JP2008150484A - Composition for hard coat - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hard coat having excellent surface hardness, not generating a crack at curing and not causing a problem such as warpage and curl of a film relative to a plastic film. <P>SOLUTION: The composition for hard coat contains (A) hexa-functional urethaneacrylate: 20-70 pts.wt., (B) tetra-functional or more of (meth)acrylic monomer: 15-60 pts.wt., (C) colloidal silica surface-treated by a silane coupling agent having a reactive (meth)acrylate group in the molecule: 10-40 pts.wt., (D) a photopolymerization initiator, and (E) a dilution solvent. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical film such as a flat panel display, and further to a surface protective coating on a transparent plastic substrate represented by polycarbonate and acrylic.

  For optical disks such as compact disks and magneto-optical disks, transparent substrates such as polycarbonate and polymethacrylate are used, and in particular, polycarbonate which is excellent in terms of workability, handleability and cost is used. However, it has advantages such as light weight and excellent impact resistance, but it has insufficient hardness and scratch resistance and is easily scratched. In particular, it can read information due to scratches and scratches on the reading surface. There was a problem of disappearing. In next-generation DVDs such as DVD, Blu-ray, and HDDVD, polycarbonate increases because the amount of recorded information per unit area increases, and fine scratches on the reading surface are more easily connected to reading defects. It is necessary to further provide a hard coat layer on the transparent plastic protective base material. As the performance required for such a hard coating film, sufficient surface hardness, abrasion resistance, scratch resistance, transparency and the like can be mentioned. In order to meet such requirements, Patent Document 1 proposes an acrylate-based composition containing colloidal silica treated with a specific silane coupling agent, and Patent Documents 2 to 4 also include a specific composition containing silica. Acrylate compositions have been proposed.

  On the other hand, in recent years, various flat panel displays such as liquid crystal panels have been developed. In the liquid crystal panel, triacetyl cellulose (TAC) having excellent optical properties is used to protect the polarizing plate, and in the plasma display panel, a plastic film layer such as polyethylene terephthalate (PET) is formed. Since such a plastic film is softer than glass and easily scratched on the surface, it is necessary to provide a hard coat layer. In particular, a hard coat for a plastic film used for such applications is required to have a higher surface hardness than the above-described conventional hard coat, and further, it is required not to cause warping or cracking of the film due to curing shrinkage.

As a hard coat for such a plastic film, Patent Document 5 proposes a hard coat agent containing colloidal silica and an isocyanate compound having an isocyanate group and a polymerizable unsaturated group. It was not enough.
JP-A-57-13214 JP 2002-245672 A JP 2003-338089 A JP 2006-63244 A JP 2005-163035 A

  The present invention provides a hard coat that solves the above-mentioned problems of the prior art, has a further improved surface hardness, does not cause cracks during curing, and does not cause problems such as warping or curling of the plastic film. With the goal.

  As a result of diligent research to solve the above-described problems of the prior art and to provide a hard coating agent having both hardness and low curing shrinkage, the present inventors have found that a hexafunctional urethane acrylate, a tetrafunctional or higher acrylic monomer, and a specific surface. It has been found that combining treated colloidal silica is extremely effective, and the present invention has been completed.

That is, the present invention
(A) Hexafunctional urethane acrylate; 20 to 70 parts by weight
(B) Tetrafunctional or higher (meth) acrylic monomer; 15-60 parts by weight
(C) Colloidal silica surface-treated with a silane coupling agent having a reactive (meth) acrylate group in the molecule; 10 to 40 parts by weight
(D) Photopolymerization initiator
(E) A hard coat composition containing a diluting solvent.

  Hereinafter, the present invention will be described in detail. The component (A) used in the present invention is a urethane acrylate having 6 or more functional groups, and is composed of a urethane skeleton having 6 or more reactive acrylate groups in one molecule. For example, it can be prepared in the form described in Japanese Patent No. 2964267, or a commercially available product as a single product or a mixture with an acrylate monomer can be used. Examples of commercially available products include urethane acrylates “purple light UV-1700B”, “purple light UV-6300B”, “purple light UV-7640B” manufactured by Nippon Synthetic Chemical Co., Ltd. "UA-306H" etc. are mentioned. These urethane acrylates having 6 or more functional groups are characterized by high hardness and less cure shrinkage than hexafunctional acrylic monomers.

  Component (B) used in the present invention is a tetrafunctional or higher polyfunctional (meth) acrylate monomer, and dipentaerythritol hexaacrylate, pentaerythritol pentaacrylate, which has been conventionally used as an acrylic resin raw material for hard coat, Examples include dipentaerythritol pentaacrylate, pentaerythritol tetraacrylate, and dipentaerythritol tetraacrylate. These monomers can achieve an improvement in the curing rate, a reduction in the viscosity of the liquid, and an improvement in the compatibility of the composition without reducing the hardness of the hard coat. In particular, dipentaerythritol hexaacrylate alone has defects such as cracks in the film, but is particularly useful for improving hardness in this system.

  The component (C) surface-treated silica used in the present invention is colloidal silica surface-treated with a silane coupling agent having a reactive (meth) acrylate group in the molecule, and disclosed in JP-A-57-131214. This is a well-known one described in Japanese Patent Laid-Open No. 2000-289172. This component improves the hardness of the hard coat composition, suppresses curing shrinkage, and suppresses the generation of cracks in the coating during curing as much as possible. Moreover, the mechanical strength regarding bending etc. of said polyfunctional acrylic resin can be improved by adding this component.

  In the present invention, the blending amount of the components (A) to (C) is (B) component: 15 to 60 parts by weight, (C) component; 10 to 40 parts by weight with respect to (A) component 20 to 70 parts by weight. It is. When outside this range, for example, when the amount of component (A) is small, insufficient hardness occurs, polymerization during curing does not proceed completely, and insufficient mechanical strength occurs. When there are many cases, there are defects such as cracks in the film. When the amount of the component (B) is small, the hardness is lowered and the compatibility of the composition may be impaired. In many cases, there is a problem that cracks are easily formed in the film during curing, and the mechanical strength of the film becomes weak and brittle. When the amount of the component (C) is small, the hardness is lowered and the film is likely to be cracked. When the amount is large, the polymerization reaction at the time of curing is delayed, and there is a problem that the hardness is lowered by the amount not completely cured.

  In order to suppress curling of the film, 20-30 parts by weight of bifunctional dimethylol dicyclopentane diacrylate having a ring structure in the molecule with respect to 100 parts by weight of the total amount of (A) to (C). However, when it is added more than this, there is a problem that the hardness is remarkably reduced. Moreover, in the bifunctional acrylate which does not have a ring structure, the malfunction which hardness falls even if it adds a little is recognized.

  As the (D) photopolymerization initiator used in the present invention, any known publicly available one can be used, but in order to ensure transparency particularly in the visible region, the maximum wavelength peak of UV absorption is 400 nm. The following are desirable: As such a polymerization initiator, acetophenone-based 1-hydroxy-cyclohexyl-phenyl ketone, 2,2-dimethoxy-1,2-diphenylethane-1-one, 2-hydroxy-2-methyl-1-phenyl-propane -1-one, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone -1-one, phosphine oxide-based 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, benzophenone and polymerization accelerators ethyl-4-dimethylaminobenzoate, 2-ethylhexyl-4-dimethylaminobenzoate Combinations such as these can also be used. These may be used singly or a plurality of them may be combined to optimize the curing conditions according to the light source during photocuring. In particular, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, which is liquid and easy to handle, is desirable because it is liquid and easy to handle, and is used by previously dissolving other polymerization initiators as described above. You can also The blending amount is an amount necessary for the initiation of photopolymerization and is not particularly limited, but generally 1 to 10 parts by weight is desirable with respect to 100 parts by weight of the total amount of the components (A) to (C), and the curing rate 3 to 8 parts by weight is more desirable in view of the balance with the stability over time.

  The (E) dilution solvent used in the present invention includes alcohol solvents such as isopropanol, butanol and 1-methoxy-2-propanol, aromatic solvents such as toluene and xylene, ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, and ethyl acetate. Well-known generally available solvents such as ester solvents such as butyl acetate can be used, and they can be used alone or in a mixed solvent system. In particular, butanol and 1-methoxy-2-propanol can be used for surface treatment of colloidal silica and azeotropic distillation of water, the synthesis process can be simplified, and the erosion of the polycarbonate substrate is further suppressed. It is desirable because transparency of the film can be easily secured. Further, when methyl ethyl ketone is used, it is possible to improve the adhesion to the triacetyl cellulose film without adding a special adhesion component.

  For the composition of the present invention, a surfactant can be used in order to improve wettability and leveling to the substrate. In particular, polyether-substituted silicone surfactants have excellent compatibility with the composition and can impart excellent leveling properties. Examples of such surfactants include trade names “BYK300” and “BYK302” manufactured by Big Chemie Japan.

  The hard coat film of the present invention may contain an antistatic agent, a matting agent, an ultraviolet stabilizer and a dye as desired. Any of these compounds can be used as long as it does not adversely affect the photocuring of the hard coating agent and does not adversely affect the transparency or translucency. Furthermore, in order to maintain hardness, the addition amount is desirably 0.1 to 10 parts by weight with respect to 100 parts by weight of the hard coating agent. When the amount is less than this, the antistatic effect and the ultraviolet ray absorbing effect cannot be expected, and when the amount is larger, the decrease in hardness and scratch resistance becomes remarkable. Especially for antistatic agents, matting agents, UV stabilizers and dyes that do not have a structure with a chemical bond with a binder resin such as an acrylic functional group, since the decrease in hardness becomes more remarkable, the amount added is a hard coating agent. 5 parts by weight or less is desirable with respect to 100 parts by weight.

  In order to produce the hard coating agent used in the present invention, aqueous colloidal silica (colloidal silica aqueous dispersion), silyl (meth) acrylate, urethane acrylate having 6 or more functional groups, a polyfunctional acrylic monomer or a mixture thereof, Any of the photoinitiators and other additives described above are incorporated as desired. Colloidal silica can be similarly dispersed in an alcohol solvent in advance, and examples of alcohol include methanol, ethanol, isopropyl alcohol, and 1-methoxy-2-propanol. The colloidal silica preferably has a primary particle size of 30 nm or less, particularly 25 nm or less in order to ensure film transparency.

  In the first step, silyl acrylate is hydrolyzed in the presence of aqueous colloidal silica and water miscible alcohol. Suitable alcohols include, for example, water miscible alcohols, specifically t-butanol, methanol, ethanol, propanol, butanol and the like, or ether alcohols such as ethoxyethanol, butoxyethanol, methoxypropanol and the like. The aqueous colloidal silica and silyl acrylate are heated and stirred until hydrolysis is completed. Hydrolysis of silyl acrylate can be carried out under atmospheric conditions or by heating and refluxing the hydrolysis mixture.

  In the second step, an acrylic resin is added to the above solution 1, and water and solvent used in the reaction are distilled off.

  Further, in the third blending step, a desired photoinitiator, photosensitizer, leveling agent, and the like are added to the acrylic resin in which the colloidal silica in the second step is dispersed.

  The order of addition of the above-described components to the hard coat agent used in the present invention is not important, but it is preferable to add a polyfunctional acrylic monomer or a mixture thereof to the above-mentioned mixture of hydrolyzed silyl acrylate and colloidal silica. Preferably, the polyfunctional acrylic monomer or mixture thereof is added to the mixture while stirring the mixture of silyl acrylate and colloidal silica in a suitable hydrolysis medium, such as a solution of a water miscible alcohol as described above. Also, when removing water by azeotropically mixing the water-miscible solvent and water in the first step, keep it at the stage where the water-miscible solvent remains, and add acrylic resin, photopolymerization initiator, and leveling agent there. The method of doing can also be used.

  When producing the hard coat agent used in the present invention, an azeotropic mixture of water and alcohol is distilled off from the above blend. If no alcohol is used in the initial hydrolysis mixture, a sufficient amount of alcohol can be added to facilitate removal of water by distillation. Other solvents such as toluene or other aromatic hydrocarbons can be added to facilitate water removal.

  The hard coat agent used in the present invention is preferably filtered before use. The material of the filter is preferably PTFE, polypropylene or the like that is not easily eroded by an acrylic compound, and the filter diameter during filtration is preferably about 0.2 to 10 microns because it is easily available. In particular, the filter diameter is divided into two stages, with the passage of 2 to 10 microns in the initial stage and 0.2 to 1 micron in the latter stage, so that colloidal silica aggregates and gels derived from acrylic resin and dust mixed in from the air are more efficient. It can be removed well and the final appearance of the film can be kept good.

  The hard coat solution described above is applied to the polycarbonate substrate surface by dipping, spinning, flow, spraying, brushing, etc., and cured with a commercially available light irradiation device by selecting a photopolymerization initiator as appropriate. can do.

  In the present invention, the hard coat agent is formed with a thickness of 3 to 25 μm, preferably 10 to 20 μm. When the film thickness is reduced, the influence of polymerization inhibition by oxygen during photocuring increases, and a curing system under an inert gas such as nitrogen is required. Further, when the hard coat layer is thinned, the damage prevention performance itself is lowered. Further, when the film thickness becomes extremely large, there is a problem that the deformation of the base material during curing shrinkage becomes large.

Examples of the present invention will be described below, but the present invention is not limited to the following examples. Moreover, a part shows a weight part in an Example.
(Preparation Example 1)
1370 parts of isopropyl alcohol, 982 parts of Snowtex O-40 (40% colloidal silica aqueous dispersion) manufactured by Nissan Chemical Industries, Ltd., 168 parts of γ-methacryloxypropyltrimethoxysilane, 4-hydroxy-2,2,6,6 -A mixture of 0.88 parts of tetramethylpiperidine-1-oxy free radical was heated to 80 ° C and stirred and refluxed for 3 hours. After cooling, 280 parts of propylene glycol monomethyl ether (hereinafter PGM) was added, and 1200 parts of isopropyl alcohol were distilled off under reduced pressure. Further, 400 parts of PGM was added, and IPA and water were distilled off under reduced pressure so that the residue was 700 parts. Further, 500 parts of PGM was added, and the solvent was distilled off at 55 ° C./50 mmHg until the residue was 700 parts. did. The nonvolatile content was measured under the conditions of 105 ° C./1 hour, and finally a PGM solution of surface-treated colloidal silica having a nonvolatile content of 60% was prepared using PGM as a diluent (hereinafter referred to as FCS solution).

Example 1
Next, 18 parts of urethane acrylate “UV-1700B” manufactured by Nippon Synthetic Chemical Co., Ltd., and 2-hydroxy-2-methyl-1-phenyl-propan-1-one as a photopolymerization initiator are added to 20.1 parts of FCS solution. 0.5 part and 12.9 parts of methyl ethyl ketone were added to obtain a hard coat agent.

  The hard coat solution thus obtained was applied to an 80 micron thick triacetyl cellulose film with a bar coater, cured at 60 ° C. for 3 minutes, and then used with a light curing system (light source H lamp) manufactured by Fusion. Cured.

The test piece was cut into a 6 cm square and examined for various physical properties.
Coating thickness:
The film thickness after curing was measured using analysis software ASPECT PLUS using an optical film thickness measuring device manufactured by Spectra Corp.
Pencil hardness:
A crack that showed a maximum hardness of less than 1 scratch under a 50% humidity environment with a load of 500 g, and cracks occurred in the appearance of the coating after photocuring. It was confirmed visually.
Adhesion:
A 100x100 (width 1 mm) grid cut was made with a cutter for the film that was placed for 1 day after photocuring, and a tape adhesion test was conducted. When there was no unpeeled area, 100/100, and when all peeled, 0/100 Expressed as:
Appearance: Regarding the film after photocuring, it was visually confirmed whether white turbidity or interference fringes were generated. Excluding the presence or absence of cracks.
curl:
The film placed for 1 day after photocuring was cut into a 6 cm square, and the curl size of the film was expressed by the curvature radius. (The smaller the number, the greater the curl, which is undesirable)
The results are shown in Table 1.

Examples 2-6
In the same manner as in Example 1, an acrylic resin, a photopolymerization initiator, and methyl ethyl ketone were added to an FCS solution to prepare a solution having a solvent concentration of 40%. The same evaluation was performed using a H-bulb.
The urethane acrylate used is as follows.
Hexafunctional urethane acrylate (1);
Purple light UV-1700B made by Nippon Synthetic Chemical Industry
Hexafunctional urethane acrylate (2);
Purple light UV-7640B made by Nippon Synthetic Chemical Industry
The hexafunctional urethane acrylate (1) includes dipentaerythritol hexaacrylate and dipentaerythritol pentaacrylate, and the hexafunctional urethane acrylate (2) includes dipentaerythritol hexaacrylate, dipentaerythritol pentaacrylate, and pentaerythritol. Tetraacrylate and pentaerythritol triacrylate are included.

Example 7
IPA 120 parts, Nalcoag 1034A (35% colloidal silica aqueous dispersion) 60.6 parts, γ-methacryloxypropyltrimethoxysilane 5.4 parts, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy A mixture of 0.03 parts of free radicals was heated to 80 ° C. and refluxed for 3 hours. After cooling, 26.0 parts of dimethylol dicyclopentane diacrylate was added, and the solvent was distilled off under reduced pressure. When about half of the solvent had been distilled, 120 parts of methoxypropanol was added and then all of the solvent was distilled to give a clear solution.

  To 40 parts of this surface-treated colloidal silica-dispersed dimethylol dicyclopentane diacrylate, 30 parts of UV-1700B, 40 parts of dipentaerythritol hexaacrylate, and 2-hydroxy-2-methyl-1-phenyl-propan-1-one were added. 5.0 parts and 66.5 parts of methyl ethyl ketone were added to prepare a 40% solvent hard coat solution.

  Evaluation similar to Examples 1-7 was performed about the hard coat liquid obtained in this way.

Comparative Examples 1-3, Comparative Example 6
An acrylic resin, an acrylic monomer, a photopolymerization initiator, and methyl ethyl ketone were mixed to prepare a 40% solvent solution, and the same evaluation as in Example 1 was performed.

Comparative Example 4
A mixture of 120 parts of IPA, 60.6 parts of Nalcoag 1034A (35% colloidal silica aqueous dispersion) and 5.4 parts of γ-methacryloxypropyltrimethoxysilane was heated to 80 ° C. and refluxed for 3 hours. After cooling, 26.0 parts of 1,6-hexanediol diacrylate was added, and the solvent was distilled off under reduced pressure. When about half of the solvent had been distilled, 120 parts of methoxypropanol was added and then all of the solvent was distilled to give a clear solution.

  25 parts of this surface-treated colloidal silica dispersion 1,6-hexanediol diacrylate, 25 parts of pentaerythritol triacrylate, and 5.0 parts of 2-hydroxy-2-methyl-1-phenyl-propan-1-one were mixed. Then, methyl ethyl ketone was added to prepare a hard coat solution of 40% solvent, and the same evaluation as in Example 1 was performed.

Comparative Example 5
40 parts of colloidal silica-dispersed 1,6-hexanediol diacrylate prepared in Comparative Example 4 30 parts of “UV-1700B”, 30 parts of dipentaerythritol hexaacrylate, and 2-hydroxy-2-methyl-1-phenyl- 5.0 parts of propan-1-one was mixed, methyl ethyl ketone was added to prepare a 40% solvent hard coat solution, and the same evaluation as in Example 1 was performed.

Example 8
In Examples 1 and 2, a silicone surfactant was added. A hard coat solution containing 0.8 parts of BYK300 brand name "BYK300" was prepared and evaluated in the same manner. A film with a slippery surface was obtained. Pencil hardness, adhesion, appearance, curl Both were equivalent.

Example 9
In Examples 1 and 2, the photopolymerization initiator was replaced with 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide to prepare a hard coat solution. ), The same evaluation results as in Example 1 were obtained.

Example 10
In Examples 1 and 2, a 100 micron thick PET film (trade name “Cosmo Shine A4100”) manufactured by Toyobo Co., Ltd. was used as the base film, and photocuring and subsequent evaluation were performed on the easily adhesive surface. Whereas the pencil hardness was 20 microns and 6H, when the hard coating agent used in Comparative Example 1 was used, the pencil hardness was 20 microns and 4H, and cracks were observed. The adhesion was 100/100 in all cases.

Claims (7)

(A) Hexafunctional urethane acrylate; 20 to 70 parts by weight
(B) Tetrafunctional or higher (meth) acrylic monomer; 15-60 parts by weight
(C) Colloidal silica surface-treated with a silane coupling agent having a reactive (meth) acrylate group in the molecule; 10 to 40 parts by weight
(D) Photopolymerization initiator
(E) A composition for hard coat containing a diluting solvent.   2 to 30 parts by weight of dimethylol dicyclopentane diacrylate, which is a bifunctional acrylic monomer, is added to 100 parts by weight of components (A), (B) and (C) in total. A composition for hard coat, further comprising D) and (E).   The hard coat composition according to claim 1 or 2, further comprising a silicone-based surfactant.   The hard coat composition according to any one of claims 1 to 3, wherein at least one of the dilution solvents is methyl ethyl ketone.   A laminate having a hard coat layer having a thickness of 10 to 20 µm, which is obtained by photocuring the hard coat composition according to any one of claims 1 to 4 on a transparent support substrate.   The laminate according to claim 5, wherein the transparent support substrate is a triacetyl cellulose (TAC) film.   The transparent support base material is a polyethylene terephthalate (PET) film, and is obtained by photocuring after applying the hard coat composition according to any one of claims 1 to 4 to a surface which has been subjected to an easy adhesion treatment in advance. 5. The laminate according to 5.