JP7615308B2 - Liquid crystal polyester resin composition, liquid crystal polyester film using said composition, metal laminate film using said film, and circuit board - Google Patents

Description

The present invention relates to a liquid crystal polyester resin composition mainly composed of a thermoplastic liquid crystal polyester capable of forming an optically anisotropic molten phase. It also relates to a liquid crystal polyester film using the resin composition, and a metal laminate film and a circuit board using the film.

In recent years, there has been a growing demand in the electronics and electrical fields for smaller and lighter devices, which has led to a demand for insulating films with excellent electrical and mechanical properties. However, conventional insulating film raw materials such as polyimide and polyethylene terephthalate have insufficient electrical properties in the high frequency range, and are highly hygroscopic, which can lead to poor electrical properties and large dimensional changes, making it difficult to create a film that meets the above demands.

In contrast, thermoplastic liquid crystal polyesters are useful in the electronics and electrical fields because they exhibit excellent mechanical and electrical properties, low dimensional change rates, high heat resistance and chemical stability, etc. In particular, thermoplastic liquid crystal polyesters with a melting point of 300°C or higher are useful for printed circuit board applications because they can be used for lead-free solder reflow. However, thermoplastic liquid crystal polyesters have rigid molecular chains that are arranged in an orderly manner even in the molten state, and the molecular chains flow smoothly without entanglement, so the molecular chains tend to be oriented in the direction of the resin flow, and simply forming them into a film does not reach a level where they can be used.

A method for producing a film made of thermoplastic liquid crystal polyester is known that utilizes an extrusion molding method such as inflation extrusion molding. (See Patent Document 1.) In the case of inflation extrusion molding, the orientation of the molecular chains can be controlled to a certain extent by appropriately adjusting the blow ratio.

However, the melt viscosity of thermoplastic liquid crystal polyester is highly dependent on shear stress, and a slight increase in shear stress causes a significant drop in melt viscosity. For this reason, when melt extruding thermoplastic liquid crystal polyester using inflation extrusion molding, the shear stress generated in the die can cause a sudden drop in melt viscosity, making it difficult to maintain the bubble shape, and there is a problem that it is difficult to stably produce a film.

Thermoplastic liquid crystal polyester also has the characteristic that its melt viscosity is highly dependent on temperature, and that a slight increase in temperature near the melting point causes a significant drop in melt viscosity. This tendency is more pronounced for thermoplastic liquid crystal polyesters with higher melting points, and thermoplastic liquid crystal polyesters with melting points of 300°C or higher in particular have low melt viscosities near the melting point, so that when a film is produced by inflation extrusion molding, holes are likely to form in the bubbles extruded from the die, making it difficult to stably produce a film.

On the other hand, Patent Document 2 is an invention relating to a liquid crystal polyester composition characterized by comprising a polyester that forms an optically anisotropic molten phase at a temperature of 250°C or higher and a polyester that forms an optically anisotropic molten phase at a temperature of 200°C or lower, and describes that by blending a liquid crystal polyester that forms an optically anisotropic molten phase at a temperature of 200°C or lower, the melt viscosity is reduced and low-temperature moldability is improved.

Patent Document 3 is an invention relating to a liquid crystal polymer blend characterized by comprising a liquid crystal polymer (A) having a tensile modulus of elasticity of 20 to 32 GPa and a melting point of 250°C or more and 330°C or less, and a liquid crystal polymer (B) having a melting point of 190°C or more and less than 250°C, and describes that blending a liquid crystal polymer with a low melting point improves fluidity and low-temperature processability during molding.

However, the examples in Patent Documents 2 and 3 only disclose the preparation of test pieces from the composition by injection molding, and make no disclosure about continuously producing a film by inflation extrusion molding.

Patent Publication No. 2005-1376 JP 5-186671 A JP2007-119639

The present invention has been made in consideration of such problems, and aims to provide a liquid crystal polyester resin composition that has excellent mechanical properties, electrical properties, and heat resistance and enables stable film formation in inflation extrusion molding.

The inventors conducted extensive research into a resin composition that would enable stable film formation by inflation extrusion molding while maintaining the excellent mechanical properties, electrical properties, and heat resistance of thermoplastic liquid crystal polyesters with high melting points (e.g., melting points of 300°C or higher). As a result, they discovered that by blending a thermoplastic liquid crystal polyester with a relatively low melting point with a thermoplastic liquid crystal polyester with a high melting point and excellent heat resistance, the dependence of the melt viscosity on temperature and shear stress is reduced, making it possible to stably form a film by inflation extrusion molding, and thus completed the present invention.

According to the present invention,
(1) A liquid crystal polyester-based resin composition comprising a thermoplastic liquid crystal polyester (A) and a thermoplastic liquid crystal polyester (B), wherein the difference in melting point between the thermoplastic liquid crystal polyester (A) and the thermoplastic liquid crystal polyester (B) is 5°C or more and 95°C or less, the thermoplastic liquid crystal polyester (A) comprises a constitutional unit derived from p-hydroxybenzoic acid and a constitutional unit derived from 6-hydroxy-2-naphthoic acid, and the thermoplastic liquid crystal polyester (B) comprises either a constitutional unit derived from p-hydroxybenzoic acid and a constitutional unit derived from 6-hydroxy-2-naphthoic acid, or a constitutional unit derived from p-hydroxybenzoic acid and a constitutional unit derived from 4,4'-dihydroxybiphenyl, and the blending ratio of the thermoplastic liquid crystal polyester (A) to the thermoplastic liquid crystal polyester (B) is (A):(B)=40-98% by weight:2-60% by weight, and the liquid crystal polyester-based resin composition is used for inflation extrusion molding,
(2) The liquid crystal polyester resin composition according to ( ¹ ) is characterized in that the melt viscosity ratio R 122 (μ Tm /μ Tm _{+10 ) between the melt viscosity (μ Tm ) at the melting point of the thermoplastic liquid crystal polyester (A) measured under the condition of a shear rate of 122 sec -1 and the melt viscosity (μ Tm + 10} ⁾ _{at the} melting point of the thermoplastic liquid crystal polyester (A) + 10°C measured under the condition of a shear rate of 122 sec -1 is less than 3.4;
(3) The ratio of the melt viscosity ratio ^R 122 (μ Tm /μ _{Tm+10 ) between the melt viscosity (μ Tm} ) at the melting point of the thermoplastic liquid crystal polyester (A) measured under the condition of a shear rate of 122 sec ^-1 and the melt viscosity (μ _{Tm+ 10} ) at the melting point + 10°C of the thermoplastic liquid crystal polyester (A) measured under the condition of a shear rate of 122 sec- ¹ to the melt viscosity ratio R ₁₂₁₆ (μ _Tm /μ Tm+10 ) between the melt viscosity (μ _Tm ) at the melting point of the thermoplastic liquid crystal polyester (A) measured under the condition of a shear rate of 1216 sec ^-1 and the melt viscosity (μ _Tm+10 ) at the melting point + 10°C of the thermoplastic liquid crystal polyester (A) measured under the condition of a shear rate of _{122 sec} - ₁ (R ₁₂₂ /R ₁₂₁₆ The liquid crystal polyester resin composition according to (1) is characterized in that the value of (a) is 1.5 or less,
(4) The liquid crystal polyester resin composition according to ( ¹ ) is characterized in that the difference (variation) between the maximum and minimum melt viscosity ratios (μ _Tm /μ Tm+10 ) between the melt viscosity (μ _Tm ) at the melting point of the thermoplastic liquid crystal polyester (A) and the melt viscosity R (μ Tm _{+10 )} at the melting point of the thermoplastic liquid crystal polyester (A) + 10° C. measured under each shear rate condition within a shear rate range of 122 to 2430 sec −1 is less than 1.2;
(5) The liquid crystal polyester resin composition according to ( ¹ ) is characterized in that the difference (variation) between the maximum and minimum values of the melt viscosity ratio R (μ _{Tm /μ Tm+10} ) between the melt viscosity (μ _Tm ) at the melting point of the thermoplastic liquid crystal polyester (A) and the melt viscosity (μ _{Tm +10} ) at the melting point of the thermoplastic liquid crystal polyester (A) + 10° C. measured under each shear rate condition within a shear rate range of 6 to 2430 sec −1 is less than 3.4;
(6) The liquid crystal polyester resin composition according to (1), wherein the melting point of the thermoplastic liquid crystal polyester (A) is 300° C. or higher, and the melting point of the thermoplastic liquid crystal polyester (B) is lower than 300° C.;
(7) The liquid crystal polyester resin composition according to (1), characterized in that the blending ratio of the thermoplastic liquid crystal polyester (A) to the thermoplastic liquid crystal polyester (B) is (A):(B)=60-96% by weight:4-40% by weight,
(8) A liquid crystal polyester film comprising the resin composition according to any one of (1) to (7),
(9) The liquid crystal polyester film according to (8) is provided, characterized in that, when F(MD) is a tensile strength in the machine direction of the film and F(TD) is a tensile strength in the width direction of the film, 0.75≦F(TD)/F(MD)≦1.25;
(10) The method for producing a liquid crystal polyester film according to (9) is provided, characterized in that the film is produced by an inflation extrusion method,
(11) A metal laminate film is provided, characterized in that a metal layer is laminated on one or both sides of the liquid crystal polyester film according to (9),
(12) There is provided a circuit board comprising at least one conductor layer and the thermoplastic liquid crystal polyester film according to (9).

The liquid crystal polyester resin composition of the present invention is a thermoplastic liquid crystal polyester having a relatively low melting point, which is blended with a thermoplastic liquid crystal polyester having a high melting point and excellent heat resistance, and thus, when a film is produced by inflation extrusion molding, it is possible to suppress the occurrence of holes in the bubbles extruded from the die, and it is possible to stably produce a film, and it is possible to maintain the excellent mechanical properties, electrical properties, and heat resistance of the thermoplastic liquid crystal polyester having a high melting point. Therefore, the liquid crystal polyester film made of the liquid crystal polyester resin composition of the present invention and the metal laminate film obtained by laminating the liquid crystal polyester film with a metal layer have excellent mechanical properties, electrical properties, and solder reflow properties, and can be suitably used for applications such as laminates for circuit boards suitable for high-speed communication applications.

The present invention will be described in detail below. Note that the present invention is not limited to the following form, and various forms are possible within the scope of the effects of the present invention.

[Liquid crystal polyester resin composition]
The liquid crystal polyester resin composition of the present invention is a resin composition containing a thermoplastic liquid crystal polyester (A) having a high melting point and excellent heat resistance and a thermoplastic liquid crystal polyester (B) having a melting point lower than that of the thermoplastic liquid crystal polyester (A), and the difference in melting point between the thermoplastic liquid crystal polyester (A) and the thermoplastic liquid crystal polyester (B) is 5°C or more and 95°C or less. The liquid crystal polyester resin composition of the present invention can be suitably used for inflation extrusion molding applications because the dependence of the melt viscosity on temperature and shear stress can be reduced by blending the thermoplastic liquid crystal polyester (A) and the thermoplastic liquid crystal polyester (B). The difference in melting point between the thermoplastic liquid crystal polyester (A) and the thermoplastic liquid crystal polyester (B) is preferably 10°C or more and 80°C or less, more preferably 20°C or more and 60°C or less, and particularly preferably 25°C or more and 55°C or less.

Thermoplastic liquid crystal polyester (A) and thermoplastic liquid crystal polyester (B) are liquid crystal polyesters that exhibit melt anisotropy (polyesters that can form an optically anisotropic molten phase). The melt anisotropy can be confirmed by a conventional polarized light inspection method using crossed polarizers. Specifically, melt anisotropy can be confirmed by using a polarizing microscope (manufactured by Olympus Corporation, etc.) to melt a sample placed on a hot stage (manufactured by Linkam Co., Ltd., etc.) and observing it at a magnification of 150 times under a nitrogen atmosphere. Liquid crystal resins that exhibit optical anisotropy when melted are optically anisotropic and transmit light when inserted between crossed polarizers. If the sample is optically anisotropic, polarized light will transmit even when it is in a molten, stationary liquid state, for example.

[Thermoplastic liquid crystal polyester (A)]
The thermoplastic liquid crystal polyester (A) used in the resin composition of the present invention contains, as essential units, a constitutional unit derived from p-hydroxybenzoic acid (sometimes referred to as monomer component A) and a constitutional unit derived from 6-hydroxy-2-naphthoic acid (sometimes referred to as monomer component B). The thermoplastic liquid crystal polyester (A) may contain another monomer component C other than the monomer components A and B. Examples of the monomer component C include aromatic or aliphatic dicarboxylic acids; aromatic or aliphatic dihydroxy compounds; aromatic hydroxycarboxylic acids; aromatic diamines, aromatic hydroxyamines, or aromatic aminocarboxylic acids; and the like, and these may be used alone or in combination of two or more.

The thermoplastic liquid crystal polyester (A) used in the resin composition of the present invention is preferably a resin having a melting point of 300°C or more. If the melting point is below 300°C, the solder reflow property is poor, so that when used for applications such as printed circuit boards, the processing method is limited. The melting point of the thermoplastic liquid crystal polyester (A) is not particularly limited, but from the viewpoint of heat resistance and moldability, it is preferably, for example, 300°C or more and 400°C or less, more preferably 305°C or more and 370°C or less, even more preferably 310°C or more and 360°C or less, and particularly preferably 315°C or more and 345°C or less. The melting point of the thermoplastic liquid crystal polyester (A) is determined by heating a sample at a rate of 10°C/min using a differential scanning calorimeter (DSC) to completely melt it, then cooling the molten product to 30°C at a rate of 10°C/min, and heating it again at a rate of 10°C/min. The position of the endothermic peak that appears when this is the melting point.

Specific examples of thermoplastic liquid crystal polyester (A) having a melting point of 300°C or higher include, for example, a binary polycondensate of p-hydroxybenzoic acid (monomer component A) and 6-hydroxy-2-naphthoic acid (monomer component B); a ternary polycondensate of p-hydroxybenzoic acid (monomer component A), 6-hydroxy-2-naphthoic acid (monomer component B), and terephthalic acid (monomer component C); a ternary or higher polycondensate of p-hydroxybenzoic acid (monomer component A), 6-hydroxy-2-naphthoic acid (monomer component B), and one or more monomers (monomer component C) selected from the group consisting of terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-dihydroxybiphenyl, bisphenol A, hydroquinone, and ethylene terephthalate; and the like.

[Thermoplastic liquid crystal polyester (B)]
The thermoplastic liquid crystal polyester (B) used in the resin composition of the present invention contains a constitutional unit derived from p-hydroxybenzoic acid (sometimes referred to as monomer component A') and a constitutional unit derived from 6-hydroxy-2-naphthoic acid (sometimes referred to as monomer component B') as essential units, or contains a constitutional unit derived from p-hydroxybenzoic acid (sometimes referred to as monomer component A') and a constitutional unit derived from 4,4'-dihydroxybiphenyl (sometimes referred to as monomer component B') as essential units. The thermoplastic polyester (B) may contain another monomer component C' other than the monomer component A' and the monomer component B', and examples of the monomer component C' include aromatic or aliphatic dicarboxylic acids; aromatic or aliphatic dihydroxy compounds; aromatic hydroxycarboxylic acids; aromatic diamines, aromatic hydroxyamines, or aromatic aminocarboxylic acids; and the like, and these can be used alone or in combination of two or more kinds.

The thermoplastic liquid crystal polyester (B) used in the resin composition of the present invention preferably has a melting point of less than 300° C. The melting point of the thermoplastic liquid crystal polyester (B) is not particularly limited, but it is preferable that the melting point of the thermoplastic liquid crystal polyester (B) maintains the heat resistance of the thermoplastic liquid crystal polyester (A) having excellent heat resistance, and
From the viewpoint of reducing the dependency of the melt viscosity on temperature and shear stress, the melting point is, for example, preferably 230° C. or more and less than 300° C., more preferably 250° C. or more and less than 295° C., even more preferably 260° C. or more and less than 290° C., and particularly preferably 265° C. or more and less than 285° C. The melting point of the thermoplastic liquid crystal polyester (B) may be measured by the same method as the method for measuring the melting point of the thermoplastic liquid crystal polyester (A) described above.

Specific examples of thermoplastic liquid crystal polyester (B) having a melting point of less than 300°C include, for example, a binary polycondensate of p-hydroxybenzoic acid (monomer component A') and 6-hydroxy-2-naphthoic acid (monomer component B'); a ternary or higher polycondensate of p-hydroxybenzoic acid (monomer component A'), 6-hydroxy-2-naphthoic acid (monomer component B'), terephthalic acid (monomer component C'), and hydroquinone (monomer component C'); a ternary polycondensate of p-hydroxybenzoic acid (monomer component A'), 4,4'-dihydroxybiphenyl (monomer component B'), and terephthalic acid (monomer component C'); and the like.

The liquid crystal polyester resin composition of the present invention contains the above-mentioned thermoplastic liquid crystal polyester (A) and thermoplastic liquid crystal polyester (B) in a ratio of (A):(B)=40-98% by weight:2-60% by weight. Preferably, (A):(B)=50-97% by weight:3-50% by weight, more preferably, (A):(B)=60-96% by weight:4-40% by weight, even more preferably, (A):(B)=65-95% by weight:5-35% by weight, and particularly preferably, (A):(B)=70-95% by weight:5-30% by weight. If the blending ratio of the thermoplastic liquid crystal polyester (B) is less than the above range, the film forming processability of the liquid crystal polyester resin composition by inflation extrusion molding cannot be improved, and stable film formation becomes difficult. Furthermore, if the blending ratio of the thermoplastic liquid crystal polyester (B) is greater than the above range, the film-forming processability of the liquid crystal polyester resin composition by inflation extrusion cannot be improved, making it difficult to perform stable film formation, and the heat resistance and mechanical properties of the liquid crystal polyester film made of the liquid crystal polyester resin composition are reduced.

The liquid crystal polyester resin composition of the present invention preferably has a melt viscosity ratio ^R 122 (μ _{Tm /μ Tm+10 ) of less than 3.4 between the melt viscosity (μ Tm} ) at the melting point of the thermoplastic liquid crystal polyester (A) measured under the condition of a shear rate of ₁₂₂ sec ^-1 and the melt viscosity (μ _{Tm+10 )} at the melting point of the thermoplastic liquid crystal polyester (A) + 10 ° C. measured under the condition of a shear rate of 122 sec ^-1 . If the melt viscosity ratio of the melt viscosity (μ _Tm ) at the melting point of the thermoplastic liquid crystal polyester (A) measured under the condition of a shear rate of 122 _sec ^-1 and the melt viscosity (μ _Tm+10 ) at the melting point of the thermoplastic liquid crystal polyester (A) + 10 ° C. measured under the condition of a shear rate of 122 sec -1 is less than the above-mentioned value, the change in melt viscosity near the extrusion temperature in inflation extrusion molding is small, and the film forming processability by inflation extrusion molding is improved. The melt viscosity ratio R ₁₂₂ (μ _Tm /μ _Tm+10 ) is more preferably less than 3.3, even more preferably less than 3.0, and particularly preferably less than 2.5. The lower limit of the melt viscosity ratio (μ _Tm /μ _Tm+10 ) is not particularly limited, but is usually 1.0 or more.

The liquid crystal polyester resin composition of the present invention has a melt viscosity ratio ^R 1216 (μ Tm /μ Tm+10 ) of the melt viscosity (μ _Tm ) at the melting point of the thermoplastic liquid crystal polyester (A) measured under a shear rate of 1216 sec ^-1 to the melt viscosity (μ _Tm+10 ) at the melting point + 10°C of the thermoplastic liquid crystal polyester (A) measured under a shear rate of 1216 sec ^-1 , and a melt viscosity ratio R ₁₂₂ (μ _Tm /μ _Tm+10 ) of the melt viscosity (μ _Tm ) at the melting point of the thermoplastic liquid crystal polyester (A) measured under a shear rate of 122 sec ^-1 to the melt viscosity ratio R 122 (μ Tm /μ _Tm+10 ) of the melt viscosity (μ Tm ) at the melting point of the thermoplastic liquid crystal polyester (A) measured under a shear rate of 122 sec -1 to the melt viscosity ratio R ₁₂₂ (μ _Tm /μ _Tm+10 ) of the melt viscosity (μ _Tm + 10 ) at the melting point of the thermoplastic liquid crystal polyester (A) measured under a shear rate of _{122 sec} -1. It is preferable that the value of the ratio (R 122 /R ₁₂₁₆ (μ _Tm /μ _Tm+10 )) (hereinafter, sometimes referred to as R ₁₂₂ /R ₁₂₁₆ ) is 1.50 or less. If the value of the ratio (R ₁₂₂ /R ₁₂₁₆ ) is the above-mentioned numerical value or less, the melt viscosity has a small dependency on temperature and shear stress, so that the change in melt viscosity near the extrusion temperature in inflation extrusion molding is small, and the film forming processability of the film by inflation extrusion molding is improved. The value of the ratio (R ₁₂₂ /R ₁₂₁₆ ) is more preferably 1.45 or less, even more preferably 1.40 or less, and particularly preferably 1.35 or less. The lower limit is not particularly limited, but is, for example, 0.5 or more, preferably 0.7 or more, and more preferably 0.85 or more.

In the liquid crystal polyester resin composition of the present invention, the difference (variation) between the maximum and minimum values of the melt viscosity ratio R (μ Tm /μ Tm+ ¹⁰ ) between the melt viscosity (μ _Tm ) at the melting point of the thermoplastic liquid crystal polyester (A) and the melt viscosity (μ _{Tm+10 )} at the melting point of the thermoplastic liquid crystal polyester ( _A ) measured under each shear rate condition in the range of shear rate 122 to 2430 sec -1 is preferably less than 1.1, and within the above range, the melt viscosity has a small dependency on temperature and shear stress, so that the change in melt viscosity near the extrusion temperature in inflation extrusion molding is small, and the film forming processability by inflation extrusion molding is improved. The variation within the shear rate range of 122 to 2430 sec ^-1 is more preferably less than 1.1, even more preferably less than 1.0, and particularly preferably less than 0.8. The lower limit is not particularly limited, but is, for example, 0.1 or more.

In the liquid crystal polyester resin composition of the present invention, the difference (variation) between the maximum and minimum values of the melt viscosity ratio R (μ Tm /μ Tm _{+10 ) between the melt viscosity (μ Tm ) at the melting point of the thermoplastic liquid crystal polyester (A) and the melt viscosity (μ Tm+10} ⁾ _{at the melting} point of the thermoplastic liquid crystal polyester (A) measured under each shear rate condition in the range of shear rate 6 to 2430 sec -1 is preferably less than 3.4, and within the above range, the melt viscosity has a small dependency on temperature and shear stress, so that the change in melt viscosity near the extrusion temperature in inflation extrusion molding is small, and the film forming processability by inflation extrusion molding is improved. The variation within the shear rate range of 6 to 2430 sec ^-1 is more preferably less than 3.2, even more preferably less than 3.0, and particularly preferably less than 2.5, less than 2.0, or less than 1.5. The lower limit is not particularly limited, but is, for example, 0.1 or more.

The liquid crystal polyester resin composition of the present invention may contain other resin components other than the above-mentioned thermoplastic liquid crystal polyester (A) and thermoplastic liquid crystal polyester (B) as long as the effects of the present invention are not impaired. Examples of other resin components include thermoplastic resins such as polyarylate, polyphenylene sulfide, polyphenylene ether, polyether ether ketone, polyetherimide, cycloolefin polymer, polyamide, polyamideimide, polyimide, epoxy group-containing olefin copolymer, and styrene resin. The liquid crystal polyester resin composition of the present invention may also contain additives such as lubricants, antioxidants, and fillers. In addition, when the liquid crystal polyester resin composition of the present invention contains other components, it is preferable to contain the total amount of the thermoplastic liquid crystal polyester (A) and the thermoplastic liquid crystal polyester (B) as the main component. Here, the main component means that the composition ratio of the components constituting the resin composition is 50% by weight or more, preferably 60% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more.

[Method of producing liquid crystal polyester film]
The present invention also proposes a film made of the above-mentioned resin composition and a method for producing the film. The liquid crystal polyester film of the present invention is obtained by blending the above-mentioned thermoplastic liquid crystal polyester (A) and thermoplastic liquid crystal polyester (B) by a known method and forming a film. In addition, when the blending ratio of the thermoplastic liquid crystal polyester (B) of the resin composition of the present invention is reduced, it is preferable to melt-knead and granulate the resin composition of the present invention prior to film formation in order to provide a stable kneaded state.

The equipment for melt kneading is not particularly limited, but examples include various known extruders such as a batch kneader, a kneader, a co-kneader, a Banbury mixer, a roll mill, and a single-screw or twin-screw extruder. Among these, single-screw extruders and twin-screw extruders are preferably used because of their excellent kneading ability and productivity.

By blending the thermoplastic liquid crystal polyester (B) in the resin composition of the present invention, it is possible to suppress a sudden decrease or change in the melt viscosity of the resin composition due to temperature, shear stress, etc., and it is possible to improve the film forming processability by inflation extrusion molding.

An example of an inflation extrusion molding method is to supply the above-mentioned resin composition to a melt extruder equipped with a die with an annular slit, extrude the molten resin composition in a bubble shape upward or downward from the annular slit of the extruder, and blow air or an inert gas into the inside of the bubble made of the molten resin composition to expand and stretch the bubble in a direction (TD direction) perpendicular to the flow direction (MD direction) to obtain a film. The cylinder temperature of the melt extruder is usually 280 to 400°C, preferably 320 to 380°C. The interval between the annular slits is usually 0.1 to 5 mm, preferably 0.2 to 2 mm. The diameter of the annular slit is usually 20 to 1000 mm, preferably 25 to 600 mm.

In inflation extrusion molding, the blow ratio is preferably 1.5 or more, more preferably 2.0 or more, even more preferably 4.0 or more, and particularly preferably 4.5 or more. The upper limit of the blow ratio is not particularly limited, but for example, the blow ratio is 10 or less. The draft ratio is preferably 1.5 to 20, more preferably 1.5 to 10. Here, the blow ratio is the stretch ratio in the TD direction, and the draft ratio is the stretch ratio in the MD direction. When the blow ratio and the draft ratio are in the above range, the anisotropy of the tensile modulus and tensile strength of the obtained film (the difference between the MD direction and the TD direction) can be improved. However, in inflation extrusion molding, increasing the blow ratio to improve the anisotropy of the film works in the direction of destabilizing the shape retention of the bubbles made of the resin composition in the molten state, making it easier for the bubbles to vibrate or have holes. In particular, when a liquid crystal polyester having a melting point of more than 300° C. is expanded and stretched by inflation extrusion molding so that the blow ratio is 4.0 or more, holes are frequently formed in the bubbles, making it difficult to form a film. In contrast, the resin composition of the present invention can suppress a sudden decrease or change in the melt viscosity of the resin composition due to temperature, shear stress, etc., by blending the thermoplastic liquid crystal polyester (B), so that even if the blow ratio is 4.0 or more, the generation of holes in the bubbles is suppressed, and the film can be stably formed while improving the anisotropy of the film.

The thickness of the liquid crystal polyester film of the present invention is not particularly limited, but is, for example, 0.5 μm or more and 1000 μm or less, and taking into consideration handleability and productivity during melt extrusion, it is preferably 5 μm or more and 500 μm or less, more preferably 10 μm or more and 300 μm or less, and even more preferably 20 μm or more and 200 μm or less.

The liquid crystal polyester film of the present invention preferably has a tensile strength of 200 MPa or more in the machine direction (MD direction) and the width direction (TD direction). The tensile strength is more preferably 220 MPa or more, and even more preferably 240 MPa or more. The upper limit of the tensile strength is not particularly limited, but is preferably 500 MPa or less, more preferably 400 MPa or less, and even more preferably 350 MPa or less. If the tensile strength is in the above range, the film has excellent handleability when processed into a laminate for a circuit board suitable for high-speed communication applications, and defects and cracks that occur at the ends of the film can be suppressed.

The liquid crystal polyester film of the present invention preferably has low anisotropy in the machine direction (MD direction) and width direction (TD direction). In particular, the tensile strength F(TD) in the width direction of the film relative to the tensile strength F(MD) in the machine direction of the film (i.e., F(TD)/F(MD)) is preferably 0.5 or more and 1.5 or less, more preferably 0.75 or more and 1.25 or less, even more preferably 0.85 or more and 1.15 or less, and particularly preferably 0.90 or more and 1.10 or less. If the tensile strength F(TD) in the width direction of the film relative to the tensile strength F(MD) in the machine direction of the film is in the above range, the anisotropy of the mechanical and electrical properties of the film is small, and the film can be suitably used for applications such as laminates for circuit boards suitable for high-speed communication applications.

The liquid crystal polyester film of the present invention can be further subjected to a heat treatment to relax the orientation of the molecular chains and improve the dimensional stability of the film. The heat treatment can be a conventionally known method, such as a contact heat treatment or a non-contact heat treatment, and the type is not particularly limited.

[Metal laminate film]
The liquid crystal polyester film of the present invention may be used as a metal laminate film by laminating a metal layer thereon. When laminating the metal layer, the surface of the liquid crystal polyester film on which the metal layer is to be laminated may be subjected to corona discharge treatment, ultraviolet irradiation treatment or plasma treatment in order to increase adhesive strength.

The method of laminating a metal layer on the liquid crystal polyester film of the present invention includes, for example, (1) a method of attaching the liquid crystal polyester film to a metal foil by heat and pressure bonding, (2) a method of attaching the liquid crystal polyester film and the metal foil with an adhesive, and (3) a method of forming a metal layer on the liquid crystal polyester film by vapor deposition. Among them, the lamination method (1) is a method of pressing the liquid crystal polyester film to the metal foil near the flow start temperature of the liquid crystal polyester film using a press or a heated roll, and is recommended because it can be easily performed. Examples of adhesives used in the lamination method (2) include hot melt adhesives and polyurethane adhesives. Among them, epoxy group-containing ethylene copolymers are preferably used as adhesives. Examples of the lamination method (3) include ion beam sputtering, high frequency sputtering, direct current magnetron sputtering, and glow discharge. Among them, the high frequency sputtering method is preferably used.

Examples of metals used in the metal layer include gold, silver, copper, copper alloys, nickel, nickel alloys, aluminum, aluminum alloys, iron, and iron alloys. Copper is preferred for tab tapes and circuit boards, and aluminum is preferred for capacitors. Examples of the structure of the metal laminate film thus obtained include a two-layer structure of a liquid crystal polyester film and a metal layer, a three-layer structure in which metal layers are laminated on both sides of a liquid crystal polyester film, and a five-layer structure in which liquid crystal polyester films and metal layers are alternately laminated. The laminate may be heat-treated as necessary to achieve high strength. The thickness of the metal layer is not particularly limited, but is preferably 1.5 to 1000 μm, more preferably 2 to 500 μm, even more preferably 5 to 150 μm, and particularly preferably 7 to 100 μm. If the thickness is thinner than this range, the mechanical strength is poor, and if the thickness is thicker than the above range, the handling and processability are poor.

[Circuit board]
The circuit board of the present invention includes at least one conductor layer and at least one insulator (or dielectric) layer, and the form is not particularly limited as long as the liquid crystal polyester film of the present invention is used as the insulator (or dielectric), and it can be used as various high-frequency circuit boards by known or conventional means. The circuit board may be a circuit board (or a semiconductor element mounting board) on which a semiconductor element (e.g., an IC chip) is mounted.

The conductor layer used in the circuit board of the present invention is formed, for example, from a metal having at least electrical conductivity, and a circuit pattern is formed on this conductor layer using a known circuit processing method. The conductor forming the conductor layer may be any of various metals having electrical conductivity, such as gold, silver, copper, iron, nickel, aluminum, or alloy metals thereof. In addition, a circuit pattern may be formed on the metal layer portion of the above-mentioned metal laminate film.

The present invention will now be described in further detail with reference to the following examples, but the present invention is not limited to the following examples.

The following resins were used in the examples and comparative examples.
LCP (1): A thermoplastic liquid crystal polyester consisting of a constitutional unit derived from p-hydroxybenzoic acid, a constitutional unit derived from 6-hydroxy-2-naphthoic acid, and a constitutional unit derived from terephthalic acid (LAPEROS (registered trademark) C950RX manufactured by Polyplastics Co., Ltd., melting point: 320°C).
LCP (2): A thermoplastic liquid crystal polyester consisting of a constitutional unit derived from p-hydroxybenzoic acid and a constitutional unit derived from 6-hydroxy-2-naphthoic acid (LAPEROS (registered trademark) A950RX manufactured by Polyplastics Co., Ltd., melting point: 280°C).
LCP (3): A thermoplastic liquid crystal polyester consisting of a constitutional unit derived from p-hydroxybenzoic acid, a constitutional unit derived from 4,4'-dihydroxybiphenyl, and a constitutional unit derived from terephthalic acid (Zaidar (registered trademark) CX-2199, manufactured by ENEOS Liquid Crystal Corporation, melting point: 280°C).
LCP (4): Thermoplastic liquid crystal polyester (UENO LCP (registered trademark) A8100, manufactured by Ueno Pharmaceutical Co., Ltd., melting point: 220°C)

(1) Production of resin composition After premixing the thermoplastic liquid crystal polyester in the ratio described in Table 1, the mixture was granulated using a twin-screw extruder (manufactured by Toshiba Machine Co., Ltd., model: TEM-18SS-12/2V) at a cylinder temperature of 330°C and an extrusion rate of 10 kg/h to obtain pellets of the liquid crystal polyester resin composition, which were used in the following measurements.

(2) Measurement of melt viscosity ratio Using a Capillograph (manufactured by Toyo Seiki Co., Ltd., model: Capillograph F1), measurements were performed using a die with a nozzle diameter of .1 mm and a nozzle length of 10 mm. Under conditions of shear rates of 6 to 2430 sec ^-1 , the melt viscosity (μ _Tm ) at the melting point of the thermoplastic liquid crystal polyester (A) and the melt viscosity (μ _Tm+10 ) at the melting point of the thermoplastic liquid crystal polyester (A) + 10 ° C. were measured, and the melt viscosity ratio was calculated from the following formula. The measurement results of the melt viscosity ratio are shown in Table 1.
Melt viscosity ratio = melt viscosity at the melting point of thermoplastic liquid crystal polyester (A) (μ _Tm ) / melt viscosity at the melting point of thermoplastic liquid crystal polyester (A) + 10°C (μ _{Tm + 10} )
The melt viscosity ratios of the liquid crystal polyester resin compositions obtained above and the thermoplastic liquid crystal polyester resins (reference examples) used in the examples and comparative examples were measured based on the melting point of LCP (1).

(3) Manufacture of film by inflation extrusion molding The liquid crystal polyester resin composition obtained above and each thermoplastic liquid crystal polyester are heated and kneaded in a single screw extruder, melt extruded from a circular inflation die (diameter 25 mm) at a discharge rate of 3 kg/h, and stretched under the conditions of draft ratio = 2 and blow ratio = 5, and a liquid crystal polyester film with a thickness of 50 μm is obtained by inflation extrusion molding. The film formability and tensile strength of the film obtained by the following evaluation method are shown in Table 2.

(Film-forming: bubble holes)
When a film was produced by inflation extrusion molding, the appearance of bubbles of molten resin extruded from a die was visually observed and evaluated according to the following criteria.
○: No holes in the bubble △: Small holes in the bubble (Air escapes from inside the bubble, making the bubble shape unstable)
×: Holes were formed in the bubbles, and stable film formation was not possible (tensile strength)
In accordance with ASTM D882, a sample cut to a size of 190 mm x 15 mm was measured using an Autograph AGS-500NX (manufactured by Shimadzu Corporation) at a tensile speed of 12.5 mm/min and a chuck distance of 125 mm. The measurement temperature was 23°C. Measurements were performed in both the machine direction (MD) and the width direction (TD) of the film.

The liquid crystal polyester films of Examples 1 to 6, which are made of a resin composition in which a thermoplastic liquid crystal polyester (A) consisting of a structural unit derived from p-hydroxybenzoic acid having a melting point of 320°C, a structural unit derived from 6-hydroxy-2-naphthoic acid, and a structural unit derived from terephthalic acid is blended with a thermoplastic liquid crystal polyester (B) consisting of a structural unit derived from p-hydroxybenzoic acid having a melting point of 280°C and a structural unit derived from 6-hydroxy-2-naphthoic acid at 3, 5, 10, 20, 30, and 50% by weight, show that the melt viscosity of the resin composition is low in dependence on temperature and shear rate, and the film forming processability of the film by inflation extrusion molding is improved even at a stretching ratio with a blow ratio exceeding 4.0. In particular, the liquid crystal polyester films made of the liquid crystal polyester resin compositions of Examples 2 to 5 showed stable film formation without holes in the bubbles of the molten resin extruded from the die. Furthermore, the liquid crystal polyester films of Examples 1 to 6 maintained the excellent mechanical properties, electrical properties, and heat resistance that thermoplastic liquid crystal polyesters having a melting point of 300° C. or higher have, and also showed small anisotropy in tensile strength.

The liquid crystal polyester film of Example 7, which is a resin composition obtained by blending 10% by weight of a thermoplastic liquid crystal polyester (B) consisting of a structural unit derived from p-hydroxybenzoic acid having a melting point of 280°C, a structural unit derived from 4,4'-dihydroxybiphenyl, and a structural unit derived from terephthalic acid with a thermoplastic liquid crystal polyester (A) consisting of a structural unit derived from p-hydroxybenzoic acid having a melting point of 320°C, a structural unit derived from 6-hydroxy-2-naphthoic acid, and a structural unit derived from terephthalic acid, showed that the resin composition had a low dependency of melt viscosity on temperature and shear rate, and showed improved film-forming processability by inflation extrusion even at a stretch ratio exceeding 4.0 in blow ratio, and stable film formation was possible without holes in the bubbles of the molten resin extruded from the die. In addition, the liquid crystal polyester film of Example 7 maintained the excellent mechanical properties, electrical properties, and heat resistance of a thermoplastic liquid crystal polyester having a melting point of 300°C or more, and showed small anisotropy in tensile strength.

The liquid crystal polyester film of Comparative Example 1, which is made of a resin composition in which a thermoplastic liquid crystal polyester (A) with a melting point of 320°C is blended with 5% by weight of a thermoplastic liquid crystal polyester (B) with a melting point of 220°C, showed results in which the melt viscosity of the resin composition is highly dependent on temperature and shear rate, and holes were generated in the bubbles of the molten resin extruded from the die at a stretch ratio exceeding 4.0, resulting in the inability to stably produce a film. In addition, the liquid crystal polyester film of Comparative Example 1 showed a large anisotropy in tensile strength, even though the stretch ratio was greater than 4.0.

The liquid crystal polyester film of Reference Example 1, which is made only of a thermoplastic liquid crystal polyester with a melting point of 320°C, showed results in which the melt viscosity was highly dependent on temperature and shear rate, and at stretching ratios exceeding a blow ratio of 4.0, bubble holes occurred in the molten resin extruded from the die, the bubble shape became unstable, and stable film production was not possible.

The liquid crystal polyester film of Reference Example 2, which is made only of a thermoplastic liquid crystal polyester with a melting point of 280°C, was capable of producing a stable film without holes in the bubbles of molten resin extruded from the die at a stretching ratio exceeding 4.0 in blow ratio, but it had a low melting point and showed poor solder reflow properties.

As described above, the liquid crystal polyester film obtained by the present invention is used for electrical insulation of motors and transformers, element formation film of flexible solar cells, etc., taking advantage of its excellent electrical properties, dimensional stability, heat resistance, etc. It can also be used in the acoustic field, such as surface protection films and diaphragms.
The metal laminate film of the present invention can also be used for circuit boards, capacitors, electromagnetic wave shielding materials, etc. The circuit board of the present invention may be used for various transmission lines and antennas (for example, microwave or millimeter wave antennas), and may also be used for antenna devices in which an antenna and a transmission line are integrated.

Claims (11)

A liquid crystal polyester-based resin composition comprising a thermoplastic liquid crystal polyester (A) and a thermoplastic liquid crystal polyester (B), wherein the difference in melting point between the thermoplastic liquid crystal polyester (A) and the thermoplastic liquid crystal polyester (B) is 5°C or more and 95°C or less, the thermoplastic liquid crystal polyester (A) comprises a constitutional unit derived from p-hydroxybenzoic acid and a constitutional unit derived from 6-hydroxy-2-naphthoic acid, and the thermoplastic liquid crystal polyester (B) comprises either a constitutional unit derived from p-hydroxybenzoic acid and a constitutional unit derived from 6-hydroxy-2-naphthoic acid, or a constitutional unit derived from p-hydroxybenzoic acid and a constitutional unit derived from 4,4'-dihydroxybiphenyl, the blending ratio of the thermoplastic liquid crystal polyester (A) to the thermoplastic liquid crystal polyester (B) is (A):(B)=40 to 98% by weight:2 to 60% by weight, and the melt viscosity (μ _Tm ) at the melting point of the thermoplastic liquid crystal polyester (A) measured under the condition of a shear rate of 122 sec ^-1 and the shear rate of 122 sec A liquid crystal polyester resin composition characterized in that the melt viscosity ratio R ₁₂₂ (μ _Tm /μ _Tm+10 ) to the melt viscosity (μ _Tm+ 10 ) at a melting point of the thermoplastic liquid crystal polyester (A ⁾ + 10°C measured under conditions of -1 is less than 3.4, and the liquid crystal polyester resin composition is used for inflation extrusion molding. A liquid crystal polyester-based resin composition comprising a thermoplastic liquid crystal polyester (A) and a thermoplastic liquid crystal polyester (B), wherein the difference in melting point between the thermoplastic liquid crystal polyester (A) and the thermoplastic liquid crystal polyester (B) is 5°C or more and 95°C or less, the thermoplastic liquid crystal polyester (A) comprises a constitutional unit derived from p-hydroxybenzoic acid and a constitutional unit derived from 6-hydroxy-2-naphthoic acid, and the thermoplastic liquid crystal polyester (B) comprises either a constitutional unit derived from p-hydroxybenzoic acid and a constitutional unit derived from 6-hydroxy-2-naphthoic acid, or a constitutional unit derived from p-hydroxybenzoic acid and a constitutional unit derived from 4,4'-dihydroxybiphenyl, the blending ratio of the thermoplastic liquid crystal polyester (A) to the thermoplastic liquid crystal polyester (B) is (A):(B)=40 to 98% by weight:2 to 60% by weight, and the melt viscosity (μ _Tm ) at the melting point of the thermoplastic liquid crystal polyester (A) measured under the condition of a shear rate of 1216 sec ^-1 and the shear rate of 1216 sec The melt viscosity ratio R ₁₂₂ (μ _Tm /μ _Tm+10 ) of the melt viscosity (μ _{Tm ) at the melting point of the thermoplastic liquid crystal polyester (A) measured under a shear rate of 122 sec-1 to the melt viscosity (μ Tm+10} ⁾ at the melting point of the thermoplastic liquid crystal polyester (A) measured under a shear rate of 122 sec ^{-1 to} the melt viscosity ratio R ₁₂₁₆ (μ _Tm /μ Tm+10 ) of the melt viscosity (μ _{Tm + 10} ) at the melting point of the thermoplastic liquid crystal polyester (A) measured under a shear rate of ₁₂₂ sec- ₁ is 1.5 or less, and the liquid crystal polyester resin composition is characterized in that it is used for inflation extrusion molding . A liquid crystal polyester-based resin composition comprising a thermoplastic liquid crystal polyester (A) and a thermoplastic liquid crystal polyester (B), wherein the difference in melting point between the thermoplastic liquid crystal polyester (A) and the thermoplastic liquid crystal polyester (B) is 5°C or more and 95°C or less, the thermoplastic liquid crystal polyester (A) comprises a constitutional unit derived from p-hydroxybenzoic acid and a constitutional unit derived from 6-hydroxy-2-naphthoic acid, and the thermoplastic liquid crystal polyester (B) comprises either a constitutional unit derived from p-hydroxybenzoic acid and a constitutional unit derived from 6-hydroxy-2-naphthoic acid, or a constitutional unit derived from p-hydroxybenzoic acid and a constitutional unit derived from 4,4'-dihydroxybiphenyl, the blending ratio of the thermoplastic liquid crystal polyester (A) to the thermoplastic liquid crystal polyester (B) is (A):(B)=40 to 98% by weight:2 to 60% by weight, and the melt viscosity (μ _Tm ) at the melting point of the thermoplastic liquid crystal polyester (A) measured under each shear rate condition within a shear rate range of 122 to 2430 sec ^-1 is a melt viscosity ratio R (μ _Tm /μ Tm _{+ 10 ) between the melt viscosity at the melting point of the thermoplastic liquid crystal polyester (A) and the melt viscosity (μ Tm+10 ) at a melting point of the thermoplastic liquid crystal polyester (A) +} 10°C, the difference (variation) between the maximum and minimum values being less than 1.2, and the liquid crystal polyester resin composition is suitable for use in inflation extrusion molding . A liquid crystal polyester-based resin composition comprising a thermoplastic liquid crystal polyester (A) and a thermoplastic liquid crystal polyester (B), wherein the difference in melting point between the thermoplastic liquid crystal polyester (A) and the thermoplastic liquid crystal polyester (B) is 5°C or more and 95°C or less, the thermoplastic liquid crystal polyester (A) comprises a constitutional unit derived from p-hydroxybenzoic acid and a constitutional unit derived from 6-hydroxy-2-naphthoic acid, and the thermoplastic liquid crystal polyester (B) comprises either a constitutional unit derived from p-hydroxybenzoic acid and a constitutional unit derived from 6-hydroxy-2-naphthoic acid, or a constitutional unit derived from p-hydroxybenzoic acid and a constitutional unit derived from 4,4'-dihydroxybiphenyl, the blending ratio of the thermoplastic liquid crystal polyester (A) to the thermoplastic liquid crystal polyester (B) is (A):(B)=40 to 98% by weight:2 to 60% by weight, and the melt viscosity (μ _Tm ) at the melting point of the thermoplastic liquid crystal polyester (A) measured under each shear rate condition within a shear rate range of 6 to 2430 sec ^-1 is a melt viscosity ratio R (μ _Tm /μ Tm _{+ 10 ) between the melt viscosity at the melting point of the thermoplastic liquid crystal polyester (A) and the melt viscosity (μ Tm+10 ) at a melting point of the thermoplastic liquid crystal polyester (A) + 10} °C, the difference (variation) between the maximum and minimum values being less than 3.4, and the liquid crystal polyester resin composition is characterized in that it is suitable for use in inflation extrusion molding . A liquid crystal polyester resin composition according to any one of claims 1 to 4, characterized in that the melting point of the thermoplastic liquid crystal polyester (A) is 300°C or higher, and the melting point of the thermoplastic liquid crystal polyester (B) is less than 300°C. The liquid crystal polyester resin composition according to any one of claims 1 to 4, characterized in that the blending ratio of the thermoplastic liquid crystal polyester (A) and the thermoplastic liquid crystal polyester (B) is (A):(B)=60-96% by weight:4-40% by weight . A liquid crystal polyester film comprising the resin composition according to any one of claims 1 to 4 . The liquid crystal polyester film according to claim 7 , characterized in that, when F (MD) is the tensile strength in the machine direction of the film and F (TD) is the tensile strength in the width direction of the film, 0.75≦F (TD) / F (MD) ≦ 1.25. 9. The method for producing a liquid crystal polyester film according to claim 8, wherein the film is produced by inflation extrusion. 8. A metal laminate film, comprising the liquid crystal polyester film according to claim 7 , and a metal layer laminated on one or both sides of the liquid crystal polyester film. A circuit board comprising at least one conductor layer and the thermoplastic liquid crystal polyester film according to claim 7 .