JP2015212065A - Flexographic printing plate and method for manufacturing liquid crystal display element using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexographic printing plate having excellent durability, in which a recess can be reliably eliminated by a printing pressure as low as possible without softening or increasing a thickness of an ink transfer layer, and uniform printing with high accuracy can be carried out, and a method for manufacturing a liquid crystal display element using the same.SOLUTION: The flexographic printing plate includes an ink transfer layer formed of a resin containing a slide-ring material. A method for manufacturing a liquid crystal display element is provided, which includes a step of forming a liquid crystal alignment film for a liquid crystal panel substrate by flexographic printing using the above flexographic printing plate.

Description

  The present invention relates to a flexographic printing plate that can be suitably used for forming, for example, a liquid crystal alignment film of a liquid crystal display element by flexographic printing, and a method for producing a liquid crystal display element using the flexographic printing plate.

In order to form a liquid crystal alignment film that is required to have high coating quality, that is, as thin as possible and free from pinholes, etc., on the electrode forming surface of the liquid crystal panel substrate constituting the liquid crystal display element A flexographic printing method with printing properties is used.
A flexographic printing plate used in the flexographic printing method includes a flat ink transfer layer having a printing surface on one side.

  In such a flexographic printing plate, for example, a flexible shaped sheet for constituting the surface shape of a printing surface such as a roughened sheet is set on a solid surface plate such as a glass plate, and an ink transfer layer is formed thereon. For example, by supplying an ultraviolet curable resin as a base and sandwiching it in layers so as to have a constant thickness between the reinforcing sheet and curing by ultraviolet exposure, the shaped sheet is peeled off, etc. (For example, Patent Document 1).

  The flexographic printing plate manufactured through such a manufacturing process is made of a cured product of an ultraviolet curable resin that is shaped into a predetermined surface shape corresponding to the surface shape of the shaped sheet from which one side (printing surface) has been peeled off. It has a two-layer structure of a flat ink transfer layer and a reinforcing sheet laminated on the opposite surface.

JP 2009-34913 A

In the above manufacturing method, for example, foreign matters such as dust are sandwiched between the shaping sheet and the surface plate, and a fine bulge occurs on the surface of the shaping sheet, and such irregular shape marks are transferred to the printing surface. In some cases, a minute recess having a depth of 50 μm or less is formed on the printed surface.
Depending on the shape and size of the dent (spread in the surface direction), the contact pressure (nip stress) to the glass substrate, etc., to be printed may weaken from the surroundings at the dent portion and be sufficiently adhered during flexographic printing. Inability to do so may cause uneven printing. In the case of a liquid crystal alignment film, printing unevenness leads to thickness unevenness and must be avoided as much as possible.

For this reason, efforts have been made to clean the surface of the surface plate and the contact surface of the shaped sheet with the surface plate as much as possible, and to make the work environment for flexographic printing as clean as possible. The occurrence cannot be completely zero.
However, conventionally, since the surface of the glass substrate as a substrate to be printed is relatively flat, it has been possible to alleviate or eliminate the printing unevenness caused by the recessed portions by adjusting the printing pressure.

However, particularly in the high-definition liquid crystal display elements that have been widely used in recent years, the surface of the glass substrate is highly minutely uneven, and extreme adjustment of the printing pressure is restricted to ensure high printing position accuracy. For this reason, the present situation is that printing unevenness cannot be solved only by adjusting the printing pressure.
Therefore, it has been studied to soften the ink transfer layer so that the dent can be eliminated with a small printing pressure. However, such a soft ink transfer layer has low wear resistance and is resistant to ink solvents and cleaning solvents. Since the swelling amount is large, there is a problem that the durability of the flexographic printing plate is lowered.

In other words, the rough surface or the like formed on the printing surface is changed or lost in a short period of time due to wear or swelling, resulting in a decrease in the affinity or retention of the ink on the printing surface, resulting in a short printing thickness. May fluctuate greatly.
Further, the printing accuracy may be reduced due to swelling.
Although it has been studied to increase the thickness of the ink transfer layer so that the dent can be eliminated with a small printing pressure, such a thick ink transfer layer is greatly deformed in the shear direction during printing, and printing accuracy is increased. There is a problem that decreases.

  The object of the present invention is to eliminate the dents with the smallest possible printing pressure without softening or increasing the thickness of the ink transfer layer, and has excellent durability capable of high-precision and non-uniform printing. An object of the present invention is to provide a flexographic printing plate and a method for producing a liquid crystal display element using the same.

The present invention is a flexographic printing plate provided with a flat ink transfer layer having a printing surface on one side, and the ink transfer layer is formed of a resin containing a slide ring material.
Moreover, this invention is a manufacturing method of the liquid crystal display element including the process of forming the liquid crystal aligning film of the board | substrate for liquid crystal panels by flexographic printing using the flexographic printing plate of this invention.

According to the present invention, a slide ring material having an annular (ring) portion that freely slides is blended in a resin forming the ink transfer layer, so that the ink transfer layer is not softened or increased in thickness. In addition, the nip stress at the time of printing can be easily relaxed in the entire nip portion.
In other words, even if a dent is formed on the printing surface, the printing pressure applied to the area around the dent is well propagated to the dent by free sliding of the annular portion of the slide ring material, thereby softening the ink transfer layer. Indentation can be reliably eliminated with as little printing pressure as possible without increasing the thickness.

  Therefore, according to the present invention, it is possible to provide a flexographic printing plate excellent in durability capable of printing with high accuracy and without unevenness, and a method for producing a liquid crystal display element using the same.

<Flexographic printing plate>
The flexographic printing plate of the present invention comprises a flat ink transfer layer having one side as a printing surface, and the ink transfer layer is formed of a resin containing a slide ring material.
(Slide ring material)
As the slide ring material, a polyrotaxane is preferably used in which the opening of a cyclic molecule is skewered by a linear molecule and both ends of the pseudopolyrotaxane are arranged at both ends (both ends of the linear molecule). The

  Examples of the linear molecules constituting the polyrotaxane include polycaprolactone, styrene-butadiene copolymer, isobutene-isoprene copolymer, polyisoprene, natural rubber (NR), polyethylene glycol, polyisobutylene, polybutadiene, polypropylene glycol, poly Examples include tetrahydrofuran, polydimethylsiloxane, polyethylene, polypropylene, and ethylene-polypropylene copolymer.

  Examples of linear molecules include aromatics such as styrene, α-methylstyrene, 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene, 4-cyclohexylstyrene, and 2,4,6-trimethylstyrene. One or more polymers of vinyl compounds, 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 2-phenyl-1,3-butadiene, 1,3-hexadiene It is also possible to use one or more polymers of conjugated diene compounds such as the above, or a copolymer of the aromatic vinyl compound and conjugated diene compound.

Any one of these linear molecules may be used alone, or two or more thereof may be used in combination.
The linear molecule preferably has a molecular weight of about 10,000 to 1,000,000.
Examples of the blocking group that blocks both ends of the linear molecule include one or more of dinitrophenyl groups, adamantyl groups, trityl groups, fluoresceins, pyrenes, and the like.

Examples of the cyclic molecule include one or more of cyclodextrins, crown ethers, benzocrowns, dibenzocrowns, dicyclohexanocrowns and the like.
In particular, one or more cyclodextrins such as α, β, or γ-cyclodextrin and derivatives thereof are preferable.

The polyrotaxane is preferably imparted with ultraviolet curability by introducing a radical reactive group into the side chain of the cyclic molecule.
A polyrotaxane imparted with ultraviolet curability, for example, forms a cross-linked structure by exposure to ultraviolet rays with another ultraviolet curable resin that forms an ink transfer layer, and imparts an appropriate hardness to the ink transfer layer. As described above, the linear pressure and the cyclic molecule slide freely in the cross-linked structure, so that the printing pressure applied to the area around the dent can be propagated well to the dent, and the smallest possible mark can be obtained. It works to reliably eliminate dents with pressure.

Examples of the ultraviolet curable polyrotaxane include Celum (registered trademark) superpolymers SM3405P, SA3405P, and SA2405P manufactured by Advanced Soft Materials. All of these products are supplied as a 70 mass% ethyl acetate solution.
As the ultraviolet curable polyrotaxane, those diluted with a reactive diluent such as an acrylic oligomer are also supplied. Such products include, for example, Celum Key Mixture SM3400C, SA3400C, SA2400C manufactured by Advanced Soft Materials Co., Ltd.

These products may be used alone or in combination of two or more.
The ink transfer layer can also be formed only by a slide ring material such as polyrotaxane. However, the ink transfer layer formed only by the slide ring material is too soft, and there is a risk that the durability of the ink transfer layer may be greatly reduced. Therefore, the ink transfer layer is preferably formed using a slide ring material and at least one other resin in combination.

In such a combined system, the ratio of the slide ring material is preferably 5% by mass or more and 40% by mass or less of the total amount of solids constituting the ink transfer layer.
If the ratio of the slide ring material is less than this range, the effect described above by using the slide ring material may not be sufficiently obtained.
On the other hand, when the ratio of the slide ring material exceeds the above range, the ink transfer layer becomes too soft as described above, and the durability thereof may be greatly reduced.

In addition, as described above, when using a product dissolved in a solvent such as ethyl acetate or a product diluted with a reactive diluent as the slide ring material, the above ratios indicate the solvent or reaction contained in these products. The ratio of the slide ring material itself, excluding the soluble diluent.
(Other resins)
As the other resin for forming the ink transfer layer together with the slide ring material, any of various conventionally known resins used for forming the ink transfer layer can be used.

  For example, other resins used in combination with UV-curable slide ring materials include prepolymers having a 1,2-butadiene structure and having an ethylenic double bond at the end, and an ethylenically unsaturated monomer as a reactive diluent A photosensitive resin composition containing a photopolymerization initiator in a predetermined ratio is supplied, and such a photosensitive resin composition is preferably used in combination as another ultraviolet curable resin.

In such a combination system, the ratio of the sliding ring material to the total amount of the sliding material and the photosensitive resin composition may be set within the range described above.
In addition, when the photosensitive resin composition contains a solvent, the above ratio is the ratio of the slide ring material itself after excluding the solvent.
Examples of the ethylenically unsaturated monomer include one or more of lauryl methacrylate, 1,3-butanediol dimethacrylate, methacrylate in polypropylene glycol, and the like.

  As the photopolymerization initiator, for example, a benzoin alkyl ether such as benzoin butyl ether is preferable, and the ratio of benzoin that causes yellowing of the flexographic printing plate by reacting with visible light from a fluorescent lamp or the like is particularly high in the photosensitive resin composition. Those having a total amount of 500 ppm or less are preferably used. Thereby, it is possible to obtain a flexographic printing plate excellent in weather resistance that does not turn yellow in a short period of time.

(Manufacture of flexographic printing plates)
The flexographic printing plate of the present invention can be produced in the same manner as before except that a slide ring material is used as a material for forming the ink transfer layer.
In other words, a flexible shaping sheet for configuring the surface shape of the printing surface, such as a roughened sheet, is set on a solid surface plate such as a glass plate, on which a slide that becomes the basis of the ink transfer layer Supplying a resin composition containing a ring material and sandwiching it in layers so as to have a constant thickness between the reinforcing sheet and, if the resin is UV curable, is cured by UV exposure and then shaped A flexographic printing plate is produced by peeling the sheet. As described above, when the resin composition contains a solvent, the shaped sheet may be removed after peeling.

As a reinforcing sheet, for example, a sheet made of a thermoplastic resin such as polyethylene (PE), polypropylene (PP), thermoplastic polyurethane (TPU), polyethylene terephthalate (PET), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), etc. Can be used.
<Manufacturing method of liquid crystal display element>
This invention is a manufacturing method of the liquid crystal display element including the process of forming the liquid crystal aligning film of the board | substrate for liquid crystal panels by flexographic printing using the flexographic printing plate of the said invention.

According to the present invention, since there is no unevenness of printing based on the dent generated on the printing surface of the flexographic printing plate, the thickness is uniform, the thickness is reproducible, and the liquid crystal alignment film has high accuracy and no pinholes. A liquid crystal display element can be manufactured.
Other steps of the production method of the present invention can be carried out in the same manner as in the prior art.
That is, a transparent electrode layer corresponding to a predetermined matrix pattern or the like is formed on the surface of a transparent substrate such as a glass substrate, and then a liquid crystal alignment film is formed by flexographic printing using the flexographic printing plate of the present invention. A liquid crystal panel substrate is produced by subjecting the surface of the film to orientation treatment by rubbing or the like, if necessary.

  Next, two liquid crystal panel substrates are prepared, and in a state where the transparent electrode layers are aligned, a liquid crystal material is sandwiched between the two liquid crystal panel substrates and fixed to each other to form a laminate. Further, if necessary, a polarizing plate is disposed on both outer sides of the laminate to produce a liquid crystal display element.

<Example 1>
(Preparation of resin composition)
As the slide ring material, an ultraviolet curable polyrotaxane [Celum Superpolymer SA2405P manufactured by Advanced Soft Materials Co., Ltd., linear molecular weight: 20,000, total molecular weight (representative value): 600,000, Polymerization group amount 0.90 mmol / g (solid), 70 mass% ethyl acetate solution] was used.

A photosensitive resin composition comprising such a polyrotaxane, a prepolymer having a 1,2-butadiene structure and having an ethylenic double bond at the terminal, an ethylenically unsaturated monomer, and a benzoin alkyl ether as a photopolymerization initiator [ NK resin manufactured by Sumitomo Rubber Industries, Ltd.] to prepare a resin composition that becomes the basis of the ink transfer layer.
The ratio of the polyrotaxane was set to 15% by mass of the total amount of the above components excluding the solids constituting the ink transfer layer, that is, ethyl acetate.

(Reinforcement sheet)
As the reinforcing sheet, a PET film [Lumirror (registered trademark) S10 manufactured by Toray Industries, Inc.] was prepared by bonding two sheets having a thickness of 0.25 mm.
(Shaping sheet)
As a shaped sheet, a roughened sheet obtained by roughening the exposed TPU surface of a TPU sheet having a 100 μm-thick PET sheet bonded on one side [Silkron (registered trademark) SNESS80 manufactured by Okura Kogyo Co., Ltd. −150 μm].

(Manufacture of flexographic printing plates)
The roughened sheet was set on a glass plate as a surface plate. At this time, fine bulges were formed on the surface of the roughened sheet by intentionally sandwiching foreign substances of various sizes between them.
Next, the resin composition prepared above is supplied onto the roughened sheet, and then the ultraviolet ray is exposed in a state where the reinforcing sheet is overlapped and held so as not to generate a gap with an interval of about 2.4 mm. The resin composition was cured.

Flexographic printing in which the roughened sheet is peeled off and dried to form a rough surface corresponding to the rough surface of the roughened sheet and a minute dent corresponding to the rising of the roughened sheet. A plate was produced.
The depth of the dent was set to 6 types of 10 μm, 25 μm, 50 μm, 75 μm, 100 μm, and 150 μm.

<Example 2>
A resin composition serving as the basis of the ink transfer layer was prepared in the same manner as in Example 1 except that the ratio of the polyrotaxane was set to 5% by mass of the total amount of solids constituting the ink transfer layer, and flexographic printing was performed. A plate was produced.
<Example 3>
A resin composition serving as the basis of the ink transfer layer was prepared in the same manner as in Example 1 except that the ratio of the polyrotaxane was set to 40% by mass of the total amount of solids constituting the ink transfer layer, and flexographic printing was performed. A plate was produced.

<Example 4>
A resin composition serving as the basis of the ink transfer layer was prepared in the same manner as in Example 1 except that the ratio of the polyrotaxane was set to 50% by mass of the total amount of solids constituting the ink transfer layer, and flexographic printing was performed. A plate was produced.
<Comparative example 1>
Flexographic printing is carried out in the same manner as in Example 1 except that only a photosensitive resin composition containing no polyrotaxane (NK resin manufactured by Sumitomo Rubber Industries, Ltd.) is used as the resin composition for the ink transfer layer. A plate was produced.

<Real machine test>
(Flexo printing)
A flexographic printing plate (G3 machine manufactured by Nakan Techno Co., Ltd.) is attached to the flexographic printing plate produced in each of the examples and comparative examples, and an anilox roll # 400 is incorporated in the flexographic printing machine, and a chromium vapor deposition film The liquid crystal alignment film was formed by flexographic printing on the surface of the glass substrate on which the liquid crystal alignment film was formed. The initial thickness of the liquid crystal alignment film was set to 900 mm.

(Evaluation of unevenness)
The portions of the printed liquid crystal alignment film corresponding to the indentations of the flexographic printing plate were checked for unevenness in thickness at the indentations at the respective depths.
When the unevenness of the thickness of the liquid crystal alignment film was eliminated in the dent having a depth of 50 μm or less, it was evaluated as good (◯), and when it was not eliminated even in the dent having a depth of 50 μm or less, it was evaluated as defective (×).

(Durability evaluation)
The flexographic printing was continuously performed, and the change in the thickness of the printed liquid crystal alignment film was continuously measured. Then, the number of printed sheets when the thickness was less than 800 mm was counted as the number of printed sheets, and the durability of the flexographic printing plate was evaluated according to the following criteria.
○: More than 20,000 sheets. Good durability.

Δ: 15,000 sheets or more and less than 20,000 sheets. Normal durability level.
X: Less than 15,000 sheets. Poor durability.
(Comprehensive evaluation)
What was x in either of the above unevenness and durability evaluation was poor (x), △ two, or ◯ and △ were normal level (△), ◯ two It was evaluated as good (◯).

  The results are shown in Table 1.

From the results of Examples 1 to 4 and Comparative Example 1 in Table 1, by forming the ink transfer layer with a resin containing a slide ring material, the dents are reliably eliminated with a small printing pressure, and high-precision and uniform printing is achieved. Was found to be possible.
Further, from the results of Examples 1 to 4, in consideration of improving the durability of the flexographic printing plate while maintaining this effect, the ratio of the slide ring material is 5 mass of the total amount of solids forming the ink transfer layer. It was found that the content is preferably not less than 40% and not more than 40% by mass.

Claims (6)

  A flexographic printing plate comprising a flat ink transfer layer having one side as a printing surface, wherein the ink transfer layer is formed of a resin containing a slide ring material.   The flexographic printing plate according to claim 1, wherein the ink transfer layer is made of a cured product of an ultraviolet curable resin including an ultraviolet curable slide ring material.   3. The flexographic printing plate according to claim 1, wherein the slide ring material is a polyrotaxane in which capping groups are arranged at both ends of a pseudopolyrotaxane in which openings of a cyclic molecule are included in a skewered manner by linear molecules. .   The flexographic printing plate according to claim 3, wherein the polyrotaxane is imparted with ultraviolet curability by introducing a radical reactive group into a side chain of the cyclic molecule.   The flexographic printing plate according to any one of claims 1 to 4, wherein the resin forming the ink transfer layer contains a slide ring material in a proportion of 5% by mass or more and 40% by mass or less.   A method for producing a liquid crystal display element, comprising a step of forming a liquid crystal alignment film of a substrate for a liquid crystal panel by flexographic printing using the flexographic printing plate according to any one of claims 1 to 5.