JP3834172B2 - Cavity-containing polyester film - Google Patents

Description

【００９２】
【表２】

【００９３】
【表３】

【００９４】
以上の方法で得られた空洞含有ポリエステル系フィルムの測定結果一覧を、表1 〜表３に示した。表１〜３の測定結果から、以下のように考察する事ができる。実施例１〜５のフィルムでは、本発明で規定される要件を満足しているので、空洞含有構造による優れた特性と良好なハンドリング性が得られることが解る。
【００９５】
これに対し、見掛け比重が本発明で規定される要件を超える比較例１では誘電率が高く、また同様に見掛け比重が本発明で規定される要件を超える比較例４では熱転写感度特性が低く、いずれも空洞含有構造に由来する優れた特性が損なわれていることが判る。
【００９６】
また、ポリオレフィン系樹脂の平均分散粒子径が本発明で規定される要件を超える比較例２および、リングクラッシュ強度が本発明で規定される要件に満たない比較例３では、いずれも電動機スロット絶縁部分への実装性テスト時の潰れ、折れ曲りによる挿入不良を多発した。
【００９７】
同様に、ポリオレフィン系樹脂の平均分散粒子径が本発明で規定される要件を超える比較例５、リングクラッシュ強度が本発明で規定される要件を外れる比較例６では、いずれも枚葉フィルムの搬送性テスト時に搬送不良を多発した。
【００９８】
【発明の効果】
以上の説明より、本発明の空洞含有ポリエステル系フィルムは、空洞含有構造に由来する特性（例えば、クッション性、低誘電性、軽量性）および後加工時のハンドリング性の両方を併せ持つので、低誘電性およびハンドリング性（実装性等）が要求される電気絶縁材（例えば、電動モータ用絶縁材）として、またクッション性およびハンドリング性（搬送性等）が要求される各種印刷用フィルムとして、極めて有用である。
【図面の簡単な説明】
【図１】図１は裁断されたフィルムであり、破線は折り返し位置を示す。なお図中の長さの単位はｍｍである。
【図２】図２は図１のフィルムを破線で折り返し、ｕ字形に曲げた状態を示す。
【図３】図３は図２のフィルムを挿入するモータースロットモデルである。なお図中の長さの単位はｍｍである。
【符号の説明】
１ フィルム
２ フィルムを折り曲げたもの
３ モータースロットモデル
４ フィルム挿入部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a void-containing polyester film having both properties derived from a void-containing structure (for example, cushioning properties, low dielectric properties, light weight) and handling properties during post-processing. More specifically, a void-containing polyester film suitable as an electrical insulating material having excellent low dielectric properties and good handling properties (mountability, etc.), and excellent handling properties (transport properties, etc.) excellent in cushioning properties. The present invention relates to a void-containing polyester film suitable as various printing films.
[0002]
[Prior art]
Synthetic papers mainly made of synthetic resins have been developed in various applications because they are excellent in water resistance, surface gloss, printability due to a smooth surface, and the like. In particular, polyester resins typified by polyethylene terephthalate are characterized by high heat resistance and high rigidity among synthetic paper raw materials, and the range of use is expanding. For example, utilization as an insulating material for an electric motor (Japanese Patent Application Laid-Open No. 9-149576) has been studied using low dielectric properties derived from a cavity-containing structure. In addition, due to the cushioning properties derived from the void-containing structure, it is widely used as various printing films including thermal transfer printing applications (Japanese Patent Laid-Open No. 63-280687).
[0003]
Cavity-containing polyester films used for such applications include those in which voids are formed around particles by mixing and stretching inorganic fine particles in polyester resins, and thermoplastic resins that are incompatible with polyester resins. And the like are mixed in a polyester resin, dispersed in the form of particles, and stretched to form cavities around the particles. In particular, the latter is widely used because it can reduce the weight of the film.
[0004]
The thermoplastic resin incompatible with the polyester resin (hereinafter also referred to as a cavity forming agent) used for forming the cavity is represented by polypropylene and polymethylpentene (Japanese Patent Laid-Open No. 49-34755). Polyolefin resins, polystyrene resins (for example, Japanese Patent Publication No. 49-2016 and Japanese Patent Publication No. 54-2955) have been proposed.
[0005]
Among these, polyolefin resins, particularly polymethylpentene, have excellent cavity forming ability, and are very excellent in that the cavity can be efficiently formed inside the film. On the other hand, it is difficult to finely disperse in polyester resin, and the voids are likely to become coarse and non-homogeneous, and the flexibility of the film (the film's followability to deformation) decreases, and the film's handling properties. Is greatly reduced. Specifically, problems such as punching failure, transportability failure, and machine insertion suitability (mountability) failure when used as an insulating material for an electric motor are caused. In order to solve these problems, the void content in the film must be limited, and characteristics derived from the void-containing structure (for example, cushioning properties, low dielectric properties, and light weight) must be sacrificed. I do not get.
[0006]
Such deterioration in handling performance is not limited to the above-mentioned use as an electrical insulating material, but also during high-speed handling in various printing methods, etc., transportability (feed failure, paper jam, etc.), printing failure at wrinkle position This causes problems. In order to solve these problems, it is necessary to limit the void content, and the characteristics derived from the void-containing structure (for example, cushioning property, low dielectric property, lightness) must be sacrificed.
[0007]
On the other hand, when a polystyrene resin is used as a cavity forming agent, it can be easily finely dispersed in a polyester resin as compared with a polyolefin resin, and a film having excellent handling properties can be obtained. However, the polystyrene resin has a lower cavity forming ability than the polyolefin resin, and the characteristics derived from the cavity-containing structure (for example, cushioning property, low dielectric property, and lightness) cannot be sufficiently exhibited.
[0008]
Some attempts have been made to finely disperse a polyolefin resin (for example, polymethylpentene) in a polyester resin. For example, the use of a surfactant (Japanese Patent Publication No. 7-17779), the use of polyethylene glycol (Japanese Patent Laid-Open No. 2-235942), or the use of a polyether ester copolymer (Japanese Patent Laid-Open No. 4-264141) A method has been proposed.
[0009]
Certainly, these methods reduce the coarsening and inhomogeneity of the cavities, improve the flexibility of the film to some extent, and thus improve the handling of the film to some extent. However, in the method using a surfactant, the adhesion between the polyester resin and the polyolefin resin (for example, polymethylpentene) is increased, and the formation of cavities when stretched is inhibited. In the method using polyethylene glycol or polyether ester copolymer, since these components have the property of acting as a plasticizer for the polyester resin, the inherent rigidity of the polyester film (waistness) The strength) is significantly reduced. And the fall of rigidity will produce the problem of reducing the handling property of a film conversely. In addition, these ether components easily oxidize and deteriorate, which themselves cause the coloring of the film, and in some cases, promote the deterioration of the polyester resin.
[0010]
As described above, in the above-described prior art, a film having excellent characteristics (for example, cushioning property, low dielectric property, lightweight property) derived from the void-containing structure and good handling properties has not been obtained.
[0011]
[Problems to be solved by the invention]
The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to obtain a film having excellent characteristics (for example, cushioning properties, low dielectric properties, light weight properties) derived from the void-containing structure and good handling properties. It is.
[0012]
[Means for Solving the Problems]
The present invention is as follows.
(1) A film formed of a polyester resin and a composition containing a thermoplastic resin incompatible with the polyester resin, and having voids due to the incompatible thermoplastic resin dispersed in the polyester resin in the form of particles A void-containing polyester-based film containing a large number of voids inside, including a polyolefin-based resin as the incompatible thermoplastic resin, and satisfying all of the following requirements (1) to (3) Cavity-containing polyester film:
(1) Apparent specific gravity is 1.3 or less;
(2) The average dispersed particle size d of the polyolefin resin is 15 μm or less;
(3) Ring crush strength G (unit: kg / mm) and film thickness t (unit: mm) satisfy the following formula.
G / t ^Three > 15
(2) The void-containing polyester film according to the above (1), wherein the dispersed particles of the thermoplastic resin incompatible with the polyester resin have an aspect ratio of 1 to 10 in the cut plane parallel to the film longitudinal direction. .
(3) The void-containing polyester system according to (1), wherein a buckling limit radius r (unit: mm) and a film thickness t (unit: mm) specified in the text satisfy the following formula: the film.
r / t <25
(4) The void-containing polyester film as described in (1) above, wherein the dielectric constant is less than 2.9.
(5) The void-containing polyester film according to the above (1), wherein the polyolefin resin is polymethylpentene and / or polypropylene.
(6) The void-containing polyester film as described in (5) above, further comprising a polystyrene resin as a thermoplastic resin incompatible with the polyester resin.
(7) The content a (wt%) of the polystyrene resin, the content b (wt%) of the polymethylpentene, and the content c (wt%) of the polypropylene in the film satisfy the following formula: The void-containing polyester film according to (6), which is characterized in that
0.01 ≦ a / (b + c) ≦ 1
c / b ≦ 1
3 ≦ a + b + c ≦ 20
[0013]
(8) The void-containing polyester film according to (1), wherein the content of the cyclic trimer in the polyester resin is 0.5% by weight or less based on the total weight of the film.
(9) The void-containing polyester film according to (8), which is an insulating material for an electric motor.
(10) The void-containing polyester film as described in (8) above, wherein the polyester resin has an intrinsic viscosity of 0.68 to 1.0 dl / g.
(11) The cavity according to (8) above, wherein the polyester resin is a polyester resin in which an increase amount of the cyclic trimer when melted at a temperature of 290 ° C. for 60 minutes is 0.5% by weight or less Contains polyester film.
(12) The polyester resin is a polyester resin that has been subjected to water treatment in the form of a chip after polycondensation, and the polyester resin is mainly composed of an aromatic dicarboxylic acid or an ester-forming derivative thereof and ethylene glycol as raw materials, and a Ge compound and / or a Ti compound. The void-containing polyester film as described in (8) above, which is obtained by using as a catalyst.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The polyester resin in the present invention is preferably a crystalline polyester resin obtained mainly from an aromatic dicarboxylic acid component and a glycol component, and more preferably contains 85 mol% or more of the aromatic dicarboxylic acid component in the total acid component. A polyester resin, particularly preferably a polyester resin containing an aromatic dicarboxylic acid component in an amount of 90 mol% or more of the total acid component.
[0015]
Examples of the aromatic dicarboxylic acid component constituting the polyester resin include aromatic dicarboxylic acids such as terephthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyl-4,4′-dicarboxylic acid, diphenoxyethanedicarboxylic acid, and ester formation thereof. Sex derivatives and the like.
[0016]
Examples of the glycol component constituting the polyester resin include aliphatic glycols such as ethylene glycol, trimethylene glycol, and tetramethylene glycol; and alicyclic glycols such as cyclohexanedimethanol.
[0017]
Examples of other acid components that are used by copolymerization in the polyester resin include aromatic dicarboxylic acids such as isophthalic acid and ester-forming derivatives thereof; oxyacids such as p-oxybenzoic acid and oxycaproic acid and the like Ester-forming derivatives; aliphatic dicarboxylic acids such as adipic acid, sebacic acid, succinic acid, glutaric acid and dimer acid and ester-forming derivatives thereof; fats such as 1,4-cyclohexanedicarboxylic acid and 1,3-cyclohexanedicarboxylic acid Examples thereof include cyclic dicarboxylic acids and ester-forming derivatives thereof.
[0018]
Examples of glycol components other than those used by copolymerization in the polyester resin include aliphatic glycols such as diethylene glycol and neopentyl glycol; aromatic glycols such as bisphenol A and alkylene oxide adducts of bisphenol A; polyethylene glycol, And polyalkylene glycols such as polybutylene glycol.
[0019]
Furthermore, polyfunctional compounds such as trimellitic acid, trimesic acid, pyromellitic acid, tricarballylic acid, glycerin, pentaerythritol, trimethylolpropane, etc. may be copolymerized within the range in which the polyester resin is substantially linear. Alternatively, monofunctional compounds such as benzoic acid and naphthoic acid may be copolymerized.
[0020]
A preferred example of the polyester resin is a polyester resin in which the main repeating unit is composed of ethylene terephthalate, more preferably a linear polyester resin containing 85 mol% or more of ethylene terephthalate units, and particularly preferably 90 units of ethylene terephthalate units. It is a linear polyester resin containing at least mol%.
[0021]
Another preferred example of the polyester resin is a polyester resin in which a main repeating unit is composed of ethylene-2,6-naphthalate, and more preferably a linear shape containing 85 mol% or more of ethylene-2,6-naphthalate units. Polyester resins, particularly preferably linear polyester resins containing 90% by mole or more of ethylene-2,6-naphthalate units.
[0022]
The intrinsic viscosity of the polyester resin, particularly a polyester resin in which the main repeating unit is composed of ethylene terephthalate, is preferably 0.50 to 1.30 dl / g, more preferably 0.55 to 1.20 dl / g, and still more preferably. The range is 0.60 to 0.90 dl / g. If the intrinsic viscosity is less than 0.50 dl / g, the mechanical properties of the obtained film may be deteriorated. Conversely, if it exceeds 1.30 dl / g, the resin temperature becomes high at the time of melt extrusion, and thermal decomposition is severe. This may cause problems such as an increase in low molecular weight compounds such as cyclic trimers and a yellow coloration of the film.
[0023]
In addition, the intrinsic viscosity of the polyester resin, particularly a polyester resin whose main repeating unit is composed of ethylene-2,6-naphthalate, is preferably 0.40 to 1.00 dl / g, more preferably 0.42 to 0.95 dl. / G, more preferably in the range of 0.45 to 0.90 dl / g. If the intrinsic viscosity is less than 0.40 dl / g, the mechanical properties of the obtained film may be deteriorated. Conversely, if it exceeds 1.00 dl / g, the resin temperature becomes high at the time of melt extrusion, and thermal decomposition is severe. This may cause problems such as an increase in low molecular weight compounds such as cyclic trimers and a yellow coloration of the film.
[0024]
Furthermore, when the void-containing polyester film of the present invention is used as an insulating material for an electric motor, the polyester resin is mainly composed of an aromatic dicarboxylic acid or an ester-forming derivative thereof and ethylene glycol as raw materials, and a Ge compound and / or a Ti compound. It is preferable to use a polyester resin obtained by using as a catalyst. In this case, the intrinsic viscosity is preferably in the range of 0.68 dl / g to 1.0 dl / g, particularly preferably in the range of 0.68 dl / g to 0.90 dl / g. An intrinsic viscosity of less than 0.68 dl / g is not preferable because it may cause a significant decrease in strength during high-temperature and long-term use as an insulating material for an electric motor. When the intrinsic viscosity exceeds 1.0 dl / g, the load on the extruder and the pressure loss of the filter in the polymer melt extrusion molding process become significant, and it is necessary to greatly limit the polymer discharge amount. As a result, the residence time in the melt line becomes longer and a large amount of the cyclic trimer precipitates, which may cause a decrease in the reliability of the motor due to the release of the cyclic trimer to the electric motor system. It is not preferable.
[0025]
Further, when the void-containing polyester film of the present invention is used as an insulating material for an electric motor, the content of the cyclic trimer of the polyester resin is preferably 0.5% by weight or less based on the total weight of the film. More preferably, it is 4% by weight or less. Here, when the content of the cyclic trimer of the polyester resin exceeds 0.5% by weight with respect to the total weight of the film, the release of the cyclic trimer to the electric motor system increases rapidly, and the motor This is not preferable because there is a risk that the reliability of the battery may be lowered.
[0026]
When the void-containing polyester film of the present invention is used as an insulating material for an electric motor, the polyester resin has an increase in cyclic trimer of 0.5% by weight or less when melted at a temperature of 290 ° C. for 60 minutes. It is preferable that the amount is 0.2% by weight or less. Here, when the increase amount of the cyclic trimer exceeds 0.5% by weight, the amount of the cyclic trimer precipitated in the melt extrusion molding process of the polymer is increased, and the content of the cyclic trimer of the polyester resin is increased. Is not preferable because it may be difficult to adjust the content to 0.5% by weight or less based on the total weight of the film. The increase amount of the cyclic trimer is measured by the method described later.
[0027]
The polyester resin having the above characteristics can be produced, for example, by subjecting a polyester chip to contact treatment with treated water in a treatment tank. Examples of the contact treatment method include a method of immersing in water. The time for the contact treatment with water is 5 minutes to 2 days, preferably 10 minutes to 1 day, more preferably 30 minutes to 10 hours, and the water temperature is 20 to 180 ° C., preferably 40 to 150. ° C, more preferably 50 to 120 ° C.
[0028]
The voids in the void-containing polyester film of the present invention are obtained by mixing the dispersed particles, the polyester resin, and the polyester resin with a thermoplastic resin that is incompatible with the polyester resin, mixed in the polyester resin, dispersed in the form of particles. Formed at the interface.
[0029]
As a thermoplastic resin that is incompatible with the polyester resin used in the present invention, it is essential to include a polyolefin resin, but as other components, a polystyrene resin, a polyacrylic resin, a polycarbonate resin, a polysulfone is included. It may contain a resin based on cellulose, a resin based on cellulose, a polyphenylene ether resin or the like. Examples of the polyolefin resin include, but are not limited to, polyethylene, polypropylene, polymethylpentene, a ring-opened polymer of cyclic olefin, a copolymer of cyclic olefin and other olefin, and the like.
[0030]
The content of the thermoplastic resin incompatible with the polyester resin varies depending on the amount of the target cavity, but is preferably 3 to 20% by weight, more preferably 5 to 18% by weight in the film. When this content is less than 3% by weight, there is a limit to increasing the amount of voids generated, and there is a possibility that characteristics derived from the void-containing structure (for example, low dielectric properties, cushioning properties, and lightness) cannot be exhibited. On the contrary, if it exceeds 20% by weight, the properties inherent to the polyester resin, that is, the stretchability, heat resistance, strength, rigidity, etc. of the film may be impaired, which is not preferable.
[0031]
As a particularly preferred embodiment, there is exemplified a case where a polystyrene resin and a polyolefin resin are used in a specific ratio, that is, a polystyrene resin / polyolefin resin is mixed in an amount of 0.01 to 1, and further, as a polyolefin resin. Polymethylpentene and polypropylene are used, that is, it is preferable to use a mixture of polystyrene resin, polymethylpentene and polypropylene.
[0032]
In the present invention, the polystyrene-based resin refers to a thermoplastic resin containing a polystyrene structure as a basic component, and grafts or other components other than homopolymers such as atactic polystyrene, syndiotactic polystyrene, and isotactic polystyrene. Block copolymerized modified resins (for example, impact-resistant polystyrene, graft copolymers of polystyrene and polyphenylene ether, etc.), and thermoplastic resins having compatibility with these polystyrene resins, for example, mixtures with polyphenylene ether including.
[0033]
In the present invention, polymethylpentene is a polymer containing units derived from 4-methylpentene-1 at 80 mol% or more, preferably 90 mol% or more, and other units include ethylene, propylene, butene Examples thereof include units derived from -1,3-methylbutene-1, and the like.
[0034]
In the present invention, the polypropylene includes homopolymers such as isotactic polypropylene and syndiotactic polypropylene, as well as modified resins obtained by grafting or block copolymerizing other components. You may use the said polypropylene in the state copolymerized in the said polymethylpentene, ie, the state which introduce | transduced the propylene unit as a copolymerization unit.
[0035]
These resins are preferably mixed and used at a specific ratio. The content a (wt%) of the polystyrene resin in the film, the content b (wt%) of the polymethylpentene and the content c (wt) of the polypropylene %) Preferably satisfies the following formula:
0.01 ≦ a / (b + c) ≦ 1
c / b ≦ 1
3 ≦ a + b + c ≦ 20
[0036]
Here, when a / (b + c) is less than 0.01, the dispersion effect of the polystyrene-based resin on the polyolefin-based resin (polymethylpentene and / or polypropylene) becomes unstable, resulting in poor film unevenness and flexibility. Therefore, handling properties may be inferior, which is not preferable. On the other hand, if a / (b + c) exceeds 1, there is a limit to increasing the amount of generated cavities, and characteristics derived from the cavities-containing structure (for example, low dielectric properties, cushioning properties, and lightweight properties) cannot be exhibited. There is a fear and it is not preferable. The upper limit of the value of a / (b + c) is particularly preferably 0.5, and the lower limit is particularly preferably 0.1.
[0037]
Similarly, when c / b exceeds 1, it is not preferable because there is a limit to increasing the amount of generated cavities. The lower limit of c / b is not particularly limited, but if it is less than 0.01, film unevenness and flexibility may be poor and handling properties may be inferior. The upper limit of the value of c / b is particularly preferably 0.5, and the lower limit is particularly preferably 0.1.
[0038]
Further, if a + b + c is less than 3% by weight, there is a limit to increasing the amount of voids generated, and there is a possibility that characteristics derived from the void-containing structure (for example, low dielectric properties, cushioning properties, lightness) cannot be exhibited. On the other hand, if a + b + c exceeds 20% by weight, the properties inherent to the polyester resin, that is, the stretchability, heat resistance, strength, rigidity, etc. of the film may be impaired and handling properties may be inferior. . The upper limit of a + b + c is particularly preferably 18% by weight, and the lower limit is particularly preferably 5% by weight.
[0039]
In addition, in the void-containing polyester film of the present invention, inorganic or organic particles may be included as necessary in order to improve the concealability and the like. Examples of usable particles include silica, kaolinite, talc, calcium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, titanium oxide, zinc sulfide, organic white pigments, and the like. is not. These particles can be contained in the film by adding them in advance into a polyester resin and / or into a thermoplastic resin incompatible with the polyester resin.
[0040]
The method for producing the void-containing polyester film of the present invention is arbitrary and is not particularly limited. For example, after forming a mixture of the above-described composition into a film to obtain an unstretched film, the unstretched film A general method of stretching the film can be used.
[0041]
The conditions for stretching / orienting the unstretched film are closely related to the formation of cavities. In the following, the stretching / orientation conditions will be described by taking as an example a sequential biaxial stretching method that is most preferably used, particularly a method of stretching an unstretched film in the machine direction (longitudinal direction) and then in the transverse direction (width direction). First, in the first-stage longitudinal stretching step, stretching is performed between two or many rolls having different peripheral speeds. As a heating means at this time, a method using a heating roll or a method using a non-contact heating method may be used, or they may be used in combination. However, in order to develop a large number of cavities at the interface between the polyester resin and the thermoplastic resin incompatible with the polyester resin, the stretching temperature is stretched 3 to 5 times at the secondary transition temperature Tg + 50 ° C. or less of the polyester resin. Next, the uniaxially stretched film is introduced into a tenter, and stretched 2.5 to 5 times in the transverse direction at a temperature of the polyester resin having a melting point Tm-10 ° C. or lower.
[0042]
The biaxially stretched film thus obtained is subjected to heat treatment as necessary. The heat treatment is preferably performed in a tenter, and is preferably performed in the range of the melting point Tm-50 ° C. to Tm of the polyester resin.
[0043]
The void-containing polyester film of the present invention may be a single layer or a multilayer structure in which the same or different synthetic resin film layers are combined. The synthetic resin film layer used for such a composite can be formed by a co-extrusion method or a lamination method through a coating method, an adhesive layer, or the like.
[0044]
In addition, as such a synthetic resin film, for example, a film mainly composed of one or more of polyethylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, polyarylate or polyimide can be used, but is not limited thereto. It is not a thing.
[0045]
Moreover, a coloring agent, a light fastness agent, a fluorescent agent, an antistatic agent, etc. can be added to the synthetic resin film layer as necessary. Moreover, you may add the above-mentioned inorganic particle and organic particle | grains.
[0046]
Moreover, the void-containing polyester film of the present invention may have a coating layer on at least one surface thereof. By providing the coating layer, it is possible to improve the paintability and adhesiveness of inks and coating agents. The compound constituting the coating layer is preferably a polyester resin, but in addition to this, a compound disclosed as a means for improving the adhesion of a normal polyester film, such as a polyurethane resin, a polyester urethane resin, an acrylic resin, etc. Etc. are applicable.
[0047]
As a method for providing the coating layer, a conventionally used method such as a gravure coating method, a kiss coating method, a dip coating method, a spray coating method, a curtain coating method, an air knife coating method, a blade coating method, or a reverse roll coating method can be applied. . As the step of applying, any method such as a method of applying before stretching of the film, a method of applying after longitudinal stretching, and a method of applying to the film surface after the stretching treatment can be used.
[0048]
The void-containing polyester film thus obtained has excellent characteristics derived from the void-containing structure (for example, cushioning properties, low dielectric properties, lightweight properties) and good handling.
[0049]
The void-containing polyester film of the present invention has an apparent specific gravity of 1.3 or less, preferably 1.2 or less, more preferably 1.15 or less. When the apparent specific gravity is larger than 1.3, the amount of voids inherent in the film is too small, and the characteristics derived from the void-containing structure (for example, low dielectric property, cushioning property, lightness) are insufficient. The lower limit of the apparent specific gravity is not particularly limited, but if the apparent specific gravity is less than 0.8, the buckling limit radius r described later cannot be set in a suitable range, and good handling properties cannot be obtained. There is a fear and it is not preferable. In the present invention, in order to make the apparent specific gravity 1.3 or less, a method of appropriately selecting the mixing amount of the thermoplastic resin incompatible with the polyester resin, the polyester resin containing the polyolefin resin, A method of appropriately selecting a combination of thermoplastic resins, a method of appropriately selecting film production conditions (stretching ratio, stretching temperature, heat treatment temperature, etc.) and the like can be employed.
[0050]
In the void-containing polyester film of the present invention, the average dispersed particle diameter d (unit: μm) of the polyolefin resin is 15 μm or less, preferably 10 μm or less. In a film in which the average dispersed particle diameter d of the polyolefin-based resin exceeds 15 μm, the dispersed particles are coarsened, and the flexibility of the film is inferior, and therefore the handling property is inferior. In the present invention, the average dispersed particle diameter d of the polyolefin-based resin refers to the average value of the maximum diameter of the dispersed particles. In the present invention, in order to set the average dispersed particle diameter d of the polyolefin resin to 15 μm or less, a method of containing a polystyrene resin together with the polyolefin resin, and a method of appropriately selecting a mixing ratio of the polyolefin resin and the polystyrene resin. (D can be reduced by increasing the proportion of polystyrene resin), controlling the shear history applied to the polymer in the melt line at the film production conditions (by applying more shear for a longer time, d Can be made small).
[0051]
Furthermore, in the void-containing polyester film of the present invention, the ring crush strength G (unit: kg / mm) and the film thickness t (unit: mm) satisfy the following formula.
G / t ^Three > 15
In the present invention, the ring crush strength G is defined by the method described in the examples described later. G/ T ^Three Is 15 or moreIn the lower case, the inherent rigidity of the polyester film is impaired, the mounting property by the machine is improved, the resistance against the bending of the seat under a load, and the like are poor, and good handling properties cannot be obtained. In the present invention, G/ T ^Three Is preferably 20 or moreAbove. In the present invention, in order for the ring crush strength G and the film thickness t to satisfy the above formula, a specific ratio of polystyrene resin and polyolefin resin, that is, polystyrene resin / polyolefin resin is 0.01. It can be achieved by mixing at a ratio of ˜1. Specifically, polymethylpentene and polypropylene are used as the polyolefin resin, and as described above, the content a (wt%) of the polystyrene resin in the film, the content b (wt%) of the polymethylpentene, and The case where the content c (% by weight) of polypropylene satisfies the following formula is particularly preferable.
0.01 ≦ a / (b + c) ≦ 1
c / b ≦ 1
3 ≦ a + b + c ≦ 20
[0052]
The void-containing polyester film of the present invention has the above requirements (1) to (3), (1) the apparent specific gravity is 1.3 or less, and (2) the average dispersed particle diameter d of the polyolefin resin is 15 μm or less. And (3) the characteristic derived from the cavity-containing structure (for example, for example) only when the ring crush strength G (unit: kg / mm) and the film thickness t (unit: mm) satisfy the above formula. A cavity-containing polyester-based film having good handling properties can be obtained while ensuring cushioning properties, low dielectric properties, and lightweight properties. If any one of these requirements is not satisfied, the void-containing polyester system having good handling properties while ensuring the characteristics derived from the void-containing structure (for example, cushioning properties, low dielectric properties, light weight) No film can be obtained.
[0053]
Further, in the void-containing polyester film of the present invention, the aspect ratio of the dispersed particles of the thermoplastic resin incompatible with the polyester resin is preferably 1 to 10 on the cut surface parallel to the film longitudinal direction. It is preferable that it is 2-8. If the aspect ratio exceeds 10, the amount of voids generated is small, and it may be difficult to make the apparent specific gravity within the above range. In the present invention, the aspect ratio means an average value of (major axis / minor axis of dispersed particles of thermoplastic resin incompatible with polyester resin). In the present invention, in order to set the aspect ratio to 1 to 10, a method of appropriately combining a plurality of polyolefin resins having different melting points or glass transition points, and a mixing ratio of the polyolefin resin and the polystyrene resin are appropriately selected. In the method and film production conditions, a method of appropriately selecting the heat treatment temperature (a method in which the aspect ratio increases as the heat treatment is performed at a higher temperature) can be employed.
[0054]
Further, the void-containing polyester film of the present invention has a buckling limit radius r (unit: mm) and a film thickness t (unit: mm) represented by the following formulae.
r / t <25
Is preferably satisfied. In the present invention, the buckling limit radius r is defined by the method described in Examples described later.. r / t25 or moreIf it is above, the inherent rigidity of the polyester film is impaired, the mountability by the machine is improved, the resistance to bending of the seat under load is poor, and good handling properties may not be obtained. . In the present invention, R / tIs more preferably 20 not yetIt's full. In the present invention, in order for the buckling limit radius r and the film thickness t to satisfy the above formula, the same method as the method for setting the average dispersed particle diameter d of the polyolefin resin to 15 μm or less, A method of including a polystyrene resin together with a polyolefin resin, a method of appropriately selecting a mixing ratio of the polyolefin resin and the polystyrene resin (r can be reduced by increasing the ratio of the polystyrene resin), and production of a film A method of controlling the shear history applied to the polymer in the melt line under conditions (r can be reduced by applying a larger shear for a long time) or the like can be adopted.
[0055]
Further, the void-containing polyester film of the present invention has a dielectric constant of preferably less than 2.9, more preferably 2.7 or less, and most preferably 2.6 or less. When the dielectric constant is 2.9 or more, when used as an electrical insulating material, the leakage current reduction effect (reduction rate relative to the leakage current of the standard PET film) may be insufficient, which is not preferable. In the present invention, to make the dielectric constant less than 2.9, the apparent specific gravity of the film needs to be 1.3 or less.
[0056]
The void-containing polyester film of the present invention is a particularly useful film as an electrical insulating material (for example, an insulating material for an electric motor, particularly an insulating material for a hermetic motor) and a printing film (for example, for thermal transfer).
[0057]
The void-containing polyester film of the present invention does not require a surfactant, polyalkylene glycol, polyether resin or the like as a dispersant for a polyolefin resin, so that it has excellent heat resistance, and the self-recovery raw material is recycled. Even when used, the change in color tone is small, and the stability during film production is also excellent. A preferable use ratio when reusing the self-recovered raw material is 5 to 50% by weight.
[0058]
In addition, the void-containing polyester film of the present invention may reuse a polymer recovered from a PET bottle or a polymer recovered from a magnetic card, an IC card, or the like.
[0059]
Next, examples and comparative examples of the present invention will be shown. The measurement / evaluation method used in the present invention is shown below.
[0060]
1) Apparent specific gravity
The JIS K-7112 floatation method was followed.
[0061]
2) Average dispersed particle diameter d of polyolefin resin
1.0 g of the film was cut finely, put into a 50 ml volumetric flask, and then hexafluoroisopropanol heated to 40 ° C. was added. The flask was heated to 40 ° C. for 2 hours to dissolve the film. This was filtered using a 0.45 μm membrane filter, and undissolved matter (polyolefin resin particles) was taken out. After drying this, 20 points were selected at random, magnified 1500 times using a scanning electron microscope (SEM), the maximum diameter was measured as the diameter, and the average value was d.
[0062]
3) Aspect ratio of dispersed particles of thermoplastic resin incompatible with polyester resin
The film is cut parallel to the longitudinal direction, and the surface of the cross section is laid out with a microtome, and 50 dispersed particles of thermoplastic resin incompatible with the polyester resin are randomly selected, and a scanning electron microscope (SEM) is used. The major axis / minor axis of each dispersed particle was measured arbitrarily, and the average value was defined as the aspect ratio.
[0063]
4) Buckling limit radius r (unit: mm)
Two films were cut into 10 mm × 100 mm each in the longitudinal direction / width direction. Using a caliper with a beak length of 50 mm or more, the film was lightly curved and inserted into a U-shape between the caliper beaks, and the dimensions were reduced in the direction of sandwiching and crushing the film. The bending width at the time when the film could not withstand bending and buckled while generating corners was read with a vernier caliper scale, and half the value was taken as the buckling limit radius r (unit: mm) of the film. Values averaged 4 points.
[0064]
5) Ring crush strength G
The board paper compressive strength test method (ring crush method) shown in JIS P-8126 was used.
Testing machine: Toyo Baldwin universal compression / tensile testing machine is used, and load cell is used at 100kg full scale.Load valueI read. Compressed at a test speed of 13 mm / min.
Test piece support: A stainless steel jig having a groove of 50 mm in diameter and 6.35 mm in depth as shown in JIS P-8126 was used.
Test piece: Two films were cut into a length of 152.4 mm and a width of 12.07 mm each in the longitudinal direction / width direction.
Measurement method: Insert a test piece into a test piece support, put it on a tester, and compress it at a test speed of 13 mm / min.loadI read. At the time of buckling of the specimenloadIs a value obtained by dividing the test piece length by 152.4 mm as ring crush strength G (unit: kg / mm). Values averaged 4 points.
[0065]
6) Film thickness t
Sony Precision Technology Inc. The thickness of the 20-point film was measured at random using a Digital Micrometer M-30 manufactured, and the average value was defined as the film thickness t (mm).
[0066]
7) Handleability of film-1 (Mountability to slot insulation part of low voltage induction motor)
100 pieces of each sample were cut out to the size shown in FIG. 1, each was bent into the shape shown in FIG. 2, inserted into the film insertion portion 4 of the motor slot model 3 shown in FIG. 3, and the mountability was evaluated. Judgment criteria are as follows.
○: There is no insertion failure due to crushing or bending in 100 sheets.
Δ: Insertion failure due to crushing or bending in 100 sheets is less than 5 times
X: Insertion failure due to crushing or bending in 100 sheets is 5 times or more
[0067]
8) Film handling properties-2 (sheet-fed film transportability)
After subjecting the film surface to antistatic and antiblocking processing, 100 samples cut to A6 postcard size were prepared. This sample was subjected to an offset printing machine (AR-010 manufactured by Texel), and a conveyance test was performed. The handling property was evaluated based on the frequency of occurrence of conveyance failures due to creases, wrinkles, paper jams, etc. caused by this test.
○: No conveyance failure occurred in 100 sheets
Δ: Less than 5 occurrences of conveyance failure in 100 sheets
×: Conveyance failure occurred 5 times or more in 100 sheets
[0068]
9) Dielectric constant
According to JIS C 2151-1990 “Testing method for plastic film for electrical use”.
[0069]
10) Thermal transfer sensitivity characteristics
Coating liquid with the following composition
Water dispersible copolyester resin: 2 parts by weight
Water-dispersible acrylic / styrene copolymer resin: 5 parts by weight
Water-dispersible isocyanate crosslinking agent: 0.5 part by weight
Water: 67.4 parts by weight
Isopropyl alcohol: 25 parts by weight
Surfactant: 0.1 part by weight
After drying, the weight is 4g / m²Then, the film surface was coated, the dimensions were fixed, and heat treatment was performed at 160 ° C. for 30 seconds to form a recording layer, whereby a thermal transfer image receiving sheet was prepared.
[0070]
About the sample which cut the thermal transfer image-receiving sheet thus obtained into A6 size, a commercially available ink ribbon (print set P-PS100 for sublimation transfer printer manufactured by Caravel Data Systems Co., Ltd.) and a commercially available thermal transfer printer (manufactured by Bon Electric Co., Ltd.) Using a thermal transfer type label printer BLP-323), printing was performed at a printing speed of 100 mm / second and a head voltage of 18V. The print pattern includes 7 solid solid letters of 9 mm x 9 mm each for 4 colors of C (cyan), M (magenta), Y (yellow), and K (black) on which these are overprinted. 28) A pattern arranged in an A6 sheet was used.
[0071]
After printing, the reflection density of each color of CMYK was measured using a Macbeth densitometer (TR-927), and the average reflection density of four colors (a total of 28 places) was obtained. Similarly, commercially available image-receiving paper (print set P-PS100 for sublimation transfer printer manufactured by Caravel Data Systems Co., Ltd .: a foamed polypropylene film laminated on both sides of natural paper to form a recording layer) in the same manner. The average reflection density was determined, and the thermal transfer sensitivity characteristic was evaluated by the ratio (%) of the average reflection density of the sample to the average reflection density of the commercially available image receiving paper.
[0072]
11) Intrinsic viscosity of polyester resin (IV)
It calculated | required from the solution viscosity at 30 degreeC in a 1,1,2,2-tetrachloroethane / phenol (2: 3 weight ratio) mixed solvent.
[0073]
12) Content of cyclic trimer of polyester resin (hereinafter referred to as “CT content”)
300 mg of the sample was dissolved in 3 ml of a hexafluoroisopropanol / chloroform mixed solution (volume ratio = 2/3), and further diluted by adding 30 ml of chloroform. To this was added 15 ml of methanol to precipitate the polymer, followed by filtration. The filtrate was evaporated to dryness, brought to a constant volume with 10 ml of dimethylformamide, and the cyclic trimer was quantified by high performance liquid chromatography.
[0074]
13) Increasing amount of cyclic trimer during melting of polyester resin (ΔCT)
3 g of the dried polyester chip was put in a glass test tube and immersed in an oil bath at 290 ° C. for 60 minutes in a nitrogen atmosphere and melted. The amount of increase in cyclic trimer at the time of melting was determined by the following formula.
Increase amount of cyclic trimer at the time of melting (wt%) =
Cyclic trimer content after melting (wt%)-cyclic trimer content before melting (wt%)
[0075]
14) Elongation retention
HFC-134a (CH₂F-CF_Three) 20 g, 50 g of POE (polyol ester) synthetic oil was used as a lubricant, and the measurement sample was placed in a 120 cc autoclave at 140 ° C. and 30 atm for 2000 hours. Prior to charging the refrigerant / oil, the measurement sample was dehydrated for 3 hours in an autoclave under a vacuum of 140 ° C. and 26 Pa (0.2 Torr). The oil used was dried and conditioned in advance to control the moisture content to 300 ppm.
The breaking elongation before and after this test was measured, and the ratio of the breaking elongation of the sample after the test to the breaking elongation of the sample before the test was evaluated as the elongation retention. In addition, the measurement of elongation at break followed the method prescribed | regulated to JIS-C2318.
[0076]
15) Reduction rate of leakage current
A combination of HFC-134a as a refrigerant and POE oil as a lubricant was used. Insert a standard PET film for electrical insulation into the electric motor of a closed compressor for a refrigerator and set the initial leakage current (X₁) Was measured. Next, the sample is replaced with a standard PET film for electrical insulation and inserted into an electric motor, and the initial value (X₂) Was measured. The reduction rate of leakage current was calculated from the following equation.
Reduction rate of leakage current (%) = [1− (X₂/ X₁] X 100
[0077]
Example 1
(Preparation of cavity forming agent)
As raw materials, 70% by weight of polyethylene terephthalate having an intrinsic viscosity of 0.62 dl / g, 6% by weight of polystyrene having a melt flow rate of 2.0 (Topolex 570-57U manufactured by Mitsui Toatsu Co., Ltd.), and a melt flow rate of 1.7 Polypropylene (Mitsui Toatsu Co., Ltd. Nobrene F0-50F) 6% by weight and melt flow rate 8 polymethylpentene (Mitsui Petrochemical Co., Ltd. TPX, DX-845) 18% by weight are mixed with pellets and biaxially extruded. It was supplied to a machine and kneaded sufficiently, and the strand was cooled and cut to prepare a master pellet (Pa) containing a cavity forming agent. Subsequently, 75% by weight of polyethylene terephthalate having an intrinsic viscosity of 0.62 dl / g and 25% by weight of the above-mentioned cavity forming agent-containing master pellets (Pa) were mixed in a vacuum and vacuum dried to obtain a film raw material.
[0078]
(Preparation of unstretched film)
Next, the raw material of the above film was supplied to an extruder and extruded onto a cooling drum adjusted to 30 ° C. using a T die to produce an unstretched film having a thickness of about 1900 μm.
[0079]
(Production of biaxially stretched film)
The obtained unstretched film was uniformly heated to 65 ° C. using a heating roll, and 3 between two pairs of nip rolls (low speed roll speed = 1 m / min, high speed roll speed = 3.4 m / min) having different peripheral speeds. Stretched 4 times. At this time, as an auxiliary heating device for the film, an infrared heater (rated 20 W / cm) provided with a gold reflective film in the middle part of the nip roll was placed facing both surfaces of the film (distance of 1 cm from the film surface) and heated. The uniaxially stretched film thus obtained was guided to a tenter, heated to 150 ° C., transversely stretched 3.7 times, fixed in width, subjected to heat treatment at 220 ° C. for 5 seconds, and further at 210 ° C. By relaxing 4% in the width direction, a void-containing polyester film (Example 1) having a thickness of 188 μm was obtained.
[0080]
Comparative Example 1
As a raw material, 90% by weight of polyethylene terephthalate having an intrinsic viscosity of 0.62 dl / g that has been vacuum-dried, and 10% by weight of polystyrene having a melt flow rate of 2.0 (Topolex 570-57U manufactured by Mitsui Toatsu Co., Ltd.) Was used. Otherwise, a void-containing polyester film (Comparative Example 1) was obtained in the same manner as in Example 1.
[0081]
Comparative Example 2
As a raw material, a mixture of 90% by weight of polyethylene terephthalate having an intrinsic viscosity of 0.62 dl / g subjected to vacuum drying and 10% by weight of polypropylene having a melt flow rate of 1.7 (Nobrene F0-50F manufactured by Mitsui Toatsu Co., Ltd.) Using. Except that, a void-containing polyester film (Comparative Example 2) was obtained in the same manner as in Example 1.
[0082]
Comparative Example 3
As raw materials, 83% by weight of polyethylene terephthalate having an intrinsic viscosity of 0.62 dl / g subjected to vacuum drying, 7% by weight of polymethylpentene (TPX, DX-820, Mitsui Petrochemical Co., Ltd.) chip having a melt flow rate of 180 and molecular weight A mixture of 4000 polyethylene glycol flakes of 10% by weight was used. Except that, a void-containing polyester film (Comparative Example 3) was obtained in the same manner as in Example 1.
[0083]
Example 2
As raw materials, 49.5% by weight of polyethylene terephthalate having an intrinsic viscosity of 0.62 dl / g, 50% by weight of anatase type titanium dioxide (TA-300 manufactured by Fuji Titanium Co., Ltd.) having an average particle size of 0.3 μm (electron microscopic method) and fluorescence A mixture of 0.5% by weight of a whitening agent (OB-1 manufactured by Eastman Chemical Co., Ltd.) is supplied to a vent type twin screw extruder and pre-kneaded, and then the molten polymer is continuously mixed with a vent type single screw. The mixture was fed to a kneader and kneaded to prepare fine particle (titanium oxide) -containing master pellets (Pb). Next, 30% by weight of the cavity-former-containing master pellets (Pa) prepared in Example 1, 5% by weight of the fine particle-containing master pellets (Pb), and 65% by weight of polyethylene terephthalate having an intrinsic viscosity of 0.64 dl / g were mixed with pellets. Then, vacuum drying was performed to obtain a film raw material (A). On the other hand, 50% by weight of the fine particle-containing master pellet (Pb) and 50% by weight of polyethylene terephthalate having an intrinsic viscosity of 0.64 dl / g were mixed and vacuum-dried to obtain a film raw material (B).
These film raw materials (A) and (B) are supplied to separate extruders, and the film raw material (B) is laminated evenly on both sides of the film raw material (A) using a feed block (B / A / B = 5 / 90/5) to prepare an unstretched film having a thickness of about 700 μm. Next, a void-containing polyester film (Example 2) having a thickness of 100 μm was obtained by the same method as in Example 1 (however, low speed roll speed = 2 m / min, high speed roll speed = 6.8 m / min).
[0084]
Comparative Example 4
80% by weight of polyethylene terephthalate having an intrinsic viscosity of 0.62 dl / g is mixed with 10% by weight of the fine particle-containing master pellets (Pb) prepared in Example 2 and vacuum-dried. Further, polystyrene having a melt flow rate of 2.0 (Topolex 570-57U manufactured by Mitsui Toatsu Co., Ltd.) 10% by weight was used as a film raw material. Next, a void-containing polyester film (Comparative Example 4) having a thickness of 100 μm was obtained by the same method as in Example 1 (however, low speed roll speed = 2 m / min, high speed roll speed = 6.8 m / min).
[0085]
Comparative Example 5
10% by weight of the fine particle-containing master pellet (Pb) prepared in Example 2 was mixed with 78% by weight of polyethylene terephthalate having an intrinsic viscosity of 0.62 dl / g, and vacuum-dried, and further a polypropylene having a melt flow rate of 1.7. (Mitsui Toatsu Co., Ltd. Nobrene F0-50F) 12% by weight was added as a film raw material. Next, a void-containing polyester film (Comparative Example 5) having a thickness of 100 μm was obtained by the same method as in Example 1 (however, low-speed roll speed = 2 m / min, high-speed roll speed = 6.8 m / min).
[0086]
Comparative Example 6
As raw materials, 80% by weight of polyethylene terephthalate having an intrinsic viscosity of 0.62 dl / g after vacuum drying, 10% by weight of polymethylpentene chips (TPX, DX-820 manufactured by Mitsui Petrochemical Co., Ltd.) having a melt flow rate of 180 and molecular weight A mixture of 4000 polyethylene glycol flakes of 10% by weight was used. Next, a void-containing polyester film (Comparative Example 6) having a thickness of 100 μm was obtained by the same method as in Example 1 (however, low-speed roll speed = 2 m / min, high-speed roll speed = 6.8 m / min).
[0087]
Example 3
(Preparation of cavity forming agent)
As raw materials, 20% by weight of polystyrene having a melt flow rate of 2.0 (Topolex 570-57U manufactured by Mitsui Toatsu Co., Ltd.), 20% by weight of polypropylene having a melt flow rate of 1.7 (Nobrene F0-50F manufactured by Mitsui Toatsu Co., Ltd.) %, And 60% by weight of polymethylpentene (TPI, DX-820, manufactured by Mitsui Petrochemical Co., Ltd.) having a melt flow rate of 180 are mixed in pellets, supplied to a twin-screw extruder, kneaded sufficiently, and the strand cooled. A master pellet (Pc) containing a cavity forming agent was prepared by cutting.
[0088]
(Film production)
Next, 90% by weight of polyethylene terephthalate having an intrinsic viscosity of 0.62 dl / g produced using an Sb catalyst is mixed with 10% by weight of master pellets (Pc) containing the cavity forming agent, and vacuum-dried to obtain a film. It was set as the raw material (C). On the other hand, polyethylene terephthalate alone having an intrinsic viscosity of 0.62 dl / g produced using an Sb catalyst was used as a film raw material (D).
These film raw materials (C) and (D) are supplied to separate extruders, melted at 290 ° C., and the film raw material (D) is laminated evenly on both sides of the film raw material (C) using a feed block (D /C/D=7.5/85/7.5), and an unstretched film having a thickness of about 2600 μm was prepared. At this time, the residence time of the molten resin until the raw material was charged into the extruder and an unstretched film was formed was about 10 minutes. Next, the unstretched film was stretched and heat treated by the same method as in Example 1 to obtain a void-containing polyester film (Example 3) having a thickness of 250 μm and an apparent specific gravity of 1.05.
[0089]
Example 4
A polyethylene terephthalate chip manufactured using a Ge catalyst instead of the polyethylene terephthalate used in Example 3 and having an intrinsic viscosity of 0.75 dl / g, a cyclic trimer amount of 0.30% by weight, and ΔCT = 0.6% by weight A void-containing polyester film (Example 4) was obtained in the same manner as in Example 3 except that was used.
[0090]
Example 5
Instead of the polyethylene terephthalate used in Example 3, the polyethylene terephthalate chip used in Example 4 was treated with water (95 ° C., 5 hours), and the intrinsic viscosity was 0.75 dl / g and the cyclic trimer amount was 0. A void-containing polyester film (Example 5) was obtained in the same manner as in Example 3 except that a polyethylene terephthalate chip with 30% by weight and ΔCT = 0.07% by weight was used.
[0091]
[Table 1]

[0092]
[Table 2]

[0093]
[Table 3]

[0094]
Tables 1 to 3 show a list of measurement results of the void-containing polyester film obtained by the above method. From the measurement results in Tables 1 to 3, it can be considered as follows. In the film of Examples 1-5, since the requirements prescribed | regulated by this invention are satisfied, it turns out that the outstanding characteristic and favorable handleability by a cavity containing structure are obtained.
[0095]
On the other hand, in Comparative Example 1 where the apparent specific gravity exceeds the requirement defined in the present invention, the dielectric constant is high, and in Comparative Example 4 where the apparent specific gravity exceeds the requirement defined in the present invention, the thermal transfer sensitivity characteristic is low, It can be seen that all of the excellent characteristics derived from the void-containing structure are impaired.
[0096]
Further, in Comparative Example 2 in which the average dispersed particle size of the polyolefin-based resin exceeds the requirement specified in the present invention and in Comparative Example 3 in which the ring crush strength does not satisfy the requirement specified in the present invention, both of the motor slot insulating portions Many insertion failures occurred due to crushing and bending during the mounting test.
[0097]
Similarly, in Comparative Example 5 in which the average dispersed particle diameter of the polyolefin-based resin exceeds the requirement stipulated in the present invention and in Comparative Example 6 in which the ring crush strength deviates from the requirement stipulated in the present invention, conveyance of the single wafer film is performed. Many conveyance failures occurred during the sex test.
[0098]
【The invention's effect】
From the above description, the void-containing polyester film of the present invention has both the characteristics derived from the void-containing structure (for example, cushioning property, low dielectric property, light weight) and handling property at the time of post-processing. Very useful as an electrical insulating material (such as an insulating material for an electric motor) that requires high performance and handling properties (mountability, etc.) and as a film for various printings that require cushioning and handling properties (such as transportability) It is.
[Brief description of the drawings]
FIG. 1 is a cut film, and a broken line indicates a folding position. The unit of length in the figure is mm.
FIG. 2 shows a state where the film of FIG. 1 is folded by a broken line and bent into a u-shape.
FIG. 3 is a motor slot model into which the film of FIG. 2 is inserted. The unit of length in the figure is mm.
[Explanation of symbols]
1 film
2 Folded film
3 Motor slot model
4 Film insertion part

Claims (5)

A polyester resin and a composition containing a thermoplastic resin that is incompatible with the polyester resin, and a large number of cavities attributed to the incompatible thermoplastic resin dispersed in the polyester resin in the form of particles in the film. A void-containing polyester film containing, wherein the incompatible thermoplastic resin comprises a polyolefin resin and a polystyrene resin, and the polyolefin resin is polymethylpentene, or polymethylpentene and A void-containing polyester film characterized by being a polypropylene and satisfying all of the following requirements <1> - <3> :
<1> Apparent specific gravity is 1.0 to 1. 3 ;
<2> The average dispersed particle size d of the polyolefin resin is 15 μm or less;
<3> The ring crush strength G (unit: kg / mm) and the film thickness t (unit: mm) satisfy the following formula.
G / t ³ > 15   2. The void-containing polyester film according to claim 1, wherein the dispersed particles of thermoplastic resin incompatible with the polyester resin have an aspect ratio of 1 to 10 at a cut surface parallel to the film longitudinal direction. 2. The void-containing polyester film according to claim 1, wherein a buckling limit radius r (unit: mm) and a film thickness t (unit: mm) defined in the text satisfy the following expressions.
r / t <25   2. The void-containing polyester film according to claim 1, wherein the dielectric constant is less than 2.9. The content a (wt%) of polystyrene resin, the content b (wt%) of polymethylpentene, and the content c (wt%) of polypropylene in the film satisfy the following formulas: The void-containing polyester film according to claim 1 .
0.01 ≦ a / (b + c) ≦ 1
c / b ≦ 1
3 ≦ a + b + c ≦ 20

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