阅读说明：本技术 复合片 (Composite sheet ) 是由 铃木潮 渡边哲哉 服部雄一朗 井出润也 水光俊介 针井知明 殿森富美夫 岩崎好博 宫 于 2019-10-18 设计创作，主要内容包括：本发明涉及复合片,其是由液晶性聚酯纤维制成的织物的一面或两面被包含热塑性树脂的涂层材料覆盖的复合片,其中,该复合片在该织物的经纱方向上的拉伸强度为300N/cm以上,该热塑性树脂的质量相对于该织物的质量的比率为5～25质量％。(The present invention relates to a composite sheet, wherein one or both sides of a woven fabric made of liquid crystalline polyester fibers are covered with a coating material containing a thermoplastic resin, wherein the tensile strength of the composite sheet in the warp direction of the woven fabric is 300N/cm or more, and the ratio of the mass of the thermoplastic resin to the mass of the woven fabric is 5 to 25% by mass.)

1. A composite sheet in which one or both sides of a fabric made of liquid crystalline polyester fibers are covered with a coating material containing a thermoplastic resin, wherein,

the composite sheet has a tensile strength of 300N/cm or more in the warp direction of the woven fabric, and the ratio of the mass of the thermoplastic resin to the mass of the woven fabric is 5 to 25% by mass.

2. The composite sheet of claim 1,

the thermoplastic resin is selected from a polyurethane resin and an acrylic resin.

3. The composite sheet of claim 1 or 2,

the composite sheet has a tensile strength of 50N/cm or more in a direction at 45 DEG to the warp direction of the fabric.

4. The composite sheet of any one of claims 1 to 3, wherein the composite sheet has a thickness of 10 to 400 μm.

5. The composite sheet according to any one of claims 1 to 4, wherein the composite sheet has a tensile strength per unit thickness in a warp direction of the fabric of 3.0N/cm/μm or more.

6. The composite sheet according to any one of claims 1 to 5, wherein the liquid crystalline polyester fiber is a multifilament.

7. The composite sheet of any of claims 1-6, wherein the composite sheet has an open area of less than 50%.

8. The composite sheet of any one of claims 1 to 7, wherein the composite sheet has a B value of bending stiffness of 4.90 x 10^-2N·cm²Less than/cm.

Technical Field

The present invention relates to a composite sheet in which one or both sides of a fabric made of liquid crystalline polyester fibers are covered with a coating material containing a thermoplastic resin.

Background

In recent years, technological progress in the field of microelectronics has attracted attention, and miniaturization and weight reduction are strongly demanded for portable electronic devices and the like. Further, in the members constituting the device, it is necessary to prevent the members constituting the members from being largely bent and coming into contact with other internal members or from being broken when a load is applied from the outside, and therefore, it is required to achieve both high strength and thinning.

As a film for electronic components, a polyimide film has been widely used because of its heat resistance, dimensional stability, flexibility, high bendability, and suitable thin film properties (patent document 1). As a protective sheet, patent document 2 proposes a composite sheet including: the composite sheet is formed by integrating the thermoplastic resin layer and the fabric-like sheet by partially impregnating the opening of the fabric-like sheet with the resin-containing material containing a resin component including a thermoplastic polyurethane resin, and the composite sheet exhibits a good balance among strength, rigidity, and heat resistance of the fabric-like sheet, and various properties of flexibility, low-temperature properties, and heating tackiness of the thermoplastic polyurethane resin. Patent document 3 proposes a composite sheet in which thermoplastic polyurethane sheets are located on both sides of a glass fiber, the thermoplastic polyurethane sheets on both sides are filled in the space of the glass fiber, and thermoplastic polyurethane is bonded to the space of the glass fiber through the glass fiber, and the thermoplastic polyurethane sheets are integrated as a whole, and in the composite sheet, the thermoplastic polyurethane sheets arranged on both sides are filled in the space of the glass fiber, and the thermoplastic polyurethane is bonded to the space of the glass fiber through the glass fiber, so that the whole sheet is integrated, and thereby a composite sheet having high tear strength, high dimensional stability, and good handling properties is obtained.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2016-183224

Patent document 2: japanese patent laid-open publication No. 2011-121284

Patent document 3: japanese patent laid-open publication No. 2013-126749

Disclosure of Invention

Problems to be solved by the invention

However, in the composite sheet of patent document 2, since fibers selected from polyester, nylon, and polypropylene are used in the woven fabric sheet, the fibers themselves have low strength and the strength as the composite sheet is insufficient, although the composite sheet has excellent flexibility and exhibits durability.

In addition, in the composite sheet of patent document 3, since glass fibers are used in order to achieve both tear strength and dimensional stability, the composite sheet has a high specific gravity and insufficient flexibility, and there are problems in weight reduction and durability. Further, since the composite sheet is produced by laminating a thermoplastic polyurethane sheet to a cloth made of glass fiber, there is a limit to the formation of a thin layer of the composite sheet.

Accordingly, an object of the present invention is to provide a composite sheet that is lightweight and has high strength, excellent flexibility, and high bending resistance.

Means for solving the problems

The present inventors have made detailed studies to solve the above problems, and have completed the present invention. That is, the present invention includes the following suitable embodiments.

[1] A composite sheet in which one or both sides of a fabric made of liquid crystalline polyester fibers are covered with a coating material containing a thermoplastic resin, wherein,

the composite sheet has a tensile strength of 300N/cm or more in the warp direction of the woven fabric, and the ratio of the mass of the thermoplastic resin to the mass of the woven fabric is 5 to 25% by mass.

[2] The composite sheet according to item [1], wherein the thermoplastic resin is selected from a polyurethane resin and an acrylic resin.

[3] The composite sheet according to the above [1] or [2], wherein a tensile strength of the composite sheet in a direction of 45 ° with respect to a warp direction of the fabric is 50N/cm or more.

[4] The composite sheet according to any one of the above [1] to [3], wherein the thickness of the composite sheet is 10 to 400 μm.

[5] The composite sheet according to any one of the above [1] to [4], wherein the composite sheet has a tensile strength per unit thickness in a warp direction of the fabric of 3.0N/cm/μm or more.

[6] The composite sheet according to any one of the above [1] to [5], wherein the liquid crystalline polyester fiber is a multifilament.

[7] The composite sheet according to any one of the above [1] to [6], wherein an aperture ratio of the composite sheet is less than 50%.

[8]According to the above [1]～[7]The composite sheet of any one of claims, wherein the composite sheet has a bending stiffness B value of 4.90 x 10^-2N·cm²Less than/cm.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention can provide a composite sheet which is lightweight and has high strength, excellent flexibility, and high bending resistance.

Detailed Description

The composite sheet is a composite sheet in which one or both sides of a woven fabric formed of liquid crystalline polyester fibers are covered with a coating material containing a thermoplastic resin, wherein the tensile strength of the composite sheet in the warp direction of the woven fabric is 300N/cm or more, and the ratio of the mass of the thermoplastic resin to the mass of the woven fabric is 5 to 25% by mass.

< liquid crystalline polyester fiber >

The "liquid crystalline polyester fiber" of the present invention can be produced by melt-spinning a liquid crystalline polyester. The liquid crystalline polyester is a polyester showing optical anisotropy (liquid crystallinity) in a melt phase, and can be confirmed, for example, by heating a sample on a heating stage under a nitrogen atmosphere and observing transmitted light of the sample. The liquid crystalline polyester is formed of a repeating structural unit derived from, for example, an aromatic diol, an aromatic dicarboxylic acid, an aromatic hydroxycarboxylic acid, or the like, and the chemical structure of the structural unit is not particularly limited as long as the effect of the present invention is not impaired. The liquid crystalline polyester may contain a structural unit derived from an aromatic diamine, an aromatic hydroxylamine, or an aromatic aminocarboxylic acid within a range not detrimental to the effects of the present invention.

For example, the preferable structural units are shown in table 1.

[ Table 1]

(wherein X in the formula is selected from the following structures)

(wherein m is 0 to 2, and Y is a substituent selected from the group consisting of hydrogen, a halogen atom, an alkyl group, an aryl group, an aralkyl group, an alkoxy group, an aryloxy group, and an aralkyloxy group)

Here, Y is present in the number of 1 to the maximum number of substitutable aromatic rings, and is independently selected from a hydrogen atom, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (e.g., a 1 to 4 carbon atom alkyl group such as a methyl group, an ethyl group, an isopropyl group, a tert-butyl group, etc.), an alkoxy group (e.g., a methoxy group, an ethoxy group, an isopropoxy group, a n-butoxy group, etc.), an aryl group (e.g., a phenyl group, a naphthyl group, etc.), an aralkyl group [ benzyl (phenylmethyl) group, phenethyl (phenylethyl) group, etc.), an aryloxy group (e.g., a phenoxy group, etc.), an aralkyloxy group.

More preferred examples of the structural units include those described in examples (1) to (18) shown in tables 2, 3 and 4 below. When the structural unit in the formula is a structural unit that can represent a plurality of structures, two or more of such structural units may be used in combination as a structural unit constituting the polymer.

[ Table 2]

[ Table 3]

[ Table 4]

In the structural units in tables 2, 3 and 4, n is an integer of 1 or 2, and each structural unit n-1 and n-2 may be present alone or in combination; y is₁And Y₂May each independently be a hydrogen atom, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (e.g., a methyl group, an ethyl group, an,Alkyl group having 1 to 4 carbon atoms such as ethyl group, isopropyl group, tert-butyl group, etc.), alkoxy group (e.g., methoxy group, ethoxy group, isopropoxy group, n-butoxy group, etc.), aryl group (e.g., phenyl group, naphthyl group, etc.), aralkyl group [ benzyl group (phenylmethyl group), phenethyl group (phenylethyl group), etc. ]]An aryloxy group (e.g., phenoxy group, etc.), an aralkyloxy group (e.g., benzyloxy, etc.), and the like. Among them, preferable examples of Y include a hydrogen atom, a chlorine atom, a bromine atom, and a methyl group.

Further, as Z, a substituent represented by the following formula can be mentioned.

[ chemical formula 1]

The preferred liquid crystalline polyester preferably has two or more naphthalene skeletons as a structural unit. Particularly preferably, the liquid crystalline polyester contains both a structural unit (a) derived from hydroxybenzoic acid and a structural unit (B) derived from hydroxynaphthoic acid. For example, the structural unit (a) may be represented by the following formula (a), the structural unit (B) may be represented by the following formula (B), and the ratio of the structural unit (a) to the structural unit (B) may be preferably 9/1 to 1/1, more preferably 7/1 to 1/1, and still more preferably 5/1 to 1/1, from the viewpoint of facilitating improvement of melt moldability.

[ chemical formula 2]

[ chemical formula 3]

The total of the structural unit of (a) and the structural unit of (B) may be, for example, 65 mol% or more, more preferably 70 mol% or more, and still more preferably 80 mol% or more, based on the total structural units. Among the polymers, a liquid crystalline polyester having a structural unit of (B) of 4 to 45 mol% is particularly preferable.

The melting point of the liquid crystalline polyester suitably used in the present invention is preferably 250 to 360 ℃, more preferably 260 to 320 ℃. Here, the melting point is a main absorption peak temperature measured by a differential scanning calorimeter (DSC; TA3000, manufactured by Mettler-Toledo Co., Ltd.) in accordance with JIS K7121 test method. Specifically, in the DSC apparatus, 10 to 20mg of a sample was taken and sealed in an aluminum pan, and then nitrogen gas as a carrier gas was introduced at 100 cc/min to measure the endothermic peak at 20 ℃/min of temperature rise. When a clear peak is not observed in the first (1st run) in DSC measurement, depending on the type of polymer, the temperature may be raised to a temperature 50 ℃ higher than the expected flow temperature at a temperature rise rate of 50 ℃/min, held at that temperature for 3 minutes, cooled to 50 ℃ at a temperature fall rate of-80 ℃/min after complete melting, and then the endothermic peak may be measured at a temperature rise rate of 20 ℃/min.

The liquid crystalline polyester may be added with a thermoplastic polymer such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyamide, polyphenylene sulfide, polyether ether ketone, and fluororesin, within a range not to impair the effects of the present invention. In addition, various additives such as inorganic substances such as titanium oxide, kaolin, silica, and barium oxide, colorants such as carbon black, dyes, and pigments, antioxidants, ultraviolet absorbers, and light stabilizers may be added.

The liquid crystalline polyester fiber contained in the composite sheet of the present invention can be produced by melt-spinning the liquid crystalline polyester by a conventional method. The spinning is usually carried out at a temperature of 10 to 50 ℃ higher than the melting point of the liquid crystalline polyester. The spun fiber may be heat treated. The solid-phase polymerization (sometimes accompanied by a partial crosslinking reaction) occurs by the heat treatment, and the strength and the elastic modulus are improved, and the melting point is further increased.

The heat treatment may be performed in an inert gas atmosphere such as nitrogen, an oxygen-containing active gas atmosphere such as air, or under reduced pressure. The heat treatment is preferably performed in a gas atmosphere of a gas having a dew point of-40 ℃ or lower. Preferable temperature conditions include a temperature condition in which the temperature is raised in order from the melting point of the liquid crystalline polyester fiber or less. The heat treatment may be performed for several seconds to several tens of hours depending on the target performance. The heat treatment is usually performed in the state of fibers, but may be performed in the state of a fabric if necessary.

The liquid crystalline polyester fiber in the present invention may be either monofilament or multifilament. The liquid crystalline polyester fiber is preferably a multifilament from the viewpoint of easily obtaining high tensile strength of the composite sheet and easily adjusting the thickness and the aperture ratio of the composite sheet by a thinning treatment after the composite sheet is made into a woven fabric.

When the liquid crystalline polyester fiber is a multifilament, the single yarn fineness of the liquid crystalline polyester fiber is preferably 0.1 to 50dtex, more preferably 1 to 20dtex, and particularly preferably 1 to 10 dtex. When the single yarn fineness is within the above range, breakage of the fibers is less likely to occur in the production of the liquid crystal polyester fiber and the woven fabric, and sufficient adhesiveness to the thermoplastic resin (i.e., tensile strength and bending resistance of the composite sheet) is easily obtained. The total fineness is, for example, 10 to 10000dtex, preferably 10 to 5000dtex, and more preferably 50 to 3000dtex (particularly 70 to 2000 dtex). The number of filaments is, for example, 2 to 500, preferably 3 to 300, and more preferably 5 to 200. When the total fineness and the number of filaments are within the above ranges, both lightweight property and high strength of the composite sheet can be easily achieved.

Although the multifilament may be subjected to weak twisting, substantially no twisting is preferred. Further, the multifilament may be subjected to a splitting treatment and/or a smoothing treatment. By producing a woven fabric using the multifilament yarn subjected to the opening treatment and/or the smoothing treatment, the woven fabric can be thinned, and the ratio of the woven fabric to the thermoplastic resin, which will be described later, can be easily adjusted to an appropriate range.

As the "liquid crystalline polyester fiber", a commercially available product can be used. Examples of such commercially available products include Vectran UM (trade name) manufactured by Coli, Inc., Vectran HT (trade name) manufactured by Coli, Inc., Ciberus (trade name) manufactured by Toray Industries, Inc., and Zxion (trade name) manufactured by KB Seiren, Inc.

The liquid crystalline polyester fibers may be used alone or in combination.

The liquid crystalline polyester fiber may be included in the composite sheet of the present invention in the form of a fabric. Thus, the composite sheet of the present invention can have excellent tensile strength and thin layer properties (lightweight property). The 1 composite sheet includes 1 woven fabric, and the composite sheet is not generally used in a stacked manner from the viewpoint of lightweight.

Examples of the woven fabric include: a woven fabric (I) in which monofilaments or multifilaments made of liquid crystalline polyester fibers are interwoven as warp yarns and weft yarns; and a woven fabric (II) comprising at least 1 layer in which monofilaments or multifilaments made of liquid crystalline polyester fibers are arranged in parallel with each other, wherein the filaments are connected together by auxiliary filaments without being entangled with each other.

Examples of the weave (I) include plain weave, twill weave, and satin weave. From the viewpoint of being less dependent on the stretching direction and easily obtaining higher tensile strength, a plain weave is preferable.

As the fabric weave (II), for example: a unidirectional fabric (for example, a cord fabric or the like) having a filament layer in which monofilaments or multifilaments made of liquid crystal polyester fibers are arranged in parallel with each other; a multi-layer woven fabric (for example, a bidirectional woven fabric, a triaxial woven fabric, etc.) in which filament layers formed by arranging monofilaments or multifilaments of liquid crystal polyester fibers in parallel with each other are arranged at different angles. Among these, a unidirectional woven fabric is preferable from the viewpoint of lightweight of the composite sheet.

In the weave (II), as described above, the single or multiple yarns formed of the liquid crystal polyester fiber are not interlaced with each other, but are integrated by the auxiliary yarn. The auxiliary yarn is not particularly limited as long as it can connect single or multiple yarns made of liquid crystalline polyester fibers, and examples thereof include yarns made of polyester, nylon, acrylic, polyolefin, polyurethane, or the like.

The state of interlacing of the auxiliary yarn with the monofilament or multifilament formed of the liquid-crystalline polyester fiber is not particularly limited as long as the yarn can be integrated.

The fabric made of the liquid crystalline polyester fiber can be produced by using the liquid crystalline polyester fiber as a warp and a weft and weaving by a usual method.

In weaving, the warp yarns may be subjected to a sizing treatment. By the sizing treatment, even if weaving is performed at a high speed, defects such as defective opening and yarn breakage are not easily generated, and weaving efficiency can be improved. Examples of the paste used for the sizing treatment include pastes containing a polyvinyl alcohol resin and an acrylate resin.

When the sizing treatment is performed, the adhesion between the thermoplastic resin-containing composition for forming the coating material and the woven fabric is reduced, and as a result, it is preferable to remove the paste from the woven fabric before the step of impregnating or adhering the thermoplastic resin-containing composition to the woven fabric in order to eliminate the possibility of reducing the strength and bending resistance of the composite sheet. As a method for removing the paste, a general removal method can be employed, and for example, the paste can be removed by washing with water, a sodium hydroxide solution, a detergent, or the like.

In order to obtain a more homogeneous fabric, it is preferable that the amplitude of the weaving wave (woven wave) formed of the monofilament or multifilament be as small as possible for both the warp and weft in either of the fabric patterns (I) and (II). For example, the amplitude of the weaving wave can be reduced by using the multifilament subjected to the opening treatment and/or the smoothing treatment as described above, or can be reduced by subjecting the woven fabric to the thinning treatment using a roller or the like after the woven fabric is produced as described later.

The weight per unit area of the fabric made of the liquid crystalline polyester fiber may be, for example, 10 to 500g/m²Preferably 15 to 200g/m². The warp density and weft density can be selected appropriately according to the fineness of the raw yarn and the opening ratio, and for example, may be 10 to 200 yarns/2.54 cm (1 inch), and preferably 30 to 150 yarns/2.54 cm. The thickness of the woven fabric may be, for example, 10 to 400 μm, preferably 20 to 200 μm. When the weight per unit area, the warp density, the weft density, and the thickness are within the above ranges, both the lightweight property and the high strength of the composite sheet can be easily achieved.

The fabric formed of the liquid crystalline polyester fiber is preferably subjected to a thinning treatment. Examples of the method of the thinning treatment include the following methods: (1) a method of subjecting the fabric to a tension treatment between rotating rolls or between heating rolls, and (2) a method of subjecting the fabric to a pressure treatment between a heating roll and a nip roll (for example, a method of performing a calendering process). By performing the thinning treatment, the woven fabric or the like is stretched to form a more homogeneous woven fabric, so that high tensile strength and bending resistance of the composite sheet can be easily obtained, and as the woven fabric becomes denser, an appropriate ratio of the woven fabric to the thermoplastic resin described later can be easily obtained, and further, the lightweight property of the composite sheet can be improved.

In the liquid crystal polyester fiber constituting the woven fabric, the ratio of the major axis to the minor axis (major axis/minor axis) of the cross section of the fiber is preferably 1.1 to 3.0. If the above ratio is less than 1.1, the effect of making the sheet thinner may not be obtained, and if it exceeds 3.0, the composite sheet which is the object of the present invention and is excellent in tensile strength and bending resistance may not be obtained due to the occurrence of cracking or breakage. The above ratio is more preferably 1.3 to 2.8.

The above ratio is an average value obtained by taking a cross section of the woven fabric by a Scanning Electron Microscope (SEM), measuring the major and minor diameters of 100 liquid crystalline polyester fibers randomly selected from the cross-sectional photograph, and calculating the ratio of the major diameter/minor diameter of each fiber.

< thermoplastic resin >

As the thermoplastic resin in the present invention, a resin capable of forming a composite sheet by covering one or both surfaces of the woven fabric with a coating material containing the resin can be used. By covering the fabric with a coating material containing a thermoplastic resin, the intersections of the warp and weft of the fabric can be joined by the coating material, and therefore, the composite sheet of the present invention has excellent tensile properties not only in the warp direction and the weft direction, but also in the direction of the diagonal of the weave (for example, the direction of 45 ° with respect to the warp direction). In addition, when the composite sheet of the present invention is joined to another member, for example, when the composite sheet of the present invention is used as a reinforcing member for another member, the coating film of the coating material containing the thermoplastic resin can function as an adhesive for the composite sheet of the present invention and another member, and the joining thereof can be satisfactorily ensured.

Examples of such thermoplastic resins include polyester resins such as polyethylene terephthalate, modified polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polyolefin resins such as polypropylene, modified polypropylene, and polyethylene, polyamide resins such as polyamide 6, polyamide 66, polyamide 12, polyamide 6-12, polyamide 9T, and polyamide 66IT, thermoplastic elastomers such as polycarbonate, polyarylate, polyimide, polyphenylene sulfide, polyether ester ketone, and fluorine resins, and polyurethane resins, acrylic resins, styrene elastomers, and olefin elastomers. These resins may be used alone or in combination of two or more. The thermoplastic resin is preferably selected from a polyurethane resin and an acrylic resin from the viewpoint of easily obtaining a composite sheet having not only excellent tensile properties in the warp direction and the weft direction but also excellent tensile properties in the diagonal direction of the knitting.

< composite sheet >

The composite sheet of the present invention has a tensile strength in the warp direction of the fabric of up to 300N/cm or more. Such high tensile strength can be achieved by the composite sheet of the present invention in which one side or both sides of a woven fabric made of liquid crystalline polyester fibers are covered with a coating material containing a thermoplastic resin. The tensile strength is preferably 400N/cm or more, more preferably 500N/cm or more. The upper limit of the tensile strength is not particularly limited, but is usually 8000N/cm or less, preferably 5000N/cm or less, and more preferably 3000N/cm or less. The composite sheet of the present invention preferably has a tensile strength of 50N/cm or more, more preferably 70N/cm or more, and still more preferably 90N/cm or more in a direction of 45 ° to the warp direction of the woven fabric. The tensile strength in the warp direction and the tensile strength in the direction at 45 ° to the warp direction can be adjusted to the lower limit or more by adjusting the basis weight of the woven fabric, the ratio of the mass of the thermoplastic resin to the mass of the woven fabric, or the opening ratio. The upper limit of the tensile strength in the direction of 45 ° to the warp direction is not particularly limited, but is usually 4000N/cm or less, preferably 2000N/cm or less, more preferably 1000N/cm or less, and particularly preferably 500N/cm or less. The tensile strength in the present invention is a value measured by the method described in the examples described later.

In the present invention, the composite sheet may have a tensile strength of 300N/cm or more and a ratio of 5 to 25 mass% of the thermoplastic resin to the mass of the woven fabric described later, and the coating material containing the thermoplastic resin may cover one surface of the woven fabric or both surfaces thereof. The composite sheet has a woven fabric and a coating material containing a thermoplastic resin integrated with each other by a coating film of the coating material.

In the composite sheet of the present invention, the ratio of the mass of the thermoplastic resin to the mass of the woven fabric (mass of thermoplastic resin/mass of woven fabric) is 5 to 25 mass%. When the ratio is less than 5% by mass, the composite sheet cannot have a desired high strength, and when the ratio is more than 25% by mass, excellent flexibility and bending resistance of the fabric cannot be sufficiently maintained, so that the composite sheet is poor in flexibility and bending resistance and also poor in lightweight property. That is, by setting the above ratio to 25 mass% or less, excellent flexibility and bending resistance of the fabric are maintained in the composite sheet, and therefore the composite sheet of the present invention can have flexibility. The composite sheet of the present invention is not a prepreg. The above ratio is preferably 6 to 25% by mass, and more preferably 8 to 20% by mass. The above ratio can be adjusted to be within the above range by adjusting the basis weight of the fabric, the thinning treatment of the fabric, or the single-side covering or the double-side covering of the fabric. The above ratio can be measured by the method described in the examples described later.

The thickness of the composite sheet of the present invention is preferably 10 to 400 μm, more preferably 20 to 300 μm, and still more preferably 30 to 200 μm. When the thickness of the composite sheet is within the above range, flexibility and lightweight property of the composite sheet can be easily obtained. The thickness of the composite sheet can be adjusted to be within the above range by adjusting the basis weight of the woven fabric, the thinning treatment of the woven fabric, the ratio of the mass of the thermoplastic resin to the mass of the woven fabric, or the single-side covering or the double-side covering of the woven fabric. The thickness of the composite sheet can be measured by the method described in the examples described later.

The tensile strength per unit thickness of the composite sheet of the present invention in the warp direction of the woven fabric is preferably 3.0N/cm/μm or more, more preferably 4.0N/cm/μm or more, and still more preferably 5.0N/cm/μm or more. The composite sheet having such a high tensile strength per unit thickness indicates that the composite sheet is high in strength even if it is thin. The tensile strength per unit thickness is not particularly limited, but is usually 800N/cm/μm or less, preferably 500N/cm/μm or less, more preferably 100N/cm/μm or less, and particularly preferably 50N/cm/μm or less.

The aperture ratio of the composite sheet of the present invention is preferably less than 50%, more preferably 30% or less, further preferably 20% or less, and particularly preferably 10% or less. The open area ratio in the present invention means a ratio of a plurality of open portions of the woven fabric (i.e., portions where the coating material is present and the yarns of the woven fabric are absent) to the area occupied by the entire area of the composite sheet. When the aperture ratio of the composite sheet is not more than the above upper limit, the ratio of the mass of the thermoplastic resin to the mass of the woven fabric is not likely to be excessively high, and thus flexibility, bending resistance, and lightweight property of the composite sheet are easily obtained. The opening ratio can be adjusted to be lower than the above upper limit value or lower than the upper limit value by adjusting the basis weight of the fabric, the thinning treatment of the fabric, or the single-side covering or the double-side covering of the fabric. The lower limit of the aperture ratio is not particularly limited. The aperture ratio is usually 0.01% or more. The aperture ratio can be measured by the method described in the examples described later.

From the viewpoint that the composite sheet of the present invention has flexibility, the bending rigidity B value indicating the bending characteristics of the composite sheet is preferably 4.90 × 10^-2N·cm²Less than/cm (5.00gf cm)²/cm or less), more preferably 3.92X 10^-2N·cm²Less than/cm (4.00gf cm)²/cm or less), more preferably 2.94X 10^-2N·cm²Less than/cm (3.00gf cm)²Less than cm), and the hysteresis width (hystersis width)2HB value is preferably 1.08X 10^-2N.cm/cm or less (1.10 gf.cm/cm or less), and furtherPreferably 1.03X 10^-2N · cm/cm or less (1.05gf · cm/cm or less), and more preferably 9.81X 10^{- 3}N · cm/cm or less (1.00gf · cm/cm or less). The bending property in the present invention is a value obtained by digitizing the degree of ease of bending, which is the flexibility of the composite sheet, and the smaller the B value and the 2HB value are, the more easy the bending is and the more excellent the flexibility is. The bending characteristics of the composite sheet can be adjusted to the above upper limit or less by adjusting the composition of the coating material, the basis weight of the fabric, the thinning treatment of the fabric, or the single-side covering or double-side covering of the fabric. Among them, a method of adjusting the bending characteristics to the above upper limit or less by using a thermoplastic resin as a component of the coating material, instead of a thermosetting resin such as an epoxy resin which has been conventionally used, is suitable. The bending characteristics can be measured by the methods described in the examples described below.

< method for producing composite sheet >

The composite sheet of the present invention can be produced by: the liquid crystal polyester fiber is produced by preparing a woven fabric made of liquid crystal polyester fibers, and impregnating or adhering the woven fabric with a composition containing a thermoplastic resin for forming a coating material.

In the preparation step of preparing the woven fabric, the woven fabric may be physically and/or chemically treated as necessary in order to improve the adhesiveness to the composition containing the thermoplastic resin to be impregnated or attached.

Examples of the physical treatment include corona discharge treatment, glow discharge treatment, plasma treatment, electron beam treatment, ultraviolet treatment, heat treatment in an oxygen-containing gas atmosphere, and heat treatment in a moisture-containing gas atmosphere. Examples of the chemical treatment include acid treatment, alkali treatment, and treatment using an oxidizing agent. The chemical treatment may be performed at normal temperature or under heating, and is preferably performed under heating. These treatments may be performed alone or in combination of two or more. Among these treatments, a physical treatment such as an ultraviolet treatment or a heat treatment is preferable from the viewpoint of efficiently producing the composite sheet.

In the ultraviolet treatment, an ultraviolet lamp such as a low-pressure mercury lamp or an excimer lamp can be used. The energy density of the ultraviolet treatment is, for example, 0.1 to 50mW/cm from the viewpoint of improving the adhesiveness without deteriorating the fabric²Preferably 1-40 mW/cm². The irradiation time may be appropriately set according to the energy density, and is, for example, 10 seconds to 10 minutes, preferably 20 seconds to 5 minutes.

In the heat treatment in the oxygen-containing gas atmosphere, the heat treatment may be performed at, for example, 230 to 350 ℃ and preferably 250 to 330 ℃. The heating time is, for example, 1 to 100 hours, preferably 10 to 80 hours.

The method for impregnating or attaching the thermoplastic resin-containing composition to the fabric is not particularly limited, and conventionally known methods such as an impregnation method, a coating method, a transfer method, and the like can be used. Specifically, the following method may be employed: a method of impregnating or attaching a composition containing a thermoplastic resin, which is prepared by dissolving a thermoplastic resin and an optional additive in a solvent, to a fabric and drying the impregnated or attached composition; a method of impregnating or attaching a thermoplastic resin-containing composition containing a thermoplastic resin and an optional additive in a heated and molten state to a woven fabric; a method of fixing a powdery thermoplastic resin to a fabric together with an optional additive; a method in which a layer of a coating material is formed on a film or sheet having releasability and then transferred to a fabric, and the like. When the composition containing a thermoplastic resin impregnated or adhered to a woven fabric is dried, it is preferably dried in a non-contact state by a vertical dryer. The solvent and the additive to be blended in the thermoplastic resin-containing composition according to circumstances are not particularly limited as long as the effects of the present invention are not impaired, and a solvent and an additive that are generally used may be used alone or in combination of two or more. When the thermoplastic resin-containing composition does not contain a solvent or an additive, the thermoplastic resin-containing composition is composed of a thermoplastic resin.

In the composite sheet of the present invention, the ratio of the mass of the thermoplastic resin to the mass of the woven fabric is 5 to 25% by mass. In order to adjust the above ratio or to make the composite sheet thinner (lighter), a part of the impregnated or adhered thermoplastic resin-containing composition may be removed as necessary. The method for removing the thermoplastic resin-containing composition is not particularly limited, and for example, a method using a roll, a doctor blade or the like can be used.

Examples

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

[ measuring method or evaluation method ]

< ratio of mass of thermoplastic resin to mass of woven fabric >

The mass of each woven fabric and the mass of each composite sheet produced in examples and comparative examples were measured, and the mass of the thermoplastic resin in each composite sheet was calculated from these values, and the ratio of the mass of the thermoplastic resin to the mass of the woven fabric was calculated.

Thickness of fabric and thickness of composite sheet

The thickness of the woven fabric and the thickness of the composite sheet were measured at 3 points using a constant-pressure thickness gauge "PG-15J" manufactured by Telock corporation, and the average values were obtained.

< tensile strength and tensile elongation of composite sheet in warp direction >

The tensile strength and tensile elongation were measured on a 1cm wide sample using an Instron model 3365 testing machine manufactured by Instron Japan Company Limited under the conditions of a sample length of 10cm and a test speed of 5 cm/min. The number of measurements was set to N ═ 3, and the average values of the tensile strength and tensile elongation were determined. The sample was cut out so that the sample length was parallel to the warp.

< tensile Strength of composite sheet in 45 DEG Direction >

The tensile strength was measured on a 1cm wide sample using an Instron model 3365 tester manufactured by Instron Japan Company Limited. under conditions of a sample length of 3cm and a test speed of 5 cm/min. The number of measurements was set to N-3, and the average value was obtained. The sample was cut out so that the sample length was parallel to the warp at 45 °.

< bending resistance of composite sheet: MIT bending test >

According to JISP 8115: 2010, the number of cycles until each fracture was measured on a 1cm wide sample using an MIT bending fatigue tester manufactured by toyoyo seiki under conditions of a load of 0.5kgf, a bending speed of 175 times/min, and a bending angle of 270 ° (about 135 ° left and right). The number of measurements was set to N-3, and the average value was obtained. The upper limit number of measurements was set to 6 ten thousand.

< aperture ratio of composite sheet >

Each of the composite sheets produced in examples and comparative examples was observed using a Microscope VHX-5000 manufactured by KEYENCE corporation, and the aperture ratio was calculated by attached image analysis software.

< bending characteristics (bending rigidity B value and hysteresis width 2HB value) >

The bending characteristics were measured using an automated pure bending tester ("KES-FB 2-AUTO-A" manufactured by KATO TECH). Each of the composite sheets produced in examples and comparative examples was cut into 2cm × 22cm so that the weft direction was a long side, and a test piece was produced. At-2.5 cm^-1～+2.5cm^-1A constant speed (deformation speed 0.5 cm) in a range of (2)^-1Second) was subjected to a bending test of the test piece. The bending test was performed for 1 cycle, and the bending stiffness B value per unit length (unit: gf cm) was determined²,/cm) and hysteresis width 2HB values (unit: gf cm/cm). The measurement number was set to N.3, and the average value was obtained and converted to SI units (value of bending stiffness B per unit length: N · cm)²,/cm, hysteresis width 2HB value: n · cm/cm).

Example 1

(1) A liquid crystalline polyester polymer having a ratio (molar ratio) of the structural unit (a) to the structural unit (B) of 75/25 was used. Logarithmic viscosity eta of the polymer_inh5.6dl/g, melting point 281 ℃. The polymer was spun from a spinneret having a nozzle diameter of 0.15 mm. phi. using a commonly used melt spinning apparatus to obtain a 220dtex/40 filament multifilament. The multifilament yarn was put at 270 ℃ in a nitrogen atmosphereThe treatment lasts for 20 hours. The tensile strength of the treated multifilament yarn was 22.2cN/dtex in accordance with JIS L1013.

(2) The treated multifilament yarn was subjected to sizing treatment. A plain woven fabric having a warp density of 35 pieces/2.54 cm and a weft density of 35 pieces/2.54 cm was produced by a usual method using the sized multifilament as the warp and the sized multifilament as the weft. The plain woven fabric was further washed with water to remove the paste used for the sizing treatment from the plain woven fabric. Then, the plain weave fabric was placed between mirror rolls made of stainless steel, and was calendered at a line pressure of 160kg/cm and a temperature of 150 ℃. The weight per unit area and the thickness of the plain woven fabric after calendering are shown in table 5.

(3) A thermoplastic resin-containing composition containing a polyurethane resin and a solvent was applied to the surface of the calendered scrim, and the scrim was dried at 120 ℃ for 5 minutes to produce a composite sheet.

(4) Using the obtained composite sheet, tensile strength and tensile elongation in the warp direction, tensile strength in the 45 ° direction, bending resistance, and open area were evaluated. In addition, the tensile strength per unit thickness of the composite sheet in the warp direction of the plain weave fabric was calculated. The obtained results are shown in table 5.

(5) Further, the adhesiveness of the obtained composite sheet to a hot-melt sheet was investigated. Specifically, a composite sheet having a width of 30mm and a length of 200mm was cut out so that the sample length was parallel to the warp, a hot melt adhesive tape manufactured by San Kasei Kogyo was thermocompression bonded at 140 ℃ for 20 seconds, and the peel strength was measured at a test speed of 200 mm/min under N-1 using a tensile tester (TENSILON RTG-1250). The results are shown in Table 6.

Examples 2 to 4

A composite sheet was produced and evaluated in the same manner as in example 1, except that the filament yarn fineness, the warp yarn density, the weft yarn density, the basis weight of the woven fabric, and the thickness were changed as shown in table 5. The obtained results are shown in table 5.

Example 5

A composite sheet was produced and evaluated in the same manner as in example 1, except that an acrylic resin was used instead of the urethane resin. The obtained results are shown in table 5.

Comparative example 1

A composite sheet was produced and evaluated in the same manner as in example 1, except that the filament yarn fineness, the warp yarn density, the weft yarn density, the basis weight of the woven fabric, and the thickness were changed as shown in table 5. The obtained results are shown in table 5.

Comparative example 2

A plain weave fabric was produced in the same manner as in example 1, except that the thickness of the fabric was changed as shown in table 5. The calendering process carried out in the examples was not carried out, and the plain woven fabric obtained after weaving was evaluated in the same manner as in the composite sheet of example 1. The obtained results are shown in table 5. In addition, the adhesiveness of the obtained plain woven fabric to a hot melt sheet was evaluated in the same manner as in example 1. The results are shown in Table 6.

Comparative examples 3 and 4

The polyimide film having a thickness of 75 μm [ made by Toray DuPont, Kapton (registered trademark) 300H ] and the polyimide film having a thickness of 125 μm [ made by Toray DuPont, Kapton (registered trademark) 500H ] were subjected to conversion of the weight per unit area, the tensile strength (MD direction), the tensile elongation (MD direction), and the tensile strength (MD direction) per unit thickness, respectively, based on the catalog, and the bending resistance was evaluated in the same manner as in example 1. The obtained results are shown in table 5.

Comparative example 5

The steps (1) and (2) of example 1 were carried out to produce a calendered plain woven fabric. The weight per unit area and the thickness are shown in Table 7.

Next, an epoxy resin blend sheet was laminated on the surface of the calendered plain woven fabric, and the laminate sheet was heated at 130 ℃ for 120 minutes to cure the epoxy resin, thereby producing a composite sheet.

The composite sheet using the thermoplastic resin obtained in example 1 and the composite sheet using the thermosetting resin obtained in comparative example 5 were measured for flexural characteristics. The obtained results are shown in table 7.

[ Table 6]

[ Table 7]

As is clear from table 5, in examples 1 to 5, the composite sheet had a small weight per unit area, high tensile strength not only in the warp direction but also in the 45 ° direction, and also high tensile strength per unit thickness, and also excellent bending resistance and flexibility. That is, the composite sheet of the present invention has light weight, high strength, excellent flexibility, and high bending resistance. On the other hand, in comparative example 1, the tensile strength in the warp direction is low and the tensile strength per unit thickness in the warp direction is also low, so that both lightweight property (thinning) and high strength cannot be achieved at the same time, while in comparative example 2, the tensile strength in the 45 ° direction is extremely low although the bending resistance is excellent, and in comparative examples 3 and 4, the results of low tensile strength, tensile strength per unit thickness, and bending resistance are obtained.

As is clear from table 6, in example 1, the coating film of the coating material containing the thermoplastic resin can function as an adhesive for the composite sheet of the present invention and the hot-melt sheet, and can ensure good bonding between them, but in comparative example 2, only low adhesiveness to the hot-melt sheet is exhibited.

As is clear from table 7, in example 1, since the composite sheet was produced using a urethane resin as a thermoplastic resin for the coating material, the sheet had a low value of bending property and a sheet having excellent flexibility was obtained. On the other hand, in comparative example 5, since the composite sheet was produced using the thermosetting resin, that is, the epoxy resin as the coating material, the sheet had a higher value of the bending property and was inferior in flexibility to example 1.

Industrial applicability

The composite sheet of the present invention can be suitably used as a reinforcing member for, for example, a flexible substrate, an interior member, various arms, various frames, various hinges, and the like used in electric/electronic devices.