JP3101367B2 - Release sheet and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a release sheet having a uniform silicone resin coating layer without pinholes provided on a support such as paper, laminated paper, synthetic paper, plastic film, metal surface, and the like. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Silicone release sheets having a release layer made of an organic polysiloxane provided on a sheet-like support such as paper, laminated paper, synthetic paper, plastic film, etc., have been used in many applications in recent years. As a method for forming the release layer, a solution of a condensation-type or addition-type silicone-based resin containing an organic tin compound or other heavy metal salt, and a platinum-based catalyst is applied, and then heated to 120 ° C. in a hot-air oven.
To 180.degree. C. to evaporate the solvent and then form a cured film by thermosetting. Most of this heat is used for solvent volatilization, and only a small amount of heat is required to cure the silicone resin. In a release sheet using paper as a support, such high-temperature heat treatment not only requires heat resistance of the paper support, but also causes wrinkles and curls due to evaporation of water inside the paper support. This has the disadvantage that the release layer is easily formed and pinholes are easily generated in the release layer due to moisture evaporation and solvent evaporation. Naturally, it is not possible to process a plastic film that cannot maintain its shape at such a temperature.

For the purpose of overcoming these drawbacks and reducing the absorption of the silicone resin forming the release layer into the paper, it is often used to use a support having a paper surface laminated with polyethylene, vinylidene chloride, or the like. It is the way to be. However, also when the silicone resin is cured, the laminate layer softens, melts, shrinks, etc., which results in unevenness of the surface of the laminate support, which hinders the peeling performance, and is particularly used for the production of marking films and synthetic leather. The resulting process paper had a fatal disadvantage that the surface gloss and surface smoothness were reduced. In the release sheet manufacturing process, a large amount of an organic solvent such as toluene or hexane is used for the purpose of reducing the amount of the silicone resin applied to the support. And the waste solvent has a serious drawback of causing environmental pollution.

As one means for overcoming such disadvantages, a solvent-free silicone resin, in particular, a functional group which can be polymerized by irradiation with ultraviolet rays and electron beams (hereinafter, ultraviolet rays and electron beams are collectively referred to as radiation) is used. A low-temperature curing-type release sheet manufacturing technology has been developed in which curing by irradiation with radiation is performed using a silicone resin that has a silicone resin solution. However, these radiation-curable silicone resins use a silicone resin solution that uses an organic solvent in terms of viscosity. However, there are still problems such as gravure eyes remaining when coated with a gravure coater or the like, and a decrease in surface gloss and surface smoothness due to poor transfer of silicone resin during high-speed coating with four or five rollers. I was

[0005]

The problem to be solved by the present invention is that when a release layer made of silicone resin is provided on a support, a silicone resin coating layer is uniformly applied to the support without pinholes, An object of the present invention is to produce a release sheet having good surface characteristics and release characteristics by curing a silicone resin without applying excessive heat to a coating layer and a support to form a release layer.

[0006]

Means for Solving the Problems The inventor of the present invention has intensively studied means for solving the above problems, and as a result, has found the following method. That is, in a release sheet having a release layer on at least one side of the support, the release layer is formed by ejecting a supercritical fluid in which the silicone resin is dissolved from a micro nozzle or orifice toward the support. An invention of a release sheet comprising a coating. The silicone resin coating layer used in the present invention can be cured by heat curing after coating to form a release layer, or can be cured by ultraviolet irradiation or electron beam irradiation to form a release layer. It is. The release sheet of the present invention includes a step of applying a silicone resin by spraying a supercritical fluid in which a silicone resin is dissolved from a micro nozzle or an orifice onto at least one surface of a support, and a component (a component constituting the supercritical fluid) Hereinafter, it is referred to as a fluid component: a step of diffusing (evaporating) carbon dioxide, nitrogen, water, and the like, and selecting the resulting silicone resin coating layer from heat curing, curing by ultraviolet irradiation, and curing by electron beam irradiation. And a step of forming a release layer by being cured by more than one kind of curing method.

According to the method for coating a silicone resin of the present invention, a silicone resin coating layer can be provided very uniformly and thinly on a support, and a fluid component is released simultaneously from a nozzle or an orifice and becomes thin. Since it is gasified and diffused into the atmosphere, there is no need to apply an excessive amount of heat to the support for solvent evaporation after coating, and even when the silicone resin is cured by thermosetting, the thin silicone resin coating layer is cured. It is enough to give only the amount of heat.
In particular, when a radiation-curable silicone resin is used, when a thin layer is applied at a high speed by a conventional method, an incompletely cured portion remains under the influence of dissolved oxygen on the surface of the silicone resin coating layer, and after the release sheet is formed. In some cases, low-molecular-weight silicone resin migrated to the adhesive layer and reduced the residual adhesion rate.However, in the method of the present invention, when dissolved in a supercritical fluid, an inert gas was completely replaced, and a thin layer coating was performed at a high speed. Even in this case, an unexpected effect of preventing the problem of such a decrease in the residual adhesion rate was observed.

Hereinafter, the present invention will be described in detail. Examples of the thermosetting silicone resin used in the present invention include a condensation silicone resin using a tin catalyst and an addition silicone resin using a platinum catalyst. UV or electron beam curable silicone resin,
Or, it is a silicone resin (mainly polydialkylsiloxane) having a functional group selected from acryloyl group, methacryloyl group, vinyl group, and epoxy group in the side chain, and optionally includes a photoreaction initiator and a sensitizer. In addition, it can be used. Furthermore, acrylates or methacrylates containing long-chain alkyl groups and silicone-modified compounds thereof can also be good radiation-curable release resins.
These silicone resins can be used alone or in combination of two or more. Also, as long as the release property is not impaired together with the release resin, other ultraviolet curable or electron beam curable resin, or a binder component, a coloring agent,
Additives such as antioxidants can be mixed.

Although the amount of the silicone resin applied is not limited, it is desired that the silicone resin be thinner from an economic viewpoint.
Preferably in the range of ^{0.1g / m 2 ~10g / m 2} . If the coating amount is less than 0.1 g / m ² , it is difficult to uniformly coat on the support, and the releasability is deteriorated. Even if the coating amount is more than 10 g / m ² , the characteristics do not change and only the cost is improved. If the coating amount is extremely large, the cured silicone is liable to fall off due to friction after curing.

In the present invention, the silicone resin is applied to a support in a state of being dissolved in a supercritical fluid, and after the fluid component is diffused (or evaporated), the silicone resin is cured by heating or irradiation with radiation. Then, the release layer is fixed. A supercritical fluid as used herein is a single phase in which a fluid component forms above the critical temperature and critical pressure of the component, and is called a high-density gas or supercritical gas in other expressions. Such a high temperature, high density gas. The present inventors have focused on the physical properties of this supercritical fluid and studied the solubility of silicone resins in supercritical fluids.As a result, certain supercritical fluids have a silicone resin solubility comparable to or higher than that of organic solvents. Not only that the silicone resin dissolved in the supercritical fluid,
When jetted toward a support at normal temperature and normal pressure via a nozzle with a small inner diameter or an orifice,
After instantaneously diffusing the constituents of the supercritical fluid, they found that a thin film of silicone resin was formed on the support. The solubility of this high silicone resin is probably due to the high density of the supercritical fluid (0.3-1.0, not constant since the density changes with temperature and pressure as with ordinary gases)
It is believed that the fluid component has a very small molecular size as compared with the organic solvent and thus has a high osmotic power. When the thin film layer of the silicone resin thus obtained is cured by heating or irradiation with ultraviolet rays or electron beams, a release sheet having a release layer composed of a silicone resin film is obtained. In the method of applying the silicone resin according to the method of the present invention, the silicone resin is applied to the support in a state of being dissolved in a supercritical fluid having a very low viscosity, or in a state close thereto, although the silicone resin is released at atmospheric pressure on the way. Therefore, it is possible to apply the coating very thinly and uniformly.

The substances used as fluid components of the supercritical fluid of the present invention include carbon dioxide (critical temperature 31 ° C., critical pressure 72.9 atm), nitrogen (critical temperature -147 ° C., critical pressure 33.5 atm). , Oxygen (critical temperature −118 ° C., critical pressure 50.1 atm), water (critical temperature 374 ° C., critical pressure 218.3 ° C.), as well as fluorocarbons, alcohols,
Many substances can be used, such as ammonia, laughing gas, sulfur dioxide, low-boiling hydrocarbons such as n-hexane and pentane, but the range of critical temperature and critical pressure, ease of processing fluid components after coating, and coating The use of carbon dioxide and nitrogen is particularly preferred from the viewpoints of safety such as flammability and harmfulness when used in the process, radical polymerization hindrance when performing irradiation, and cost.

The step of applying a silicone resin using the supercritical fluid of the present invention can be performed by the following system. That is, the fluid component is pumped by a high-pressure pump, the silicone resin is supplied by another high-pressure pump, and the two components are mixed in a dissolution column whose temperature and pressure are controlled to the critical temperature of the fluid component and the critical pressure or higher. Guide to the opening or orifice and squirt towards the support. A back pressure control device can be provided near the opening. When the fluid component and the silicone resin are mixed, dissolution can be promoted by spraying in a dissolution column. The support coated with the silicone resin together with the fluid component may be directly cured, but may be subjected to a surface smoothing treatment using a blade, a smoothing bar, or a roll. In addition, in order to help the diffusion of fluid components after ejection,
Heat treatment and exhaust treatment may be performed. Pumps, dissolution columns, nozzles, orifices, back pressure control devices used in the present invention and pipes and valves connecting these, the above-mentioned blades, smoothing bars, rolls, a support before applying the silicone resin, or a silicone resin was applied. Each of the subsequent supports can be temperature controlled.

As the support used in the present invention, glassine paper, woodfree paper, coated paper, a synthetic resin film such as polyethylene, polypropylene, polyethylene terephthalate, polyamide or the like, or a paper obtained by laminating these synthetic resins on one side or both sides There are laminated paper, metal foil, or a bonded product of metal foil and paper or synthetic resin film. In addition, heat-sensitive paper, pressure-sensitive paper, photographic printing paper, information recording paper such as thermal transfer image-receiving paper, and tapes such as adhesive tape and masking tape can be used as the support. The basis weight of the support is not particularly limited, but is preferably 5 to 250 g / m ² , and its surface is preferably smooth.However, on the basis of release performance or control of molding when used as process paper, The surface may be rough or embossed. The support used in the present invention has a surface treatment such as corona treatment, ozone treatment, surface roughening, an aqueous coat layer, a polyolefin resin, etc. for the purpose of enhancing the adhesion between the support and the silicone resin coating layer. Or a primer layer made of a radiation curable resin.

The electron beam irradiation conditions used for curing the silicone resin coating layer in the present invention are as follows: an acceleration voltage is 50 to 750 KV, more preferably 100 to 300 Kv, in terms of electron beam characteristics in terms of transmission power and curing power. It is preferable that the absorbed dose in one pass is 0.1 to 20 Mrad using the electron beam accelerator of the above.

The electron beam accelerator may be, for example, any of an electron curtain system, a scanning type, a double scanning type and the like. During electron beam irradiation, since the curing of the peeling layer is hindered when the oxygen concentration is high, replacement with an inert gas such as nitrogen, helium, or carbon dioxide is performed to suppress the oxygen concentration to 600 ppm or less, preferably 400 ppm or less. The irradiation is preferably performed in an atmosphere.

The photoinitiators used in the present invention, particularly when using the ultraviolet curing method, include acetophenones such as di- and trichloroacetophenone, benzophenone, Michler's ketone, benzyl, benzoin, benzoin alkyl ether, benzyldimethyl ketal, tetrabenzyl There are methylthiuram monosulfide, thioxanthones, azo compounds, onium salts, and the like, which are selected from the viewpoint of the type and stability of the polymerization reaction of the ultraviolet-curable silicone resin and the ultraviolet-curable resin, and the suitability for an ultraviolet irradiation device. The amount of the photoinitiator to be used is generally 0.1 to UV curable silicone resin or UV curable resin.
The range is 5%. A storage stabilizer such as hydroquinone may be used in combination with the photoinitiator.

The sensitizers used in the present invention include aliphatic amines, amines containing aromatic groups, nitrogen heterocyclic compounds, allylic ureas, O-tolylthiourea, sodium diethyldithiophosphate, and aromatic sulfonic acids. Soluble salt, N, N-disubstituted-P-aminobenzonitrile compound, tri-n-butylphosphine, sodium diethylthiophosphate, Michler's ketone, N-nitrosohydroxylamine derivative, oxazoline compound, carbon tetrachloride,
There is hexachloroethane and the like, and by using the photoinitiator in common, the curing speed can be generally improved.

As the ultraviolet irradiation device used for curing the silicone resin coating layer in the present invention, for example, there are a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, a metal halide lamp, and the like, and an ozone-less type which generates less ozone. Generally, a plurality of lamps having an output of 30 w / cm or more are used in parallel.

[0019]

According to the present invention, in the production of a release sheet, a silicone resin is dissolved in a supercritical fluid and applied.
The viscosity of the silicone resin can be remarkably improved, and the silicone resin coating layer can be uniformly and thinly applied on the support. As a result, even when the silicone resin coating layer is heat-cured, it is not necessary to apply heat for evaporating the solvent, and the heat is sufficient for the silicone resin to react, so that no excessive heat is applied to the support. Therefore, it is possible to form a uniform silicone resin coating layer without pinholes.
A release sheet having good surface characteristics can be manufactured. According to the method of the present invention, similarly, in the curing of silicone resin by irradiation of ultraviolet rays or electron beams without heating,
These high-viscosity silicone resins can be applied thinly and uniformly. As described above, according to the method of the present invention, curling, wrinkles, and high-viscosity derived from the high viscosity of the resin can be suppressed from occurring, such as pinholes in the release layer.
In addition, the amount of silicone resin applied can be reduced while maintaining good surface characteristics. Since no waste solvent or waste heat is generated in the production of the release sheet, not only the working environment is good, but also the surrounding environment is not polluted.

[0020]

EXAMPLES The present invention will be described below in detail with reference to examples, but the contents of the present invention are not limited to the examples.

Example 1 A low-density polyethylene was laminated on one side of a high-quality paper having a basis weight of 50 g / m ² and subjected to corona treatment to obtain a support. An electron beam-curable silicone resin (Shin-Etsu Chemical Co., Ltd., trade name X-62-7177) and liquefied carbon dioxide are sent into the pressure-resistant dissolution column by separate high-pressure pumps, and mixed and dissolved in the column. Was. The inside of the dissolution column was kept at 150 atm and 100 ° C. The supercritical fluid in which the silicone resin is dissolved is taken out from the micropipe provided at the upper part of the dissolution column, and is ejected from the nozzle at the tip of the micropipe through the pressure control valve.
The composition was applied to the surface of the support and homogenized with a temperature-controlled blade. An electron beam irradiator (ESI, trade name: ElectroCurtain, TYPE :) in which a support on which a carbon dioxide gas is diffused and a silicone resin is uniformly applied is replaced with a nitrogen gas to reduce the oxygen concentration in the electron beam irradiation chamber to 200 ppm or less.
CB200 / 45/300) and irradiated with an electron beam under the conditions of an electron beam acceleration voltage of 200 kV and an irradiation current of 20 mA so as to have an absorbed dose of 4 Mrad to obtain a peeling sheet.

Example 2 A 50 μm thick polyester resin film was subjected to a corona treatment to provide a support. Ultraviolet-curable silicone resin (Shin-Etsu Chemical Co., Ltd., trade name KNS-
5003A / B) and liquefied nitrogen were sent by different high-pressure liquid sending pumps, respectively, and mixed and dissolved in the column. 1 in the lysis column
It was kept at 50 atm and 100 ° C. The supercritical fluid in which the silicone resin was dissolved was taken out of the micropipe provided in the upper part of the dissolution column, and was ejected from the orifice attached to the tip of the micropipe via a pressure control valve, and applied to the surface of the support. The support coated with this silicone resin is
UV irradiation device (80W / cm, ozone condensing type, irradiation distance 10c
m) and irradiated with ultraviolet rays to obtain a release sheet.

Example 3 A low-density polyethylene was laminated on one surface of a high-quality paper having a basis weight of 50 g / m ² and subjected to corona treatment to obtain a support. A thermosetting silicone resin (Shin-Etsu Chemical Co., Ltd., trade name: KL-838 and a 1% by weight platinum catalyst CAT PL-8) and liquefied carbon dioxide are separately pumped into the pressure-resistant dissolving column by separate high-pressure pumps. It was fed and mixed and dissolved in the column.
The inside of the dissolution column was kept at 150 atm and 100 ° C. The supercritical fluid in which the silicone resin has been dissolved is taken out of the micropipe provided at the top of the dissolution column, ejected from the nozzle at the tip of the micropipe via a pressure control valve, applied to the surface of the support, and a temperature-controlled smoothing bar. And homogenized. The support to which carbon dioxide was diffused and the silicone resin was uniformly applied was heat-cured in a hot air circulating dryer at 120 ° C. until the silicone resin was sufficiently cured to obtain a release sheet.

Comparative Example 1 The same high-quality paper laminated with polyethylene as in Example 1 was used as a support, and the same electron beam curable silicone resin as in Example 1 was applied without a solvent using a gravure offset coater. After the application, the oxygen concentration in the electron beam irradiation chamber was reduced to 200 ppm or less by replacing with nitrogen gas.
SI curtain, trade name: Electro curtain, TYPE: CB
200/45/300) and the electron beam accelerating voltage 20
Electron beam irradiation was performed under the conditions of 0 kV and an irradiation current of 20 mA so that the absorbed dose was 4 Mrad to obtain a peeling sheet.

Comparative Example 2 The same polyester resin film as in Example 2 was used as a support, and the same ultraviolet-curable silicone resin as in Example 2 was applied without solvent using a five-roller coater. After application, UV irradiation device (80W / cm, ozone focusing type, irradiation distance
10 cm) and irradiated with ultraviolet rays to obtain a release sheet.

Comparative Example 3 A high-quality paper laminated with polyethylene as in Example 1 was used as a support, and a thermosetting silicone resin as in Example 3 diluted with toluene (90% dilution) was coated with a gravure coater. Was applied. After the application, the silicone resin was heat-cured in a hot air circulating drier at 120 ° C. until the silicone resin was sufficiently cured to obtain a release sheet.

With respect to the release sheets prepared in Examples and Comparative Examples, the amount of silicone resin applied, the peel strength with respect to the adhesive, the residual adhesion rate, rub-off, curl, wrinkles, presence or absence of pinholes, surface smoothness, and production process Table 1 shows the results such as whether or not the waste solvent was discharged.

[0028]

[Table 1]

The test method is as follows.

[Silicone Resin Amount] The amount of silicone resin applied was determined by subjecting the sample after curing of the silicone resin film to fluorescent X-ray analysis.

[Peel strength] An adhesive (product name: BPS, manufactured by Toyo Ink Co., Ltd.) was applied on high-quality paper and used as a standard adhesive sheet. The obtained release sheet and release sheet (25 mm width) were allowed to stand in a thermo-hygrostat at 20 ° C. and 65% humidity for 24 hours, and then pressed against a standard pressure-sensitive adhesive sheet with a 2000 g weight pressure roller at 20 ° C. After leaving for 2 hours in a 65% constant temperature and humidity chamber, the load when peeling continuously with Tensilon (manufactured by Toyo Baldwin Co., Ltd.) at a peeling angle of 180 ° and a peeling speed of 30 cm / min. And

[Residual Adhesion Ratio] The obtained peeling sheet (width 25 mm) was allowed to stand in a thermo-hygrostat at 20 ° C. and 65% humidity for 24 hours, and then pressed against a standard pressure-sensitive adhesive sheet with a pressing roller weighing 2000 g. 20 ° C, humidity 65%, pressure 0.1kg / c
The pressure was increased for 24 hours under the condition of m ² . After peeling the standard adhesive sheet from the peeling sheet, the surface is polished well 0.5mm thick
And crushed with a pressure roller of 2000g in a thermo-hygrostat at 20 ° C and 65% humidity.
After leaving for a period of time, peel angle 180 ° with Tensilon, peel speed 3
The load when peeled continuously at 0 cm / min is determined as the peel strength. Next, a well polished surface with a thickness of 0.5
Attach a standard adhesive sheet to a stainless steel
Pressure was applied for 24 hours under the conditions of ° C, a humidity of 65%, and a pressure of 0.1 kg / cm ² . After returning to normal pressure, it was pressed with a pressing roller weighing 2000 g and placed in a thermo-hygrostat at 20 ° C and 65% humidity.
After standing for a period of time, the load at the time of continuous peeling at a peel angle of 180 ° and a peeling speed of 30 cm / min using Tensilon is determined as the peel strength. The residual adhesion rate R (%) is determined by the following equation (1). Assuming that the peel strength of the pressure-sensitive adhesive sheet after contacting the release sheet = A and the peel strength of the pressure-sensitive adhesive sheet not in contact with the release sheet paper = B,

[0033]

R = (A / B) × 100

[Love-off] The silicone surface of the release sheet was strongly rubbed with a finger, and the release of the silicone surface was visually determined.

[Curl and wrinkle] 20 ° C., humidity 65%
Judgment was made by relative comparison under the following conditions.

[Pinhole] The silicone surface of the release sheet was wet with toluene in which a dye was dissolved, and the degree of penetration was observed from the back surface.

[Surface Smoothness] The peeled surface exposed to oblique light was evaluated by microscopic observation.

[Waste Solvent] Whether or not waste solvent was discharged in the production process was described.

Evaluation; Example as evident from Table 1.
The release sheets obtained by the methods 1, 2, and 3 were compared with the release sheets obtained by the corresponding comparative examples 1, 2, and 3,
A very small amount of silicone resin can be applied, and the peel strength to the pressure-sensitive adhesive is equivalent to that of the comparative example.
Further, since no excessive heat is applied to the support, no curling or wrinkling occurs. The low occurrence of wrinkles when cured by irradiation is due to the fact that the viscosity when applying the silicone resin is particularly low in the case of the present invention. Seems to be less. In addition, since the silicone resin is dissolved in (or close to) a low-viscosity supercritical fluid and applied, it spreads quickly on the support surface at the time of application, and a release sheet without pinholes even with a low application amount is obtained. Can be In contrast, in the case of the thermosetting method using a solvent (Comparative Example 3), on the other hand, the surface of the applied silicone resin film is dried when the solvent or moisture evaporates, and the surface is roughened. The problem is inevitable.

In the case of the radiation curing method using no solvent (Examples 2 and 3 and Comparative Examples 2 and 3), the viscosity at the time of coating is low in Examples, and the support and the liquid silicone resin are directly Since it does not contact, the surface property is very good, but in the comparative example, since the high-viscosity silicone resin must be applied to the support as it is, the gravure nick or the roll and the silicone resin surface are separated. The surface roughness in that case is fixed as it is by radiation curing. Such a decrease in surface smoothness may cause a problem when used in an application (such as process paper) for transferring the peeled surface to another material.

[0041]

As described above, in the method for producing a release sheet according to the present invention, a non-toxic and inert carbon dioxide or nitrogen is used as a substitute for a solvent. Without this, the peeling sheet can be manufactured safely in terms of work and environmental protection. Further, the release sheet and the method for producing the same according to the present invention are very efficient, have good surface properties and release properties, can be produced safely and inexpensively, and have great industrial value. is there.

Claims (3)

(57) [Claims] 1. A release layer provided on at least one surface of a support, comprising: a supercritical fluid formed by dissolving a silicone resin;
A release sheet comprising a silicone resin coating layer formed by jetting from a minute nozzle or an orifice toward a support. 2. The release sheet according to claim 1, wherein the silicone resin film layer is a release layer formed by curing the film by heat , ultraviolet irradiation or electron beam irradiation after the film is formed. 3. A step of applying a supercritical fluid in which a silicone resin is dissolved by spraying it from a minute nozzle or an orifice onto at least one surface of a support, and a step of diffusing components constituting the supercritical fluid. The resulting silicone resin film is cured by heat or ultraviolet irradiation.
Other production method of the release sheet, characterized in that comprising the step of forming a release layer was cured by one or more curing method selected from the curing by electron beam irradiation.