JPS5934283B2 - Polarizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improving the practical characteristics of a polarizing plate with a pressure-sensitive adhesive used in a liquid crystal display device.

In recent years, as electronic watches, electronic desktop calculators, etc. have become smaller and lighter, their display devices are being replaced with conventional light-emitting diode displays, which are thinner and consume less power, such as liquid crystal display devices.

The structure of this liquid crystal display device is generally such that polarizing plates are attached to both sides of a liquid crystal panel using a pressure-sensitive adhesive or an adhesive so that their polarization axes are perpendicular to each other. The polarizing plate currently used in such liquid crystal display devices is a polarizing film made of a polyvinyl alcohol film that adsorbs and aligns iodine, etc. Cellulose diacetate, triacetic acid It is made by laminating cellulose-based films such as cellulose.

A pressure-sensitive adhesive is usually used to bond the polarizing plate and the liquid crystal panel.

Then, the liquid crystal display device formed by bonding the polarizing plate and the liquid crystal panel was heated at 9°C for 100 hours and heated at 65°C.
When an accelerated test is carried out at ℃ for 24 hours (95% R.H.), foaming occurs at the interface between the pressure-sensitive adhesive and the polarizing plate, interfacial peeling occurs, and the polarizing plate deteriorates. It has the disadvantage that it curls and stands out.

On the other hand, in addition to the above-mentioned property problems, conventional polarizing plates with pressure-sensitive adhesive layers have problems in cutting processing.

That is, in order to adhere a polarizing plate to a liquid crystal panel, an original sheet of the polarizing plate with a pressure-sensitive adhesive layer (for example, 500 mm square) is punched out to a desired size using a cutting die, and then adhered to the liquid crystal panel.

There is a problem in that fine whisker-like burrs due to the double cut of the lever during punching, and fine cracks and cracks due to the pressure of the blade during punching occur on the cut surface of the polarizing plate.

These cracks and cracks not only reduce the product yield, but also become a source of dust in subsequent work processes, and this dust is attached to the interface when the polarizing plate is attached to the liquid crystal panel, causing damage to the polarizing plate. It has drawbacks such as lifting from the liquid crystal panel and causing bubbling at the interface.

Most of these drawbacks are thought to be due to the characteristics of the cellulose film used as the surface protection film of the polarizing plate.

The reason why cellulose-based films are still being used despite the known drawbacks is that there have been no known films that are optically transparent, have no orientation, and do not inhibit polarization properties as surface protection materials for polarizing plates. This is due to the fact that there is no such thing.

The inventors of this invention were able to overcome all such drawbacks and
In other words, we conducted various studies on resins that satisfy the following conditions: optical transparency, no orientation and no inhibition of polarization, moisture resistance, and good compatibility with pressure-sensitive adhesives. Ta.

As a result, it was found that using a polarizing plate in which a coating layer made of urethane resin was formed on the polarizing film surface could sufficiently withstand accelerated tests under heating or heating and humidification.

However, a polarizing plate made by forming a coating layer made of urethane resin on a polarizing film and further applying a pressure-sensitive adhesive has characteristics that can sufficiently withstand accelerated tests, but it suffers from the aforementioned problems in cutting processing. turned out to be unsolvable.

That is, as a surface protection film for a polarizing film, the apparent elastic modulus at room temperature is 400K7/MTU. When a polarizing plate with a pressure-sensitive adhesive layer on which a hard urethane resin coating layer is formed is punched out with a blade, fine cracks and cracks will occur on the cut end surface, and the elastic modulus will decrease. 200 Immediate/i
When a polarizing plate on which a relatively soft urethane resin coating layer is formed is punched out with a blade die, the above-mentioned cracks will not occur, but burrs will occur. It had the same drawbacks as when it was pasted. Based on this knowledge, the inventors conducted further studies on a polarizing plate that takes advantage of the optical transparency of urethane resin and has good cutting processability. A pressure-sensitive adhesive layer formed on the surface of a polarizing film with a multilayered urethane resin composite layer having a layer with a low apparent elastic modulus at room temperature as the contacting inner layer, and a multilayer urethane resin composite layer with an elastic modulus at least 40/〒 higher than the inner layer as the outer layer. It was discovered that the punching characteristics of a polarizing plate with a polarizing plate were significantly improved, leading to the present invention. That is, in this invention, a composite layer consisting of two or more types of urethane thin film layers and a transparent pressure-sensitive adhesive are formed on one or both sides of a polarizing film made of a polyvinyl alcohol film, and the outer layer of the composite layer is The inner layer is at room temperature (20
The present invention provides a polarizing plate having an apparent elastic modulus of at least 40K7/↑ in 'C). The polarizing plate of the present invention not only has good cutting workability, but also exhibits excellent properties in which no foaming, lifting, or peeling is observed in accelerated tests conducted after pasting it on a liquid crystal panel. This is a characteristic that cannot be expected from a polarizing plate with a pressure-sensitive adhesive layer formed by forming a single coating layer of urethane resin on the surface of the polarizing plate.

The urethane resin used in this invention has 2
It is a resin obtained by the reaction of a compound having 1 or more NCO groups and a hydroxyl group-containing compound.

As the polyisocyanate compound having an NCO group, (1) aliphatic diisocyanates such as ethylene diisocyanate, 1,4-butane diisocyanate, 1,6-hexane diisocyanate, and modified products thereof;
(2) Alicyclic isocyanates such as synchrohexylmethane diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate and modified products thereof, (3) 2.4- and 2.6-tolylene diisocyanate, methylene diphenyl diisocyanate, 4.4 /-diphenylmethane diisocyanate, m-
One or more of aromatic diisocyanates such as xylylene diisocyanate and modified products thereof, and (4) aromatic triisocyanates such as triphenylmethane triisocyanate and modified products thereof are used. Further, as a hydroxyl group-containing compound, as a polyol, (1) diol type such as mono-di or tri-ethylene mono- or -propylene glycol, 1,4-butanediol S2, 2-bis-(4-hydroxylhexyl)propane, Alternatively, triol polyols such as glycerin, hexanetriol, trimethylolpropane, trimethylolethane, and trimethylolbenzene, (2) copolymers of adipic acid, succinic acid, phthalic acid, terephthalic acid, or acrylic acid and maleic acid, etc. Polyester polyols which are condensation products of polycarboxylic acids and said polyols, (3) glycerade esters of castor oil or other hydroxylated fatty acids, (4) polyalkylene glycols such as polyethylene glycol, polypropylene glycol. or (5) a hydroxyl group-containing polymer or oligomer such as an epoxy-modified compound, a terminally hydroxylated polybutadiene, or a hydroxyethyl acrylate copolymer.

For the purpose of this invention, the urethane resin obtained by the reaction of a compound having an NCO group and a compound containing a hydroxyl group has a cross-linking number whose apparent elastic modulus at room temperature is adjusted by adjusting the degree of reaction of the resin. By increasing or decreasing the amount of urethane resin, or by lengthening or shortening the molecular chains between crosslinks, it is possible to adjust the elastic modulus of the urethane resin thin film after layer formation to be used.

The urethane resin, whose apparent elastic modulus at room temperature of the urethane resin thin film after layer formation has been adjusted in advance, is applied to one or both sides of a polarizing film that is oriented by adsorbing iodine to a polyvinyl alcohol film. , a solvent that does not inhibit the polarization properties of the polarizing film, such as ethyl acetate, butyl acetate, cellosolve acetate, methyl glycol acetate,
The solution is diluted with ethyl glycol acetate, methoxybutyl acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methylene chloride, toluene, xylene, mineral spirits, cresol, furfural, naphtha, etc. to the desired solution viscosity, and applied to the polarizing film surface at room temperature. The coating is applied and cured to form a composite structure consisting of two or more urethane resin thin film layers having different apparent moduli of elasticity.

However, such a composite structure is formed by selecting the urethane resin forming each layer so that the outer resin thin film layer has an apparent elastic modulus of at least 40 Kf/1 at room temperature than the inner resin thin film layer. be done.

The composite is made by applying a urethane resin solution whose apparent elastic modulus at room temperature of the urethane resin thin film after layer formation has been measured and hardening it to the surface of the polarizing film to form an inner layer, and then Modulus of elasticity after layer formation is at least 40
It is obtained by coating a solution of a bulky urethane resin on the inner layer and curing it to form the outer layer.

The inner layer is firmly adhered to the polarizing film surface by applying a urethane resin solution to the polarizing film surface so that the thickness after coating and curing is 1 to 140 μm, preferably 5 to 60 μm, and then drying and curing. It is formed in a state of

Drying and curing conditions vary depending on the type of resin and solvent used, and the presence or absence of a curing catalyst, but are usually 80 to 130'C.
The process lasts from several seconds to several hours. The apparent elastic modulus of the inner layer at room temperature varies depending on the elastic modulus of the outer layer, which will be described later, but after layer formation, the apparent elastic modulus is 5 to 500 Kf/m, preferably 10 to 2.
It is preferable to use a urethane resin in the range of 0.00 ml/ml. Further, the outer layer must have an apparent elastic modulus at room temperature of at least 40K7/m higher than that of the inner layer.

The outer layer is strongly laminated and adhered to the inner layer, and the thickness after coating and curing is preferably in the range of 5 to 60 microns, preferably 10 to 40 microns. If the outer layer is less than 5μ, the formed effect will be weak and burrs will often occur on the inner layer when punching the polarizing plate with a blade die, and if it is more than 60μ, cracks such as cracks will occur during punching, so it is preferable. It's something that doesn't exist.
The outer layer has an apparent elastic modulus of 50 to 100 at room temperature after layer formation.
From the viewpoint of mechanical strength, it is preferable to use a urethane resin having a value of 0K7/MlE or 200 to 700Kf/M7l. Therefore, an intermediate layer having a thickness of 1 to 70 μm after coating and curing, preferably 5 to 50 μm, can be provided between the inner layer and the outer layer, and in this case, the thickness of the inner layer is 1 to 1 μm.
00μ, preferably 5 to 40μ.

As can be seen from the above explanation, the apparent elastic modulus of the intermediate layer at room temperature after layer formation is at least 40 greater than that of the inner layer.
At least 40Kf/Mit from its outer layer
A low urethane resin is selected and used. The polarizing plate of the present invention has a composite layer composed of two or more urethane resin thin film layers formed on one or both sides of a polarizing film, and the outer layer has a higher apparent elastic modulus at room temperature than the inner layer. It is characterized by having a structure formed by compositely forming a urethane resin thin film layer with a high urethane resin thin film layer of at least 40 instant/↑, therefore, the method for forming a composite layer consisting of a urethane resin thin film layer is also the same as described above. In addition to the coating and curing method, methods such as a multi-layer simultaneous coating method and a depping method are also effective.

Furthermore, urethane resins with different apparent moduli of elasticity at room temperature after layer formation can be obtained by adjusting the number of crosslinks or molecular chains as described above, but it is possible to obtain urethane resins with different apparent moduli of elasticity at room temperature by adjusting the number of crosslinks or molecular chains as described above. The inner layer, outer layer and intermediate layer can be formed by selecting and combining materials having a unique difference in elastic modulus of at least 40 mm/Md, and utilizing this difference in elastic modulus. Next, a transparent pressure-sensitive adhesive layer is formed on the surface of the urethane resin composite layer by a commonly known method. The adhesive layer includes acrylic esters such as butyl acrylate, ethyl acrylate, methyl acrylate, 2-ethylhexyl acrylate, etc. and α-monoolefin carboxylic acids such as acrylic acid, maleic acid, itaconic acid, methacrylic acid, crotonic acid. Copolymers (including those with additions of acrylonitrile, vinyl acetate, styrene, etc.) have excellent compatibility with the resin composite layer and do not interfere with the polarizing properties of the polarizing film. Therefore, it is particularly preferable, but the adhesive is not particularly limited to this, and many other transparent pressure-sensitive adhesives may be used, such as polyvinyl ether type, rubber type, etc. The adhesive layer is made of a polyethylene terephthalate film having a smooth surface with a surface roughness of 1.5 μm or less (average height between peaks and valleys of unevenness within a stylus-type surface roughness meter of 2 mm). It can be formed by forming a substantially air-free state in advance on the smooth surface of a release material made of a heat-resistant release film, and then bonding this to the surface of the resin composite layer without enclosing air bubbles.

Therefore, even if it is applied directly to the resin composite surface, it can be formed in a substantially bubble-free state. Note that at least one layer constituting the composite layer made of the urethane resin or each of the pressure-sensitive adhesive layers is coated with an ultraviolet absorber such as a benzophenone type, a benzotriazole type, or a metal chelate type (preferably with an absorption wavelength range of about 300 nm). ~500 mμ) is effective because it prevents deterioration of polarizing films, liquid crystal elements, etc. The polarizing plate of the present invention has excellent optical transparency, moisture resistance, and cutting workability, and since a transparent pressure-sensitive adhesive layer of uniform thickness is formed on the surface of the resin composite layer, it can withstand harsh conditions such as heating or humidification. It is a suitable adhesive type polarizing plate that does not cause floating, peeling, or foaming even under the liquid crystal panel, is easy to attach to a liquid crystal panel, and contains few air bubbles.

Examples of the present invention will be shown below, but the present invention is not limited to the following examples.

In the text, % or parts indicate weight units. Example
1. Polyvinyl alcohol film (trade name, Kuraray Vinylon Film #7500) was immersed for 3 minutes in an aqueous solution adjusted to an iodine concentration of 1%, a potassium iodide concentration of 2%, and a boric acid concentration of 470, and then heated at 50°C for 3 minutes. The film is stretched up to 4 times, washed with water and dried in that state to produce a polarizing film.

The average transmittance of this film in the visible light range is 42%.
, the degree of polarization is 95%. On the other hand, both sides of the above film were immersed in a bath containing a thin film forming solution of the following formulation (a) so that the thickness after drying would be the value shown in Table 1, dried at 80°C for 20 minutes, and the urethane-based resin A thin film-like inner layer was formed.

The apparent elastic modulus of this inner layer at room temperature (20°C) is 10
There is 0 immediate/ML. Further, both sides of the film with the urethane resin thin film formed as the inner layer were immersed in a bath of a thin film forming solution having the following formulation (b) so that the thickness after drying would be the value shown in Table 1. It is dried at ℃ for 30 minutes to form a thin film-like outer layer, and the matrix AO, B of the polarizing plate of the present invention is formed.
l and C1 are obtained.

The elastic modulus of the outer layer is 400K7/Mlll. Note that the first
B shown in the table was immersed twice in the solution bath of formulation (a) under the same conditions as above, and then twice immersed in the solution bath of formulation (b) under the same conditions as above. Similarly, C1 was dipped once in formulation (a) and three times in formulation (b). Blend (a) Styrene ptadiene oligomer 100 parts (manufactured by Arco, USA, trade name CS-15) Tolylene diisocyanate modified product 95 parts dibutyltin silaurate
0.02 parts toluene 3
00 parts blend (b) Polyester polyol 50 parts Tolylene diisocyanate modified product 100 parts Ethyl acetate
50 parts butyl acetate
50 parts ethyl glycol acetate
50 parts toluene 200
The apparent elastic modulus at room temperature is room temperature (20℃) x 6
5%R. H. A sample was measured using the following formula under the following conditions.

However, F: Force required to stretch the sample (K9/!1L
711) S: Cross-sectional area of the sample Δ': Extended length of the sample': Original size of the sample A transparent pressure-sensitive adhesive layer is formed on the urethane resin outer layer of the polarizing plates Al, Bl and C1, and this invention Polarizing plates A2, B2 and C2 with adhesive layers are obtained.

The adhesive was formed on the polarizing plates Al, Bl and C1 by applying 100 parts of a copolymer of 2-ethylhexyl acrylate and methacrylic acid to one side of a polyethylene terephthalate film having a surface roughness of 0.3μ and a thickness of 50μ. 2 parts of triepoxypropyl isocyanate, 400 parts of toluene
A pressure-sensitive adhesive layer was formed by coating the adhesive solution to a dry thickness of about 20μ and drying at 140°C for 14 minutes to form a pressure-sensitive adhesive layer.
It is completed by pasting them together via an adhesive layer.

As for its properties, Table 1 shows the cutting workability, Table 2 shows the heat foaming test, and Table 3 shows the floating test. Example 2 The polarizing film of Example 1 was placed in a bath of a thin film forming solution having the following composition (c), so that both sides of the polarizing film had a dry thickness of 5.
20 minutes at 80℃ to form a thin film-like inner layer, and then similarly immersed in a solution bath of formulation (d) to form a 5μ thin film-like intermediate layer on the inner layer surface. and blend (
A thin film-like outer layer having a thickness of 25 μm is formed by immersing it in the solution bath of (e) to obtain a matrix D1 of the polarizing plate of the present invention.

The apparent elastic modulus of this urethane resin at room temperature is 20 Kf/Md for the inner layer, 120 Kf/Md for the intermediate layer, and 430 Kf/Md for the outer layer. Blend (c) Putadiene oligomer 100 parts (manufactured by Arco, USA, trade name R-45HT) Tolylene diisocyanate modified product 1 part dibutyltin dilaurate
0.02 parts toluene
500 parts mixture (d) Putadiene oligomer (same as above) 100 parts modified tolylene diisocyanate 10 parts toluene
500 parts blend (e) Polyester polyol 50 parts Adduct of hexamethylene diisocyanate and 150 parts water Ethyl acetate 50 parts Butyl acetate 50 parts Ethyl glycol acetate 100 parts Toluene
200 copies On the other hand, the pressure sensitive adhesive of Example 1 is formed on the outer layer surface of polarizing plate D1 in the same manner as in Example 1 to obtain polarizing plate D with an adhesive layer.

Its properties are shown in Tables 1-3. Comparative Example 1 The polarizing film used in Example 1 was placed in a bath of the thin film forming solution of formulation (A) used in Example 1, and the thickness after drying was 1.
Soaked three times to obtain the values shown in the table and at 80°C each time.
was dried for 20 minutes to form a single layer of urethane resin to create a polarizing plate matrix E1, and the pressure sensitive adhesive of Example 1 was formed on this layer surface in the same manner as in Example 1 to form an adhesive layer. A polarizing plate E is obtained.

Comparative Example 2 A polarizing plate F2 is obtained in the same manner as in Comparative Example 1, except that the polarizing plate matrix F is made using the formulation (b) of Example 1 as a thin film forming solution.

Comparative Example 3 Cellulose triacetate film with a thickness of 80 μm was coated with vinyl acetate adhesive (thickness: 5 μm) on both sides of the polarizing film used in Example 1.
μ) to prepare a polarizing plate matrix G1, and the pressure sensitive adhesive of Example 1 was formed on the surface of this cellulose film in the same manner as in Example 1 to form a polarizing plate G1 with an adhesive layer. , get.

Cutting workability measurement method: Punch out 10 sheets of polarizing plate (A2-{2) into 5 square pieces using a Thomson type punching machine, and observe the cut end surface of the punched polarizing plate with a 20x magnifying glass. Then, count the number of sheets with cracks and burrs.

Test method A sample body (a 25 mm square sample pressed with a 1Kf rubber roll onto a slide glass whose surface had been cleaned with toluene) was stored for a certain period of time in a hot air dryer (90°C) set to the test conditions. The foaming state at the interface between the glass and the glass was observed using a 20x magnifying glass.

Test method: Store the sample (same as in Table 2) for a certain period of time in a constant temperature and humidity chamber (65°C , 25
The discrimination was made visually from a distance of c1rL.

Claims (1)

[Claims] 1. A composite layer consisting of two or more urethane resin thin film layers and a transparent pressure-sensitive adhesive layer are formed on one or both sides of a polarizing film made of a polyvinyl alcohol film, and the composite layer is made of a transparent pressure-sensitive adhesive layer. The outer layer of the layer is at room temperature (
apparent modulus at 20°C) of at least 40 Kg/m
A polarizing plate characterized by having a height of m^2. 2 A composite layer consisting of a urethane resin thin film layer is laminated and adhered to a urethane resin thin film layer with a thickness of 1 to 140 μm that is firmly adhered to the polarizing film surface, and the inner layer has an elastic modulus at room temperature than that of the inner layer. The polarizing plate according to claim 1, comprising a urethane resin thin film outer layer having a thickness of 1 to 60 μm and having a thickness of at least 40 kg/mm^2. 3 A composite layer consisting of a urethane resin thin film layer is firmly adhered to the polarizing film surface, and has a urethane resin thin film inner layer with a thickness of 1 to 100 μm, and is laminated and adhered to the inner layer, and has an apparent elastic modulus at room temperature than that of the inner layer. is at least 40Kg/mm^
2. A urethane resin thin film intermediate layer having a thickness of 1 to 70 μm, and a layer having a thickness of 1 to 70 μm that is laminated and bonded to the intermediate layer and has an apparent elastic modulus at room temperature of at least 40 Kg/mm^2 higher than that of the intermediate layer.
The polarizing plate according to claim 1, comprising a urethane resin thin film outer layer having a thickness of 60 μm. 4 The inner layer of the composite layer consisting of a urethane resin thin film layer is 5~
The polarizing plate according to claim 2 or 3, which has an apparent elastic modulus at room temperature of 500 Kg/mm^2. 5 The outer layer of the composite layer consisting of a urethane resin thin film layer is 50
The polarizing plate according to claim 2 or 3, which has an apparent elastic modulus at room temperature of ~1000 Kg/mm^2. 6 The intermediate layer of the composite layer consisting of urethane resin thin film layer is 3
The polarizing plate according to claim 3, which has an apparent elastic modulus at room temperature of 0 to 700 Kg/mm^2. 7 The inner layer of the composite layer consisting of a urethane resin thin film layer is a urethane resin in which a polyisocyanate compound is reacted with one or more selected from the group of epoxy modified compounds, terminal hydroxylated polybutadiene, and hydroxyethyl acrylate copolymers. A polarizing plate according to claim 1, which is comprised of: 8. The polarizing plate according to claim 1, wherein the transparent pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive.