Provided are: chopped carbon fiber bundles which have high fluidity without decreasing the dispersibility of carbon fibers and the physical properties of a molded product; and a method for producing chopped carbon fiber bundles with high productivity. Chopped carbon fiber bundles, each of which contain a carbon fiber bundle having a total fineness of from 25,000 dtex to 45,000 dtex (inclusive) and a sizing agent in an amount of from 1% by mass to 5% by mass (inclusive) relative to the total mass of the chopped carbon fiber bundle. The length (L) of each chopped carbon fiber bundle along the fiber direction of the carbon fiber bundle is from 1 mm to 50 mm (inclusive); the ratio of the longest diameter (Dmax) to the shortest diameter (Dmin) of a cross section perpendicular to the fiber direction of each chopped carbon fiber bundle, namely Dmax/Dmin is from 6.0 to 18.0 (inclusive); and the orientation parameter of the single fibers present in the surface of each chopped carbon fiber bundle is 4.0 or less.

A partially separated fiber bundle includes a separated fiber section and an unseparated fiber section, being configured to give a ratio A.sub.max/A.sub.min of 1.1 or larger and 3 or smaller, when the number of fiber bundles contained in the width direction of the partially separated fiber bundle (fiber separating number: N.sub.n) measured at a freely selected point P.sub.n (where, n represents an integer of 1 to 100, and freely selected points P.sub.n and P.sub.n+1, excluding n=100, being 50 cm or more away from each other), is divided by a full width of W.sub.n of the partially separated fiber bundle, to calculate the fiber separating number per unit width A.sub.n, and assuming its maximum value as A.sub.max and its minimum value as A.sub.min.

A partially separated fiber bundle includes a separated fiber section and an unseparated fiber section, being configured to give a ratio A.sub.max/A.sub.min of 1.1 or larger and 3 or smaller, when the number of fiber bundles contained in the width direction of the partially separated fiber bundle (fiber separating number: N.sub.n) measured at a freely selected point P.sub.n (where, n represents an integer of 1 to 100, and freely selected points P.sub.n and P.sub.n+1, excluding n=100, being 50 cm or more away from each other), is divided by a full width of W.sub.n of the partially separated fiber bundle, to calculate the fiber separating number per unit width A.sub.n, and assuming its maximum value as A.sub.max and its minimum value as A.sub.min.

In accordance with one embodiment, a polymer composite comprises a filler and a matrix. The filler comprises an electrospun polymer mat. The matrix comprises a polymer film. The filler is arranged to respond to stimuli by altering its mechanical properties. In one example, the mat can be electrospun from poly(vinyl alcohol), and the matrix can be formed from ethylene oxide-epichlorohydrin 1:1 copolymer. The filler can be arranged so that the tensile storage modulus of the polymer composite changes in response to the filler being exposed to a stimulus. In another example, the filler is about four percent by weight of the polymer composite.

In accordance with one embodiment, a polymer composite comprises a filler and a matrix. The filler comprises an electrospun polymer mat. The matrix comprises a polymer film. The filler is arranged to respond to stimuli by altering its mechanical properties. In one example, the mat can be electrospun from poly(vinyl alcohol), and the matrix can be formed from ethylene oxide-epichlorohydrin 1:1 copolymer. The filler can be arranged so that the tensile storage modulus of the polymer composite changes in response to the filler being exposed to a stimulus. In another example, the filler is about four percent by weight of the polymer composite.

A carbon fiber washer is provided and includes a carbon fiber fabric made of a plurality of fiber bundles being woven, in which each of the plurality of fiber bundles is made of discontinuous fibers; the advantage of the carbon fiber washer of the present invention includes high temperature and fatigue resisting, and weather proofing. The structure of the carbon fiber washer is stable due to the use of discontinuous fibers; breakages of discontinuous fibers do not affect other unbroken discontinuous fibers, so that the structure of the carbon fiber washer would not be loosened or delaminated and the service life can be prolonged accordingly.

A yarn for reinforcing composite material includes carbon nanotubes. The yarn has also been treated to promote interaction with a resinous matrix.

The object is to provide a resin composition for a printed circuit board capable of realizing a printed circuit board that not only has heat resistance and flame retardancy but also is excellent in heat resistance after moisture absorption. The resin composition is a resin composition for a printed circuit board containing a cyanate ester compound (A) obtained by cyanation of a naphthol-dihydroxynaphthalene aralkyl resin or a dihydroxynaphthalene aralkyl resin, and an epoxy resin (B).

The object is to provide a resin composition for a printed circuit board capable of realizing a printed circuit board that not only has heat resistance and flame retardancy but also is excellent in heat resistance after moisture absorption. The resin composition is a resin composition for a printed circuit board containing a cyanate ester compound (A) obtained by cyanation of a naphthol-dihydroxynaphthalene aralkyl resin or a dihydroxynaphthalene aralkyl resin, and an epoxy resin (B).

A sizing composition for glass fiber direct roving for producing multiaxial fabrics is provided. The sizing composition includes, based on the total solids mass of the composition, 0.1 to 5.0% by solid mass of a first silane coupling agent, 2.5 to 11.0% by solid mass of a second silane coupling agent, 3.0 to 20.0% by solid mass of a first film former, 45.0 to 75.0% by solid mass of a second film former, 0 to 5.0% by solid mass of a plasticizer, 0.2 to 4.0% by solid mass of a first lubricant, 5.0 to 20.0% by solid mass of a second lubricant, and 0.01 to 3.0% by solid mass of a pH regulator. The first film former is a multifunctional epoxy emulsion, and the second film former is a low-molecular-weight liquid epoxy emulsion.