JPH0439490B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an advanced composite material that is required to have high strength, high elastic modulus, and high specific strength and high specific elastic modulus, which are obtained by dividing these by specific gravity. The present invention relates to composite materials used in structures such as More specifically, strength in directions other than the direction of reinforcing fibers, especially non-fiber axial tensile strength,
This invention relates to a composite material that has significantly improved interlaminar strength, interlaminar toughness, impact resistance, fatigue properties, etc.

[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 resistance to falling weight impact is controlled by delamination strength, so improving the strength of reinforcing fibers does not lead to drastic improvements. For this reason,
In addition to improving the toughness of matrix resins, various improvements have been proposed for the purpose of improving physical properties in directions other than the fiber axis direction.

According to USP 3472730 (1969), delamination resistance is improved by disposing a separate exterior film made of a thermosetting resin modified with an elastomer material on one or both sides of a fiber-reinforced sheet. This is disclosed.

In Japanese Patent Publication No. 51-58484 (Special Publication No. 58-31296),
It is disclosed that moldability and bending strength can be improved by providing a polyether sulfone film on the surface of a fiber-reinforced epoxy resin prepreg.

JP-A-54-3879, JP-A-56-115216, JP-A-Sho
No. 60-44334 discloses that short fiber chips, chopped strands, or milled fibers are arranged between the layers of a fiber-reinforced sheet to improve the interlayer strength.

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.

USP4539253 (1985) (corresponding to Japanese Patent Application Publication No. 1986-
231738), non-woven fabrics, woven fabrics, matte,
It is disclosed that the interlaminar strength is improved by disposing a film impregnated with an epoxy resin modified with an elastomer in the carrier.

USP4604319 (1986) (corresponding to Japanese Patent Application Publication No. 1986-
231738) discloses that the interlayer strength can be improved by disposing a thermoplastic resin film between the layers of fiber-reinforced prepreg.

[Problems to be Solved by the Invention] These methods are not only insufficiently effective, but also have their own drawbacks. In the case of using an independent outer layer film containing an elastomer-modified thermosetting resin, the heat resistance decreases as the elastomer content increases, and the improvement in interlaminar strength is very little cured as the elastomer content decreases.

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, but the adhesiveness, which is an advantage of thermosetting resin, is 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.

The present inventors have conducted extensive research on fiber-reinforced composite materials that do not have the above-mentioned drawbacks and have excellent physical properties other than the fiber direction, especially impact resistance. As a result, a new component [C] has been discovered between the layers of the composite material. B] or component [A] when formed as a separate phase while having a large contact area, it overcomes these drawbacks and significantly improves physical properties in directions other than the fiber axis direction, far exceeding expectations. It was discovered that the present invention can be used as an improved composite material, and the present invention was completed.

[Means for Solving the Problems] The present invention is as described in the claims section above.

That is, a laminated composite material that requires the following components [A], [B], and [C], in which 90% or more of the component [C] is localized in the "interlayer region",
A composite material characterized in that the "boundary length coefficient" of the component [C] in the "interlayer region" is 2.5 or more.

[A]: Reinforcing fiber made of long fibers [B]: Matrix resin [C]: Resin separated from [B] without being compatible (description of reinforcing fiber made of long fibers) Constituent element of the present invention [A] is a reinforcing fiber consisting of long fibers. 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 the tensile strength
High-strength, high-elongation carbon fiber with a tensile strength of 450 kgf/mm ² and a tensile elongation of 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 the length is shorter than that, it becomes 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. Also,
The reinforcing fibers are not limited in their shape or arrangement, and may be used, for example, in a unidirectional direction, a random direction, a sheet shape, a mat shape, a fiber shape, or a braided cord shape. 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, 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, it is also preferable to use an oligomer having a functional group capable of reacting with the thermosetting resin at the end or in the molecular chain.

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.

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 BT resin manufactured by Mitsubishi Gas Chemical Co., Ltd. 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.

(Description of resin that formed a phase separated from component [B]) Material of component [C] Component [C] is a resin that is separated from [B] without being compatible with it. Here, "separated without being compatible with [B]" means that components [B] and [C], which are matrix resins, are compatible even after being subjected to heat and pressure in the process of manufacturing the composite material. This means that it forms an independent phase without any In addition, if the shape of [C] is a particle, it is spherical,
It may have a cylindrical shape (short fiber shape), a cubic shape, a rectangular parallelepiped shape, an irregular shape, or a shape in which a plurality of these shapes are joined. Usually a thermoplastic resin,
Preferably, the resin is made from one or both of thermosetting resins.

The thermosetting resin that can be used as component [C] refers to all resins that are 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 component [C]. Thermoplastic resins suitable for the present invention include carbon-carbon bonds in the main chain.
It is a thermoplastic resin that has bonds selected from amide bonds, imide bonds, ester bonds, ether bonds, carbonate bonds, urethane bonds, urea bonds, thioether bonds, sulfone bonds, imidazole bonds, and carbonyl bonds, but there are some bonds in the molecule. A material having a crosslinked structure may also be used. especially,
Polyamide, polycarbonate, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyarylate, polyester, polyamideimide, polyimide, polyetherimide, polysulfone, polyethersulfone, polyetheretherketone, polyaramid, polybenzimidazole are resistant. Since it has excellent impact resistance, it is suitable as a material for component [C] used in the present invention. Among these, polyamide has particularly excellent toughness, and by using a polyamide that belongs to the amorphous transparent nylon group, it can also have heat resistance.

It is also suitable to use a mixture of a thermosetting resin and a thermoplastic resin as the component [C]. Suitable thermosetting resins and thermoplastic resins in this case are the same as those mentioned above. For example, if a mixture of phenolic resin and nylon resin is used, the water absorption rate of the nylon resin will be lowered while maintaining the toughness of the nylon resin.
Components with excellent heat and water resistance [C]
It can be an ingredient.

Distribution of component [C] Regarding the distribution of component [C], the presence of component [C] unevenly between the layers of the composite material and the large contact area with component [B] make it a composite material with excellent impact resistance. It is important because

When component [C] is uniformly distributed, only a modification effect corresponding to the content of component [C] in the matrix resin is expected;
If it exists unevenly between the layers of a composite material and can secure a wide contact area with the matrix resin and reinforcing fibers, it will far exceed expectations based on mere additivity, and the improvement in impact resistance will be completely unexpected. A remarkable effect was found that could not be achieved with other methods.
Furthermore, the large contact area between component [C] and other components surprisingly had an effect on improving fatigue properties.

Conditions that satisfy this include the following () and ().

() First, component [A] and component [B]
In a composite material made up of multiple layers of
It is necessary that 90% or more of the total amount of component [C] be localized in the "interlayer region" sandwiched between layers.

In the present invention, the "interlayer region" is a region formed in the contact area between a layer consisting of a component [A] and a component [B] and the layers above and below the layer, as shown in FIG. If the average thickness of the layer is t, then this is a region with a thickness of 0.3t, which is 0.15t vertically in the thickness direction from the surface where the layers contact each other.

() In the present invention, the length of the interface where component [C] contacts its surroundings is referred to as "boundary length." In addition, as shown in Figure 8, the "boundary length coefficient" α
Assuming that the "interlayer region" is cut perpendicularly to the layer direction to an appropriate length in the layer longitudinal direction, the total length S of the boundary B in this closed region Value divided by length S/
means. And this “boundary length coefficient” α is
Must be 2.5 or higher.

By the way, if the above-mentioned conditions are not met and a large amount of component [C] is present deep inside the layer beyond the interlayer region, the impact resistance of the composite material will be greatly reduced. On the other hand, it is more preferable if 90% or more of the component [C] is localized within 10% of the layer thickness from the surface of the layer because a more significant effect appears.

Furthermore, if the boundary length coefficient is less than 2.5, the impact resistance and fatigue properties of the composite material will not be sufficiently improved. When the boundary length coefficient is 2.5 or more, both impact resistance and fatigue properties are excellent, and when it is 3.0 or more, the improvement in fatigue properties is large, so it can be said to be more suitable.
More preferably, the boundary length coefficient is 3.5 or more.

It should be noted that at least one part of the cross section of the composite material that satisfies these conditions should exist, but preferably 30% or more of the whole, more preferably 30% or more of the whole.
It is preferable that 50% or more of the parts satisfy this condition.

Details of the method for evaluating the ratio of component [C] existing in the "interlayer region" and "boundary length coefficient" The distribution state of component [C] in the composite material is evaluated as follows.

First, the composite material is cut perpendicular to the laminated surface, and the cross section is enlarged 70 times or more to create a photograph of 200 mm x 200 mm or more. The photo should be taken so that the surface direction of the layer is parallel to one side of the photo.

Using this cross-sectional photograph, first determine the average layer thickness. The average thickness of the layers is at least 5
The thickness of the laminated portion of more than one layer is measured at five arbitrarily selected locations, and the value is divided by the number of laminated layers.

Next, a cross-section of the same composite material is enlarged 500 times or more to create a photograph of 200 mm x 200 mm or more. Using this photograph, focus on one interlayer and draw a line approximately in the center of that interlayer.

Next, two lines with a spacing of 30% of the average thickness of the layers determined previously and two lines with a spacing of 50% of the average thickness of the layers are drawn symmetrically with respect to the center line. The spacing is 30% of the average thickness of the layers in the photo2.
The area surrounded by the lines of the book is the interlayer area.

Next, quantify the area of component [C] in the interlayer region between two lines with an interval of 50% of the area of component [C] and the average thickness of the layer, and By taking the ratio, the proportion of the component [C] present in the interlayer region is calculated. To quantify the area of component [C], cut out all the component [C] parts present in a predetermined area from the cross-sectional photograph,
This is done by weighing the weight.

The boundary length coefficient is evaluated as described above using a photograph of the cross section of the composite material enlarged 500 times or more and measuring 200 mm x 200 mm or more, as described below. First, using the same method as above, focus on one interlayer and draw a line indicating the interlayer region. Next, place tracing paper with a grid of 1 mm on top of this photo, and make a square ( 1mm square). Component [C] and component [B] with the total number of filled squares.
Alternatively, it is the total length of the boundary with component [A]. The value obtained by dividing this by the length (mm) in the layer direction on the photograph is taken as the boundary length coefficient.

When it is difficult to distinguish between component [C] and component [B], one of them is selectively stained and observed. Although it is possible to observe using an optical microscope,
Depending on the stain, a scanning electron microscope may be more suitable for observation.

[Function] The fact that component [C] has a large adhesion area with the matrix resin and is localized in the interlayer region reduces the internal stress that occurs when the fiber-reinforced composite material is subjected to stress such as impact. It has the effect of delaying fracture under relaxed stress and changing from a brittle fracture mode to a highly tough fracture mode.
This effect of component [C] is mainly due to the large allowable strain of component [C] component itself, the adhesiveness with the matrix resin, and the adhesive interface with the matrix resin based on the distribution pattern in the matrix resin. This is thought to be due to the length.

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

[Example 1] A unidirectional prepreg having the following configuration was manufactured. To manufacture prepreg, first prepare a prepreg with a weight fraction of 21% of the following resins A and B, and then paste a resin film on both sides of the prepreg with a thin layer of release paper coated with a blended resin of C and B. This was done by Note that the part by weight C below is the amount of fine particles contained in the prepreg resin finally obtained through the above two-step process.

A Reinforcing fiber - carbon fiber T800 (manufactured by Toray Industries, Inc.) B Matrix resin - a resin composition having the following composition 1 Tetraglycidyldiaminodiphenylmethane (manufactured by Sumitomo Chemical Co., Ltd., ELM434)
...70 parts by weight 2 Bisphenol A type epoxy resin (manufactured by Yuka Ciel Epoxy Co., Ltd., Epicort 828) ...10 parts by weight 3 Bisphenol F type epoxy resin (manufactured by Dainippon Ink Industries Co., Ltd., Epicron)
830) ...20 parts by weight 4 4,4'diaminodiphenyl sulfone (manufactured by Sumitomo Chemical Co., Ltd., Sumikiure S)
...45.2 parts by weight C Amorphous transparent nylon (Trogamide manufactured by Dayminut Novel Co., Ltd.)
Fine particles with an average particle size of 22μ obtained by freeze-pulverizing T)
...15 parts by weight The weight fraction of the resin in the prepreg was 30%. The amount of resin per unit area was 69 g/m ² and the amount of carbon fiber per unit area was 149 g/m ² .

Next, 32 sheets of this prepreg were laminated in a quasi-isomorphic manner and molded using a normal autoclave at 180°C.
The test was carried out for 2 hours under a pressure of kgf/cm ² .

The cross section of the molded product was polished, the amorphous transparent nylon portion was selectively stained with osmium tetroxide, and the cross section was observed using a scanning electron microscope. The amorphous transparent nylon formed a separate layer from the matrix resin.

The average thickness of the layer was evaluated using five photographs each magnified 70 times and 200 times, and the average thickness was found to be 156μ. Examples of cross-sectional photographs used are shown in Figure 1 (70x magnification) and Figure 2 (200x magnification).
times). The amorphous transparent nylon appears slightly brighter and contrasts with the matrix resin. Next, we evaluated the percentage of amorphous transparent nylon existing in the interlayer region using five cross-sectional photographs of arbitrary locations magnified 1000 times, and found that it was 97% (width of the interlayer region was 46.8μ). The transparent nylon was localized between the layers. In addition, when the boundary length coefficient was determined using the same cross-sectional photograph, it was 3.2, indicating a large contact area. An example of the cross-sectional photograph used is shown in Figure 3a (1000x magnification). In order to calculate the boundary length coefficient from Figure 3a, the boundary between component [C] and component [A] or component [B] is shown. Figure 3b shows graph paper in which the squares (1 mm square) through which the lines pass are filled in.

After cutting a quasi-isotropically hardened board 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 1.2 square inches. . Then,
The compressive strength after impact was measured according to ASTM D-695 and was 30.3 kg/mm ² .

Next, fatigue properties were evaluated by applying repeated loads (tensile) in EDS (edge peel strength) test mode. As a result, no peeling occurred even after repeated loading 10 ⁶ times under a stress of 15 Kg/mm ² .

[Example 2] A unidirectional prepreg having the following configuration was manufactured in the same manner as in Example 1.

A Reinforcing fiber - carbon fiber T800 (manufactured by Toray Industries, Inc.) B Matrix resin - a resin composition having the following composition 1 Tetraglycidyldiaminodiphenylmethane (manufactured by Sumitomo Chemical Co., Ltd., ELM434)
...60 parts by weight 2 Bisphenol A type epoxy resin (manufactured by Yuka Ciel Epoxy Co., Ltd., Epicoat 828 ...20 parts by weight 3 Trifunctional aminophenol type epoxy resin (manufactured by Sumitomo Chemical Co., Ltd., ELM100)
...20 parts by weight 4 4,4'diaminodiphenylsulfone (manufactured by Sumitomo Chemical Co., Ltd., Sumikiure S
...47.3 parts by weight 5 Polyethersulfone 5003P (manufactured by Mitsui Toatsu Co., Ltd.) ...16 parts by weight C Nylon 6 particles (SP1000 manufactured by Toray Industries, Ltd., average particle size 8 μm)
...14 parts by weight The weight fraction of the 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 148 g/m ² .

This prepreg was molded in the same manner as in Example 1, and its cross section was observed using a scanning electron microscope. Phosphorous tungstic acid was used to dye nylon 6. Nylon 6 appeared bright and formed a separate layer from the matrix resin.

The average thickness of the layers was evaluated in the same manner as in Example 1 and found to be 159μ, and the proportion of nylon 6 present in the interlayer region and the boundary length coefficient were 98%, respectively.
They were 3.18 and 2.82.

Figure 4 (70x magnification) shows an example of a cross-sectional photograph used for evaluation.
In order to obtain the boundary length coefficient from Fig. 5 (200 times) and Fig. 6 a, the boundary line between component [C] and component [A] or component [B] passes through. A graph paper with square grids (1 mm square) filled in is shown in Figure 6b.

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-pounds/inch to the center, the damage area was measured using an ultrasonic flaw detector and was found to be 0.7 square inches. . Then,
The compressive strength after impact was measured according to ASTM D-695 and was 36.2 Kg/mm ² .

Next, fatigue properties were evaluated by applying repeated loads (tensile) in EDS (edge peel strength) test mode. As a result, no peeling occurred even after repeated loading 10 ⁶ times under a stress of 15 Kg/mm ² .

[Comparative Example] A prepreg was prepared by removing the amorphous transparent nylon from the structure of Example 1, and a prepreg with a thickness of 15 μm of separately prepared amorphous transparent nylon (Trogamide-T manufactured by Dayminut Novel Co., Ltd.) was prepared. Films were alternately laminated and molded in the same manner. Otherwise, the same procedure as in Example 1 was repeated.

When cross-sectionally observed using a scanning electron microscope, it was found that the amorphous transparent nylon formed a layer separate from the matrix resin.

When the percentage of amorphous transparent nylon present in the interlayer region was evaluated, it was 100%, indicating that the amorphous transparent nylon was localized between the layers. However, the boundary length coefficient was 2.2, and the contact area between the amorphous transparent nylon and the matrix resin or carbon fiber was quite small.

After cutting a quasi-isotropically hardened board to a length of 150 mm and width of 100 mm, and applying a falling weight impact of 1,500 inch pounds/inch to the center, the damage area was measured using an ultrasonic flaw detector and was found to be 1.6 square inches. . Then,
When the compressive strength after impact was measured according to ASTM D-695, it was 27.0 Kg/mm ² , which was inferior to Example 1.

In addition, the fatigue characteristics in EDS mode are 15Kg/
When a stress of mm ² was applied repeatedly 2×10 ⁵ times, sheet edge peeling occurred.

[Effects of the Invention] The composite material in which the component [C] of the present invention is localized between layers with a large contact area exhibits high compressive, tensile and bending strengths and the ability to withstand impact damage, and is superior to conventional It has greater toughness, shear impact resistance, impact damage resistance and crack growth resistance than fiber reinforced composite materials. In addition, the composite material of the present invention not only has the above properties, but also has
It has significant effects on improving 90° tensile elongation at break and strength, as well as creep resistance.

[Brief explanation of drawings]

Figures 1, 2 and 3a are scanning electron micrographs showing the shape of the fibers in the composite material obtained in Example 1, and are taken at 70x, 200x, respectively.
It is magnified 1000 times. FIG. 3b is a graph paper for determining the boundary length coefficient from FIG. 3a. Figures 4, 5, and 6a are scanning electron micrographs showing the shape of fibers in the composite material obtained in Example 2, magnified 70 times, 200 times, and 1000 times, respectively. It is. FIG. 6b is a graph paper for determining the boundary length coefficient from FIG. 6a. 7th
The figure is a model diagram for explaining the interlayer region.
FIG. 8 is a model diagram for explaining the process of determining the boundary length coefficient. In the figure, [C]...Component [C]...Longitudinal length, B...Boundary, X...Interlayer region of interest.

Claims (1)

[Scope of Claims] 1. A laminated composite material that essentially includes the following constituent elements [A], [B], and [C], in which 90% of the constituent elements [C]
A composite material characterized in that the above amount is localized in the "interlayer region" and the "boundary length coefficient" of component [C] in the "interlayer region" is 2.5 or more. [A]: Reinforced fiber consisting of long fibers [B]: Matrix resin [C]: Resin separated without being compatible with [B]