JP2006267513A - Spacer for liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spacer for a liquid crystal display element which is hardly moved after being spread. <P>SOLUTION: This spacer for a liquid crystal dislay element is composed of polymer particles polymerized by using polymeric unsaturated monomer and polymerization initiator distributed in basin system solvent by adding polycarboxylic acid or its salt as distributed stabilizer, wherein polycarboxylic acid or its slat exists on the surfaces of the polymer particles. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a spacer for a liquid crystal display element that hardly moves after being spread on a liquid crystal panel.

  Conventionally, in a liquid crystal display element, spacers are generally dispersed and used in order to keep a gap between substrates constant. The spacer for a liquid crystal display element is required to have a uniform particle size. As a method for obtaining such a fine particle having a uniform particle size, the fine particle obtained mainly by suspension polymerization is classified to obtain a fine particle. The method of performing the homogenization is used.

  Another method for producing monodispersed fine particles having a uniform particle size is to absorb the vinyl monomer in monodispersed fine particles such as styrene polymer and then polymerize to increase the particle size. A seed polymerization method is known. In this method, fine particles having a uniform particle diameter of about 1 to 10 μm, which are generally used as spacers for liquid crystal display elements, can be obtained.

  Such a seed polymerization method is known to exhibit high swelling ability if seed particles with a low degree of polymerization are used. For example, in Patent Document 1, seed particles having a weight average molecular weight of 1000 to 20000 are used. A method for producing highly monodispersed fine particles by seed polymerization is disclosed.

  On the other hand, polymer fine particles used for spacers for liquid crystal display elements are required to have a uniform particle diameter and not to move the spacers after being dispersed on the liquid crystal panel.

JP-A-8-176214

  The movement of the spacer after spraying on the liquid crystal panel described above may be influenced by the surface state of the polymer fine particles resulting from the polymerization method, that is, the smoothness of the surface, and the polymer obtained by the suspension polymerization method Compared with the fine particles, the polymer fine particles obtained by the seed polymerization method are inferior in smoothness, and the movement of the spacer after spraying may easily occur.

  However, the movement of the spacer after spraying is not only due to the smoothness of the surface of the polymer fine particles, but also due to the presence of the dispersion stabilizer remaining on the surface of the polymer fine particles at the time of polymerization, the surface composition is considered to be large Regardless of this, there has been a demand for polymer fine particles used for spacers for liquid crystal display elements in which the movement of spacers after spraying hardly occurs.

  An object of the present invention is to provide a spacer for a liquid crystal display element that hardly moves after being spread on a liquid crystal panel in view of the above-described present situation.

  The spacer for a liquid crystal display device of the present invention is a polymer obtained by adding a polycarboxylic acid or a salt thereof as a dispersion stabilizer and polymerizing using a polymerizable unsaturated monomer and a polymerization initiator dispersed in an aqueous solvent. A spacer for a liquid crystal display element comprising fine particles, wherein polycarboxylic acid or a salt thereof is present on the surface of the polymer fine particles.

Details of the present invention will be described below.
The spacer for a liquid crystal display device of the present invention is a polymer obtained by adding a polycarboxylic acid or a salt thereof as a dispersion stabilizer and polymerizing using a polymerizable unsaturated monomer and a polymerization initiator dispersed in an aqueous solvent. It consists of fine particles.
Therefore, the polymer fine particles are polymerized using a polymerizable unsaturated monomer and a polymerization initiator dispersed in an aqueous solvent. That is, the polymer fine particles are dispersed in an aqueous solvent to form a polymerizable unsaturated monomer. The polymer is polymerized by, for example, suspension polymerization or seed polymerization.

  Further, when the polymerizable unsaturated monomer and the polymerization initiator are dispersed in the aqueous solvent, it is necessary to add polycarboxylic acid or a salt thereof as a dispersion stabilizer. The addition of polycarboxylic acid or a salt thereof as a dispersion stabilizer may be added to the aqueous solvent before dispersing the polymerizable unsaturated monomer and the polymerization initiator in the aqueous solvent. The unsaturated monomer and the polymerization initiator may be added after being dispersed in an aqueous solvent.

Furthermore, the spacer for a liquid crystal display element of the present invention requires that a polycarboxylic acid or a salt thereof is present on the surface of the polymer fine particles.
Due to the presence of polycarboxylic acid or a salt thereof on the surface of the polymer fine particles, the obtained polymer fine particles become a spacer for a liquid crystal display element that hardly moves after being dispersed on the liquid crystal panel.

In the present invention, the presence of polycarboxylic acid or a salt thereof on the surface of the polymer fine particles means that the polycarboxylic acid or the salt is not removed on the surface of the polymer fine particles without being washed away even after the polymer fine particles are sufficiently washed with heating. The salt is present.
The polycarboxylic acid or salt thereof as the dispersion stabilizer is allowed to react while adsorbed on the surface of the particles in the middle of polymer formation or the surface of the swollen seed particles that are dispersed in an aqueous solvent and become suspended during polymerization. Most of them are less likely to be entangled with the crosslinked structure of the partially crosslinked polymer fine particle surface, and some are adsorbed at multiple points on the surface, so that they can be present on the surface of the polymer fine particle.

In the spacer for a liquid crystal display element of the present invention, the confirmation that the polycarboxylic acid or a salt thereof is present on the surface of the polymer fine particle is obtained by thoroughly washing the polymer fine particle while heating, It can be performed by analyzing with a TOF-SIMS (time-of-flight secondary ion mass spectrometry) apparatus.
As the TOF-SIMS analysis method, for example, a method in which polymer fine particles are attached on a silicon wafer and a mass ratio is measured by ion spectrum intensity on the surface of the fine particles is used.

  As the method for producing the spacer for a liquid crystal display element of the present invention, as described above, the polymerizable unsaturated monomer may be polymerized by being dispersed in an aqueous solvent, for example, suspension polymerization method, seed polymerization method. Etc. are preferably used.

  Among the above production methods, the suspension polymerization method is suitable for the purpose of producing fine particles having a variety of particle sizes because the particle size distribution is relatively wide and polydisperse fine particles can be obtained. However, when fine particles obtained by the suspension polymerization method are used as spacers for liquid crystal display elements, it is preferable to perform classification operation and select and use those having a desired particle size or particle size distribution. Further, the seed polymerization method is suitable for the purpose of producing a large amount of fine particles having a specific particle diameter because monodisperse fine particles can be obtained without requiring classification operation.

  The above suspension polymerization method uses a poor solvent of a polymerizable unsaturated monomer as a medium, and a monomer composition comprising a polymerizable unsaturated monomer and a polymerization initiator, and has a target particle size and particle size. This is a method of polymerizing by dispersing in the medium so as to obtain a diameter distribution. In the present invention, a medium obtained by adding a dispersion stabilizer to an aqueous solvent is used as a medium in the suspension polymerization method. The aqueous solvent may be water or a mixture of water and an organic solvent that is compatible with water.

  The polymerization conditions of the suspension polymerization method may be appropriately determined depending on the type of polymerization initiator and polymerizable unsaturated monomer to be used, and are not particularly limited. Usually, the polymerization temperature is 50 to 80 ° C. And it is preferable that polymerization time is 3 to 24 hours.

  Therefore, when the spacer for a liquid crystal display element of the present invention is produced using a suspension polymerization method, a polycarboxylic acid or a salt thereof is added as a dispersion stabilizer, and a polymerizable unsaturated monomer and a polymerization initiator are added. Is then dispersed in an aqueous solvent, and then polymer particles are polymerized to produce polycarboxylic acid or a salt thereof on the surface of the polymer particles.

  The seed polymerization method is a polymerization method in which monodispersed seed particles (seed particles) are further absorbed with a polymerizable unsaturated monomer to expand to a target particle diameter. Therefore, the polymer fine particles obtained have a very narrow particle size distribution and a uniform particle size.

  The medium used in the seed polymerization method is appropriately determined depending on the type of polymerizable unsaturated monomer used. In the present invention, a medium obtained by adding a dispersion stabilizer to an aqueous solvent is used. The aqueous solvent may be water or a mixture of water and an organic solvent that is compatible with water.

  Therefore, when the liquid crystal display element spacer of the present invention is produced using a seed polymerization method, polycarboxylic acid or a salt thereof is added as a dispersion stabilizer, and the polymerizable unsaturated monomer and the polymerization initiator are added. A production method is used in which the particles are dispersed in an aqueous solvent and then absorbed by the seed particles, polymer particles are polymerized, and polycarboxylic acid or a salt thereof is present on the surface of the polymer particles.

  The polycarboxylic acid or salt thereof in the present invention is not particularly limited as long as it is used as a dispersion stabilizer. For example, poly (meth) acrylic acid, a copolymer of (meth) acrylic acid and maleic acid, Polycarboxylic acids such as polyitaconic acid; poly (meth) acrylic acid sodium salt, poly (meth) acrylic acid ammonium salt, sodium salt of a copolymer of (meth) acrylic acid and maleic acid, (meth) acrylic acid and maleic acid Examples thereof include ammonium salts of copolymers with acids, and salts of polycarboxylic acids such as sodium polyitaconate. These may be used alone or in combination of two or more. Here, for example, poly (meth) acrylic acid means polyacrylic acid or polymethacrylic acid.

  It is preferable that the addition amount of the said polycarboxylic acid or its salt is 5-300 weight part with respect to 100 weight part of polymerizable unsaturated monomers. When the addition amount is less than 5 parts by weight, the effect as a dispersion stabilizer may be reduced, and when it exceeds 300 parts by weight, the stirring efficiency may deteriorate and polydispersed fine particles may be obtained. More preferably, it is 10 to 100 parts by weight.

The polymerizable unsaturated monomer in the present invention is not particularly limited, and examples thereof include monofunctional monomers and polyfunctional monomers. These may be used alone or in combination of two kinds. May be.
The proportion of the polyfunctional monomer in the polymerizable unsaturated monomer is preferably 15% by weight or more, more preferably 30% by weight or more because the mechanical strength of the polymer fine particles is reduced when the ratio is reduced. It is. In addition, the ratio of the polyfunctional monomer may be 100% by weight, that is, all may be polyfunctional monomers.

  The monofunctional monomer is not particularly limited. For example, styrene; styrene derivatives such as α-methylstyrene, p-methylstyrene, p-chlorostyrene, chloromethylstyrene; vinyl chloride; vinyl acetate, propionic acid. Vinyl esters such as vinyl; unsaturated nitriles such as acrylonitrile; methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (meth) acrylic acid (Meth) acrylic acid esters such as stearyl; (meth) acrylic acid ester derivatives; conjugated dienes such as butadiene and isoprene, and the like may be used alone or in combination of two or more. Good.

  The polyfunctional monomer is not particularly limited. For example, divinylbenzene, ethylene oxide di (meth) acrylate, tetraethylene oxide di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate , Polytetramethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylolmethane tri (meth) acrylate, Examples thereof include tetramethylolpropane tetra (meth) acrylate, and these may be used alone or in combination of two or more.

The polymerization initiator in the present invention is not particularly limited as long as it can be dispersed in an aqueous solvent. For example, an oil-soluble polymerization initiator is preferably used.
Examples of the oil-soluble polymerization initiator include benzoyl peroxide, lauroyl peroxide, orthochlorobenzoyl peroxide, orthomethoxybenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, t-butylperoxy-2- Organic peroxides such as ethyl hexanoate and di-t-butyl peroxide; azobisisobutyronitrile, azobiscyclohexacarbonitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), etc. Examples thereof include azo compounds.

In the present invention, in order to improve the dispersion stability, a surfactant or a polymer dispersion stabilizer may be further added.
Examples of the surfactant include anionic surfactants such as sodium lauryl sulfate, triethanolamine lauryl sulfate, and sodium lauryl benzene sulfonate.
Examples of the polymer dispersion stabilizer include polyvinyl alcohol, polyvinyl pyrrolidone, gelatin, starch, hydroxyethyl cellulose, and polyvinyl ether.
These may be used alone or in combination of two or more.

Next, the seed polymerization method will be described in more detail.
The seed particles used in the seed polymerization method are not particularly limited as long as they absorb a polymerizable unsaturated monomer and a polymerization initiator, but a polymer containing 50% by weight or more of styrene and its derivatives is preferable. Used for.

Examples of the styrene derivative include p-methylstyrene, p-chlorostyrene, p-chloromethylstyrene, and p-methoxystyrene. These may be used alone or in combination of two or more.
As components other than the styrene and derivatives thereof, (meth) acrylic acid esters and derivatives thereof, butadiene and the like are used.

  When the weight average molecular weight of the seed particles is small, the seed particles are likely to coalesce and monodisperse spherical particles are difficult to be formed. When the weight average molecular weight is large, it is difficult to absorb a polymerizable unsaturated monomer added later. Since the swelling ability is lowered, 2,000 to 100,000 is preferable.

  As a method for polymerizing the seed particles, for example, a soap-free polymerization method or a dispersion polymerization method is used, but it is not limited to these methods, and a known technique can be applied.

  The polymerization initiator used in the polymerization of the seed particles can be one used in a normal soap-free polymerization method or dispersion polymerization method, and is not particularly limited. For example, potassium persulfate or an azo initiator is used. Can be used.

  In the polymerization of the seed particles, a chain transfer agent may be used to obtain seed particles having a low molecular weight. As the chain transfer agent, a chain transfer agent generally used in the polymerization can be used, and is not particularly limited. For example, an alkyl mercaptan chain transfer agent having 10 or less carbon atoms can be used. .

  The seed particles are non-crosslinked particles having an average particle size of 0.1 to 10 μm and a CV value (value obtained by dividing the standard deviation of the particle size distribution by the average particle size as a percentage) of 10% or less. preferable.

  In the seed polymerization method, if the amount of the polymerizable unsaturated monomer added is small, the crosslinking component is insufficient, resulting in insufficient mechanical strength of the polymer fine particles. Since accuracy deteriorates, the amount is preferably 1 to 200 parts by weight with respect to 1 part by weight of the seed particles.

  In the seed polymerization method, specifically, for example, the polymerizable unsaturated monomer is finely dispersed in an aqueous solvent together with an oil-soluble polymerization initiator to form a finely dispersed emulsion, and then the finely dispersed emulsion and the aqueous system are mixed. Polymerization is performed after mixing seed particles (seed particle dispersion) dispersed in a solvent, adsorbing and absorbing the polymerizable unsaturated monomer and the oil-soluble polymerization initiator on the seed particles.

  The polycarboxylic acid or salt thereof used in the present invention is a dispersion stabilizer for seed particles when the seed particles are dispersed in an aqueous solvent, and further includes a polymerizable unsaturated monomer and a polymerization initiator in the seed particles. It can also act as a dispersion stabilizer for the swollen seed particles after being absorbed and swollen. Therefore, the polycarboxylic acid or a salt thereof may be added when the seed particles are dispersed in an aqueous solvent (hereinafter also referred to as initial addition), or a polymerizable unsaturated monomer and a polymerization initiator are added to the seed particles. May be added after being absorbed and swollen (hereinafter also referred to as late addition). Moreover, you may use initial addition and late addition together. Especially, since the polycarboxylic acid or its salt added initially becomes easy to exist in the polymer fine particle surface, initial addition is preferable.

In the above seed polymerization method, in order to disperse the polymerizable unsaturated monomer and the polymerization initiator in the aqueous solvent, it may be finely dispersed by a homogenizer or the like, and may be subjected to ultrasonic treatment, nanomizer or mount gaurine type fine emulsification. It may be finely dispersed by a machine.
In addition, in order to obtain a finely dispersed emulsion of both components, both components may be mixed and finely dispersed in advance, or both components may be mixed after finely dispersing each component separately.

  The particle size of the finely dispersed emulsion is preferably smaller than the particle size of the seed particles. By selecting such a particle size, it is possible to increase the speed at which the polymerizable unsaturated monomer and the polymerization initiator are finely dispersed in the aqueous solvent and adsorbed and diffused on the seed particles. When this diffusion rate is slow, the particle size distribution accuracy of the polymer fine particles to be produced is deteriorated.

  In order to adsorb the finely dispersed emulsion to the seed particles, for example, the seed particle dispersion and the finely dispersed emulsion are mixed and stirred at room temperature for 1 to 12 hours, but heated to 30 to 50 ° C. By doing so, adsorption can be promoted.

The swelling degree of the seed particles due to the adsorption of the finely dispersed emulsion can be arbitrarily selected by adjusting the mixing ratio of the seed particle dispersion and the finely dispersed emulsion. Is preferred.
The degree of swelling here is defined by the volume ratio of the fine particles after swelling to the seed particles before swelling. The end of adsorption is determined by confirming the enlargement of the particle diameter by observation with an optical microscope.

The polymerization temperature in the seed polymerization method can be appropriately selected depending on the type of polymerizable unsaturated monomer and polymerization initiator to be used, but is usually preferably 25 to 100 ° C, more preferably 60 to 90. ° C.
The polymerization is preferably started after the polymerizable unsaturated monomer and the polymerization initiator are completely adsorbed and absorbed by the seed particles.

  The polymer fine particles after polymerization can usually be separated from the medium by centrifugation or the like. The separated polymer fine particles can be purified by repeatedly washing with alcohol or water. After washing, the polymer fine particles can be isolated by spray drying or reduced pressure drying.

  The spacer for a liquid crystal display element of the present invention is a particle size control or classification operation by stirring or the like when the suspension polymerization method is used, and the seed particle size or polymerizable unsaturated monomer amount when the seed polymerization method is used. The particle size can be freely designed depending on the mixing ratio of the body and the seed particles, but the particle size is preferably 1 to 10 μm and the CV value is preferably 5% or less.

  When the polymer fine particles in the present invention are used as a spacer for a liquid crystal display element, treatment with carbon black, a disperse dye, an acid dye, a basic dye, a metal oxide, or the like is performed to improve the contrast of the liquid crystal display element. Colored polymer fine particles may be used.

  The polymer fine particles can also be used as a functional spacer among liquid crystal display element spacers by providing a new surface layer on the surface thereof. For example, by forming an adhesive layer on the surface, it is possible to provide a migration-preventing spacer that is more adherent to the substrate, and by providing a layer with a small surface energy, the ability to regulate the alignment of liquid crystals is reduced. It is also possible to provide an abnormal alignment prevention spacer. These surface layers can be formed by a coating method such as a coacervation method, an interfacial polymerization method, or a mechanochemical method.

  Since this invention consists of the above-mentioned structure, it became possible to obtain the spacer for liquid crystal display elements with which the movement after spraying to a liquid crystal panel did not occur easily.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited to a following example.

Example 1
Put 1.2 parts by weight of dry polystyrene seed particles having a particle size of 1.5 μm into a separable flask, add lauryl sulfate triethanolamine aqueous solution and 40 parts by weight of polyacrylic acid 5% by weight aqueous solution for initial addition, and ultrasonic treatment. For 30 minutes to prepare a seed particle dispersion.
To the obtained seed particle dispersion, 66 parts by weight of divinylbenzene, 4 parts by weight of benzoyl peroxide, ethanol, and an aqueous solution of triethanolamine lauryl sulfate were added to ion-exchanged water and finely dispersed using a static dispersion device. The emulsion was added dropwise with stirring.
Absorbed by the seed particles, after completion of swelling, 200 parts by weight of a 5% by weight polyacrylic acid aqueous solution was added for later addition, and heat polymerization was carried out while stirring to obtain a dispersion of polymer fine particles.
The obtained dispersion was washed with hot water and centrifuged, then further washed, filtered, and vacuum dried at a heating temperature of 75 ° C. to obtain polymer fine particles, which were used as spacers for liquid crystal display elements.

  About the obtained spacer for liquid crystal display elements, the average particle diameter, CV value, surface analysis by TOF-SIMS, and sticking property were evaluated by the following methods. These results are shown in Table 1.

(Average particle size, CV value)
The average particle size and CV value were determined by “Multisizer 3” manufactured by Beckman Coulter.

(Surface analysis by TOF-SIMS)
After sufficiently washing the polymer fine particles while heating, it was examined whether or not polycarboxylic acid or a salt thereof was present on the surface using a TOF-SIMS apparatus (manufactured by PHI Evans, “TFS-2000”).
The analysis conditions were primary ions: ⁶⁹ Ga ⁺ .

(Fixability)
The obtained polymer fine particles are used as spacers for a liquid crystal display element, and are sprayed on a liquid crystal panel with a sprayer manufactured by Nissin Engineering Co., Ltd., and sprayed to the liquid crystal panel at an air pressure of 49 kPa from a distance of 30 mm obliquely in a 45 ° direction for 5 seconds. Air blow was performed, and the number of particles before and after the air blow was counted. The ratio of the number of remaining particles after air blowing was calculated with respect to the number of particles on the liquid crystal panel before air blowing, and the percentage was obtained as a percentage.

(Example 2)
In Example 1, 40 parts by weight of 5% by weight aqueous solution of polyacrylic acid was not used for initial addition, and 40 parts by weight of 5% by weight aqueous solution of hydroxyethyl cellulose was used instead. A spacer was obtained.
About the obtained spacer for liquid crystal display elements, it carried out similarly to Example 1, and evaluated the average particle diameter, CV value, surface analysis by TOF-SIMS, and adhesiveness. These results are shown in Table 1.

(Example 3)
In Example 1, a liquid crystal display device was prepared in the same manner as in Example 1 except that 40 parts by weight of a 5% by weight aqueous solution of polyacrylic acid was not used for initial addition, and 40 parts by weight of a 5% by weight aqueous solution of polyvinyl alcohol was used instead. A spacer was obtained.
About the obtained spacer for liquid crystal display elements, it carried out similarly to Example 1, and evaluated the average particle diameter, CV value, surface analysis by TOF-SIMS, and adhesiveness. These results are shown in Table 1.

(Comparative Example 1)
In Example 1, 40 parts by weight of a 5% by weight aqueous solution of polyacrylic acid was not used for initial addition, but 40 parts by weight of a 5% by weight aqueous solution of polyvinyl alcohol was used instead. A spacer for a liquid crystal display element was obtained in the same manner as in Example 1 except that 200 parts by weight of a 5% by weight aqueous polyvinyl alcohol solution was used instead.
About the obtained spacer for liquid crystal display elements, it carried out similarly to Example 1, and evaluated the average particle diameter, CV value, surface analysis by TOF-SIMS, and adhesiveness. These results are shown in Table 1.

  From Table 1, it can be seen that those using polycarboxylic acid or a salt thereof as a dispersion stabilizer are excellent in fixing rate and hardly move after being sprayed onto the liquid crystal panel.

  ADVANTAGE OF THE INVENTION According to this invention, the spacer for liquid crystal display elements which cannot move easily after spraying to a liquid crystal panel can be provided.

Claims (1)

A spacer for a liquid crystal display element comprising polymer fine particles polymerized by using a polymerizable unsaturated monomer and a polymerization initiator added with a polycarboxylic acid or a salt thereof as a dispersion stabilizer and dispersed in an aqueous solvent. And
A spacer for a liquid crystal display element, wherein polycarboxylic acid or a salt thereof is present on the surface of polymer fine particles.