JP4096136B2 - Powder adhesive - Google Patents

Description

【００５５】
注）Ａ液：イソプロピルアルコール、Ｂ液：ｎ−ヘキサン
【００５６】
上記表１から、以下のことが分かる。
本発明の粉末状接着剤はイソプロピルアルコールやｎ−ヘキサン等の溶媒に容易に分散させることができ、分散後３日経過しても良好な分散状態が保持されており、担持物の剥離もない。
一方、金属アルコキシドを担持させなかった比較例１や金属アルコキシドとしてテトラエトキシシランを担持させた比較例３では、上記の溶媒に分散後３日経過すると凝集した粒子が発生してしまう。
又、金属アルコキシドに代えてシリカ微粒子を担持させた比較例２では、溶媒に分散した直後においてシリカ微粒子が剥離してしまう。
【００５７】
【発明の効果】
本発明の粉末状接着剤は、イソプロピルアルコール等のアルコール系溶剤や、ｎ−ヘキサン等の炭化水素系溶剤中での安定性が高く、溶剤に分散した状態で、１日以上放置しても粉末状接着剤は凝集しないので、沈降法による高精度の分級や、スプレー等で噴霧する方法により、接着剤粉末を凝集することなく液晶表示セルの接着面への均一な散布を可能にする。
特に、本発明の粉末状接着剤は、電子材料関係の接着剤として好適であり、例えば液晶表示パネルの基板間の点接着剤として表示性能を損なわずに高い接着力を示し、優れた液晶表示パネルを製作することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display cell in which a liquid crystal material such as a nematic liquid crystal or a ferroelectric liquid crystal is sealed in a gap between two substrates, and more specifically, a liquid crystal display cell in which the gap between the two substrates is kept uniform on the order of μm. It is related with the epoxy-type powdery adhesive which can be used suitably for carrying out point adhesion of the display site | part.
[0002]
[Prior art]
As a conventional technique, a powdery adhesive made of an epoxy resin containing a latent curing agent is disclosed in JP-A-7-301809.
[0003]
This powdery adhesive, which is produced by mixing an epoxy resin and a latent curing agent in a solution and spray-drying it, exhibits a strong adhesive force in the point bonding of the display part of a liquid crystal display cell, Furthermore, there is a feature that does not disturb the alignment of the liquid crystal around the cured adhesive.
[0004]
[Problems to be solved by the invention]
When the particle size of the powdery adhesive used for point bonding of the display part of the liquid crystal display cell is large, its presence is noticeable in the liquid crystal display cell, and particles smaller than the substrate interval of the liquid crystal display cell do not contribute to the adhesion. . Therefore, it is strongly desired that large particles and small particles are not contained in the powder adhesive. The particle size preferably used for this purpose is 0.3 to 500 μm, and the particle size variation rate (the ratio of the standard deviation to the average particle size) is 20% or less. It is generally difficult to directly produce a powder having a particle size variation rate of 20% or less by spray drying, and a powder having a sharper particle size distribution is preferred, so that the particle size is usually adjusted by classification.
[0005]
As classification methods, there are generally wet and dry cyclones, sieving, and sedimentation classification methods using the difference in sedimentation speed in the liquid. From the viewpoint of classification accuracy, sedimentation classification methods are used. However, in order to perform the sedimentation classification method, it is an indispensable condition that the powdery adhesive is present stably in a dispersion liquid of water, alcohol, hydrocarbon or the like for a long time without aggregation.
[0006]
The powdery adhesive disclosed in Japanese Patent Application Laid-Open No. 7-301809 manufactured by spray drying has a slightly poor stability in such a dispersion and tends to agglomerate, so that a highly accurate classification effect by the sedimentation classification method can be obtained. There is a problem that can not be.
[0007]
The poor stability in the dispersion also affects the dispersion of the powdered adhesive on the bonding surface. The powdered adhesive used for point bonding of the display part of the liquid crystal display cell is conspicuous in the same way as large particles when sprayed on the adhesive surface in a state where the powdered adhesive is agglomerated. It is necessary to disperse and disperse uniformly. In order to prevent agglomeration of the powdery adhesive, a method in which the powdery adhesive is dispersed in advance in a relatively highly volatile solvent such as isopropyl alcohol and sprayed onto the adhesive surface to dry is used for this purpose.
[0008]
When the powdery adhesive produced by spray drying described in JP-A-7-301809 is allowed to stand for 1 day or more in a state of being dispersed in a solvent, the powdery adhesive partially aggregates and becomes uniform on the adhesive surface. There was a problem that it became impossible to spray.
[0009]
As a method for improving the stability of epoxy resin particles in a dispersion, JP-A-4-175351 proposes a method in which resin particles are treated in sol and inorganic fine particles are adhered to the particle surface. Yes.
[0010]
Resin particles prepared by this method are excellent in stability in a solvent such as isopropyl alcohol, and can be uniformly dispersed with little aggregation of particles. However, the inorganic fine particles adhering to the particle surface affect the sedimentation speed of the particles in the sedimentation classification, so that the classification accuracy is deteriorated and may be separated by an operation of dispersing in the solvent. May be dispersed on the alignment film.
[0011]
When inorganic fine particles are dispersed on the alignment film, there is a problem that the display performance of the liquid crystal display panel is remarkably deteriorated by disturbing the alignment of the liquid crystal or preventing the transmission of light.
[0012]
[Means for Solving the Problems]
As a result of repeated studies to solve the above problems, the present inventors solved the above problems by supporting metal alkoxide and / or a hydrolyzate thereof on the surface of particles made of epoxy resin. The inventors have found what can be done and have completed the present invention.
[0013]
That is, the present invention contains an epoxy resin having two or more epoxy groups in one molecule and a curing agent, and carries a metal alkoxide represented by the following general formula (1) and / or a hydrolyzate thereof on the surface. It is a powdery adhesive characterized by becoming.
[0014]
[Chemical 2]
R _na -M- (OR) _a (1)
[0015]
(In the formula, M is titanium, zirconium, aluminum, or boron, R is an alkyl group or aryl group having 1 to 8 carbon atoms, n is a valence of M, and a is 1 or more and n or less. Is an integer.)
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
Epoxy resin The epoxy resin in the present invention has two or more epoxy groups in one molecule.
Preferred examples include bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, and cresol novolac type epoxy resin. Besides these, polyhydric alcohols such as (poly) ethylene glycol or glycerin, or aniline Or there are polycondensates of amine compounds such as diaminodiphenylmethane and epichlorohydrin.
You may mix and use multiple types as an epoxy resin in this invention.
[0017]
In order to make the adhesive of the present invention excellent in the adhesion of a liquid crystal display cell, the softening point by the ring and ball method [RB softening point measured based on JIS-K-7234 (hereinafter referred to as “RB softening point”) .)] Is preferably 60 to 120 ° C, more preferably 75 to 100 ° C.
[0018]
When the RB softening point is less than 60 ° C., the dried semi-cured epoxy resin particles are likely to be fused, so that it is difficult to obtain spherical particles. It may be difficult to melt and cure the cured epoxy resin and adjust the pressure to a predetermined distance between the substrates.
[0019]
Preferable specific examples of the epoxy resin having an RB softening point of 60 to 120 ° C. include, for example, bisphenol A type epoxy resin and bisphenol F type epoxy resin having an epoxy equivalent of 200 to 900 and a weight average molecular weight of about 800 to 2000, and an epoxy equivalent of 170. There are phenol novolak-type and cresol novolak-type epoxy resins having a molecular weight of about ~ 230 and a molecular weight of about 600-1800.
[0020]
In addition to these general epoxy resins, special purpose such as diglycidyl ether of polyethylene glycol or polypropylene glycol, glycidyl ester of higher fatty acid, or glycidyl amine type epoxy resin, for the purpose of imparting heat resistance and flexibility after curing. Epoxy resin can be used.
[0021]
Curing agent The curing agent in the present invention is a component for curing the epoxy resin, and those conventionally used can be used.
Preferred curing agents include Lewis acid complexes, phenol resins, phenol novolac resins, polyvinyl phenol resins, acid anhydrides, acidic polyesters, styrene maleic acid copolymers, carboxyl group-containing polymers, polyamines and modified polyamines.
A preferable curing agent is a so-called latent curing agent, and preferred specific examples are dicyandiamide, an imidazole compound, and an adduct of an imidazole compound and an epoxy resin.
[0022]
Curing accelerator In the present invention, in addition to the epoxy resin and the curing agent, a curing accelerator is preferably used in combination for the purpose of lowering the temperature when the adhesive of the present invention is finally heat-cured.
Preferred curing accelerators include tertiary amine-based or phosphine-based compounds, and tertiary amine-based imidazole compounds are most preferable from the viewpoint of storage stability of the solution prepared in the granulation step described later and a curing acceleration effect.
Preferred examples include 1-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 2-phenylimidazole, 2-C11 imidazole (C11 is an alkyl having 11 carbon atoms). Group) and 1-phenylimidazole.
The imidazole compound is easily dissolved in methyl ethyl ketone or isopropyl alcohol, and a solution having a solid concentration of 30 to 50% by weight can be easily obtained.
[0023]
Granulation A preferred method of preparing particles containing the epoxy resin, curing agent and curing accelerator added as needed is the spray drying method.
It is preferable to mix each component in solution before spray drying. A particularly preferable method is a method in which a semi-cured epoxy resin (so-called B-stage) obtained by adding a latent curing agent such as dicyandiamide to the epoxy group of the epoxy resin is mixed and mixed.
A preferred method for preparing the semi-cured epoxy resin is a method in which the epoxy resin solution and the latent curing agent solution are heated for 2 to 10 hours while circulating at 70 to 90 ° C. under normal pressure.
[0024]
A preferred method of compatibilizing an epoxy resin with a latent curing agent such as dicyandiamide will be described below.
The epoxy resin is preferably dissolved in a solvent in advance to prepare a solution having a solid concentration of about 30 to 50% by weight. As the solvent, methyl ethyl ketone is most suitable in terms of boiling point and solubility. On the other hand, the latent curing agent such as dicyandiamide is preferably dissolved in a highly polar solvent such as dimethylformamide, dimethylacetamide or N-methylpyrrolidone to obtain a solution having a solid content of about 20 to 40%.
The spray-drying method performed using the mixed solution of the epoxy resin and the curing agent obtained as described above may be in accordance with a regular method, and the solution is made into droplets by continuously discharging the solution and air from the nozzle. It is sprayed and collected as spherical particles by volatilizing the solvent in the air. The preferable average particle diameter of the powdery adhesive in the present invention is 0.3 to 500 μm.
[0025]
Metal alkoxide The metal alkoxide in the present invention is a component supported on the surface of the epoxy resin particles obtained as described above, and is represented by the following formula (1).
[0026]
[Chemical 3]
R _na -M- (OR) _a (1)
(In the formula, M is titanium, zirconium, aluminum, or boron, R is an alkyl group or aryl group having 1 to 8 carbon atoms, n is a valence of M, and a is 1 or more and n or less. Is an integer.)
[0027]
Preferred specific examples of titanium alkoxide are monomethyltrimethoxy titanium, dimethyldimethoxy titanium, trimethyl monomethoxy titanium, tetramethoxy titanium, tetraethoxy titanium, tetraisopropoxy titanium, tetrabutoxy titanium, and the like, and tetraalkylalkoxy titanium is particularly preferable. It is kind.
[0028]
Specific examples of the zirconium alkoxide include monomethyltrimethoxyzirconium, dimethyldimethoxyzirconium, trimethylmonomethoxyzirconium, tetramethoxyzirconium, tetraethoxyzirconium, tetrapropoxyzirconium, tetrabutoxyzirconium, and the like, and tetraalkylalkoxyzirconium is particularly preferred. It is.
[0029]
Preferable specific examples of the aluminum alkoxide include monomethyldimethoxyaluminum, dimethylmonomethoxyaluminum, trimethoxyaluminum, triethoxyaluminum, tripropoxyaluminum, tributoxyaluminum and the like, and particularly preferable are trialkylalkoxyaluminums.
[0030]
Preferred specific examples of the boron alkoxide include monomethyldimethoxyborane, dimethylmonomethoxyborane, trimethoxyborane, triethoxyborane, tripropoxyborane, and tributoxyborane, and particularly preferred are trialkylalkoxyboranes.
As the metal alkoxide in the present invention, two or more of the above metal alkoxides may be used in combination, or a hydrolyzate of metal alkoxide may be used.
[0031]
Supporting method The method of supporting the metal alkoxide and / or the hydrolyzate thereof on the surface of the epoxy resin particles may be any method conventionally employed, and preferred methods include a dry method and a wet method. There are spray methods. A wet method is particularly preferable in order to make the surface of the epoxy resin particles thin and uniform.
[0032]
The wet method is a method in which epoxy resin particles are dispersed in a solvent and a metal alkoxide and / or a hydrolysis product thereof is added and supported on the surface of the particles.
[0033]
The amount of the metal alkoxide and / or the hydrolysis product thereof is the amount of particles used (g) × the specific surface area of the particles (cm ² / g) × the thickness to be supported (cm) × the metal alkoxide and / or the hydrolysis product thereof. Although it is calculated | required by specific gravity (g / cm < ³ >), the quantity from which the thickness to carry | support is 0.01 micrometer to 50 micrometers normally is preferable. When the thickness is less than 0.01 μm, the effect of preventing the aggregation of particles is low, and the classification accuracy is deteriorated and uniform dispersion is impossible. When the thickness exceeds 50 μm, the sedimentation speed in the liquid varies due to the change in specific gravity of the powdery adhesive, and the classification accuracy deteriorates. In addition, since the powdery adhesive is less likely to be crushed, it affects the accuracy of the cell gap in the adhesion of the liquid crystal display cell, and further decreases in the adhesive strength.
[0034]
As a solvent for dispersing the epoxy resin particles, it is necessary to select a solvent which does not dissolve or swell the epoxy resin and the latent curing agent. A hydrocarbon solvent such as n-hexane or isopropyl alcohol is required. Alcohol solvents are preferred.
[0035]
In order to uniformly support the surface of the epoxy resin particles, it is necessary to support the epoxy resin particles in a sufficiently dispersed state. The method for sufficiently dispersing the epoxy resin particles is not particularly limited, and examples thereof include a method of adding glass beads and stirring, a method of using an ultrasonic homogenizer, and the like. Since the epoxy resin particles easily aggregate when the liquid temperature rises by the operation of dispersing the epoxy resin particles, it is desirable to perform the dispersion operation while cooling with ice or the like.
[0036]
Water is added to hydrolyze the metal alkoxide. Although a trace amount of water contained in the epoxy resin particles and the solvent may be sufficient, it is preferable to add an appropriate amount of water in order to promote hydrolysis of the metal alkoxide. When the amount of water is small, the hydrolysis of the metal alkoxide does not proceed. Conversely, when the amount is too large, single particles of the hydrolyzate of the metal alkoxide are likely to be generated. A suitable addition amount is 0.1 to 100 times the theoretical amount required for hydrolysis of the metal alkoxide. Preferably it is 0.5 to 10 times.
[0037]
In addition to water, it is also possible to add a catalyst such as an imidazole compound for the purpose of promoting hydrolysis of the metal alkoxide.
[0038]
Other components The adhesive of the present invention may contain so-called spacers such as pulverized glass fiber, spherical silica, and spherical cross-linked polystyrene within the range not impairing the original performance, or cured adhesive. A rubber component, an acrylic resin, or the like can be included in order to lower the elastic modulus of the resin or to increase the impact resistance.
[0039]
【Example】
The present invention will be specifically described with reference to examples.
[0040]
Example 1
(Preparation of semi-cured epoxy resin)
20 parts by weight of cresol novolac type epoxy resin [EOCN-103S (RB softening point: 80 ° C., epoxy equivalent: 220 g / eq) manufactured by Nippon Kayaku Co., Ltd.] and 80 parts by weight of bisphenol A type epoxy resin [Dow Chemical Japan DER-661 (RB softening point: 80 ° C., epoxy equivalent: 530 g / eq)] was dissolved in 200 parts by weight of methyl ethyl ketone (solution A).
Further, 4 parts by weight of dicyandiamide as a curing agent was dissolved in 12 parts by weight of dimethylformamide (Liquid B).
Next, 0.3 part by weight of 2-ethyl-4-methylimidazole was dissolved in 0.6 part by weight of methyl ethyl ketone as a curing accelerator (C solution).
Mix all the A liquid, B liquid, and C liquid respectively, heat to 80 ° C. under reflux in a reaction kettle, react for 3 hours, cool to room temperature, and filter with a 25 μm filter to make a semi-cured epoxy resin. A solution was obtained.
[0041]
(Spray drying)
Methyl ethyl ketone was further added to the solution of the semi-cured epoxy resin obtained above, and diluted to a solid content concentration of 20% by weight. This liquid is spray-dried at a hot air temperature of 70 ° C. with a spray dryer, and the powder has an average particle size of 15 μm and a particle size variation rate of 55% (the particle size variation rate is the ratio of the standard deviation to the average particle size). Got.
[0042]
(Supporting metal alkoxide)
2 g of the powder obtained above and 500 ml of isopropyl alcohol were added to the flask, and after sufficiently dispersing by ultrasonic waves, 1 g of tetraisopropyl titanate and 5 g of water were added and stirred at room temperature for 10 hours.
The powder was washed, dried under reduced pressure, and classified to obtain a powdery adhesive of the present invention having an average particle size of 6 μm and a particle size variation rate of 20%.
[0043]
Example 2
In Example 1, a powdery adhesive was produced under the same conditions as in Example 1 except that n-hexane was used as the solvent used for supporting the metal alkoxide.
[0044]
Example 3
In Example 1, a powdery adhesive was produced under the same conditions as in Example 1 except that tetraisopropoxyzirconium was used as the metal alkoxide.
[0045]
Reference example 1
In Example 1, a powdery adhesive was produced under the same conditions as in Example 1 except that triethoxyaluminum was used as the metal alkoxide.
[0046]
Example 5
In Example 1, a powdery adhesive was produced under the same conditions as in Example 1 except that triethoxyborane was used as the metal alkoxide.
[0047]
Example 6
In preparation of the semi-cured epoxy resin of Example 1, in addition to epoxy resin, dicyandiamide and 2-ethyl-4-methylimidazole, 30 parts by weight of a rubber component (CTBN 1300 × 8 manufactured by Ube Industries) was added, and the reaction kettle A powdery adhesive was produced under the same conditions as in Example 1 except that the mixture was heated to 80 ° C. under reflux and reacted for 3 hours.
[0048]
Example 7
In the preparation of the semi-cured epoxy resin of Example 1, in addition to the epoxy resin, dicyandiamide and 2-ethyl-4-methylimidazole, a 50% by weight methyl ethyl ketone solution of acrylic resin (Dainal BR-80 manufactured by Mitsubishi Rayon Co., Ltd.) A powdered adhesive was produced under the same conditions as in Example 1 except that 100 parts by weight were added, heated to 80 ° C. under reflux in a reaction kettle, and allowed to react for 3 hours.
[0049]
Comparative Example 1
In Example 1, a powdery adhesive was produced under the same conditions as in Example 1 except that no metal alkoxide was supported.
[0050]
Comparative Example 2
In Example 1, a powdery adhesive was produced under the same conditions as Example 1 except that silica fine particles were supported by the following method instead of the metal alkoxide.
(Method for supporting silica fine particles)
In Example 1, 2 g of powder immediately after spray drying and 500 ml of water not supporting metal alkoxide and 500 ml of water were added to a flask and sufficiently dispersed by ultrasonic waves. Silica fine particles (anhydrous particles having a particle size of 10 to 20 nm) were obtained. 5 g of silica sol having a silicic acid content of 20% by weight and a product name Snowtex 20) manufactured by Nissan Chemical Industries, Ltd. were added and stirred at room temperature for 30 minutes.
Washing with water was repeated 5 times, and the powdery adhesive was recovered by spray drying. Thereafter, classification was performed to obtain a powdery adhesive having an average particle size of 6 μm and a particle size variation rate of 30%.
[0051]
Comparative Example 3
In Example 1, a powdery adhesive was produced under the same conditions as in Example 1 except that tetraethoxysilane was used as the metal alkoxide.
[0052]
The powdery adhesive obtained as described above was evaluated for the average particle size, the variation rate of the particle size, the dispersion stability in the solvent and the adhesive strength as follows, and the results are shown in Table 1 below.
(Average particle size, particle size fluctuation rate)
The particle size distribution of the powdery adhesive was measured by LA-910 manufactured by Horiba, Ltd., and the average particle size and the particle size variation rate were determined.
(Evaluation of dispersion stability)
0.15 g of the powdery adhesive obtained above was added to 30 ml of isopropyl alcohol (liquid A) or n-hexane (liquid B), and stirred while applying ultrasonic waves to prepare a dispersion.
Immediately after dispersion and after standing for 3 days at room temperature, the dispersion was sprayed on a glass plate, and after drying, the dispersion state of the powdery adhesive particles and the peeled state of the support were observed with an electron microscope.
Depending on the result in a square area with a side of 1 mm arbitrarily selected in the field of view of electron microscope observation, the following was displayed.
When there are no aggregated particles → The dispersion state is “○”
When there are aggregated particles → The dispersion state is “×”
When the carrier is not peeled → The peeled state is “○”
When the carrier is peeled → The peeled state is “×”
[0053]
(Adhesive strength evaluation)
A liquid in which 10 mg of silica particles (number average particle size 2.0 μm) as a hard spacer and 100 mg of the above powdery adhesive are dispersed in 100 g of isopropyl alcohol is spun onto a glass substrate (100 mm × 100 mm × 0.7 mm) for a liquid crystal display panel. Sprayed with a coat. At this time, the silica particles spread on the substrate were 3.2 × 10 ⁻⁴ mg / cm ² , and the powdery adhesive was 3.2 × 10 ⁻³ mg / cm ² .
Wipe off the powdery adhesive on the substrate over a width of 5 cm from one side of the substrate, and superimpose the substrate that is not sprayed with the powdery adhesive on this substrate, then cure it at 150 ° C for 30 minutes Then, the substrate was bonded.
A wedge was inserted between the two glass substrates bonded as described above, and the manner of peeling of the glass plate was observed. The evaluation results were displayed as follows.
If the glass substrate is broken → “○”
If peeled off easily → “×”
[0054]
[Table 1]

[0055]
Note) A liquid: isopropyl alcohol, B liquid: n-hexane
From Table 1 above, the following can be understood.
The powdery adhesive of the present invention can be easily dispersed in a solvent such as isopropyl alcohol or n-hexane, and a good dispersion state is maintained even after 3 days from the dispersion, and the carrier is not peeled off. .
On the other hand, in Comparative Example 1 in which the metal alkoxide is not supported and in Comparative Example 3 in which tetraethoxysilane is supported as the metal alkoxide, aggregated particles are generated after 3 days from dispersion in the solvent.
Further, in Comparative Example 2 in which silica fine particles are supported instead of the metal alkoxide, the silica fine particles peel off immediately after being dispersed in the solvent.
[0057]
【The invention's effect】
The powdery adhesive of the present invention is highly stable in alcohol solvents such as isopropyl alcohol and hydrocarbon solvents such as n-hexane, and is a powder that can be left in a state of being dispersed in a solvent for more than one day. Since the adhesive is not agglomerated, it can be uniformly distributed on the adhesive surface of the liquid crystal display cell without agglomerating the adhesive powder by a highly accurate classification by a sedimentation method or a spraying method.
In particular, the powdery adhesive of the present invention is suitable as an adhesive for electronic materials. For example, as a point adhesive between substrates of a liquid crystal display panel, it exhibits a high adhesive force without impairing display performance, and an excellent liquid crystal display Panels can be made.

Claims (1)

It contains an epoxy resin having two or more epoxy groups in one molecule and a curing agent, and has a metal alkoxide represented by the following general formula (1) and / or a hydrolyzate thereof supported on the surface. Powder adhesive.

(In the formula, M is titanium, zirconium or boron, R is an alkyl group or aryl group having 1 to 8 carbon atoms, n is a valence of M, and a is an integer of 1 to n. .)