JPH0221425B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a release paper used for adhesive sheets and adhesive tapes, and particularly to a release paper that has good dimensional stability when absorbing moisture. Conventionally, solution-type and emulsion-type release agents of silicone resins have been used as release agents for release paper used in adhesive tapes, labels, and the like. These require high-temperature heating of 120° C. to 180° C. during curing, and release paper based on paper has the disadvantage that the paper tends to wrinkle or curl due to the dissipation of moisture accompanying the heating. To eliminate this drawback, paper can be extruded and coated with low-density polyethylene on both sides and then treated with a release agent, or one side is coated with low-density polyethylene and the back side is coated with polyvinylidene chloride, etc. Products coated with a barrier layer are known. However, in release paper with such a structure, polyethylene (PE) etc. soften or melt at high temperatures, so PE etc. causes foaming. This foaming impairs the smoothness of the surface and generates pinholes, making the release layer non-uniform and having the disadvantage that good release performance is difficult to obtain. Furthermore, one side is coated with low-density polyethylene, etc.
Release paper with a metal foil such as Al foil bonded to the back side or a metal foil such as Al foil bonded to the back side, and double-sided coated release paper with a pigment coated layer on one or both sides. During release treatment, pinholes may occur in the coated layer due to the dissipation of moisture from the base paper due to the high-temperature heat curing of the silicone, resulting in the release layer becoming non-uniform, or the interface between the coated layer and the base paper or the base paper. It has the disadvantage that peeling occurs inside the layer, resulting in a punctured state and impairing its performance as a release paper. Therefore, attempts were made to reduce the curing temperature of silicone to below 100°C to eliminate the above drawbacks, but silicones that inherently require temperatures of 120°C or above often cannot be cured at such low temperatures. This causes insufficient curing of the silicone, resulting in poor peeling. In order to improve these drawbacks, the inventors of the present invention have conducted extensive research and found that by using a radiation curing release agent and adjusting the moisture content of the paper to a range of 5 to 10%, the above-mentioned peeling defects and pinholes can be eliminated. The present inventors have discovered that problems such as interfacial and/or internal peeling can be solved, leading to the present invention.
In other words, the water vapor permeability of polyethylene, polyvinylidene chloride, metal foil, pigment coated layer, etc. is 80g/
A water vapor barrier layer of less than m ² / 24 hr / atm is placed on one side of the paper, and the moisture content of the paper is adjusted to within the range of 5 to 10%, and then polyethylene, polyvinylidene chloride is placed on the other side of the base paper. , metal foil, etc. are arranged to obtain double-sided processed paper. Furthermore, a radiation-curable silicone release agent is coated on at least one side of this double-sided treated paper, and the silicone is cured using ultraviolet rays or electron beams. In the release paper according to the present invention, a sufficiently crosslinked release layer is formed by using ultraviolet rays or electron beams without high temperature treatment. Therefore,
It does not exhibit interfacial or internal peeling (punk state), has excellent surface smoothness, and can have both releasability and dimensional stability against humidity (curl resistance). Generally, when an adhesive film is bonded to a double-sided coated release paper, the relationship between the moisture content in the paper and the curl height is as shown in FIG. Here, the solid line shows an example when left at a relative humidity of 85% and a temperature of 20°C, and the broken line shows an example when left at a relative humidity of 20% and a temperature of 20°C. Further, curl may occur with the film surface on the inside, or may occur with the paper base (release paper surface) on the inside, and in both cases, the larger the value, the greater the curl. As is clear from FIG. 1, the moisture content of the release paper base paper of the present invention, which can minimize curling (can bring the curl height close to 0), is 5 to 10% regardless of the atmospheric humidity conditions.
Must be within the range of . Here, when the water content in the paper is less than 5%, the base paper absorbs significant moisture in a high humidity atmosphere, and the dimensions of the base paper accordingly increase significantly compared to when the water content in the paper is 5 to 10%. Curls and edge waving (unevenness due to moisture absorption) occur. On the other hand, if the water content in the paper exceeds 10%, curling will occur due to dehumidification at low humidity, and at the same time foaming will occur at the interface between the base paper and the barrier layer when the silicone is cured, even if the curing temperature is low. , it is difficult to obtain good peeling performance. According to the principle of the radiation curing method using ultraviolet rays or electron beams, the surface temperature of the substrate to be cured is maintained at approximately room temperature, or at a maximum of 60°C even if incidental thermal radiation is present. This was done based on the knowledge that the time required for curing is also very short. The technical problem of curing silicone without dissipating the water content in the paper, which was previously maintained at 5 to 10%, could only be solved by this radiation curing method. With the conventional heat curing method, which requires a curing temperature of 120°C or higher, it was impossible to apply a barrier coat to the back of the release paper to prevent curling before curing the silicone, but with the radiation curing method, Keep the moisture in the release paper at 5-10%,
In addition, it is possible to maintain the barrier properties of the back surface, so the curl resistance is significantly improved. In addition, the water vapor permeability of the double-sided processed layer to the base paper is 80.
The essential condition is that it is less than g/ ^m2・24hr・atm. If the processed layer exceeds this value, the barrier effect against the external atmosphere (humidity) will be significantly reduced, and the base paper will easily absorb and desorb moisture.
This is because, as a result, the curl resistance of the release paper is impaired. Radiation in the present invention refers to ultraviolet rays, electron beams, etc. The ultraviolet ray or electron beam curable silicone resin used in the present invention includes, for example, a mercapto group-containing organopolysiloxane and a vinyl group that utilize a radical addition polymerization reaction or dimerization reaction initiated by ultraviolet ray or electron beam irradiation. Mixed composition with containing organopolysiloxane 2 Organopolysiloxane composition containing acrylic group, methacrylic group, or cinnamoyl group 3 Organopolysiloxane composition containing maleimide group or phenylmaleimide group 4 Containing organopolysiloxane containing azide group and vinyl group Mixed composition with organopolysiloxane 5 Organopolysiloxane composition containing thioacrylic group, thiomethacrylic group or thiocinnamoyl group 6 Organopolysiloxane composition containing acrylamide group, methacrylamide group or cinnamoylamide group. Also, a mixed composition of an epoxy group-containing organopolysiloxane using ultraviolet-initiated cationic polymerization and a diazonium Lewis acid salt as a photodegradable initiator can also be used. In the case of ultraviolet curing, known curing initiators such as benzoyl alkyl ether and its derivatives, acetophenone and its derivatives, benzophenone and its derivatives, and thioxanthone and its derivatives are used. In the case of electron beam curing, no curing initiator is required. These compositions can be used as 100% solids or diluted with a solvent such as toluene, ethyl acetate, hexane, or the like. The coating amount of radiation-curable release agent is 0.1g/m ² to 1.5g/m ² (solid content)
is effective, and Mayer bar, roll coating, gravure coating, and other known coating methods can be applied. Films that function as a water vapor barrier layer include low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, polymethylpentene, copolymers of these, ethylene/α-olefin copolymers, polyester, polychloride, etc. Synthetic resin coating layer such as vinylidene, Al foil,
This includes a metal foil bonding layer such as Fe foil, or a coating consisting of a pigment coated layer. The release paper according to the present invention is also fully applicable to release papers for manufacturing prepreg sheets, ceramic green sheets, synthetic leather, and the like. For example, for the production of synthetic leather, a release paper may be used in which a polyethylene coating having a predetermined surface profile is formed on one side of a paper base, and a release treatment is performed using a heat-curable silicone resin. Since polyethylene softens at high temperatures, the surface profile of such a release paper is damaged by the high temperatures during the release process, and the release paper loses its properties as a release paper for synthetic leather production. When a radiation-curable release agent is used as a release agent, as mentioned above, a sufficiently crosslinked release layer is formed without using high temperatures, so the surface properties of the polyethylene are not impaired in any way. . Therefore, it has become possible to produce a release paper that maintains optimal surface properties and release properties as a release paper for the production of synthetic leather. Specific examples of the present invention will be shown below to clarify the effects of the present invention, but these examples are not intended to limit the scope of the present invention. Example 1 Low-density polyethylene (manufactured by Mitsubishi Yuka Co., Ltd., product name LK30) was coated on one side of high-quality paper with a basis weight of 116 g/ ^m2.
It was extruded to a size of 20 μm and laminated onto high-quality paper, and the moisture content in the paper was adjusted to about 8%. The water vapor permeability of the obtained laminated paper was 48 g/m ² ·24 hr ·atm. Next, low-density polyethylene (manufactured by Mitsubishi Yuka Co., Ltd., trade name LK30) was extruded on the back side of the laminated paper to a thickness of 20 μm, and the laminated paper was further laminated to obtain a double-sided laminated paper. On one side of the double-sided laminated paper, 0.4 g/ ^m2 of ultraviolet curing silicone (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: X-62-783) was applied and cured at 160 W/cm and a curing speed of 20 m/min. I let it happen. The ultraviolet curing device was manufactured by Ushio Electric Co., Ltd. and has the trade name Konikiure UV4000. Table 1 shows the results of peel resistance to adhesive, residual adhesion rate, rub-off, smoothness of the peeled surface, and pinholes for the release paper obtained. Example ² Polyvinylidene chloride emulsion (manufactured by Kureha Kagaku Co., Ltd., trade name NR
-1804) was coated to a dry weight of 14 g/m ² and dried and solidified at 100°C for 1 minute. The water vapor permeability of the coated paper obtained was 12 g/m ² ·24 hr ·atm. After adjusting the water content of the coated paper to approximately 8%, low-density polyethylene (manufactured by Showa Denko, trade name L-171) was extruded on one side to a thickness of 20μ and laminated onto the single-sided coated paper. , a double-sided resin-treated paper was obtained. As in Example 1, this processed paper was coated with ultraviolet curable silicone (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: X-62-783) on the polyethylene side and cured.
Table 1 shows the results of the release paper obtained, including the peel resistance value against the adhesive. Example 3 Moisture content in paper obtained in the same manner as Example 1: approximately 8%
Electron beam curing type silicone (manufactured by Gold Schmidt AG, product name RC) is coated on one side of the double-sided laminated paper.
-300) was applied at a rate of 1.1 g/m ² and cured at an electron beam irradiation dose of 3 Mrad. The electron beam curing device is an electron curtain type CB manufactured by ESI.
-150 was used. Table 1 shows the results of the release paper obtained, including the peel resistance value against the adhesive. Comparative Example 1 Low-density polyethylene (manufactured by Showa Denko, product name L-171) was coated on one side of high-quality paper with a basis weight of 116 g/ ^m2.
It was extruded to 20μ and laminated to high quality paper. The water vapor permeability of the obtained laminated paper was 47g/ ^m2 .
It was 24 hours/ATM. This laminated paper does not undergo any particular moisture adjustment, and is coated with 20 μm of low-density polyethylene (manufactured by Showa Denko Co., Ltd., product name L-171) on the back side.
The above laminated paper was then further laminated. The moisture content of the obtained double-sided laminated paper was measured and was found to be 3.5%. Ultraviolet curing type silicone (manufactured by Shin-Etsu Chemical Co., Ltd., trade ^name I let it happen. Comparative Example 2 Moisture in paper obtained in the same manner as Example 1: approximately 8%
Thermosetting silicone (manufactured by Toray Silicone Co., Ltd., trade name SRX) was applied to one side of the double-sided laminated paper so that the dry weight was 0.6 g/ ^m2 , and 180
It was dried and cured at ℃ for 60 seconds. The resulting release paper had a low water content of 4.1%, and foaming occurred on the polyethylene surface. Comparative Example 3 Moisture in paper obtained in the same manner as Comparative Example 2: approximately 8%
Thermosetting silicone (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KS) was applied by dry weight to one side of the double-sided laminated paper.
Apply at a concentration of 0.6 g/m ² under low temperature conditions, i.e. 100°C, without the risk of foaming on the polyethylene surface.
Drying/curing was performed for 2 minutes. The moisture content of the release paper obtained was 7.5%. The physical properties of the release papers obtained in Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3 are shown in Table 1, and the relationship between the moisture content in the paper and the curl height after film lamination is shown in Table 2. show. From Table 1, the release papers obtained in Examples 1, 2, and 3 have low peel resistance to adhesives and high residual adhesion rates of 88 to 90%. Furthermore, it is clear that it has excellent properties such as high smoothness and no pinholes. On the other hand, the release paper according to Comparative Example 2
Due to the high temperature curing of 180°C, foaming occurred on the polyethylene surface, the peel resistance to the adhesive was high, and many pinholes were observed, which impaired the peelability. In addition, in the release paper according to Comparative Example 3, crosslinking of the silicone resin was insufficient due to low temperature curing, and the peel resistance value against the adhesive was 140 g / 15 mm, compared to Example 1.
It was 7 to 10 times higher than release paper Nos. 2 and 3, and lacked release suitability, as changes were observed in the rub-off test. Next, based on Table 2, the superiority of the present invention will be clarified. In the release papers obtained in Examples 1, 2, and 3, there was almost no change in the moisture content in the paper before and after silicone curing, and the moisture content in the paper was maintained at approximately 8%.
Even in a high humidity atmosphere, the curl height was kept to an extremely low value of 6 to 7 mm. On the other hand, the release paper of Comparative Example 1 has a low moisture content of approximately 3% before and after silicone curing, so the curl height in a high humidity atmosphere (80% RH) is 20 mm, which is compared to the example. showed a much larger value. In addition, the release paper of Comparative Example 2 also has a large release of moisture in the paper due to silicone curing, and the moisture content in the paper after curing is 4.1.
As in Comparative Example 1, the curl height in a high humidity atmosphere was as large as 18 mm. In Comparative Example 3, since the curing was performed at a low temperature, the change in the moisture content in the paper before and after curing was extremely small, and the moisture content in the paper after curing could be maintained at a high value of 7.5%. Therefore, the curl height was approximately the same as that of the release paper obtained in the example. However, the first problem is that the release properties are lost due to insufficient crosslinking due to low temperature curing.
It was as shown in the table. As described above, the release paper according to the present invention is obtained by achieving high degree of crosslinking of silicone resin at a low curing temperature, and has excellent release properties and curl resistance.

【table】

[Table] The temperature for measuring the curl height of film-bonded products is 20°C. The curl axis is the longitudinal direction (TD), and the curl occurs with the film surface facing inside. In addition, each physical property value described in the present invention was measured by the method described below. Γ Water vapor permeability Performed by cup method based on JIS L-0208. Note that the measurements are performed using coated paper in which a barrier coating film is formed on a paper base. Γ Moisture content in base paper Based on JIS P-8127, it is measured using a coated paper with a barrier coating formed on the paper base, and the measured value is expressed as a percentage of the water content based on the basic weight of the paper. Γ Peel resistance value The obtained release paper was left in an atmosphere with a temperature of 20℃ and a relative humidity of 65% for 24 hours, then an adhesive was applied to the silicone surface to a thickness of 125μ (wet), Dry in a hot air dryer for 1 minute. After cooling to room temperature, paste 67 g/m ² of high-quality paper on this surface, press it with a 2 kg tape roller, leave it in an atmosphere of 20°C and 65% RH for 3 hours, and then peel it off with Tensilon at a peel angle of 180°C. speed
The force required for peeling when peeled off at 300 and 1000 mm/min is determined, and this is taken as the peel resistance value. Γ Residual adhesion rate After leaving the obtained release paper in an atmosphere with a temperature of 20°C and a relative humidity of 65% for 24 hours, apply a commercially available adhesive tape (manufactured by Nitto Denko Corporation, product name Lumirror) to the silicone surface.
31B), 20℃, 65%RH, pressure 0.1Kg/cm ²
After applying pressure for 24 hours under these conditions, peel off the tape, adhere it to a stainless steel plate, press it using a roller with a load of 2 kg, and leave it for 30 minutes at 20°C and 65% RH. Next, apply the adhesive tape at a peeling angle of 180°C and a peeling speed of 300°.
It is pulled at a rate of mm/min, and the force required for peeling at this time is determined, and this is taken as the peel resistance value. Attach the same adhesive tape (Lumirror 31B above) to a stainless steel plate and heat at 20℃, 65%RH, and pressure 0.1.
After pressurizing for 24 hours under the conditions of Kg/ ^cm2 , remove the pressure and
After standing for a period of time, peeling angle 180℃, peeling speed 300mm/min
The force required for peeling when peeled off is determined, and this is taken as the peel resistance value. The ratio between the peel resistance and the peel resistance is determined, and this is taken as the residual adhesion rate. Γ Rub-off Rub the silicone surface with your finger (10 times) and visually observe the condition of the silicone surface after rubbing. Γ Smoothness Measure the semi-smoothness of the silicone surface using an Oken type smoothness meter. Γ Pinhole test A toluene solution containing a dye dissolved is applied to the surface.
Evaluation was made based on the degree of penetration into the back surface. Γ Curl height Apply adhesive to the silicone side of the release paper obtained.
Coat to a thickness of 125μ (wet) and dry in a hot air dryer at 100℃ for 1 minute. After cooling to room temperature, a 50μ thick PEI film was attached to this surface and pressed with a 2Kg tape roller. 10cm of the obtained adhesive film paper
Cut into 10cm x 10cm pieces and place in the specified atmosphere for 3
After leaving it for a while, measure the height of the four corners and display the average value as the curl height.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between paper moisture and curl height.

Claims (1)

[Claims] 1. Both sides of the paper substrate have a water vapor permeability of 80 g/m ² .
It is made of double-sided treated paper with a coating of 24hr・ATM or less and whose moisture content is adjusted to a range of 5 to 10%, and a radiation-curable silicone resin layer is provided on one or both sides. A release paper characterized by: 2. The release paper according to claim 1, wherein the coating having a water vapor permeability of 80 g/m ² ·24 hr ·atm or less is a synthetic resin-treated layer. 3. The release paper according to claim 1, wherein the coating having a water vapor permeability of 80 g/m ² ·24 hr ·atm or less is a metal foil bonding layer. 4 Claim 1 in which the coating having a water vapor permeability of 80 g/m ² 24 hr atm or less is a pigment coated layer.
Release paper as described in section.