JP2024049819A - Release paper - Google Patents

Abstract

[Problem] To provide a release paper with excellent solvent resistance. [Solution] A release paper 100 comprising a paper base material 10, a filling layer 20 containing cellulose acetate provided on one surface 11 of the paper base material 10, and a release agent layer 30 containing a silicone-modified alkyd resin and a melamine resin provided on the surface of the filling layer 20 opposite to the paper base material 10 side. [Selected Figure] Figure 1

Description

The present invention relates to release paper.

Conventionally, release papers have been widely used for various applications, such as protective sheets for adhesive layers in adhesive sheets, process papers for producing resin sheets, and process papers for producing synthetic leather. Release papers, for example, have a paper base material and a release agent layer provided on the paper base material, and if necessary, a sealing layer may be provided between the paper base material and the release agent layer.

For example, Patent Document 1 proposes a release paper for synthetic leather production, which comprises a paper base layer, an ionizing radiation cured resin layer provided on the paper base layer, and a release layer having a thickness of 0.01 to 20 μm formed on the ionizing radiation cured resin layer. In the release paper for synthetic leather production described in Patent Document 1, the ionizing radiation cured composition constituting the ionizing radiation cured resin layer comprises a (meth)acryloyl group-containing acrylic copolymer (I), or a (meth)acryloyl group-containing acrylic copolymer (II) obtained by reacting 10 to 30 parts by mass of (meth)acrylic acid with a copolymer consisting of 35 to 80 parts by mass of (meth)acrylic acid ester, 20 to 60 parts by mass of glycidyl (meth)acrylic acid ester, and 0 to 30 parts by mass of other (meth)acrylic acid ester. The ionizing radiation cured resin layer contains phenolic particles having an average particle size of 1 to 30 μm in the range of 10 to 80 mass % in the dried ionizing radiation cured resin layer, the particles containing a phenolic resin made of a reaction product of phenols and aldehydes.

Japanese Patent No. 5724448

One use of release paper is release paper for the production of synthetic leather (also called synthetic leather processing paper), which is used, for example, to produce synthetic leather whose main raw material is a resin such as polyurethane resin. Synthetic leather whose main raw material is a resin such as polyurethane resin is produced by applying a resin composition for forming synthetic leather, which contains polyurethane resin and an organic solvent, onto the release agent layer of the release paper, and drying the composition to form a synthetic resin layer. The synthetic resin layer is then finally peeled off from the interface of the release agent layer to obtain the product. In this way, solvent resistance is required in applications in which a coating liquid containing an organic solvent is applied onto the release agent layer of the release paper.

The object of the present invention is to provide a release paper that has excellent solvent resistance, even when used in applications where a coating liquid containing an organic solvent is applied onto the release agent layer of the release paper.

[1] A paper base material,
A filling layer containing cellulose acetate provided on one surface of the paper base material;
a release agent layer including a silicone-modified alkyd resin and a melamine resin provided on a surface of the filling layer opposite to the paper substrate;
A release paper comprising:

[2] The release paper according to [1],
The thickness of the filling layer is 2 μm or more and 20 μm or less.
Release paper.

[3] The release paper according to [1] or [2],
The acetylation degree of the cellulose acetate is 50% or more and 62% or less.
Release paper.

[4] The release paper according to any one of [1] to [3],
The cellulose acetate has a total degree of acetyl substitution of 2.3 or more and 2.6 or less.
Release paper.

[5] The release paper according to any one of [1] to [4],
The filling layer is a layer formed by coating a coating liquid in which the cellulose acetate is dissolved in an organic solvent.
Release paper.

According to one aspect of the present invention, a release paper with excellent solvent resistance can be provided, even when the release paper is used in an application in which a coating liquid containing an organic solvent is applied onto the release agent layer of the release paper.

FIG. 2 is a cross-sectional view showing a schematic example of a release paper according to the present embodiment.

<Release paper>
The release paper according to this embodiment comprises a paper base material, a filling layer containing cellulose acetate provided on one side of the paper base material, and a release agent layer containing a silicone-modified alkyd resin and a melamine resin provided on the side of the filling layer opposite the paper base material.

The release paper according to this embodiment has the above-mentioned configuration, and therefore has excellent solvent resistance, even when used in applications where a coating liquid containing an organic solvent is applied onto the release agent layer of the release paper. Although the reason is unclear, it is believed that cellulose acetate has a high sealing effect, and therefore when the release agent layer is provided, the penetration of the release agent composition containing a silicone-modified alkyd resin and a melamine resin into the paper substrate is suppressed. It is presumed that this gives the obtained release paper excellent solvent resistance.

The release paper according to this embodiment will be described with reference to the drawings. The release paper 100 shown in FIG. 1 comprises a paper substrate 10, a filler layer 20 provided on one side of the paper substrate 10 (first main surface 11 of the paper substrate 10), and a release agent layer 30 provided on the side of the filler layer 20 opposite the paper substrate 10 (main surface 21 of the filler layer 20), and the paper substrate 10, the filler layer 20, and the release agent layer 30 are laminated in this order from the paper substrate 10 toward the release agent layer 30. The filler layer 20 and the release agent layer 30 are not provided on the second main surface 13 of the paper substrate 10, and the second main surface 13 of the paper substrate 10 is exposed. The filler layer 20 contains cellulose acetate, and the release agent layer 30 contains a silicone-modified alkyd resin and a melamine resin. In the release paper 100, the main surface 31 of the release agent layer 30 becomes the surface that comes into contact with the object to be peeled (the release surface). Here, the main surface refers to the largest surface of the paper base material, the filling layer, or the release agent layer, and refers to the surface facing the thickness direction (i.e., the stacking direction of each layer).

Although an example of the release paper according to this embodiment has been described above with reference to FIG. 1, the release paper according to this embodiment is not limited to this. The release paper according to this embodiment may take various forms as long as it has the above-mentioned configuration.

(Paper base material)
The paper substrate is not particularly limited as long as it can support the filling layer described below. Examples of the paper substrate include kraft paper, glassine paper, uncoated paper (e.g., fine paper, medium-quality paper, and thin paper), and coated paper (e.g., art paper, clay-coated paper, and cast-coated paper).

In this specification, the coated paper comprises a base paper mainly composed of pulp fibers and a pigment coating layer provided on the base paper. The base paper is obtained by a known method, for example, by adding the desired additives to pulp fibers as the main component. The pigment coating layer is provided on the base paper by a known method. The pigment coating layer may have a single layer structure or a multilayer structure. The pigment coating layer contains, for example, an adhesive such as a water-based resin in a range of 2 parts by mass or more and 50 parts by mass or less per 100 parts by mass of one or more pigments such as calcium carbonate, kaolin, clay, talc, satin white, titanium oxide, and plastic pigment.

By providing the paper base material with a pigment coating layer, the sealing effect of the sealing layer containing cellulose acetate is likely to be improved. In addition, the sealing effect is also likely to be improved when a release agent layer is provided on the sealing layer.

The basis weight of the paper substrate is not particularly limited, and is preferably, for example, 50 g/m ² or more, and more preferably, 100 g/m ² or more. The basis weight of the paper substrate is preferably, for example, 300 g/m ² or less, and more preferably, 200 g/m ² or less. The thickness of the paper substrate is not particularly limited, and is preferably, for example, 5 μm or more, and more preferably, 10 μm or more. The thickness of the paper substrate is preferably, for example, 300 μm or less, and more preferably, 200 μm or less.

When the paper substrate is a coated paper, the thickness of the base paper is preferably 50 μm or more, and more preferably 100 μm or more. The thickness of the base paper is preferably 250 μm or less, and more preferably 200 μm or less. The thickness of the pigment coating layer is preferably 5 μm or more, and more preferably 10 μm or more. The thickness of the pigment coating layer is preferably 40 μm or less, and more preferably 30 μm or less.

(Sealing layer)
The filling layer contains cellulose acetate. It is sufficient that the filling layer contains cellulose acetate as a resin component, and it may contain only cellulose acetate as a resin component.

The thickness of the filling layer is not particularly limited. From the viewpoint of easily obtaining solvent resistance, the thickness of the filling layer is, for example, preferably 2 μm or more, more preferably 3 μm or more, and even more preferably 4 μm or more. The thickness of the filling layer is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. In addition, if the thickness of the filling layer is 20 μm or less, for example, the occurrence of curling is easily suppressed.

In the release paper according to this embodiment, the sealing layer has an excellent sealing effect even if it is less than 10 μm thick (for example, 9 μm or less). Therefore, it has the advantage that it can be made thinner than the sealing layer made of polyethylene resin that has been used conventionally.

Considering the environmental impact, it is preferable that the acetylation degree of cellulose acetate is 50% or more, from the viewpoint of easily obtaining biodegradability. The acetylation degree of cellulose acetate may be 52% or more, 53% or more, or 54% or more. It is preferable that the acetylation degree of cellulose acetate is 62% or less, from the viewpoint of easily obtaining biodegradability.

The acetylation degree of cellulose acetate can be measured in accordance with the acetylation degree measurement method of ASTM D-817-91 (test method for cellulose acetate, etc.).

Considering the environmental impact, the total degree of acetyl substitution of cellulose acetate is preferably 2.3 or more, more preferably 2.4 or more, from the viewpoint of easily obtaining biodegradability. The total degree of acetyl substitution of cellulose acetate is preferably 2.6 or less, more preferably 2.5 or less, from the viewpoint of easily obtaining biodegradability.

The total degree of acetyl substitution of cellulose acetate can be calculated from the acetylation degree of cellulose acetate by the following formula (F1).
DS = 162.14 × AV / (6005.2 - AV × 42.037) ... (F1)
In formula (F1), DS represents the total degree of acetyl substitution, and AV represents the degree of acetylation (%).

In addition, it is preferable that the 6% viscosity of the cellulose acetate (viscosity when diluted to 6%) at 25±1°C is 50 mPa·s or more and 200 mPa·s or less. The 6% viscosity can be measured, for example, by dissolving 3 g of a dry sample in 39.9 g of a 95% aqueous acetone solution to give a solution with a concentration of 6 wt/vol% (mass/volume%) using an Ostwald viscometer.

The melting point of cellulose acetate is preferably 230°C or higher and 300°C or lower. The melting point of cellulose acetate can be measured, for example, according to the method specified in JIS K7121:1987.

The viscosity of a solution containing cellulose acetate, such as the coating solution of the composition for forming the filling layer described below, can be measured, for example, according to the method specified in JIS K7117-1:1999.

The filling layer may be (i) a layer (resin layer) formed by melt extrusion of cellulose acetate, or (ii) a layer formed by coating with a coating liquid in which cellulose acetate is dissolved in an organic solvent. From the viewpoint of ease of forming the filling layer and of adhesion to the paper substrate, it is preferable that the filling layer is a layer formed by coating with a coating liquid in which cellulose acetate is dissolved in an organic solvent (coating liquid of a composition for forming a filling layer).

In addition to cellulose acetate, the filling layer may contain other components such as additives (e.g., plasticizers) as necessary, provided that the effect of this embodiment is not impaired.

(Release Agent Layer)
The release agent layer is formed from a release agent composition containing a mixed resin of a silicone-modified alkyd resin and a melamine resin. The silicone-modified alkyd resin is an alkyd resin chemically modified with a polyorganosiloxane. The melamine resin is a hardener component of the release agent composition.

The release agent layer containing silicone-modified alkyd resin and melamine resin contains melamine resin as a hardener component, and the silicone-modified alkyd resin is crosslinked with the melamine resin, thereby hardening the release agent layer and improving the release properties. By containing silicone-modified alkyd resin and melamine resin in the release agent layer, when the release paper is used, for example, as process paper for the production of synthetic leather, the modified components remain on the surface of the release agent layer even if the synthetic leather is repeatedly formed. Therefore, the release agent layer is more likely to maintain its release properties. Note that when the silicone-modified alkyd resin is crosslinked with the melamine resin, amino groups are generated. Therefore, the release agent layer containing silicone-modified alkyd resin and melamine resin is also a release agent layer containing silicone-modified amino alkyd resin.

The thickness of the release agent layer is not particularly limited, and the thickness of the release agent layer after drying and curing is preferably 3 μm or more. The thickness of the release agent layer is not particularly limited, and the thickness of the release agent layer after drying and curing is preferably 15 μm or less, and more preferably 8 μm or less.

In addition to the silicone-modified alkyd resin and melamine resin, the release agent layer may contain other components such as additives as necessary, provided that the effects of this embodiment are not impaired.

(Production method of release paper)
The method for producing the release paper according to the present embodiment is not particularly limited. A preferred example of the method for producing the release paper according to the present embodiment includes, for example, a step of preparing a paper substrate, a step of providing a sealing layer containing cellulose acetate on one side of the paper substrate, and a step of providing a release agent layer containing a silicone-modified alkyd resin and a melamine resin on the side of the sealing layer opposite to the paper substrate side.

The paper base material preparation process can be carried out by preparing the paper base material described above.

The step of providing a filling layer is not particularly limited as long as a filling layer containing cellulose acetate can be provided on one surface of the paper base material.
Specifically, the step of providing the filling layer may be a step of preparing a filling layer forming composition containing cellulose acetate, and then applying the filling layer forming composition onto a paper substrate and drying to form a coating film. For example, a method of providing a filling layer on a paper substrate may include a method of coating a paper substrate with a coating liquid of a filling layer forming composition prepared by dissolving a filling layer forming material containing cellulose acetate in an organic solvent. The coating liquid of the filling layer forming composition is coated onto the paper substrate and then dried to form a filling layer.

The organic solvent for dissolving cellulose acetate is not particularly limited, and examples thereof include ketones (acetone, cyclohexanone, methyl ethyl ketone (MEK), etc.), ethers (diethyl ether, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, etc.), amides (dimethylformamide, etc.), and esters (ethyl acetate, butyl acetate, etc.). These organic solvents may be used alone or in combination of two or more. Among these organic solvents, from the viewpoint of ease of dissolving cellulose acetate, at least one selected from the group consisting of ethyl methyl ketone, dimethylformamide, and cyclohexanone is preferable.

The viscosity of the coating solution of the composition for forming the filling layer at 25°C is preferably 20 mPa·s or more and 2000 mPa·s or less. If the viscosity is within the above range, it becomes easier to form an appropriate filling layer using the coating solution. This viscosity can be measured, for example, in accordance with the method specified in JIS K7117-1:1999. There are no particular limitations on the non-volatile content concentration in the coating solution of the composition for forming the filling layer, so long as the viscosity at 25°C can be adjusted to be within the above range.

Examples of methods for coating the coating liquid of the composition for forming a filling layer on a paper substrate include bar coating, knife coating, roll knife coating, roll coating, blade coating, die coating, curtain coating, and gravure coating. The coating amount of the coating liquid of the composition for forming a filling layer is preferably, for example, an amount that results in a thickness of the filling layer after drying in the range of 2 μm or more and 20 μm or less. When the filling layer is a layer consisting of only cellulose acetate, the coating amount of the coating liquid of the composition for forming a filling layer is not particularly limited, and may be, for example, 3 g/m ² or more and 30 g/m ² or less.

The step of providing a release agent layer is not particularly limited as long as the release agent layer can be provided on the filling layer provided on the paper base material.
Specifically, the step of providing the release agent layer may be a step of preparing a release agent composition containing a silicone-modified alkyd resin and a melamine resin, and then applying the release agent composition onto the filling layer formed on the paper substrate, and drying the composition to form a coating film. The method of providing the release agent layer on the filling layer is, for example, to apply a coating liquid of a release agent composition containing a silicone-modified alkyd resin and a melamine resin onto the filling layer formed on the paper substrate, and then heat to form a coating film, and provide the release agent layer on the filling layer. The heating when forming the coating film is preferably performed by drying and thermal curing at the same time. The heating when forming the coating film may be performed by drying and thermal curing in one step, or may be performed by drying in multiple steps, including an initial drying step and a post-drying step performed immediately thereafter.

The coating solution of the release agent composition preferably contains an organic solvent in addition to the mixed resin of the silicone-modified alkyd resin and the melamine resin. Examples of the organic solvent include toluene, xylene, hexane, heptane, methanol, ethanol, isopropanol, isobutanol, n-butanol, acetone, methyl ethyl ketone, and tetrahydrofuran. These organic solvents may be used alone or in combination of two or more.

From the viewpoint of coating suitability and drying property, the non-volatile content concentration in the coating solution of the stripping agent composition is preferably 5% by mass or more and 60% by mass or less. The non-volatile content concentration may be 10% by mass or more, or 20% by mass or more. The non-volatile content concentration may be 50% by mass or less, or 40% by mass or less.

Examples of methods for applying the release agent composition include curtain coating, spray coating, bar coating, knife coating, roll coating, roll knife coating, blade coating, die coating, gravure coating, and air knife coating.

By performing the above steps, the release paper according to this embodiment is obtained.

(Use of release paper)
The release paper according to the present embodiment can be applied to general release sheet applications.The release paper according to the present embodiment can be used as a process paper used in the process of forming a sheet-like object on the release surface of the release agent layer of the release paper.Specifically, the release paper according to the present embodiment can be used as various process papers when producing various resin sheets, synthetic leather, various composite materials, etc.

The release paper according to this embodiment has excellent solvent resistance, and is therefore useful, among the various applications mentioned above, for example, as a processing paper for synthetic leather.

As an example of an application of the release paper according to this embodiment, a method of manufacturing synthetic leather using the release paper will be described, but the application of the release paper according to this embodiment is not limited to this.

The method for producing synthetic leather is not particularly limited, and may be, for example, a method having the following steps. The method for producing synthetic leather includes a step of applying a coating liquid containing a synthetic resin to the main surface of the release agent layer in the release paper according to this embodiment, a step of drying the applied coating liquid to form synthetic leather containing a synthetic resin, and a step of peeling the release paper from the synthetic leather after drying. The step of forming synthetic leather may be a step of drying the applied coating liquid to form a synthetic resin layer, applying an adhesive to the synthetic resin layer, and then bonding a base fabric and maturing. In this case, the step of peeling the release paper from the synthetic leather may be a step of peeling the release paper from the synthetic leather together with the base fabric after maturing.

The present invention is not limited to the above-described embodiment. The present invention may include modifications and improvements within the scope of the invention.

The following examples are provided, but the present invention is not limited to these examples.

The following raw materials were prepared as raw materials for producing the release paper of each Example and Comparative Example.

(Paper base material)
P-1: High-quality paper (manufactured by Nippon Paper Industries Co., Ltd., npi high-quality, basis weight 64 g/m ² )
P-2: Glassine paper (manufactured by Lintec Corporation, basis weight 62 g/m ² )
P-3: Cast coated paper (manufactured by Nippon Paper Industries Co., Ltd., Esprit C, basis weight 157 g/m ² )

(Cellulose acetate)
CA-1: Cellulose acetate having an acetylation degree of 55% (total degree of acetyl substitution of 2.4) (manufactured by Daicel Corporation, L-20)

(paint remover)
MSAA: A mixture of silicone-modified alkyd resin and melamine resin (TA31-209E, manufactured by Showa Denko Materials Co., Ltd.)

Example 1
A coating solution (viscosity at 25°C 1200 mPa·s) of a composition for forming a filler layer prepared by dissolving cellulose acetate (CA-1) in methyl ethyl ketone was applied to one side of a fine paper (P-1) with an applicator, and then dried at 120°C for 1 minute to form a filler layer with a thickness of 3 μm. Next, a mixture of silicone-modified alkyd resin and melamine resin (MSAA) was coated on the surface of the filler layer with a Mayer bar so that the coating amount after drying was 8 g/ ^m2 . After coating, the mixture was dried and cured at 180°C for 60 seconds to form a release agent layer with a thickness of 5 μm after curing, and the release paper of Example 1 was obtained.

Example 2
A release paper of Example 2 was obtained in the same manner as in Example 1, except that the thickness of the filling layer was changed according to Table 1.

Example 3
According to Table 1, the release paper of Example 3 was obtained in the same manner as in Example 1, except that the wood-free paper was changed to glassine paper.

<Comparative Example 1>
A release paper of Comparative Example 1 was obtained in the same manner as in Example 1, except that a release agent layer was formed directly on the fine paper without providing a filling layer.

<Comparative Example 2>
A release paper of Comparative Example 2 was obtained in the same manner as in Example 1, except that the wood-free paper was changed to cast-coated paper, and a release agent layer was formed directly on the cast-coated paper without providing a filling layer.

[Evaluation of Solvent Resistance]
In a sealed container, a paper wiper soaked with toluene (Kimwipe (registered trademark), manufactured by Nippon Paper Crecia Co., Ltd.) was placed on the surface of the release agent layer of the release paper obtained in each example. After 30 minutes, 1 hour, 2 hours, 4 hours, 8 hours, 16 hours, and 24 hours, the toluene-soaked paper wiper was removed, and a polyester adhesive tape (No. 31B, manufactured by Nitto Denko Corporation, polyester base material, acrylic adhesive) was attached to the area where the paper wiper was removed. Thereafter, the attached polyester adhesive tape was peeled off by hand and visually observed, and evaluated according to the following evaluation criteria.

(Evaluation criteria)
A: No tearing of the paper layer occurs.
F: Paper layer tearing occurred.

[Evaluation of peel strength]
A polyester adhesive tape (manufactured by Nitto Denko Corporation, No. 31B, polyester base material, acrylic adhesive) was attached to the release agent layer, and the tape was allowed to stand for 30 minutes under conditions of a temperature of 23° C. and a relative humidity of 50%, after which the peel strength was measured by a 180° peel test at a peel speed of 0.3 m/min in accordance with JIS Z0237:2022.

The release paper of each example is found to have superior solvent resistance compared to the release paper of Comparative Example 1, which does not have a sealing layer.

The release paper in each example has a sealing layer containing cellulose acetate. Therefore, the release paper according to this embodiment has excellent biodegradability and is likely to have a reduced impact on the environment.

10...paper base material, 11...first main surface (first main surface of paper base material 10), 13...second main surface (second main surface of paper base material 10), 20...filler layer, 21...main surface (main surface of filling layer 20), 30...release agent layer, 31...main surface (main surface of release agent layer 30), 100...release paper.

Claims (5)

A paper substrate;
A filling layer containing cellulose acetate provided on one surface of the paper base material;
a release agent layer including a silicone-modified alkyd resin and a melamine resin provided on a surface of the filling layer opposite to the paper substrate;
A release paper comprising: The release paper according to claim 1,
The thickness of the filling layer is 2 μm or more and 20 μm or less.
Release paper. The release paper according to claim 1 or 2,
The acetylation degree of the cellulose acetate is 50% or more and 62% or less.
Release paper. The release paper according to claim 1 or 2,
The cellulose acetate has a total degree of acetyl substitution of 2.3 or more and 2.6 or less.
Release paper. The release paper according to claim 1 or 2,
The filling layer is a layer formed by coating a coating liquid in which the cellulose acetate is dissolved in an organic solvent.
Release paper.

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