JPH0759645B2 - Molded body manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a novel molded article using a unidirectionally aligned carbon fiber prepreg and a method for producing the same.

[Conventional technology]

A carbon fiber reinforced resin molded body, in which oriented carbon fibers are impregnated with a thermosetting resin to form a unidirectionally aligned prepreg, and then laminated and cured, is used for industrial materials such as leaf springs and honeycomb structure materials, or for fishing rods and golf shafts. It is widely used as equipment for sports cashiers. Furthermore, recently, it is being used as a member for aircrafts, automobiles, ships and the like.

The performance of the carbon fibers used has also improved significantly in recent years, with polyacrylonitrile-based carbon fibers of high strength and high elongation type already having a tensile strength of over 600 kg / mm ² , and 300 kg / mm ^2.
A high-strength, high-elasticity type with a tensile strength of mm ² or more and a tensile elastic modulus of 46 to 50 ton / mm ² has been developed and put on the market, and the required performance for molded products obtained by using them as reinforcing fibers The performance of the raw material carbon fiber is becoming higher and higher.

The first step in improving the performance of the carbon fiber reinforced resin molding was to improve the interfacial adhesion strength between the carbon fiber and the matrix resin.
With respect to this point, many researches and developments have been vigorously carried out for the past ten years or so, and at present, it has been settled down to a considerably high level by the electrolytic oxidation method and the gas phase oxidation method. However, no significant progress has been made in this technology over the past few years, and it is unlikely that properties such as interlaminar shear strength (ILSS) will be further improved in the near future.

It has also been reported in the past that the modification of the matrix resin contributes to the improvement of the performance of the carbon fiber reinforced resin molding (Japanese Patent Laid-Open No. 57-49612, etc.), but the curing temperature is similar. In resin systems, it is not so expected that the performance of the molded product itself will be greatly improved by modifying the resin. However, where the present inventors have learned from experience, generally, a matrix resin having a high curing temperature, a high crosslinking density and a high rigidity exhibits higher interlaminar shear strength and bending strength.

[Problems to be solved by the invention]

In any case, in the conventional technology, the combination with the matrix resin of the same curing temperature grade does not lead to the improvement of the performance of the composite material molded body despite the recent remarkable performance improvement of the carbon fiber itself. Especially, the problem is that the improvement of the tensile strength of carbon fiber does not contribute to the improvement of the bending strength or the compression strength of the molded product using the respective reinforcing fibers, and if the matrix resin is the same, how high the strength of carbon fiber is This means that even if the above is used, the bending strength or the compression strength is not improved to some extent.

Fig. 1 shows the three-point bending strength of unidirectionally oriented fiber reinforced resin molded board prepared by combining four kinds of carbon fibers with different tensile strengths with bisphenol A type epoxy resin (curing temperature 130 ℃ type) It is the graph which showed the relationship with the used carbon fiber strand strength. The measurement conditions for the three-point bending test are the sample dimensions: fiber axis direction length 100 mm x width 10 m.
m × thickness 2mm, span length = 80mm, span thickness ratio = 40, nose and support radius = 1 / 8inch, crosshead speed 5mm / min, measurement environment is 21 ℃ 50% RH. The measured value was a fiber volume content of 60 vol%.

As is clear from FIG. 1, even a test piece of carbon strength fiber having high strand strength has a bending strength of about 180 kg / mm ² and does not exhibit a higher value.

Also, when observing the fractured specimens after these measurements, A in FIG.
Shows the fracture from the tensile side, but B, C, and D, which have high strand strength, all show the fracture from the compression side. This indicates that even if the tensile strength is improved, the compression failure is not accompanied by the improvement of the compression strength, and therefore the bending failure is the compression failure rate limiting. It is considered that this is because in the case of compression, complicated factors such as buckling of fibers, adhesive strength between fibers and matrix resin, or elastic modulus of matrix resin act to cause fracture by a mechanism different from tension. .

The fact that it is not possible to obtain a product with high bending strength in this way means that when actually using a carbon fiber reinforced resin molded product, almost all usage forms, whether it is a leaf spring, a fishing rod or a golf shaft, are used. It can be said that this is a very serious problem because it is deformation and bending failure.

On the other hand, another major problem in using the carbon fiber reinforced resin molded product as an industrial material or as an equipment for sports registrars is that when a molded product with high elasticity or high rigidity is obtained, it is generally extremely expensive. This means that the carbon fiber of high elasticity type must be used, and generally, the higher the elasticity becomes, the more the compressive strength and bending strength are greatly reduced.

In order to improve the flexural strength and the elastic modulus of the carbon fiber reinforced resin molded body at the same time as the inventors, the carbon fiber content in the molded body is significantly increased from the generally applied level. Various investigations have been made to reach the present invention.

In the prior art, attempts were made to increase the carbon fiber content in the molded body.-Lower the resin content in the intermediate material stage such as prepreg.-Suck out the resin with a bleeder cloth during molding, or squeeze out with excessive pressure. Generally implemented by Industrial Materials, No. 31
As reported in Volume No. 2, pp. 24 to 28 (1983), etc., in the case of a molded article having a high fiber content, the fiber volume content (hereinafter abbreviated as Vf) is 65 to 67 vol% or more, especially the interlaminar shear strength. Was sharply decreased, and along with that, the bending strength was also greatly decreased due to interlaminar fracture rate control. Therefore, considering variations, Vf = 65vol
%, Carbon fiber reinforced resin moldings are considered to be dangerous in terms of physical properties, and moldings with a Vf region higher than this have not been studied at all and there is no example of their practical application.

The inventors of the present invention have the lowest resin weight content of the existing commercially available unidirectionally aligned carbon fiber prepreg up to about 30 wt%, and in molding with suppressed resin flow it depends on the carbon fiber density and the resin density Vf should be at most 63-64vol%,
Focusing on the fact that in the conventional technology, a molded body with a Vf of 65 vol% or more cannot be obtained unless the resin is sucked out by a prepreader cloth or squeezed out by pressurization, the resin movement during molding is high Vf molded body. It has been found that the fiber distribution or dispersion state in the inside is made non-uniform and the interlaminar shear strength and bending strength are significantly reduced.

[Means for solving problems]

The present invention is a unidirectionally aligned carbon fiber prepreg having a resin content of 19 to 27 wt% is laminated and molded so that the decrease in the resin content due to the resin flow is 2 wt% or less, preferably 1 wt% or less. A method for producing a molded body, which is characterized in that a molded body of a carbon fiber reinforced curable resin having a fiber volume content of 67 to 75 vol% is provided as means for solving the above problems.

According to the present invention, it is possible to obtain a carbon fiber reinforced thermosetting resin molded product having sufficient interlaminar shear strength, flexural strength commensurate with Vf, and elastic modulus. The prepreg used in the present invention is preferably a solvent-free hot melt impregnation type. This is because the prepreg of the solvent-diluted impregnation method has microvoids in the molded body due to residual volatile components.

Even in the hot melt impregnation method, the release paper in which the resin film is formed only on one side is used, rather than the so-called double film method in which the resin film formed on the release paper is applied by impregnating it from the upper and lower surfaces of the carbon fiber fiber bundle sheet. The single film method of applying and impregnating is preferred.

In the double film method, in order to obtain a prepreg having a low resin content as in the present invention, it is necessary to accurately form a very thin resin film on the release paper depending on the weight of the prepreg. Even if a resin film is formed, since resin impregnation is performed from above and below, a large amount of unimpregnated portion remains in the central portion of the prepreg, which may cause voids after molding.

However, in the conventional solvent-free hot melt impregnation type prepreg, it is extremely difficult to impregnate the resin when the resin weight content is 27 wt% or less, and there is no commercially available prepreg. Therefore, the present inventors have conducted studies on the appropriate viscosity level of the impregnated resin in order to obtain such a prepreg having a low resin content.

FIG. 2 is a schematic diagram of the prepreg manufacturing apparatus used for this impregnation study.

In FIG. 2, 1 is a creel, 2 is a comb, 3 is a feed roll, 4 and 5 are opening bars, 6 is a release paper coated with epoxy resin, 7 is a dancer roll for tension control, 8 is a polyolefin film for cover, Reference numeral 9 is a plate heater for preheating and impregnation, 10, 11 and 12 are heating nip rolls for impregnation, 13 is a winding device for a cover film, and 14 is a winding device for a prepreg.

The carbon fiber tow was prepared in this device so that the fiber areal weight was 100 g / m ^2, and the impregnation study was carried out by changing the viscosity of the epoxy resin coated on the release paper. The results are shown in Table 1. For the sake of convenience, the resin viscosity used is the lowest viscosity measured at 90 ± 0.2 ° C. using a rotational viscometer. As is clear from Table 1, the prepreg having a resin weight content of about 30 wt% has good impregnation and tackiness. At the resin viscosity level, impregnation becomes extremely difficult as the resin weight content decreases to 27 wt% or even 19 wt%. Become. However, as the resin viscosity level is lowered, impregnation is possible even with low resin weight content prepregs. Also, with a prepreg having a resin weight content of 30 wt%, the tack becomes too strong, and even a resin with a low viscosity level that has a problem in workability becomes less problematic as the prepreg with a low resin weight content becomes less tacky. . If the resin weight content is 23 wt% or less, the resin layer will not be formed on the surface layer of the prepreg even when a resin with a low viscosity level is used, so that almost no tack exists and it becomes a dry tack state, making it difficult to bond during lamination. Will it be heated with an iron etc. when stacking,
It can be used in combination with a prepreg having a high resin weight content and tack.

Further, in such a prepreg having a low resin weight content, the workability may be deteriorated due to the lack of the adhesive force between the prepreg and the release paper in a normal prepreg release paper. This can be solved by using a release paper with a different release property to make the release property heavy.

The present inventors evaluated the release property of the release paper by the 180 ° peeling method of the adhesive tape shown in FIG. 4, and as a result, the release force for the prepreg carrying surface of the release paper for prepreg used in the present invention was 300 to 600g / 25mm width is suitable, preferably 350-500
It is g / 25mm wide.

Peeling force measurement 21 ° C, 50% RH for crushing, standard adhesive tape used for measuring peeling force is Scotch single-sided adhesive tape # 250 manufactured by Sumitomo 3M Ltd., peeling speed by tensile tester is 50m
The peeling force was evaluated according to JIS Z 0237 for m / min and other measurement conditions.

The peeling force of the prepreg-bearing surface of the release paper for prepreg currently on the market measured by the same method is 50 to 250 g / 25 mm.
It was heated in the width. When the peeling force exceeds 600 g / 25 mm width, the peeling becomes too heavy, and even the prepreg having the resin content according to the present invention makes it difficult to peel off the release paper.

However, if the resin viscosity becomes excessively low, the strength of the prepreg as a prepreg in a direction (90 °) perpendicular to the fiber axis direction is lost, and a tear tends to occur in the lateral direction, resulting in poor workability.

In any case, if an appropriate resin viscosity is selected, the resin weight content will be improved depending on the release property of the release paper and the usage method.
It can also be used with prepregs with low resin content of 27 wt% or less.

After confirming that prepregs having a resin weight content of 27 wt% or less can be produced by using a resin having an appropriate viscosity level through the examination as shown in Table 1, the unidirectionally aligned carbon fiber prepregs are prepared. Was used to form a unidirectional laminated plate of about 2 mm, a rectangular test piece having a length (fiber axis direction) of 100 mm and a width of 10 mm was prepared, and a three-point bending test and an interlaminar shear strength test by a short beam method were performed. The conditions of the interlaminar shear strength test are length (fiber axis direction) 12 mm × width 10 mm × thickness 2 mm,
Span length 10mm, span: thickness ratio = 5: 1, nose and support radius 1 / 8inch, crosshead speed 5mm / min, measurement environment is 21 ° C, 50% RH. For comparison, a similar sample was prepared for a prepreg with a resin weight content of about 29 wt% and a fiber weight per unit area of 100 g / m ² and was subjected to measurement. The carbon fiber used is one with a tensile strength of 360 kg / mm ² and a tensile modulus of 24 ton / mm ² and the epoxy resin is a bisphenol A diglycidyl ether type epoxy modified with diaminodiphenyl sulfone. The main component of this was dichlorophenyldimethylurea as a curing catalyst, and bisphenol A as a diluent.
Alternatively, bisphenol F diglycidyl ether type epoxy (n = 0 to 1) was used. The resin viscosity was adjusted by adjusting the degree of modification of the main component epoxy and the amount of diluent added.

The molding plate was produced by compression molding. Resin flow adjustment is a. Lay nylon taffeta and glass fiber bleeder cloth on top and bottom of the laminate. The molding pressure was changed in two ways.

Table 2 shows the results of the three-point bending test and the shear beam interlaminar shear strength test.

As is clear from the table, even in the high Vf region of 67 vol% or higher, the interlaminar shear strength does not decrease much in the sample with the resin flow suppressed during molding, and both the bending strength and the bending elastic modulus are small.
There is an increasing tendency proportional to Vf. On the other hand, a prepreg with a resin prepreg content of about 29 wt% or about 33 wt% that causes a large amount of resin flow to achieve a high Vf has a low interlaminar shear strength and a high bending strength despite a high Vf. I won't. Further, the greater the amount of resin flow at that time, the greater the decrease in interlaminar shear strength and the lower bending strength.

From Table 2, in the case of complex molding with a prepreg with a resin weight content of 27 wt% or less, the decrease in the resin weight content due to the resin flow was only about 1 wt% and the decrease in the interlaminar shear strength at a pressure of about 15 kg / cm ^2. At a low level, the pressure is further increased to cause a large amount of resin flow, and when the resin weight content reduction exceeds about 2 wt%, the interlaminar shear strength is considerably reduced. On the other hand, even in the case where the resin flow is caused by the bleeder cloth, similarly, when the amount of the resin is caused to be 2 to 3 wt%, the interlaminar shear strength is remarkably lowered. Such decrease in interlaminar shear strength due to resin flow was relatively small and did not pose a problem when Vf of the molded product was 65 vol% or less.

This is because in the case of moldings in the high Vf region that exceed 67 vol%, if a molding method that increases the resin flow during molding is adopted,
The resin flow does not occur uniformly in the entire molded body, and in the case of the complex molding, the resin moves selectively from the end portion in the fiber axis direction, and when the bleeder cloth is used, the resin moves selectively from the surface layer in contact with the cloth. It is considered that this is due to the fact that the resin amount between the single fibers is small due to the small amount of resin, and microvoids and the like are concentratedly generated, and the properties such as the interlaminar shear strength, bending strength, and compressive strength are reduced.

From the experimental results shown in Table 2 and other examinations, the limit for not lowering the physical properties of the molded article is a reduction of the resin content by weight of about wt% or less, preferably 1 wt% or less.

In molding by a tape lapping method such as a fishing rod or a golf shaft, it is generally difficult to control the resin flow, and it is difficult to flow a large amount of resin during molding. For example, using a prepreg with a resin content of 30 wt%, Vf = 67vol
It is quite difficult to finish above%. For example, even if molding is possible, only resin flow that is non-uniformly produced can be obtained, resulting in a decrease in interlaminar shear strength and bending strength. In the molding using a prepreg having a resin weight content of 19 to 27 wt% according to the present invention, carbon fiber density, 67 vol% depending on the resin density, but a high Vf molded body of not less than 100 vol%, a high bending strength proportional to Vf, High flexural modulus can be developed.

Further, when an epoxy resin having a higher resin rigidity after curing than the bisphenol A diglycidyl ether type epoxy resin is used, in addition to originally high bending strength, higher strength can be exhibited by the effect of Vf of the present invention.

However, there are limits to high Vf. For example, when Vf exceeds about 75 vol% even when molding is performed with the resin flow kept low, the interlaminar shear strength is remarkably reduced and the bending strength is reduced. Therefore, when the prepreg is used so that the resin content by weight is less than about 19%, the Vf of the obtained molded article is unfavorably higher than 75 vol% no matter how the resin flow is suppressed.

The more preferable carbon fiber volume content of the molded body of the present invention is 69
It is ~ 73vol%.

If Vf grows too much like this, even if the resin flow at the time of molding is suppressed, the single fibers come into direct contact without interposing the mitricex resin, or so-called voids of microvoids are frequently generated.

〔Example〕

 The present invention will be specifically described below with reference to examples.

Example 1 Using a prepreg manufacturing apparatus as shown in FIG. 2, high strength carbon fibers (tensile strength 360 kg / mm ² , tensile elastic modulus 24 ton / mm ² ) and 130
A prepreg with a resin weight content of 23.0 wt% and a fiber weight of 165 g / m ² was created by combining the resin film with a release paper with a peeling force of 400 g / 25 mm width coated with a ℃ curing resin. Commercially available ultra-thin unidirectionally aligned carbon fiber prepreg for reinforcement (resin weight content
37.3 wt%, fiber basis weight 27 g / m ² , 130 ° C. curable epoxy resin matrix) were applied orthogonally, then the fiber axis direction of the former prepreg was the longitudinal direction, and the latter prepreg was the inward winding direction, and 10φ Wrapped around the iron mandrel of 4 times and polypropylene tape (width 15mm) with tape tension 3k
It was lapped at g / 15 mm, placed in a curing furnace and cured at 130 ° C. for 2 hours to form a pipe having a flow of 600 mm. The resin flow at the time of molding was within 0.5 wt% as the reduction amount of the resin weight content including the lateral reinforcing prepreg.

For comparison, a commercially available unidirectionally aligned carbon fiber prepreg (carbon fiber tensile strength 360 kg / mm ² , tensile elastic modulus 24 ton / m
m ² , resin weight content 30 wt%, fiber basis weight 150 g / m ² , 130 ° C. curable epoxy resin matrix) and the same ultra-thin prepreg as in the example was affixed. A 600 mm pipe was molded. The decrease in the resin weight content due to the resin flow during molding of this pipe was 0.5w.
It was within t%.

Four-point bending tests were performed on these pipes, and bending strength and bending elastic modulus were measured. The measurement result is the third
Shown in the table. Further, FIG. 3 shows a schematic view of the measuring jig used for this measurement. In the figure, 1 is a movable indenter, 2 is a fixed indenter, 3 is a sample CFRP pipe, and 4 is a metal ring having an inner diameter of 11.5 mm, a thickness of 2 mm, and a width of 10 mm, which is mounted to prevent stress concentration in the indenter portion. The measurement conditions were a movable indenter span length of 500 mm, a fixed indenter span length of 150 mm, a crosshead speed of 5 mm / min, and a measurement atmosphere of 21 ° C. and 50% RH.

As is clear from Table 3, the pipe formed by the method of the present invention has almost the same weight and the same wall thickness as the pipe obtained by the conventional method of forming using a commercially available prepreg, though the bending strength is the same. , The flexural modulus is about 15% higher.

Example 2 In the same manner as in Example 1, high-strength, high-strength carbon fiber (tensile strength 420 kg / mm ² , tensile elastic modulus 40 ton / mm ² , density 1.81 g / c)
m ³ ) and 130 ° C curing type epoxy resin were combined to make a prepreg with a resin weight content of 25 wt% and a fiber areal weight of 152 g / m ² , and a commercially available ultra-thin unidirectionally aligned prepreg was prepared for lateral reinforcement. Carbon fiber prepreg (resin weight content 37.3
wt% fiber basis weight 27 g / m ² , 130 ° C. curable epoxy resin matrix) are applied at right angles, then the former prepreg has the fiber axis as the longitudinal direction and the latter prepreg as the inward winding direction. A polypropylene tape (width: 15 mm) was wrapped around the tape at a tape tension of 3 kg / 15 mm, placed in a curing furnace, and cured at 130 ° C. for 2 hours to form a pipe having a flow of 600 mm.

The resin flow at the time of molding was within 0.5 wt% as the reduction amount of the resin weight content including the lateral reinforcing prepreg. After the test, the outermost layer of the pipe was peeled off, and the resin weight content was determined by an acid decomposition method. In all cases, the reduction amount was 1 wt% or less.

In addition, as a comparison, a commercially available unidirectional draw-aligned prepreg using super high modulus carbon fiber with a tensile modulus of 46 ton / mm ² (carbon fiber tensile strength 330 kg / mm ² , carbon fiber density 1.88 g / cm ³ resin weight The same ultra-thin prepreg was attached to a content of 33 wt%, fiber weight of 139 g / m ² , 130 ° C curing type epoxy resin matrix,
A pipe having a length of 600 mm was formed by the same method.

A four-point bending test was performed on these pipes in the same manner as in Example 1, and the measurement results are shown in Table 4.

Further, a prepreg with a resin weight content of 25 wt% using a high elastic carbon fiber having a tensile elastic modulus of 40 ton / mm ² used for this measurement, and a commercially available ultra-high elastic carbon fiber prepreg used for comparison are used as a complex mold. 100m length in the fiber axial direction by molding
Create a test piece of m, width 10 mm, thickness 2 mm, span length 80 mm,
Span: Thickness ratio 40: 1, nose and support are 1/8 inc
h, cross head speed 5mm / min, measurement environment 21 ℃, 50
% RH, 3-point bending test, and Table 2 interlayer shear strength (ILS
Under the same measurement conditions as in (S), an interlaminar shear strength test was conducted.
The results are shown in Table 5.

Note that Vf in Table 5 was calculated by the following equation using the resin density (1.25 g / cm ³ ) and the carbon fiber density obtained by obtaining the fiber weight content by the acid decomposition method.

(Here, ρR = resin density, ρCF = carbon fiber density, Wf = fiber weight content%). As is clear from Table 4, even if the weight, wall thickness and flexural modulus are the same, an example according to the present invention Gives a pipe with a bending strength as high as 40% compared to the comparative example. This is because it is possible to select a prepreg made of carbonic fiber that can develop high bending strength even if the elasticity is low when viewed at the same Vf when obtaining pipes with similar bending elasticity. This is because it can be improved. This is also clear from the results of the three-point bending test shown in Table 5. Same Vf in this case
(60vol%) converted value is about 23% in bending strength difference, but V
Without the f conversion, in the example of the present invention, the measured value of the bending strength which is about 40% higher than that of the comparative example is obtained with substantially the same elastic modulus.

Further, in Table 4, in the pipe according to the present invention, the weight of carbon fiber used in the longitudinal direction is about 10% higher than that of the comparative example.
The carbon fiber having a tensile elastic modulus of 40 ton / mm ² grade used for the pipe according to the present invention is generally much more expensive than the carbon fiber having a tensile elastic modulus of 46 ton / mm ² grade used in Comparative Example as a market price due to the firing cost and the like. Moreover, the pipe according to the present invention can be manufactured at a sufficiently low cost as compared with the pipe of the comparative example.

Comparative Example 1 Resin weight content in Example 1 was 30 wt%, and fiber weight was 165 g.
/ m ² prepreg was prepared, and ultra-thin carbon fiber prepreg was applied in the same manner as in Example 1, and it was wrapped around a 10φ iron mandrel for 4 turns and a release tape was applied to one side of the polyester tape (15 mm width ) In the direction in which the release treated surface is in contact with the prepreg surface, the tape tension is double that in Example 1, 6 kg / 15 mm is lapped, and then the molded product is cured and molded at 130 ° C. for 2 hours, and the length is 600 mm.
Got the pipe. Note that the resin flow during pipe molding is about 6 wt as a reduction in the total resin content including the ultra-thin prepreg.
It was in%.

A four-point bending test was conducted on this pipe in the same manner as in Example 1. The results are shown in Table 6.

After bending and breaking, the outermost layer of the pipe (the layer having the fiber axis in the longitudinal direction) was peeled with a cutter knife, and the resin weight content was measured to be about 19 wt%. That is, the amount of decrease in the resin weight content ratio due to the resin flow in the outermost layer is very large at 11 wt%,
It was found that the resin flow occurred in the outermost layer in a fairly concentrated manner.

As is clear from the results in Table 6, in the high Vf pipe molded by the conventional technique, a high elastic modulus can be obtained, but the bending strength is conversely low.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the bending strength of a molded plate and the tensile strength of carbon fiber strands, FIG. 2 is a schematic view of the prepreg manufacturing apparatus used in the present invention, and FIG. 3 is a pipe four-point bending test measuring apparatus. FIG. 4 is a schematic solution diagram showing a measuring device for measuring the releasability of the release paper.

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Claims (1)

[Claims] 1. A unidirectionally aligned carbon fiber prepreg having a resin content of 19 to 27 wt% is laminated and molded so that the decrease in the resin content due to the resin flow is 2 wt% or less, and the carbon fiber volume content is A method for producing a molded article, which is a molded article of a carbon fiber reinforced curable resin of 67 to 75 vol%.