WO2004111138A1

WO2004111138A1 - Hard-coating composition

Info

Publication number: WO2004111138A1
Application number: PCT/KR2004/001413
Authority: WO
Inventors: Kyung Won Jung
Original assignee: Kyung Won Jung
Priority date: 2003-06-14
Filing date: 2004-06-14
Publication date: 2004-12-23
Also published as: JP2006527299A

Abstract

The present invention relates to a UV (ultraviolet) cured hard coating composition, more particularly to a UV curable hard coating composition prepared by adding or not adding pentaerythritol triacrylate (PETA), which has been widely used as curable binder precursor, to a hard coating composition comprising a nano-sized colloidal inorganic oxide particle, a curable binder precursor, a cross-linking silane compound, a colloid stabilizer and an additive, wherein the colloid stabilizer is a morpholine that stabilizes colloid by UV-induced polymerization and has little toxicity unlike the conventional colloid stabilizers, thereby rendering superior compatibility, uniform coating surface due to much improved viscosity, harmlessness to humans and environments with little toxicity, optically transparency, superior wear resistance and raising no curling problem.

Description

HARD-COATING COMPOSITION

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a UV (ultraviolet) cured hard coating composition, more particularly to a UV curable hard coating composition prepared by adding or not adding pentaerythritol triacrylate (PETA), which has been widely used as a curable binder precursor, to a hard coating composition comprising a nano-sized colloidal inorganic oxide particle, a curable binder precursor, a cross- linking silane compound, a colloid stabilizer and an additive, wherein the colloid stabilizer is a morpholine that stabilizes colloid by UV-induced polymerization and has little toxicity unlike the conventional colloid stabilizers, thereby having superior compatibility, offering uniform coating surface due to outstandingly improved viscosity, being harmless to human and environment-friendly with little toxicity, being optically transparent, raising no curling problem and having superior wear resistance.

Description of the Related Art

Conventionally, hard coating compositions having good wear resistance and scratch resistance have been used to protect their surface a variety of plastic products in coating and cured. Of them, hard coating compositions comprising a binder matrix prepared from a radiation (e.g., UV) cured prepolymer such as a

(meth) aery late monomer are disclosed in U.S. Pat. Nos. 5,541,049 and No. 5,176,943. These hard coating compositions are preferably transparent, hybrid polymerized composites comprising a nanometer sized inorganic oxide particle (e.g., silica) dispersed on an organic binder matrix. These hard coating compositions can be prepared from an aqueous sol of an inorganic colloid as the curable binder precursor and the other constituents are mixed in the aqueous sol. However, the colloid is too sensitive to prepare a hard coating composition having superior physical properties.

Particularly, if the other constituents, such as the binder matrix precursor or other additives, are added to the sol, the colloid becomes unstable and precipitates form the sol.

Such agglomeration makes it difficult to obtain a high quality coating. That is, agglomeration of the colloid results in a cloudy or turbid hard coating composition. A hard coating film prepared from such a hard coating composition may also be cloudy or turbid. The conventional hard coating film is prepared by forming a thin film of a hard coating composition having a thickness ranging from about 2 to about 15 μm directly on a plastic material or on a primer film having a thickness of about 1 μm.

Although the conventional hard coating film has sufficient hardness, it is so thin that the hard coating film is also deformed when the plastic material below it is deformed. As a result, the hard coating film has an insufficient hardness and it does not render sufficient durability.

In order to solve this problem, a thin film, such as a polyester film having a thickness ranging from 25 to 100 μnx, may be formed on the hard coating film. However, if the thickness of the coating is increased by this method, the hard coating film may be crack or peeled off easily. Also, the hard coating film may bend due to the curing contraction, which is called 'curling effect'.

In addition, surface contamination tends to occur on the coating film and some toxic constituents of the hard coating composition raise the environmental problems. For the foregoing reasons, it was difficult to obtain a hard coating film having good characteristics by the conventional techniques.

To take an example, a hard coating composition using pentaerythritol triacrylate (PETA) as binder matrix precursor and N,N'-dimethyl (meth)acrylate (DMA), silane and silica as additives has been proposed.

Although this composition has improved wear resistance, the pentaerythritol triacrylate (PETA) is not compatible with the inorganic oxide and the colloid due to relatively high viscosity, so that gelation or precipitation of the inorganic oxide occurs during stripping of water. Also, the preparing process is complicated and it is difficult to obtain a uniform coating when coating the hard coating composition on an acryl or a polycarbonate plate.

The DMA, which acts as both a colloid stabilizer and a polymerization monomer, is not environment-friendly due to its high toxicity. Further, it has a relatively low boiling point, and thus part of it may be released from the colloid during stripping of water, thus causing environmental pollution. In addition, when it is coated on a thin polyester film having a thickness of about 20 μ - m. and UV is illuminated to cure it, the film may experience the curling effect and will be easily contaminated by acidic substances (e.g., juice, coffee, etc.). Use of fluorine compounds instead of the DMA has been proposed to solve these problems. However, although the resulting composition has improved contamination resistance, another pollution problem occurs during preparation of the fluorine compounds and the occurrence of curling is not resolved. Recently, a variety of functions including printing characteristics as in mirror printing of cell phone displays and contamination resistance as in the touch screen of PCs are required, as well as the traditional surface protection function of plastic products.

SUMMARY OF THE INVENTION

The UV curable hard coating composition of the present invention employs alone or in combination of trimethylolpropane triacrylate (TMPTA), which has low viscosity as curable binder precursor thus being highly compatible with colloidal inorganic oxide particles, and a multifunctional acrylate which is easily miscible with the colloid as main constituent. For the multifunctional acrylate, an alkoxylated multifunctional acrylate which is easily miscible with the colloid due to its hydrophilic group is used; dipentaerythrol pentaacrylate (DPPA) or dipentaerythrol hexaacrylate (DPHA) is used alone or in combination when a hard coating with very high viscosity is required; and pentaerythritol triacrylate (PETA) may be used in addition upon necessity.

Also, the UV curable hard coating composition of the present invention uses acryloyl morpholine having little toxicity as a colloid stabilizer, instead of the conventional dimethyl(meth)acrylamide (DMA). With the selective use of a curable binder precursor and a colloid stabilizer, comprising a colloidal inorganic oxide particle and a cross-linking silane compound, and optimally mixing various additives according to the needs of target products to which the hard coating composition will be applied to, the hard coating composition of the present invention experiences no colloid agglomeration because the colloidal inorganic oxide particles are well dispersed on the organic matrix, is optically transparent, experiences no curling problem, is environment-friendly and has superior contamination resistance and wear resistance. Thus, it can be utilized for hard coating film used in various fields of industries, as well as in a variety of plastic materials.

Accordingly, it is an aspect of the present invention to provide a UV curable hard coating composition capable of preventing precipitation or gelation of colloidal inorganic oxide particles, thus offering optically transparent coating surface, incurring no curling problem, having superior wear resistance, scratch resistance, contamination resistance, printing characteristics, adhesion properties and hydrolysis resistance, being harmless to humans because of little toxicity and being environment-friendly.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a test sample prepared to determine adhesive force by the cross hatch method.

FIG. 2 shows a curled polyester film on a plate. FIG. 3 shows a hard coating film sample prepared by coating the hard coating composition to determine heat stability.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a UV curable hard coating composition comprising a colloidal inorganic oxide particle, a curable binder precursor, a cross- linking silane compound, a colloid stabilizer and an additive, more specifically, 10 to 50 wt % of a colloidal inorganic oxide particle; 5 to 60 wt% of at least one selected from the group consisting of dipentaerythrol pentaacrylate (DPPA), dipentaerythrol hexaacrylate (DPHA), pentaerythritol triacrylate (PETA), trimethylolpropane triacrylate (TMPTA), trimethylolpropane methoxylated triacrylate (TMP(MO)sTA) and trimethylolpropane ethoxylated triacrylate (TMP(EO)sTA) as the curable binder precursor; 5 to 20 wt% of a cross-linking silane compound ; 5 to 20 wt% of acryloyl morpholine as the colloid stabilizer; and 0.01 to 10 wt% of an additive selected from the group consisting of a stabilizer, an absorbent, an antioxidant, an anti-scratch agent and an anti-contamination agent, based on the solid content.

The present invention relates to a UV curable hard coating composition comprising a nano-sized colloidal inorganic oxide, a curable binder precursor, a cross-linking silane compound, a colloid stabilizer and an additive, wherein the conventionally widely used pentaerythritol triacrylate (PETA) is used in small amount as the curable binder precursor and a morpholine, which stabilizes the colloid as polymerization occurs by irradiation of UV and has little toxicity unlike the conventional colloid stabilizers, is selectively used as the colloid stabilizer. Hereinafter, each constituent of the UV curable hard coating composition of the present invention is described in more detail. The contents in wt% are based on the solid weight of the hard coating composition.

First, the hard coating composition of the present invention comprises 10 to 50 wt % of a colloidal inorganic oxide.

The colloidal inorganic oxide may be a particle, powder or a solution. Preferably, it is a non-agglomerated spherical particle having an average diameter ranging from 10 to 100 run. If the diameter of the particle is below 10 ran, it is difficult to process the particle. In contrast, if it exceeds 100 ran, the particle is not well dispersed in the hard coating composition, so that the surface becomes rough and optically opaque and has poor scratch resistance.

It is preferable that the colloidal inorganic oxide not be agglomerated (separated from one another). If it is agglomerated, precipitation or gelation may occur and the sol viscosity may increase significantly, so that adhesion properties and optical transparency may be worsened. Typically, the colloidal inorganic oxide may be silica. Although it can be used along with a colloidal metal oxide, great care should be taken because the colloid may become unstable due to the difference in pH of the silica and the colloid if the pH of the colloidal metal oxide becomes more acidic. Although the colloidal inorganic oxide may be a powder, a gel or a sol, the sol form is most preferable. In a sol state, the colloidal inorganic oxide particle is dispersed in a liquid medium. The preferable liquid medium for the colloidal particle is water. When the colloidal particle is dispersed in water, it is stabilized due to the common charge present at the surface of each particle. The common charge tends to promote dispersing over agglomeration. It is because the similarly charged particles repulse one another.

The sol used in the present invention may be prepared by the methods well known in the field of the present invention. Also, it is possible to use a commercially available sol. For example, the Nalco series (Nalco of the U.S.) may be used as colloidal silica sol dispersed in water.

As the second constituent, the UV curable hard coating composition of the present invention comprises 5 to 60 wt% of at least one selected from the group consisting of dipentaerythrol pentaacrylate (DPPA), dipentaerythrol hexaacrylate (DPHA), trimethylolpropane triacrylate (TMPTA), trimethylolpropane methoxylated triacrylate (TMP(MO)sTA) and trimethylolpropane ethoxylated triacrylate (TMP(EO)3TA), as curable binder precursor.

The curable binder precursor may further comprise pentaerythritol triacrylate (PETA), if required. Its content ranges from 5 to 45 wt%, and if a higher viscosity is required, 5 to 60 wt% of DPPA, DPHA or a mixture thereof may be used. However, the content of the total curable binder precursor including all of PETA, DPPA, DPHA, etc. should be in the range of 5 to 60 wt%.

The curable binder precursor is the most important constituent of the present invention. It has good adhesion property for materials such as acryl, polycarbonate, polyester film, etc., has good coating characteristics and stabilizes the colloid. Especially, if ethoxylated or methoxylated multifunctional acrylate is used alone or in combination, viscosity of the composition may be reduced. The curable binder precursor may be selected depending on the material to be used. To take the case of using ethoxylated or methoxylated multifunctional acrylate alone or in combination as an example, the viscosity may be improved by using DMA as a colloid stabilizer. The TMPTA and the like reduce viscosity of the CeRing (CeRing is the commercial name of the hard coating composition of the present invention) while maintaining inorganic oxide particle distribution in the CeRing superior. Therefore, no precipitation of inorganic oxides or gelation occurs during preparation of the CeRing. Also, because of good flow properties, a hard coating film having a very clean surface and a uniform thickness can be obtained by flow coating or dip coating the film on materials like acryl and polycarbonate.

If DPPA or DPHA is used alone or in combination as a curable binder precursor or along with PETA, the hard coating composition becomes too viscous to obtain a uniform coating film by flow coating. However, if the hard coating composition is coated on a polyester film by gravure printing or bar coating, it is possible to obtain good adhesive force to the material, good wear resistance and reduced rainbow effect. Physical properties of the curable binder precursor used in the hard coating composition of the present invention are compared in Table 1 below. [Table 1]

The data given in Table 1 is taken from the products catalogue of Miwon Commercial Co., Ltd. of Korea.

As the third constituent, the hard coating composition of the present invention comprises 5 to 20 wt% of a cross-linking silane compound. The cross-linking silane compound is used to enhance dispersibility of the colloidal inorganic oxide particles in the composition through surface treatment. If its content is below 5 wt%, the dispersibility is worsened, so that the transparency or quality may become poor. In contrast, if it exceeds 20 wt%, the hard coating properties may be deteriorated. The cross-linking silane compound has a hydrolysable silane group and a polymerizable functional group. An example of the commercially available cross-linking silane compound is KBM-503 (Shin-Etsu Chemical of Japan).

As the fourth constituent, which is a special feature of the present invention, the hard coating composition of the present invention comprises 5 to 20 wt% of an acryloyl morpholine as a colloid stabilizer.

The acryloyl morpholine functions as both a colloid stabilizer and a binder precursor. It stabilizes the colloidal inorganic oxide, thereby aiding the curable binder precursor and the cross-linking silane compound to be stably mixed into the colloid, and functions as binder precursor, i.e. it is cured by photopolymerizatin when exposed to UV.

Conventionally, acrylamides such as N,N'-dimethyl(meth)acrylamide (DMA) have been mainly used as such binder precursor. But, the DMA is highly toxic and stripped off along with water during vacuum stripping.

The acryloyl morpholine (ACMO), which is a characteristic feature of the present invention, has little toxicity, is environment-friendly, superior in performance than DMA and causes no curling problem when coated on a polyester film material and exposed to UV. However, in some cases, a trimethylolpropane alkoxylated triacrylate having a hydrophilic may be selectively used as a curable binder precursor to obtain a composition having superior physical properties.

The acryloyl morpholine is comprised in 5 to 20 wt%. If its content is below 5 wt%, the colloid stabilizing effect is insufficient. In contrast, if it exceeds 20 wt%, the wear resistance becomes worsened. The following toxicity data of the ACMO and the DMA given in Table 2 below are taken from the MSDS of Kojin of Japan. [Table 2]

Besides the above main constituents, the hard coating composition of the present invention comprises 0.01 to 5 wt% of an additive such as a stabilizer, an absorbent, an antioxidant, an anti-scratch agent, an anti-contamination agent, etc.

To be specific, the hard coating composition of the present invention may comprise a photoinitiator which generates free radicals when exposed to UV to initiate cross-liking of polymers. Typically, benzophenone may be used as the photoinitiator. The photoinitiator is preferably comprised in 0.01 to 2 wt%.

In general, all polymer materials are known to be decomposed by a variety of mechanisms. Such decomposition may be reduced, although not completely prevented, by adding a certain additive. Typical additives used for such a purpose are a stabilizer, an absorbent, an antioxidant, etc. These additives may be used alone or in combination.

In general, a UV stabilizer or a UV absorbent improves weather resistance of the hard coating film and reduces yellowing with time by UV, an antioxidant prevents decomposition of the hard coating film by reaction of ozone or oxygen in the air, and a heat stabilizer prevents decomposition by heat treatment at high temperature or yellowing by weathering.

The UV stabilizer, UV absorbent, an antioxidant, a heat stabilizer, etc. may be used alone or in combination. Preferably, they are comprised in 0.01 to 5 wt%. Examples of the commercially available UV stabilizer or UV absorbent are

Tinuvin292 and Tinuvinl23 (Ciba Geigy of Switzerland). An example of the commercially available antioxidant is Anitoxidant BHT (Infochems, Inc. of the U.S.). The hard coating film formed by the hard coating composition of the present invention has superior wear resistance and scratch resistance. But, they can be further improved by offering a little slipping property using an additive. For this purpose, a silicon based material is used in general. However, care should be taken because transparency of the hard coating film may be worsened due to poor compatibility with the composition. Preferably, it is comprised in 0.01 to 1 wt%. The commercially available DC-57 (Dow Corning of the U.S.) has been proved to be very effective.

DMA, which has been traditionally used in the composition for preparing a hard coating film, tends to be contaminated by acidic substances such as juice, coffee, etc., because of its relatively strong alkalinity. Because the hard coating composition of the present invention uses ACMO instead of DMA, the contamination resistance is significantly improved. However, the contamination resistance may be further improved or the water repellency may be offered by using a certain additive. For this purpose, it is preferable to add 0.1 to 5 wt% of Zonyl (Dupont of the U.S.), which is highly compatible with the hard coating composition of the present invention because, per 100 wt% of the hard coating composition.

The hard coating composition of the present invention may be prepared by the following process. However, the addition sequence of each constituent may be different from the one proposed below.

First, a colloidal inorganic oxide (using water as medium) is added to a slightly heated (to about 50 ^°C) curable binder precursor. Then, a separately prepared mixture of a cross-linking silane compound and a colloid stabilizer is added and additives such as a photoinitiator, an antioxidant, etc. are added. The mixture is heated under the vacuum while being stirred, so that over 98 % of water is removed from the colloid. Then, a highly viscous and transparent liquid is obtained.

An organic solvent selected from the group consisting of ketones, alcohols, acetates, etc. is added to this transparent liquid. The solid content of the resultant transparent hard coating composition is injected while stirring to prepare a hard coating composition having a concentration ranging from about 15 to about 40 wt%.

For reference, specific examples of the hard coating composition of the present invention, with the content of each constituent determined depending on the material to use, are given hereinafter. First, a hard coating composition that can be used for any plastic material is as follows.

It is a hard coating composition comprising 25 to 35 wt% of a colloidal inorganic oxide particle, 30 to 45 wt% of PETA or 5 to 20 wt% of DPPA or DPHA as curable binder precursor, 5 to 10 wt% of a cross-linking silane compound, 5 to 15wt% of ACMO as colloid stabilizer, 0.01 to 1 wt% of silicone oil, 0.01 to 1 wt% of a photoinitiator and 0.01 to 1 wt% of an antioxidant. The hard coating composition has a particularly good scratch resistance, is optically very transparent and incurs a few curling problems. Also, because ACMO having little toxicity is used instead of DMA, it is environment-friendly.

Second, a hard coating composition to be used in hard coating of an acryl plate, which is widely used as a display of cell phones, requires superior optical transparency, wear resistance, scratch resistance and printing properties. Here, the printing property means a strong adhesive force to printing medium such as special ink used in printing, transferring or deposition. Besides the printing characteristics, the hard coating film should have a smooth and uniform surface. Particularly, although the acryl plate has a size of as large as about 1220 mm X 2420 mm, the hard coating composition should be coated on the entire surface of the plate by flow coating, and there should be little difference in thickness, and the surface should not be modified during the curing by UV radiation. A hard coating composition that satisfies these requirements comprises 0 to 30 wt% of PETA as a cured binder precursor, 20 to 40 wt% of TMPTA having low viscosity, 10 to 30 wt % of TMP(EO)STA having a hydrophilic group thus being stably dispersed in the colloidal inorganic oxide, 25 to 35 wt% of a colloidal inorganic oxide particle, 5 to 15 wt% of ACMO, 0.01 to 1 wt% of a photoinitiator and 0.01 to lwt% of an antioxidant.

Such prepared hard coating composition showed no precipitation of the inorganic oxide or gelation during stripping of water under vacuum. As a result, flow coating on the acryl plate was performed smoothly. Also, leveling characteristics, wear resistance and transparency were superior. The third is a hard coating composition formed into a hard coating film on a polyester film material to be used as a touch screen of a computer. In general, a transparent polyester film experiences the rainbow effect, in itself. If a transparent hard coating film is formed on the polyester film, the rainbow effect may become more severe, and in some cases, makes it difficult to be used. The hard coating composition of the present invention reduces the rainbow effect of the polyester film even when cured into a transparent hard coating film. A specific example of such hard coating composition is the one comprising 20 to 45 wt% of DPHA with a very high viscosity as curable binder precursor, 10 to 20 wt% of PETA, 25 to 35 wt% of a colloidal inorganic oxide particle, 5 to 10 wt% of a cross-linking silane compound, 5 to 15 wt% of ACMO as a colloid stabilizer, 0.01 to 1 wt% of an initiator and 0.01 to lwt% of an antioxidant.

Because such a hard coating composition has a high viscosity, it can reduce the rainbow effect of the polyester film material when coated on the polyester film material by gravure coating or bar coating and cured, while offering very superior optical transparency, wear resistance, scratch resistance, etc.

That is, a hard coating composition having different a composition depending on the material to be used is prepared and coated on the material to improve wear resistance, scratch resistance, etc. The coating may be performed by dip coating, flow coating, spray coating, knife coating, gravure coating, roll coating, etc. depending on the nature of the material, viscosity of the hard coating composition, etc. Preferably, coating the thickness ranges from 5 to 15 μm. After coating, the solvent is removed by drying. If curing is performed without completely removing the solvent, it may be impossible to obtain an optically transparent film due to haze. Therefore, the solvent should be dried off completely. After the solvent has been completely dried off, UV is illuminated to the coating film for curing purpose.

As a result, a hard coating film having superior wear resistance, being optically very transparent and having superior adhesive force to a variety of materials, in which the curable binder precursor, the surface-treated colloidal inorganic oxide and the selectively added additives are uniformly distributed in the polymer matrix, is obtained.

Hereinafter, the present invention is described in more detail through examples. However, the following examples are only for the understanding of the present invention and they should not be construed limiting the scope of the present invention.

EXAMPLES Example 1 15 wt% of DPHA, a curable binder precursor, and 40 wt% of PETA were added to a 2 L flask and heated to about 50 ^°C . Then, 26.3 wt% of Nalco 2327, 7 wt % of 3-methacryloxapropyltrimethosilane (KBM-503), a cross-linking silane compound, 11 wt% of ACMO, 0.5 wt% of silicone oil (DC-57 of Dow Corning of the U.S.), 0.1 wt% of benzophenone and 0.1 wt% of BHT were added thereto. Most of water and methanol were removed from the resulting mixture by applying a mild vacuum (100 mmHg) at 52 ^°C . About 2 wt% of water remained in the mixture.

As the stripping process came to an end, the mixture was diluted to a solid content of 25 % using isopropyl alcohol. Then, the CeRing composition was coated on an acryl plate to a thickness of 10 ^m by the conventional flow coating method to form a hard coating film. The plate was flash dried in an air-circulating oven at about 60 "C for 2.5 minutes. Then, the coating film was cured on a UV treatment conveyor belt using a high-pressure mercury lamp (J-H4000 of Korea Jeil UV). The curing condition was: belt speed = 6 m/min, 100 watts and energy =

800 mj/cm².

The resultant hard coating film was perfectly transparent and perfectly adhered to the acryl plate. Physical properties of the hard coating film are given in Table 3 below.

Example 2

20 wt% of TMPTA, a curable binder precursor, 20 wt% of TMP(EO)₃TA,

15wt% of PETA, 26.8 wt% of Nalco 2327, 11 wt% of ACMO, 7 wt% of KBM-503, 0.1 wt% of an initiator (benzophenone) and 0.1 wt% of an antioxidant (BHT) were mixed. Stripping, coating on an acryl plate, curing by UV illumination, etc. were performed similarly as in Example 1.

The viscosity of the composition when most of water and methanol were stripped off by vacuum was about 100 poise at 50 ^°C, which was much lower than that of Example 1 (220 poise). Therefore, precipitation of inorganic oxides or gelation did not occur during the stripping, and the resulting composition was very transparent.

The CeRing composition was coated on an acryl plate by flow coating to obtain a highly uniform coating film.

The resultant hard coating film was optically very transparent with no yellowing at all. Also, it had very superior wear resistance, adhesion properties, etc.

Example 3

The procedure of Example 1 was carried out, except for mixing 40 wt% of

DPHA, 15 wt% of PETA, 26.8 wt% of Nalco 2327, 7 wt% of KBM-503, 11 wt% of

ACMO, 0.1 wt% of an initiator (benzophenone) and 0.1 wt% of an antioxidant (BHT).

The viscosity of the composition when most of water and methanol were stripped off by vacuum was about 350 poise at 50 "C .

The CeRing composition was diluted to a solid content of 25 % by adding methyl ethyl ketone (MEK) and coated on a polyester film material having a thickness of 186 μm. by bar coating. Then, the solvent was dried off and curing was performed by illuminating UV. Light was illuminated to the polyester film on which the CeRing hard coating film had been formed using a special fluorescent lamp (FO32w/850, SYLVANIA of Germany). The result was reduced rainbow effect than that of the polyester film material itself. Also, optical transparency, wear resistance and scratch resistance were superior. The polyester film material on which the hard coating film had been formed experienced less curling when heat-treated than that of Example 1.

Example 4

The CeRing composition was prepared as in Example 1, except for using 8wt% of ACMO and 3 wt% of Zonyl (Dupont of the U.S.) instead of llwt% of ACMO in order to improve contamination resistance.

The composition was coated on an acryl plate and cured by illuminating UV. The result was superior as in Example 1. The result of contact angle measurement shows that the contamination resistance was significantly improved.

Comparative Example

55 wt% of PETA, a curable binder precursor, 29.8 wt% of Nalco 2327 (Nalco of the U.S.), an inorganic oxide colloid, 7 wt% of A-174 (Union Carbide of the U.S.), a cross-linking silane compound, 8 wt% of DMA, a binder precursor, 0.1wt% of an initiator and 0.1 wt% of an antioxidant were mixed to prepare a hard coating composition, as in Example 1.

The resultant hard coating composition was coated on an acryl plate or a polyester film and cured by illuminating UV. Test was performed to compare the hard coating composition with the CeRing compositions of Examples 1 to 3. It had the stability problem because highly toxic DMA was used. In addition, the DMA, although very little, was stripped off during stripping of water and methanol by vacuum. Therefore, it may cause an environmental problem.

Test Example

1. Taber wear test on a plastic plate

The hard coating film was worn by spinning at room temperature under the load of 500 g for 100, 300 and 500 cycles according to ASTMD 1044. Difference in turbidity due to wearing was determined in % .

2. Scratch resistance

The hard coating film was scratched with pencil heads having different hardness at room temperature according to JIS D-0202. The hardness of the pencil head at which scratch was observed was recorded.

3. Optical transmission

Light was illuminated to the hard coating film. The amount of light transmitting the hard coating film was measured with a visible light transmission/ refection meter (HA-TR of Suga Test Instruments Co., Ltd. of Japan) in %.

4. Adhesive force Adhesive force was measured by Cross Hatch method. A test sample measuring 10 mm x 10 mm was cut using a sharp knife with vertical and horizontal lines spaced by 1 mm each, as shown in FIG. 1. A cellophane tape (JIS Z-1522 of Ichiban Cellophane Tape of Japan) having a width of 18 mm was applied tight by pressing with a hand. The tape was detached instantly at the vertical direction. The number of detached squared lattices from the 100 (10 x 10) lattices was counted.

100/100 means that the tape is completely attached with the plastic material and 0/100 means that there is no adhesive force at all.

5. Hydrolysis

The hard-coated part of the material was immersed in water at 80 ^°C for 1, 3 and 5 days. To check if the hard coating film was hydrolyzed by the hot water, adhesive force of the hard coating film with the material was measured as in the adhesive force test.

6. Curling

The CeRing composition having a solid content of 30 % was coated on a polyester film material having a thickness of 50 μm using a No. 8 bar (wet film thickness = 18.3 ^m). The film was put in an oven at 60 ⁰C for 3 minutes o dry off the solvent completely and cured by illuminating UV.

The curing condition was belt speed = 6.0 m/min, 100 watts, energy = 800 mj/cm² and spacing of the belt and the high-pressure mercury lamp 0-H4OOO of

Korea Jeil UV) = 12 cm. The polyester film on which the hard coating film had been formed was cut to a size of 20 cm X 20 cm. The film was placed on a plate and the angle between the plate and the curled film was measured (see FIG. 2).

7. Heat stability Change of physical properties of the hard coating film before and after heat treatment was examined.

The hard coating film formed on a polyester film (thickness = 186 μm) was cut using a sharp knife.

Thus obtained sample was put in a constant-temperature oven at 150 °C for 0.5 hour. The degree of rising of the point where the diagonals meet with each other was measured to evaluate heat stability.

8. Contact angle

Contact angle of a liquid drop on a plastic plate on which the hard coating film has been formed refers to a measured hydrophilicity of a hard coating film.

The larger the contact angle, the more hydrophobic the hard coating film, and the smaller the contact angle, the more hydrophilic it is. The fact that the hard coating film is hydrophilic indicates that it has good affinity to the printing ink. That is, the smaller the contact angle, the better the printing property The contact angle was measured with DSD Fast/ 60 Contact Angle Meter (GBX

Instrumentation Scientifique of France). [Table 3]

As described above, the hard coating composition (CeRing, the commercial name of the hard coating composition of the present invention) of the present invention comprising a colloidal inorganic oxide particle, a curable binder precursor, a cross-linking silane compound, a binder precursor and a variety of additives experiences no agglomeration of colloid, is optically very transparent, has superior wear resistance, contamination resistance, etc. is environment-friendly and with little toxicity.

The hard coating composition of the present invention can be applied to the IT electronics products developed recently.

Because the CeRing composition is optically very transparent and has very superior wear resistance, scratch resistance, etc., it can be utilized in a variety of plastic products including optical lenses, displays of cell phones, control panel windows of electronics products, touch screens of computers, and the like to protect them from physical or mechanical damages. The hard coating film may be coated on the plastic product and cured by illuminating UV.

While the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art will appreciate that various modifications and substitutions can be made thereto without departing from the spirit and scope of the present invention as set forth in the appended claims.

Claims

What is claimed is:

1. A UV curable hard coating composition comprising a colloidal inorganic oxide, a curable binder precursor, a cross-linking silane compound, a colloid stabilizer and an additive, which comprises

10 to 50 wt % of a colloidal inorganic oxide;

5 to 60 wt% of at least one selected from the group consisting of dipentaerythrol pentaacrylate (DPPA), dipentaerythrol hexaacrylate (DPHA), trimethylolpropane triacrylate (TMPTA), trimethylolpropane methoxylated triacrylate (TMP(MO)3TA) and trimethylolpropane ethoxylated triacrylate

(TMP(EO)3TA) as the curable binder precursor;

5 to 20 wt % of a cross-linking silane compound; 5 to 20 wt% of acryloyl morpholine as the colloid stabilizer; and 0.01 to 5 wt% of at least one selected from a group consisting of a stabilizer, an absorbent, an antioxidant, an anti-scratch agent and an anti-contamination agent as the additive, based on the solid content.

2. The UV curable hard coating composition of claim 1, which further comprises 5 to 30 wt% of pentaerythritol triacrylate per 100 wt% of the composition as the curable binder precursor.

3. The UV curable hard coating composition of claim 2, which comprises: 25 to 35 wt % of a colloidal inorganic oxide; 0 to 55 wt% of dipentaerythrol hexaacrylate; 5 to 30 wt% of pentaerythritol triacrylate; 5 to 10 wt% of a cross-linking silane compound; 5 to 15 wt% of acryloyl morpholine;

0.01 to 1 wt% of a photoinitiator; and 0.01 to 1 wt% of an antioxidant.

4. The UV curable hard coating composition of claim 3, which comprises: 25 to 35 wt% of a colloidal inorganic oxide;

20 to 45 wt % of dipentaerythrol hexaacrylate; 10 to 20 wt % of pentaerythritol triacrylate; 5 to 10 wt% of a cross-linking silane compound; 5 to 15 wt% of acryloyl morpholine; 0.01 to lwt% of a photoinitiator; and

0.01 to 1 wt % of an antioxidant.

5. The UV curable hard coating composition of claim 2, which comprises: 25 to 35 wt% of a colloidal inorganic oxide; 20 to 40 wt% of trimethylolpropane triacrylate (TMPTA);

10 to 30 wt% of trimethylolpropane ethoxylated triacrylate (TMP(EO)₃TA); 5 to 30 wt% of pentaerythritol triacrylate (PETA);

5 to 10 wt% of a cross-linking silane compound; 5 to 15 wt % of acryloyl morpholine; 0:01 to 1 wt% of a photoinitiator; and 0.01 to 1 wt % of an antioxidant.

6. The UV curable hard coating composition of claim 2, which comprises:

25 to 35 wt % of a colloidal inorganic oxide; 20 to 40 wt% of trimethylolpropane triacrylate (TMPTA); 10 to 30 wt% of trimethylolpropane methoxylated triacrylate (TMP(MO)3TA); 10 to 30 wt% of trimethylolpropane ethoxylated triacrylate (TMP(EO)₃TA); 5 to 10 wt% of a cross-linking silane compound;

5 to 10wt% of dimethyl(meth)acrylamide (DMA); 0.01 to 1 wt% of a photoinitiator; and 0.01 to 1 wt% of an antioxidant.

7. The UV curable hard coating composition of claim 1, which comprises:

25 to 35 wt % of a colloidal inorganic oxide;

10 to 20 wt% of dipentaerythrol hexaacrylate;

5 to 10 wt% of a cross-linking silane compound;

5 to 10 wt% of acryloyl morpholine; 1 to 5 wt% of an anti-contamination agent;

0.01 to 1 wt% of a photoinitiator; and

0.01 to 1 wt% of an antioxidant and further comprises 20 to 45 wt% of pentaerythritol triacrylate.

8. The UV curable hard coating composition of claim 1, which comprises: 25 to 35 wt% of a colloidal inorganic oxide;

10 to 30 wt% of trimethylolpropane methoxylated triacrylate (TMP(MO)3TA); 10 to 30 wt% of trimethylolpropane ethoxylated triacrylate (TMP(EO)₃TA);

5 to 10 wt% of a cross-linking silane compound; 5 to 10 wt % of acryloyl morpholine; 1 to 5 wt % of an anti-contamination agent; 0.01 to 1 wt% of a photoinitiator; and 0.01 to 1 wt% of an antioxidant.

9. The UV curable hard coating composition of claim 8, which comprises: 25 to 35 wt % of a colloidal inorganic oxide;

10 to 30 wt% of trimethylolpropane methoxylated triacrylate (TMP(MO)₃TA); 10 to 30 wt% of trimethylolpropane ethoxylated triacrylate (TMP(EO)₃TA);

5 to 10 wt% of a cross-linking silane compound;

5 to 10 wt% of dimethyl(meth)acrylamide (DMA) instead of acryloyl morpholine as the colloid stabilizer;

1 to 5 wt% of an anti-contamination agent; 0.01 to 1 wt% of a photoinitiator; and

0.01 to 1 wt% of an antioxidant.