Patent Application
20090215351
The present application claims priority from Japanese application JP 2008-39722 filed on Feb. 21, 2008, the content of which is hereby incorporated by reference into this application.
1. Technical Field
The present invention relates to a display device manufacturing method, and particularly, to a method of manufacturing a display device in which a transparent substrate (a protective cover) is bonded to a display panel by means of an adhesive.
2. Related Art
Display devices, such as liquid crystal display devices, are employed as display devices of various sizes from a small one for a portable telephone to a large one for a TV set.
The display panel PNL is disposed in such a way as to overlap an opening provided in the casing CAS. A transparent substrate (a protective cover) COV, made of, for example, glass or acryl (PMMA), is affixed over the opening of the casing CAS by means of a double sided tape TAP or the like. Then, in the case of the liquid crystal display device shown in the figure, a space SP in which an air layer is interposed has existed between the display panel PNL and the transparent substrate COV.
Apart from the liquid crystal display device shown in
In addition, regarding a technology which suppresses a remaining of air bubbles, there are, for example, JP-A-2006-36865 and JP-A-2005-243413. In JP-A-2006-36865, it is described that, a thermosetting adhesive and air bubbles being disposed in a pattern, the air bubbles are dissolved under a first heating temperature, at which the adhesive is not cured, as well as a reduced pressure (vacuum), and subsequently, as well as a pressure being applied, the adhesive is cured at a second heating temperature. At this time, it is described that the adhesive is formed into dots or cross stripes (a grid), and a viscosity of the adhesive when applied is 1000 cP or more, while a viscosity of the adhesive when heated at the first heating temperature is 100 cP or less.
Also, in JP-A-2005-243413, it is described that, when carrying out a vacuum bonding in such a way that there is no remaining of air bubbles, an ultraviolet curable adhesive resin for temporary fixing is disposed at corners, and a thermosetting adhesive resin for sealing is formed into lines or dots.
Also, prior to the present application, the present applicant has filed an application relating to a method of manufacturing a display device in which a transparent substrate is bonded to a display panel by means of an adhesive (Japanese Patent Application No. 2006-346932)
However, in the case of the configuration shown in
Also, in the case of the technology described in JP-A-10-254380, as the viscosity of the low viscosity adhesive is low, it is necessary to provide the high viscosity adhesive on the perimeter. Consequently, an application step becomes complicated. Furthermore, unless a height of the low viscosity adhesive is controlled with a high accuracy, a difference occurs in level between the low viscosity adhesive and the high viscosity adhesive, there is a possibility of larger air bubbles occurring.
Also, in the case of the technology described in JP-A-2006-36865, when the viscosity is increased at the first heating temperature at which the thermosetting adhesive is not cured, an upper temperature limit of the display panel may be exceeded.
Also, in the case of the technology described in JP-A-2005-243413, no description being given of a size or viscosity when the thermosetting adhesive resin for sealing is formed in lines or dots, in the event that adjacent sealing adhesive resin lines or dots are spaced wide apart, there is a possibility of drawing in large air bubbles. Also, as the adhesive resin is thermosetting, the upper temperature limit of the display panel may be exceeded.
Also, in the case of the technology described in Patent Application No. 2006-346932, although the viscosity of the adhesive before being cured is made 2000 to 5000 mPa·s, in the case in which the viscosity is 5000 mPa s or less, when a screen printing is carried out, the adhesive being likely to encroach upon an underside of a screen plate, it is necessary to clean the underside of the screen plate after 20 to 30 shots, resulting in an increasing length of time being required for the manufacturing.
In the display device manufacturing method of the invention, when bonding the display panel and the transparent substrate together by means of the adhesive under a reduced pressure atmosphere, by adjusting one or more of an adhesive viscosity and application pattern, a size of air bubbles at the time of the bonding, a curing method, and the like, it is possible to suppress the remaining of the air bubbles, and shorten the time required for the manufacturing.
As the configuration of the invention, it is possible to adopt, for example, the following one.
1. A display device manufacturing method in which a transparent substrate is bonded to a display panel by means of an adhesive, includes:
an application step which applies the adhesive to the display panel or the transparent substrate in a predetermined pattern;
a bonding step which bonds the display panel and the transparent substrate together by means of the adhesive after the application step; and
a curing step which cures the adhesive after the bonding step.
In the application step, a viscosity of the adhesive being more than 5000 mPa·s and 15000 mPa·s or less, the application of the adhesive is carried out by means of a screen printing,
a time from a finishing point of the application of the adhesive in the application step until a starting point of the bonding in the bonding step is 10 seconds or more and 120 seconds or less,
in the bonding step, in a condition in which the adhesive applied in the application step is spreading, with air bubbles remaining, and a maximum size of the air bubbles is 0.5 mm or less, the display panel and the transparent substrate are bonded together by means of the adhesive under a reduced pressure atmosphere lower than the atmospheric pressure, and
in the curing step, after the maximum size of the air bubbles have reached 0.1 mm or less, ultraviolet light is applied, curing the adhesive.
2. According to 1, it is also acceptable to adopt a configuration such that the time from the adhesive application finishing point in the application step until the bonding starting point in the bonding step is 30 seconds or more and 60 seconds or less.
3. According to 1 or 2, it is also acceptable to adopt a configuration such that the predetermined pattern of the adhesive is a pattern of a plurality of dots.
4. According to 3, it is also acceptable to adopt a configuration such that the pattern of the plurality of dots is a pattern of staggered dots.
5. According to 1 or 2, it is also acceptable to adopt a configuration such that the predetermined pattern of the adhesive is a grid pattern.
6. According to any one of 1 to 5, it is also acceptable to adopt a configuration such that, in the bonding step, a vacuum is 1 to 50 Torr.
7. According to any one of 1 to 6, it is also acceptable to adopt a configuration such that, in the bonding step, the display panel and the transparent substrate are bonded together by means of the adhesive while the display panel is being bent in such a way as to be convex on a surface to be bonded.
8. According to 7, it is also acceptable to adopt a configuration such that the display panel has a first substrate, and a second substrate disposed facing the first substrate, and
a sum of a thickness of the first substrate and a thickness of the second substrate is 0.6 mm or less.
9. According to any one of 1 to 8, it is also acceptable to adopt a configuration such that, in the curing step, the adhesive is cured using both heat and the ultraviolet light.
10. According to 9, it is also acceptable to adopt a configuration such that a light shield is included in one portion of the transparent substrate.
11. According to 9 or 10, it is also acceptable to adopt a configuration such that the heat is of 50 to 80° C.
12. According to any one of 1 to 11, it is also acceptable to adopt a configuration such that the transparent substrate contains one or more of glass, an acrylic resin, and a polycarbonate resin.
13. According to any one of 1 to 12, it is also acceptable to adopt a configuration such that the adhesive contains an acrylic resin or an epoxy resin.
14. According to any one of 1 to 13, it is also acceptable to adopt a configuration such that, in the bonding step and the curing step, in a condition in which the display panel and the transparent substrate are bonded together, each of the display panel and the transparent substrate is fixed into position with a jig.
15. According to any one of 1 to 14, it is also acceptable to adopt a configuration such that an elastic modulus of the adhesive after being cured is 1,000 to 250,000 Pa at 25° C.
16. According to any one of 1 to 15, it is also acceptable to adopt a configuration such that the display panel is a liquid crystal display panel.
The heretofore described configuration being only one example, the invention can be appropriately modified without departing from the scope of the technological idea. Also, a configuration example of the invention other than the heretofore described configuration will be made apparent from the description of the whole of the specification of the invention, and the drawings.
Typical advantages achieved by the invention are as follows.
It is possible to suppress the remaining of the air bubbles when bonding the transparent substrate to the display panel by means of the adhesive.
It is possible to shorten the time required for the manufacturing when bonding the transparent substrate to the display panel by means of the adhesive.
Other advantages of the invention will be made apparent from the description of the whole of the specification.
A description will be given of embodiments of the invention, referring to the drawings. In each drawing and each embodiment, identical or similar components being identified by the same reference numbers and characters, a description will be omitted.
The display panel PNL has a substrate SUB1, which is a transmissive insulating substrate made of, for example, glass, a substrate SUB2, which is a transmissive insulating substrate made of, for example, glass, a seal material SL, which bonds the substrate SUB1 and the substrate SUB2 together, a liquid crystal LC sealed in within a portion surrounded by the substrate SUB1, the substrate SUB2, and the seal material SL, a polarizing plate POL1 disposed on a side of the substrate SUB1 opposite the liquid crystal LC, and a polarizing plate POL2 disposed on a side of the substrate SUB2 opposite the liquid crystal LC. Also, although not shown in the figure, thin film transistors, pixel electrodes, and the like, being formed in a matrix form on a liquid crystal LC side of the substrate SUB1, the substrate SUB1 may be called a TFT substrate. Although not shown in the figure, a color filter, opposing electrodes, and the like, being formed on a liquid crystal LC side of the substrate SUB2, the substrate SUB2 may be called an opposing substrate. Also, it is also acceptable to dispose a retardation film or the like in at least one of a space between the substrate SUB1 and the polarizing plate POLL or a space between the substrate SUB2 and the polarizing plate POL2. As the invention is not particularly limited to a configuration of the display panel PNL, it is also acceptable to adopt a configuration other than the configuration described here.
Then, a transparent substrate (a protective cover) COV containing one or more of, for example, glass, an acrylic resin, a polycarbonate resin, and the like, is bonded to the display panel PNL by means of an adhesive AD.
Herein, in the event that materials having approximately equal refractive indices are used as materials of the transparent substrate COV, adhesive AD, polarizing plate POL2 and the like, as it is possible to suppress a surface reflection, it is possible to suppress a reduction in visibility. In particular, as glass and an acrylic resin have approximately equal refractive indices, it is desirable to employ these materials. However, this combination not being limiting, it is also acceptable to use materials, a refractive index difference between two of which is 0.1 or less. Needless to say, as long as the surface reflection is within an allowable range, a use of materials having a refractive index of 0.1 or more shall not be precluded.
A spacer SPC is disposed between the display panel PNL and the casing CAS. Provided that the spacer SPC is provided with a viscosity or an adhesiveness, a fixing becomes possible. Also, it is also acceptable to use a material having an elasticity for the spacer SPC. Furthermore, provided that the spacer SPC is formed in a frame shape from a waterproof material such as, for example, silicon rubber, it is possible to prevent water or the like from entering through the opening of the casing CAS.
Firstly, as shown in
Next, as shown in
In the invention, a time from a finishing point of the application of the adhesive AD to the transparent substrate COV until a starting point of the bonding is made 10 seconds or more and 120 seconds or less (desirably, 30 seconds or more and 60 seconds or less). This length of time suffices for a transfer time from a printing step to a bonding step. With this length of time, in the case of applying the adhesive AD of the heretofore described viscosity in the predetermined pattern, the adhesive AD spreading, it is possible to obtain a condition in which the maximum size of air bubbles is 0.5 mm or less. Moreover, by adopting this length of time, rather than causing the air bubbles to disappear completely, it is possible to obtain a condition in which some air bubbles remain. On carrying out the bonding in this condition, it is possible to carry out the bonding without drawing in large air bubbles, and moreover, vacuum air bubbles are diffused and made inconspicuous after the bonding. By this means, it is possible to suppress a remaining of air bubbles.
Also, in the invention, in the case of applying the adhesive AD, the screen printing is used. By this means, it is possible to apply the adhesive AD to the transparent substrate COV in the predetermined pattern in an extremely short time. For example, in a case of using a dispenser method, for example, for each two inch display panel PNL, it takes around 300 seconds to lift and move an applicator nozzle, resulting in an increasing length of time being required for the manufacturing.
Also, in the invention, as heretofore described, the viscosity of the adhesive AD is made more than 5000 mPa·s and 15000 mPa·s or less in the condition in which it has not yet been cured. In the case in which the viscosity is 5000 mPa·s or less, when the screen printing is carried out, the adhesive AD being likely to encroach upon an underside of a screen plate, it is necessary to clean the underside of the screen plate after 20 to 30 shots, resulting in the increasing length of time being required for the manufacturing. Conversely, in the case in which the viscosity is more than 15000 mPa·s, as a wet spread property of the adhesive AD becomes lower, it takes a longer time until obtaining the condition in which the maximum size of air bubbles is 0.5 mm or less, resulting in the increasing length of time being required for the manufacturing. Moreover, in the event that the viscosity is high, it is difficult to apply the adhesive AD in an ideal pattern by means of the screen printing and, as a result thereof, a problem occurs in that, it being impossible to control the size of air bubbles, air bubbles remain.
Also, within the heretofore described range of viscosity, in a case of adopting, for example, a pattern in which dots are disposed as the predetermined pattern of the adhesive AD, it is possible to make a minimum dot size immediately after the screen printing Ø 1.0 to 1.1 mm.
Although it is desirable that the adhesive AD contains an acrylic resin or an epoxy resin, it is also possible to use another material such as, for example, a silicon resin. Also, it is also acceptable that it is a mixed material such as epoxy acrylate.
Next, as shown in
In the condition in which the transparent substrate COV is bonded, it is possible to spread the adhesive AD to an extremity of the transparent substrate COV, as shown in
Herein, in the heretofore described bonding step and curing step, it is desirable that, in the condition in which the display panel PNL and the transparent substrate COV are bonded together, each of the display panel PNL and the transparent substrate COV is fixed into position with an unshown jig until the curing finishes.
It is desirable that an elastic modulus of the adhesive AD after being cured is 1,000 to 250,000 Pa at room temperature (25° C.). By this means, even in a case in which materials having different coefficients of thermal expansion are bonded together, it is possible to reduce stress by means of the adhesive AD. It is possible to measure the elastic modulus of the adhesive AD after being cured by means of a Thermo Mechanical Analysis (TMA).
Next, a description will be given of an example of a pattern in which the adhesive AD is applied.
What is important here is that, rather than applying the adhesive AD uniformly and evenly, a pattern is deliberately adopted such that small air bubbles remain when the adhesive AD spreads, and furthermore that, as the air bubble is divided, the size d2 of each air bubble is small. In a case in which the adhesive AD is made uniformly even, or in a case in which an area to which no adhesive AD is applied (an air bubble) is large, although there is a possibility of drawing in large air bubbles, by deliberately carrying out the bonding with the divided small air bubbles remaining, it is possible to reduce the possibility of drawing in the large air bubbles at a time of the bonding. Consequently, it is possible to hold a size of vacuum air bubbles down to a degree such that the vacuum air bubbles can be diffused and made inconspicuous even after the bonding (in the embodiment, an arrangement is such that, at a stage of bonding the display panel PNL and the transparent substrate COV together, air bubbles remain, and a maximum value of a size of the air bubbles is 0.5 mm or less). Vacuum air bubbles remaining after the bonding are diffused, and made inconspicuous, by the time the curing of the adhesive AD is finished. As the fact that, by reducing the maximum size of air bubbles after the adhesive AD has been cured to 0.1 mm or less, it is possible to reduce the bright spots caused by the air bubbles to the invisible level, is as previously described, it is sufficient to wait until the air bubbles are diffused after the bonding, and the maximum size reach 0.1 mm or less, to cure the adhesive AD.
By staggering dots, as shown in
Although
Also, although it is also acceptable that the pitch P1 is taken to be P1>2W1, P1=2W1 or P1<2W1 is more preferable because adjacent dots become closer to each other.
As shown in
Furthermore,
The invention not being limited to the patterns described in
Although
The ultraviolet cure using the heat assist described in the embodiment 5 can also be applied to a display device in which no light shield SHD is formed on the transparent substrate COV.
In the embodiments 1 to 6, it is also acceptable that a gap between the casing CAS and the transparent substrate COV is occluded by a second spacer configured of an unshown waterproof material such as silicon rubber, in place of the spacer SPC, or together with the spacer SPC. By this means, a waterproofing becomes possible. Also, it is also acceptable that the spacer SPC and the second spacer are integrally configured.
The display panel PNL not being limited to the liquid crystal display panel, it is also possible to apply it to, for example, another type of display panel such as an inorganic EL display panel.
A description has heretofore been given of the invention, using the embodiments, but the configuration described so far in each embodiment being only one example, the invention can be appropriately modified without departing from the scope of the technological idea. Also, it is also acceptable that the configurations described in the individual embodiments are used in combination unless they conflict with each other.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-039722 | Feb 2008 | JP | national |
