JPH0435495B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an advanced composite material with high strength, elastic modulus,
Furthermore, the present invention relates to prepregs used in structures that are required to have high specific strength and specific modulus of elasticity, which are obtained by dividing these by specific gravity. More specifically, the present invention relates to a prepreg that provides a structure with markedly improved strength in directions other than the reinforcing fiber direction, that is, non-fiber axial tensile strength and post-impact compressive strength, while ensuring the adhesiveness and flexibility of the prepreg.

[Prior Art] Fiber-reinforced composite materials are heterogeneous materials that have reinforcing fibers and matrix resin as essential components.
Therefore, there is a large difference between the physical properties in the fiber axis direction and the physical properties in other directions. For example, it is known that improving the strength of reinforcing fibers does not lead to drastic improvements because resistance to falling weight impact is controlled by delamination strength. Therefore, in addition to improving the toughness of the matrix resin, various improvements have been proposed for the purpose of improving physical properties in directions other than the fiber axis direction.

USP 3472730 (1969) describes a separate exterior film consisting of a thermosetting resin modified with an elastomeric substance on one or both sides of a fiber-reinforced sheet.
It has been disclosed that the delamination resistance can be improved by disposing a .

JP-A-51-58484 (JP-A-58-31296) discloses that moldability and bending strength can be improved by the presence of a polyether sulfone film on the surface of a fiber-reinforced epoxy resin prepreg. has been done.

In JP-A-54-3879, JP-A-56-115216, and JP-A-60-44334, short fiber chips, chopped strands, and milled fibers are arranged between the layers of a fiber reinforced sheet, It is disclosed that interlaminar strength is improved.

JP-A-60-63229 discloses that an epoxy resin film modified with an elastomer is disposed between the layers of fiber-reinforced prepreg to improve the interlayer strength.

USP 4539253 (1985) (corresponding to Japanese Patent Application Laid-Open No. 60-231738) discloses that nonwoven fabrics, woven fabrics, mats, and carriers are made of epoxy resin modified with elastomer, using lightweight fibers as a base material between layers of fiber-reinforced prepreg. It is disclosed that interlaminar strength can be improved by disposing a resin-impregnated film.

USP 4604319 (1986) (corresponding to Japanese Patent Application Laid-Open No. 60-231738) discloses that interlaminar strength can be improved by disposing a thermoplastic resin film between the layers of fiber-reinforced prepreg.

However, these methods are not only insufficiently effective, but also have their own drawbacks. When an independent outer layer film containing an elastomer-modified thermosetting resin is used, the heat resistance decreases as the elastomer content increases, and the effect of improving interlaminar strength is very small when the elastomer content is low.

In addition, when a thermoplastic resin film is used, it is possible to achieve both heat resistance and interlaminar strength improvement effects by using a thermoplastic resin film with good heat resistance. (stickiness) and drape properties are lost. Moreover, the general drawback of thermoplastic resins, such as poor solvent resistance, is reflected in the composite material.

Furthermore, the use of chopped short fibers or chopped strand milled fibers increases the thickness of the interlayers, resulting in a decrease in the strength of the composite as a whole.

[Problems to be Solved by the Invention] Therefore, the present inventors conducted extensive research on prepregs that do not have the above-mentioned drawbacks and provide excellent impact resistance. Furthermore, by controlling the distribution state of these fine particles, it was possible to obtain a prepreg that had far superior impact resistance than expected, leading to the present invention.

[Means for Solving the Problems] The present invention has the following configuration in order to solve the above problems. In other words, the following components [A], [B], and [C] are required,
More than half of the particulate shapes of component [C] are substantially spherical, and more than 90% of component [C] is distributed from the surface of the prepreg to the thickness of 30% of the thickness of the prepreg.
A prepreg having spherical fine particles characterized in that they are localized within a depth of %.

[A]: Reinforced fiber made of long fibers [B]: Matrix resin [C]: Spherical fine particles made of resin (Description of reinforced fiber made of long fibers) Component [A] of the present invention is made of long fibers It is a reinforcing fiber. The reinforcing fibers used in the present invention are generally used as high-performance reinforcing fibers and have good heat resistance and tensile strength. For example, the reinforcing fibers include carbon fiber, graphite fiber, aramid fiber,
Examples include silicon carbide fiber, alumina fiber, and boron fiber. Among these, carbon fibers and graphite fibers are most suitable for the present invention because they have good specific strength and specific modulus and are recognized to greatly contribute to weight reduction. All kinds of carbon fibers and graphite fibers can be used depending on the purpose, but tensile strength
High strength and high elongation carbon fiber with a tensile elongation of 450 Kgf/mm ² and 1.6% or more is most suitable. Further, although long reinforcing fibers are used in the present invention, the length thereof is preferably 5 cm or more. If it is shorter than that, it will be difficult to fully develop the strength of the reinforcing fibers as a composite material. Further, carbon fibers and graphite fibers may be used in combination with other reinforcing fibers. Furthermore, the reinforcing fibers are not limited in their shape or arrangement, and can be used in, for example, unidirectional, random directional, sheet-like, mat-like, woven-like, or braid-like forms. In particular, for applications that require high specific strength and inelastic modulus, an arrangement in which reinforcing fibers are aligned in a single direction is most suitable, but a cross (woven) arrangement is easier to handle. are also suitable for the present invention.

(Description of matrix resin) Component [B] of the present invention is a matrix resin.

The matrix resin used in the present invention includes thermosetting resins and resins obtained by mixing thermosetting resins and thermoplastic resins.

The thermosetting resin used in the present invention is not particularly limited as long as it is a resin that can be cured by heat or external energy such as light or an electron beam to at least partially form a three-dimensional cured product. Preferred thermosetting resins include epoxy resins, which are generally used in combination with curing agents and curing catalysts. As epoxy resins suitable for the present invention, epoxy resins whose precursors are amines, phenols, and compounds having carbon-carbon double bonds are particularly preferred.

Further, these epoxy resins may be used alone or in an appropriate combination.

Epoxy resins are preferably used in combination with epoxy curing agents. Any compound having an active group capable of reacting with an epoxy group can be used as the epoxy curing agent. Preferably, an amino group,
Compounds having an acid anhydride group or an azide group are suitable.

In the present invention, maleimide resins, resins with acetylene ends, resins with nadic acid ends, resins with cyanate ester ends, resins with vinyl ends, and resins with allyl ends are preferably used as the matrix resin in the present invention. These may be mixed with epoxy resin or other resins as appropriate. Further, a reactive diluent may be used, or a modifier such as a thermoplastic resin or an elastomer may be mixed and used.

A maleimide resin is a compound containing an average of two or more maleimide groups at its terminal ends. As the resin having a cyanate ester terminal, a cyanate ester compound of a polyhydric phenol typified by bisphenol A is suitable. Cyanate ester resin can be made into a resin suitable for prepregs, especially when combined with bismaleimide resin, and Mitsubishi Gas Chemical Co., Ltd.
BT resin is commercially available and suitable for the present invention. These generally have better heat resistance and water resistance than epoxy resins, but are inferior in toughness and impact resistance, so they are selected and used depending on the application. Even if these other thermosetting resins are used in place of the epoxy resin in the present invention, the effects of the present invention are the same. Furthermore, commercially available general-purpose resins are used as the vinyl-terminated resin and the allyl-terminated resin, but their heat resistance is inferior to the former group of resins, so they are mainly used as diluents.

In the present invention, it is also suitable to use a mixture of the above-mentioned thermosetting resin and a thermoplastic resin as the matrix resin. Thermoplastic resins suitable for the present invention are:
Carbon-carbon bonds, amide bonds, imide bonds in the main chain,
It is a thermoplastic resin having bonds selected from ester bonds, ether bonds, carbonate bonds, urethane bonds, urea bonds, thioether bonds, sulfone bonds, imidazole bonds, and carbonyl bonds.

As these thermoplastic resins, commercially available polymers may be used, or so-called oligomers having a lower molecular weight than commercially available polymers may be used. As the oligomer, an oligomer having a functional group capable of reacting with the thermosetting resin at the terminal or in the molecular chain is more preferable.

Mixtures of thermosets and thermoplastics give better results than when they are used alone.
This is because thermosetting resins generally have the disadvantage of being brittle but can be molded at low pressure in an autoclave, while thermoplastic resins have the advantage of being tough but are difficult to mold at low pressure in an autoclave. In order to exhibit contradictory characteristics,
This is because by using a mixture of these, the physical properties and moldability can be balanced.

It is also possible to mix a small amount of inorganic fine particles such as finely powdered silica or an elastomer with the epoxy resin.

(Description of Fine Particles) The fact that component [C] is fine particles has the following advantages. That is, since fine particles exist in a dispersed state in the matrix resin, the tackiness and drape properties of the matrix resin are reflected in the prepreg properties, resulting in a prepreg with excellent handling properties. Therefore, since adhesiveness and drapability are not required as characteristics of the fine particles, there is a wide range of materials that can be selected for the fine particles.

For this reason, even resins that have conventionally been difficult to use as matrix resins despite their excellent performance can be used as components of matrix resins by being made into fine particles and used.
The performance of the matrix resin can be improved.

Shape of Fine Particles However, since fine particles are used by being blended into a matrix resin, the viscosity of a matrix resin blended with fine particles is higher than that of a matrix resin without blended fine particles.

Normally, when producing prepreg, a resin film is prepared in advance by coating release paper with resin to a uniform thickness at a predetermined basis weight, and this is transferred to reinforcing fibers while impregnating them.
In order to produce this resin film, it is necessary to lower the viscosity of the resin to a level that allows it to be applied to release paper at a temperature lower than the temperature at which the curing reaction of the resin begins.

That is, if the viscosity of the matrix resin increases significantly by blending fine particles, it becomes extremely difficult to manufacture prepregs. Therefore, there is a limit to the amount of fine particles that can be blended.

In addition, reducing the particle size of the fine particles increases the surface area of the fine particles, leading to an increase in the viscosity of the matrix resin, so there is a limit to the size of the fine particles that can be used depending on the amount of fine particles to be blended.

However, according to the present invention, it has been found that by making the fine particles spherical, the increase in the viscosity of the matrix resin is significantly suppressed, and these drawbacks can be greatly improved. In the present invention, the term "spherical" means that more than half of the particles are substantially spherical, and does not include, for example, irregular shapes such as those obtained by mechanical crushing. In order to make the fine particles spherical, for example, known means such as reprecipitation from a resin solution can be applied.

As fine particles, mechanically pulverized amorphous particles are generally easily available, but the rate of increase in viscosity when blending spherical particles is less than 1/2 compared to the rate of increase in viscosity when blending these amorphous particles. .
In other words, the use of spherical fine particles in the production of prepregs has an extremely large effect in that it alleviates restrictions on the blending amount of fine particles and the particle size of fine particles. Moreover, the ability to introduce fine particles with a high particle size into the prepreg at a high fine particle content has the effect of reducing the disturbance of fiber arrangement due to the presence of fine particles, which results in unexpectedly high strength in the fiber direction and less variation. This had a significant effect on the development of stable composite physical properties.

Material of Fine Particles Component [C] needs to be made of either a thermoplastic resin, a thermosetting resin, or both.

The thermosetting resin used as fine particles refers to all resins that are or have been cured by heat or external energy such as light or electron beams to at least partially form a three-dimensional crosslinked body.

It is also suitable for the present invention to use a thermoplastic resin as the fine particles. Thermoplastic resins suitable for the fine particles of the present invention include carbon-carbon bonds, amide bonds, imide bonds, ester bonds, ether bonds, carbonate bonds, urethane bonds, urea bonds, thioether bonds, sulfone bonds, imidazole bonds, It is a thermoplastic resin having a bond selected from carbonyl bonds. Specifically, vinyl resins represented by polyacrylate, polyvinyl acetate, and polystyrene, polyamide, polyaramid, polyester, polyacetal, polycarbonate, polyphenylene oxide, polyphenylene sulfide, polyarylate, and polybenzimidazole. , thermoplastic resins that belong to engineering plastics such as polyimide, polyamideimide, polyetherimide, polysulfone, polyethersulfone, and polyetheretherketone, hydrocarbon resins such as polyethylene and polypropylene, and cellulose acetate and cellulose butyrate. Examples include cellulose derivatives.
In particular, polyamide, polycarbonate, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyarylate, polyester,
Polyamideimide, polyimide, polyetherimide, polysulfone, polyethersulfone, polyetheretherketone, polyaramid, and polybenzimidazole have excellent impact resistance and are therefore suitable as materials for the fine particles used in the present invention. Among these, polyamide, polyetherimide, polyether sulfone, and polysulfone have high toughness and good heat resistance, and are suitable for the present invention. Polyamide has particularly excellent toughness, and by using a polyamide that belongs to the amorphous transparent nylon category, it can also have heat resistance.

Distribution of fine particles Regarding the distribution of fine particles, the presence of uneven particles in the surface layer of the prepreg, that is, between the prepreg sheets when molded into a composite material, gives a composite material with excellent impact resistance. It is important for

With the addition of normal fine particles, only the modification effect corresponding to the content of fine particles in the matrix resin can be expected, but if they are concentrated in the surface layer of the prepreg, the prediction based on the additivity described above cannot be expected. Far beyond, especially when it comes to improving impact resistance,
A completely unexpected and remarkable effect was discovered. The condition that satisfies this is that 90% or more of the fine particles are from the surface of the prepreg to the thickness of the prepreg.
This means that it is localized within a 30% depth range. If this condition is exceeded and fine particles enter deep inside the prepreg, the impact resistance of the composite material will be inferior to that of a composite material that meets these conditions.

It is more preferable if 90% or more of the fine particles are localized within a depth range of 10% of the thickness of the prepreg from the surface of the prepreg, since a more significant effect appears.

Note that the prepreg according to the present invention has fine particles unevenly distributed on both sides of the prepreg.
It is optimal because it can be laminated freely regardless of the front and back sides of the prepreg. but,
Even if the prepreg has a similar distribution of fine particles on only one side of the prepreg, the same effect can be obtained if care is taken to ensure that the fine particles are between the prepregs when stacking the prepregs.
The present invention also includes a distribution in which fine particles are biased only on one side of the prepreg.

Method for evaluating the distribution of fine particles The distribution state of fine particles in the prepreg is evaluated as follows.

First, the prepreg is sandwiched between two smooth support plates and brought into close contact with each other, and the temperature is gradually raised over a long period of time to harden the prepreg. What is important at this time is to gel at the lowest possible temperature. If the temperature is raised before gelation occurs, the resin in the prepreg will flow and the fine particles will move, making it impossible to accurately evaluate the distribution state in the prepreg.

After gelation, the prepreg is cured by gradually increasing the temperature over an additional period of time. Using this cured prepreg, the cross section is enlarged 200 times or more and a photograph of 200 mm x 200 mm or more is taken.

Using this cross-sectional photograph, first determine the average thickness of the prepreg. The average thickness of the layer is measured at at least 5 arbitrarily selected points on the photograph, and the average thickness is taken. Next, draw a line parallel to the surface direction of the prepreg at a position 30% of the thickness of the prepreg from the surface that was in contact with both support plates. 30% of the surface that was in contact with the support plate
Quantify the area of fine particles existing between parallel lines on both sides of the prepreg, quantify this and the area of fine particles existing over the entire width of the prepreg, and calculate the ratio from the surface of the prepreg to the thickness of the prepreg. The amount of fine particles present within 30% of the area is calculated. The area of the microparticles is determined by cutting out all the microparticles present in a predetermined area from a cross-sectional photograph and weighing them. In order to eliminate the influence of variations in the local distribution of fine particles, this evaluation was performed over the entire width of the obtained photograph, and the same evaluation was performed on five or more randomly selected photographs, and the average It is necessary to take

If it is difficult to distinguish between fine particles and matrix resin, selectively stain one of them and observe. Although it is possible to observe using an optical microscope, depending on the stain, a scanning electron microscope may be more suitable for observation.

Size of fine particles The size of fine particles is expressed by particle size, and particle size in this case means the volume average particle size determined by centrifugal sedimentation velocity method or the like.

The size of the fine particles need not be so large as to significantly disturb the alignment of reinforcing fibers when formed into a composite material. If the particle size exceeds 150 μm, the arrangement of the reinforcing fibers may be disturbed or the interlayers of the composite material obtained by lamination may become thicker than necessary, resulting in a disadvantage of deteriorating the physical properties of the composite material.

Amount of fine particles A suitable amount of fine particles is in the range of 1 part by weight to 100 parts by weight per 100 parts by weight of matrix resin. If the amount is less than 1 part by weight, the effect of the fine particles will hardly be exhibited, and if it exceeds 100 parts by weight, it will be difficult to mix with the matrix resin, and the tackiness and drapability of the prepreg will be significantly reduced.

In particular, if the stiffness of the matrix resin is utilized to develop the compressive strength of the composite material, but when using fine particles with flexible properties with high elongation at break to increase the toughness between the layers of the composite material, it is preferable to A smaller range of 30 parts by weight is more suitable.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

[Example] A prepreg was created through a two-step resin impregnation process. First, a resin composition having the following composition was created.

1) Tetraglycidyldiaminodiphenylmethane (manufactured by Sumitomo Chemical Co., Ltd., ELM134)
...60 parts by weight 2) Bisphenol A type epoxy resin (manufactured by Yuka Ciel Epoxy Co., Ltd., Epicoat 828)
...40 parts by weight 3) 4,4'diaminodiphenylsulfone (manufactured by Sumitomo Chemical Co., Ltd., Sumikiure S) ...42 parts by weight 4) Polyether sulfone 5200G (Mitsui Toatsu Co., Ltd.)
(manufactured by Toray Industries, Inc.) ...10 parts by weight This resin composition was applied onto release paper to form a resin film, and this was used to impregnate carbon fiber T800 (manufactured by Toray Industries, Inc.) aligned in one direction to form a primary prepreg. Obtained.

Next, nylon 6 spherical particles were added to the above resin composition.
30 parts by weight of SP-1000 (average particle size 15 μm, manufactured by Toray Industries, Inc.) were mixed in a kneader. The viscosity of this mixed resin at 80°C was measured and found to be 150 poise.
When the mixed resin was heated to 80°C and coated on release paper using a reverse coater, a good resin film with uniform thickness was obtained. This resin film was applied to both sides of the primary prepreg previously prepared and further impregnated to produce a unidirectional prepreg having fine particles on the surface.

The weight fraction of resin in the prepreg was 32%. The amount of resin per unit area was 71 g/m ² and the amount of carbon fiber per unit area was 149 g/m ² .

This prepreg was sandwiched between two smooth Teflon plates, and the temperature was gradually raised to 150°C for 7 days to cure it, and its cross section was observed. When the amount of fine particles present in the range from the surface of the prepreg to 30% of the thickness of the prepreg was evaluated, the value was 96%. Cross-sectional observation was performed by selectively staining the microparticles with phosphotungstic acid and using a scanning electron microscope.

Next, 32 sheets of this prepreg were laminated in a quasi-isotropic manner and molded using a normal autoclave at 180°C.
The test was carried out for 2 hours under a pressure of 6 kgf/cm ² . After molding, the cross section was observed under an optical microscope, and it was confirmed that the fine particles were concentrated in the interlayer portions of the laminate.

After cutting a quasi-isotropically hardened plate to 150 mm long and 100 mm wide, and applying a falling weight impact of 1500 inch-pounds/inch to the center, the damage area was measured using an ultrasonic flaw detector and was found to be 0.5 square inches. . Then,
The compressive strength after impact was measured according to ASTM D-695 and was 42.2 Kg/mm ² .

[Comparative Example] The same procedure as in Example was repeated, except that amorphous particles with an average particle size of 28 μm obtained by freeze-pulverizing nylon 6 (manufactured by Toray Industries, Inc.) were used as the particles.

The viscosity of the resin composition mixed with the fine particles at 80° C. was measured to be 820 poise, making the mixed resin extremely viscous compared to the examples. When this mixed resin was heated to 80° C. and coated on release paper using a reverse coater, uniform coating could not be achieved and only a resin film with large thickness unevenness was obtained. Next, carbon fiber T800 (manufactured by Toray Industries, Inc.) was impregnated with this resin film to produce a unidirectional prepreg.

The cross section was observed in the same manner as in Examples, and the amount of fine particles present in the range from the surface of the prepreg to 30% of the thickness of the prepreg was evaluated, and the value was 91%. Cross-sectional observation was performed by selectively staining the microparticles with phosphotungstic acid and using a scanning electron microscope.

Next, 32 sheets of this prepreg were laminated in a quasi-isotropic manner and molded using a normal autoclave at 180°C.
The test was carried out for 2 hours under a pressure of 6 kgf/cm ² . After molding, when the cross section was observed under an optical microscope, the thickness of the layer was found to be uneven in many areas, and the distribution of fine particles was correspondingly disordered. In addition, there were many areas with poor impregnation, and many voids were observed.

After cutting a quasi-isotropically hardened plate to 150 mm in length and 100 mm in width and applying a falling weight impact of 1500 inch-lb/inch to the center, the damage area was measured with an ultrasonic flaw detector and was found to be 0.9 square inches. . Then,
When the compressive strength after impact was measured according to ASTM D-695, it was 30.2 Kg/mm ² , which was significantly inferior to the examples.

[Effects of the Invention] According to the present invention, (1) it is possible to obtain a prepreg with a high content of fine particles, so when it is made into a composite, it is possible to obtain high impact resistance and non-fiber axis tensile strength.

(2) Since it is possible to obtain a prepreg with a high content of fine particles even with fine particles having a small particle size, there is no disturbance in the fiber arrangement due to the presence of fine particles, and when it is made into a composite, it exhibits high strength in the fiber direction. Furthermore, variations in various composite physical properties are also small.

(3) While ensuring excellent tackiness and drapability as a prepreg, high impact resistance and non-fiber axial tensile strength can be obtained when made into a composite.

Claims (1)

[Scope of Claims] 1. The following components [A], [B], and [C] are essential, and half or more of the fine particles of component [C] are substantially spherical; ] A prepreg having spherical fine particles, characterized in that 90% or more of the amount is localized within a depth range of 30% of the thickness of the prepreg from the surface of the prepreg. [A]: Reinforced fiber made of long fibers [B]: Matrix resin [C]: Spherical fine particles made of resin.