Liquid crystal display

The invention relates to a liquid crystal display, and more specifically to a polyimide liquid crystal display.

With advances in information and digitization, light, thin, and portable electronic products utilizing thin display panels have become popular. However, it is inconvenient for porterage and its complicated fabrication may cause low yields.

Thus, a transparent and flexible plastic substrate (0.1˜0.2 mm) has been developed. Such plastic substrate is thin, light, durable, and portable, and produced by a continuous rolling process, significantly reducing costs

Unfortunately, problems such as deposition of indium tin oxide (ITO) and thin film transistor (TFT) thereon and backend panel assembly occur. Additionally, the glass transition temperature (Tg) of the optical-level plastic substrate such as PET, PEN, PC, or m-COC (Arton or Zeonor) is lower than 200° C., being unfavorable to fabrication. Also, PES substrate has insufficient solvent resistance, with yellowing and cracking at high temperatures (200° C.). Furthermore, some polyimide plastic substrates capable of thermal and solvent resistance, being dark brown, are only suitable for use in reflective LCD panels, not transmission LCD panels.

Additionally, the plastic substrate must be fixed to a glass substrate by resin glue to facilitate subsequent multi-lithography and etching due to its difficulty in handling. However, TFT element breakage and residual resin glue may easily occur when the plastic substrate is taken off the glass substrate.

The invention provides a liquid crystal display comprising a color filter substrate and an array substrate, wherein at least one of the color filter substrate and the array substrate comprises polyimide having formula (I):

wherein A and A′ are the same or different and comprise cycloaliphatic compounds or aromatic compounds, B and B′ are the same or different and comprise aromatic compounds, and x and y are 10˜10000, wherein at least one of A and A′ is a cycloaliphatic compound.

A detailed description is given in the following embodiments with reference to the accompanying drawing.

The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawing, wherein:

FIG. 1 is a cross section of a liquid crystal display of the invention.

The invention provides a liquid crystal display comprising a color filter substrate and an array substrate. At least one of the color filter substrate and the array substrate comprises polyimide having formula (I):

In formula (I), A and A′ may be the same or different and comprise cycloaliphatic compounds such as

wherein X, Y, and Z may comprise hydrogen, methyl, trifluoromethyl, hydroxyl, C 1-18 alkyl, bromine, chlorine, or iodine, or aromatic compounds such as

wherein X and Y may comprise hydrogen, methyl, trifluoromethyl, hydroxyl, C 1-18 alkyl, bromine, chlorine, or iodine and Z may comprise —O—, —CH 2 —, —S—, —SO 2 —, —C(CH 3 ) 2 —, —Ar—O—Ar—, —Ar—CH 2 —Ar—, —O—Ar—C(CH 3 ) 2 —Ar—O—, —O—Ar—Ar—O—, —O—Ar—C(CF 3 ) 2 —Ar—O—, or —Ar—C(CH 3 ) 2 —Ar—, wherein Ar is phenyl.

B and B′ may be the same or different and comprise aromatic compounds such as

wherein X and Y may comprise hydrogen, methyl, trifluoromethyl, hydroxyl, C 1-18 alkoxy, bromine, chlorine, or iodine and Z may comprise —O—, —SO 2 —, —CH 2 —, —C(CH 3 ) 2 —, —COO(CH 3 ) 2 COO—, —C(CF 3 ) 2 —, —Ar—O—Ar—, —O—Ar—O—, —Ar—CH 2 —Ar—, —O—Ar—C(CH 3 ) 2 —Ar—O—, —O—Ar—Ar—O—, —O—Ar—C(CF 3 ) 2 —Ar—O—, or —Ar—C(CH 3 ) 2 —Ar—, wherein Ar is phenyl. B and B′ may be

and x and y may be 10˜10000.

The polyimide having formula (I) provided by the invention comprises

wherein x and y may be 10˜10000.

The polyimide provided by the invention may have formula (II):

In formula (II), A may be a cycloaliphatic compound such as

wherein X, Y, and Z may comprise hydrogen, methyl, trifluoromethyl, hydroxyl, C1-18 alkyl, bromine, chlorine, or iodine.

B may be an aromatic compound such as

wherein X and Y may comprise hydrogen, methyl, trifluoromethyl, hydroxyl, C 1-18 alkoxy, bromine, chlorine, or iodine and Z may comprise —O—, —SO 2 —, —CH 2 —, —C(CH 3 ) 2 —, —COO(CH 3 ) 2 COO—, —C(CF 3 ) 2 —, —Ar—O—Ar—, —O—Ar—O—, —Ar—CH 2 —Ar—, —O—Ar—C(CH 3 ) 2 —Ar—O—, —O—Ar—Ar—O—, —O—Ar—C(CF 3 ) 2 —Ar—O—, or —Ar—C(CH 3 ) 2 —Ar—, wherein Ar is phenyl. B and B′ may be

and n may be 10˜10000.

The polyimide having formula (II) provided by the invention comprises

The compound of formula (II) is prepared in two steps as follows. First, a diamine such as 4,4-methylene bis(cyclohexylamine) (DACH), a dianhydride monomer such as 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), and a polar solvent such as N-methyl-2-pyrrolidone (NMP) or N,N-dimethylacetamide (DMAc) are added to a flask and reacted to form a poly(amic acid) (PAA). The PAA is then imidized at about 300˜400° C. to form a polyimide via dehydration and cyclization. The reaction scheme is shown below.

Second, a diamine such as 4,4-methylene bis(cyclohexylamine) (DACH), a dianhydride monomer such as 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), and a solvent such as m-cresol or phenol are added to a flask and reacted at a reflux temperature to form a polyimide via PAA formation, dehydration, and cyclization. The reaction scheme is shown below.

Compared to the traditional polyimide, the novel polyimide, a partial phenyl structure, comprising a cycloaliphatic diamine monomer and an aromatic dianhydride monomer, provides higher thermal resistance and transmission rate and improved workability and chemical resistance due to conduction of the cycloaliphatic compounds thereto.

The polyimide film has haze less than 3%, a transmission rate exceeding 70%, a yellow index less than 6.5, a glass transition temperature of about 250˜350° C., a coefficient of thermal expansion of about 20˜75 ppm/° C., and a thickness of about 20˜200 μm, preferably 50˜150 μm.

In FIG. 1 , a liquid crystal display structure of the invention is illustrated. A liquid crystal display 10 comprises an array substrate 11 , a color filter substrate 12 , spacers 13 , and liquid crystals 14 . At least one of the array substrate 11 and color filter substrate 12 is composed of polyimide. The array substrate 11 is opposite to the color filter substrate 12 and the spacers 13 and liquid crystals 14 are formed therebetween.