JP7488248B2 - Polyester Release Film - Google Patents

Description

The present invention relates to a polyester release film. More specifically, the present invention relates to a release film for surface protection used in electronic materials such as multi-layer ceramic condensers (MLCCs), polarizing plate protection, and OCAs.

Polyester film has excellent physical property stability over a wide temperature range from low to high temperatures, and is more chemically resistant than other polymer resins. It also has good mechanical strength, surface properties, and thickness uniformity, making it applicable to a variety of uses and process conditions. It is used in capacitors, photographic films, labels, pressure-sensitive tapes, decorative laminates, transfer tapes, polarizing plates, and ceramic release green sheets, and demand has been increasing in recent years in line with the trend toward higher speeds and automation.

In recent years, electronic components such as capacitors and inductors have become smaller in size in response to the trend toward miniaturization of electronic devices. In the process, ceramic green sheets themselves have also become thinner, and the key is to manufacture ceramic sheets in thin films and stack more ceramic layers in the same volume. A ceramic slurry in which ceramic powder and binder are dispersed in a liquid medium is applied to a silicone release layer formed on the surface of a polyester release film to manufacture a thin ceramic sheet, and then the release film is removed during the process of manufacturing a ceramic capacitor. However, if the surface roughness of the release film is high, the release film itself satisfies the physical properties such as slip property and winding onto a roll, but the shape of the protruding particles on the surface of the release film is transferred onto the ceramic sheet. In addition, during the production of the release film, when the film is conveyed at high speed in contact with the conveying roll, the particles detach and become chips, which adhere to the contacting roll, causing dirt and scratches on the film. The chips and detached particles adhere to the conveying roll, causing scratches on the surface of the film, and become foreign matter in the subsequent process.

Conversely, if the surface roughness of the film is reduced too much, the coating stability, film running property, and slippage will decrease when applying the ceramic slurry, and after the release film is manufactured, the foam roll may fall off when it is wound onto a roll, and scratches may occur on the surface of the film during the process of applying a silicone release layer to the surface of the release film.

Therefore, there is a demand for the development of a thin release film that minimizes surface roughness while also having excellent slip properties and winding properties on a roll, produces little cutting chips even when transported at high speeds, and generates little dust when cutting the film, when the film is cut.

Korean Patent Publication No. 2003-0055118 (2003.07.02)

The present invention provides a surface-protecting release film for use in electronic materials such as multilayer ceramic capacitors (MLCCs), polarizing plate protection, and OCAs.
Specifically, the present invention aims to provide a polyester release film that is a thin film having a thickness of 50 μm or less and yet has excellent winding properties and slip properties on a roll, so that it can be applied to release films for thin-film ceramic multilayer capacitors (MLCCs).

Another object of the present invention is to provide a polyester release film which reduces the occurrence of pinholes when a thin ceramic sheet is produced by coating a ceramic slurry thereon.
Another object of the present invention is to provide a polyester release film which generates little cutting chips even when conveyed at high speed during film production, and generates little dust when the film is cut.

As a result of research conducted to achieve the above object, the inventors discovered that the above objective could be achieved by producing a film containing bimodal particles that satisfy specific physical properties, and thus completed the present invention.

One embodiment of the present invention is a biaxially oriented polyester film having at least one laminated layer,
Provided is a polyester release film which contains particles on at least one surface, and when the particle size distribution of the particles contained in a particle-containing polyester layer is measured and the particle diameter is plotted horizontally and the number of particles (volume fraction (vol%)) vertically, the film contains particles A and B having average particle sizes within ranges which satisfy the following formulas 1 and 2, and the weight ratio of the particles A and B satisfies the following formula 3.

0.1 μm≦A≦0.5 μm [Formula 1]
0.6 μm≦B≦1.2 μm [Formula 2]
2≦A/B [Formula 3]

In one embodiment of the present invention, the formula 3 may satisfy 2≦A/B≦10.
In one embodiment of the present invention, the average particle diameters of the particles A and B may satisfy the following formula 4.
B-A≦0.5 μm [Formula 4]

In one embodiment of the present invention, the release film may have a total thickness of 10 to 50 μm.
In one embodiment of the present invention, the content of the particles may be 0.01 to 0.3 wt % based on the total weight of the film.
In one aspect of the present invention, the particles may be a mixture of one or more particles selected from inorganic particles and organic particles.

In one aspect of the present invention, the inorganic particles are selected from calcium carbonate, titanium oxide, silica, kaolin, and barium sulfate, and the organic particles may be any one or a mixture of two or more selected from silicone resin, cross-linked divinylbenzene polymethacrylate, cross-linked polymethacrylate, cross-linked polystyrene resin, benzoguanamine-formaldehyde resin, benzoguanamine-melamine-formaldehyde resin, and melamine-formaldehyde resin.

In one embodiment of the present invention, the inorganic particles may be silica or calcium carbonate.
In one aspect of the present invention, the inorganic particles may be silica (A) having an average particle size of 0.1 to 0.5 μm and calcium carbonate (B) having an average particle size of 0.6 to 1.0 μm, and the difference between the average particle size of the calcium carbonate (B) and the average particle size of the silica (A) may be 0.5 μm or less.

The polyester release film according to the present invention is a thin film, yet has excellent winding properties and slip properties on a roll, and when a ceramic slurry is applied to produce a thin ceramic sheet, a polyester release film with little pinhole generation can be provided.
Furthermore, a polyester release film can be provided which generates little cutting chips even when conveyed at high speed during film production, and which generates little dust when the film is cut.

The present invention will be described in more detail below. However, the following specific examples or embodiments are merely a reference for explaining the present invention in detail, and the present invention is not limited thereto and may be realized in various forms.

Furthermore, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. The terms used in the description of the present invention are merely for the purpose of effectively describing specific examples and are not intended to limit the present invention.

Additionally, as used in the specification and the appended claims, the singular forms "a,""an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
Furthermore, when a part "comprises" certain components, this does not mean excluding other components, but may further include other components, unless specifically stated to the contrary.

Each of the configurations of the present invention will now be described in more detail.
In one embodiment of the present invention, the polyester resin may be used as a masterbatch chip for producing a polyester film.

The inventors of the present invention discovered that by mixing two types of inorganic particles with different particle sizes and combining these particle sizes and contents within a specific range, a film can be provided that has a flat surface, includes effective protrusions for improving handling in post-processing and winding properties of the film, and generates little dust when cut, and thus completed the present invention.

In one embodiment of the present invention, the polyester resin is not particularly limited, and a normal polyester resin may be used. Specifically, the polyester resin may be one obtained by polycondensation of an acid component mainly composed of a dicarboxylic acid and a glycol component mainly composed of an alkylene glycol. The dicarboxylic acid is not limited, and terephthalic acid or its alkyl ester or phenyl ester may be used, and a part of the dicarboxylic acid may be replaced with a bifunctional carboxylic acid or its ester-forming derivative such as isophthalic acid, oxyethoxybenzoic acid, adipic acid, sebacic acid, and 5-sodium sulfoisophthalic acid. The glycol component is not limited, and ethylene glycol may be used mainly, and propylene glycol, neopentyl glycol, trimethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4-bisoxyethoxybenzene, bisphenol, and polyoxyethylene glycol may be used in combination, and a monofunctional compound or a trifunctional compound may be used in combination.

In addition, the composition may contain one or more components selected from additives commonly used in the polymerization of polyester resins, namely, pinning agents, antistatic agents, UV stabilizers, waterproofing agents, slip agents, and heat stabilizers, but is not limited thereto.

The polyester resin may be produced by a polymerization method commonly used in the art, such as a TPA (terephthalic acid) polymerization method or a DMT (dimethyl terephthalate) polymerization method, but is not limited thereto.

In one embodiment of the present invention, the polyester resin may be polyethylene terephthalate. That is, the polyester resin may be polyethylene terephthalate produced using terephthalic acid as the dicarboxylic acid and ethylene glycol as the glycol.

In addition, when the polyester film of the present invention is used as a base film for a release film by reducing the surface roughness, it is preferable that the polyester film contains two specific types of inorganic particles in order to prevent the occurrence of pinholes and thickness unevenness in the layer applied to the release layer due to the transfer of surface roughness, and to significantly improve productivity by improving handling properties such as roll running and winding properties.

More specifically, the particle may contain particles that simultaneously satisfy the following formulas 1 to 3.
Specifically, when the particle size distribution of the particles contained in the particle-containing polyester layer is measured and the particle diameter is plotted horizontally and the volume fraction (vol%) of the particles is plotted vertically, the particles A and B have average particle sizes within a range that satisfies the following formulas 1 and 2, and the weight ratio of the particles A and B may satisfy the following formula 3.

0.1 μm≦A≦0.5 μm [Formula 1]
0.6 μm≦B≦1.2 μm [Formula 2]
2≦A/B [Formula 3]

That is, the formulas 1 and 2 mean that the particle diameter has one or more average particle diameters in the ranges of 0.1 to 0.5 μm and 0.6 to 1.2 μm, respectively, and the formula 3 means that the content ratio (weight ratio) (A/B) of particles A having an average particle diameter in the range of 0.1 to 0.5 μm and particles B having an average particle diameter in the range of 0.6 to 1.2 μm may be 2 or more, 3 or more, and more specifically, 2 to 10, 2 to 11, 3 to 10, 3 to 11, or 3 to 11.5.

When formulas 1 to 3 are simultaneously satisfied, it is possible to provide a polyester release film that, as the object of the present application, is a thin film during film production, yet has excellent winding properties and slippage around a roll, has excellent smoothness, and produces few pinholes when a ceramic slurry is applied to produce a thin ceramic sheet.

In other words, it is possible to provide a film that simultaneously satisfies smoothness, slippage, and windability, which are in a trade-off relationship with each other. Specifically, it is possible to provide a film that has a flat surface, but includes effective protrusions for improving handling in post-processing and winding properties of the film, and can reduce the occurrence of pinholes due to transfer of surface texture and the rate of MLCC short defects.

In addition, we can provide a polyester release film that produces little cutting chips even when transported at high speed during film production, and generates little dust when cutting the film.

The average particle diameters of the particles A and B may satisfy the following formula 4.
B-A≦0.5 μm [Formula 4]
As shown in formula 4, the difference between the average particle size in the range of 0.1 to 0.5 μm and the average particle size in the range of 0.6 to 1.2 μm may be 0.5 μm or less, more specifically, in the range of 0.1 to 0.5 μm. Within this range, the surface smoothness is more excellent, the occurrence of pinholes can be further reduced when applied to ceramic capacitors, and the amount of chips can be reduced when cutting the film, thereby reducing the occurrence of foreign matter.

In one aspect of the present invention, the particles may be a mixture of one or more particles selected from inorganic particles and organic particles.
The inorganic particles are selected from calcium carbonate, titanium oxide, silica, kaolin, barium sulfate, etc., and the organic particles may be any one or a mixture of two or more selected from silicone resin, crosslinked divinylbenzene polymethacrylate, crosslinked polymethacrylate, crosslinked polystyrene resin, benzoguanamine-formaldehyde resin, benzoguanamine-melamine-formaldehyde resin, melamine-formaldehyde resin, etc., but are not limited thereto.

Preferably, the particles may be a mixture of particles A having an average particle size of 0.1 to 0.5 μm and particles B having an average particle size of 0.6 to 1.2 μm. The difference between the average particle size of particles B and the average particle size of particles A may be 0.5 μm or less, more specifically, 0.1 to 0.5 μm, 0.2 to 0.5 μm, or 0.3 to 0.5 μm.

More preferably, the particles may be silica particles (particles A) with an average particle size of 0.1 to 0.5 μm and calcium carbonate (particles B) with an average particle size of 0.6 to 1.2 μm. In addition, the difference between the average particle size of the calcium carbonate (particles B) and the average particle size of the silica particles (particles A) may be 0.5 μm or less, more specifically, 0.1 to 0.5 μm, 0.2 to 0.5 μm, or 0.3 to 0.5 μm.

In one embodiment of the present invention, the content of the particles may be 0.01 to 0.3 wt %, preferably 0.05 to 0.25 wt %, and more preferably 0.1 to 0.2 wt %, based on the total weight of the film. Within the above range, a film can be provided that has excellent particle dispersibility, prevents particle aggregation, and generates little chipping.

In one aspect of the present invention, the particles are effectively added in the form of a particle slurry dispersed in a glycol component during the synthesis of the polyester resin, since this has excellent dispersibility and can prevent re-aggregation of the particles, but the present invention is not limited to this. In other words, the particles may be added after the end of the esterification reaction or the ester exchange reaction and before the start of the polycondensation reaction, but the present invention is not limited to this.

The polyester release film according to one embodiment of the present invention is a biaxially oriented polyester film having at least one layer laminated thereon, and contains particles satisfying the above formulas 1 to 3 on at least one surface.
Specifically, the film may be a biaxially oriented polyester film having two or three laminated layers, and may contain particles satisfying the above formulas 1 to 3 on at least one surface.

More preferably, the biaxially oriented polyester film may be a laminate of three or more layers, and at least one of the surface layers may contain particles that satisfy the above formulas 1 to 3. By laminating three or more layers, the inner layer may be reused by mixing recovered raw materials from the edge portions generated in the film production process or recycled raw materials from other film production processes, within the range that does not affect the roughness of the surface layer, making it possible to recycle resources and reduce costs.

The biaxial stretching means that the film shows a biaxially oriented pattern in X-ray diffraction. The stretching may be sequential biaxial stretching, which can be achieved by stretching the film in the longitudinal direction (machine direction) and then stretching the film in the width direction (horizontal direction). By stretching the film in this way, the strength and crystallization state in the longitudinal and width directions can be made uniform, and cutting can be performed efficiently in each direction.

The polyester release film according to one embodiment of the present invention satisfies the above formulas 1 to 3, and thus a film having a surface roughness peak count Pc of 2.0 pieces/mm2 or less, more specifically 0.1 to 2 pieces/ ^mm2 or less, measured using a three-dimensional surface roughness measuring device (Tokyo Seimitsu, Surfcom 590A-3DF- ¹² ) in accordance with JIS B-0601, can be provided. In the above range, the surface roughness is reduced and winding and running properties are satisfied, so that a film with improved productivity can be provided, which is preferable, but is not limited thereto.

The polyester release film according to one embodiment of the present invention may have a centerline average surface roughness Ra of 20 nm or less, more preferably 15 nm or less, measured using a contact-type three-dimensional surface roughness meter with a 0.08 mm cut-off value. Specifically, the centerline average surface roughness Ra may be 1 to 20 nm, more specifically 4 to 15 nm. The above range is preferable because it provides a film with low surface roughness and excellent smoothness, and almost no pinholes when used as a release film for MLCC, but is not limited thereto.

The release film may have a total thickness of 10 to 50 μm, more specifically 20 to 40 μm. The above range is sufficient for application as a base film of a release film, but is not limited thereto. The polyester film used as the base film of a release film for MLCC tends to be continuously thinner in thickness, so it is suitable for application in the above range. In addition, when laminating at least three layers, a core layer and skin layers may be formed on both sides of the core layer, and the thickness ratio of the core layer to the skin layer may be 50%:50% to 90%:10%, more preferably 60%:40% to 80%:20%. The above range is preferable because it provides a film with excellent running properties, excellent slip properties, improved winding properties on a roll, and less chipping.

In one embodiment of the present invention, the polyester film may be a biaxially stretched film. Specifically, the polyester film may be biaxially stretched 3 to 5 times in the machine direction and 4 to 6 times in the width direction. This stretch ratio is preferred because it further increases the thermal dimensional stability of the polymer structure and reduces thermal shrinkage, but is not limited thereto.

In one aspect of the present invention, the polyester film may be biaxially stretched, followed by heat treatment at 200 to 250°C and relaxation of 1 to 10%. Specifically, relaxation may be imparted simultaneously with heat treatment, more specifically, relaxation of 1 to 10% in the width direction, and even more specifically, relaxation of 2 to 4% in the width direction. Within the above range, the film maintains a tensioned state in the width direction, increasing the density of the polymer structure and reducing deformation due to heat, which is preferable, but is not limited to this.

Hereinafter, the present invention will be described in more detail based on examples and comparative examples. However, the following examples and comparative examples are merely examples for explaining the present invention in more detail, and the present invention is not limited by the following examples and comparative examples.

The physical properties were evaluated as follows.
[Average particle size]
The particle size was measured using a particle size distribution analyzer (LS13 320 manufactured by Beckman). That is, the volume distribution of the particle size was obtained using the LS13 320 manufactured by Beckman (laser diffraction/scattering method), and the value represented by Dmean was calculated as the average particle size (volume average particle size) (related international standard: ISO 13320).
(Reference: http://www.polymer.co.kr/kor/02_service/equipment_6_1.jsp?gclid=EAIaIQobChMI-Zbrx6qD9QIVGtxMAh2A1wBrEAMYAiAAEgKiMvD_BwE)

[Surface roughness (Ra)]
In accordance with JIS B-0601, the polyester film was cut into three pieces, left/center/right, and then measured using a three-dimensional surface roughness measuring device (Tokyo Seimitsu, Surfcom 590A-3DF-12) under the following conditions: measurement speed 0.03 mm/sec, stylus radius 2 μm, load 0.7 mm/N, measurement area 1.0 mm ² , and cutoff value 0.08 mm.

（Ｌ：基準長さ（Cut-Off）） With the center line as the x-axis and the vertical direction as the y-axis, and the roughness curve expressed as y = f(x), calculation was performed according to the following formula.

(L: Reference length (Cut-Off))

[Winding yield]
The polyester films produced in the Examples and Comparative Examples were evaluated as follows by calculating the product yield relative to the input amount during production.
Winding yield (%) = product production volume/input volume x 100

◎: Yield is 65% or more. ○: Yield is 55% or more but less than 65%. △: Yield is less than 55%.

[Level of chip generation]
The produced film was slit to a width of 500 mm at a speed of 300 m/min, and the surface of the 500 mm film roll after slitting was checked for the presence or absence of granules due to PET cutting chips. If the number of granules per ¹ m2 was 0 points, it was rated as Grade 1, if it was 1 to 3 points, it was rated as Grade 2, if it was 4 to 6 points, it was rated as Grade 3, if it was 7 to 9 points, it was rated as Grade 4, if it was 10 to 12 points, it was rated as Grade 5, and if it was 13 points or more, it was rated as Grade 6. Grades 1 and 2 were considered to be pass, and any other grades were considered to be fail.

[Production yield]
A roll of the polyester film master roll manufactured in the examples and comparative examples was used as a base film, a silicone release layer was formed, and then a ceramic slurry was applied to manufacture a ceramic green sheet having a thickness of 1.5 to 3.0 μm. In this case, depending on whether pinholes were generated or not, the evaluation was performed as follows. The production yield was calculated as the area of the ceramic green sheet finally produced relative to the area of one roll of the polyester film master roll supplied.
Production yield (%)=area of ceramic green sheet/area of one roll of polyester film master roll×100

Excellent: No pinholes occurred in one roll of polyester film master. Good: Some pinholes occurred in one roll of polyester film master, and the production yield was 70% or more. Average: Some pinholes occurred in one roll of polyester film master, and the production yield was 30% or more. Poor: Many pinholes occurred in one roll of polyester film master, and the production yield was less than 30%.

[Example 1]
1) Preparation of polyester chip (1) 50 parts by weight of ethylene glycol, 400 ppm of magnesium acetate and 200 ppm of calcium acetate as electrostatic pinning agents, and 150 ppm of antimony trioxide as a polymerization catalyst were added to an esterification reactor, and an ester exchange reaction was carried out at room temperature up to 230°C for 4 hours to produce a prepolymer BHET (bis-βterephthalate). Methanol, a by-product generated during the reaction, was discharged out of the reactor and separated through a distillation column, and ethylene glycol additionally generated after the esterification reaction was completed was also separated through a distillation column. At this time, 200 ppm of trimethyl phosphate was added as a thermal stabilizer, and the temperature was gradually increased to 285°C, and the pressure was reduced to 0.3 torr. Polycondensation reaction was carried out under high vacuum for 4 hours to produce polyethylene terephthalate (PET) resin chips (hereinafter referred to as "wet chips") with an intrinsic viscosity of 0.630 dl/g.

2) Production of Polyester Chips (2) 1% by weight of silica (particles A) having an average particle size of 0.3 μm was added to the polyester chips (1), and the mixture was melt-extruded using a twin-screw kneader to produce polyester chips (2).

3) Production of Polyester Chips (3) 1% by weight of calcium carbonate (particles B) having an average particle size of 0.7 μm was added to the polyester chips (1), and the mixture was melt-extruded using a twin-screw kneader to produce polyester chips (3).

4) Film Production For the core layer, polyethylene terephthalate (PET) chips (1) containing no inorganic particles were used, and for the skin layer, the polyethylene terephthalate (PET) chips (1), polyester chips (2) and polyester chips (3) were mixed in the amounts shown in Table 1 below.

A three-layer film consisting of a skin layer/core layer/skin layer was co-extruded and cast onto a cooling roll to produce an unstretched sheet. In this case, the core layer was 80% by weight of the total film weight, and the skin layer was 20% by weight of the total film weight.

After melt extrusion through an extruder, the mixture was quenched and solidified on a cast drum with a surface temperature of 20°C to produce a sheet. The produced sheet was stretched 3.5 times in the machine direction (longitudinal direction) and 4.0 times in the transverse direction at 95°C and heat-treated at 230°C to produce a biaxially stretched film with a thickness of 31 μm and a particle content of 0.2 wt%. The core layer had a thickness of 24.8 μm, and the skin layers had thicknesses of 3.1 μm. The physical properties of the produced film were measured and are shown in Table 2 below.

[Examples 2 to 6]
A film was prepared in the same manner as in Example 1, except that the content ratio of particles was adjusted as shown in Table 1 below. The physical properties of the prepared film were measured and are shown in Table 2 below.

[Comparative Example 1]
A film was prepared in the same manner as in Example 1, except that the content ratio of particles was adjusted as shown in Table 1 below. The physical properties of the prepared film were measured and are shown in Table 2 below.

[Comparative Example 2]
A film was produced in the same manner as in Example 1, except that polyester chips (4) were used instead of polyester chips (3) in Example 1. The physical properties of the produced film were measured and are shown in Table 2 below.

The polyester chips (4) were produced by adding 1% by weight of cross-linked polystyrene particles (particles B) having an average particle size of 1.0 μm to the polyester chips (1) and melt-extruding the mixture using a twin-screw kneader.

As can be seen from Table 2 above, even if two types of particles are used, if the particle size ratio between the particle types and the bimodal particle size distribution are outside the range of the present invention, the production yield is poor. It was also confirmed that the generation of cutting chips increases, the winding yield decreases, and the surface roughness increases.

The present invention has been described above using specific details and limited embodiments, but this is merely provided for a more general understanding of the present invention, and the present invention is not limited to the above embodiments. A person having ordinary knowledge in the field to which the present invention belongs can make various modifications and variations from such descriptions.

Therefore, the concept of the present invention should not be limited to the described embodiments, and all aspects that are equivalent to or have equivalent modifications to the scope of the appended claims, as well as the scope of the concept of the present invention, are within the scope of the present invention.

Claims (5)

Two or more layers of polyester film are laminated,
A silicone release layer is formed on the surface of the polyester film,
At least one surface layer of the polyester film contains particles;
The particles are inorganic particles,
The content of the particles is 0.01 to 0.2 % by weight based on the total weight of the film;
A polyester release film, comprising particles A and B having average particle sizes that satisfy the following formulas 1 and 2 when a particle size distribution of particles contained in the particle-containing polyester layer is measured and the particle diameter is plotted horizontally and the number of particles vertically, the weight ratio of the particles A and B satisfies the following formula 3, and the average particle size of the particles A and B satisfies the following formula 4:
0.1 μm≦A≦0.5 μm [Formula 1]
0.6 μm≦B≦1.0 μm [Formula 2]
2≦A/B≦10 [Formula 3]
B-A≦0.5 μm [Equation 4]. The polyester release film according to claim 1, wherein the release film has a total thickness of 10 to 50 μm. 2. The polyester release film according to claim 1 , wherein the inorganic particles are any one or a mixture of two or more selected from the group consisting of calcium carbonate, titanium oxide, silica, kaolin, and barium sulfate. 2. The polyester release film according to claim 1 , wherein the inorganic particles are silica or calcium carbonate. The inorganic particles are silica (A) having an average particle size of 0.1 to 0.5 μm and calcium carbonate (B) having an average particle size of 0.6 to 1.0 μm,
2. The polyester release film according to claim 1 , wherein the difference between the average particle size of the calcium carbonate (B) and the average particle size of the silica (A) is 0.5 μm or less.