.

In the method of manufacturing a window cover for a display device according to an embodiment of the present invention, the compression speed can be controlled to have 1.8 to 2.2 mm/s in section 1 and the acceleration to be 1.8 to 2.2 mm/s ² in section 2.

In the method of manufacturing a window cover for a display device according to an embodiment of the present invention, the compression speed may increase as the compression gap increases.

In the method of manufacturing a window cover for a display device according to an embodiment of the present invention, in the step of injecting an injection material into a mold, the injection speed can be controlled for each of four stroke sections.

In the method of manufacturing a window cover for a display device according to an embodiment of the present invention, the stroke section is 33 to 37 mm, 23 to 27 mm, 10 to 14 mm, and 5 to 9 mm when the position of the tip of the screw is assumed to be 0 mm. Based on the location, it can be divided into section 1, section 2, section 3, and section 4.

In the method of manufacturing a window cover for a display device according to an embodiment of the present invention, the injection speed in two sections may be greater than the injection speed in one section.

In the method of manufacturing a window cover for a display device according to an embodiment of the present invention, the injection speed is 40 to 50 mm/s in section 1, 75 to 85 mm/s in section 2, 75 to 85 mm/s in section 3, and 75 to 85 mm/s in section 4. It can be 65~75mm/s.

In the method of manufacturing a window cover for a display device according to an embodiment of the present invention, the compression gap may be 40 to 50% of the thickness of the window cover for a display device.

In the method of manufacturing a window cover for a display device according to an embodiment of the present invention, the melt index of the injection material may be 30 to 50 cm ³ /10 min at 300°C.

In the method of manufacturing a window cover for a display device according to an embodiment of the present invention, the impact strength of the injection material may be 50 to 60 kJ/m ² .

A window cover for a display device according to an embodiment of the present invention can be manufactured by the method of manufacturing a window cover for a display device of the present invention.

The window cover for a display device according to an embodiment of the present invention may have a flat side average retardation value of 50 nm or less.

The window cover for a display device according to an embodiment of the present invention may have an average retardation value of 270 nm or less at an incident angle of 45°.

The window cover for a display device according to an embodiment of the present invention may have an average retardation deviation value of 20 nm or less depending on the angle of incidence.

A window cover for a display device according to an embodiment of the present invention may have a flatness of 0.8 or less.

According to an embodiment of the present invention, the method of manufacturing a window cover for a display device can reduce retardation by controlling the mold temperature, and thus a window cover for a display device with excellent optical performance can be manufactured.

1 is a diagram showing the schematic structure of a window cover for a display device of the present invention.
Figure 2 is a diagram schematically showing the structure of the film layer of the present invention.
Figure 3 is a schematic configuration diagram of the film layer.
Figure 4 is a schematic configuration diagram of a film layer according to another embodiment.
Figure 5 is a diagram schematically showing the window cover of the present invention.
Figure 6 is a schematic AA cross-sectional view of the window cover shown in Figure 5.
FIG. 7 is a configuration diagram schematically showing technical features of the detailed configuration of the window cover shown in FIG. 5.
FIG. 8 is a configuration diagram schematically showing technical features of the film layer gate area in the window cover shown in FIG. 7.
Figure 9 is a configuration diagram schematically showing an embodiment of a mold and an injection material ejection device for implementing a method of manufacturing a window cover.
Figure 10 is a configuration diagram schematically showing a preforming film mounted on a mold.
Figure 11 is a flow chart showing a method of manufacturing a window cover for a display device according to an embodiment of the present invention.
Figures 12 and 13 are diagrams schematically showing a specific example of implementing the insert film upper mold mounting step.
Figure 14 is a configuration diagram schematically showing a specific example of implementing the injection material ejection step.
Figure 15 is a schematic state diagram of the injection material discharging step shown in Figure 14.
Figure 16 is a configuration diagram schematically showing a specific example of implementing the lower mold pressing step.
Figure 17 is a flowchart showing a method of manufacturing a window cover for a display device according to a second embodiment of the present invention.
Figure 18 is a flowchart showing a method of manufacturing a window cover for a display device according to a third embodiment of the present invention.
Figure 19 is a diagram showing the compression gap (G) in the method of manufacturing a window cover for a display device according to an embodiment of the present invention.
Figure 20 is a diagram showing the compression speed in the method of manufacturing a window cover for a display device according to an embodiment of the present invention.
Figure 21 is a diagram showing a stroke section in the method of manufacturing a window cover for a display device according to an embodiment of the present invention.
Figure 22 is a schematic diagram showing resin flowing into a cylinder. Figure 23 is a diagram showing a state in which a window cover is warped during the manufacturing process of a window cover for a display device.
Figure 24 is a diagram showing a plurality of measurement positions for measuring flatness.
Figure 25 is a diagram showing a film layer in a window cover for a display device according to an embodiment of the present invention.
Figure 26 is a diagram showing a first area and a second area in a window cover for a display device according to an embodiment of the present invention.
Figure 27 is a diagram showing the flow of injection material in the base layer forming step of a window cover for a display device according to an embodiment of the present invention.
Figure 28 is a diagram showing the results of visual evaluation of birefringence performance in the first area and the second area in the window cover for the display device of the present invention.
Figure 29 is a diagram showing a flow mark on the window cover for a display device of the present invention.
Figure 30 is a diagram showing a first area and a second area in a window cover for a display device according to an embodiment of the present invention.
Figure 31 is a diagram showing a first area and a second area in a window cover for a display device according to an embodiment of the present invention.
Figure 32 is a diagram showing a flow mark on a window cover for a display device according to an embodiment of the present invention.
Figure 33 is a flow chart schematically showing a method for manufacturing a window cover material according to the sixth embodiment of the present invention.
Figure 34 is a diagram schematically showing an embodiment of a suction device for implementing the method for manufacturing a window cover material shown in Figure 31.
Figure 35 is a configuration diagram schematically showing a specific example of implementing the insert film suction step.
Figure 36 is a configuration diagram schematically showing a window cover material according to a sixth embodiment of the present invention.
Figure 37 is a schematic configuration diagram of a window cover for a display device according to an embodiment of the present invention.
FIG. 38 is a schematic BB cross-sectional view of the window cover for the display device shown in FIG. 37.

Since the present invention can be modified in various ways and can have various embodiments, specific embodiments will be exemplified and explained in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all transformations, equivalents, and substitutes included in the spirit and technical scope of the present invention.

The terms used in the present invention are only used to describe specific embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In the present invention, terms such as 'include' or 'have' are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features. It should be understood that this does not exclude in advance the possibility of the existence or addition of elements, numbers, steps, operations, components, parts, or combinations thereof.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. At this time, note that in the attached drawings, like components are indicated by the same symbols whenever possible. Additionally, detailed descriptions of well-known functions and configurations that may obscure the gist of the present invention will be omitted. For the same reason, some components are exaggerated, omitted, or schematically shown in the accompanying drawings.

Window covers protect the panels of display devices and require excellent optical properties. The conventional use of glass as a material for window covers is being replaced by plastic materials. Window covers made of plastic have the advantage of being lightweight and resistant to shock.

Window covers are generally manufactured by injection molding. Injection molding refers to molding by injecting resin, etc. between the upper and lower molds and pressurizing them. However, injection molding applies high pressure to the cavity, and as the molded window cover shrinks due to large temperature changes, large residual stress remains in the window cover. Residual stress leads to a decrease in optical properties, such as an increase in the birefringence value of the manufactured window cover.

Accordingly, the present invention uses an injection compression molding (ICM) process to minimize residual stress when molding a window cover. Injection compression molding can control the pressure within the cavity to be low and uniform, and by reducing the cavity volume itself through compression, the effect of molding shrinkage of the resin can be minimized.

Injection compression molding involves partially injecting injection material into the cavity before the mold is completely closed during the filling stage, and operating until the clamping device completely closes the mold. The injection material enters the cavity by compressing the cavity surface, completing filling. There is a process of becoming.

In the present invention, a separate compression core is installed in the mold to compress the cavity with the compression core. This is a method of partially opening the compression core while the upper and lower molds are closed, partially injecting the injection material, then closing the compression core, and compressing the injection material to complete the final molding. The injection compression molding process applies compressive force uniformly to the entire surface of the window cover, resulting in products with uniform physical properties and low residual stress, which can greatly reduce optical problems such as birefringence.

Figure 1 is a diagram showing the schematic structure of a window cover for a display device of the present invention, Figure 2 is a diagram schematically showing the structure of the film layer of the present invention, Figure 3 is a schematic diagram of the structure of the film layer, Figure 4 is a schematic configuration diagram of a film layer according to another embodiment, Figure 5 is a diagram schematically showing the window cover of the present invention, Figure 6 is a schematic cross-sectional view taken along line A-A of the window cover shown in Figure 5, FIG. 7 is a diagram schematically showing the technical features of the detailed configuration of the window cover shown in FIG. 5, and FIG. 8 schematically shows the technical features of the gate area of the film layer in the window cover shown in FIG. 7. This is a configuration diagram.

As shown in FIG. 1, the window cover 1000 for a display device includes a base layer 1100 and a film layer 1200. The window cover 1000 for a display device serves to protect the panel of the display device.

The base layer 1100 is a layer that provides rigidity to the window cover and protects the display panel. The base layer 1100 may be formed of a material such as PC (PolyCarbonate), PMMA (PolyMethyl Methacrylate), or polyacrylate. PC is a thermoplastic plastic that has excellent heat resistance, visibility, transparency, electrical insulation, and durability, and window covers made of PC have the advantage of having high impact strength. PMMA has the advantages of excellent visibility, transparency, weather resistance, and colorability. However, the material of the base layer is not limited to this, and any material that is optically transparent can be used as the base layer.

The base layer 1100 may be formed to have a thickness of 1500 to 2500 μm. If the base layer 1100 is formed to be less than 1500㎛, it is difficult to secure the minimum surface hardness, there is a high probability that non-molding will occur during injection, and deviation and bending may occur due to uneven thickness. If the base layer 1100 exceeds 2500㎛, cracks may occur due to external impact, and sensitivity may decrease when touching the rear display.

The film layer 1200 is disposed on top of the base layer 1100. The film layer 1200 may be formed of a material such as PC or PMMA. The film layer 1200 may be formed of a single layer of PC or PMMA, or a two-layer co-extruded sheet in which PC and PMMA layers are formed simultaneously may be used. If necessary, a 3-layer sheet in which PMMA, PC, and PMMA layers are sequentially laminated can be used. The film layer 1200 can be hard coated with a PC or PMMA material film to improve the surface hardness, scratch resistance, and weather resistance of the window cover.

The film layer 1200 may be formed to have a thickness of 100 to 500 μm, preferably 180 to 220 μm.

In this embodiment, the film layer 1200 is formed by applying a hard coating for scratch resistance on a two-layer PC/PMMA sheet, and then forming an antireflection coating layer (LR coating layer) and an antifouling functional coating layer (AF coating layer). In the film layer 1200 of this embodiment, the thickness of the two-layer PC/PMMA sheet is 200㎛, the thickness of the hard coating layer is 3㎛, and the thickness of the LR/AF coating layer is 0.2㎛.

The film layer 1200 may be integrally molded by combining with the injection material during injection compression molding of the base layer 1100.

Meanwhile, the film layer 1200 is provided with a gate area 1250 that can be placed on the injection material injection hole 31 for molding the window cover 1000. As shown in FIGS. 2 and 3, a gate region 1250 is formed in the film layer 1200. The gate area 1250 serves as a film layer gate area (G) through which the injection material flows when the injection material is discharged to the back of the film layer 1200. In addition, the gate area 1250 simultaneously serves as a film hanger (F) for fixing the film layer 1200 during the injection compression process.

To this end, the injection material injection device 30 is provided with an injection material injection port 31 through which the injection material is discharged, and an end of the injection material injection port 31 is formed to correspond to the gate area 1250. The injection material injection hole 31 passes through the front (FS) gate area 1250 of the film layer 1200 and injects the injection material to the rear side (RS) of the film layer 1200 ( A base layer 1100 is formed in RS).

At this time, the gate area 1250 is mounted on the injection material injection port 31 and serves as a film hanger (F) that fixes the film layer 1200 during injection.

In the present invention, the gate area 1250 fixes the film layer 1200 without a separate fixing member for fixing the film layer 1200 in the step of spraying the injection material to the rear of the film layer 1200 during the injection compression process. As it performs the role of a hanger, the process becomes simpler.

Here, the gate area 1250 of the film layer 1200 may be formed in the buttonhole area of the film layer 1200 corresponding to the buttonhole area of the window cover for the display device. The button hole area refers to the hole area corresponding to the button portion of the display device when the window cover for the display device is coupled to the display device.

In another embodiment, as shown in FIG. 4, a gate region 1250' may be formed in the film layer 1200'. The gate area 1250' serves as a gate (G) when the injection material is discharged to the film layer 1200'. In addition, the gate area 1250' simultaneously serves as a hanger (F) for fixing the film layer during the injection compression process. In this embodiment, the gate area 1250' is formed in the external area 1200b' extending from the display area 1200a' of the display device when the window cover for the display device is coupled to the display device. That is, the gate area 1250 is removed from the finally manufactured window cover.

More specifically, the film layer 1200 may be made of a preformed IML (In Mold Label) film. The film layer 1200 may include a transparent portion 1260 and a light blocking portion 1270 so that the window cover 1000 is implemented as a window cover for a display device. That is, the transparent part 1260 is formed to correspond to the display area, and the light blocking part 1270 is formed to surround the outer periphery of the transparent part 1260.

Additionally, a film layer gate area 1271 and a film layer buttonhole area 1272 are formed in the light blocking portion 1270. The film layer gate area 1271 is a gate area for spraying injection material into the film layer 1200. That is, the film layer gate area 1271 is a gate area through which injection material flows. At the same time, the film layer gate area 1271 also serves as a film hanger for fixing the film layer during the injection and compression process.

In addition, FIGS. 5 to 8 are examples of positions where the film layer gate area 1271 is formed, and show that the film layer gate area 1271 is formed in the film layer buttonhole area 1272.

The film layer buttonhole area 1272 may be formed to protrude in the direction in which the base layer 1100 is located with respect to the film layer 1200. This is so that the base layer buttonhole area 1272 is used as a hanging area when the injection material is supplied. That is, the hook area is formed as a step with respect to one side of the film layer.

Additionally, the base layer 1100 is combined with the film layer 1200. To this end, the base layer 1100 is formed by injecting and compressing the injection material onto the back of the IML film, which is the film layer 1200, and at the same time, the base layer 1100 is combined with the film layer 1200.

And in the base layer 1100, a base layer gate area 1160 corresponding to the film layer gate area 1271 of the film layer 1200 is formed, and a base layer buttonhole area corresponding to the film layer buttonhole area 1272 is formed. (1170) is formed.

Hereinafter, with reference to FIGS. 7 and 8, the detailed configuration and shape of the film layer gate area and the film layer buttonhole area will be described in more detail.

As shown in FIG. 7, the film layer 1200 of the window cover 1000 has a first center line (C1) in one axis (X-axis) direction and a second center line (C2) in the other axis (Y-axis) direction. It has one side that includes The first center line (C1) is an imaginary line that passes through the midpoint of the final manufactured window cover and is parallel to the Y-axis direction, and the second center line (C2) is an imaginary center line on the window cover and is the midpoint of the final manufactured window cover. It is a line parallel to the X-axis direction. That is, in the They have the same distance (D2).

The film layer gate area 1271 and the film layer buttonhole area 1272 of the film layer 1200 may be located on one side with respect to the second center line C2. For example, the film layer gate area 1271 and the film layer buttonhole area 1272 of the film layer 1200 may be located below the second center line C2. This is considering that the film layer gate area 1271 is formed on one side so that when the injection material is ejected into the film layer 1200, it flows without obstruction from one side to the other.

Additionally, in the display device, as the button portion is formed at the bottom of the display portion, the film layer buttonhole area 1272 is formed on one side.

Additionally, the base layer buttonhole area 1170 and the base layer gate area 1160 are also located below the second center line C2.

More specifically, the film layer gate area 1271 is located at the first center line C1.

In addition, it is preferable that the separation distance D3 of the film layer gate area, which can be formed away from the first center line C1, is 10% or less compared to the total distance D4 of the window cover.

At this time, the insert film and the base layer may have a symmetrical shape with respect to the first center line.

This means that when the film layer gate area 1271 serves as a gate through which the injection material flows during injection molding, if the allowable separation distance from the center line is within 10% as described above, the effect of improving optical performance due to the symmetry of birefringence is achieved. You can get it.

In addition, the base layer gate area 1160 is also located on the first center line C1, and the distance between the base layer gate areas that can be formed by separating the base layer gate area 1160 from the first center line C1 covers the window. It is preferable that it is formed to be 10% or less compared to the total distance (D4).

Figure 9 is a configuration diagram schematically showing an embodiment of a mold and an injection material ejection device for implementing a method of manufacturing a window cover, and Figure 10 is a configuration diagram schematically showing a preforming film mounted on a mold.

A mold and an injection material ejection device for manufacturing a window cover will be described.

As shown in FIG. 9, the mold 100 includes an upper mold 110 and a lower mold 120. An upper mold button hole hanger 111, a hot runner 112, and an upper mold gate step 113 are formed in the upper mold 110.

More specifically, the upper mold buttonhole hanger 111 is made of a protrusion corresponding to the film layer buttonhole area of the insert film so that the film layer buttonhole area of the insert film is inserted and supported. The hot runner 112 is formed in the upper mold button hole hook 111 to communicate with the upper mold gate step 113.

The upper mold gate step 113 is used to support the film layer gate area 1271 of the film layer 1200 and has a protruding shape. Accordingly, it is possible to provide the injection material while the film layer 1200 is more accurately restrained in the upper mold.

A groove 121 corresponding to the upper mold button hole hook 111 of the upper mold 110 is formed in the lower mold 120. As the outer shape of the upper mold 110 and the lower mold 120 are formed to correspond to each other, the insert film in contact with the upper mold and the injection material in contact with the lower mold have the same shape.

Meanwhile, in another embodiment, a hot runner may be formed in the lower mold and an injection nozzle may be inserted through the lower mold to provide an injection material.

As shown in FIG. 10, the insert film, which is the film layer 1200 of the film injection molded body, includes a transparent portion 1260 and a light blocking portion 1270. Additionally, a film layer gate area 1270 and a film layer buttonhole area 1272 are formed in the light blocking portion 1270.

The film layer gate area 1270 of the insert film layer 1200 is implemented as a gate for providing injection material to the insert film layer 1200.

In addition, the insert film layer 1200 for injection molding has a film layer buttonhole area 1272 and a film layer gate area 1271, unlike the insert film layer 1200 of the window cover 1000 shown in FIG. 10. It is positioned to face upward.

This is to place the insert film through the film layer buttonhole area 1272 when supplying the injection material through the film layer gate area 1271.

Figure 11 is a flowchart showing a method of manufacturing a window cover for a display device according to an embodiment of the present invention, and Figures 12 and 13 are configuration diagrams schematically showing a specific example of implementing the insert film upper mold mounting step, Figure 14 is a configuration diagram schematically showing a specific example of implementing the injection material discharge step, Figure 15 is a schematic state diagram of the injection material discharge step shown in Figure 14, and Figure 16 is a diagram of the lower mold pressurizing step. It is a configuration diagram schematically showing a specific example, and Figure 17 is a flowchart showing a method of manufacturing a window cover for a display device according to a second embodiment of the present invention, and Figure 18 is a display according to a third embodiment of the present invention. It is a flow chart showing a method of manufacturing a window cover for a display device, and Figure 19 is a diagram showing the compression gap (G) in the method of manufacturing a window cover for a display device according to an embodiment of the present invention, and Figure 20 is an embodiment of the present invention. It is a diagram showing the compression speed in the method of manufacturing a window cover for a display device according to , and Figure 21 is a diagram showing a stroke section in the method of manufacturing a window cover for a display device according to an embodiment of the present invention.

Next, a method for manufacturing the window cover 1000 for a display device of the present invention will be described.

As shown in Figure 11, in order to manufacture a window cover according to the first embodiment of the present invention, the insert film is preformed (S1110). The insert film can form an optical coating layer to satisfy the optical properties required to form a film layer. Through the insert film preforming step, a gate area for injecting injection material and a button hole area for holding the insert film can be formed in the insert film. The gate area may be formed within the area of the final window cover, or may be located outside the final window cover area and removed after injection and curing of the injection material.

Next, the insert film is placed in the upper mold (S1120). Ensure that the gate area and buttonhole area of the insert film are located at corresponding positions in the upper mold. The gate area of the insert film is positioned opposite the hot runner of the upper mold.

Specifically, as shown in FIG. 12, the film layer button hole area 1272 is mounted on the upper mold gate step 113 so that the insert film layer 1200 is supported on the upper mold 110, and the upper mold button is pressed. The film layer button hole area 1272 of the insert film layer 1200 is placed on the hole hanger 111.

Additionally, when mounting the film layer button hole area 1272 on the upper mold gate step 113, the film layer gate area 1271 is positioned to face the hot runner 112.

The film layer buttonhole area 1272 and the film layer buttonhole area 1272 of the insert film layer 1200 are connected to the upper mold gate step 113 and the upper mold buttonhole hanger 111 of the upper mold 110, respectively. By placing the insert film layer 1200 on the upper mold 110 by inserting it into the , it is possible to fix the film for injection molding without a separate film hanger.

Accordingly, it is possible to apply the injection material to the other side of the insert film layer 1200, one side of which is in contact with the upper mold 110.

The lower mold is positioned so that the lower mold is spaced apart from the upper mold by a predetermined distance (S1130). The lower mold is moved toward the upper mold so that a cavity of a predetermined volume is formed within the mold.

Inject injection material into the mold (S1140). The injection material is sprayed onto the back of the film by a hot runner. The injection material may be PC or PMMA material. The injection material is cured to form the base layer 1100. The temperature of the injection material may be 270 to 320°C, preferably 280°C.

Specifically, while one side of the insert film is placed in contact with the upper mold, an injection material is provided to the other side of the insert film through a hot runner. Accordingly, the injection material is combined with the insert film.

As shown in FIG. 14, the injection material is discharged through the film layer gate area 1121 of the insert film layer 1100 through the hot runner 112. At this time, the flow of the injection material in the discharge direction is restricted by the lower mold 120 and flows in the downward direction.

More specifically, as shown in FIG. 15, the flow of injection material includes a first flow stream (F1), a second flow stream (F2), and a third flow stream (F3).

The first flow flow (F1) defines the flow of the injection material discharged through the film layer gate area 1121, which is the gate of the injection material, and the second flow flow (F2) defines the flow of the injection material in the horizontal direction. 3 Flow flow (F3) defines the vertical flow of the injection material according to the fluid pressure of the injection material.

Additionally, the vertical flow of the injection material may correspond to the direction of gravity.

As described above, as the injection material flows into the first flow stream (F1), the second flow stream (F2), and the third flow stream (F3), the effect of reducing the backflow of the injection material and the formation of a melt line can be obtained. .

Pressurize the compression core (S1150). When a predetermined amount of injection material is filled in the mold, the compression core is pressed to compress the cavity surface. As the compression core is pressed, the volume of the cavity decreases, and as the injection material flows under compression within the cavity, the base layer is molded and bonded to the film layer. Additionally, the thickness of the injection material bonded to the insert film is adjusted by the compression core pressing step. The compression holding time may be 8 to 10 seconds, preferably 9 seconds. Additionally, the clamping force that pressurizes the compression core may be 250 to 600 tons.

Meanwhile, the window cover manufacturing method may further include a base layer gate region forming step. In the base layer gate area forming step, after the injection material is supplied to the insert film, a base layer gate area forming bar is inserted from the upper mold through the film layer gate area of the insert film to form the base layer gate area. It can be.

In other embodiments, the lower mold rather than the compression core may move. As shown in FIG. 16, the lower mold 120 is moved while the injection material is discharged between the upper mold 110 and the lower mold 120.

That is, the discharge material is discharged between the upper mold 110 and the lower mold 120 in an amount less than the specified amount, and the lower mold 120 is moved to the upper mold 110. Accordingly, rapid changes in the flow of the injection material are prevented due to the initial discharge pressure, the injection material flows stably, and the thickness of the injection material can be adjusted by adjusting the gap between the upper mold 110 and the lower mold 120.

The second embodiment according to the present invention may further include checking the upper and lower mold temperatures. The same content as the previous embodiment will be briefly described.

As shown in Figure 17, in order to manufacture a window cover according to the present invention, the insert film is preformed (S1210). The insert film can form an optical coating layer to satisfy the optical properties required to form a film layer, or form a gate area to allow injection of injection material, and a button hole area to hold the insert film.

Place the insert film in the upper mold (S1220). Ensure that the gate area and buttonhole area of the insert film are located at corresponding positions in the upper mold. The gate area of the insert film is positioned opposite the hot runner of the upper mold.

Next, the lower mold is positioned so that the lower mold is spaced apart from the upper mold by a predetermined distance (S1230). The lower mold is moved toward the upper mold so that a cavity of a predetermined volume is formed within the mold.

Check the temperatures of the upper mold and lower mold (S1240). The temperatures of the upper and lower molds affect the flow and residual stress of the injection material. Therefore, the upper and lower molds must be maintained at a temperature within a certain range. The temperatures of the upper and lower molds are maintained by fluid of a predetermined temperature. The temperature of the mold can be checked by checking the flow rate of the fluid, and the temperature can also be checked by installing a temperature sensor in the mold.

The temperature of the upper mold and lower mold may be 70 to 95°C, preferably 80°C. If the upper and lower mold temperatures are lower than 70°C, there is a problem in that the flow resistance of the injection material increases and residual stress increases. As the upper and lower mold temperatures increase, the shear stress of the resin and the residual stress of the product decrease during injection compression, which can improve the birefringence characteristics. However, due to changes in resin flow, reproducibility is poor and dimensional differences due to mass differences in the final product may occur. there is. In particular, if the upper and lower mold temperatures exceed 105°C, strain will be placed on the mold, and mold damage or scaling may occur. In general, water is used as a constant temperature medium to control the temperature of the mold, but mold damage and scaling problems occur near 100℃ due to the boiling point of water. However, it was confirmed through experiments that there was no problem in operating the injection molding machine up to 105°C without major damage because the constant temperature medium was not placed under a 1-atmosphere atmosphere but circulated inside the mold. The above results are valid when water is used as the medium, and the above values may change when a medium with a high boiling point is used as the constant temperature medium.

The temperature of the gate through which the injection material is injected may be 20 to 40°C, preferably 30°C. The temperature of the compression core may be 80 to 105°C, preferably 90°C.

In this embodiment, the temperatures of the upper mold and lower mold are checked, but in other embodiments, the temperatures of the compression core and gate in addition to the upper mold and lower mold can be further checked. The temperature of the compression core is set higher than the temperature of the upper and lower molds, but the temperature difference between the upper and lower molds and the compression core can be at least 10℃.

If the temperature difference between the upper and lower mold temperatures and the compression core is less than 10℃, there is a problem that compression burrs and silver burrs (silveri) are generated in the parting line. Specifically, the thermal expansion rate must be different between molds. When the temperature of the compression core is low, the expansion of the mold becomes smaller compared to the upper and lower sides, which reduces the pressure in the parting line during injection. As a result, compression burr and silver burr are released into the parting line. may occur. If production continues while the temperature of the compression core is low, not only will burrs continue to be generated in the product produced by the burrs generated in the compression parting line, but the mold parting line may collapse, increasing the defective rate of the product.

Inject injection material into the mold (S1250). The injection material is sprayed onto the back of the film by a hot runner. The injection material may be PC or PMMA material. The injection material is cured to form the base layer 1100. The temperature of the injection material may be 270 to 320°C, preferably 280°C.

Pressurize the compression core (S1260). When a predetermined amount of injection material is filled in the mold, the compression core is pressed to compress the cavity surface. As the compression core is pressed, the volume of the cavity decreases, and as the injection material flows under compression within the cavity, the base layer is molded and bonded to the film layer. The compression holding time may be 8 to 10 seconds, preferably 9 seconds. Additionally, the clamping force that pressurizes the compression core may be 250 to 600 tons.

In the third embodiment according to the present invention, the compression speed can be controlled in multiple stages in the compression stage. The same content as the previous embodiment will be briefly described.

As shown in Figure 18, in order to manufacture a window cover according to the present invention, the insert film is preformed (S1310). The insert film can form an optical coating layer to satisfy the optical properties required to form a film layer, or form a gate area to allow injection of injection material, and a button hole area to hold the insert film.

Place the insert film in the upper mold (S1320). Ensure that the gate area and buttonhole area of the insert film are located at corresponding positions in the upper mold. The gate area of the insert film is positioned opposite the hot runner of the upper mold.

The lower mold is positioned so that the lower mold is spaced apart from the upper mold by a predetermined distance (S1330). The lower mold is moved toward the upper mold so that a cavity of a predetermined volume is formed within the mold.

Inject injection material into the mold (S1340). The injection material 1100a is sprayed onto the back of the film by a hot runner. The injection material 1100a may be made of PC or PMMA material. The injection material 1100a is hardened to form the base layer 1100. The temperature of the injection material 1100a may be 270 to 320°C, preferably 280°C.

The compression core is pressurized by controlling the compression speed in two stages (S1350). When the mold is filled with a predetermined amount of injection material 1100a, the compression core 130 is pressed to compress the inside of the cavity. As the compression core 130 is pressed, the volume of the cavity decreases, and the injection material 1100a compresses and flows within the cavity, forming the base layer 1100 and bonding to the film layer 1200.

As shown in Figures 19 and 20, the compression speed is controlled in two stages based on the compression gap (G). Compression speed is the speed at which the compression core moves. The compression gap (G) refers to the compression distance, and the compression speed is divided into section 1 (G1) and section 2 (G2) based on 1/2 of the compression gap and is controlled in two stages.

Section 1 (G1) is the first half section in which the compression core 130 moves toward the upper mold 110, and refers to the period from the initial position of the compression core 130 to the 1/2 point of the compression gap. Section 2 (G2) is the latter section in which the compression core 130 moves toward the upper mold 110, and refers to the period from 1/2 of the compression gap to the final movement point of the compression core 130. For example, if the compression gap is 1mm and the initial position of the compression core is 0, section 1 (G1) is from 0 to -0.5mm, section 2 (G2) is from -0.5mm to -1mm. It means section.

The compression speed in section 1 (G1) is constant, and the compression speed in section 2 (G2) can increase linearly. In other words, the compression speed in section 2 may have constant acceleration. In section 2, compression marks occur on the injection material and the shear stress of the injection material increases, so the compression speed is increased and compression is performed before the flow of the injection material decreases.

In one embodiment of the present invention, the compression speed is 1.8 to 2.2 mm/s in section 1 (G1), the acceleration is 1.8 to 2.2 mm/s2 in section 2 (G2), preferably 2 mm/s in section 1 (G1), In section 2 (G2), the acceleration can be set to 2 mm/s ² . In other words, the speed in section 2 has an acceleration of 1.8 to 2.2 mm/s ² using the speed in section 1 as the initial speed. If the compression speed in one section is lower than 1.8 mm/s, the resin stagnates and the frozen layer increases, and if the compression speed in one section is higher than 2.2 mm/s, shear stress increases and birefringence performance may deteriorate.

As the compression gap increases, the compression speed can also increase. Meanwhile, the compression holding time may be 8 to 10 seconds, preferably 9 seconds. Additionally, the clamping force that pressurizes the compression core may be 250 to 600 tons.

In the fourth embodiment according to the present invention, the injection speed can be controlled for each stroke section. The same content as the previous embodiment will be briefly described.

In order to manufacture a window cover according to the present invention, the insert film is preformed (S1110). The insert film can form an optical coating layer to satisfy the optical properties required to form a film layer, or form a gate area to allow injection of injection material, and a button hole area to hold the insert film.

Place the insert film in the upper mold (S1320). Ensure that the gate area and buttonhole area of the insert film are located at corresponding positions in the upper mold. The gate area of the insert film is positioned opposite the hot runner of the upper mold.

The lower mold is positioned so that the lower mold is spaced apart from the upper mold by a predetermined distance (S1130). The lower mold is moved toward the upper mold so that a cavity of a predetermined volume is formed within the mold. The temperature of the upper mold and lower mold may be 70 to 95°C, the temperature of the gate may be 20 to 40°C, and the temperature of the compression core may be 80 to 105°C.

Inject injection material into the mold (S1140). The injection material is sprayed onto the back of the film by a hot runner. The injection material may be PC or PMMA material. The injection material is cured to form the base layer 1100. The temperature of the injection material may be 270 to 320°C, preferably 280°C.

Injection speed is the speed at which the injection material is injected, and refers to the amount of injection material filled into the mold in unit time. As the injection speed increases, the flow distance of the injection material increases. By dividing the stroke section, the injection speed can be adjusted for each section. As shown in Figure 21, the stroke section is defined in the longitudinal direction of the cylinder with the nozzle tip position at 0 mm, and according to the position of the screw tip. The stroke section can be adjusted depending on the shape of the mold.

Flow resistance in the mold may occur during the process of injecting the injection material. The flow resistance of the mold causes surface defects in molded products such as jetting, flow marks, and weld lines. Flow resistance can vary depending on the shape of the mold, and the point at which injection speed is controlled can vary depending on the shape of the mold. For example, the stroke section can be divided based on the points where the screw tip is located at 33 to 37 mm, 23 to 27 mm, 10 to 14 mm, and 5 to 9 mm. In this embodiment, the stroke section was divided into 4 sections based on the screw tip positions of 35mm, 25mm, 12mm, and 7mm, and one section (S ₄ - S ₃ ), the point between 25 and 12 mm is divided into 2 sections (S ₃ -S ₂ ), the point between 12 and 7 mm is divided into 3 sections (S ₂ -S ₁ ), and the point between 7 and 0 mm is divided into 4 sections (S ₁ -S ₀₎ . ) is defined as. The injection speed is controlled in sections 1, 2, 3, and 4, respectively.

The injection speed is 40~50mm/s in section 1, 75~85mm/s in section 2, 75~85mm/s in section 3, 65~75mm/s in section 4, preferably 45mm/s in section 1, 2 The speed was set at 80mm/s in section 3, 80mm/s in section 3, and 70mm/s in section 4. The speed of sections 2 and 3 has a significant effect on birefringence, and if the speed of sections 2 and 3 increases compared to section 1, birefringence can be improved. That is, the injection speed in sections 2 and 3 is set larger than the injection speed in section 1.

Pressurize the compression core (S1350). When a predetermined amount of injection material is filled in the mold, the compression core is pressed to compress the cavity surface. As the compression core is pressed, the volume of the cavity decreases, and as the injection material flows under compression within the cavity, the base layer is molded and bonded to the film layer. Meanwhile, the compression holding time may be 8 to 10 seconds, preferably 9 seconds. Additionally, the clamping force that pressurizes the compression core may be 250 to 600 tons.

Compression speed is controlled in two stages based on the compression gap. As the compression gap increases, the compression speed can increase. The compression gap may be 40 to 50% of the thickness of the window cover for the display device, which is the final molded product.

In the fifth embodiment according to the present invention, the compression gap can be set to 0.8 to 1.2 mm. The same content as the previous embodiment will be briefly described.

In order to manufacture a window cover according to the present invention, the insert film is preformed (S1310). The insert film can form an optical coating layer to satisfy the optical properties required to form a film layer, or form a gate area to allow injection of injection material, and a button hole area to hold the insert film.

Place the insert film in the upper mold (S1320). Ensure that the gate area and buttonhole area of the insert film are located at corresponding positions in the upper mold. The gate area of the insert film is positioned opposite the hot runner of the upper mold.

The lower mold is positioned so that the lower mold is spaced apart from the upper mold by a predetermined distance (S1330). The lower mold is moved toward the upper mold so that a cavity of a predetermined volume is formed within the mold. The temperature of the upper mold and lower mold may be 70 to 95°C, the temperature of the gate may be 20 to 40°C, and the temperature of the compression core may be 80 to 105°C.

Inject injection material into the mold (S1340). The injection material is sprayed onto the back of the film by a hot runner. The injection material may be PC or PMMA material. The injection material is cured to form the base layer 1100. The temperature of the injection material may be 270 to 320°C, preferably 280°C.

The injection speed can be divided into stroke sections and adjusted for each section. The stroke section can be divided into four sections based on the screw tip position (S) of 35mm, 25mm, 12mm, and 7mm.

Pressurize the compression core (S1350). When a predetermined amount of injection material is filled in the mold, the compression core is pressed to compress the cavity surface. As the compression core is pressed, the volume of the cavity decreases, and as the injection material flows under compression within the cavity, the base layer is molded and bonded to the film layer.

The compression gap refers to the compression distance at which the injection material is compressed, and the compression gap affects the point at which the injection material stagnates. As the compression gap becomes smaller, the overall stress transfer becomes faster and the overall retardation value increases. As the compression gap increases, stress relief after filling and an increase in stress due to the frozen layer occur simultaneously, causing retardation to concentrate at the compression location. In this embodiment, the compression gap is 0.8 to 1.2 mm, preferably 1 mm. When the compression gap is less than 0.8mm, stress transfer is accelerated, birefringence characteristics deteriorate, and compression burrs may occur at the parting line. When the compression gap is more than 1.2mm, the injection material may stagnate and cause compression marks. It is desirable to set the compression gap to 40-50% of the thickness of the window cover.

As the compression gap increases, the compression speed can increase. The compression holding time may be 8 to 10 seconds, preferably 9 seconds. Additionally, the clamping force that pressurizes the compression core may be 250 to 600 tons.

Meanwhile, during the manufacturing process of the window cover, factors that affect the optical properties of the injection compression molded window cover include mold temperature, compression speed, injection speed, compression gap, impact strength of the resin, and melt index (MI) of the resin. there is.

In the present invention, the mold temperature conditions define the temperatures of the upper mold, lower mold, compression core, and gate. Mold temperature affects the flow state and residual stress of the injection material.

In one embodiment of the present invention, PC was used as an injection material, and in the case of PC, the mold temperature of the upper and lower mold, compression core, and gate is preferably in the range of 70 to 95 ℃, 80 to 105 ℃, and 20 to 40 ℃, respectively. Can be injection-compression molded under conditions of 80℃, 90℃, and 30℃. If the temperatures of the upper and lower mold, compression core, and gate are lower than 70℃, 80℃, and 20℃, respectively, there is a problem that the flow resistance of the injection material increases and residual stress increases. As the temperature of the upper and lower molds, compression core, and gate increases, the shear stress of the resin and the residual stress of the product decrease during injection compression, which can improve birefringence characteristics, but the variation in compression gap becomes worse due to changes in resin flow, resulting in poor reproducibility. . In particular, if the temperature of the upper and lower molds or compression cores exceeds 105°C, strain is placed on the mold itself, and the upper and lower molds or compression cores may be damaged or scaling may occur. In general, water is used as a constant temperature medium to control the temperature of the mold, but mold damage and scaling problems occur near 100℃ due to the boiling point of water. However, it was confirmed through experiments that there was no problem in operating the injection molding machine up to 105°C without major damage because the constant temperature medium was not placed under a 1-atmosphere atmosphere but circulated inside the mold. The above results are valid when water is used as the medium, and the above values may change when a medium with a high boiling point is used as the constant temperature medium.

Meanwhile, the injection material injected into the upper and lower molds is compressed by the compression core, and the injection material disposed on the compression surface of the compression core receives greater pressure than the injection material disposed inside the upper mold. Therefore, in order to reduce the residual stress on the compression core side, it is desirable that the temperature of the compression core be greater than the temperature of the upper mold. The temperature difference between the upper and lower molds and the compression core can be at least 10℃.

If the temperature difference between the upper and lower mold temperatures and the compression core is less than 10℃, there is a problem that compression burrs and silver burrs (silveri) are generated in the parting line. Specifically, the thermal expansion rate must be different between molds. When the temperature of the compression core is low, the expansion of the mold becomes smaller compared to the upper and lower sides, which reduces the pressure in the parting line during injection. As a result, compression burr and silver burr are released into the parting line. may occur. If production continues while the temperature of the compression core is low, burrs generated in the compression parting line not only continuously generate burrs in the products produced, but also cause the mold parting line to collapse, increasing the defective rate of the product.

Compression speed defines the speed at which the compression core moves, and is controlled in two stages by dividing it into section 1 and section 2 based on 1/2 section of the compression gap.

Section 1 is the first section in which the compression core moves toward the upper mold, meaning from the initial position of the compression core to 1/2 of the compression gap. Section 2 is the latter section in which the compression core moves toward the upper mold, meaning from 1/2 of the compression gap to the final movement point of the compression core. For example, if the compression gap is 1mm and the initial position of the compression core is 0, section 1 means the section from 0 to -0.5mm, and section 2 means the section from -0.5mm to -1mm.

The compression speed in section 1 is constant, and the compression speed in section 2 can have a constant acceleration that increases linearly. The compression speed in section 2 may be a predetermined acceleration added to the speed in section 1. In section 2, compression marks occur on the injection material and the shear stress of the injection material increases, so the compression speed is increased and compression is performed before the flow of the injection material decreases.

In one embodiment of the present invention, the compression speed is 1.8 to 2.2 mm/s in section 1, acceleration 1.8 to 2.2 mm/s ² in section 2, and preferably 2 mm/s in section 1 and 2 mm/s ^{2 in section 2} . You can. In other words, the speed in section 2 has an acceleration of 1.8 to 2.2 mm/s2, using the speed in section 1 as the initial speed. If the compression speed in one section is lower than 1.8 mm/s, the resin stagnates and the frozen layer increases, and if the compression speed in one section is higher than 2.2 mm/s, shear stress increases and birefringence performance may deteriorate.

Injection speed is the speed at which the injection material is injected and refers to the amount of injection material filled into the mold in unit time. As the injection speed increases, the flow distance of the injection material increases.

Injection speed can be controlled depending on where the screw is positioned. In other words, the injection speed can be adjusted for each section by dividing the stroke section. Flow resistance in the mold may occur during the process of injecting the injection material. The flow resistance of the mold causes surface defects in molded products such as jetting, flow marks, and weld lines. Flow resistance can vary depending on the shape of the mold, and the point at which injection speed is controlled can vary depending on the shape of the mold. The stroke section is defined in the longitudinal direction of the cylinder with the nozzle tip position at 0 mm, and according to the position of the screw tip. The stroke section can be divided into multiple sections depending on the shape of the mold. For example, the stroke section can be divided based on the points where the screw tip is located at 33~37mm, 23~27mm, 10~14mm, and 5~9mm. You can.

In one embodiment of the present invention, the stroke section is divided into four sections based on the positions of the tip of the screw (S) of 35mm, 25mm, 12mm, and 7mm, and a point between 35 and 25mm in the section where the screw moves toward the tip of the nozzle. Section 1 (S ₄ -S ₃ ), section 2 (S ₃ -S ₂ ) at 25~12 mm, section 3 (S ₂ -S ₁ ) at 12~7 mm, section 4 at 7~0 mm. It is defined as a section (S ₁ -S ₀ ). The injection speed is controlled in sections 1, 2, 3, and 4, respectively.

The injection speed is 40 to 50 mm/s in section 1, 75 to 85 mm/s in section 2, 75 to 85 mm/s in section 3, 65 to 75 mm/s in section 4, preferably 45 mm/s in section 1, 2 The speed was set at 80mm/s in section 3, 80mm/s in section 3, and 70mm/s in section 4. The speed of sections 2 and 3 has a significant effect on birefringence, and if the speed of sections 2 and 3 increases compared to section 1, birefringence can be improved.

The compression gap refers to the compression distance, and the compression gap affects the stagnation point of the injection material. As the compression gap becomes smaller, the overall stress transfer becomes faster and the overall retardation value increases. As the compression gap increases, stress relief after filling and an increase in stress due to the frozen layer occur simultaneously, causing retardation to concentrate at the compression location. In this embodiment, the compression gap is 0.8 to 1.2 mm, preferably 1 mm. When the compression gap is less than 0.8mm, stress transfer is accelerated, birefringence characteristics deteriorate, and compression burrs may occur at the parting line. When the compression gap is more than 1.2mm, the injection material may stagnate and cause compression marks. It is desirable to set the compression gap to 40-50% of the thickness of the window cover.

The compression force acts after injection of the injection material, allowing the injection material to flow and fill the unfilled portion. In addition, by compressing the injection material considering the amount of shrinkage of the injection material, stress due to shrinkage occurring after molding can be eliminated.

Retardation refers to the phase difference between polarization elements passing through the window cover. In the present invention, the retardation value on the plane side and the retardation value at an incident angle of 45 degrees are measured. The retardation deviation value refers to the difference in retardation value depending on the angle of incidence.

On the other hand, in order to manufacture a window cover with fewer defects and reduced retardation, the conditions of the injection material can be defined.

Transparent materials such as PC or PMMA are used as injection materials for manufacturing window covers. For use as an automobile interior material, it is desirable to use a resin that satisfies heat resistance with a heat deflection temperature (HDT) of 120°C or higher to prevent post-deformation. In addition, the window cover protects the display panel and transmits the image displayed on the display panel, so it is required to be strong against shock, have few defects, and have excellent birefringence performance.

In order to supply injection material into the mold, as shown in FIG. 22, resin particles are supplied into the cylinder 1510 through the hopper 1530. Resin can be used in the form of pellets. The amount of resin input can be adjusted depending on the shape and size of the product being manufactured. The average particle diameter of the injected resin particles may be 2 to 3 mm. A fixed amount of resin in the form of pellets is introduced into the cylinder 1510 through the hopper 1530, is melted within the cylinder 1510, and is sprayed through a nozzle.

Inside the cylinder 1510, a screw 1520 is located coaxially with the cylinder 1510, and a warming device (not shown) capable of heating the inside of the cylinder 1510 is provided. The resin particles in the cylinder are melted by the heating device, and the molten injection material advances toward the tip of the nozzle as the screw 1520 rotates. Since the temperature of the cylinder 1510 greatly affects the fluidity of the injection material, it is controlled to maintain a constant temperature during molding. The injection cylinder 1540 and the hydraulic motor 1550 advance the screw 1520 and generate injection pressure, injection speed, and back pressure.

When adding resin, which is the raw material of the injection material, to the injection molding machine, dust may be generated due to friction, impact, etc. during the processing or transport of the resin. In particular, when the impact strength of the resin is low, there is a problem that the amount of dust generated increases. Dust may take the form of fine resin powder, chip-shaped fine pieces, etc. Dust may flow into the mold along with the injection material and be carbonized during the processing process, and may cause problems such as surface defects and microcracks in the manufactured window cover.

In order to manufacture a good window cover, the amount of dust generated is preferably 120 ppm or less per 25 kg of injection material, and preferably 100 ppm or less per 25 kg. In order for the dust generated during the processing or transport of the resin to satisfy less than 100 ppm per 25 kg, the impact strength of the resin is required to be 50 to 60 kJ/m ² , preferably 55 kJ/m ² . If the impact strength is less than 50kJ/m ² , the amount of dust generated increases and the quality of the final product deteriorates, including defects on the surface. In the case of PC, it is difficult for the impact strength to exceed 60kJ/m ² , and when fillers such as glass fiber are added to PC to increase impact strength, there is a problem that the transparency of the manufactured product deteriorates and it cannot be used for optical purposes. In this example, PC was used as the resin, and the impact strength of the resin was measured by notching a 3 mm thick specimen at 23°C according to the ISO 179 standard.

Meanwhile, it is important to adjust the melt index (MI) value to reduce defects and improve birefringence performance. The melt index is the flow rate when thermoplastic polymer melt is extruded from a piston at the load and temperature specified for each specific resin. It is an index indicating the ease of flow of the melt and is related to molecular weight. The higher the molecular weight, the lower the melt index.

The melt index (MI) is measured by measuring the amount released when the resin is sufficiently melted above the melting point (Tm) and pushed out at a constant speed. It is calculated as the weight or volume of the sample flowing out for 10 minutes, and the units are g/10min or cm ³ /10min. In this example, PC was used as the resin, and the melt index was measured with an MI meter.

If the melt index is low, the birefringence performance of the manufactured window cover is reduced due to poor fluidity. If the melt index is high, birefringence performance is good, but if fluidity is excessively high, the weight of the final product changes and injection reproducibility becomes poor.

In the sixth embodiment of the present invention, the MI value of the resin is 30 to 50 cm ³ /10 min at 300°C, preferably 35 cm ³ /10 min. If the melt index is less than 30 cm ³ /10 min, the retardation value is more than 100 nm at the front and 300 nm at 45 degrees, resulting in poor birefringence performance. If the MI value exceeds 50 cm ³ /10 min, injection reproducibility is poor, fluidity is high, so checking ring changes are required, and changes to injection conditions are limited. Additionally, in general, when the MI value is high, the impact strength is low, so there is a high possibility of dust generation. A high MI value means that the resin has a low molecular weight. Low molecular weight resin improves processability, but reduces rigidity and stress resistance, which may cause crazing, which causes thin cracks during reliability tests.

Let's look at examples and comparative examples of each compression factor value for the retardation value.

During the manufacturing process of window covers, factors that affect the optical properties of injection-compressed window covers include mold temperature, compression speed, injection speed, compression gap, impact strength of the resin, and melt index (MI) of the resin. In order to derive the optimal conditions for each compression factor, the following experiment was performed for each factor. Depending on the order of the experiment, conditions excluding the factors to be compared may be different. In each experiment, the comparative parameter conditions of Examples and Comparative Examples were applied differently to derive the optimal value of the corresponding compression factor. PC (Teijin L1225 ZL 100M) was used as the injection material, and a 2-layer PC/PMMA sheet was used as the film.

<Mold temperature>

Among the compression factors, we look at the optimal value for mold temperature.

A window cover was molded at an injection temperature of 300°C, compression point at V/P switching point, compression holding time at 3 seconds, and clamping force at 250 tons. Mold temperature indicates the temperature of the upper and lower mold, element core, and gate.

The mold temperature conditions of Examples and Comparative Examples are as follows.

mold temperature Example 1 95/105/30 Example 2 80/90/30 Comparative Example 1 70/80/30 Comparative Example 2 110/120/30

Visual evaluation and retardation value measurements were performed on the retardation values of window covers molded under each condition. Visual evaluation and retardation value measurement were performed using a birefringence confirmation device and a birefringence meter WPA-200, respectively. In the case of visual evaluation, the evaluation was made based on the maximum visual value based on the Levy chart. When measuring with the naked eye, the light source is measured after placing a surface light source of 200 to 500 lux at a distance of 0.3 to 1 m, and in this example, a surface light source of 300 lux is measured at a distance of 0.3 m. It was measured. In the case of retardation value, it was evaluated based on the average value for a specific area.

mold temperature visual evaluation Plane side retardation value (nm) 45˚ side retardation value (nm) Retardation deviation value (nm, flat side/45° side) Example 1 45 200 12/59 Example 2 50 270 13/62 Comparative Example 1 97 411 19/99 Comparative Example 2 68 285 17/67

As the mold temperature increased, the shear stress of the resin and the residual stress of the window cover decreased during compression injection, improving birefringence performance and reducing the retardation value. Example 1 showed the best birefringence performance with a flat side retardation value of 45 nm and a 45° side retardation value of 200 nm. In Example 2, the flat side retardation value was measured to be 50 nm, and the 45° side retardation value was measured to be 270 nm. The flat side retardation value of Comparative Example 2 is 68 nm, the 45° side retardation value is 285 nm, and the retardation value of Comparative Example 1 where the mold temperature (°C) is 70/80/30, respectively (the flat side retardation value is The retardation value at 97nm and 45° side showed excellent birefringence performance compared to 411nm), but the variation in compression gap increased due to changes in resin flow, resulting in poor reproducibility. The compression core is operated by hydraulic pressure. If the mold temperature is above 105℃, the expansion of the mold as the temperature inside the mold rises affects the hydraulic pressure within the mold, and the compression gap is not maintained constant at the start of actual compression, resulting in deviation. Due to this difference, the reproducibility of the product is poor. As a result, dimensional differences due to mass differences occurred in the final product. Additionally, in the case of Comparative Example 2, there is a risk of damage to the mold as the temperatures of the upper mold and lower mold and the temperature of the compression core exceed 105°C, which is not preferable.

Therefore, considering that reproducibility deteriorates when the mold temperature increases, the mold temperature conditions of Example 2, 80/90/30°C, are preferable.

<Compression speed>

Among the compression factors, we look at the optimal value for compression speed.

A window cover was molded at an injection temperature of 300°C, compression point at V/P switching point, compression holding time at 9 seconds, and clamping force at 250 tons.

The compression speed was controlled stepwise in two stages, with a constant speed up to 1/2 of the compression gap, and the compression speed increased linearly after 1/2 of the compression gap.

Compression speed conditions and results of examples and comparative examples are as follows.

2 section speed (mm/s ² )
(Plane side retardation value (nm)/ 45° side retardation value (nm)/ retardation value
Deviation) One 2 3 4 1st section speed
(mm/s) One
98/425/99


68/338/69
75/368/73
78/372/70 2
67/342/70


55/327/75
72/367/73
79/382/88 4
69/345/71


70/346/70
72/365/86
73/363/84 8
70/350/68


72/357/67
77/369/77
81/385/86

In the case of the comparative example where the speed of section 1 was 1 mm/s, compression marks were severe, and this was because the resin was stagnant due to the low initial speed. It can be seen that when the speed of the second section is high, the compression speed is high, the shear stress increases, and the birefringence characteristics deteriorate.

It can be confirmed that when the compression speed of sections 1 and 2 is 2-2 mm/s, the retardation value on the flat side is 55 nm and the retardation value on the 45° side is 327 nm, which is the optimal value. In other words, the optimal value of the compression speed condition is 2 mm/s in section 1 and acceleration 2 mm/s ² in section 2.

<Injection speed>

Among compression factors, we look at the optimal value for injection speed.

A window cover was molded with an injection temperature of 290°C, a compression point of V/P switching point, a compression holding time of 9 seconds, and a clamping force of 250 tons.

The speed profile of the injection speed was different for each section, and the speed was adjusted by dividing it into 4 sections. The injection speed is controlled based on the stroke positions of 35mm, 25mm, 12mm, and 7mm.

In order to confirm the effect of the injection speed in sections 2 and 3, a window cover was manufactured under the same conditions as the injection speed in other sections except for the corresponding section. Sections 1 and 4 are the point at which the injection material begins to be ejected and the last section at which it is ejected, and were excluded because they did not have a significant effect on the birefringence performance.

The injection speed conditions of Comparative Examples 1 to 6 are as follows.

Injection speed (mm/s) Section 1 Section 2 Section 3 Section 4 Comparative Example 1 20 20 60 80 Comparative Example 2 20 40 60 80 Comparative Example 3 20 60 60 80 Comparative Example 4 10 20 20 60 Comparative Example 5 10 20 40 60 Comparative Example 6 10 20 60 60

Visual evaluation and retardation value measurements were performed on the retardation values of window covers molded under each condition.

visual evaluation Comparison of speed changes in 2 sections (20/40/60) Comparative Example 1

378 Comparative Example 2

382 Comparative Example 3

376 Speed change in 3 sections (20/40/60) Comparative Example 4

386 Comparative Example 5

364 Comparative Example 6

356

The range of change in birefringence performance as the speed of the two sections changes was confirmed to be small, at 4 to 6 nm. In section 3, the range of change in birefringence performance depending on speed is 8 to 20 nm, and it can be seen that the higher the speed, the better the birefringence performance. It can be seen that the faster the central speed, the more it affects the flow of the injection material and has a great influence on stress control during compression.

Birefringence performance according to speed in sections 3 and 4 was compared.

injection speed Section 1
(mm/s) Section 2
(mm/s) Section 3
(mm/s) Section 4
(mm/s) Flat side retardation value (nm)/45° side retardation value (nm)/deviation of retardation value Example 45 80 80 70
55/280/68 Comparative Example 1 40 60 60 60
64/354/73 Comparative example 2 20 60 60 20
63/356/75 Comparative Example 3 20 40 40 40
85/423/98

If the injection speed is 45mm/s in section 1, 80mm/s in section 2, 80mm/s in section 3, and 70mm/s in section 4, the retardation value on the flat side is 55nm and the retardation value on the 45° side is 280nm. It can be confirmed that it has the optimal value.

<Compression Gap>

Among the compression factors, we look at the optimal value for the compression gap.

A window cover was molded at an injection temperature of 300°C, compression point at V/P switching point, compression holding time at 3 seconds, and clamping force at 250 tons.

The compression gaps of Examples and Comparative Examples are as follows.

Compression gap (mm) Comparative Example 1 0.2 Comparative example 2 0.5 Example One Comparative Example 3 1.5 Comparative Example 4 2

Visual evaluation and retardation value measurements were performed on the retardation values of window covers molded under each condition.

compression gap Visual evaluation Plane side retardation value (nm) 45˚ side retardation value (nm) Retardation deviation value (nm) Comparative Example 1 310 328 79 Comparative example 2 290 301 77 Example 276 290 65 Comparative example 3 357 398 89 Comparative example 4 400 412 97

When the compression gap was 1 mm, the retardation value on the flat side was 276 nm and the retardation value on the 45° side was 290 nm, confirming that the birefringence performance was the best.

In order to derive an appropriate range of impact strength and melt index values, we look at the following experimental results for impact strength and melt index values.

MI( ^cm3 /10min)
impact strength
(kJ/ ^m2 )
over 50
30~50
less than 30 50~60 Birefringence: OK
Injection reproducibility: NG
Appearance: OK Birefringence: OK
Injection reproducibility: OK
Appearance: OK Birefringence: NG
Injection reproducibility: OK
Appearance: OK less than 50 Birefringence: OK
Injection reproducibility: NG
Appearance: NG Birefringence: OK
Injection reproducibility: OK
Appearance: NG Birefringence: NG
Injection reproducibility: OK
Appearance: NG

In the case of PC, the impact strength is difficult to exceed 60 kJ/m ² , and in order for the impact strength of resin to exceed 60 kJ/m ² , fillers such as glass fiber must be added to PC. In this case, the transparency of the manufactured product decreases and it cannot be used for optical purposes, so the range where the impact strength exceeds 60 kJ/m ² is excluded.

When the melt index of the resin exceeds 50 cm ³ /10 min and the impact strength is in the range of 50 to 60 kJ/m ² , the fluidity of the resin is high and the impact strength is high, so the birefringence performance is good and the appearance is good, but due to excessively high fluidity, it has a good appearance. Due to this, injection reproducibility is poor. On the other hand, when the melt index of the resin is less than 30 cm ³ /10 min and the impact strength is in the range of 50 to 60 kJ/m ² , the fluidity of the resin is low and the impact strength is high, so injection reproducibility is good and the appearance is good, but fluidity is reduced. As a result, residual stress increases and birefringence performance is poor.

When the melt index of the resin is 30 to 50 cm ³ /10 min and the impact strength is in the range of 50 to 60 kJ/m ² , the impact strength is high and the fluidity is high, so the product has a good appearance and good injection reproducibility and birefringence performance.

Next, in the range where the impact strength of the resin is less than 50kJ/m ² , a large amount of dust is generated, resulting in a poor appearance of the product. In the range where the melt index of the resin exceeds 50 cm ³ /10 min and the impact strength is less than 50 kJ/m ² , the fluidity of the resin is good but the impact strength is low, and although birefringence performance is good, injection reproducibility is poor and defects in appearance occur.

When the melt index of the resin is 30 to 50 cm ³ /10 min and the impact strength is less than 50 kJ/m ² , fluidity is good, but as the impact strength is low, injection reproducibility and birefringence performance are good, but the appearance of the product is poor.

In the range where the melt index of the resin is less than 30 cm ³ /10 min and the impact strength is less than 50 kJ/m ² , the fluidity of the resin is low and the impact strength is also low, and injection reproducibility is good, but the residual stress increases due to the decrease in fluidity, resulting in poor birefringence performance. This is not good and the appearance of the product is also not good.

Meanwhile, the above-mentioned ranges are values when the resin is PC, and when other materials such as PMMA are used, the desirable ranges of impact strength and melt index may vary.

Based on the above-mentioned range, we look at examples and comparative examples regarding the MI value and impact strength value of the resin.

The present invention defines the MI value and impact strength value of the resin in order to reduce defects and improve optical properties such as birefringence of the injection-compressed window cover during the manufacturing process of the window cover. In order to derive the optimal conditions for each factor regarding the MI value and impact strength value of the resin, the following experiment was performed for each factor. Depending on the order of the experiment, conditions excluding the factors to be compared may be different. In each experiment, the comparative parameter conditions of Examples and Comparative Examples were applied differently to derive the optimal value of the corresponding compression factor. PC (Teijin L1225 ZL 100M) was used as the injection material, and a 2-layer PC/PMMA sheet was used as the film.

Among the compression factors, we look at the optimal values for the MI value and impact strength of the resin.

Injection material temperature is 300℃, injection pressure is 800~1500bar, upper and lower mold temperature is 80℃, compression core temperature is 90℃, compression time is V/P switching point, compression holding time is 9 seconds, clamping force is 250ton, and window cover is set. was molded.

The MI values and impact strength values of Examples and Comparative Examples are as follows.

MI ( ^cm3 /10min) Impact strength (kJ/m ² ) Example 35 55 Comparative example 24 35

Visual evaluation and retardation value measurements were performed on the retardation values of window covers molded under each condition. Visual evaluation and retardation value measurement were performed using a birefringence confirmation device and a birefringence meter WPA-200, respectively. In the case of visual evaluation, the evaluation was based on the maximum visual value based on the levy chart, and in the case of retardation value, it was evaluated based on the average value for a specific area.

Plane side retardation value (nm) 45˚ side retardation value (nm) Example
66
270 Comparative example
142
477

When the melt index was 35 cm ³ /10 min (300°C) and the impact strength value was 55 kJ/m ² (Example), the appearance was good and the birefringence aspect was good even when seen with the naked eye, and the planar retardation value was 66 nm. It was confirmed that the retardation value on the 45° side was 270nm.

When the melt index is 24cm ³ /10min (300℃) and the impact strength value is 35kJ/m ² (comparative example), bright-colored patterns and rainbow-colored patterns occur when viewed with the naked eye, and a black color is formed in the lower center part. It was confirmed that defects occurred. In addition, the retardation value on the flat side was measured as high at 142 nm, and the retardation value on the 45° side was measured as high at 477 nm. It can be seen that if the melt index is low, the fluidity of the resin is poor, resulting in large residual stress, and thus birefringence performance deteriorates. In addition, it can be seen that due to low impact strength, a lot of dust is generated, which deteriorates the external quality of the product.

Summarizing the above experimental results, as a result, the window cover according to the present invention has a mold temperature of 80/90/30°C, a compression gap of 1mm, a compression point of V/P switching point, a compression speed of 2-2mm/s, and injection. The retardation value is minimized when the speed is 45-80-80-70mm/s, the compression holding time is 3 seconds, the melt index of the injection material is 35cm ³ /10min (300℃), and the impact strength value is 55kJ/m ² .

The average retardation value of the window cover molded under the above conditions is 50 nm or less in a plane and 270 nm or less at a 45° angle.

A plurality of compression factors may affect each other, and birefringence may be alleviated by mutually adjusting the plurality of factors. For example, when the compression gap increases, the compression speed can be increased to prevent the resin from stagnating.

The optimal conditions for injection compression molding may vary depending on the type of resin, and the above examples and comparative examples show conditions when the injection material is PC.

Figure 23 is a diagram showing a state in which a bending phenomenon occurred in the window cover during the manufacturing process of the window cover for a display device, and Figure 24 is a diagram showing a plurality of measurement positions for measuring flatness.

Meanwhile, among the compression factors, the temperature difference between the upper mold and the lower mold affects the flatness of the manufactured window cover.

The window cover 1000' is formed by placing the insert film 200 in an upper mold, injecting injection material into the mold, and then pressing the compression core. The injection material is integrally combined with the insert film 200 to form the base layer 100. The temperature of the injection material injected into the mold is 270~320℃. The lower the temperature of the injection material, the smaller the heat transfer amount deviation, and the temperature of the injection material may preferably be 280°C. The injection material forms the base layer 100 while cooling after the pressurization step. However, the cooling rate of the injection material varies in the thickness direction. As the insert film 200 acts as an insulator, the injection material cools slowly in the upper part of the base layer 100, and the injection material cools more quickly in the lower part of the base layer 100 disposed on the lower mold side. That is, based on the midpoint of the thickness direction of the base layer 100, the temperature gradient at the top is smaller than the temperature gradient at the bottom. That is, the heat transfer rate at the top is smaller than the heat transfer rate at the bottom. Due to this difference in cooling rate of the injection material, the window cover 1000' is bent so that the insert film 200 side is convex. This is because the side opposite to the insert film 200 hardens first and shrinks. Therefore, in order to prevent the window cover from bending during the cooling process, it is necessary to make the heat transfer rates of the upper and lower parts of the base layer similar. In the present invention, the temperature of the upper mold is adjusted to reduce the difference in heat transfer rates between the upper and lower base layers.

In the seventh to ninth embodiments of the present invention, the flatness of the window cover is improved by adjusting the temperature difference, mold clamping force, and hydraulic core pressure conditions between the upper mold and the lower mold.

In order to manufacture the window cover 1000 according to the seventh embodiment of the present invention, the insert film is preformed (S1310). The insert film can form an optical coating layer to satisfy the optical properties required to form a film layer. The present invention can provide black masking and a functional surface by applying the IML (In Mold Label) method.

A gate area for injecting injection material and a button hole area for holding the insert film may be formed in the insert film. The gate area may be formed within the area of the final window cover, or may be located outside the final window cover area and removed after injection and curing of the injection material.

The insert film has a different heat transfer rate from the injection material and reduces the cooling rate of the adjacent injection material. The thicker the insert film, the greater the heat transfer deviation along the thickness direction of the injection material, and accordingly, the greater the difference in cooling rate in the thickness direction of the injection material. The thickness of the insert film may be 0.15 to 0.3 mm, preferably 0.2 mm. When the thickness of the insert film is greater than 0.3 mm, the difference in cooling rate in the thickness direction of the injection material increases, resulting in a decrease in the flatness of the manufactured window cover. If the thickness of the insert film is less than 0.15 mm, the physical strength of the insert film may be weakened. The heat transfer rate of the insert film may be 0.23w/mk or more. When the heat transfer rate of the insert film is less than 0.23w/mk, the insulation effect becomes better and the cooling rate slows down. Accordingly, the deviation of the cooling rate in the thickness direction of the injection material increases and warping may occur. The shrinkage rate of the insert film may be 1.4% or less based on JIS K7133, 160°C, 30min. The lower the shrinkage rate of the insert film, the less shrinkage the injection material has when cooling, reducing the effect on flatness.

Next, the insert film is placed in the upper mold (S1320). Ensure that the gate area and buttonhole area of the insert film are located at corresponding positions in the upper mold. The gate area of the insert film is positioned opposite the hot runner of the upper mold.

The lower mold is positioned so that the lower mold is spaced apart from the upper mold by a predetermined distance (S1330). The lower mold is moved toward the upper mold so that a cavity of a predetermined volume is formed within the mold. The clamping force acting on the upper mold and lower mold may be 250 to 600 tons.

The temperatures of the upper and lower molds affect the flow and residual stress of the injection material. Therefore, the upper and lower molds must be maintained at a temperature within a certain range. The temperatures of the upper and lower molds are maintained by fluid of a predetermined temperature. However, when the temperature of the injection material is too high or a film layer is formed, the heat distribution in the thickness direction of the injection material is different, which causes a difference in the cooling rate of the injection material. The temperatures of the upper and lower molds are controlled to minimize the heat transfer rate deviation in the thickness direction of the injection material. The temperature of the upper mold may be 70 to 95°C, preferably 90°C. The temperature of the lower mold is set lower than that of the upper mold, and the temperature difference between the upper and lower molds may be more than 10°C. As the temperature difference between the upper and lower molds increases, flatness can improve. If the temperature difference between the upper mold and the lower mold decreases during the manufacturing process, the clamping force can be increased to suppress the bending phenomenon. If the clamping force increases, the density of the injection material increases and the shrinkage rate can be reduced.

Inject injection material into the mold (S1340). The injection material is sprayed onto the back of the film by a hot runner. The injection material may be PC or PMMA material. The injection material is cured to form the base layer 1100. The higher the temperature of the injection material, the greater the deviation of heat transfer in the thickness direction of the injection material. Therefore, in order to improve flatness, the lower the temperature of the injection material, the better. However, as the temperature of the injection material decreases, the residual stress in the injection material increases, which may reduce the birefringence performance of the manufactured window cover. In this embodiment, the temperature of the injection material is set to 270-320°C to improve flatness while maintaining birefringence performance. The temperature of the injection material may preferably be 280°C. The heat transfer rate of the injection material may be 0.2 w/mk or more. If the heat transfer rate of the injection material is less than 0.2 w/mk, the cooling time increases and productivity decreases. The smaller the difference between the heat transfer rate of the injection material and the heat transfer rate of the insert film, the better the flatness.

Pressurize the compression core (S1350). When a predetermined amount of injection material is filled in the mold, the compression core is pressed to compress the cavity surface. As the compression core is pressed, the volume of the cavity decreases, and the base layer is formed as the injection material flows under compression within the cavity. The base layer is combined with the insert film. The thickness of the injection material bonded to the insert film is adjusted by the compression core pressing step.

Meanwhile, the temperature difference between the upper mold and the lower mold affects the cooling rate of the injection material injected into the mold. The top of the injection material injected into the mold is in contact with the insert film, so the heat transfer rate is reduced due to the insulating effect of the film. On the other hand, the lower part of the injection material has a higher heat transfer rate than the injection material located at the top. Therefore, this difference in heat transfer rate must be minimized. To minimize the heat transfer rate difference, the temperature of the upper mold can be set higher than the temperature of the lower mold. In this embodiment, the temperature of the upper mold may be 70 to 95°C, preferably 90°C. The temperature of the lower mold may be 70 to 85°C, preferably 80°C. The temperature difference between the upper mold and the lower mold may be 10°C or more.

The compression holding time of the compression core may be 8 to 10 seconds, preferably 9 seconds. Additionally, the clamping force acting on the upper mold and lower mold may be 250 to 600 tons. After the compression core pressurization step, the hydraulic core pressure can be maintained at 70-80%. This is to minimize the shrinkage of the injection material in the mold by changing the pressure acting on the lower mold.

The final thickness of the manufactured window cover may be 1.5 to 3 mm, preferably 2.5 mm. The thicker the final product, the less likely it is to bend.

We examine in detail the temperature difference between the upper and lower molds, clamping force, and hydraulic core output as compression factor conditions for manufacturing window covers with improved flatness.

The present invention minimizes the variation in heat transfer amount in the thickness direction of the window cover to prevent warping.

In the seventh embodiment of the present invention, the temperatures of the upper mold and the lower mold are defined. The smaller the difference in heat transfer rate between the upper and lower sides of the window cover, the better the flatness. However, an insert film is disposed on the upper side of the window cover, which inhibits cooling of the upper side of the window cover and reduces the heat transfer rate. On the other hand, the lower side of the window cover has a higher heat transfer rate than the upper side. That is, the temperature distribution is formed asymmetrically in the thickness direction of the window cover. In order to reduce this difference in heat transfer rate, it is preferable that the temperature of the upper mold is higher than the temperature of the lower mold. In this embodiment, the gap in heat transfer rate between the injection materials disposed on the upper and lower sides of the window cover can be reduced by increasing the temperature of the upper mold. The larger the temperature difference between the upper mold and the lower mold, the better the flatness.

The temperature of the upper mold may be 70 to 95°C, preferably 90°C, and the temperature of the lower mold may be 70 to 85°C, preferably 80°C.

If the temperatures of the upper mold and lower mold are lower than 70°C, there is a problem in that the flow resistance of the injection material increases and residual stress increases. On the other hand, as the temperature of the upper mold and lower mold increases, the shear stress of the resin and the residual stress of the product during injection compression are reduced, which may improve the birefringence characteristics, but the variation in the compression gap becomes worse due to changes in resin flow, resulting in poor reproducibility. not. The temperatures of the upper mold and lower mold are preferably 95°C and 85°C or lower, respectively.

The temperature difference between the upper mold and the lower mold can be at least 10℃.

If the temperature difference between the upper mold temperature and the lower mold exceeds 20°C, in addition to a decrease in flatness, problems such as compression burrs and silver burrs may occur in the parting line. Specifically, the thermal expansion rate must be different between molds. When the temperature of the lower mold is low, the expansion of the mold is smaller than that of the upper and lower molds, which reduces the pressure in the parting line during injection. As a result, compression burrs and silver burrs are released into the parting line. may occur. If production continues while the temperature of the lower mold is low, burrs generated in the compression parting line not only continuously generate burrs in the products produced, but also cause the mold parting line to collapse, increasing the defective rate of the product.

In the eighth embodiment, clamping force is specified to prevent bending of the window cover.

Clamping force refers to the force that fastens the upper mold and lower mold, and the required clamping force is related to the material or amount of injection material, gate size or number, etc. In this example, PC was used as the injection material, and the clamping force may be 250 to 600 t, preferably 450 t. When the clamping force is set to 250 to 600 tons, the amount of shrinkage due to cooling of the injection material can be suppressed.

In order to reduce the temperature difference depending on the position of the injection material, the temperature difference between the upper mold and the lower mold is specified, but if the temperature difference between the upper mold and the lower mold becomes small during the manufacturing process, the clamping force can be increased to suppress the bending phenomenon.

In the ninth embodiment, the maintenance pressure output is specified to prevent the window cover from bending.

The maintenance pressure output is the force that pressurizes the compression core, and the force acting on the compression core in the cooling stage after the compression core pressurization stage can be maintained at 70 to 80% of the output. While the injection material is cooling, the force pressing the injection material can be kept to a minimum to prevent the injection material from bending while cooling. If the maintenance pressure output exceeds 80%, overload within the injection molding machine may cause damage to the mold, etc.

In other embodiments, the final thickness of the window cover, insert film thickness, etc. may be specified. The final thickness of the window cover may be 1.5 to 3 mm, preferably 2.5 mm. The insert film thickness may be 0.15 to 0.3 mm, preferably 0.2 mm.

Let's look at examples and comparative examples of compression factors related to flatness improvement.

Flatness was measured in each example and comparative example. Flatness refers to the degree to which the window cover is curved. Flatness is calculated by measuring z values at multiple points on the window cover and calculating the difference between the maximum and minimum values.

In this example, flatness is measured in the following manner. Set a plurality of virtual points on the window cover surface to be measured. The point created by the intersection of the lines connecting the four origin points on the left, right, and top and bottom of the measurement object is used as the origin of measurement. Among the four origin points on the left and right/top and bottom of the measurement object, set the midpoint of the line connecting neighboring origin points as the measurement point. The plurality of virtual points including the Origin Point are referred to as P1, P2, P3, P4, P5, P6, P7, P8, and P9 from the top and left, respectively. In Figure 24, P1, P3, P7, and P9 are four origin points, and P5 is the origin. Among the four Origin Points, the midpoints of the lines connecting neighboring Origin Points are set to P2, P4, P6, and P8, respectively, and the flatness is calculated using the z values of the origin P5 and P2, P4, P6, and P8.

Measure dimensions at multiple points on the window cover of the measurement object. Dimensions are measured using a 3D measuring device. The 3D measuring device used is a vision inspection type, and the flatness is also focused using a camera to measure the z value. In the case of fascia, the flatness measurement part is the A/A part, so the flatness of the transparent part is measured by setting the mesh. To calculate flatness, the measured values of P2, P4, P5, P6, and P8 are used.

Flatness can be obtained by the following equation.

Flatness=Zmax-Zmin (Equation 1)

(Zmax=maximum z value, Zmin=minimum z value)

Calculate the maximum and minimum values among the measured z values of P2, P4, P5, P6, and P8, and find the difference between the maximum and minimum values. In this embodiment, measured values of points corresponding to P2, P4, P5, P6, and P8 in FIG. 24 are used, but in other embodiments, measured values of a plurality of arbitrary points other than the corresponding points may be used.

In order to derive the optimal conditions for each factor, the following experiment was performed for each factor. Depending on the order of the experiment, conditions excluding the factors to be compared may be different. In each experiment, the comparative parameter conditions of Examples and Comparative Examples were applied differently to derive the optimal value of the corresponding flatness-related factor. PC (Ai2217 from Covrstro) was used as the injection material, and a 2-layer PC/PMMA sheet was used as the film.

<Upper mold temperature>

Among the flatness-related factors, we look at the optimal value for the upper mold temperature.

The window cover was molded with the temperature of the lower mold being 80℃, the temperature of the injection material being 280℃, the holding pressure output being 80%, and the clamping force being 450t.

The upper mold temperature conditions of Examples and Comparative Examples are as follows.

Upper mold temperature (℃) Example 90 Comparative Example 1 70 Comparative example 2 60

The flatness measurement results of Examples and Comparative Examples are as follows.

P2 P4 P5 P6 P8 flatness Example 0.09 0.16 0.03 0.14 -0.63 0.79 Comparative Example 1 0.12 -0.49 -0.82 -0.44 -0.93 1.05 Comparative example 2 -0.13 -0.26 -0.94 -0.1 -1.33 1.23

In the example, the flatness was measured at points P2 to P8 to be 0.79, Comparative Example 1, where the upper mold temperature was 70°C, had a flatness value of 1.05, and Comparative Example 2, where the upper mold temperature was 60°C, had a flatness value of 1.05. The value was measured to be 1.23. It can be seen that as the upper mold temperature decreases, the flatness value increases, that is, the flatness decreases. It can be seen that the best flatness is achieved when the temperature of the upper mold is 90°C (Example).

<Clamp force>

Among the factors related to flatness, we look at the optimal value for clamping force.

A window cover was molded at an upper mold temperature of 90°C, a lower mold temperature of 80°C, an injection material temperature of 280°C, and a holding pressure output of 80%.

The clamping force conditions of the examples and comparative examples are as follows.

Clamp force (t) Example 450 Comparative Example 1 350 Comparative example 2 250

The flatness measurement results of Examples and Comparative Examples are as follows.

P2 P4 P5 P6 P8 flatness Example 0.09 0.16 0.03 0.14 -0.63 0.79 Comparative Example 1 0.19 0.04 -0.21 0.05 -0.95 1.14 Comparative example 2 0.24 -0.04 0.41 0.11 -1.25 1.66

In the example, the flatness was measured at points P2 to P8 to be 0.79, in Comparative Example 1, the flatness was 1.14, and in Comparative Example 2, the flatness was 1.66. It can be seen that as the clamping force decreases, the flatness value increases. It can be seen that the example in which the clamping force is 450t has the best flatness.

<Maintenance pressure output>

Among flatness-related factors, we look at the optimal value for maintenance pressure output.

A window cover was molded at an upper mold temperature of 90°C, a lower mold temperature of 80°C, an injection material temperature of 280°C, and a clamping force of 450t.

The maintenance pressure output conditions of the examples and comparative examples are as follows.

Holding pressure output (%) Example 80 Comparative Example 1 60 Comparative example 2 30

The flatness measurement results of Examples and Comparative Examples are as follows.

P2 P4 P5 P6 P8 flatness Example 0.09 0.16 0.03 0.14 -0.63 0.79 Comparative Example 1 0.34 -0.02 0.52 0.16 -1.72 2.24 Comparative example 2 0.54 -0.14 0.62 0.21 -1.93 2.55

In the example, the flatness was measured at points P2 to P8 to be 0.79, in Comparative Example 1 the flatness value was 2.24, and in Comparative Example 2 the flatness value was 2.55. It can be seen that as the holding pressure output increases, the flatness value decreases, that is, the bending phenomenon is reduced. It can be seen that the embodiment in which the holding pressure output is 80% has the best flatness.

The optimal conditions for injection compression molding may vary depending on the type of resin, and the above examples and comparative examples show the case where the material of the injection material is PC.

<Injection Thickness>

Among the factors related to flatness, we look at the optimal value for injection thickness.

A window cover was molded at an upper mold temperature of 90°C, a lower mold temperature of 80°C, an injection material temperature of 280°C, a film thickness of 0.2mm, and a clamping force of 450t.

The injection thickness conditions for Examples and Comparative Examples are as follows.

Injection thickness (mm) Example 3.0 Comparative Example 1 2.8 Comparative Example 2 2.5 Comparative Example 3 2.2

The flatness measurement results of Examples and Comparative Examples are as follows.

P2 P4 P5 P6 P8 flatness Example 0.02 0.11 0.01 0.11 -0.50 0.61 Comparative Example 1 0.04 0.13 0.02 0.12 -0.56 0.69 Comparative example 2 0.06 0.15 0.03 0.11 -0.61 0.74 Comparative Example 3 0.09 0.16 0.03 0.14 -0.63 0.79

In the case of the example, the flatness was measured at points P2 to P8, showing good results of 0.61. Comparative Example 1 had a flatness value of 0.69, and Comparative Example 2 had a flatness value of 0.74. Comparative Example 3 had a flatness value of 0.79. It can be seen that the thicker the injection thickness, the better the flatness. It can be seen that the best flatness is achieved when the injection thickness is 3.0 mm. However, if the injection thickness is 2.5 mm or more, touch sensitivity decreases during use, and the injection thickness may be determined by considering other conditions.

<Film Thickness>

Among flatness-related factors, we look at the optimal value for film thickness.

A window cover was molded at an upper mold temperature of 90°C, a lower mold temperature of 80°C, an injection material temperature of 280°C, and a clamping force of 450t.

The film thickness conditions of Examples and Comparative Examples are as follows.

Film thickness (mm) Example 0.2 Comparative Example 1 0.25 Comparative example 2 0.3

The flatness measurement results of Examples and Comparative Examples are as follows.

P2 P4 P5 P6 P8 flatness Example 0.09 0.16 0.03 0.14 -0.63 0.79 Comparative Example 1 0.13 0.19 0.04 0.17 -1.10 1.29 Comparative example 2 0.22 0.24 0.07 0.21 -1.56 1.80

In the case of the example, the flatness was measured at points P2 to P8, showing good results of 0.79. Comparative Example 1 had a flatness value of 1.29, and Comparative Example 2 had a flatness value of 1.80. It can be seen that the thinner the film thickness, the better the flatness. It can be seen that the best flatness is achieved when the film thickness is 0.2mm.

<Film shrinkage rate>

Among flatness-related factors, we look at the optimal value for film shrinkage.

A window cover was molded at an upper mold temperature of 90°C, a lower mold temperature of 80°C, an injection material temperature of 280°C, and a clamping force of 450t.

The film shrinkage conditions of Examples and Comparative Examples are as follows. The shrinkage rate is measured in the MD direction after 30 minutes at 160℃.

Film shrinkage (%) Example 1.4 Comparative Example 1 2.7 Comparative Example 2 3.4 Comparative Example 3 4.2

The flatness measurement results of Examples and Comparative Examples are as follows.

P2 P4 P5 P6 P8 flatness Example 0.09 0.16 0.03 0.14 -0.63 0.79 Comparative Example 1 0.12 0.30 0.05 0.19 -1.22 1.52 Comparative Example 2 0.18 0.30 0.07 0.22 -1.54 1.84 Comparative Example 3 0.25 0.52 0.09 0.33 -1.70 2.22

In the case of the example, the flatness was measured at points P2 to P8, showing good results of 0.79. Comparative Example 1 had a flatness value of 1.52, Comparative Example 2 had a flatness value of 1.84, and Comparative Example 3 had a flatness value of 2.22. It can be seen that the lower the film shrinkage rate, the better the flatness. It can be seen that the film has the best flatness when the film shrinkage rate is 1.4%.

Summarizing the above experimental results, as a result, the window cover according to the present invention is flat when the temperature of the upper mold is 90°C, the clamping force is 450t, the holding pressure output is 80%, the injection thickness is 3.0mm, the film thickness is 0.2mm, and the film shrinkage rate is 1.4%. The degree value is lowered and bending phenomenon is suppressed.

The flatness of the window cover molded under the above conditions is 0.8 or less.

The optimal conditions for injection compression molding may vary depending on the type of resin, and the above examples and comparative examples show the case where the material of the injection material is PC.

Meanwhile, the present invention uses a compression injection method to minimize the residual stress after molding of the injection material that appears in the general injection process, and the birefringence performance of the manufactured window cover is superior to the birefringence performance of the window cover produced by the general injection process.

Comparing the retardation values of the window cover according to the above-described embodiment and the window cover manufactured through a general injection process is as follows.

Example: Injection Compression Process

<Conditions>

Melt index of resin: 30~50cm ³ /10min,

Injection temperature: 300℃,

Mold temperature: 80/90/30℃,

Compression Gap: 1mm,

Compression point: V/P switching point,

Compression speed: 2-2mm/s,

Injection speed: 45-80-80-70mm/s,

Compression holding time: 3 seconds

Clamp force: 250ton

Comparative example: general injection process

<Conditions>

Melt index of resin: 30~50cm ³ /10min,

Injection temperature: 300℃,

Mold temperature: 80/90/30℃,

Injection speed: 45-80-80-70mm/s,

Injection pressure (holding pressure): 10bar

Clamp force: 250ton

Visual evaluation (side view) Plane side retardation value (nm, average/deviation) 45˚side retardation value (nm, average/deviation) Example (window cover manufactured by compression injection process)
50/13 270/62 Comparative example (window cover manufactured by general injection process) 180/110 473/164

In the case of a window cover manufactured by a general injection process, the flat side retardation value is 180 nm and the 45° side retardation value is 473 nm, whereas in the case of a window cover manufactured by an injection compression process according to the present invention, the flat side retardation value is 180 nm and 473 nm. It can be seen that the retardation value at this 50nm and 45° side is 270nm, and the retardation value is significantly reduced. Additionally, in the case of a window cover manufactured by the injection compression process according to the present invention, it can be seen that the retardation deviation values on the flat side and 45° side are also reduced.

Figure 25 is a diagram showing a film layer in a window cover for a display device according to an embodiment of the present invention.

Meanwhile, the film layer 1200 may include a film, a hard coating layer to protect the film, and various optical coating layers. The film layer 1200 is an optical coating layer and may include one or more of an anti-glare (AG) coating layer, an anti-reflective (AR) coating layer, and an anti-finger (AF) coating layer. AG (Anti-Glare) coating is designed to prevent glare and blocks light refraction by forming irregularities on the film surface to induce diffuse reflection. AR (Anti-Reflective) coating is used to prevent light from being reflected from the surface, and improves transparency by lowering the reflectance by lowering the refractive index. AF (Anti-Finger) coating is designed to prevent fingerprints from remaining on the surface. It increases the wetness of the hard coat material to prevent fingerprints from standing out.

As shown in FIG. 23, the film layer 1200 may include two coating layers. A hard coating layer 1220 may be formed on the film 1210, and an optical coating layer 1230 may be formed on the hard coating layer 1220. The hard coating layer 1220 protects the film surface and improves scratch resistance. The optical coating layer 1220 may include one or more of an anti-glare (AG) coating layer, an anti-reflective (AR) coating layer, and an anti-finger (AF) coating layer.

Coating can be done by simultaneously applying AG treatment to the hard coating layer, and in the case of AG coating, silica is used. LR coating, a wet coating, can be applied on the AG coating layer, and in the case of LR coating, hollow silica is used. Multi-layer coating can be achieved through simultaneous coating by adding -F additive that can function as AF during coating treatment. The thickness of the hard coating layer 1220 is 2 to 5 ㎛, the thickness of the optical coating layer 1230 is 0.1 to 0.5 ㎛, preferably the thickness of the hard coating layer 1220 is 3 ㎛, and the thickness of the optical coating layer 1230 is 0.2 ㎛. It can be.

The optical coating layer may be formed using micro gravure coating, slot die coating, spray coating, or flow coating, but is not limited thereto.

The film layer 1200 may have a light blocking area and a transparent area. The transparent area corresponds to the area where information is displayed, and the light blocking area is arranged to surround the transparent area. The light blocking area corresponds to a non-display area called the so-called bezel area in a display device, and is an area where images produced by the display device are not visible. The light blocking area may have a color and/or pattern. For example, the light blocking area may appear black. The light transmitting area can induce diffuse reflection of external light, such as sunlight, to reduce the surface reflectance of external light and increase the visibility of images created in the display device.

Figure 26 is a view showing the first area and the second area in the window cover for a display device according to an embodiment of the present invention, and Figure 27 is an injection view in the base layer forming step of the window cover for a display device according to an embodiment of the present invention. It is a diagram showing the flow of material, and Figure 28 is a diagram showing the results of visual evaluation of birefringence performance in the first area and the second area in the window cover for the display device of the present invention.

During injection molding of the window cover 1000, the molecular orientation is solidified in the flow direction of the injection material due to shear flow, and after molding is completed, residual stress remains inside the material, causing birefringence. In order to minimize birefringence, residual stress occurring within the material after molding must be minimized. However, from the viewpoint of manufacturing efficiency, optimization of the birefringence value is necessary considering manufacturing cost and time required. The present invention optimizes the birefringence value of the window cover according to the above-described manufacturing conditions. The average retardation value in the plane of the window cover manufactured by the above-described manufacturing method may be 60 nm or less, and preferably 50 nm or less. The average retardation value of the manufactured window cover at an incident angle of 45° may be 280 nm or less, and preferably 270 nm or less.

Meanwhile, the retardation value may be different for each area of the window cover. The window cover of the present invention is manufactured through compression flow as the injection material is injected into the gate area located on the center line (C1) of the film material, and stress occurs due to solidification of the injection material. Accordingly, the retardation value may increase toward the outside of the window cover 1000.

As shown in FIG. 26, the window cover 1000 may include a first area 1110 and a second area 1120. The first area 1110 and the second area 1120 may be divided into inside and outside by an arbitrary line on the window cover. The arbitrary line may be a line connecting the points that bisect the line connecting the center of the window cover to the outer part of the window cover in a 1:1 manner. Here, the outer part refers to the outer edge of the rectangular window cover. On the window cover, that is, the first area 1110 and the second area 1120 are divided by an imaginary line connecting the midpoints of a line connecting the midpoint of the film layer to an arbitrary point on the outer edge of the film layer. The inner area including the midpoint of the window cover 1000 may be the first area 1110, and the outer area including the outer portion of the window cover may be the second area 1120.

The average of the planar side retardation value of the first area 1110 may be 60 nm or less, and preferably 50 nm or less. The average of the planar side retardation values of the second area 1120 is different from the planar side retardation value of the first area 1110. The planar retardation value of the second area 1120 may be 50 nm or less and may be smaller than the planar retardation value of the first area 1110. These differences in retardation values for each region are due to differences in the shear speed of the injection material.

As shown in Figure 27, the injection material injected into the gate area flows within the mold. At this time, the shear speed value of the injection material in the first area occurs at the maximum value and is injected, and as a result, a lot of residual stress exists in the first area of the window cover, so the retardation value of the first area 1110 may be large. there is. Relatively, the retardation value of the second area 1120 may be smaller than that of the first area 1110.

The difference in the plane side average retardation value between the first area 1110 and the second area 1120 may be 10 nm or less, and the difference in the retardation deviation value may be 3 nm or less.

As shown in FIG. 28, it can be seen from the visual evaluation results that the retardation values of the first area and the second area are different. Figure 26 is a distribution chart of retardation values according to the contour line, and shows the distribution of retardation values based on 0 to 300 nm. Looking at the retardation distribution chart, it can be seen that the retardation value of the first area 1110 is greater than the retardation value of the second area 1120.

Meanwhile, when the angle of incidence is 45°, the retardation value of the first area 1110 may be 280 nm or less, and preferably 270 nm or less. The retardation value of the second area 1120 is different from the retardation value of the first area 1110. The retardation value of the second area 1120 may be 270 nm or less and may be smaller than the retardation value of the first area 1110. The difference in the average retardation value at 45° between the first area 1110 and the second area 1120 may be 15 nm or less, and the difference in the retardation deviation value may be 5 nm.

In another embodiment, the retardation deviation values may be different in the first area 1110 and the second area 1120 of the window cover 1000. The first area 1110 and the second area 1120 may be divided into the inside and outside of the window cover 1000. The inner area may be the first area 1110, and the outer area may be the second area 1120. The average retardation deviation value according to the angle of incidence of the first area 1110 may be 20 nm or less, and preferably 10 nm or less. The retardation deviation value of the second area 1120 may be different from the retardation deviation value of the first area 1110. The retardation deviation value of the second area 1120 may be 15 nm or less and may be smaller than the retardation deviation value of the first area 1110.

Figure 29 is a diagram showing a flow mark in a window cover for a display device according to an embodiment of the present invention, Figure 30 is a diagram showing a first area and a second area in a window cover for a display device according to an embodiment of the present invention, and Figure 31 is a diagram showing a flow mark in a window cover for a display device according to an embodiment of the present invention. It is a diagram showing a first area and a second area in a window cover for a display device according to an embodiment of the present invention, and Figure 32 is a diagram showing a flow mark in a window cover for a display device according to an embodiment of the present invention.

In the present invention, the injection material forms a base layer while compressing and flowing within the cavity. The injection material is injected into the gate area located on the center line C1 of the film material, and some of the injected injection material flows horizontally to the left and right near the gate area, and some flows downward. Due to shear flow, the molecular orientation of the injection material is solidified in the flow direction, and these flow traces form flow marks. The flow mark defines a characteristic of the window cover.

During the manufacturing process of the base layer 1100 of the window cover 1000, various types of flow marks 1300 may be formed. The flow mark 1300 can be confirmed during visual evaluation and is divided into visually distinguishable flow line areas. When measuring with the naked eye, the light source is measured with a 200-500 lux surface light source spaced 0.3-1 m apart, and in this example, a 300 lux surface light source was measured 0.3 m apart.

A flow mark 1300 is formed on the base layer 1100. The base layer 1100 is formed by injecting and compressing injection material between the upper mold and the lower mold. As shown in Figure 5, part of the injection material discharged to the gate area flows horizontally to the left and right near the gate area, and part flows downward. As the injection material moves downward of the mold, it forms a main flow line and sub-flow lines to the left and right around the main flow line on the base layer 1100.

As shown in FIG. 27, the flow mark 1300 is formed with a plurality of main flow lines and sub flow lines downward from the upper gate area of the base layer 1100, and is formed in a shape that spreads wider downward. That is, the flow mark 1300 is formed symmetrically with respect to the first center line C1 of the window cover 1000, and the overall outline may be formed in a fan shape. In this case, birefringence characteristics may be formed symmetrically.

The retardation value of the window cover may be substantially symmetrical with respect to the virtual center line of the window cover 1000. In one embodiment, the window cover 1000 includes a first area 1110' and a second area 1120'. As shown in FIG. 28, the first area 1110' and the second area 1120' may be divided into left and right sides based on the first center line C1. The first center line (C1) is an imaginary line that passes through the midpoint of the final manufactured window cover and is parallel to the Y-axis direction.

In the window cover of the present invention, the injection material is injected into the gate area located on the center line (C1) of the film material, and the injected injection material flows compressively within the cavity. The flow of the injection material can be defined in the vertical and horizontal directions, and the distribution of the retardation value along the center line (C1) of the film material is formed to be substantially symmetrical.

That is, the average retardation value on the plane side of the first region 1110' and the second region 1120' may be 60 nm or less, preferably 50 nm or less, and the retardation distribution based on the first center line C1 is It has a substantially symmetrical aspect.

Meanwhile, the distribution of retardation values at an incident angle of 45° in the first area 1110' and the second area 1120' of the window cover 1000 is also substantially symmetrical with respect to the first center line C1. has The retardation value of the first area 1110' and the second area 1120' at an incident angle of 45° is 220 nm or less, and preferably is 200 nm or less. The difference in the average retardation value on the plane side may be 10 nm or less, and the difference in the retardation deviation value may be 3 nm or less.

As shown in FIG. 29 , in another embodiment, the first area 1110" and the second area 1120" may be divided up and down based on the second center line C2. The second center line (C2) is a virtual center line on the window cover, passes through the midpoint of the final manufactured window cover, and is parallel to the X-axis direction. The area below the second center line C2 may be the first area 1110", and the area above may be the second area 1120".

The average of the planar side retardation values of the first area 1110" and the second area 1120" may be 60 nm or less, and preferably 50 nm or less, and the distribution of each retardation value may be located at the second center line C2. It has a symmetrical aspect based on .

Meanwhile, the distribution of retardation values at an incident angle of 45° in the first area 1110" and the second area 1120" of the window cover 1000 is also symmetrical with respect to the second center line C2. . The retardation value of the first area 1110" and the second area 1120" at an incident angle of 45° is 220 nm or less, preferably 200 nm or less, and the distribution of each retardation value is along the second center line. It has a symmetrical aspect based on (C2). The difference in the average retardation value at 45° between the first area 1110 and the second area 1120 may be 15 nm or less, and the difference in the retardation deviation value may be 5 nm.

In another embodiment, a retardation deviation value may be defined in the first area 1110' and the second area 1120' of the window cover 1000.

The first area 1110' and the second area 1120' may be divided into left and right sides based on the first center line C1. The average retardation deviation value according to the angle of incidence of the first area 1110' may be 20 nm or less, and preferably 10 nm or less. The retardation deviation value distribution of the second area 1120' is symmetrical to the retardation deviation value distribution of the first area 1110'.

In another embodiment, the first area 1110" and the second area 1120" may be divided up and down based on the second center line C2. The lower area may be the first area (1110"), and the upper area may be the second area (1120").

The average retardation deviation value according to the angle of incidence of the first area 1110" may be 20 nm or less, and preferably 10 nm or less. The distribution of the retardation deviation value of the second area 1120" is similar to that of the first area 1110". It may be symmetrical with respect to the retardation deviation value distribution and the second center line C2.

The shape of the flow mark may vary depending on the injection compression conditions, the location of the gate, and the size and shape of the window cover. For example, if the length of the product becomes longer in the longitudinal direction, the length of the flow mark may change, and if the length in the width direction becomes longer, the flow mark may become wider. Additionally, if the mold temperature is low or the injection speed is slow, flow marks may become noticeable due to cooling of the injection material.

Meanwhile, the position where the injection material is injected, the number of gate areas, injection speed, molding conditions, etc. can be estimated from the shape of the flow mark 1300. For example, as shown in FIG. 27, the pattern in which the flow mark 1300 develops is a short, narrow fan shape downward based on one main flow line, and between the sub flow lines of the flow mark 1300. If the gap is larger at the bottom than at the top, it can be assumed that the gate area exists inside the window cover and is located at the top on the center line (C1) of the window cover 1000.

As shown in FIG. 30, the pattern in which the flow mark 1300 is developed is fan-shaped downward based on one main flow line, but if the downward flow mark 1300 is formed long and wide, the injection The current gate area exists outside the final window cover area, and it can be assumed that the gate area is located above the center line (C1) of the window cover 1000.

The area where the flow mark 1300 is formed is preferably 60% or less of the total area of the window cover 1000. If the area where the flow mark 1300 is formed exceeds 60% of the total area of the window cover, the overall retardation value of the window cover may increase and optical characteristics may deteriorate. The width of the flow mark 1300 in the horizontal direction is preferably 80% or less of the width of the window cover 1000.

Figure 33 is a flow chart schematically showing a method of manufacturing a window cover material according to the sixth embodiment of the present invention, and Figure 34 is a schematic diagram of an embodiment of a suction device for implementing the method of manufacturing a window cover material shown in Figure 32. 35 is a configuration diagram schematically showing a specific example of implementing the insert film suction step, and Figure 36 is a configuration diagram schematically showing a window cover material according to the tenth embodiment of the present invention. am.

Next, a window cover manufacturing method according to the tenth embodiment of the present invention will be described.

As shown in Figure 33, the window cover manufacturing method according to the sixth embodiment further includes an insert film suction step compared to the previous embodiment.

More specifically, the window cover manufacturing method (S2000) includes an insert film preforming step (S2100), an insert film upper mold holding step (S2200), an insert film suction step (S2300), an injection material discharging step (S2400), and a lower mold Includes a pressurization step (S2500).

In addition, the insert film preforming step (S2100) and the insert film upper mold mounting step (S2200) are the insert film preforming step (S1100) and the insert film upper mold mounting step of the window cover manufacturing method (S1000) according to the first embodiment. Same as (S1200).

Next, the insert film suction step (S2300) is a step of fixing the insert film to the upper mold by providing suction force to the insert film through the suction part. Accordingly, the insert film mounted on the upper mold is maintained in a state adsorbed to the upper mold by suction force.

As described above, as the insert film is adsorbed to the upper mold, more stable support of the insert film is possible when the injection material is supplied to the insert film in the injection material discharge step.

Next, the injection material discharging step (S2400) and the lower mold pressing step (S2500) are the same as the injection material discharging step (S1300) and the lower mold pressing step (S1400) of the window cover manufacturing method (S1000) according to the first embodiment. As mentioned above, detailed explanation will be omitted.

As shown in FIG. 34, a suction part 200 may be coupled to the upper mold 110 so as to extend to the upper mold button hole hook 111.

In addition, when suction force is provided to the insert film, the film layer buttonhole area 1122 comes into close contact with the upper mold button hole hanger 111 of the upper mold 110, forming a large contact area (S). Fixation efficiency is increased (Figure 33).

As described above, the insert film can be sucked in during the injection material discharge step and more effectively fixed to the upper mold. As the injection material is discharged onto the insert film while the insert film is in close contact, the insert film is not pushed away. Such phenomena are prevented in advance and efficient application is possible.

As shown in FIG. 36, the window cover 2000 does not have a gate area formed in the buttonhole area compared to the window cover 1000 shown in FIG. 35.

More specifically, the window cover 2000 includes a film layer 2100 and a base layer (not shown).

The film layer 2100 may be made of a preformed IML (In Mold Label) film. The film layer 2100 includes a transparent part 2110 and a light blocking part 2120 so that the window cover 2000 is implemented as a window cover.

Additionally, a film layer buttonhole area 2111 and a gate area 2112 are formed in the transparent portion 2110. The gate area 2112 is implemented as a gate for supplying injection material to the insert film during the injection process.

As described above, the film layer buttonhole area 2111 is formed to protrude from one side where the transparent portion 2110 is formed toward the other side.

The film layer buttonhole area 2111 serves as an upper mold buttonhole hanger in the manufacturing stage of the window cover, and detailed description thereof is omitted as described above.

In addition, the base layer (not shown) is bonded to the film layer 2100 by injection molding an injection material on the back of the film layer 2100. And the base layer (not shown) includes a base layer buttonhole area (not shown) and a base layer gate area (not shown) corresponding to the film layer buttonhole area 2111 and the film layer gate area 2112 of the film layer 2100, respectively. poetry) is formed.

Additionally, the film layer gate area 2112 and the base layer gate area are formed in an extension portion extending outward from the light blocking portion 2120.

In addition, the film layer has a first center line in one axis direction (shown as C1 in FIG. 7) and a second center line in the other axis direction (shown as C2 in FIG. 7) excluding the extension portion for forming the film layer gate area 2112. (shown), and the film layer buttonhole area of the film layer and the base layer buttonhole area are located below the second center line. The first center line (C1) is an imaginary line that passes through the midpoint of the final manufactured window cover and is parallel to the Y-axis direction, and the second center line (C2) is an imaginary center line on the window cover and is the midpoint of the final manufactured window cover. It is a line parallel to the X-axis direction.

Since the window cover according to the tenth embodiment of the present invention is made as described above, productivity is improved as injection molding is implemented with the insert film held by the button hole area of the film layer.

Figure 37 is a schematic configuration diagram of a window cover for a display device according to an embodiment of the present invention, and Figure 38 is a schematic B-B cross-sectional view of the window cover for a display device shown in Figure 37.

As shown in FIG. 37, compared to the window cover 1000 shown in FIG. 5, the window cover 3000 for a display device is formed into a penetrating portion by cutting the film layer buttonhole area and the injection unit buttonhole area.

More specifically, the window cover 3000 for a display device includes a film layer 3100 and a base layer 3200.

More specifically, the film layer 3100 may be made of a preformed IML (In Mold Label) film. The film layer 3100 may include a transparent part 3110 and a light blocking part 3120. That is, the transparent part 3110 is formed to correspond to the display area, and the light blocking part 3120 is formed to surround the outer periphery of the transparent part 3110.

Additionally, a penetrating film layer buttonhole area 3121 is formed in the light blocking portion 3120.

Additionally, the base layer 3200 is coupled to the film layer 3100. The base layer 3200 is formed by injection molding an injection material on the back of the IML film, which is the film layer 3100, and at the same time, the base layer 3200 is bonded to the film layer 3100.

And a base layer buttonhole area 3210 corresponding to the film layer buttonhole area 3121 is formed in the base layer 3200.

In addition, the window cover 3000 for a display device is formed through the window cover 1000, as the gate area through which the injection material flows out is formed inside the film layer buttonhole area 3121, so that the film layer gate, which is a hanger, is formed. With the film layer placed through the region (shown as 1271 in FIG. 5), the flow of the injection material forming the base layer 3200 is directed from the base layer buttonhole region 3210 toward the outer periphery of the base layer 3200. can confirm.

Additionally, the flow of the injection material forming the base layer 3200 in the window cover 3000 for a display device can be confirmed through Moldex3D, Optic Module.

Above, an embodiment of the present invention has been described, but those skilled in the art can add, change, delete or add components without departing from the spirit of the present invention as set forth in the patent claims. The present invention may be modified and changed in various ways, and this will also be included within the scope of rights of the present invention.

1000: Window cover 1100: Base layer
1110, 1110', 1110": first area
1120, 1120', 1120": Second area
1200: film layer 1250: gate area
1271: Film layer gate area 1272: Film layer buttonhole area
1300: flow mark

Claims (23)

In the method of manufacturing a window cover for a display device with improved birefringence performance,
Placing the insert film on the upper mold;
Positioning the lower mold at a predetermined distance from the upper mold;
Injecting injection material into the mold; and
Comprising: pressurizing the compression core,
The temperature of the upper mold and the lower mold is 70 to 95 ° C,
A method of manufacturing a window cover for a display device, characterized in that the temperature of the compressed core is 80 to 95 ° C. According to paragraph 1,
Before mounting the insert film on the upper mold
A method of manufacturing a window cover for a display device, further comprising the step of preforming an insert film. According to paragraph 1,
A method of manufacturing a window cover for a display device, characterized in that the temperature of the gate into which the injection material is injected is 20 to 40 ° C. delete According to paragraph 1,
A method of manufacturing a window cover for a display device, characterized in that the temperature difference between the upper mold and the compression core is 10°C or more. According to paragraph 1,
A method of manufacturing a window cover for a display device, characterized in that the temperature of the injection material is 270 ~ 320 ℃. According to paragraph 1,
A method of manufacturing a window cover for a display device, characterized in that the compression holding time in the step of pressurizing the compression core is 8 to 10 seconds. According to paragraph 1,
A method of manufacturing a window cover for a display device, characterized in that the clamping force in the step of pressurizing the compression core is 250 to 600 t. According to paragraph 1,
In the step of pressurizing the compression core, the compression speed is controlled in two stages,
When the section from the initial position of the compression core to the 1/2 point of the compression gap is referred to as section 1, and the section from the 1/2 point of the compression gap to the final position of the compression core is referred to as section 2,
A method of manufacturing a window cover for a display device, characterized in that the compression speed is controlled to have a constant speed in the first section and a constant acceleration in the second section. According to clause 9,
A method of manufacturing a window cover for a display device, characterized in that the compression speed is controlled to have an acceleration of 1.8 to 2.2 mm/s 2 in the first section and an acceleration of 1.8 to 2.2 mm/s ² in the second section. According to paragraph 1,
A method of manufacturing a window cover for a display device, characterized in that the compression speed increases as the compression gap increases. According to paragraph 1,
In the step of injecting the injection material into the mold,
A method of manufacturing a window cover for a display device, wherein the injection speed is controlled for each of four stroke sections. According to clause 12,
The stroke section is 1 section, 2 section, 3 section, and 4 section based on the position of the screw tip at 33~37mm, 23~27mm, 10~14mm, and 5~9mm, assuming that the nozzle tip position is 0mm. A method of manufacturing a window cover for a display device, characterized in that it is divided into: According to clause 13,
The injection speed is a method of manufacturing a window cover for a display device, characterized in that the injection speed in section 2 is greater than the injection speed in section 1. According to clause 13,
The injection speed is 40 to 50 mm/s in section 1, 75 to 85 mm/s in section 2, 75 to 85 mm/s in section 3, and 65 to 75 mm/s in section 4. Manufacturing method. According to paragraph 1,
A method of manufacturing a window cover for a display device, characterized in that the compression gap is 40 to 50% of the thickness of the window cover for the display device. According to paragraph 1,
A method of manufacturing a window cover for a display device, characterized in that the melt index of the injection material is 30 to 50 cm ³ /10 min at 300 ° C. According to paragraph 1,
A method of manufacturing a window cover for a display device, characterized in that the impact strength of the injection material is 50 to 60 kJ/m ² . As a window cover for a display device,
A window cover for a display device manufactured by the method for manufacturing a window cover for a display device according to any one of claims 1 to 3 and 5 to 18. According to clause 19,
A window cover for a display device, characterized in that the average retardation value on the flat side is 50 nm or less. According to clause 19,
A window cover for a display device, characterized in that the average retardation value at an incident angle of 45° is 270 nm or less. According to clause 19,
A window cover for a display device, characterized in that the average retardation deviation value according to the angle of incidence is 20 nm or less. According to clause 19,
A window cover for a display device, characterized in that the flatness is 0.8 or less.

Images