JP7701133B2 - Manufacturing method of hard coat film - Google Patents

Description

The present invention relates to a hard-coated film that is suitable for applications such as printing films, and has excellent heat resistance, printability, and hardness.

Plastic film substrates are widely used as substrates for optical films and the like because they have good transparency and are lightweight. In particular, polyester films such as polyethylene terephthalate are widely used for the above optical films because they are highly transparent and inexpensive. In addition to the above characteristics, optical films also have excellent flexibility, so they are used as flexible circuit boards for components with metal wiring formed on the film.

However, since conductive materials such as silver or copper are laminated onto a plastic film substrate, it is difficult to obtain good adhesion, and the substrate can be deformed by the thermal energy or light energy used to bake the conductive material, so the film substrates that can be used are very limited.

In this context, Patent Document 1 discloses a plastic substrate with a hard coat film, which is provided with a hard coat film that is excellent in transparency, anti-blocking property, electrical conductivity, and film-forming property.
Furthermore, Patent Document 2 discloses a hard coat film in which the surface free energy of the film surface is adjusted to provide excellent adhesion between the hard coat layer and a printed layer (for example, a conductive layer).

Patent document 3 discloses a substrate in which a transparent resin layer is formed on the surface of the substrate, the transparent resin layer being made of a non-crystalline thermoplastic resin with a Tg of 200°C or less, or a curable resin prepolymer with a Tg of 200°C or less that forms a three-dimensional crosslinked structure when irradiated with light, thereby improving adhesion to a metal (conductive layer).

Furthermore, Patent Document 4 discloses a hard-coated film in which a functional layer is provided on the front surface of a polyester film and a hard-coat layer is provided on the back surface, and the total thickness of the functional layers and the thickness of the hard-coat layer are adjusted to an appropriate range to suppress curling.

JP 2014-189596 A JP 2016-108568 A JP 2014-062375 A JP 2011-20406 A

However, in the conventional film substrates or hard coat films disclosed in the above Patent Documents 1 to 3, although improvements were made in terms of improving the adhesion (adhesion) between the conductive layer and the hard coat layer, the heat shrinkage characteristics (heat resistance) were poor (the thermal shrinkage rate was large), and there was room for improvement in terms of damage and deformation of the film caused by heat, for example, when baking the conductive layer (printed layer) formed on the hard coat layer.

In addition, while conventional hard-coated films such as those disclosed in Patent Document 4 have shown improvements in terms of curling, their thermal shrinkage properties (heat resistance) are insufficient.

In order to solve the problems of the past, the object of the present invention is, first, to provide a hard-coated film with excellent heat shrinkage properties (heat resistance), and, second, to provide a hard-coated film that, in addition to heat shrinkage properties (heat resistance), maintains high printability and is also excellent in adhesion of the printing layer, optical properties, hardness, and curl suppression.

The present inventors have conducted extensive research to solve the above problems and have found that a hard coat film having excellent heat shrinkage properties (heat resistance) can be obtained with a predetermined heat shrinkage rate.
Furthermore, the present inventors have conducted extensive research and found that by adjusting the surface free energy of the hard coat layer within a predetermined range, when a printed layer (e.g., a conductive layer) is formed on the hard coat layer, the adhesion between the printed layer and the hard coat layer is excellent. In addition, by setting the film thickness of the hard coat layer to a predetermined thickness, it is possible to suppress damage to the film caused by heat when, for example, a conductive layer formed on the hard coat layer is baked. In addition, it has been found that by adjusting the surface hardness of the hard coat layer within a predetermined range, the adhesion with the printed layer is improved and curling is reduced.

The present invention was completed as a result of investigations based on these various findings.
That is, the present invention is as follows.

(First Invention)
The hard-coated film is characterized in that it has a hard-coat layer formed on both sides of a film substrate, and has a thermal shrinkage rate of 0.3% or less when the hard-coated film is heat-treated at 150°C for 30 minutes.

(Second Invention)
The hard coat film according to the first aspect of the present invention is characterized in that it satisfies the following conditions (I), (II) and (III).
Condition (I): The hard coat layer A formed on at least one surface has a surface free energy in the range of 30 mN/m to 55 mN/m.
Condition (II): The film thickness D _A of the hard coat layer A is 1 μm or more.
Condition (III): the surface hardness C _A of the hard coat layer A represented by the following formula (1) is in the range of 3 to 15.
Surface hardening degree C _A = (P1/P2) x 100...Formula (1)
(Here, the peak area of 794 to 823 cm ⁻¹ obtained by infrared spectroscopy of the surface of the hard coat layer A is defined as P1, and the peak area of 1658 to 1778 cm ⁻¹ is defined as P2.)

(Third Invention)
The hard coat layer A is a hard coat film according to the first or second invention, characterized in that it contains a polyfunctional (meth)acrylate resin having a weight average molecular weight of 600 or more and having three or more (meth)acryloyl groups in the molecule.

(Fourth Invention)
The hard coat film according to any one of the first to third aspects of the present invention, characterized in that the thickness D _B of the hard coat layer B formed on the other surface of the hard coat film and the thickness D _A of the hard coat layer A are in the range of |D _A -D _B |≦3 μm.

(Fifth Invention)
The hard coat film according to any one of the first to fourth aspects of the present invention is characterized in that a surface hardness C _A of the hard coat layer A and a surface hardness C _B of the hard coat layer B, which is represented by the following formula (2), are in the range of |C _A -C _B |≦3.
Surface hardening degree C _B = (P3/P4) x 100...Formula (2)
(However, the peak area of 794 to 823 cm ⁻¹ obtained by infrared spectroscopy of the surface of the hard coat layer B is designated as P3, and the peak area of 1658 to 1778 cm ⁻¹ is designated as P4.)

(Sixth Invention)
The hard coat film according to any one of the first to fifth aspects of the present invention is characterized in that the film substrate is a polyethylene terephthalate film.

(Seventh Invention)
The method for producing a hard coat film is characterized in that the hard coat film, which satisfies the following conditions (I), (II), and (III), is subjected to a heat treatment at 150° C. or higher for 30 seconds or longer.
Condition (I): The hard coat layer A formed on at least one surface has a surface free energy in the range of 30 mN/m to 55 mN/m.
Condition (II): The film thickness D _A of the hard coat layer A is 1 μm or more.
Condition (III): the surface hardness C _A of the hard coat layer A represented by the following formula (1) is in the range of 3 to 15.
Surface hardening degree C _A = (P1/P2) x 100...Formula (1)
(Here, the peak area of 794 to 823 cm ⁻¹ obtained by infrared spectroscopy of the surface of the hard coat layer A is defined as P1, and the peak area of 1658 to 1778 cm ⁻¹ is defined as P2.)

According to the present invention, it is possible to provide a hard coat film having excellent heat shrinkage properties (heat resistance).
Furthermore, according to the present invention, in addition to this heat shrinkage property (heat resistance), it is possible to provide a hard coat film that maintains high printability while also exhibiting excellent adhesion of the printed layer, optical properties, hardness, and curl suppression.

Hereinafter, an embodiment of the present invention will be described in detail.
In the present invention, unless otherwise specified, "XX to △△" means "not less than XX and not more than △△."

As described above, the present invention is a hard-coated film in which a hard-coat layer is formed on both sides of a film substrate, and the hard-coated film is characterized in that the thermal shrinkage rate of the hard-coated film when heated at 150°C for 30 minutes is 0.3% or less (the first invention described above).

Further, in the first aspect of the present invention, the hard coat film satisfies the following conditions (I), (II) and (III) (the second aspect of the present invention):
Condition (I): The hard coat layer A formed on at least one surface has a surface free energy in the range of 30 mN/m to 55 mN/m.
Condition (II): The film thickness D _A of the hard coat layer A is 1 μm or more.
Condition (III): the surface hardness C _A of the hard coat layer A represented by the following formula (1) is in the range of 3 to 15.
Surface hardening degree C _A = (P1/P2) x 100...Formula (1)
(Here, the peak area of 794 to 823 cm ⁻¹ obtained by infrared spectroscopy of the surface of the hard coat layer A is defined as P1, and the peak area of 1658 to 1778 cm ⁻¹ is defined as P2.)

(Film substrate)
First, the film substrate will be described.
The film substrate used in the present invention is not particularly limited, and examples thereof include triacetyl cellulose, polyethylene terephthalate, cycloolefin polymer, polycarbonate, polyethylene naphthalate, polyethylene, polytrimethylene terephthalate, polypropylene, polybutylene terephthalate, polybutylene naphthalate, polystyrene, polymethyl methacrylate, polystyrene glycidyl methacrylate, aromatic polyimide, alicyclic polyimide, polyamideimide, and mixtures thereof, but from the viewpoints of heat resistance, availability, and economy, it is preferable to use a thermoplastic resin film made of polyethylene terephthalate, polyethylene naphthalate, or triacetyl cellulose. In particular, polyethylene terephthalate film is preferable because it is highly transparent, inexpensive, and easily available.

(Hard Coat Layer)
Next, the hard coat layer will be described.
The hard coat film of the present invention has a hard coat layer formed on each side of the film substrate. The hard coat layer formed on one side of the film substrate is called "hard coat layer A" and the hard coat layer formed on the other side is called "hard coat layer B."

The hard coat film of the present invention has a hard coat layer formed on each side of the above-mentioned film substrate, for example, hard coat layer A formed on one side of the film substrate and hard coat layer B formed on the other side, and is characterized in that the heat shrinkage rate of this hard coat film when heated at 150°C for 30 minutes is 0.3% or less.

In the present invention, the "thermal shrinkage rate" is a value measured by the following test method and calculated from the measurement results using the following formulas (3) and (4).

[Test Method]
In a test method according to Japanese Industrial Standard JIS-K-7133, the hard coat film is cut into a size of 120 mm x 120 mm, and the distance between the two marks (L ₀ and T ₀ ) before the test is measured. In this case, the lengthwise direction and the widthwise direction are defined as the flow direction of the film when the hard coat is applied, and the perpendicular direction is defined as the widthwise direction. Next, the film is heated for a specified time (30 minutes) in a hot air drying oven heated to a specified temperature (150°C), and then conditioned at room temperature for at least 30 minutes, and the lengthwise and widthwise distances (L and T) are measured again, and the change in the lengthwise and widthwise distances (ΔL and ΔT) of the test piece is calculated using the following formulas (3) and (4).
ΔL=[(L-L ₀ )/L ₀ ]×100(%) ...(3)
ΔT=[(T-T ₀ )/T ₀ ]×100(%) ...(4)

The change in the gauge line distance in the vertical direction (ΔL) is called the film's vertical thermal shrinkage rate, and the change in the gauge line distance in the horizontal direction (ΔT) is called the film's horizontal thermal shrinkage rate.

In the present invention, when a hard coat film is heat treated at 150°C for 30 minutes, the heat shrinkage rate of 0.3% or less means that both the heat shrinkage rate of the film in the longitudinal direction and the heat shrinkage rate of the film in the transverse direction are 0.3% or less.

Such a hard-coated film having a thermal shrinkage rate of 0.3% or less when heated at 150°C for 30 minutes can be obtained, for example, by adjusting the heating conditions (temperature, time, etc.) when performing a heat treatment (annealing treatment) on a hard-coated film having a hard-coated layer formed on each side of a film substrate. In addition, it is also possible to obtain the above-mentioned hard-coated film by, for example, changing the type of film substrate or the type of binder resin used in the hard-coat layer.

The hard coat film of the present invention has excellent heat shrinkage properties (heat resistance) because the heat shrinkage rate when the hard coat film is heated at 150°C for 30 minutes is 0.3% or less, and can prevent damage or deformation of the film caused by heat, for example, when a printed layer (e.g., a conductive layer) formed on the hard coat layer is baked. In addition, a small heat shrinkage rate reduces dimensional changes in subsequent processes, which has the advantage of making alignment easier in the process and expanding the range of applications to precision electronic devices (printed wiring boards, TFT substrates, etc.). On the other hand, if the heat shrinkage rate exceeds 0.3%, the above-mentioned damage or deformation of the film cannot be prevented, and heat resistance is poor.

<Hard Coat Layer A>
As described above, the hard coat film of the present invention has, for example, a hard coat layer A on one side of a film substrate and a hard coat layer B on the other side, and it is preferable that the hard coat layer A formed on at least one side has a surface free energy adjusted to a predetermined range (specifically, a range of 30 mN/m to 55 mN/m) (the above condition (I)).
This hard coat layer A contains an electron beam curable resin as a binder resin, and a leveling agent for adjusting the surface free energy to within the above-mentioned predetermined range.

In the present invention, the above surface free energy refers to the excess energy that the surface of the hard coat layer A has compared to the inside of the layer (bulk). This surface free energy can be measured by analyzing the contact angles of water and hexadecane using a contact angle meter (such as the fully automatic contact angle meter DM-701 manufactured by Kyowa Interface Science Co., Ltd.) using the Kaelble-Uy method.

As described above, the hard coat film of the present invention preferably has a surface free energy of the hard coat layer A on at least one side in the range of 30 mN/m to 55 mN/m. By adjusting the surface free energy of the hard coat layer A to within the above-mentioned range, when a printed layer (e.g., a conductive layer) is formed on the hard coat layer A, the adhesion between the printed layer and the hard coat layer A is excellent. Such a hard coat layer A can be adjusted to the surface free energy of the hard coat layer A in the range of 30 mN/m to 55 mN/m by, for example, containing a fluorine-based leveling agent containing at least a hexafluoropropene oligomer derivative.

Specific examples of the above-mentioned fluorine-based leveling agents that are preferably used in the present invention include commercially available products such as Futergent 681 (product name, manufactured by Neos Corporation), Futergent 184 (product name, manufactured by Neos Corporation), and Futergent 602A (product name, manufactured by Neos Corporation).

In the present invention, the above-mentioned fluorine-based leveling agent may be used in combination with other types of leveling agents as long as the desired effect is not impaired. Examples of other types of leveling agents include acrylic leveling agents and silicone leveling agents.

The amount of the fluorine-based leveling agent blended in order to adjust the surface free energy in the hard coat layer A of the present invention to within the above range is preferably in the range of 0.1% by weight to 3.0% by weight relative to the electron beam curable resin, which is the binder resin of the hard coat layer A. If the amount of the leveling agent blended is less than 0.1% by weight, the absolute amount of the leveling agent is small, making it difficult to obtain the effect of adjusting the surface free energy, and if it exceeds 3.0% by weight, impurities in the coating film increase, which may result in a decrease in hardness.

In the hard coat film of the present invention, the thickness _DA of the hard coat layer A is preferably 1 μm or more (condition (II) above). Here, the thickness _DA refers to the thickness of the hard coat layer A after curing.

If the thickness D _A of the hard coat layer A is less than 1 μm, the heat resistance is insufficient, and it is difficult to suppress deformation of the substrate due to, for example, thermal energy or light energy (heat of baking) for baking the conductive material, which is not preferable. On the other hand, if the thickness D _A of the hard coat layer A is too thick, the flexibility when used as a printing film is impaired, so in the present invention, the thickness D _A is preferably 20 μm or less.

In addition, in the hard coat film of the present invention, the surface hardening degree C _A of the hard coat layer A is preferably in the range of 3 to 15 (condition (III) above). In the present invention, the range of 5 to 15 is particularly preferable, and the range of 6 to 12 is more preferable. If the surface hardening degree C _A of the hard coat layer A is less than 3, the hardening of the hard coat layer A proceeds too much, and the flexibility when used as a printing film is impaired, and the adhesion to a printing layer (e.g., a conductive layer) is deteriorated. On the other hand, if the surface hardening degree C _A of the hard coat layer A exceeds 15, the hardening of the hard coat layer A is insufficient, and the desired hardness as the hard coat layer A cannot be obtained, and the desired heat resistance required for the hard coat layer A is difficult to obtain, and the hard coat film is easily deteriorated by the heat of baking, which is undesirable.

The surface hardness _CA of the hard coat layer A can be calculated by the following formula (1).
Surface hardening degree C _A = (P1/P2) x 100...Formula (1)

Here, P1 is the peak area at 794 to 823 cm ⁻¹ obtained by infrared spectroscopy of the surface of the hard coat layer A, and represents a peak derived from the carbon-carbon double bond of the (meth)acryloyl group. P2 is the peak area at 1658 to 1778 cm ⁻¹ obtained by infrared spectroscopy of the surface of the hard coat layer A, and represents a peak of carbon-oxygen stretching vibration derived from the carbonyl group. Thus, the surface hardening degree C _A indicates the degree of progress of hardening of the hard coat layer A, and for example, the larger this value, the more unreacted (meth)acryloyl groups remain.

The above-mentioned infrared spectrum measurement can be performed using an infrared spectrophotometer (for example, FT-IR Spectrometer Spectrum 100 (manufactured by PerkinElmer Japan)). On the obtained spectrum chart with the horizontal axis representing wave number (cm ⁻¹ ) and the vertical axis representing absorbance, baselines are drawn at 794 to 823 cm ⁻¹ and 1658 to 1778 cm ⁻¹ , and the areas enclosed by these baselines and the spectral curve are defined as the above-mentioned P1 and P2, respectively.

In the hard coat film of the present invention, the degree of surface hardening C _A of the hard coat layer A can be adjusted to the above-mentioned predetermined range by, for example, adjusting the cumulative amount of light of ultraviolet light or electron beam irradiation during hard coat layer A curing. The cumulative amount of light differs depending on the electron beam curable resin used as the binder resin of the hard coat layer A and is not generally determined, but when a polyfunctional (meth)acrylate resin having three or more (meth)acryloyl groups is included, for example, the cumulative amount of light is preferably in the range of 150 to 270 mJ/ ^cm2 .

The electron beam curable resin used in the hard coat layer A of the present invention preferably contains at least a multifunctional (meth)acrylate resin having three or more (meth)acryloyl groups in the molecule in order to obtain heat resistance that prevents deformation of the substrate due to the heat of baking generated by thermal energy or light energy when forming an electric circuit while stably ensuring adhesion between the hard coat layer A and the film substrate.

The polyfunctional (meth)acrylate resin having three or more (meth)acryloyl groups in the molecule, which is preferably used in the present invention, refers to a (meth)acrylate resin having three or more (meth)acryloyl groups in the molecule and capable of being cured by electron beam or ultraviolet light. The number of (meth)acryloyl groups contained in the molecule is preferably 3 to 6, more preferably 4 to 6. When the molecule contains more than six (meth)acryloyl groups, for example, when a heat treatment is performed to bake the ink of the printing layer in a later process, the unreacted (meth)acryloyl groups may become active again, causing the hard coat film to curl. On the other hand, when the number of (meth)acryloyl groups contained in the molecule is less than three, it is difficult to obtain the desired heat resistance required for the hard coat layer A, and the hard coat film may be easily deteriorated by the heat of baking.

Specific examples of polyfunctional (meth)acrylate resins having three or more (meth)acryloyl groups in the molecule that are preferably used in the present invention include polyol poly(meth)acrylates such as neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, pentaerythritol tetra(meth)acrylate, and pentaerythritol tri(meth)acrylate.

Furthermore, such polyfunctional (meth)acrylate resins preferably have a weight average molecular weight of 600 or more, and more preferably 750 or more. If the weight average molecular weight is less than 600, curling due to cure shrinkage is too strong, which is undesirable. Furthermore, the upper limit of the weight average molecular weight is preferably 2000 or less, and more preferably 1500 or less. If the weight average molecular weight is greater than 2000, it is difficult to obtain the desired heat resistance required for the hard coat layer A, and there is a risk that the hard coat film will be easily deteriorated by the heat of baking.

In addition, in the present invention, the above-mentioned trifunctional or more polyfunctional (meth)acrylate resin, i.e., having three or more (meth)acryloyl groups in the molecule, can be used in combination with other electron beam curable resins to the extent that the desired effect is not hindered. The other electron beam curable resins used in combination are transparent resins that are polymerized and cured by irradiation with electron beams or ultraviolet rays, and can be appropriately selected from, for example, acrylic monomers, urethane acrylate resins, polyester acrylate resins, epoxy acrylate resins, and other oligomers and polymers. Preferred monomers include those made of ultraviolet-curable polyfunctional acrylates having two or more (meth)acryloyl groups in the molecule. Specific examples of ultraviolet-curable polyfunctional acrylates having two or more (meth)acryloyl groups in the molecule include polyol polyacrylates such as neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; diacyl acrylate of bisphenol A diglycidyl ether; Examples of such acrylates include epoxy (meth)acrylates such as diacrylate of neopentyl glycol diglycidyl ether and di(meth)acrylate of 1,6-hexanediol diglycidyl ether, polyester (meth)acrylates obtained by esterifying a polyhydric alcohol with a polycarboxylic acid and/or its anhydride and acrylic acid, urethane (meth)acrylates obtained by reacting a polyhydric alcohol, a polyisocyanate and a hydroxyl group-containing (meth)acrylate, and polysiloxane poly(meth)acrylate.

In the hard coat film of the present invention, when a polyfunctional (meth)acrylate resin having three or more (meth)acryloyl groups in the molecule is used as the electron beam curable resin, which is the binder resin of the hard coat layer A, the amount of such a polyfunctional (meth)acrylate resin is preferably 25 to 100% by mass, more preferably 50 to 100% by mass, and even more preferably 80 to 100% by mass, based on the total weight of the electron beam curable resin in the hard coat layer A.

In the coating liquid for forming the hard coat layer A, in addition to the above-mentioned electron beam curable resin and leveling agent, a photopolymerization initiator, an antifoaming agent, a lubricant, an ultraviolet absorber, a light stabilizer, a polymerization inhibitor, a wetting and dispersing agent, a rheology control agent, an antioxidant, an antifouling agent, an antistatic agent, a conductive agent, etc. are blended in a solvent as necessary. The above-mentioned solvent can be appropriately selected from known organic solvents, etc.

The hard coat layer A is formed by applying a coating liquid for forming the hard coat layer A to one side of the film substrate, drying the coating liquid, and then curing the coating liquid by ultraviolet or electron beam irradiation. The integrated amount of ultraviolet or electron beam irradiation during curing of the hard coat layer A is adjusted as described above.

To apply the coating liquid for forming the hard coat layer A onto the film substrate, any known coating method can be used. Examples include reverse coating, gravure coating, bar coating, die coating, spray coating, kiss coating, wire bar coating, and curtain coating, and these coating methods may be used alone or in combination.

The hard coat layer A formed on one side of the film substrate as described above preferably has an arithmetic mean height (Sa) of its surface of 2.0 nm or less. This is preferable because a uniform printed layer (such as a conductive layer) can be formed on the hard coat layer A by having the arithmetic mean height (Sa) of the hard coat layer A surface of 2.0 nm or less.

The arithmetic mean height (Sa) is defined in ISO 25178 and is a parameter obtained by expanding Ra (arithmetic mean roughness of lines: defined in the appendix of JIS B 0031 (1994)/JIS B 0061 (1994)) to a surface, and represents the average of the absolute values of the differences in height of each point with respect to the average surface of the surface. Specifically, it can be calculated from the data of the film surface roughness curve measured with a surface roughness meter.
Generally, by providing a hard coat coating layer with a thickness of 1 μm or more, it is possible to make Sa 2.0 nm or less without being affected by the roughness of the substrate surface.

<Hard Coat Layer B>
The hard coat film of the present invention has the above-mentioned hard coat layer A formed on one surface of a film substrate, and a hard coat layer B formed on the other surface.

As mentioned above, in a high-temperature, high-humidity environment, polyester films such as polyethylene terephthalate, which are suitable as film substrates, can experience a phenomenon in which oligomers precipitate on the film surface, causing the substrate to whiten. However, by providing the above-mentioned hard coat layers A and B on both sides of the film substrate, respectively, it is possible to prevent oligomer precipitation, and to suppress changes in optical properties such as transmittance and haze of a conductive film to which the hard coat film of the present invention is applied, even in a high-temperature, high-humidity environment.

This hard coat layer B contains at least an electron beam curable resin as a binder resin. There are no particular limitations on the electron beam curable resin used in the hard coat layer B of the present invention, and for example, the same resin as that used in the hard coat layer A described above can be used.

In addition to the electron beam curable resin, which is the binder resin, the hard coat layer B can contain a leveling agent for adjusting the surface free energy to within a predetermined range, as in the case of the hard coat layer A. In this case, the leveling agent can be, for example, a fluorine-based leveling agent used in the hard coat layer A. By adjusting the surface free energy of the hard coat layer B to within a predetermined range, when a printed layer (e.g., a conductive layer) is formed on the hard coat layer B, the adhesion between the printed layer and the hard coat layer B can be improved.

In the present invention, the thickness D _B of the hard coat layer B and the thickness D _A of the hard coat layer A are preferably in the range of |D _A -D _B |≦3 μm, and more preferably in the range of |D _A -D _B |≦1 μm. It is preferable that the thickness difference between the hard coat layer A and the hard coat layer B is in the above range, because curling of the hard coat layer due to cure shrinkage is offset. Note that the thickness D _B here refers to the thickness of the hard coat layer B after curing.

In the present invention, the surface hardness C _A of the hard coat layer A and the surface hardness C _B of the hard coat layer B represented by the following formula (2) are preferably in the range of |C _A -C _B |≦3, and more preferably in the range of |C _A -C _B |≦1.
Surface hardening degree C _B = (P3/P4) x 100...Formula (2)

Here, P3 is the peak area at 794 to 823 cm ⁻¹ obtained by infrared spectroscopy of the surface of the hard coat layer B, and represents a peak derived from the carbon-carbon double bond of the (meth)acryloyl group. P4 is the peak area at 1658 to 1778 cm ⁻¹ obtained by infrared spectroscopy of the surface of the hard coat layer B, and represents a peak of carbon-oxygen stretching vibration derived from the carbonyl group. Thus, the surface hardening degree C _B indicates the degree of progress of hardening of the hard coat layer B, and for example, the larger this value, the more unreacted (meth)acryloyl groups remain. The infrared spectroscopy of the hard coat layer B can be measured in the same manner as the hard coat layer A described above.

It is preferable that the difference in the degree of surface hardening between hard coat layer A and hard coat layer B is within the above range, since the stresses of cure shrinkage occurring in hard coat layer A and hard coat layer B tend to be counterbalanced on both sides of the film substrate, and curling is offset.

In order to adjust the difference in the surface hardness between the hard coat layer A and the hard coat layer B within the above range, the surface hardness of the hard coat layer B can be adjusted, for example, by adjusting the integrated light amount of ultraviolet light or electron beam irradiation during hardening of the hard coat layer B. The integrated light amount differs depending on the presence or absence of a resin or additive used in the hard coat layer B and cannot be determined in general, but it is preferable that the integrated light amount is within the range of ±50 mJ/ ^cm2 compared to the integrated light amount of the hard coat layer A, for example.

In addition to the electron beam curable resin, the coating liquid for forming the hard coat layer B contains a leveling agent, a photopolymerization initiator, an antifoaming agent, a lubricant, an ultraviolet absorber, a light stabilizer, a polymerization inhibitor, a wetting and dispersing agent, a rheology control agent, an antioxidant, an antifouling agent, an antistatic agent, a conductive agent, etc., as necessary. The solvent can be appropriately selected from known organic solvents, etc.

The hard coat layer B is formed by applying a coating liquid for forming the hard coat layer B to the surface of the film substrate opposite to the surface on which the hard coat layer A is formed, drying the coating liquid, and then curing the coating liquid by ultraviolet or electron beam irradiation. The integrated light amount of the ultraviolet or electron beam irradiation during the curing of the hard coat layer B is adjusted as described above.

The method for applying the coating liquid for forming the hard coat layer B onto the film substrate is not particularly limited, and the same application method as for the hard coat layer A described above can be used.

The hard coat layer B formed as described above preferably has an arithmetic mean height (Sa) of the surface of 3 nm or more, and preferably 30 nm or less. If the arithmetic mean height (Sa) of the surface of the hard coat layer B is 3 nm or more, a hard coat film having excellent blocking resistance during film winding can be obtained. In addition, if the arithmetic mean height (Sa) of the surface of the hard coat layer B is greater than 30 nm, the haze of the hard coat film may increase, which is not preferable. The arithmetic mean height (Sa) is as described above, so a repeated explanation will be omitted.

One method for adjusting the surface roughness of the hard coat layer B to a predetermined range is, for example, to include a method in which the hard coat layer B contains inorganic or organic fine particles having an average primary particle size of about 10 nm to 100 nm.

A heat treatment (annealing treatment) may be performed on the hard-coated film having hard-coat layers formed on both sides of the above-mentioned film substrate. By appropriately adjusting the heating conditions (temperature, time, etc.) during this heat treatment, it is suitable to obtain a hard-coated film having excellent heat shrinkage characteristics (heat resistance) with a heat shrinkage rate of 0.3% or less when the hard-coated film having hard-coat layers formed on both sides of the film substrate is heated at 150°C for 30 minutes. In this case, the heating conditions are preferably, for example, a temperature of 150°C or higher and a time of 30 seconds or more. This heat treatment can also be performed, for example, in a hot air drying oven.

The present invention also provides a method for producing a hard coat film, which is a method for producing a hard coat film having hard coat layers formed on both sides of a film substrate, and is characterized in that the hard coat film satisfying the following conditions (I), (II), and (III) is subjected to a heat treatment at 150° C. or higher for 30 seconds or longer.
Condition (I): The hard coat layer A formed on at least one surface has a surface free energy in the range of 30 mN/m to 55 mN/m.
Condition (II): The film thickness D _A of the hard coat layer A is 1 μm or more.
Condition (III): the surface hardness C _A of the hard coat layer A represented by the following formula (1) is in the range of 3 to 15.
Surface hardening degree C _A = (P1/P2) x 100...Formula (1)
(Here, the peak area of 794 to 823 cm ⁻¹ obtained by infrared spectroscopy of the surface of the hard coat layer A is defined as P1, and the peak area of 1658 to 1778 cm ⁻¹ is defined as P2.)

The above conditions (I), (II) and (III) have been described above, so a duplicate explanation will be omitted here. The above heat treatment has also been described above.

By using the above-described method for producing a hard-coated film of the present invention, it is possible to obtain a hard-coated film that has excellent heat shrinkage characteristics (heat resistance), and also has excellent adhesion of the printed layer, optical properties, hardness, and curl suppression while maintaining high printability.

As described above in detail, according to the present invention, a hard-coated film having hard-coat layers formed on both sides of a film substrate has a heat shrinkage rate of 0.3% or less when heat-treated at 150° C. for 30 minutes, and therefore a hard-coated film having excellent heat resistance (heat shrinkage characteristics) can be obtained.
Furthermore, according to the present invention, by the hard coat film further satisfying the above-mentioned three conditions (I), (II), and (III), it is possible to obtain a hard coat film that, in addition to this heat resistance (thermal shrinkage characteristics), maintains high printability, and also has excellent adhesion of the printing layer, optical characteristics, hardness, and curl suppression.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1
Butyl acetate/1-propanol (NPA) = 70/30 parts by weight, 100 parts by weight of an electron beam curable resin (trade name: EBECRYL5129, manufactured by Daicel Allnex Corporation, weight average molecular weight 800) mainly composed of urethane acrylate having four (meth)acryloyl groups, 2 parts by weight of a photopolymerization initiator (trade name: Omunirad-184, manufactured by BASF Japan Ltd.), and 0.3 parts by weight of a leveling agent (trade name: Ftergent 184, manufactured by Neos Corporation) were mixed to prepare a hard coat layer coating solution A having a solid content concentration of 40%, and the coating solution was applied to one side of a 125 μm thick polyethylene terephthalate (PET) film (trade name: A4300, manufactured by Toyobo Co., Ltd.) using a Meyer bar so that the film thickness after drying would be 3 μm. Next, this coating layer was dried at 80° C. for 1 minute to volatilize the solvent, and then cured by ultraviolet irradiation treatment with an integrated light quantity of 250 mJ/cm ² to obtain a hard coat film having a hard coat layer A formed thereon.

Next, the hard coat layer coating liquid B having the same composition as the hard coat layer coating liquid A was coated on the other surface of the hard coat film on which the hard coat layer A was formed, using a Mayer bar, so that the film thickness after drying would be 3 μm. Next, this coating layer was dried at 80° C. for 1 minute to volatilize the solvent, and then cured by ultraviolet irradiation treatment with an integrated light amount of 250 mJ/cm ² to form a hard coat layer B.

Next, the double-sided hard-coated film having the hard-coat layer A and the hard-coat layer B formed on both sides as described above was placed in a drying oven (a small hot-air circulating drying oven manufactured by Abezel Co., Ltd.) heated to 150° C. to perform an annealing treatment, and was then removed after 30 seconds and cooled to room temperature in the air.
In this manner, a hard coat film of Example 1 was obtained having a hard coat layer A and a hard coat layer B on both sides of the PET film.

Example 2
The electron beam curable resin of the hard coat layer coating solution A in Example 1 was changed to an electron beam curable resin mainly composed of an oligomer acrylate having three (meth)acryloyl groups (product name: NK Ester A-GL-Y-9E, manufactured by Shin-Nakamura Chemical Co., Ltd., weight average molecular weight 1500), and the resin was coated using a Mayer bar so that the film thickness after drying would be 4 μm to form a hard coat layer A. The hard coat layer B was formed in the same manner as in Example 1, except that the hard coat film of Example 2 was produced in the same manner as in Example 1.

Example 3
A double-sided hard-coated film having a hard-coat layer A and a hard-coat layer B formed on both sides in the same manner as in Example 1 was placed in the drying furnace heated to 200° C. and removed after 60 seconds, and the hard-coated film of Example 3 was produced in the same manner as in Example 1, except that the double-sided hard-coated film was placed in the drying furnace heated to 200° C. and removed after 60 seconds.

Example 4
The electron beam curable resin of the hard coat layer coating solution B of Example 1 was changed to an electron beam curable resin mainly composed of a urethane acrylate having three (meth)acryloyl groups (product name: EBECRYL4265, manufactured by Daicel-Allnex Corporation, weight average molecular weight: 700), and the resin was coated using a Mayer bar so that the film thickness after drying would be 6 μm to form a hard coat layer B. The hard coat layer A was formed in the same manner as in Example 1, except that the hard coat film of Example 4 was produced in the same manner as in Example 1.

Example 5
The electron beam curable resin of the hard coat layer coating solution B of Example 1 was changed to an electron beam curable resin (product name: EBECRYL220, manufactured by Daicel Allnex Corporation, weight average molecular weight 1000) mainly composed of urethane acrylate having six (meth)acryloyl groups, and the resin was coated using a Mayer bar so that the film thickness after drying would be 4 μm to form a hard coat layer B. The hard coat layer A was formed in the same manner as in Example 1, except that the hard coat film of Example 5 was produced in the same manner as in Example 1.

(Comparative Example 1)
A double-sided hard-coated film having a hard-coat layer A and a hard-coat layer B formed on both sides in the same manner as in Example 1 was left to stand in the drying furnace heated to 120°C and removed after 10 seconds, and the hard-coated film of Comparative Example 1 was produced in the same manner as in Example 1.

(Comparative Example 2)
The electron beam curable resin of the hard coat layer coating solution A in Example 1 was changed to an electron beam curable resin mainly composed of a urethane acrylate having two (meth)acryloyl groups (product name: EBECRYL4858, manufactured by Daicel-Allnex Corporation, weight average molecular weight: 400), and the resin was coated using a Mayer bar so that the film thickness after drying would be 7 μm to form a hard coat layer A. Except for this, the hard coat layer B was formed in the same manner as in Example 1. A hard coat film of Comparative Example 2 was produced in the same manner as in Example 1.

<Evaluation>
The hard coat films of the Examples and Comparative Examples prepared as described above were evaluated for the following items, and the results are summarized in Table 2. The configurations of the hard coat films of the Examples and Comparative Examples are summarized in Table 1.

<Surface free energy>
The surface free energy of the hard coat layer A of each hard coat film was measured as follows.
The contact angle of the hard coat layer surface was measured using a contact angle meter (Kyowa Interface Science Co., Ltd. fully automatic contact angle meter DM-701) with pure water and hexadecane, and the surface free energy was calculated from the contact angle value by analysis using the Kaelble-Uy method.

<Film Thickness of Hard Coat Layer>
The thickness D _A of the hard coat layer A and the thickness D _B of the hard coat layer B of each hard coat film were measured using a coating thickness measurement system F20 (manufactured by Filmetrics Inc.). From the results, the value of |D _A -D _B | was calculated. The film thickness after coating and drying was the same as the film thickness after curing by UV irradiation.

<Surface hardening degree of hard coat layer>
The degree of surface hardening _CA of the hard coat layer A of each hard coat film was determined as follows.
Using an infrared spectrophotometer (FT-IR Spectrometer Spectrum 100 (manufactured by PerkinElmer Japan)), infrared spectroscopy measurement was performed on the surface of the hard coat layer A. On the obtained spectrum chart with the horizontal axis representing wave number (cm ^-1 ) and the vertical axis representing absorbance, baselines were drawn at 794 to 823 cm ^-1 and 1658 to 1778 cm ^-1 , respectively, and the areas surrounded by these baselines and the spectrum curve were defined as peak areas P1 and P2, respectively, and the above-mentioned surface hardening degree C _A was calculated by the above-mentioned formula (1).
The degree of surface hardening _CB of the hard coat layer B of each hard coat film was also determined by infrared spectroscopy of the surface of the hard coat layer B in the same manner as above, and calculated according to the above-mentioned formula (2).
From the above results, the value of |C _A −C _B | was calculated.

<Heat shrinkage rate>
The thermal shrinkage rate in the machine direction and the transverse direction of each hard coat film were determined by the above-mentioned test method. In Table 2, "TD" indicates the thermal shrinkage rate in the machine direction, and "MD" indicates the thermal shrinkage rate in the transverse direction.

<Surface flatness>
The roughness curve of the film surface was measured using a three-dimensional surface roughness meter "VertScan 2.0" manufactured by Ryoka Systems Co., Ltd., and the arithmetic mean height (Sa) of the hard coat layer A surface was calculated from the data of this film surface roughness curve.

<Optical properties>
The total light transmittance and haze value (ΔHaze) of each hard-coated film were measured using a haze meter "HM150" manufactured by Murakami Color Research Laboratory. Visual evaluation was performed by placing each hard-coated film between a light source (fluorescent lamp) and the line of sight, tilting the hard-coated film at an appropriate angle so that the entire amount of light from the light source could be transmitted, and evaluating the film according to the following criteria.
Good: No problems with transparency even through hard coat film, and excellent optical properties.
×: Appears whitish when viewed through the hard coat film, and has poor optical properties.

<Adhesion of printed layer>
On the hard coat layer A of each hard coat film obtained in the examples and comparative examples, a copper nanoparticle paste (product name: CP-100, manufactured by Harima Chemical Co., Ltd.) was applied to a film thickness of 20 μm and a 5 × 5 cm square using a desktop screen printer (product name: DP-320, manufactured by Newlong Precision Industry Co., Ltd.), and photo-baked by xenon flash light irradiation (xenon pulse light irradiation device S-200, manufactured by XENON Corporation) to obtain a conductive film having a printed layer (conductive layer).
The adhesion of the printed layer (conductive layer) of the obtained conductive film was evaluated in accordance with the cross-cut method described in JIS-K5600-5-6. Specifically, 100 cross-cuts of 1 ^mm2 were made on the printed layer (conductive layer) surface of the obtained conductive film using a checkerboard peel test jig, and adhesive tape No. 252 manufactured by Sekisui Chemical Co., Ltd. was attached thereon and pressed evenly with a spatula, after which the adhesive tape was peeled off in a 180° direction to determine the remaining rate of the printed layer (conductive layer) (the ratio of the number of remaining cross-cuts), which was evaluated according to the following three-level criteria. If the evaluation was ◎ or ○, the adhesion was judged to be good.
◎: Residual rate 95% or more 〇: Residual rate 75% to less than 95% ×: Residual rate less than 75%

<Scratch resistance>
In a test method conforming to JIS-K5600-5-10, a 25 mm diameter steel wool #0000 (manufactured by Japan Steel Wool Co., Ltd.) was pressed against the hard coat layer A surface of each hard coat film at 1 kgf and reciprocated 10 times, and the scratch state of the hard coat surface was visually observed from above at an angle using a three-wavelength neutral white fluorescent lamp (Panasonic Paluc, F.L 15EX-N 15W) as a light source. The evaluation criteria are as follows. Products evaluated as ⊚ or ◯ were deemed to have passed the scratch resistance.
◎: No scratches are visible.
◯: Some scratches are observed, but not to a level that causes any practical problems.
△: Minor scratches are observed.
x: The scratches are very noticeable.

<Heat resistance>
On the hard coat layer A of each hard coat film, copper nanoparticle paste (product name: CP-100, manufactured by Harima Chemical Co., Ltd.) was used to form printed lines with line widths of 200 μm, 100 μm, and 50 μm using a tabletop screen printer (product name: DP-320, manufactured by Newlong Precision Industry Co., Ltd.). After printing, the film was photo-cured according to the usual method by xenon flash light irradiation (xenon pulse light irradiation device S-200, manufactured by XENON Corporation) (irradiation voltage 3 kV, irradiation time 1.2 ms). Each printed line after photo-curing was magnified and observed with a laser microscope (product name: VH-6300, manufactured by Nikon Corporation) to determine the presence or absence of film damage. This film damage, specifically, refers to the entire or partial deformation of the film, or the depression or swelling of the light-irradiated part. The evaluation criteria are as follows.
○: No film damage ×: Film damage

<Printability>
On the hard coat layer A of each hard coat film, a copper nanoparticle paste (product name: CP-100, manufactured by Harima Chemical Co., Ltd.) was applied to a film thickness of 20 μm and a 5 × 5 cm square using a desktop screen printer (product name: DP-320, manufactured by Newlong Precision Industry Co., Ltd.), and photo-cured by xenon flash light irradiation (xenon pulse light irradiation device S-200, manufactured by XENON Corporation) to obtain a conductive film of the printed layer (conductive layer).
When the area of the obtained printed layer was X ^cm2 , the reproducibility of the wiring was calculated using the following formula and evaluated according to the following two-level criteria: If the evaluation was ◯, the printability was judged to be good.
Formula: (5×5)/X×100
○: Within 100% ±5 ×: 100% ±5 or more

<Curling characteristics>
Each hard-coated film was cut into a 10×10 cm square using a cutter, and left flat for 2 hours in a Safe Bend Dryer (product name: N50-S5, manufactured by Satake Chemical Machinery Co., Ltd.) heated to 150° C., and then visually observed for the presence or absence of warping of the film. The evaluation criteria are as follows:
○: No warping ×: Warping

From the results in Tables 1 and 2, it can be seen that the hard coat films according to the embodiments of the present invention all have good heat resistance, and furthermore, the adhesion of the printed layer, optical properties, scratch resistance, printability, and curl properties are good. That is, according to the present invention, it is possible to provide a hard coat film having excellent heat resistance (thermal shrinkage properties), and further, in addition to this heat resistance (thermal shrinkage properties), it is possible to provide a hard coat film having excellent adhesion of the printed layer, optical properties, hardness, and curl suppression while maintaining high printability. Therefore, the hard coat film of the present invention is suitable for applications such as a conductive film having a printed layer such as a conductive layer formed thereon.

On the other hand, the hard coat films of Comparative Examples 1 and 2, which have a thermal shrinkage rate of more than 0.3%, do not have the required heat resistance. In other words, it is difficult to obtain a hard coat film having excellent heat resistance (thermal shrinkage characteristics) in the comparative examples that do not satisfy the requirements of the hard coat film of the present invention.

Claims (2)

A method for producing a hard coat film in which a hard coat layer is formed on both sides of a film substrate, comprising the steps of:
The film substrate is a polyethylene terephthalate film,
the hard coat layer A formed on at least one surface of the film substrate contains an electron beam curable resin, the electron beam curable resin being a polyfunctional (meth)acrylate resin having a weight average molecular weight of 600 or more and having three or more (meth)acryloyl groups in the molecule;
The hard-coated film is subjected to a heat treatment at 150° C. or more and 200° C. or less for 30 seconds or more and 60 seconds or less without applying tension , and the hard-coated film after the heat treatment satisfies the following conditions (I), (II), and (III),
The method for producing a hard coat film, characterized in that when the hard coat film after the heat treatment is heated at 150°C for 30 minutes, the heat shrinkage rate in the longitudinal direction and the heat shrinkage rate in the transverse direction are both 0.2% or less .
Condition (I): The hard coat layer A formed on at least one surface has a surface free energy in the range of 30 mN/m to 55 mN/m.
Condition (II): The film thickness D _A of the hard coat layer A is 1 μm or more.
Condition (III): the surface hardness C _A of the hard coat layer A represented by the following formula (1) is in the range of 3 to 15.
Surface hardening degree C _A = (P1/P2) x 100...Formula (1)
(Here, the peak area of 794 to 823 cm ⁻¹ obtained by infrared spectroscopy of the surface of the hard coat layer A is defined as P1, and the peak area of 1658 to 1778 cm ⁻¹ is defined as P2.) 2. The method for producing a hard coat film according to claim 1 , wherein the heat treatment of the hard coat film is performed at 150° C. for 30 seconds or at 200° C. for 60 seconds .