TW202417248A - Release film - Google Patents

Abstract

The present invention is a release film having a laminated film and a release layer C located on at least one side of the laminated film; the laminated film is laminated in sequence with at least a first coating layer B1 containing a polyester resin containing an inorganic pigment, a void-containing layer A containing voids inside, and a second coating layer B2 containing a polyester resin containing an inorganic pigment; the void-containing layer A contains a first component containing a polyester resin and a polyolefin resin; the release layer C is composed of a second component containing a polysilicone resin; and the apparent density is greater than 0.80 g/cm ³ and less than 1.20 g/cm ³ .

Description

Release film

The present invention (the first invention, the second invention) relates to a release film containing a cavity inside.

As a method for obtaining a film having a function similar to that of paper, a method of making a film contain a large number of fine cavities is known.

The method comprises mixing an immiscible thermoplastic resin (hereinafter referred to as the immiscible resin) into a polyester resin to obtain a sheet in which the immiscible resin is dispersed in the polyester resin and extends in at least a uniaxial direction. In this way, the method reveals voids by exfoliation of the interface between the polyester resin and the immiscible resin. As such an immiscible resin, for example, polyolefin resins such as polyethylene resin or polypropylene resin, polymethylpentene resin (for example, refer to Patent Documents 1 to 3) or polystyrene resin (for example, refer to Patent Documents 4 and 5) are proposed. In particular, from the perspective of void visibility or cost efficiency, polypropylene resin is preferably used among these immiscible resins.

Here, when a polyolefin resin containing a polypropylene resin is simply dispersed in a polyester resin, the dispersion diameter of the polyolefin dispersed particles becomes larger. Therefore, although voids are easily revealed, on the other hand, the voids become larger, and sufficient concealment cannot be obtained, and the film-forming property also deteriorates. Therefore, a method of microdispersing the polyolefin resin has been adopted. So far, as a method of microdispersing, a method of adding a dispersant such as a surfactant or polyethylene glycol has been proposed (for example, refer to Patent Document 6 and Patent Document 7). [Prior Technical Document] [Patent Document]

[Patent Document 1] Japanese Patent Publication No. 49-134755. [Patent Document 2] Japanese Patent Publication No. 2-284929. [Patent Document 3] Japanese Patent Publication No. 2-180933. [Patent Document 4] Japanese Patent Publication No. 54-29550. [Patent Document 5] Japanese Patent Publication No. 11-116716. [Patent Document 6] Japanese Patent Publication No. 7-17779. [Patent Document 7] Japanese Patent Publication No. 8-252857.

[The problem that the invention wants to solve]

However, when adding a dispersant such as a surfactant or polyethylene glycol, although the polyolefin resin has a micro-dispersion effect, the polyolefin resin will be deformed in the heat extension step or the heat fixing step. Therefore, the obtained voids are also easily destroyed, and sufficient lightness and cushioning properties cannot be obtained. In addition, since the heat resistance of surfactants and polyethylene glycol is relatively poor, thermal degradation is easily generated in the melt extrusion step of the polyester resin, resulting in a decrease in the whiteness of the obtained film. Sometimes there is a problem that the degradation of the polyester resin is promoted and the film-making properties are deteriorated.

In recent years, in release films used to protect display components and various engineering films for electronic parts manufacturing, the peeling identification of release films is sometimes necessary. In addition, in various electronic parts manufacturing steps, there are sometimes heat treatment steps, and sometimes engineering release films need heat resistance/dimensional stability. In addition, in recent years, from the perspective of environmental protection, it is necessary to reduce the use of raw materials/weight reduction and resource recycling. For release films composed of colorless and transparent polyester films, although they can fully meet the requirements of heat resistance and dimensional stability, there is a problem that it is difficult to meet the peeling suitability of the film and reduce the amount of raw materials/weight reduction.

The purpose of the present invention (the first invention and the second invention) is to provide a release film that improves the problems of the above-mentioned prior art, mainly contains a polyolefin resin as a void revealing agent, and has excellent environmental compatibility, lightness, heat resistance, dimensional stability, film forming properties, concealing properties, whiteness, and release properties relative to a peeling body. [Means for solving the problem]

As a result of the research conducted by the inventors, it was found that by adjusting the melt viscosity and melt viscosity ratio of the polyester resin and the polyolefin resin to be within a specific range for film formation, the dispersed particle size of the polyolefin resin in the polyester resin can be controlled to an appropriate size, and further, by providing a release layer on at least one side of the laminated film, a polyester film containing voids having excellent lightness, heat resistance, dimensional stability, film forming properties, concealing properties, whiteness, and release properties can be obtained. This release property is, for example, the release property relative to a peel-off body such as an adhesive label.

That is, the first release film of the present invention is provided as follows. 1. A release film having a laminate film and a release layer C located on at least one side of the laminate film; the laminate film is laminated in sequence with at least a first coating layer B1 containing a polyester resin containing an inorganic pigment, a void-containing layer A containing voids inside, and a second coating layer B2 containing a polyester resin containing an inorganic pigment; the void-containing layer A contains a first component containing a polyester resin and a polyolefin resin; the release layer C is composed of a second component containing a polysilicone resin; and the apparent density is 0.80 g/cm ³ or more and 1.20 g/cm ³ or less. 2. The release film as described in 1. above, wherein the polysilicone resin is composed of polydimethylsiloxane containing at least one alkenyl group in one molecule and polydimethylsiloxane containing at least one hydrosilyl group in one molecule. 3. The release film as described in 1. above, wherein the content of the polysilicone resin in the release layer C is 90 mass % or more and 100 mass % or less relative to the total mass of the release layer C. 4. The release film as described in 1. above, wherein the polyester resin and the polyolefin resin contained in the void-containing layer A satisfy the following requirements (1) to (3): (1) The melt viscosity (η1) of the polyester resin at a melting temperature of 280°C and a shear rate of 121.6 sec ^{- 1} is 90 Pa·s or more and 400 Pa·s or less. (2) The melt viscosity (η2) of the polyolefin resin at a melting temperature of 280°C and a shear rate of 121.6 sec ^{- 1} is 300 Pa·s or more and 700 Pa·s or less. (3) The melt viscosity ratio (η2/η1) of the polyester resin to the polyolefin resin at a melting temperature of 280°C and a shear rate of 121.6 sec ^{- 1} is 1.5 or more and 4.5 or less. 5. The release film as described in 1. above, wherein the inorganic pigment in the first coating layer B1 and the second coating layer B2 is titanium oxide. 6. The release film as described in 1. above, wherein the ratio of the total thickness of the first coating layer B1 and the thickness of the second coating layer B2 to the total thickness of the first coating layer B1, the thickness of the layer A containing voids, and the thickness of the second coating layer B2 is 6% or more and 40% or less. 7. The release film as described in 1. above, wherein the normal peeling force of the surface of the release layer C is 40mN/50mm or more and 500mN/50mm or less. 8. The release film as described in 1. above, characterized in that it is used as a separator for labels or a release film for engineering use.

In addition, the second release film of the present invention is provided as follows. 1. A release film having a laminate film and a release layer C on at least one side of the laminate film; the laminate film is laminated in sequence with at least a first coating layer B1 containing a polyester resin containing an inorganic pigment, a void-containing layer A containing voids inside, and a second coating layer B2 containing a polyester resin containing an inorganic pigment; the void-containing layer A contains a first component containing a polyester resin and a polyolefin resin; the release layer C is composed of a second component containing a non-polysilicone release resin; and the apparent density is 0.80 g/cm ³ or more and 1.20 g/cm ³ or less. 2. The release film as described in 1. above, wherein the non-silicone release resin contains at least one resin selected from the group consisting of polyolefin resins, alkyd resins, melamine resins, acrylic resins having long-chain alkyl groups, and fluorine resins. 3. The release film as described in 1. above, wherein the polyester resin and the polyolefin resin contained in the void-containing layer A satisfy the following requirements (1) to (3): (1) The melt viscosity (η1) of the polyester resin at a melting temperature of 280°C and a shear rate of 121.6 sec ^{- 1} is from 90 Pa·s to 400 Pa·s. (2) The melt viscosity (η2) of the polyolefin resin at a melting temperature of 280°C and a shear rate of 121.6 sec ^{- 1} is 300 Pa·s or more and 700 Pa·s or less. (3) The melt viscosity ratio (η2/η1) of the polyester resin to the polyolefin resin at a melting temperature of 280°C and a shear rate of 121.6 sec ^{- 1} is 1.5 or more and 4.5 or less. 4. The release film as described in 1. above, wherein the inorganic pigment in the first coating layer B1 and the second coating layer B2 is titanium oxide. 5. The release film as described in 1. above, wherein the total ratio of the thickness of the first coating layer B1 and the thickness of the second coating layer B2 to the total thickness of the first coating layer B1, the thickness of the layer A containing voids, and the thickness of the second coating layer B2 is 6% or more and 40% or less. 6. The release film as described in 1. above, wherein the normal peeling force of the surface of the release layer C is 400mN/50mm or more and 6000mN/50mm or less. 7. The release film as described in 1. above, characterized in that it is used as a separator for labels or a release film for engineering use. [Effect of the invention]

The present invention (the first invention, the second invention) can provide a release film which mainly contains a polyolefin resin as a void visualizer and has excellent environmental compatibility, lightness, film-forming properties, concealing properties, whiteness, and release properties.

The first invention is described in detail below.

The first release film of the present invention is a film formed by laminating at least a laminated film and a release layer C in this order. The laminated film is a polyester film containing voids, which is formed by laminating at least a first coating layer B1 composed of a polyester resin containing an inorganic pigment, a void-containing layer A containing voids inside, and a second coating layer B2 composed of a polyester resin containing an inorganic pigment in this order. The release layer C is disposed on at least one side of the laminated film. The void-containing layer A is composed of a first component containing a polyester resin and a polyolefin resin. The release layer C is composed of a second component containing a polysilicone resin. In addition, the apparent density of the release film is 0.80 g/cm ³ or more and 1.20 g/cm ³ or less.

The polyester resin as the main component of the void-containing layer A, the first coating layer B1, and the second coating layer B2 is a polymer synthesized from dicarboxylic acid or its ester-forming derivative and diol or its ester-forming derivative. Representative examples of such polyester resins include polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate. Among them, polyethylene terephthalate is preferred from the viewpoints of mechanical properties, heat resistance, cost, etc.

In addition, other components may be copolymerized with these polyester resins as long as the purpose of the first invention is not impaired. Specifically, as copolymerization components, dicarboxylic acid components include: isophthalic acid, naphthalene dicarboxylic acid, 4,4- biphenyl dicarboxylic acid , adipic acid, sebacic acid and its ester-forming derivatives. In addition, as diol components, diethylene glycol, hexanediol, neopentyl glycol, cyclohexanedimethanol may be listed. In addition, polyoxyalkylene glycols such as polyethylene glycol and polypropylene glycol may also be listed. As the copolymerization amount, it is preferably within 10 mol% in each repeating unit, and more preferably within 5 mol%.

The polyester resin can be produced, for example, by the following method: first, the aforementioned dicarboxylic acid or its ester-forming derivative and diol or its ester-forming derivative are used as main starting materials, and then, after esterification or transesterification reaction is carried out according to a conventional method, polycondensation reaction is carried out at high temperature and reduced pressure.

In terms of film-forming properties and recyclability, the limiting viscosity of the polyester resin is preferably from 0.50 dl/g to 0.9 dl/g, and more preferably from 0.55 dl/g to 0.85 dl/g.

The content of the polyester resin is preferably 70% by mass or more and 97% by mass or less, and more preferably 75% by mass or more and 95% by mass or less, relative to 100% by mass of the total components contained in the void-containing layer A. When the content of the polyester resin is 70% by mass or more, the deterioration of the film-forming property of the release film can be suppressed. When the content of the polyester resin is 97% or less, the release film can form voids by adding a polyolefin resin.

From the viewpoint of film-forming property and whiteness, the melt viscosity (η1) of the polyester resin as the main component of the void-containing layer A, the first coating layer B1, and the second coating layer B2 at a melting temperature of 280°C and a shear rate of 121.6 sec ^{- 1} is preferably 90 Pa·s or more and 400 Pa·s or less, and more preferably 130 Pa·s or more and 350 Pa·s or less. When η1 is 90 Pa·s or more, the first invention can prevent the whiteness of the obtained film from being reduced or the film-forming property from being deteriorated. On the other hand, when η1 is 400 Pa·s or less, the first invention can prevent problems such as deterioration of compressibility and increase in back pressure in the melt extrusion step.

Next, the polyolefin resin used as the immiscible resin of the void revealing agent in the first invention is described. The release film of the first invention can maintain void revealing properties by adopting a specific layer structure and using a specific polyolefin resin. The polyolefin resin is, for example, polyethylene resin, polypropylene resin, etc., preferably polypropylene resin. Therefore, the release film of the first invention not only obtains sufficient lightness and cushioning properties, but also has excellent film-making properties, concealing properties, and whiteness.

The polyolefin resin used in the first invention is preferably a crystalline polyolefin having 95 mol% or more, more preferably 98 mol% or more of olefin units, and is particularly preferably a crystalline polyolefin homopolymer having 100 mol% of olefin units.

From the viewpoint of void visibility or film forming properties, the melt flow rate (MFR) of the polyolefin resin used in the first invention is preferably 1.0 g/10 min or more and 10.0 g/10 min or less, and further preferably 1.5 g/10 min or more and 7.0 g/10 min or less. When the MFR is 1.0 g/10 min or more and 10.0 g/10 min or less, the polyolefin dispersed particles are not easily deformed when extruded from the die, so voids are easily formed. Furthermore, when the MFR is 1.0 g/10 min or more and 10.0 g/10 min or less, the dispersibility of the polyolefin dispersed particles is also excellent, sufficient concealment can be obtained, and film forming properties are also excellent. In addition, the melt flow rate (MFR) is a value measured at 230°C and a load of 2.16 kg in accordance with JIS K 7210.

From the viewpoint of void visibility, the heat distortion temperature of the polyolefin resin used in the first invention is preferably 85°C or higher, more preferably 90°C or higher, and further preferably 95°C or higher. As the upper limit, there is no need to specifically limit it, but it is preferably 135°C or lower. When the heat distortion temperature is 85°C or higher, especially in the longitudinal stretching step of stretching the film by heating at a temperature higher than the glass transition temperature of the polyester resin described later, the polyolefin dispersed particles are not easily destroyed, so voids are easily formed. In addition, the heat distortion temperature is a measured value based on the B method of JIS K 7191-1 and JIS K 7191-2 and when the bending stress of the test piece is 0.45 MPa.

The polyolefin resin used in the first invention preferably has a weight average molecular weight (Mw) of 200,000 to 450,000, and more preferably 250,000 to 400,000, from the viewpoint of void visibility and suppression of thermal degradation in the extrusion step and the recovery step. When the Mw is 450,000 or less, the dispersibility of the polyolefin dispersed particles becomes better, sufficient concealment is obtained, and excellent film-forming properties are obtained. When the Mw is 200,000 or more, voids are easily formed because the polyolefin dispersed particles are not easily deformed. When the Mw is 200,000 or more, even when recycled raw materials are used, it is preferred because the decrease in void visibility can be suppressed.

In addition, the molecular weight distribution (Mw/Mn), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), is preferably 2 or more and 6 or less, and more preferably 2 or more and 5 or less. Mw/Mn is an index indicating the breadth of the molecular weight distribution. The larger the value of Mw/Mn, the wider the molecular weight distribution. When Mw/Mn is 6 or less, the low molecular weight components are reduced, so even when recycled raw materials are used, the reduction in whiteness and void visibility can be suppressed, so it is better. In addition, if Mw/Mn is 2 or more, it is suitable for industrial production from the perspective of cost. In addition, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are values measured using gel permeation chromatography (GPC).

In addition, from the perspective of void visibility and film forming properties, the melt viscosity (η2) of the polyolefin resin used in the first invention at a melting temperature of 280°C and a shear rate of 121.6 sec ^{- 1} is preferably 300 Pa·s to 700 Pa·s, and more preferably 350 Pa·s to 650 Pa·s. When η2 is 300 Pa·s or more, it is difficult to deform the polyolefin resin during the melt extrusion step due to extrusion from the die, so it becomes easy to form voids. In addition, when recycled raw materials are used, the whiteness of the obtained film is reduced. On the other hand, when η2 is 700 Pa·s or less, it is possible to prevent problems such as deterioration of compostability and increase in back pressure during the melt extrusion step.

The melt viscosity ratio (η2/η1) of the polyester resin and the polyolefin resin used in the first invention at a melting temperature of 280°C and a shear rate of 121.6 sec ^{- 1} is preferably controlled within a range of 1.5 to 4.5. As shown in Wu's empirical formula, if the melt viscosity ratio (η2/η1) is increased, the particle size of the polyolefin resin dispersion (island component) in the polyester resin matrix (sea component) will also increase (see S. Wu, Polym. Eng. Sci., 27, 335 (1987)). Although the larger the dispersed particle size of the polyolefin resin, the larger the voids that appear and the lower the specific gravity, which is better, on the contrary, if the above-mentioned dispersed particle size becomes too large, the reflection efficiency of the film will decrease and the concealment will decrease, which is not good. Therefore, in the first invention, from the viewpoint of achieving both low specific gravity and high concealment, it is preferable to control the melt viscosity ratio (η2/η1) within the range of 1.5 or more and 4.5 or less.

From the viewpoint of void visibility and film forming properties, the content of the polyolefin resin is preferably 3 mass % or more and 30 mass % or less, and more preferably 5 mass % or more and 25 mass % or less, relative to 100 mass % of the total of all components contained in the void-containing layer A. When the content of the polyolefin resin is 3 mass % or more and 30 mass % or less, not only can voids be formed to obtain sufficient lightness and cushioning properties, but also excellent film forming properties are achieved.

In addition, as long as the purpose of the first invention is not impaired, an immiscible resin other than a polyolefin resin may be contained in the void-containing layer A. With respect to 100% by mass of the total immiscible resin in the void-containing layer A, it is preferred that 90% by mass or more of the polyolefin resin is contained, more preferably 95% by mass or more, and most preferably 100% by mass. In addition, from the viewpoint of whiteness and void visibility, it is preferred that a dispersant such as polyethylene glycol or a surfactant is not contained.

In addition, within the scope of not impairing the purpose of the first invention, a small amount of other polymers or antioxidants, heat stabilizers, matting agents, pigments, ultraviolet absorbers, fluorescent whitening agents, plasticizers or other additives may be contained in these polyester resins or polyolefin resins. In particular, in order to inhibit the oxidative degradation of polyolefin resins, it is preferred to contain antioxidants or heat stabilizers. There is no particular limitation on the types of antioxidants and heat stabilizers, for example, hindered phenol series, phosphorus series, hindered amine series, etc. The above antioxidants or heat stabilizers can be used alone or in combination. The added amount is preferably 1 ppm or more and 50000 ppm or less relative to the total mass of the void-containing layer A. In addition, in the first invention, even if the fluorescent whitening agent is not added to the void-containing layer A, excellent whiteness can still be ensured.

In the first invention, in order to improve concealment or whiteness, the release film may contain inorganic pigments in the polyester resin or the polyolefin resin as necessary. Examples of inorganic pigments include silicon oxide, kaolinite, talc, calcium carbonate, zeolite, aluminum oxide, barium sulfate, titanium oxide, zinc sulfide, etc. Among them, titanium oxide, calcium carbonate, and barium sulfate are preferred from the perspective of concealment or whiteness. In addition, these inorganic pigments may be used alone, or two or more may be used in combination. These inorganic pigments may be included in the release film by being added to the polyester resin or the polyolefin resin in advance.

There is no particular limitation on the method of mixing the inorganic pigment with the polyester resin or the polyolefin resin, and the following methods can be cited. For example, the polyester resin and the polyolefin resin are dry-blended and then directly loaded into a film-making machine; the polyester resin and the polyolefin resin are dry-blended and then melt-blended using various common mixers to form a masterbatch, etc.

The first release film of the present invention has a laminated structure in which at least a first coating layer B1 composed of a polyester resin containing an inorganic pigment, a void-containing layer A containing voids inside, and a second coating layer B2 composed of a polyester resin containing an inorganic pigment are laminated in this order. Here, when the void-containing layer A containing a polyolefin resin is exposed on the surface, the polyolefin dispersed particles in the exposed portion are contaminated by the step of roller dirt, etc. In addition, the void-containing layer A is coated with the first coating layer B1 containing an inorganic pigment and the second coating layer B2, which has the effect of preventing the whiteness from decreasing. The first coating layer B1 and the second coating layer B2 may be layers of the same composition or layers of different compositions.

The ratio of the total thickness of the first covering layer B1 and the thickness of the second covering layer B2 to the total thickness of the first covering layer B1, the thickness of the layer A containing voids, and the thickness of the second covering layer B2 (hereinafter sometimes referred to as the layer ratio) is preferably from 6% to 40%, and more preferably from 8% to 30%, from the viewpoint of void visibility and suppression of exposure of the polyolefin resin. When the layer ratio is from 6% to 40%, the exposure of the polyolefin resin can be suppressed, and the contact angle of water and the contact angle of diiodomethane can be reduced. Furthermore, when the layer ratio is from 6% to 40%, it is easy to form voids for obtaining sufficient lightness and cushioning properties.

Examples of the inorganic pigments contained in the first coating layer B1 and the second coating layer B2 include silicon oxide, kaolinite, talc, calcium carbonate, zeolite, aluminum oxide, barium sulfate, titanium oxide, zinc sulfide, etc. Among them, titanium oxide, calcium carbonate, and barium sulfate are preferred from the perspective of concealment or whiteness, and titanium oxide is particularly preferred. In addition, these inorganic pigments may be used alone or in combination of two or more. These pigments may be included in the film by being added to the polyester resin in advance.

The amount of inorganic pigment added to the first coating layer B1 is not particularly limited, but is preferably 1% to 35% by mass, and more preferably 2% to 30% by mass, relative to 100% by mass of the total components constituting the first coating layer B1. When the amount of inorganic pigment added is 1% to 35% by mass, it is easy to improve the concealment and whiteness of the release film, and the film forming properties and mechanical strength of the release film. The amount of inorganic pigment added to the second coating layer B2 is not particularly limited, but is preferably the same as the amount of inorganic pigment added to the first coating layer B1.

The average particle size of the inorganic pigment is preferably 0.01 μm to 3 μm, more preferably 0.05 μm to 2 μm, and particularly preferably 0.1 μm to 1.5 μm. The “average particle size” refers to the particle size of 50% of the cumulative value of the particle size distribution obtained by, for example, laser diffraction/scattering method or electron microscopy method.

In the laminated film of the first invention, at least one side has a release layer C. Therefore, the release film can have the following laminated structure. That is, it can have a laminated structure in which the release layer C, the first coating layer B1, the layer A containing voids, and the second coating layer B2 are laminated in the order of C/B1/A/B2 or B1/A/B2/C.

The release layer C is composed of a second component containing a silicone resin. Examples of the silicone resin include silicone polymers (e.g., partially cross-linked silicone polymers (i.e., silicone synthetic resins in the narrow sense of silicone resins)) and linear silicone polymers (i.e., silicone rubbers). Specifically, methyl silicone resins, methylphenyl silicone resins, , phenyl silicone resin, alkyd modified silicone resin, polyester modified silicone resin, urethane modified silicone resin, epoxy modified silicone resin, acrylic modified silicone resin. From the viewpoint of forming the release layer C by coating, a thermoaddition silicone resin that is crosslinked by applying heat is preferred.

Examples of thermoforming silicone resins include polydimethylsiloxane containing at least one alkenyl group in one molecule and polydimethylsiloxane containing at least one hydrosilyl group in one molecule, which are hardened. The alkenyl group and the hydrosilyl group may be contained in the same polydimethylsiloxane molecule.

As the alkenyl group contained in polydimethylsiloxane, there can be listed monocyclic hydrocarbon groups such as vinyl, allyl, propenyl, butenyl, pentenyl, hexenyl, heptenyl, and octenyl, among which vinyl is preferred because it has high reactivity with respect to hydrosilicone and excellent thermosetting properties. In addition, the hardening polysilicone resin containing polydimethylsiloxane containing vinyl and hydrosilicone groups in the molecular chain as the main component is easy to adhere to the inorganic pigment and polyester resin constituting the first coating layer B1 or the second coating layer B2, so it is preferred.

In addition, the second component constituting the release layer C may also contain a non-silicone release resin within the scope of not impairing the effect of the first invention. The non-silicone release resin may contain at least one resin selected from the group consisting of polyolefin resins, alkyd resins, melamine resins, acrylic resins having long-chain alkyl groups, and fluorine resins.

The second component constituting the release layer C may also contain a catalyst. The catalyst is not particularly limited as long as it can harden the heat addition type polysilicone resin composition of this embodiment, and preferably is a platinum group metal compound. Examples of platinum group metal compounds include: particulate platinum, particulate platinum adsorbed on a carbon powder carrier, chloroplatinic acid, alcohol-modified chloroplatinic acid, olefin complex of chloroplatinic acid, palladium, rhodium, etc. By containing the aforementioned catalyst in the second component composed of the polysilicone resin, the hardening reaction can be carried out more efficiently.

The polysilicone resin constituting the release layer C is preferably 90 mass % or more and 100 mass % or less, and more preferably 94 mass % or more and 100 mass % or less, relative to the entire resin in the release layer C. By setting the polysilicone resin to be 90 mass % or more, when removing a label or the like, it can be removed without leaving any adhesive residue.

The content of the catalyst contained in the second component constituting the release layer C is preferably 1 ppm or more and 1000 ppm or less relative to the total amount of all components of the second component.

The coating amount of the release layer C is preferably 0.030 g/m ² or more and 0.200 g/m ² or less, and more preferably 0.050 g/m ² or more and 0.150 g/m ² or less. By setting it to 0.030 g/m ² or more, when removing a label, it can be removed without leaving any sticky residue. By setting it to 0.200 g/m ² or less, the label can be made less likely to be removed.

As a method for providing the coating layer, commonly used methods such as gravure coating, kiss coating, dip coating, spray coating, curtain coating, air knife coating, knife coating, reverse roll coating, etc. can be applied. As a coating stage, any method can be used, such as a method of coating before stretching the film, a method of coating after longitudinal stretching, or a method of coating on the surface of the film after the stretching treatment has been completed.

The normal peeling force of the release surface coated with the release layer C in an environment of 25°C and 40% RH is preferably 40mN/50mm to 500mN/50mm, and more preferably 50mN/50mm to 400mN/50mm. By setting it to 40mN/50mm or more, when removing labels, etc., it can be removed without leaving any residual adhesion. By setting it to 500mN/50mm or less, it can be made difficult to remove the release body such as labels. That is, as long as the normal peeling force is in the range of 40mN/50mm to 500mN/50mm, the release layer C has a moderate peeling force relative to the release body. The release film of the first invention is suitably used as a release film used in manufacturing separators of labels, polarizing plates, laminated ceramic capacitors, etc.

In addition, in order to prevent static electricity, the release film of the first invention may also be provided with a coating layer on the surface opposite to the surface of the release layer C. The compound constituting the coating layer is preferably a polyester resin. In addition, compounds generally disclosed as means for improving the adhesion of polyester films, such as polyurethane resin, polyester urethane resin, and acrylic resin, can be applied.

As a method for providing the coating layer, commonly used methods such as gravure coating, touch coating, dip coating, spray coating, curtain coating, air knife coating, knife coating, reverse roll coating, etc. can be applied. As a coating stage, any method can be used, such as a method of coating before stretching the film, a method of coating after longitudinal stretching, or a method of coating on the surface of the film after the stretching treatment has been completed.

The method for producing the release film in the first invention is described. For example, after drying the mixed particles composed of the first component containing the polyester resin and the polyolefin resin, the mixed particles are melt-extruded from a T-shaped die into a sheet, and the obtained sheet is brought into close contact with a casting drum by electrostatic application, etc., and then cooled and solidified to obtain an unstretched film.

Then, the unstretched film is stretched and oriented. The following is an example of the most commonly used stepwise biaxial stretching method, especially the method of stretching the unstretched film longitudinally in the length direction and then stretching it transversely in the width direction. First, in the longitudinal stretching step in the length direction, the film is heated and stretched to 2.5 to 5.0 times between two or more rollers with different peripheral speeds. As a heating means at this time, it can be a method using a heating roller, or a method using a non-contact heating medium, and these methods can also be used in combination. At this time, it is better to set the temperature of the film to a range of (Tg-10°C) to (Tg+50°C). Then, the uniaxially stretched film is introduced into a tenter and stretched to 2.5 to 5 times in the width direction at a temperature below (Tg-10°C) to (Tm-10°C), thereby obtaining a biaxially stretched film.

Here, Tg is the glass transition temperature of the polyester resin, and Tm is the melting point of the polyester. In addition, it is preferred that the film obtained as described above be subjected to heat treatment as necessary, and the treatment temperature is preferably in the range of (Tm-60°C) to Tm.

In addition, the ears and film scraps produced by the film-making process of the first invention due to cracking problems can also be used as recycled raw materials.

The amount of recycled raw materials added is preferably 5% to 80% by mass relative to 100% by mass of the total mass of the layer A containing voids, from the viewpoint of reducing raw material costs, whiteness, and film-forming properties. Also, the first coating layer B1 or the second coating layer B2 may also contain recycled raw materials, but from the viewpoint of deterioration of whiteness and exposure of polyolefin resin in the recycled raw materials, it is preferred not to contain recycled raw materials.

In the first invention, the apparent density of the release film is preferably 0.80 g/cm ³ or more and 1.2 g/cm ³ or less, and more preferably 0.80 g/cm ³ or more and 1.10 g/cm ³ or less. When the apparent density is 0.80 g/cm ³ or more and 1.20 g/cm ³ or less, the proportion of all voids in the release film becomes appropriate, and it is easy to handle during subsequent processing such as printing or during use. In addition, when the apparent density is 0.80 g/cm ³ or more and 1.20 g/cm ³ or less, sufficient lightness and cushioning properties can be obtained.

The apparent density is a value obtained by the measurement method described in the evaluation method described later.

The total light transmittance of the release film in the first invention is preferably 30% or less, more preferably 25% or less. When the total light transmittance is 30% or less, sufficient concealment can be obtained. For example, when used for labels, the image printed on the labels is clear. In addition, the total light transmittance is a value converted to a thickness of 50 μm obtained by the measurement method described in the evaluation method described later.

In the first invention, the color tone b value of the release film is preferably 4.0 or less, and more preferably 3.0 or less. When the color tone b value is greater than 4.0, the whiteness is deteriorated, and when it is made into a label, the clarity during printing is reduced, which may damage the value of the product.

The thickness of the release film of the first invention is arbitrary, but is preferably 20 μm or more and 300 μm or less.

In summary, the release film of the first invention has excellent lightness, film-forming property, concealing property and whiteness even when the apparent density is 0.80 to 1.20. In addition, the release film of the first invention has a moderate peeling force relative to the peeling body, and is suitably used as a release film used in the manufacture of label separators, polarizing plates, laminated ceramic capacitors, etc.

The above is an explanation of the first invention.

The second invention is described below in detail.

The second release film of the present invention is a film formed by laminating at least a laminate film and a release layer C in this order. The laminate film is a polyester film containing voids, which is formed by laminating at least a first coating layer B1 composed of a polyester resin containing an inorganic pigment, a void-containing layer A containing voids inside, and a second coating layer B2 composed of a polyester resin containing an inorganic pigment in this order. The release layer C is disposed on at least one side of the laminate film. The void-containing layer A is composed of a first component containing a polyester resin and a polyolefin resin. The release layer C is composed of a second component containing a non-silicone release resin. In addition, the apparent density of the release film is 0.80 g/cm ³ or more and 1.20 g/cm ³ or less.

In the first invention, the release layer C is composed of a second component containing a silicone resin, while in the second invention, the release layer C is composed of a second component containing a non-silicone release resin. However, in other aspects, the two are the same. Therefore, in the following description, the description of the parts common to the first invention is made with reference to the items of the first invention, and the description of the parts different from the first invention is mainly made.

As the void-containing layer A, the first coating layer B1 and the second coating layer B2 are the same as those in the first invention, their description is omitted here.

In the laminated film of the second invention, at least one side has a release layer C. Therefore, the release film can have the following laminated structure. That is, it can have a laminated structure in which the release layer C, the first coating layer B1, the layer A containing voids, and the second coating layer B2 are laminated in the order of C/B1/A/B2 or B1/A/B2/C.

The release layer C of the second invention is composed of a second component containing a non-silicone release resin. Examples of the non-silicone release resin include resins containing at least one of the group consisting of polyolefin resins, alkyd resins, melamine resins, acrylic resins having long-chain alkyl groups, and fluorine resins.

Examples of the polyolefin resin include homopolymers of polyethylene, polypropylene, polybutene, and polyhexene, or copolymers thereof.

Alkyd resins are resins obtained by condensation reaction of polyols and polyacids, including non-converted alkyd resins modified with condensates of dibasic acids and diols or with non-drying oil fatty acids, and converted alkyd resins of condensates of dibasic acids and trivalent or higher alcohols. Any of them can be used in the second invention.

Examples of polyols used as raw materials for the alkyd resin include diols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, butanediol, and neopentyl glycol; triols such as glycerol, trihydroxymethylethane, and trihydroxymethylpropane; and tetrahydric or higher polyols such as diglycerol, triglycerol, pentaerythritol, dipentaerythritol, mannitol, and sorbitol. One type may be used alone, or two or more types may be used in combination.

In addition, examples of polyacids include aromatic polyacids such as phthalic anhydride, terephthalic acid, isophthalic acid, and trimellitic anhydride; aliphatic saturated polyacids such as succinic acid, adipic acid, and sebacic acid; aliphatic unsaturated polyacids such as maleic acid, maleic anhydride, fumaric acid, itaconic acid, and linaconic anhydride; polyacids formed by Diels-Alder reaction such as cyclopentadiene-maleic anhydride adducts, terpene-maleic anhydride adducts, and rosin-maleic anhydride adducts, etc. One type may be used alone, or two or more types may be used in combination.

On the other hand, as a modifier, for example, caprylic acid, lauric acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, oleostearic acid, ricinoleic acid, dehydrated ricinoleic acid, or coconut oil, linseed oil, tung oil, castor oil, dehydrated castor oil, soybean oil, safflower oil, and fatty acids thereof can be used. One type can be used alone, or two or more types can be used in combination.

Furthermore, alkyd resins obtained by the reaction of methylated melamine can also be cited. As aminoalkyd resins obtained by the reaction of methylated melamine, Tesfine 303, Tesfine 305, Tesfine 314, etc. manufactured by Showa Denko Materials Co., Ltd. can be cited. The aminoalkyd resin has excellent adhesion to the polyester resin constituting the first coating layer B1 and the second coating layer B2 (that is, the surface of the laminate film). In addition, since the aminoalkyd resin forms a three-dimensional cross-linked structure by thermal reaction, the component transfer to the exfoliate is small, and the exfoliation property lasts for a long time, so it can be used appropriately.

As the melamine resin used in the second invention, for example, melamine, hydroxymethylated melamine derivatives obtained by condensing melamine with formaldehyde, compounds partially or completely etherified by reacting hydroxymethylated melamine with lower alcohols, and mixtures thereof can be used. In addition, the melamine resin can be any condensate composed of a monomer or a polymer of dimer or higher, or a mixture thereof. As the lower alcohol used for etherification, methanol, ethanol, isopropanol, n-butanol, isobutanol, etc. can be used. The functional group is an imino group, a hydroxymethyl group, or a functional group having an alkoxymethyl group in one molecule such as a methoxymethyl group or a butoxymethyl group, and there are imino type methylated melamine resins, hydroxymethyl type methylated melamine resins, hydroxymethyl type methylated melamine resins, and completely alkyl type methylated melamine resins.

The acrylic resin having a long chain alkyl group includes, for example, an acrylic resin having a straight chain or branched alkyl group with a carbon number of 6 to 20 in the side chain. By having the aforementioned carbon number, the surface free energy of the obtained resin can be reduced, so it is preferred. In addition, the more the side chain number of the long chain alkyl group is, the more the surface free energy of the resin can be reduced, so it is preferred, for example: a long chain alkyl pendant polymer, etc.

Examples of fluororesins include ethylene-tetrafluoroethylene copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymers, etc. In addition, the second component constituting the release layer C may also contain a polysilicone-based release agent component within the scope of not impairing the efficacy of the second invention.

The coating amount of the release layer C is preferably 0.030 g/m ² or more and 0.200 g/m ² or less, and more preferably 0.050 g/m ² or more and 0.150 g/m ² or less. By setting it to 0.030 g/m ² or more, when removing a label or the like, it can be removed without leaving any sticky residue. By setting it to 0.200 g/m ² or less, the label can be made less likely to be removed.

As a method for providing the coating layer, commonly used methods such as gravure coating, touch coating, dip coating, spray coating, curtain coating, air knife coating, knife coating, reverse roll coating, etc. can be applied. As a coating stage, any method can be used, such as a method of coating before stretching the film, a method of coating after longitudinal stretching, or a method of coating on the surface of the film after the stretching treatment has been completed.

The normal peeling force of the release surface coated with the release layer C in an environment of 25°C and 40% RH is preferably 400mN/50mm or more and 6000mN/50mm or less, and more preferably 600mN/50mm or more and 5000mN/50mm or less. By setting the peeling force to 400mN/50mm or more and 6000mN/50mm or less, the balance between the adhesion stability and the peeling property of the release layer C relative to the peeling body can be well maintained. That is, as long as the normal peeling force is in the range of 400mN/50mm or more and 6000mN/50mm or less, the release layer C has an appropriate peeling force relative to the peeling body. The release film of the second invention is suitably used as a release film used in the manufacture of separators for labels, polarizing plates, laminated ceramic capacitors, etc.

In addition, the release film of the second invention may also be provided with a coating layer on the surface opposite to the surface of the release layer C in order to prevent static electricity.

The method of providing the coating layer on the surface opposite to the surface of the release layer C has been described in the first invention, so the description thereof will be omitted here.

The second invention is described in detail with respect to the method for producing the release film. For example, after drying the mixed particles composed of the first component containing the polyester resin and the polyolefin resin, the mixed particles are melt-extruded from a T-shaped die into a sheet, and the obtained sheet is brought into close contact with a casting drum by electrostatic application or the like, and then cooled and solidified to obtain an unstretched film.

Then, the unstretched film is stretched and oriented. The following is an example of the most commonly used stepwise biaxial stretching method, especially the method of stretching the unstretched film longitudinally in the length direction and then stretching it transversely in the width direction. First, in the longitudinal stretching step in the length direction, the film is heated and stretched to 2.5 to 5.0 times between two or more rollers with different peripheral speeds. As a heating means at this time, it can be a method using a heating roller, or a method using a non-contact heating medium, and these methods can also be used in combination. At this time, it is better to set the temperature of the film to a range of (Tg-10°C) to (Tg+50°C). Then, the uniaxially stretched film is introduced into a tenter and stretched to 2.5 to 5 times in the width direction at a temperature below (Tg-10°C) to (Tm-10°C), thereby obtaining a biaxially stretched film.

Here, Tg is the glass transition temperature of the polyester resin, and Tm is the melting point of the polyester. In addition, it is preferred that the film obtained as described above be subjected to heat treatment as necessary, and the treatment temperature is preferably in the range of (Tm-60°C) to Tm.

In addition, the ears and film scraps produced by the film-making process of the laminated film of the second invention due to cracking problems can also be used as recycled raw materials.

The amount of recycled raw materials added is preferably 5% to 80% by mass relative to 100% by mass of the total mass of the layer A containing voids, from the viewpoint of reducing raw material costs, whiteness, and film-forming properties. Also, the first coating layer B1 or the second coating layer B2 may also contain recycled raw materials, but from the viewpoint of deterioration of whiteness and exposure of polyolefin resin in the recycled raw materials, it is preferred not to contain recycled raw materials.

The apparent density of the release film of the second invention is preferably 0.80 g/cm ³ or more and 1.2 g/cm ³ or less, and more preferably 0.80 g/cm ³ or more and 1.10 g/cm ³ or less. When the apparent density is 0.80 g/cm ³ or more and 1.20 g/cm ³ or less, the proportion of all voids in the release film becomes appropriate, and it is easy to handle during subsequent processing such as printing or during use. In addition, when the apparent density is 0.80 g/cm ³ or more and 1.20 g/cm ³ or less, sufficient lightness and cushioning properties can be obtained.

The apparent density is a value obtained by the measurement method described in the evaluation method described later.

The release film of the second invention preferably has a total light transmittance of 30% or less, and more preferably 25% or less. When the total light transmittance is 30% or less, sufficient concealment can be obtained. For example, when used in a label, the image printed on the label is clear. In addition, the total light transmittance is a value converted to a thickness of 50 μm obtained by the measurement method described in the evaluation method described later.

The release film of the second invention preferably has a color tone b value of 4.0 or less, and more preferably 3.0 or less. When the color tone b value is greater than 4.0, the whiteness is deteriorated, and when it is made into a label, the clarity during printing is reduced, which may damage the value of the product.

The thickness of the release film of the second invention is arbitrary, but is preferably 20 μm or more and 300 μm or less.

In summary, the release film of the second invention has excellent lightness, film-making properties, concealing properties, and whiteness even when the apparent density is 0.80 to 1.20. In addition, the release film of the second invention has a moderate peeling force relative to the peeling body, and is suitable for use as a separator for manufacturing labels, a release film used in the manufacture of polarizing plates and multilayer ceramic capacitors, etc. In particular, the release film of the second invention is suitable for use in electronic devices where polysilicon is likely to have adverse effects. Generally speaking, in silicone release agents, silicone resin components migrate to the exfoliant, which can cause silicone gas to be generated, which may cause corrosion, malfunction, or misoperation inside electronic devices. Although the amount of silicone gas generated is suppressed to a relatively low level that does not cause problems in actual use, it is not suitable for electronic device applications where impurities such as silicone gas may cause misoperation even in trace amounts. [Example]

The present invention (the first invention and the second invention) is specifically described below by way of examples. In addition, the present invention (the first invention and the second invention) is not limited to the examples described below. In addition, each evaluation item in the examples and comparative examples is measured using the following method. (1) Melt viscosity (η1, η2) The melt viscosity of each polyester resin and polypropylene resin is measured using a capillary recorder 1D (capillary length: 10 mm, capillary diameter: 1 mm) manufactured by Toyo Seiki Seisaku-sho Co., Ltd. at a melting temperature of 280°C and a shear rate of 121.6 sec ^-1 .

(2) Film-forming properties The film-forming conditions described in the laminated film production described later were used to evaluate the number of breaks during the film-forming time of 2 hours as follows. ○: No break. △: Break 1 to 3 times. ×: Break 4 or more times, and film-forming was impossible.

(3) Apparent density Cut the release film into 4 square pieces of 5.0 cm square, overlap 4 polyester films, and use a micrometer to measure the total thickness at 10 locations with 4 significant digits. Calculate the average thickness of the 4 overlapping polyester films. Divide the average by 4 and round it to 3 significant digits to obtain the average thickness of each piece (t: μm). Use an automatic plate-loading balance to measure the mass (w: g) of the 4 samples with 4 significant digits, and calculate the apparent density using the following formula. In addition, the apparent density is rounded to 3 significant digits. Apparent density (g/cm ³ ) = w/(5.0×5.0×t×10-4×4)

(4) Total light transmittance Use a haze meter (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.) to measure the release film and convert it into a value per unit film thickness of 50 μm. Perform the same measurement three times and use the arithmetic mean.

(5) Color tone b value The color tone b value is measured on the opposite side of the release layer C of the release film using a colorimeter (ZE6000) manufactured by Nippon Denshoku Industries Co., Ltd. and in accordance with JIS-8722. The smaller the color tone b value, the higher the whiteness and the weaker the yellowness.

(6) Evaluation of normal peeling force of release surface The surface of release layer C of a release film bonded to the adhesive layer of an acrylic adhesive tape (Nitto 31B, width 25 mm, manufactured by Nitto Denko Co., Ltd.) (hereinafter sometimes referred to as "release surface") was rolled back and forth once by a 5 kg iron cylinder from above (i.e., after being pressed by a press roller), and then left at 20°C and 15% RH for 24 hours. The peeling load was then measured using AUTOGRAPH (registered trademark) (AG-X) manufactured by Shimadzu Corporation at a peeling angle of 90 degrees and a tensile speed of 300 mm/min. Multiply the value obtained by 2 and convert the unit to mN/50mm.

The following embodiments 1 to 8 correspond to the embodiments of the first invention.

(Example 1) [Manufacturing of titanium oxide masterbatch (M1)] 50% by mass of sphene-type titanium dioxide having an average particle size of 0.3 μm (electron microscope method) was mixed with 50% by mass of polyethylene terephthalate resin having an ultimate viscosity of 0.62 dl/g. Next, the mixture was supplied to an exhaust double-shaft extruder for mixing to manufacture a masterbatch containing titanium oxide (M1).

[Manufacturing of unstretched film] 87.5% by mass of polyethylene terephthalate resin with a melt viscosity of 200 Pa・s and 12.5% by mass of polypropylene resin with a melt viscosity of 500 Pa・s are mixed. Next, the mixture is vacuum dried to produce the raw material of layer A containing voids. On the other hand, 30% by mass of the masterbatch (M1) containing titanium oxide and 70% by mass of polyethylene terephthalate resin with a melt viscosity of 200 Pa・s are granulated and mixed. Next, the mixture is vacuum dried to produce the raw material of the first coating layer B1 and the second coating layer B2. These raw materials are fed to different extruders and melted at 285°C, and the first coating layer B1, the layer A containing voids, and the second coating layer B2 are stacked in the order of B1/A/B2. The stacked body is joined using a feed block in a thickness ratio of 10/80/10. The joined body is extruded from a T-shaped die onto a cooling drum adjusted to 30°C to produce an unstretched film having two layers and a three-layer structure.

[Laminar film production] Laminated films were produced under the following film production conditions. That is, the obtained unstretched film was uniformly heated to 70°C using a heating roller, and longitudinally stretched to 3.4 times between two pairs of rollers with different peripheral speeds. At this time, an infrared heater (rated value 20W/cm) with a gold reflective film as an auxiliary heating device for the unstretched film was set opposite to both sides of the film (at a distance of 1cm from the film surface) in the middle of the rollers for heating. The uniaxially stretched film obtained in the above manner was introduced into a tenter, heated to 140°C and stretched to 4.0 times in the transverse direction, the width was fixed, heat treated at 235°C, and then relaxed by 3% in the width direction at 210°C, thereby obtaining a laminated film with a thickness of 50μm.

[Preparation of release film] A hardening silicone resin KS-774 (manufactured by Shin-Etsu Chemical Co., Ltd.) containing vinyl and hydrosilicone groups in the molecular chain as the main component was diluted in a mixed solvent of methyl ethyl ketone and toluene. A hardener containing platinum (manufactured by Shin-Etsu Chemical Co., Ltd., CAT-PL-3) was added to the solution at 3% by mass relative to 100% by mass of the above-mentioned silicone resin to prepare a solution with a total solid concentration of 1.5% by mass. The solution was applied to one side of the laminate film by a conventional roller coating method so that the thickness of the release layer C after drying was 0.10 g/ ^m2 . Thus, a release film was obtained in which the release layer C, the first coating layer B1, the layer A containing voids, and the second coating layer B2 were laminated in the order of C/B1/A/B2. The heat drying in the roll coating method was performed at 150°C for 20 seconds. The results of the apparent density, the normal peeling force of the release surface, the color tone b value, the total light transmittance, and the film forming properties are shown in Table 1.

(Example 2, Example 3, Example 4, Example 5, Example 6, Example 7) The release film was obtained in the same manner as in Example 1 except that the raw material ratio of the layer A containing voids was changed as shown in Table 1.

(Example 8) A release film is obtained in the same manner as in Example 1, except that in Example 1, the first coating layer B1, the layer A containing voids, and the second coating layer B2 are laminated in the order of B1/A/B2, and the thickness ratio of the laminate is changed to 5/90/5.

(Comparative Example 1) A release film is obtained in the same manner as in Example 1, except that 87.5 mass % of a polyethylene terephthalate resin having a melt viscosity of 200 Pa·s and 12.5 mass % of a polypropylene resin having a melt viscosity of 200 Pa·s are mixed, the mixture is vacuum dried, and the raw material of layer A containing voids is changed. The release film of Comparative Example 1 is out of the scope of the first invention because its apparent density exceeds 1.20 g/cm ³ . Therefore, in Example 1, the lightness and cushioning properties are poor. In addition, in Example 1, the manufacturing cost is also high due to the large mass. In addition, the total light transmittance of the release film of Comparative Example 1 is also high, and its concealing property is poor compared to Examples 1 to 8.

(Comparative Example 2) A release film is obtained in the same manner as in Example 1, except that in Example 1, the first coating layer B1, the layer A containing voids, and the second coating layer B2 are laminated in the order of B1/A/B2, and the thickness ratio of the laminate is changed to 0/100/0. Since Comparative Example 2 does not have the first coating layer B1 and the second coating layer B2, it is outside the scope of the first invention. In Comparative Example 2, the voids of the layer A containing voids are exposed on the surface, and the surface of Comparative Example 2 becomes extremely rough. In the labeled release film of Comparative Example 2, the total light transmittance is high, and the concealing property is poor compared to Examples 1 to 8. In addition, in Comparative Example 2, the color tone b value is large, and compared with Examples 1 to 8, the whiteness is low and the yellowness is strong.

In summary, the release film of the first invention has the melt viscosity and melt viscosity ratio of the polyester resin and the polyolefin resin constituting the layer A containing the voids adjusted within a specific range, and the dispersed particle size of the polyolefin resin in the polyester resin is controlled to an appropriate size, so that at least one side of the laminate film has a release layer. Therefore, the release film of the first invention has excellent lightness, heat resistance, dimensional stability, film forming properties, concealing properties, whiteness, and release properties even if the apparent density is 0.80 to 1.20.

[Table 1] Unit Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Embodiment 5 Embodiment 6 Embodiment 7 Embodiment 8 Comparison Example 1 Comparison Example 2 A layer Polyethylene terephthalate resin Melt viscosity (280℃) Pa・s 200 200 200 132 310 200 185 200 200 200 Composition ratio Quality% 87.5 93.0 82.5 87.5 87.5 87.5 87.5 87.5 87.5 87.5 Polypropylene resin Melt viscosity (280℃) Pa・s 500 500 500 500 500 610 372 500 200 500 Composition ratio Quality% 12.5 7.0 17.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 Melt viscosity ratio (η2/η1) 2.5 2.5 2.5 3.8 1.6 3.1 2.0 2.5 1.0 2.5 C-layer Polydimethylsiloxane containing alkenyl - ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ Hydrogenated polydimethylsiloxane - ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ Silicone resin content Quality% ＞99 ＞99 ＞99 ＞99 ＞99 ＞99 ＞99 ＞99 ＞99 ＞99 Layer ratio of substrate First coating layer B1 % 10 10 10 10 10 10 10 5 10 0 Layer A containing voids % 80 80 80 80 80 80 80 90 80 100 Second coating layer B2 % 10 10 10 10 10 10 10 5 10 0 Apparent density g／cm ³ 1.07 1.19 0.98 1.01 1.16 1.01 1.12 1.02 1.28 0.93 Normal peeling force of the release surface mN/50mm 80 81 87 86 80 86 82 90 81 91 Whiteness Hue b value - 1.3 1.3 1.3 1.4 1.4 1.5 1.4 1.6 1.4 1.8 Concealment Total light transmittance % twenty two twenty three 20 20 twenty three 20 twenty two twenty three 26 26 Film making properties Whether there is any breakage, etc. - ○ ○ ○ ○ ○ ○ ○ ○ ○ ○

The above description is directed to the embodiment corresponding to the first invention.

The following embodiments 9 to 17 correspond to the embodiments of the second invention.

(Example 9) [Manufacturing of titanium oxide masterbatch (M1)] 50% by mass of sphene-type titanium dioxide having an average particle size of 0.3 μm (electron microscope method) was mixed with 50% by mass of polyethylene terephthalate resin having an ultimate viscosity of 0.62 dl/g. Then, the mixture was supplied to an exhaust double-shaft extruder for mixing to manufacture a masterbatch (M1) containing titanium oxide.

[Manufacturing of unstretched film] 87.5% by mass of polyethylene terephthalate resin with a melt viscosity of 200 Pa・s and 12.5% by mass of polypropylene resin with a melt viscosity of 500 Pa・s are mixed. Next, the mixture is vacuum dried to prepare the raw material of layer A containing voids. On the other hand, 30% by mass of the masterbatch (M1) containing titanium oxide and 70% by mass of polyethylene terephthalate resin with a melt viscosity of 200 Pa・s are mixed in pellet form. Next, the mixture is vacuum dried to prepare the raw material of the first coating layer B1 and the second coating layer B2. These raw materials are fed to different extruders and melted at 285°C, and the first coating layer B1, the layer A containing voids, and the second coating layer B2 are stacked in the order of B1/A/B2. The stacked body is joined using a feed block in a thickness ratio of 10/80/10. The joined body is extruded from a T-shaped die onto a cooling drum adjusted to 30°C to produce an unstretched film having two layers and a three-layer structure.

[Laminar film production] Laminated films were produced under the following film production conditions. That is, the obtained unstretched film was uniformly heated to 70°C using a heating roller, and longitudinally stretched to 3.4 times between two pairs of rollers with different peripheral speeds. At this time, an infrared heater (rated value 20W/cm) with a gold reflective film as an auxiliary heating device for the unstretched film was set opposite to both sides of the film (at a distance of 1cm from the film surface) in the middle of the rollers for heating. The uniaxially stretched film obtained in the above manner was introduced into a tenter, heated to 140°C and stretched to 4.0 times in the transverse direction, the width was fixed, heat treated at 235°C, and then relaxed by 3% in the width direction at 210°C, thereby obtaining a laminated film with a thickness of 50μm.

[Preparation of release film] As a coating solution, aminoalkyd resin (Tesfine 305 manufactured by Showa Denko Materials Co., Ltd.) was diluted in a mixed solvent of methyl ethyl ketone and toluene, and 2.5% by mass of p-toluenesulfonic acid was added to the solution relative to 100% by mass of the aminoalkyd resin to make the total solid concentration 1.0% by mass. The solution was applied to one side of the laminate film by a conventional roller coating method so that the thickness of the release layer C after drying was 0.10 g/ ^m2 . Thus, a release film was obtained in which the release layer C, the first coating layer B1, the layer A containing voids, and the second coating layer B2 were laminated in the order of C/B1/A/B2. The heat drying in the roll coating method was performed at 150°C for 20 seconds. The results of the apparent density, the normal peeling force of the release surface, the color tone b value, the total light transmittance, and the film forming properties are shown in Table 2.

(Example 10 to Example 15) In Example 9, except that the raw material ratio of the layer A containing voids is changed as shown in Table 2, a release film is obtained in the same manner as in Example 9.

(Example 16) In Example 9, the first coating layer B1, the layer A containing voids, and the second coating layer B2 are laminated in the order of B1/A/B2, and the thickness ratio of the laminate is changed to 5/90/5. The release film is obtained in the same manner as in Example 9.

(Example 17) In Example 9, as a coating solution in the preparation of the release film, a long-chain alkyl pendant polymer (Peeloil 1010S manufactured by Lion Specialty Chemicals Co., Ltd.) was diluted in a mixed solvent of toluene, isopropyl alcohol, and cyclohexanone to obtain a total solid concentration of 1.0 mass %. The release film was obtained in the same manner as in Example 9 except that the solution was applied to one side of the laminate film by a conventional roller coating method so that the thickness of the release layer C after drying was 0.10 g/ ^m2 .

(Comparative Example 3) A release film is obtained in the same manner as in Example 9, except that in Example 9, 87.5 mass % of a polyethylene terephthalate resin having a melt viscosity of 200 Pa·s and 12.5 mass % of a polypropylene resin having a melt viscosity of 200 Pa·s are mixed, and the mixture is vacuum dried to convert it into a raw material for layer A containing voids. The release film of Comparative Example 3 is outside the scope of the second invention because its apparent density exceeds 1.20 g/cm ³ . Therefore, in Example 9, the lightness and cushioning properties are poor. In addition, in Example 9, the manufacturing cost is also increased due to the large mass. In addition, the total light transmittance of the release film of Comparative Example 3 is also high, and its concealing properties are also poor compared to Examples 9 to 17.

(Comparative Example 4) In Example 9, the first coating layer B1, the layer A containing voids, and the second coating layer B2 are laminated in the order of B1/A/B2, and the thickness ratio of the laminate is changed to 0/100/0. Since Comparative Example 4 does not have the first coating layer B1 and the second coating layer B2, it is outside the scope of the second invention. In Comparative Example 4, the voids of the layer A containing voids are exposed on the surface, and the surface of Comparative Example 4 becomes extremely rough. In the labeled release film of Comparative Example 4, the total light transmittance is high, and the concealment is poor compared to Examples 9 to 17. In addition, in Comparative Example 4, the color tone b value is large, the whiteness is low compared to Examples 9 to 17, and the yellowness is strong.

In summary, the release film of the second invention has the melt viscosity and melt viscosity ratio of the polyester resin and the polyolefin resin constituting the layer A containing the voids adjusted within a specific range, and the dispersed particle size of the polyolefin resin in the polyester resin is controlled to an appropriate size, so that at least one side of the laminate film has a release layer. Therefore, even if the apparent density of the release film of the second invention is 0.80 to 1.20, it still has excellent lightness, heat resistance, dimensional stability, film forming properties, concealing properties, whiteness, and release properties.

[Table 2] Unit Embodiment 9 Embodiment 10 Embodiment 11 Embodiment 12 Embodiment 13 Embodiment 14 Embodiment 15 Embodiment 16 Embodiment 17 Comparison Example 3 Comparison Example 4 A layer Polyethylene terephthalate resin Melt viscosity (280℃) Pa・s 200 200 200 132 310 200 185 200 200 200 200 Composition ratio Quality% 87.5 93.0 82.5 87.5 87.5 87.5 87.5 87.5 87.5 87.5 87.5 Polypropylene resin Melt viscosity (280℃) Pa・s 500 500 500 500 500 610 372 500 500 200 500 Composition ratio Quality% 12.5 7.0 17.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 Melt viscosity ratio (η2/η1) 2.5 2.5 2.5 3.8 1.6 3.1 2.0 2.5 2.5 1.0 2.5 C-layer Polydimethylsiloxane containing alkenyl - ○ ○ ○ ○ ○ ○ ○ ○ - ○ ○ Hydrogenated polydimethylsiloxane - - - - - - - - - ○ - - Silicone resin content Quality% - - - - - - - - - - - Layer ratio of substrate First coating layer B1 % 10 10 10 10 10 10 10 5 10 10 0 Layer A containing voids % 80 80 80 80 80 80 80 90 80 80 100 Second coating layer B2 % 10 10 10 10 10 10 10 5 10 10 0 Apparent density g／cm ³ 1.07 1.19 0.98 1.01 1.16 1.01 1.12 1.02 1.07 1.28 0.93 Normal peeling force of the release surface mN/50mm 4900 4910 5010 4950 4900 4990 4920 5010 420 4910 5020 Whiteness Hue b value - 1.3 1.3 1.3 1.4 1.4 1.5 1.4 1.6 1.3 1.4 1.8 Concealment Total light transmittance % twenty two twenty three 20 20 twenty three 20 twenty two twenty three twenty two 26 26 Film making properties Whether there is any breakage, etc. - ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ [Industry Availability]

As described above, the release film of the present invention (the first invention, the second invention) is excellent in environmental compatibility, lightness, film forming properties, concealing properties, whiteness, and release properties, and is suitably used as a release film used in manufacturing separators for labels, polarizing plates, and laminated ceramic capacitors. In particular, the release film of the second invention is suitably used in electronic devices where polysilicon is likely to have adverse effects.

Claims (8)

A release film comprises a laminated film and a release layer C located on at least one side of the laminated film; the laminated film is laminated in sequence with at least a first coating layer B1 comprising a polyester resin containing an inorganic pigment, a void-containing layer A containing voids inside, and a second coating layer B2 comprising a polyester resin containing an inorganic pigment; the void-containing layer A comprises a first component comprising a polyester resin and a polyolefin resin; the release layer C is composed of a second component comprising a polysilicone resin; and the apparent density is greater than 0.80 g/ ^cm3 and less than 1.20 g/ ^cm3 . The release film as claimed in claim 1, wherein the polysilicone resin is composed of polydimethylsiloxane containing at least one alkenyl group in one molecule and polydimethylsiloxane containing at least one hydrosilicone group in one molecule. The release film as claimed in claim 1, wherein the content of the polysilicone resin in the release layer C is 90 mass % or more and 100 mass % or less relative to the total mass of the release layer C. The release film as described in claim 1, wherein the polyester resin and the polyolefin resin contained in the layer A containing voids satisfy the following requirements (1) to (3): (1) the melt viscosity (η1) of the polyester resin at a melting temperature of 280°C and a shear rate of 121.6 sec ^{- 1} is greater than 90 Pa·s and less than 400 Pa·s; (2) the melt viscosity (η2) of the polyolefin resin at a melting temperature of 280°C and a shear rate of 121.6 sec ^{- 1} is greater than 300 Pa·s and less than 700 Pa·s; and (3) the melt viscosity ratio (η2/η1) of the polyester resin to the polyolefin resin at a melting temperature of 280°C and a shear rate of 121.6 sec ^{- 1} is greater than 1.5 and less than 4.5. In the release film as claimed in claim 1, the inorganic pigment in the first coating layer B1 and the second coating layer B2 is titanium oxide. The release film as described in claim 1, wherein the ratio of the total thickness of the first coating layer B1 and the second coating layer B2 to the total thickness of the first coating layer B1, the thickness of the layer A containing voids, and the thickness of the second coating layer B2 is greater than 6% and less than 40%. The release film as claimed in claim 1, wherein the normal peeling force of the surface of the release layer C is greater than 40 mN/50 mm and less than 500 mN/50 mm. The release film described in claim 1 is used as a separator for labels or a release film for engineering purposes.