JPH07196752A - Modification of crosslinked polymer particles - Google Patents

Abstract

PURPOSE:To obtain a crosslinked polymer having high compression stress and fracture strength suitably useful as a fine space supporter such as a spacer for liquid crystal displays by adding a crosslinking monomer and an organic solvent to crosslinked polymer particles, then removing the solvent and polymerizing the crosslinking monomer. CONSTITUTION:Particles of a crosslinked polymer in an amount of 100 pts.wt. prepared by polymerization of a monomer mixture of at least 20wt.%, preferably more than 50wt.%, of a crosslinking monomer such as divinylbenzene with an uncrosslinking monomer such as styrene are combined with 5 to 300 pts.wt., preferably 7 to 100 pts.wt., of a crosslinking polymer and an organic solvent (preferably high volatile and having high surface tension; for example, acetone or methanol is suitable). Then, the solvent is removed and the crosslinking monomer is polymerized to give the objective polymer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for modifying fine particles of a crosslinked polymer having a high compressive stress and a high fracture strength, which is suitable for a minute gap retaining material such as a spacer for a liquid crystal display panel, and a particle thereof.

[0002]

2. Description of the Related Art Generally, in a liquid crystal display panel, it is necessary to hold two glass substrates having a liquid crystal substance in a gap in a certain gap. A method is adopted in which a spacer is interposed therebetween and both glass substrates are pressed and fixed until a desired cell gap is obtained. The spacer material is roughly classified into glass-based and plastic-based materials.Because the glass-based spacer is a hard material with too high a particle compressive stress, it may easily damage the alignment film or cause electrode disconnection. Recently, plastic-based spacers, which have drawbacks and have excellent elasticity, have been widely used. As such a plastic spacer, polymer fine particles obtained by suspension polymerization of a styrene monomer or the like have been conventionally used. However, styrene-based polymer fine particles generally have low mechanical strength, the spacer is broken or deformed by the pressure at the time of pressing, an appropriate cell gap cannot be obtained, and the solvent resistance is poor and the liquid crystal is contaminated. Occurs. As means for solving these problems, cross-linked polymer particles using a cross-linkable monomer have been proposed, but this also has a low particle strength, particularly low compression displacement, low anti-compression force in a practical use region, This has been a big problem in securing a cell gap as a spacer.

[0003]

Means for Solving the Problems As a result of intensive investigations by the present inventors, as a result of conventional suspension polymerization, dispersion polymerization, swelling polymerization, seed polymerization and membrane emulsion polymerization, crosslinkable particles were treated with a crosslinkable monomer. Provided is a method for producing crosslinked particles capable of modifying the internal composition and structure of the crosslinkable particles by adding an organic solvent, subjecting to organic solvent removal treatment, further impregnating the crosslinkable monomer into the inside of the crosslinkable particles, and then polymerizing. To do.

The 10% displacement particle compressive stress in the present invention means one particle having a particle diameter d (μm) placed on a horizontal metal plate, a load is applied at a constant speed with the particle center direction directed, and the diameter of the particle. When the load corresponding to 10% is compressed, that is, when the load when the particle diameter reaches 90% is P (g), 10% displacement particle compressive stress = 2.8P / (πd ² )
It is defined by × 10 ³ (kg / mm ² ). The breaking strength of particles can be calculated by substituting the load when the particles are broken into the above equation.

The crosslinkable monomer used in the present invention is
Generally, it is not particularly limited as long as it is polymerized from a crosslinkable vinyl monomer having two or more unsaturated double bonds capable of radical polymerization. For example, vinyl compounds such as divinylbenzene, 1,4-divinyloxybutane, and divinylsulfone; allyl compounds such as diallyl phthalate, diallyl acrylamide, triallyl (iso) cyanurate, and triallyl trimellitate; (poly) ethylene glycol di ( (Poly) oxyalkylene glycol di (meth) acrylates such as (meth) acrylate, (poly) propylene glycol di (meth) acrylate; pentaerythritol tetra (meth) acrylate, pentaerythritol tri (meth) acrylate,
Pentaerythritol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, dipentaerythritol penta (meth) acrylate and glycerol tri (meth) acrylate, glycerol di (meth) acrylate And so on. These crosslinkable vinyl monomers may be used alone or in combination of two or more. Among them, acrylate-based monomers having a polyfunctional group such as ethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, or divinylbenzene are particularly preferable. Usually, commercially available divinylbenzene has a purity of about 55 to 96% by weight and contains impurities such as ethylstyrene.
The main component, divinylbenzene itself, is also a mixture of para-form and meta-form (60-70% by weight of para-form). To obtain higher 10% displacement compressive stress and fracture strength,
Highly pure divinylbenzene, particularly a highly pure meta form, is preferred. Further, for the purpose of modifying the surface of the particles, a monomer having a polar functional group may be mixed and used in the crosslinkable monomer. Specifically, acrylic acid monomers such as methacrylic acid, acrylic acid, and itaconic acid; methacrylic acid ester-based monomers such as methyl methacrylate, lauryl methacrylate, and diethylaminoethyl methacrylate; acrylic acid esters such as lauryl acrylate and diethylaminoethyl acrylate. System monomers; acrylamide monomers such as N-methylmethacrylamide and N-methylacrylamide. The mixed polymerization ratio of the polar monomer and the crosslinkable monomer varies depending on the purpose, but generally can be arbitrarily adjusted from 1: 100 to 100: 1.

Specific examples of non-crosslinkable monomers include styrene, α-methylstyrene, vinyltoluene,
Aromatic vinyl compounds such as vinyl pyridine; (meth)
Unsaturated carboxylic acids such as acrylic acid, α-chloroacrylic acid, crotonic acid, maleic anhydride; methyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, t-butyl (meth) acrylate, (meth ) N-hexyl acrylate, cyclohexyl (meth) acrylate,
2-Ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, benzyl (meth) acrylate, mono or di (meth) acrylate of (poly) ethylene glycol, (poly) propylene glycol Mono or di (meth) acrylate, 1,4-butanediol mono- or di- (meth) acrylate, trimethylolpropane mono,
Unsaturated carboxylic acid esters such as di- or tri- (meth) acrylate; (meth) acrylamide, N-
Methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N-methyllol (meth) acrylamide, N-2-hydroxyethyl ( Unsaturated amides such as (meth) acrylamide, N, N′-methylenebis (meth) acrylamide, N, N′-ethylenebis (meth) acrylamide; (meth) acrylonitrile, α-chloroacrylonitrile,
Unsaturated nitriles such as α-chloromethylacrylonitrile, α-methoxyacrylonitrile, and vinylidene cyanide can be mentioned. The crosslinkable monomer is not particularly limited as long as it is a monomer having two or more radically polymerizable unsaturated double bonds.

The crosslinkable monomer is at least 20% by weight, preferably 50% by weight or more of the total monomers. The cross-linking or non-cross-linking monomers, or a mixture of these cross-linking monomers can be used to obtain a polymer by a generally known polymerization method.
Crosslinked particles of 10 μm can be produced. Normal,
Examples of the polymerization method often used include suspension polymerization, dispersion polymerization, seed polymerization, swelling polymerization, film emulsion polymerization and the like.

The most important feature of the present invention is the step of impregnating the crosslinked polymer particles obtained as described above with a crosslinkable monomer. This impregnation step is a process in which a solution of a crosslinkable monomer dissolved in an organic solvent is impregnated into the inside of the crosslinked particles, and then the organic solvent is removed from the inside of the crosslinked polymer particles by a deorganization solvent operation to perform polymerization. is there. That is, the use of the organic solvent is essential in the step of impregnating the inside of the particles with the crosslinkable monomer. Examples of the crosslinkable monomer that can be used here include the same as those mentioned above, and a preferable crosslinkable monomer is divinylbenzene. Further, the organic solvent varies depending on the type of the crosslinkable monomer used, but is highly volatile for the purpose of efficiently performing the replacement with the organic solvent and the monomer,
Alternatively, those having a high surface tension are preferable. Specifically, alcohols such as methyl alcohol, ethyl alcohol, isoamyl alcohol, isopropyl alcohol and octyl alcohol; esters such as methyl acetate, ethyl acetate and isoamyl acetate; ketones such as acetone and methyl ethyl ketone; acetonitrile, propionitrile Nitriles such as; or aromatics such as toluene, xylene, and benzene can also be used. Among these,
Particularly preferred are low molecular weight acetone and methyl alcohol. The organic solvent removing step in the present invention is generally preferably carried out at room temperature and atmospheric pressure. When the amount of the organic solvent used increases, it may be carried out under reduced pressure, heat treatment, or by flowing a gas such as air to accelerate the evaporation of the organic solvent.

As the radical polymerization initiator used in the present invention, a generally used oil-soluble radical polymerization initiator can be used. Specifically, peroxides such as benzoyl peroxide and lauroyl peroxide; azo compounds such as 2,2′-azobisisobutyronitrile and 2,2′-azobis (2,4-dimethylvaleronitrile) Is mentioned. These radical polymerization initiators are used as the monomer mixture 100.
Usually, 0.1 to 20 parts by weight, preferably 3 to 15 parts by weight is used with respect to parts by weight. The initiator may be used by dissolving it in the crosslinkable monomer and the organic solvent in the monomer impregnation step, or may be used by adding it during the aqueous heating polymerization. It is preferable to impregnate the inside of the crosslinked particles together with the crosslinkable monomer in advance, since the polymerization reaction is carried out to the inside of the particles and the polymerization other than the aqueous polymerization is utilized.

The mixing weight ratio of the base crosslinked particles and the crosslinkable monomer in the present invention is 5 to 300 parts by weight, preferably 7 to 100 parts by weight with respect to 100 parts by weight of the base crosslinked particles. When the mixing amount of the crosslinkable monomer is 5 parts by weight or less relative to 100 parts by weight of the base crosslinked particles, the compressive stress and the breaking strength of the particles are not so high as those of the base crosslinked particles, which is not preferable. Further, when the amount of the crosslinkable monomer is 300 parts by weight or more based on 100 parts by weight of the base crosslinked particles, the dispersibility in aqueous polymerization is remarkably poor, and the base crosslinked particles are agglomerated, which is not preferable.

In the present invention, the mixing weight ratio of the base crosslinked particles and the organic solvent may basically be an amount such that the whole organic particles can be made to flow like a fluid by the organic solvent. Depending on the weight ratio of the added organic solvent to the base crosslinked particles and the crosslinkable monomer, the speed at which the crosslinkable monomer is impregnated into the inside of the base crosslinked particles by substituting the organic solvent impregnated inside the particles is different. If it is too small, the crosslinkable monomer cannot be impregnated inside the particles,
Particle compressive stress and fracture strength cannot be increased so much. On the other hand, if the amount of the organic solvent is too large, there is a drawback that it takes a lot of time to remove the solvent. Therefore, the weight ratio of the base crosslinked particles to the organic solvent is preferably 1 to 1,000 parts by weight with respect to 100 parts by weight of the base crosslinked particles.

The mixed system of the base crosslinked particles, the crosslinkable monomer, the initiator and the organic solvent is deorganized by a known method. The temperature at that time varies depending on the initiator and organic solvent used, but is generally preferably 35 ° C. or lower. When the amount of the organic solvent used is large, the pressure may be reduced. The mixed system of the base crosslinked particles after the deorganization solvent, the crosslinkable monomer and the initiator is powder or slurry,
Water containing a surfactant or a water-soluble polymer stabilizer can be added and dispersed. If necessary, dispersion treatment may be carried out with a homomixer or homogenizer.

As the surfactant that can be used here, nonionic or anionic ones that are generally used can be used. Specifically, surfactants such as sodium dodecyl sulfate, sodium lauryl sulfate, polyoxyethylene derivative, polyoxyethylene nonylphenyl ether, and polyvinyl alcohol, polyvinylpyrrolidone, gelatin, hydroxyethyl cellulose, polyvinyl alkyl ether, carboxymethyl cellulose, etc. Examples of the stabilizer include water-soluble polymers. The amount of the surfactant added varies depending on the amount of the monomer used, but is generally 0.01 to 10% by weight, preferably 0.01 to 1
% By weight.

In the present invention, the fine dispersion of the crosslinkable monomer and the base crosslinked particles after impregnation with the initiator depends on the amount of the crosslinkable monomer to be impregnated, but an aqueous solution containing the above-mentioned surfactant or water-soluble polymer stabilizer. In some cases, it may be dispersed by a simple addition operation, and in some cases it may not be possible to obtain a good dispersion without irradiating ultrasonic waves to some extent or treating with a homomixer. The ultrasonic treatment may be direct irradiation or indirect irradiation. The polymerization initiator at the time of this polymerization may be mixed with the crosslinkable monomer in advance when the crosslinkable monomer is absorbed by the base crosslinked particles, or the base crosslinked particles having absorbed the crosslinkable monomer may be dispersed in water. You may add after doing.

By heating and polymerizing the fine dispersion of the crosslinkable monomer and the particles impregnated with the initiator, the crosslinked particles having high compressive stress and breaking strength of the present invention can be obtained.
The polymerization temperature is generally 50 to 100 ° C., and the time is 0.5 to 1
It may be 0 hours. When the initiator is added at the time of aqueous polymerization, the initiator may be added to the fine dispersion of the crosslinkable monomer-impregnated base crosslinked particles for polymerization. The initiator at that time may be added in the form of an emulsion or in the form of oil drops. Further, in addition to dispersing the crosslinkable monomer and the initiator-impregnated particles in an aqueous system and polymerizing by heating, it may be polymerized by heating in a powder or slurry state without being dispersed in an aqueous system. In particular, when the amount of the crosslinkable monomer used is small relative to the particles, the powder heat polymerization is simpler and preferred because the powder particles do not aggregate. Crosslinked particles having a predetermined compressive stress and breaking strength can be obtained by a method other than heat polymerization, such as irradiation with light, ultraviolet rays, or electron beams.

The standard deviation value (CV value) of the crosslinked polymer particles modified by the method of the present invention is the same as the CV value of the base crosslinked particles or the CV value of the base crosslinked particles.
It becomes sharper than the V value, and no foreign particles other than the base crosslinked particles, small particles, and giant particles are generated. Further, when the amount of the crosslinkable monomer to be added was 20 parts by weight or less with respect to 100 parts by weight of the base crosslinked particles, there was almost no change in particle size before and after the modification, and particles having excellent dispersibility were obtained.

According to the method of the present invention, crosslinked polymer particles having a high anticompressive force of the crosslinked polymer particles can be obtained. The 10% compressive displacement stress of the crosslinked particles obtained in the present invention is 5.0 to
It is in the range of 10.0 kg / mm ² . The value of conventionally known crosslinked polymer particles is generally 2 to 3.5 kg /
Since it is in the range of mm ² , the spacer particles have a problem in securing a gap under severe usage conditions. On the other hand, with an inorganic spacer made of inorganic particles such as silica particles, glass particles, and glass fiber pieces, the 10% compressive displacement stress exceeds 50 kg / mm ² , and there is a problem that the material is damaged because it is too hard. The crosslinked particles of the present invention have an appropriate compressive stress.

[0017]

[Operation] To briefly describe the features of the present invention, the crosslinked particles are further impregnated with a crosslinkable monomer, a polar group-containing monomer, or a mixture thereof inside the crosslinked particles, and then the organic solvent is added. By evaporating and then heating and polymerizing, the inside of the particles is further supplemented with a polymer, whereby both the compressive stress and the breaking strength of the base crosslinked particles can be increased and the hydrophilic / hydrophobic property of the particle surface can be modified. Using the method of the present invention, the modified particles are harder and stronger, and the CV value of the particles is at the same level as the base crosslinked particles or even sharper. further,
The hydrophilicity / hydrophobicity of the surface of the base crosslinked particles can be freely adjusted. The crosslinked particles produced using the present invention are particularly suitable as spacer particles for liquid crystal display panels.

[0018]

EXAMPLES The polymerization method according to the present invention will be further described below with reference to examples, but the present invention is not limited to these examples. Example 1 81% by weight of divinylbenzene and 19% by weight of styrene
Of base cross-linked particles (particle size: 7.12 μm, CV value: 1.10%, 10% compressive stress: 3.5 kg / mm ² , breaking strength: 85 kg / mm ² ) each into four 1-liter scale Marzoco flasks. 100 g each was weighed and added. Divinylbenzene [hereinafter referred to as "DVB", purity 96%, manufactured by Nippon Steel Chemical Co., Ltd.], ethylene glycol dimethacrylate (hereinafter referred to as "EG"), trimethyl roll propane trimethacrylate [hereinafter referred to as "TMP", respectively, in four Maruzoko flasks. Kyoeisha Chemical Co., Ltd.], a mixture of DVB and N-methylmethacrylamide [MMAA, Wako reagent, weight ratio 1: 1] 2
After adding 0 g each, 0.6 g of benzoyl peroxide [BPO, Wako reagent] and 50 g of acetone were added, and after stirring well, the mixture was allowed to stand at room temperature for 1 hour. Next, the Marzoco flask was set in an evaporator, the water bath temperature was set to 25 ° C., and acetone was removed while rotating at normal pressure. Subsequently, 1 liter of an aqueous solution containing 0.5% by weight sodium dodecyl sulfate and 3.0% by weight Emulgen (manufactured by Kao) was added to the four Marzoco flasks, and after thoroughly stirring,
High-speed rotary homomixer [Polytron, Kinematica]
The mixture was stirred at 20,000 rpm for 1 minute. The obtained dispersion was placed in a 1 liter separable flask and polymerized at 80 ° C. for 5 hours to obtain 148 g of crosslinked polymer particles having a uniform particle size.
Got There were no foreign particles other than the base crosslinked particles. The results are shown in Table 1. The particle size is an electron microscopic value, and the 10% compressive stress and the fracture strength were measured using a micro compression tester [MCTM-200, manufactured by Shimadzu Corporation].

[0019]

[Table 1]

Example 2 Using 55% by weight of DVB and 45% by weight of styrene, suspension polymerization and dispersion polymerization were carried out according to a conventional method (supervised by M. Otake, superorganic compounds I and II, Asakura). The base crosslinked particles were prepared at a bookstore. 100 g of each of these base crosslinked particles was placed in two Marzoco flasks as in Example 1. Then, 10 g, 0.5 g, and 50 g of TMP, BPO, and methyl alcohol were added to the two Marzoco flasks, respectively, and after stirring well, they were left to stand overnight. Next, set the water bath temperature to 25 ° C.
While depressurizing with an aspirator, the Marzoco flask was rotated, and demethanol was carried out in about 30 minutes. Subsequently, the reduced pressure was returned to normal pressure, the water bath temperature was reset to 85 ° C., and the rotation was polymerized for 5 hours. The dispersed powder particles thus obtained weighed 110 g each, and no heterogeneous particles other than the base crosslinked particles were observed. The results are summarized in Table 2.

[0021]

[Table 2]

Comparative Example 1 Using the same base crosslinked particles as in Example 1, a solid content of 10
1 liter of a weight% dispersion was prepared. On the other hand, 10% by weight of EG prepared by 1% by weight of Emulgen A60 (manufactured by Kao Corporation), 0.3% by weight of BPO, and 1 liter of emulsion dispersion were added to the base crosslinked particle dispersion. After slowly stirring at 35 ° C for 24 hours, the temperature was raised to 85 ° C. After 8 hours of polymerization, the same method as in Example 1 was evaluated. The particle size was 7.01 μm, the CV value was 1.10%, and the particle size was 10
% Compressive stress is 3.5 kg / mm ² , breaking strength is 80 kg
/ Mm ² .

Comparative Example 2 In Example 2, No. in Table 2 was used as the base crosslinked particles.
The same operation as in Example 2 was performed except that the particles of No. 2-1 were used and methyl alcohol was not added. The obtained particles after polymerization became aggregates and could not be redispersed.

[0024]

As is clear from the results of the above examples, according to the present invention, the base crosslinked particles are polymerized by impregnating the inside of the particles with a crosslinking monomer and an initiator through an organic solvent. Thereby, both the 10% compressive stress and the fracture strength of the particles can be remarkably improved as compared with the base crosslinked particles.
The particles thus obtained can be suitably used as spacer particles for a liquid crystal display panel.

Claims (1)

[Claims] 1. At least 20% by weight of a crosslinkable monomer.
Crosslinked polymer particles 10 obtained by polymerizing a monomer containing
A method for modifying crosslinked polymer particles, which comprises adding 5 to 300 parts by weight of a crosslinkable monomer and an organic solvent to 0 part by weight, followed by a treatment for removing an organic solvent, and then polymerizing the crosslinkable monomer.