JPH05261729A - Carbon fiber chops and production thereof - Google Patents

Abstract

PURPOSE:To achieve the supply to a fiber reinforced composite material without cracking carbon fiber chops by subjecting a carbon fiber to sizing treatment or water treatment and cutting the treated fiber before drying by a roving cutter to produce carbon fiber chops. CONSTITUTION:A carbon fiber bundle consisting of 12000 carbon fibers produced using polyacrylonitrile as a raw material is delivered at a speed of 60m/min while water is sprayed to the carbon fiber bundle so that the adhesion amount of water becomes 3-5wt.% and the tension thereof is adjusted to 0.5-0.7kg/yarn through a tension roll and a godet roll. The carbon fiber bundle is subjected to sizing treatment by a touch roll and the number of rotations of the touch roll is adjusted so that the pickup amount of a sizing agent becomes 43-47%. The non-dried carbon fiber bundle thus obtained is cut into a length of 6m/m by a loading cutter to produce carbon fiber chops. Since the carbon fiber bundle is cut in a non-dried state, the cracking of chops is reduced and carbon fiber chops of high quality excellent in bundling properties can be obtained in a low sizing agent adhesion rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a carbon fiber chop and the obtained carbon fiber chop. More specifically, the present invention relates to a method for producing a carbon fiber having a low sizing agent deposition rate and an excellent sizing property, which is to be used for a fiber-reinforced composite material, with high productivity.

[0002]

2. Description of the Related Art In recent years, fiber-reinforced composite materials obtained by mixing carbon fibers and various matrices have excellent properties,
That is, it has been attracting attention as an industrially important material because of its high strength, high elastic modulus, high electrical conductivity, high wear resistance, low specific gravity and the like.

When a fiber reinforced composite material is to be obtained by using a thermoplastic resin as a matrix, carbon fibers are previously cut into 1 to several tens of mm to obtain carbon fiber chops, and this and thermoplastic resin pellets or powder are used. The mixture is put into an extruder, melt-kneaded to form mixed pellets which are a fiber-reinforced composite material, and the mixed pellets are put into a molding machine to obtain a desired molded body.

What is important in obtaining the mixed pellets is that the carbon fiber chops are quantitatively fed into the extruder. If this is not the case, there will be uneven discharge,
A constant extrusion speed cannot be obtained and strand breakage occurs, resulting in a significant decrease in productivity. A factor that greatly influences the quantitative supply is the biteability of the carbon fiber chop in the hopper of the extruder, which is closely related to the bundling property of the carbon fiber chop.

When the carbon fiber chop has a low bundling property, the carbon fiber chop is opened at a portion in contact with the screw at the lower part of the hopper to form a fluff mass, and the quantitative supply is hindered. Besides this,
When resin pellets and carbon fiber chops are premixed before being put into the hopper, fluff is generated when the focusing property is low, and the quantitative supply property to the extruder is impaired. For these reasons, the focusing property is an important index when evaluating carbon fiber chops.

By the way, in order to obtain a carbon fiber chop for use in a fiber reinforced composite material, the following method is generally used. First, the carbon fiber is immersed in a sizing agent to impregnate it, and then the solvent such as water is removed in the subsequent drying step to bundle the focused carbon fiber with a roping cutter or a guillotine cutter for a predetermined length. Cut into pieces to make carbon fiber chops.

The carbon fiber is sized, then passed through a dryer to be dried, and then cut into a predetermined length with a cutter. The drying process takes the longest time among these processes, and the processing speed is from several m / min to several tens of m / mi.
n. Therefore, if it is attempted to increase the treatment amount, it is conceivable to increase the drying capacity by increasing the amount of carbon fibers passed through the dryer or increasing the drying distance or increasing the drying temperature. However, in any case, this method requires large-scale equipment or modification and is economically disadvantageous.

Further, since the carbon fibers after drying are bundled only with the binder component of the sizing agent, if an impact shearing force is applied during cutting, chop cracking occurs, and this defect causes fluff without being repaired. As a result, it becomes difficult to quantitatively supply the extruder in the next step. As is clear from this, the conventional carbon fiber chop manufacturing method tends to increase the sizing agent adhesion rate in order to maintain the sizing property at a good level. However, an increase in the sizing agent adhesion rate may cause a deterioration in final composite properties, and is not preferable.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to efficiently produce a carbon fiber chop for use in a fiber reinforced composite material.

[0010]

The gist of the present invention resides in a method for producing a carbon fiber chop, which comprises subjecting the carbon fiber to a sizing treatment or a water treatment and cutting with a roving cutter before drying. ..

As described above, since the carbon fibers dried after the sanding treatment are bundled only with the binder component of the sizing agent, when an impactive shearing force is applied when cutting, chop cracking occurs, and this defect cannot be repaired. As it is, it causes fluff, which makes it difficult to quantitatively supply the extruder to the next step. Therefore, in the present invention, the effect of focusing the carbon fibers due to the surface tension of water or the sizing agent used, and the impact shearing force at the time of cutting are absorbed in a soft state that is not dried to prevent chop cracking, and the resulting defects By utilizing the effect of repairing, the carbon fiber chops of high quality are obtained.

The roving cutter referred to in the present invention is a cutter roll having a plurality of blades mounted on the roll,
It refers to a rubber anvil roll that is pressed against a cutter roll for cutting, and a nip roll that is pressed against the anvil roll that supplies a fiber bundle to the cutting portion.

In the present invention, the liquid retaining amount of the carbon fiber when the roving cutter is cut is usually 30 to 60% by weight, preferably 40 to 50% by weight of the picked up amount of water or sizing agent. If this amount is less than 30% by weight, the carbon fiber chops will have many cracks and fluffs during cutting, and the quantitative supply to the extruder will be hindered. On the other hand, if it exceeds 60% by weight, the carbon fiber chops adhere to the rolls of the roving cutter, causing clogging of the blades and miscutting, which lowers the productivity of the carbon fiber chops.

The sizing agent in the present invention is an emulsion of the binder component in water using an emulsifier,
Alternatively, the binder component is directly dissolved or dispersed in a solvent, and the concentration is 0.8 to 17% by weight, preferably 1.7 to 9% by weight. If this amount is less than 0.8% by weight, the effect as a binder is not exerted, and if it exceeds 17% by weight, it becomes difficult to obtain the target size adhesion ratio within the range of the pickup amount suitable for cutting.

The binder component of the sizing agent is not particularly limited, and any one of various known binders suitable for the present application may be appropriately used. For example, from the viewpoint of sizing property, one method is to use a mixed system of a high molecular weight component and a low molecular weight component as a binder component, and find the optimum condition by changing the ratio. Here, the high molecular weight component gives rigidity to the carbon fiber chop, and the low molecular weight component gives tackiness and bundling property to the carbon fiber chop. Further, in actual selection, it is necessary to consider the bundling property of the carbon fiber chop, the chopping process passing property, the gum-up property, the influence on the composite property, and the like.

The sizing treatment in the present invention may be carried out by any method as long as the amount of water or sizing agent picked up can be arbitrarily controlled, whereby the liquid retention amount of carbon fiber at the time of cutting is adjusted within an appropriate range. It becomes possible to do. The tension of the carbon fiber during the sizing treatment is 0.1 to 2 kg / yarn, preferably 0.3 to 1 kg / yarn. If this tension is less than 0.1 kg / yarn, the amount of water or sizing agent picked up is not constant, and if it exceeds 2 kg / yarn, fluffing tends to occur.

The carbon fiber chopping step in the present invention and the subsequent steps of drying, sorting and metal removal can be continuously operated, and is a highly productive process.

In the step of drying the carbon fiber chops manufactured by the method of the present invention, attention should be paid to the adhesion of the carbon fiber chops during the drying process. In addition, productivity can be improved by continuous drying. It is necessary to obtain appropriate values for the drying temperature and the drying speed depending on the chopping speed and the type of sizing agent. Appropriate equipment must be used to maintain the required quality for sorting and metal removal.

In the present invention, the water spraying treatment can be carried out before the sizing treatment. For example, when water is directly sprayed onto the bobbin in which the carbon fiber is being unwound, the carbon fiber is better bundled and the process passability and workability are improved. The property is improved. The amount of water sprayed at this time is 0.1 to 10% by weight, and preferably 0.3 to 5% by weight, of the carbon fiber in terms of the amount of the attached water. If this amount is less than 0.1% by weight, it will not be sufficient, and if it exceeds 10% by weight, the sizing agent will not be sufficiently replaced during the sizing treatment, and the sizing properties of the carbon fiber chops will deteriorate.

According to another method of the present invention, it is possible to obtain short carbon fibers without adhering the sizing agent by using water instead of the sizing agent in the sizing treatment. Moreover, if necessary, various treating agents can be dissolved or dispersed in water before use. The short carbon fibers obtained by this method have excellent dispersibility because they do not have a sizing agent attached, and can be applied to carbon fiber nonwoven fabrics used for CFRC and C / C composite substrates. The carbon fiber in the present invention is not particularly limited and can be arbitrarily selected from various known carbon fibers and used.

In the present invention, the carbon fiber chops bundled with a sizing agent obtained by cutting with a roving cutter after sizing treatment and before drying have a sizing agent deposition rate of 0.5 to 5% by weight. The focusing property is 1.05 or less. The sizing agent adhesion rate is closely related to the characteristics of carbon fiber chops. That is, as the sizing agent attachment rate increases, the bulk density and apparent density of the carbon fiber chops increase, and the bundling property improves. However, on the other hand, the increase in the sizing agent adhesion rate is
There is a concern that the final composite properties may be deteriorated, which is not preferable. The preferred sizing agent coverage is 0.5
Is in the range of up to 5% by weight. If this amount is less than 0.5% by weight, the carbon fiber chops are opened to generate fluff or fluff, and it is difficult to quantitatively supply into the extruder, resulting in uneven discharge, resulting in strand breakage and reduced productivity. To do. On the other hand, if it exceeds 5% by weight, the composite properties may be deteriorated, which is not preferable.

The bundling property of the carbon fiber chop is 1.05 or less, and when it exceeds this value, it is similar to the case of the sizing agent adhesion rate.
The fibers are likely to be opened to form fluff, and quantitative supply into the extruder is difficult, resulting in uneven discharge, and strand breakage occurs, resulting in reduced productivity. The focusing property is described in the next section.

The present invention will be described in more detail with reference to Examples. Various evaluations in this example were performed as follows. (1) Bulk density of carbon fiber chop 70 g of carbon fiber chop was put into a 500 ml graduated cylinder, and the weight was divided by the volume of the carbon fiber chop after the graduated cylinder was vertically vibrated 60 times. Ask. (2) Convergence of carbon fiber chops The bulk density of the carbon fiber chops after stirring the carbon fiber chops with a mixer at 400 rpm for 3 minutes is divided by the bulk density before the stirring treatment. 1 is the best value, and as the value becomes larger, the focusing property becomes worse.

Example 1 Carbon fiber 1200 made from polyacrylonitrile
A carbon fiber bundle consisting of 0 pieces was wound out at a speed of 60 m / min while spraying water with an amount of 3 to 5% by weight attached, and a tension of 0.5 to 0. The weight was adjusted to 7 kg / yarn and the sizing treatment was performed by the touch roll method. The rotation speed was adjusted so that the pick-up amount of the sizing agent was 43 to 47% by weight.

The undried carbon fiber bundle thus obtained was continuously cut into a length of 6 mm by a roving cutter to produce a carbon fiber chop. The sizing agent used was a mixture of bisphenol A type epoxy resin / water-based emulsion having a molecular weight of 470 and 2,900, which was adjusted to a solid content concentration of 8% by weight. As a result, a carbon fiber chop having a low size ratio and an excellent bundling property was obtained. The results are shown in Table 1.

Comparative Example 1 As a conventional method, carbon fibers were immersed and impregnated in 7% by weight of the same sizing emulsion solution as in Example 1 to a pickup amount of 82 to 86%, and then a treatment speed of 2 using a hot air dryer. Dry at 0.6 m / min. This was decapsulated to further bundle the carbon fibers, and the carbon fibers were cut into a length of 6 mm using a guillotine cutter at a cutting speed of 1.6 m / min to prepare carbon fiber chops. The obtained carbon fiber chops had a poor sizing property in spite of the high size attachment rate. The results are shown in Table 1.

Examples 2 and 3 Carbon fiber chops were prepared in the same manner as in Example 1 except that the amount of sizing agent attached was changed as shown in Table 1. The results are shown in Table 1.
Shown in.

[0027]

[Table 1]

[0028]

According to the present invention, it becomes possible to obtain a carbon fiber chop by cutting the carbon fiber at a high processing speed.
Productivity is greatly improved. Furthermore, since the carbon fibers are cut in an undried state, there are few cracks in the carbon fiber chops,
Moreover, a high-quality carbon fiber chop excellent in bundling property can be obtained with a low sizing agent adhesion rate, which is extremely high in industrial value.

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[Procedure amendment]

[Submission date] December 10, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Title of invention

[Correction method] Change

[Correction content]

Title: Carbon fiber chop and method for producing the same

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display area D06M 13/00 // B29K 105: 06 D06M 101: 40

Claims (3)

[Claims] 1. A method for producing a carbon fiber chop, which comprises subjecting carbon fibers to a sizing treatment or a water treatment and cutting them with a roving cutter before drying. 2. The sizing agent or water contained in the carbon fiber when cut with a roving cutter is 30 to 60% by weight with respect to the carbon fiber.
Manufacturing method of carbon fiber chop. 3. A carbon fiber chop obtained by sizing according to the method of claim 1, wherein the carbon fiber chop has a sizing agent non-adhesion rate of 0.5 to 5% by weight and a bundling property of 1.05. Carbon fiber chop characterized by being