JP7438818B2 - Manufacturing method of hard coat film for window film - Google Patents

Description

The present invention particularly relates to a method for manufacturing a hard coat film suitable for use in window films and the like.

Currently, window films are often used for partitions in offices, for example. In consideration of such uses, window films are required to provide scratch resistance so that the partition surface is not scratched and visibility is not deteriorated. Therefore, as a window film, a hard coat film in which a hard coat layer is provided on a base film is generally used to impart scratch resistance to the partition surface. Additionally, if the partition is made of a highly transparent material (e.g. glass material, transparent plastic material, etc.), it is required that the transparency of the partition is not impaired by using a window film on its surface. Ru. Conversely, even if the partition is made of a highly transparent material, using a window film on its surface will make the partition opaque and give it some degree of light-blocking or shielding properties. In some cases, it may be desirable to do so. Furthermore, even if the surface of the partition is touched by hand, it may be required to provide stain resistance so that dirt such as fingerprints can be easily wiped off.
As described above, the functional requirements for hard coat films used as window films for partition applications, for example, are increasing.

Conventionally, the hard coat film described above is produced by, for example, coating a coating liquid for a hard coat layer on a base film, drying the coating layer, and then irradiating the coating layer with ultraviolet rays. It can be manufactured by forming a hard coat layer on a base film by curing the base film.
Patent Document 1 listed below, for example, discloses a coating method using a die coating method.

Patent No. 4573550

As mentioned above, the functional requirements for hard coat films used as window films for partitions, for example, are increasing, and in order to obtain such hard coat films, it is necessary to ensure that the obtained hard coat film has the necessary physical properties. Of course, it is also important to have coating stability, which means that good quality products without coating defects can be stably obtained.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for producing a hard coat film that has target physical properties and has coating stability that allows a good quality hard coat film with no coating defects to be stably obtained. That's true.

The present inventors have conducted intensive studies to solve the above problems, and have found that, in particular, in order to stably obtain a high-quality hard coat film without coating defects, it is necessary to It has been found that it is necessary to control the processing conditions in the drying process after the coating process to form the coating layer.
The present invention was completed as a result of studies based on various findings obtained.
That is, the present invention has the following configuration.

(First invention)
A method for producing a hard coat film having a hard coat layer containing an ionizing radiation curable resin on a base material, the ionizing radiation curable resin containing a urethane acrylate resin, and forming a hard coat layer on the base material. The hard coat layer is formed on the base material by comprising a coating step of applying a coating liquid to form a hard coat layer, and a drying step of drying the hard coat layer. The method for producing a hard coat film is characterized in that in the drying step, the drying temperature is controlled in multiple stages within the range of 40° C. to 80° C.

(Second invention)
The method for producing a hard coat film according to the first aspect of the present invention is characterized in that in the drying step, the drying temperature is raised from the lowest temperature to the highest temperature and then lowered from the highest temperature.

(Third invention)
The method for producing a hard coat film according to the second aspect of the present invention is characterized in that in the drying step, the drying temperature is raised from 40°C to 80°C and then lowered from 80°C.

(Fourth invention)
The method for producing a hard coat film according to any one of the first to third inventions, wherein the hard coat layer has antifouling properties.

(Fifth invention)
The method for producing a hard coat film according to any one of the first to fourth inventions, wherein the base material is an acrylic film base material.

According to the present invention, it is possible to provide a method for producing a hard coat film that has target physical properties and has coating stability that allows a good quality hard coat film without coating defects to be stably obtained. can.

Embodiments of the present invention will be described in detail below.
In the present invention, unless otherwise specified, the description "○○ to △△" means "more than or equal to ○○ and less than or equal to △△."

The method for producing a hard coat film according to the present invention will be explained below.
As described above, the method for producing a hard coat film according to the present invention is a method for producing a hard coat film having a hard coat layer containing an ionizing radiation curable resin on a base material, the ionizing radiation curable resin comprising: A coating process that includes a urethane acrylate resin and forms a hard coat layer by coating a coating liquid for forming a hard coat layer on a substrate, and a drying process that dries the hard coat layer. The hard coat layer is formed on the base material, and in the drying step, the drying temperature is controlled in a plurality of stages within the range of 40° C. to 80° C.

A film base material is usually used as the base material to be coated with this hard coat film.
The film base material used in the present invention is not particularly limited, and examples thereof include acrylic resin, triacetyl cellulose, polyethylene terephthalate, cycloolefin polymer, polycarbonate, polyethylene naphthalate, polyethylene, polytrimethylene terephthalate, and polypropylene. , polybutylene terephthalate, polybutylene naphthalate, polystyrene, polymethyl methacrylate, polystyrene glycidyl methacrylate, aromatic polyimide, alicyclic polyimide, polyamideimide, and mixtures thereof. For example, the acrylic resin film base material has UV-cutting performance.

Next, the hard coat layer will be explained.
The resin contained in the hard coat layer can be used without any particular restriction as long as it forms a film. It is preferable to use an ionizing radiation-curable resin because it allows the degree of crosslinking to be adjusted by irradiation, and the surface hardness of the hard coat layer to be adjusted.

The ionizing radiation-curable resin used in the present invention is a transparent resin that can be cured by irradiation with ultraviolet rays (hereinafter abbreviated as "UV") or electron beams (hereinafter abbreviated as "EB"). Although not particularly limited, UV or EB treatment having three or more (meth)acryloyloxy groups in one molecule in order to improve coating hardness and form a three-dimensional crosslinked structure in the hard coat layer. Those made of curable polyfunctional acrylate are preferred. Specific examples of UV or EB curable polyfunctional acrylates include urethane acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol tri(meth)acrylate. acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane ethoxy triacrylate, glycerin propoxy triacrylate, ditrimethylolpropane tetraacrylate, etc. I can do it. In addition, polyfunctional acrylates may be used not only alone, but also as a mixture of two or more types.

Further, the ionizing radiation curable resin used in the present invention preferably has a weight average molecular weight of, for example, in the range of 700 to 3,600, more preferably a weight average molecular weight of 700 to 3,000, and has a weight average molecular weight of 700 to 3,600. More preferably 700-2400. If the weight average molecular weight is less than 700, curing shrinkage will be large when cured by UV or EB irradiation, and the phenomenon that the hard coat film will curl back toward the hard coat layer side will become large, and the hard coat film will not be able to pass through the subsequent processing steps. Defects occur and processing suitability is poor. Furthermore, if the weight average molecular weight exceeds 3,600, the flexibility of the hard coat layer will increase, but the hardness will be insufficient, so it is not suitable.

Further, when the ionizing radiation-curable resin used in the present invention has a weight average molecular weight of less than 1500, it is desirable that the number of functional groups in one molecule is 3 or more and less than 10. Further, when the weight average molecular weight of the ionizing radiation curable resin is 1,500 or more, the number of functional groups in one molecule is preferably 3 or more and 20 or less. Within the above range, it is possible to suppress the occurrence of cracks under heat-resistant conditions (storage at 100° C. for 5 minutes), suppress curling, and maintain appropriate processing suitability.

In addition to the above-mentioned ionizing radiation-curable resins, the resins contained in the hard coat layer include thermoplastic resins such as polyethylene, polypropylene, polystyrene, polycarbonate, polyester, acrylic, styrene-acrylic, cellulose, and phenol. Thermosetting resins such as resins, urea resins, unsaturated polyesters, epoxy, and silicone resins may be blended within a range that does not impair the hardness and scratch resistance of the hard coat layer.

It is also possible to further improve the surface hardness (scratch resistance) by incorporating inorganic oxide fine particles into the hard coat layer. In this case, the average particle size of the inorganic oxide fine particles is preferably in the range of 5 to 50 nm, more preferably in the range of 10 to 20 nm. When the average particle diameter is less than 5 nm, it is difficult to obtain sufficient surface hardness. On the other hand, when the average particle diameter exceeds 50 nm, the gloss and transparency of the hard coat layer tend to decrease, and the flexibility may also decrease.

In the present invention, examples of the inorganic oxide fine particles include alumina and silica. Among these, alumina whose main component is aluminum is particularly suitable because it has high hardness and can produce effects with a smaller amount than silica.

The coating solution for forming a hard coat layer (paint for hard coat) for forming the above-mentioned hard coat layer can contain a known photopolymerization initiator. As such a photopolymerization initiator, acetophenones and benzophenones can be used.

A leveling agent can be used in the hard coat layer for the purpose of improving coating properties. For example, known leveling agents such as fluorine-based, acrylic-based, siloxane-based, and adducts or mixtures thereof can be used. It is. In addition, in touch panel applications, etc., adhesive resistance using optical transparent adhesive OCR is required for the purpose of adhesion to cover glass (CG), transparent conductive material (TSP), liquid crystal module (LCM), etc. of touch panel terminals. In such cases, it is preferable to use an acrylic leveling agent or a fluorine leveling agent that has a high surface free energy (approximately 40 mN/m or more).

In order to impart antifouling properties to the hard coat film of the present invention, a fluorine-based antifouling agent (leveling agent, surfactant, etc.) can be added to the hard coat layer. The amount of the antifouling agent added is not particularly limited, but it is preferably 0.05% to 1.0% by weight based on the resin solid content in the hard coat paint.

Furthermore, in order to impart antiglare properties to the hard coat film of the present invention, it is necessary to form an uneven shape on the surface of the hard coat layer. For this purpose, it is preferable to add organic fine particles or inorganic fine particles to the hard coat layer. Examples of the organic fine particles include fine particles of vinyl chloride resin, acrylic resin, (meth)acrylic resin, polystyrene resin, melamine resin, polyethylene resin, polycarbonate resin, acrylic-styrene copolymer resin, silicone resin, and the like. In addition, examples of the inorganic fine particles include the above-mentioned inorganic oxide fine particles such as silica.
The amount of the fine particles added is preferably in the range of 10% to 60% by weight based on the resin solid content in the hard coat paint from the viewpoint of achieving good anti-glare properties.

Furthermore, in order to impart opacity to the hard coat film of the present invention, it is preferable to increase the internal haze value of the hard coat layer, for example. For this purpose, there is a method of adding the above-mentioned fine particles to the above-mentioned hard coat layer. Internal haze occurs when light is refracted and scattered due to the presence of fine particles in the hard coat layer.
In order to increase the internal haze value, the amount of the fine particles added is preferably in the range of 10% to 60% by weight based on the resin solid content in the hard coat paint.

As other additives added to the hard coat layer, ultraviolet absorbers, antifoaming agents, surface tension regulators, antioxidants, antistatic agents, light stabilizers, etc. may be added as necessary.

The above-mentioned hard coat layer is prepared by applying a coating liquid for forming a hard coat layer in which a photopolymerization initiator, other additives, etc. are dissolved and dispersed in an appropriate solvent in addition to the above-mentioned ionizing radiation curable resin. After coating on a substrate and drying, photopolymerization occurs by irradiating ionizing radiation such as UV or EB, and a hard coat layer with excellent hardness can be obtained.

The solvent can be appropriately selected depending on the solubility of the resin to be blended, and any solvent may be used as long as it can uniformly dissolve or disperse at least the solid content (resin, photopolymerization initiator, other additives, etc.). Examples of such solvents include aromatic solvents such as toluene, xylene, and n-heptane, aliphatic solvents such as cyclohexane, methylcyclohexane, and ethylcyclohexane, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, and acetic acid. Known organic solvents such as ester solvents such as butyl and methyl lactate, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, and alcohol solvents such as methanol, ethanol, isopropyl alcohol, and n-propyl alcohol are used alone. Alternatively, several types can be used in combination as appropriate.

Further, the concentration (solid content concentration) of the coating liquid is not particularly limited, but may be in the range of, for example, about 20% by weight to 70% by weight.

The irradiation amount of ionizing radiation (UV, EB, etc.) after applying and drying the above-mentioned coating liquid for forming a hard coat layer may be any amount necessary to give the hard coat layer sufficient hardness. , can be appropriately set depending on the type of ionizing radiation curable resin, etc.

There are no particular limitations on the coating method of the hard coat forming coating liquid for forming the hard coat layer, but examples include gravure coating, microgravure coating, fountain bar coating, slide die coating, and slot die coating. Known coating methods include coating, screen printing, and spray coating.

Furthermore, there are no particular restrictions on the coating speed, but in consideration of productivity and the like, an appropriate coating speed is about 10 to 40 m/min.

In the present invention, the drying temperature is set within the range of 40°C to 80°C in the drying process after the coating process in which the hard coat layer forming coating liquid is applied onto the base material to form the hard coat coated layer. Therefore, it is important to dry the hard coat layer by controlling it in multiple stages. This makes it possible to ensure coating stability in which a high-quality hard coat film without coating defects can be stably obtained.

In addition, if the lower limit of the drying temperature is less than 40° C., drying may be insufficient and the adhesion of the hard coat layer to the substrate may deteriorate. On the other hand, if the upper limit of the drying temperature is higher than 80°C, coating defects such as dent-like defects may occur on the coated surface, and the coating appearance (coating quality) of the hard coat film will deteriorate. do.

In the present invention, in the drying process, the drying temperature is controlled in multiple stages within the range of 40°C to 80°C, but considering productivity etc., the drying temperature is controlled in the range of 3 to 7 stages, for example. Preferably controlled.

Further, in a preferred embodiment of the present invention, the drying temperature is controlled to be raised from the lowest temperature to the highest temperature and then lowered from the highest temperature. Specifically, in one preferred embodiment, the drying temperature is controlled to be raised from 40°C to 80°C and then lowered from 80°C.

For example, when carrying out the above drying process using a drying oven, the inside of the drying oven is composed of a plurality of regions, and the drying temperature is controlled in multiple stages within the range of 40°C to 80°C in the plurality of regions. The above-mentioned drying process can be carried out by transporting the hard coat film through the drying oven. In addition, with the hard coat film stopped in the drying oven, the drying process is carried out by controlling the drying temperature in multiple stages within the range of 40°C to 80°C and performing multiple heating stages. You can also.

Further, the heating time (drying time) at each stage of the drying process can be set as appropriate, and the heating time at each stage may be the same or different. Additionally, the overall drying time varies depending on the composition of the coating solution (types of resin, solvent, etc.) and cannot be generalized, but the total drying time in the above drying process is, for example, in the range of 1 minute to 5 minutes. It is appropriate to do so.

The coating thickness (after drying) of the hard coat layer is not particularly limited as it varies depending on the use of the hard coat film, but it is generally in the range of 1.0 μm to 10.0 μm, for example. suitable. If the coating film thickness is less than 1.0 μm, it is not preferable because it is difficult to obtain the necessary scratch resistance. Moreover, if the coating film thickness exceeds 10.0 μm, it is not preferable because curling is likely to occur and handleability during the manufacturing process etc. is deteriorated.

As explained in detail above, according to the present invention, the hard coat film has coating stability that allows a good quality hard coat film to be stably obtained that has target physical properties and is free from coating defects. A manufacturing method can be provided.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
[Preparation of coating liquid for forming hard coat layer]
100 parts by weight of electron beam curable resin whose main component is urethane acrylate (manufactured by Toyochem Co., Ltd.), appropriate amount of photopolymerization initiator (product name: Omunirad-184, manufactured by BASF Japan Co., Ltd.), leveling agent (product name: RS75-) A, 0.1 part by weight (manufactured by DIC Corporation), 2.6 parts by weight of a hindered amine light stabilizer (product name: TINUBIN 292, manufactured by BASF Japan Ltd.), n-propyl alcohol/butyl acetate/butyl cellosolve = 60 /30/10 parts by weight to prepare a coating solution for forming a hard coat layer (hereinafter also referred to as "paint for hard coat") having a solid content concentration of 40% by weight.

[Production of hard coat film]
The above hard coat paint was applied to one side of a 1330 mm wide acrylic film substrate (manufactured by Toyo Kohan Co., Ltd.) with a thickness of 40 μm so that the coating layer thickness after drying was 5 μm. did.

Next, this coating layer was dried in a drying oven. In this drying process, the drying temperature was controlled in multiple stages within the range of 40°C to 80°C. In this example, the interior of the drying oven is composed of four regions (A, B, C, and D), and the drying temperature from region A to region D is 40°C → 80°C → 80°C → 70°C. controlled in stages.

The hard coat film is dried at a drying temperature controlled in multiple stages while being transported from area A to area D in the drying oven. The heating time in each area was approximately the same, and the total drying time (heating time) in this drying step was 1 minute.

Next, the coating layer that had undergone the drying process was cured by ultraviolet irradiation treatment at a cumulative light intensity of 150 mJ/cm ² to form a hard coat layer.
In the manner described above, the hard coat film of this example was obtained.

(Example 2)
In this example, the drying process was performed by controlling the drying temperature in four steps from area A to area D in the drying oven: 40°C → 60°C → 80°C → 70°C. A hard coat film of Example 2 was produced in the same manner as in Example 1.

(Comparative example 1)
In this comparative example, the drying process was performed by controlling the drying temperature in four steps from area A to area D in the drying oven: 50°C → 95°C → 95°C → 70°C. A hard coat film of Comparative Example 1 was produced in the same manner as in Example 1.

(Example 3)
[Preparation of hard coat paint]
100 parts by weight of electron beam curable resin whose main component is urethane acrylate (manufactured by Toyochem Co., Ltd.), appropriate amount of photopolymerization initiator (product name: Omunirad-184, manufactured by BASF Japan Co., Ltd.), leveling agent (product name: RS75-) A, manufactured by DIC Corporation) 0.5 parts by weight, hindered amine light stabilizer (product name: TINUBIN 292, manufactured by BASF Japan Ltd.) 6.4 parts by weight, silicon fine particles (Momentive Performance Materials Japan jointly) A hard coat paint having a solid content concentration of 40% by weight was prepared by diluting 116 parts by weight of a dispersant (manufactured by Bick Chemie) and 35 parts by weight of a dispersant (manufactured by Bikkemie) with toluene/butyl cellosolve = 70/30 parts by weight.

[Production of hard coat film]
As in Example 1, the above hard coat paint was applied to one side of an acrylic film base material (manufactured by Toyo Kohan Co., Ltd.) with a thickness of 40 μm and a width of 1330 mm, so that the coating layer thickness after drying was 7. It was coated to a thickness of .5 μm.

Next, this coating layer was dried in the same manner as in Example 1. In this embodiment, the drying temperature from area A to area D in the drying oven is controlled in four stages: 40°C → 80°C → 80°C → 70°C. The heating time in each area was approximately the same, and the total drying time (heating time) in this drying step was 1 minute.

Next, the coating layer that had undergone the drying process was cured by ultraviolet irradiation treatment at a cumulative light intensity of 150 mJ/cm ² to form a hard coat layer.
In the manner described above, the hard coat film of this example was obtained.

(Example 4)
In this example, the drying process was performed by controlling the drying temperature in four steps from area A to area D in the drying oven: 40°C → 60°C → 80°C → 70°C. A hard coat film of Example 4 was produced in the same manner as in Example 3.

(Comparative example 2)
In this comparative example, the drying process was performed by controlling the drying temperature in four steps from area A to area D in the drying oven: 50°C → 95°C → 95°C → 70°C. A hard coat film of Comparative Example 2 was produced in the same manner as in Example 3.

[evaluation]
The hard coat films of Examples and Comparative Examples produced as described above were evaluated for physical properties and quality in the following items, and the results are summarized in Table 1. Table 1 also summarizes the control temperature conditions in the drying process in each of the Examples and Comparative Examples described above.

<Total light transmittance>
It was measured using a haze meter "HM150" manufactured by Murakami Color Research Institute.

<Haze value>
It was measured using a haze meter "HM150" manufactured by Murakami Color Research Institute.

<Adhesion>
The adhesion between the base material and the hard coat layer was evaluated according to JIS-K5600-5-6. Specifically, for each hard coat film, 100 crosscuts of 1 mm ² were made using a checkerboard peel test jig under normal conditions, that is, constant temperature and humidity conditions (23 ° C., 50% RH). Adhesive tape No. 252 manufactured by Sekisui Chemical Co., Ltd. was pasted on it, pressed uniformly using a spatula, and then peeled off in a 60 degree direction to determine the residual rate of the hard coat layer (remaining number of hard coat layers). evaluated. Adhesion was determined to be acceptable if the residual rate of the hard coat layer was 90% or more.

<Scratch resistance>
For each hard coat film, the hard coat layer surface was rubbed back and forth 10 times using steel wool #0000 under a load of 250 gf/cm ² to prevent scratches. The condition was evaluated using the following criteria. Products evaluated from A to B were judged to be acceptable in terms of scratch resistance.
A: No scratches occurred.
B: Some scratches occur.
C: 10 or more scratches occur D: Innumerable scratches occur

<Fouling resistance>
On the surface of each hard coat film, draw a 5 cm long line with an oil-based black marker (manufactured by Zebra, product number YYTS5-BK) and wipe it off with a cotton cloth. It was evaluated based on the residual rate (residual rate with respect to a height of 5 cm). If the residual rate of ink was less than 10%, the antifouling property was determined to be acceptable.

<Coating appearance>
The presence or absence of coating defects such as dent-like defects on the coated surface was visually observed to evaluate the coating appearance (coating quality) of the hard coat film.

From the results in Table 1, it can be seen that according to the examples of the present invention, a high-quality hard coat film with target physical properties such as adhesion, scratch resistance, and antifouling properties and without coating defects can be stably produced. You can see that it can be obtained by
On the other hand, in the case of the comparative example, although the target physical properties were obtained to some extent, coating defects occurred and a good coating appearance could not be obtained.

Claims (5)

A method for producing a hard coat film having a hard coat layer containing an ionizing radiation curable resin and silicon fine particles on a base material, the method comprising:
The ionizing radiation curable resin includes a urethane acrylate resin,
The hard coat film has a haze value of 81.7% or more and is for window film,
a coating step of coating a coating liquid for forming a hard coat layer on a base material to form a hard coat coating layer;
a drying step of drying the hard coat coating layer;
forming the hard coat layer on the base material,
A method for producing a hard coat film for a window film , characterized in that, in the drying step, the drying temperature is controlled in multiple stages within the range of 40° C. to 80° C. 2. The method for manufacturing a hard coat film for a window film according to claim 1, wherein in the drying step, the drying temperature is raised from a minimum temperature to a maximum temperature and then lowered from the maximum temperature. The method for manufacturing a hard coat film for a window film according to claim 2, wherein in the drying step, the drying temperature is raised from 40°C to 80°C and then lowered from 80°C. 4. The method for producing a hard coat film for a window film according to claim 1, wherein the hard coat layer has antifouling properties. The method for producing a hard coat film for a window film according to any one of claims 1 to 4, wherein the base material is an acrylic film base material.