JP7777482B2 - Method for producing release film - Google Patents

Description

The present invention relates to a method for producing a release film.

Release films are used as adhesive labels, carrier sheets in the production of resin sheets, various protective sheets, and more. These release films have a release layer composed of a silicone-based release agent or the like provided on a substrate such as paper or plastic film. These release films are manufactured using a coating liquid containing a solvent-based silicone-based release agent containing an organic solvent, which is then applied to a substrate such as a plastic film and heated to form a release layer on the substrate.

As a method for producing such a release film, Patent Document 1 discloses a release film having a sheet-like substrate and, provided thereon, a cured layer of an addition-reaction type silicone resin composition containing a photosensitizer, wherein the cured layer is formed by heating an addition-reaction type silicone resin composition layer containing at least one photosensitizer selected from α-hydroxyketones and α-diketone dialkyl acetals, followed by ultraviolet irradiation.

Japanese Patent Application Laid-Open No. 2001-205746

However, while it is possible to reduce the amount of organic solvent used in the coating liquid used to form the release layer and use a solvent-free silicone release agent, etc., this can result in insufficient adhesion to the substrate, making it difficult to achieve the release properties required of a release film. This problem is particularly pronounced when using a polyethylene terephthalate substrate; for example, even light rubbing of the surface of the release layer can cause the release agent to come off.

The present invention was made in consideration of these circumstances, and aims to provide a method for producing a release film that can impart practical release properties to the film and has excellent adhesion to the substrate.

As a result of extensive research into achieving the above-mentioned object, the present inventors discovered that the process involves (1) applying a coating liquid containing an addition reaction type solventless silicone release agent to a polyethylene terephthalate substrate to obtain a laminate including a coating layer, (2) a pre-irradiation step in which the coating layer of the laminate is irradiated with ultraviolet light so that the integrated light amount is 8 to 1400 mJ/ ^m2 , and (3) after step (2), heating the laminate to reactively cure the coating layer and form a release layer, thereby completing the present invention.

In other words, the present invention is as follows:

[1]
This method for producing a release film includes the following steps: (1) applying a coating solution containing an addition reaction type solventless silicone release agent to a polyethylene terephthalate substrate to obtain a laminate including a coating layer; (2) a pre-irradiation step of irradiating the coating layer of the laminate with ultraviolet light so that the cumulative light amount is 8 to 1400 mJ/ ^m2 ; and (3) after step (2), heating the laminate to reactively cure the coating layer and form a release layer.
[2]
In the method for producing a release film according to [1], the process (3) is a process in which, after the process (2), the laminate is heated and then further irradiated with ultraviolet light to reactively harden the coating layer and form a release layer.
[3]
The method for producing a release film according to [1] or [2], wherein the coating liquid containing the solventless silicone release agent exhibits a weight loss rate of 8.0% by mass or less at 150°C when heated from room temperature to 170°C at a heating rate of 10°C/min.

The present invention provides a method for producing a release film that can impart practical release properties to the film and has excellent adhesion to the substrate.

The following describes in detail the form for carrying out the present invention (hereinafter simply referred to as the "present embodiment"). The following present embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content. The present invention can be carried out with appropriate modifications within the scope of its gist.

The method for producing a release film according to this embodiment includes the following steps: (1) applying a coating solution containing an addition-reaction-type solventless silicone release agent to a polyethylene terephthalate substrate to obtain a laminate including a coating layer; (2) irradiating the coating layer of the laminate with ultraviolet light at an integrated dose of 8 to 1,400 mJ/ ^m2 ; and (3) after step (2), heating the laminate to reactively cure the coating layer and form a release layer. Note that the term "film" in this specification also encompasses what is sometimes called a "sheet." Therefore, the term "release film" in this embodiment also encompasses what is sometimes called a "release sheet," etc.

Here, an example of a conventional release film that uses a silicone release agent is described. To ensure coatability, obtain a thin coating, and ensure adhesion to the substrate, solvent-based silicone release agents diluted with an organic solvent are sometimes used. Furthermore, among silicone release agents, addition reaction-type silicone release agents are sometimes used because they cause less migration after curing.

In these conventional methods, attempts have been made to use solventless silicone release agents instead of solvent-based silicones as a manufacturing method that minimizes the use of organic solvents, taking into consideration factors such as the environmental impact. However, this method presents the problem of poor adhesion to the substrate. This problem can become particularly pronounced when an addition-reaction type solventless silicone release agent is combined with a polyethylene terephthalate-based substrate.

Furthermore, with conventional methods that involve diluting the release agent by adding an organic solvent to create a coating solution, or using solvent-based silicone release agents that already contain a predetermined amount of organic solvent, safety restrictions may be placed on irradiating the material with UV light in the presence of a solvent. For example, if UV light is irradiated while the material contains a solvent, the evaporation of the solvent may cause the explosion limit to be exceeded within the UV irradiation equipment. For these reasons, with the conventional methods described above, UV irradiation before heating is not possible, or irradiation before heating is avoided. For these reasons, using an addition-reaction-type solventless silicone release agent on a polyethylene terephthalate substrate has been considered impractical for producing a release film that can withstand practical use.

With these points in mind, the inventors changed their approach and conducted extensive research into incorporating a solventless silicone release agent into the coating liquid and applying this coating liquid to a polyethylene terephthalate-based substrate. They then came up with the idea of pre-irradiating the coating with ultraviolet light under specific conditions before heating, and perfected the manufacturing method of this embodiment. In other words, the inventors unexpectedly discovered that even with an addition-reaction-type solventless silicone and a polyethylene terephthalate-based substrate, a combination that is thought to be poor from the perspective of adhesion, it is possible to achieve both releasability as a release film and adhesion to the substrate.

Below, we will provide an example of each process that can be performed in this embodiment and the materials that can be used.

<Coating process>

(1) A coating solution containing an addition reaction type solventless silicone release agent is applied to a polyethylene terephthalate substrate (PET substrate) to obtain a laminate including a coating layer.

(Polyethylene terephthalate (PET) substrate)

In this embodiment, a PET-based substrate is used as the film substrate. The PET-based substrate is a substrate containing polyethylene terephthalate (PET), and is preferably a polyethylene terephthalate substrate. The polyethylene terephthalate may be stretched or unstretched; for example, biaxially stretched polyethylene terephthalate is preferably used.

The PET-based substrate may be a single layer consisting of only one layer, or may be a multi-layer consisting of two or more layers. If it is a multi-layer substrate, the layer to which the coating liquid is applied (the outermost layer of the substrate) should be a polyethylene terephthalate-based substrate. For example, it may be a laminate composed of multiple layers of PET-based substrates.

The thickness of the PET substrate is not particularly limited, but is preferably 2 to 500 μm. The upper limit of this thickness is more preferably 250 μm or less, and even more preferably 188 μm or less. The lower limit of this thickness is more preferably 10 μm or more, and even more preferably 15 μm or more.

(Addition reaction type, solventless silicone release agent)

In this embodiment, the solvent-free silicone release agent of the addition reaction type may contain, for example, a low-molecular-weight silicone such as a reactive diluent. Low-molecular-weight silicone may volatilize slightly at high temperatures. In this embodiment, a preferred aspect of the "solvent-free (system)" is a weight loss rate of 8.0% by mass or less at 150°C when heated from room temperature to 170°C at a heating rate of 10°C/min. This weight loss rate can serve as an indicator of the degree of solvent-freeness, and is more preferably 6.0% by mass or less, even more preferably 5.0% by mass or less, and even more preferably 0% by mass. While a content loss rate of 0% by mass is preferred, the lower limit may exceed 0% by mass, as long as the effects of this embodiment are achieved. Therefore, for example, the solvent-free silicone release agent of the addition reaction type described above may not contain an organic solvent, but the weight loss rate may be within the above-mentioned range.

The weight loss rate (%) can be calculated by applying the weight at 150°C ("weight at 150°C") and the weight before heating ("weight before heating") to the following formula when the temperature is raised from room temperature to 170°C at a heating rate of 10°C/min.

Weight loss rate (%) = (weight before heating - weight at 150°C) / weight before heating x 100

Preferred examples of addition-reaction-type silicone release agents include those containing (a) a polyorganosiloxane having at least one addition-reactive group per molecule and (b) a polyorganosiloxane having at least one hydrosilyl group per molecule. Examples of the addition-reactive group in component (a) include alkenyl groups. The addition-reactive group in component (a) and the hydrosilyl group in component (b) react and cure through a hydrosilylation reaction or the like to form a release layer with sufficient releasability for practical use as a release film, and the release layer can also be adhered to a PET-based substrate.

More preferably, the solventless silicone release agent used in the coating solution contains (a) an alkenyl group-containing polyorganosiloxane containing alkenyl groups having 2 to 10 carbon atoms, and (b) a hydrosilyl group-containing polyorganosiloxane containing hydrosilyl groups. This combination allows the viscosity to be kept low enough to be coatable without diluting with a solvent, and components (a) and (b) can be sufficiently reacted and cured to form a release layer.

Examples of component (a) include vinyl group-containing polyorganosiloxanes, allyl group-containing polyorganosiloxanes, butenyl group-containing polyorganosiloxanes, pentenyl group-containing polyorganosiloxanes, hexenyl group-containing polyorganosiloxanes, heptenyl group-containing polyorganosiloxanes, octenyl group-containing polyorganosiloxanes, nonenyl group-containing polyorganosiloxanes, and decenyl group-containing polyorganosiloxanes.

Component (b) can be a compound that functions as a crosslinking agent, such as a hydrosilyl group-containing polyorganosiloxane that has one or more, preferably two or more, silicon-bonded hydrogen atoms in the molecule. Specific examples include hydrosilyl group-containing polyorganosiloxanes such as polymethylhydrogensiloxane, polyethylhydrogensiloxane, poly(dimethylsiloxane-methylhydrogensiloxane), dimethylhydrogensiloxy group-endblocked dimethylsiloxane-methylhydrogensiloxane copolymer, trimethylsiloxy group-endblocked dimethylsiloxane-methylhydrogensiloxane copolymer, trimethylsiloxy group-endblocked poly(methylhydrogensiloxane), and poly(hydrogensilsesquioxane).

The addition reaction type solventless silicone release agent of this embodiment can be any commercially available solventless silicone release agent, such as "DOWSIL™ LTC1057L," "LTC1067M," and "(Dow-Toray Industries, Inc.)" (all manufactured by Dow-Toray Industries, Inc.); "KNS 3056," "KNS 320A," and "X-62-1387" (all manufactured by Shin-Etsu Chemical Co., Ltd.).

The amount of component (b) relative to component (a) is not particularly limited as long as it is controlled to a ratio that allows for a curing reaction, but it is preferably 0.1 to 100 parts by mass, and more preferably 0.3 to 50 parts by mass, per 100 parts by mass of component (a).

The polyorganosiloxane skeletons of components (a) and (b) include polyalkylalkylsiloxanes such as polydimethylsiloxane, polydiethylsiloxane, and polymethylethylsiloxane; polyalkylarylsiloxanes; and the like. Of these, polydimethylsiloxane is preferred.

The skeleton of the polyorganosiloxane may be a modified polyorganosiloxane in which one or more organic groups are bonded to silicon atoms (Si). Examples of organic groups include amino groups, silanol groups, acrylic groups, methacrylic groups, epoxy groups, and carboxyl groups.

The coating fluid preferably contains a platinum-based catalyst. Specific examples of platinum-based catalysts include fine particle platinum, fine particle platinum adsorbed on a carbon powder support, chloroplatinic acid, alcohol-modified chloroplatinic acid, olefin complexes of chloroplatinic acid, and platinum group metal compounds such as palladium and rhodium. The catalyst content is not particularly limited, but is preferably 1 to 10 parts by mass per 100 parts by mass of the total amount of components (a) and (b). The upper limit is more preferably 8 parts by mass or less, and even more preferably 5 parts by mass or less.

The coating liquid may also contain a sensitizer, if necessary. There are no particular limitations on the sensitizer, and any sensitizer commonly used in ultraviolet resin curing, as described below, can be used. Specific examples of sensitizers include benzoins, benzophenones, acetophenones, α-hydroxyketones, α-aminoketones, α-diketones, α-diketone dialkyl acetals, anthraquinones, thioxanthones, and other compounds.

Examples of benzoins include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-butyl ether, benzoin isobutyl ether, and compounds in which benzoin is ether-bonded to both ends of polydimethylsiloxane.

Examples of benzophenones include benzophenone, p-phenylbenzophenone, 4,4'-diethylaminobenzophenone, dichlorobenzophenone, trimethylsilylated benzophenone, and 4-methoxybenzophenone.

Examples of acetophenones include acetophenone, dimethylaminoacetophenone, 3-methylacetophenone, 4-methylacetophenone, 4-allylacetophenone, 3-pentylacetophenone, and propiophenone.

Examples of α-hydroxyketones include 2-hydroxy-1-(4-isopropyl)phenyl-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methylpropan-1-one, and 1-hydroxycyclohexyl phenyl ketone.

Examples of α-aminoketones include 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one.

Examples of α-diketones include benzyl and diacetyl.

Examples of α-diketone dialkyl acetals include benzyl dimethyl acetal and benzyl diethyl acetal.

Examples of anthraquinones include 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, and 2-aminoanthraquinone.

Examples of thioxanthones include 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, and 2,4-diethylthioxanthone.

Other compounds include, for example, tertiary amines such as triphenylamine and p-dimethylaminobenzoic acid ester, and azo compounds such as azobisisobutyronitrile.

When using these photosensitizers, one type may be used alone, or two or more types may be used in combination. Furthermore, the content thereof is preferably 0.01 to 30 parts by mass, and more preferably 0.05 to 20 parts by mass, per 100 parts by mass of the total amount of components (a) and (b).

In this embodiment, it is not necessary to actively add a solvent during coating; a solventless silicone release agent can be used. For example, in conventional methods such as actively adding a solvent to the coating liquid or using a solvent-based silicone release agent that already contains a certain amount of solvent, the solvent content in the coating liquid is high, unlike in this embodiment. In contrast, in this embodiment, the solvent content in the coating liquid is low, but sufficient release properties and adhesion to the substrate can be imparted. For example, when a coating liquid containing a solventless silicone release agent is heated from room temperature to 170°C at a heating rate of 10°C/min, the weight loss rate at 150°C is preferably 8.0% by mass or less, more preferably 6.0% by mass or less, even more preferably 5.0% by mass or less, and even more preferably 0% by mass. Note that while a content loss rate of 0% by mass is preferred, the lower limit may be, for example, greater than 0% by mass, as long as the effect of this embodiment is achieved.

The weight loss rate of the coating liquid can be calculated by applying the weight at 150°C ("weight at 150°C") and the weight before heating ("weight before heating") to the following formula when the temperature is raised from room temperature to 170°C at a heating rate of 10°C/min. Specifically, the weight loss rate can be calculated in accordance with the method described in the examples.

Weight loss rate (%) = (weight before heating - weight at 150°C) / weight before heating x 100

The coating liquid of this embodiment can be prepared by mixing the above-mentioned metal catalyst, photosensitizer, etc. with the above-mentioned solventless silicone release agent. For example, when using a coating liquid containing the above-mentioned catalyst (platinum-based catalyst, etc.), the coating liquid can be prepared by mixing the solventless silicone release agent with the metal catalyst to obtain the coating liquid without adding a solvent. The same applies when a photosensitizer, etc. is added. The solvent referred to here includes organic solvents, and specific examples thereof include aromatic solvents (benzene, toluene, xylene, etc.), hydrocarbon solvents (hexane, heptane, etc.), alcohol solvents (methanol, ethanol, propanol, butanol, cellosolves, propylene glycol monomethyl ethers, etc.), ester solvents (ethyl acetate, γ-butyl lactone, etc.), ketone solvents (acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc.), ether solvents (tetrahydrofuran, etc.), nitrogen-containing solvents (dimethylformamide, dimethylacetamide, N-methylpyrrolidone, etc.), and sulfur-containing solvents (dimethyl sulfoxide, etc.).

In this embodiment, a coating liquid containing the above components is applied to one or both sides of a PET-based substrate. The coating method is not particularly limited, and examples include gravure coating, bar coating, spray coating, spin coating, etc.

The coating amount of the coating liquid is preferably 0.03 to 0.5 g/m ² , more preferably 0.05 to 0.4 g/m ² , and even more preferably 0.08 to 0.3 g/m ^2. By setting the coating amount within this range, the thickness of the release layer can be made thin enough for practical use, sufficient releasability can be imparted to the release layer, and sufficient adhesion to the PET-based substrate can be ensured.

In this way, a laminate including a coating layer formed by applying the coating liquid onto a PET substrate can be obtained.

<Pre-irradiation process>
Next, (2) a pre-irradiation step is performed in which the coating layer of the laminate is irradiated with ultraviolet light so that the cumulative light amount is 8 to 1400 mJ/m ^2. Note that by performing this pre-irradiation before the heating step, only the outermost surface of the PET-based substrate is heated, which is expected to increase the flow of the release agent and impart an anchoring effect to the substrate (however, the effects of this embodiment are not limited to these).

UV irradiation may be performed in-line. Conventional UV lamps, such as high-pressure mercury lamps, metal halide lamps, high-power metal halide lamps, and electrodeless UV lamps, can be used, but electrodeless UV lamps are preferred. Electrodeless UV lamps include D bulbs, H bulbs, H+ bulbs, and V bulbs manufactured by Fusion, with H bulbs and H+ bulbs being preferred.

The cumulative light dose of ultraviolet irradiation is 8 to 1400 mJ/ ^m2 , with the upper limit being preferably 1000 mJ/ ^m2 or less, more preferably 700 mJ/ ^m2 or less, and even more preferably 600 mJ/ ^m2 or less. The lower limit is preferably 9 mJ/ ^m2 or more, more preferably 10 mJ/ ^m2 or more, and even more preferably 15 mJ/ ^m2 or more. By setting the dose within this range, it is possible to achieve a higher level of compatibility between coating film formation, release layer releasability, and adhesion to the substrate. By setting the dose at or above the lower limit, adhesion to the substrate is particularly improved. By setting the dose at or below the lower limit, damage to the substrate can be more effectively reduced, and the occurrence of shrinkage and wrinkles can be more effectively prevented.

The illuminance of ultraviolet irradiation is not particularly limited, but the upper limit is preferably 500 mW/ ^m2 or less, more preferably less than 300 mW/ ^m2 , and even more preferably 250 mW/ ^m2 or less. The lower limit is preferably 80 mW/ ^m2 or more, more preferably 100 mW/ ^m2 or more, even more preferably 120 mW/ ^m2 or more, even more preferably 150 mW/ ^m2 or more, and even more preferably 170 mW/ ^m2 or more.

<Heating process>
(3) After the above step (2), a step is carried out in which the laminate is heated to react and cure the coating layer, thereby forming a release layer.

The heating temperature in step (3) is not particularly limited, but is preferably 50°C or higher and 200°C or lower. The upper limit is more preferably 170°C or lower, and even more preferably 150°C or lower. The lower limit is more preferably 70°C or higher, and even more preferably 80°C or higher. By keeping the heating temperature within this range, it is possible to achieve a higher level of compatibility between coating film formation, releasability of the release layer, and adhesion to the substrate.

The heating time is not particularly limited, but the upper limit is preferably 60 seconds or less, and more preferably 40 seconds or less. The lower limit is preferably 15 seconds or more, and more preferably 20 seconds or more. By keeping the heating time within this range, it is possible to achieve a higher level of compatibility between coating film formation, releasability of the release layer, and adhesion to the substrate.

The heating method is not particularly limited, but methods such as using a hair dryer, oven, or infrared furnace can be used.

(Post-irradiation process)
In this embodiment, if necessary, post-irradiation with ultraviolet light may be performed after the heating step. That is, step (3) may be performed after step (2) above, by heating the laminate and then irradiating it with ultraviolet light to reactively cure the coating layer and form a release layer.

The post-irradiation of ultraviolet light can be performed within the range of conditions described for the pre-irradiation process. The post-irradiation conditions may be the same as or different from the pre-irradiation conditions.

In addition, the total integrated light amount of ultraviolet irradiation in this embodiment (the total of the pre-irradiation step and the post-irradiation step) is preferably 8 to 1400 mJ/ ^m2 . The upper limit of this total integrated light amount is preferably 1000 mJ/ ^m2 or less, more preferably 700 mJ/ ^m2 or less, and even more preferably 600 mJ/ ^m2 or less. The lower limit of this total integrated light amount is preferably 9 mJ/ ^m2 or more, more preferably 10 mJ/ ^m2 or more, and even more preferably 15 mJ/ ^m2 or more. By setting it within this range, it is possible to achieve a higher level of compatibility between coating film formation, release layer releasability, and adhesion to the substrate. Furthermore, by setting it at or above the above lower limit, adhesion to the substrate is particularly improved, and by setting it at or below the above lower limit, damage to the substrate can be more effectively reduced and the occurrence of shrinkage and wrinkles can be more effectively prevented.

Next, we will explain preferred aspects of the release film obtained by the manufacturing method of this embodiment.

The thickness of the release layer of the release film is not particularly limited, but it can be as thin as 0.03 to 0.6 μm. The upper limit of this thickness is preferably 0.5 μm or less, and even more preferably 0.3 μm or less. The lower limit of this thickness is preferably 0.04 μm or more, and even more preferably 0.06 μm or more.

The release strength of the release film is comparable to that of release films obtained by conventional manufacturing methods, and is able to maintain a practical level of release strength. According to this embodiment, the release strength can be appropriately controlled depending on the application or field; for example, it is 10 to 1000 mN/25 mm, and preferably 20 to 800 mN/25 mm. The upper limit is more preferably 600 mN/25 mm or less, and even more preferably 500 mN/25 mm or less. The lower limit is more preferably 20 mN/25 mm or more, and even more preferably 25 mN/25 mm or more.

As explained above, the release film obtained by the manufacturing method of this embodiment has excellent releasability and adhesion to the substrate, effectively preventing the release layer from peeling off the PET-based substrate even when stored or left stationary for long periods of time. Furthermore, even when left stationary for several days (1 to 10 days or more) or when the release layer is rubbed, the release agent is effectively prevented from falling off the release film. Release films with such properties are suitable for use as adhesive protective materials in adhesive sheets used in optical devices such as displays, and adhesive sheets for semiconductor processing. Furthermore, the manufacturing method of this embodiment is expected to reduce the amount of solvent used, or even eliminate the use of solvent, making it an environmentally friendly manufacturing method.

The present invention will be explained in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples in any way. Note that percentages and parts are by weight unless otherwise specified.

In this example, the following materials were used:

(Removal agent)
Dow-Toray Industries, Inc., product name "DOWSIL™ LTC1057L":
Addition reaction type solventless silicone release agent (a solventless addition reaction type silicone containing a polyorganosiloxane having an alkenyl group in the molecule and a polyorganosiloxane crosslinker having a hydrosilyl group in the molecule)
Shin-Etsu Chemical Co., Ltd., product name "KNS 3056":
Addition reaction type solventless silicone release agent (a solventless addition reaction type silicone containing a polyorganosiloxane with a vinyl group in the molecule and a polyorganosiloxane crosslinker with a hydrosilyl group in the molecule)
(catalyst)
- Dow-Toray Industries, Inc., product name "DOWSIL™ SRX-212 Catalyst":
Platinum catalyst, product name "CAT-PL-56" manufactured by Shin-Etsu Chemical Co., Ltd.:
platinum catalyst

<Example 1>

First, a polyethylene terephthalate (PET) film (manufactured by Mitsubishi Chemical Corporation, trade name "Diafoil T-100"; thickness 38 μm) was prepared as a substrate.
Then, 100 parts by mass of an addition reaction type solventless silicone release agent (manufactured by Dow-Toray Industries, Inc., trade name "DOWSIL™ LTC1057L") and a platinum catalyst (manufactured by Dow-Toray Industries, Inc., trade name "DOWSIL™ SRX-212 Catalyst") were mixed without adding a solvent to prepare a solventless coating fluid (weight loss rate of coating fluid at 150°C: 2.1% by mass; see "Weight loss rate at 150°C (%)" in Table 1).

The "weight loss rate" was determined according to the following method.
First, 20 mg of the coating liquid was prepared as a sample. Then, using a TG-DTA (Shimadzu Corporation, differential thermal and thermogravimetric simultaneous analyzer "DTG-60"), the sample was heated from room temperature to 170°C at a heating rate of 10°C/min, and the weight at 150°C ("weight at 150°C") and the weight before heating ("weight before heating") were determined. These values were then applied to the following formula to determine the weight loss rate (%).

Weight loss rate (%) = (weight before heating - weight at 150°C) / weight before heating x 100

Then, using a coating device (manufactured by Kumagai Riki Kogyo Co., Ltd., device name "RI Tester"), the above coating liquid was applied to one surface of the above substrate so as to give a coating amount of 0.25 g/ ^m2 , thereby forming a coating layer (coating film).
Next, while the coating layer was still wet (uncured), it was irradiated with ultraviolet (UV) light from the coated surface (cumulative light amount 100 mJ/ ^m2 , illuminance 200 mW/ ^m2 , see "UV irradiation before thermal curing" in Table 1). It was then placed in an oven and cured at 100°C for 30 seconds. These treatments cured the coating layer, forming a release layer and obtaining a release film.

<Examples 2-10>

Release films were obtained in the same manner as in Example 1, except that the conditions were changed as shown in Table 1. For Example 6, after removal from the oven, post-irradiation was performed by irradiating the coated surface with ultraviolet (UV) light (integrated light amount 100 mJ/m ² , illuminance 200 mW/m ² , see "UV irradiation before thermal curing" in Table 1) (see "UV irradiation after curing" in Table 1). The weight loss rates at 150°C of the solventless coating solutions prepared in Examples 2 to 10 were as shown in "Weight loss rate at 150°C (%)" in Table 1.

<Comparative Examples 1-5>

A release film was obtained in accordance with the same procedure as in Example 1, except for the changes in conditions listed in Table 1. Note that Comparative Examples 1 and 2 were not subjected to UV irradiation, and Comparative Example 3 was not subjected to UV irradiation before heating (pre-irradiation), but was subjected to UV irradiation after heating (post-irradiation).

<Evaluation Method>

The physical properties of each of the resulting release films were evaluated according to the methods described below.

(Evaluation of peeling properties and peeling force)
An acrylic adhesive (manufactured by Toyochem Co., Ltd., product name "Olivine (registered trademark) BPS-5127") was applied using an applicator to the release surface of the release film produced in each Example and Comparative Example, and dried at 100°C for 2 minutes to form an adhesive layer with a thickness of 125 μm. Furthermore, a PET film (manufactured by Toray Industries, Inc., product name "Lumirror (registered trademark) T-60", thickness: 50 μm) was attached to the surface of the adhesive layer opposite the release film, to obtain an adhesive sheet as a measurement sample.
This measurement sample was fixed to a universal tensile tester (Shimadzu Corporation, product name "Autograph AGS-20NX"), and the force when the release film was peeled in the 180° direction at a tensile speed of 0.3 m/min was measured in accordance with JIS K6854:1999, and this was taken as the peel force (mN/25 mm).

(exterior)
The appearance of the prepared release film was visually observed under a fluorescent lamp, and the evaluation criteria were as follows:
◯: No strong wrinkles and no distortion of the film.
×: Strong wrinkles were observed and the film was distorted.

(Rub-off test)
The adhesion of the release layer of the release film was evaluated. Specifically, immediately after processing (immediately after production), 1 day later, 3 days later, and 10 days later, the surface of the release layer was rubbed with a finger five times in the X direction (a predetermined direction), and then rubbed with a finger five times in the Y direction perpendicular to the X direction, and the smear (cloudiness) and rub-off (fall-off) at the intersection of the X direction and the Y direction were visually confirmed. The evaluation criteria were as follows.
"◯": Neither clouding nor falling off was observed.
"△": Cloudiness was observed.
"X": Dropout was confirmed.

The manufacturing conditions for each example and comparative example are shown in Table 1, and the evaluation results are shown in Table 2.

From the above, it was confirmed that this example at least provides release properties sufficient for practical use as a release film, and that it is possible to produce a release film that has excellent adhesion to the substrate. Furthermore, since the manufacturing method of this example was confirmed to be able to provide sufficient physical properties using a solventless silicone release agent as the release agent, without using a solvent, it is also expected to be an environmentally friendly manufacturing method.

Claims (3)

(1) applying a coating solution containing an addition reaction type solventless silicone release agent to a polyethylene terephthalate substrate to obtain a laminate including a coating layer;
(2) a pre-irradiation step of irradiating the coating layer of the laminate with ultraviolet light so that the cumulative light amount is 8 to 500 mJ/ ^m2;
(3) after the step (2), heating the laminate to reactively cure the coating layer and form a release layer;
A method for producing a release film, comprising: The step (3) is a step of, after the step (2), heating the laminate and then further irradiating it with ultraviolet light to reactively cure the coating layer and form a release layer.
A method for producing the release film according to claim 1. the coating liquid containing the solventless silicone release agent has a weight loss rate of 8.0% by mass or less at 150°C when heated from room temperature to 170°C at a heating rate of 10°C/min;
A method for producing the release film according to claim 1 or 2.