Polymer particles

Details Polymer particles Polymer particles

2000-11-10

2001-11-27

Thomas, Alexander S. (Department: 1772)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

With bonding or intermediate layer of specified composition

C428S407000, C428S402000, C428S403000, C349S001000

Reexamination Certificate

active

06322861

ABSTRACT:

This invention relates generally to polymeric compositions made from multifunctional monomers. More particularly, this invention relates to polymeric compositions made from multifunctional (meth)acrylate monomers and multifunctional aromatic monomers.
It is very important to have precise control of the thickness of the liquid-crystal layer in liquid-crystal-based displays. The liquid-crystal layer acts as an electro-optic light valve that works in conjunction with polarizers to modulate the transmission of light through a display between two states one of off, where the liquid crystals block substantially all light, and one of on, where the liquid crystals allow transmission of light. Irregularities in the thickness of the liquid-crystal layer, also known as the cell gap, result in uneven display performance affecting such properties as contrast, transmittance, and the response time of the liquid-crystal layer to an electric signal.
Liquid crystal displays have a structure such that two substrates, generally glass or plastic sheets, are disposed opposite to each other through optionally a color filter on the inside surface of the top substrate (top is the side toward the viewer), an alignment layer, an electrode layer, a spacer particle, and a liquid crystal layer. Spacers are used to control the thickness of the liquid crystal layer and as well as to provide a uniform thickness of the liquid crystal layer over the entire active area of the display. Other means for controlling the cell gap include the flatness of the substrate material, the flatness of the layers between the substrates, the number of spacer particles in any given area, and the spatial distribution of spacer particles with respect to one another.
Particles generally suitable for use as spacers in liquid crystal displays are chosen from among glass; oxides of silica, alumina or other ceramics; and plastics. The shape of particles generally suitable for use as spacers in liquid crystal displays are chosen from among cylindrical rods having aspect ratios from about 1:2 to greater than 1:10, and spherical balls. The choice of spacer particles is largely dictated by the characteristics of the spacer particles that include but are not limited to: uniformity of the particle diameter, amount of impurities that may leach into the liquid crystal layer, compatibility with the liquid crystal layer, hardness, compressibility, coefficient of thermal expansion, elastic modulus, refractive index, thermal stability, and dielectric constant.
In addition to maintaining the cell gap, spacer particles are very important in establishing the correct cell gap during the assembly of liquid crystal displays. The liquid-crystal display assembly process generally requires the following steps: a) spacer particles are deposited in a pre-determined concentration onto one sheet of glass or plastic substrate, b) a sealant is applied along the edge of the same substrate in a fashion similar to a picture frame leaving a small gap that will later be used to fill the liquid crystal material, c) a second sheet of glass or plastic substrate is placed over the first substrate containing the spacer particles and the adhesive, d) the two substrates are pressed together at an elevated temperature to cure the adhesive and therefore sealing the substrates together. The properties of the spacer particles must be such that the particles do not degrade during the application of heat and pressure in the sealing process; the spacer particles must have sufficient thermal stability to withstand heating and also good compression strength so as to not break or fracture under load.
Plastic spacers will deform in the edge-sealing process described above. The extent of deformation can vary significantly, and is a function of the composition of the spacer, the amount of pressure applied during the sealing process, and the heat applied during the sealing process. It is preferred that a plastic spacer deform slightly when exposed to heat and pressure and then recover some or all of its original shape when the heat and pressure are removed. The extent of recovery, or alternatively, the extent to which the spacer particle is deformed and then resumes some or all or its original diameter, is known as the recovery factor. The recovery factor is described in detail in W.O. Pat. Appl. No. 9206402, see in particular FIG. 4 of the cited patent application. In the measurement of recovery factor a given load is applied to a spacer particle and the displacement of the spacer caused by the load is measured (L
1
). The load is then removed and the extent to which the original particle diameter recovers is given as (L
2
). The recovery factor is calculated by (L
2
/L
1
). In view of the variations in display quality, there is a continuing need for spacer particles that have a balance of properties affecting control of the cell gap during, and after, the cell sealing process and impacting both the thermal stability and the recovery factor of the spacer.
W.O. Pat. Appl. No. 9206402 discloses spheres with certain elastic modulus and recovery factor properties. The spheres may be applied as spacers for liquid-crystal display elements. The spheres are made of polydivinylbenzene, divinylbenzene-styrene copolymer, divinylbenzene-acrylate copolymers, or polydiallylphthalate.
U.S. Pat. No. 5,231,527 discloses a liquid crystal display with two sheets of substrates disposed opposite to each other, transparent electrodes, orientation films, a spacer particle with a certain range of elastic modulus, and a liquid crystal layer. The spacer particle may be made of a crosslinked vinyl copolymer.
U.S. Pat. No. 5,846,657 (Wu) discloses spacer particles with certain compression values and recovery factors. The particles are polymers of a 1,4-butanediol diacrylate or 1,6-hexanediol diacrylate. These particles have a high compression strength such that they withstand high loads before breaking. However, these particles have a low initial compression strength, such that the load these particles can withstand before deforming 10% of their original size is limited. A high initial load compression strength is important because it allows for the use of fewer particles to achieve the same result.
Despite the teachings of the disclosures, there is a continuing need to provide improved spacer particles of uniform size which, and which possess, desirable physical characteristics.
The present invention is directed to a plurality of polymer particles comprising a copolymer of 1 to 30% wt, based on the total weight of the monomers in the copolymer, of a multifunctional (meth)acrylate monomer and 70 to 99% wt, based on the total weight of the monomers in the copolymer, of a multifunctional aromatic monomer, said particle having a particle size of 1 to 15 microns with a standard deviation of less than 4% of the mean diameter; and a recovery factor greater than 35%.
The present invention is also directed to a method of improving the compression characteristics of a (meth)acrylate polymer particle by copolymerizing with a multifunctional (meth)acrylate monomer from 1 to 99%, based on the total weight of the monomers in the copolymer, of a multifunctional aromatic monomer.
The present invention is further directed to a liquid crystal display containing a spacer particle formed from a copolymer of 1 to 30% wt, based on the total weight of the monomers in the copolymer, of a multifunctional (meth)acrylate monomer and 70 to 99% wt, based on the total weight of the monomers in the copolymer, of a multifunctional aromatic monomer.
As used throughout the specification, multifunctional monomers are understood to contain two or more polymerizable groups. Suitable multifunctional monomers may contain two, three, four or more polymerizable groups. As used herein, the term “(meth)acrylate” refers to methacrylate and acrylate.
Suitable multifunctional (meth)acrylate monomers include, but are not limited to, (C
2
-C
18
)alkanediol di(meth)acrylates. It is preferred that the multifunctional (meth)acrylate monomers are (C
2
-C
10
)alka

Affiliated with

Also associated with

Rating

Polymer particles does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Polymer particles, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polymer particles will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2610323