WO2017151721A1 - Epoxy resin composition comprising carbon fiber sized with a block copolymer of ethylene oxide and propylene oxide - Google Patents

Abstract

The present invention provides epoxy resin compositions of from 30 to 50 parts by weight, as solids, of one or more epoxy resins, and from more than 50 to 70 parts by weight of sized carbon fibers treated with from 0.1 to 5 wt.%, based on the total weight of the thus sized carbon fibers, of a sizing composition of from 50 to 100 wt.%, or, preferably, from 75 to 100 wt.%, based on the total solids in the sizing composition, of a block copolymer of ethylene oxide (EO) and propylene oxide (PO). The block copolymer of ethylene oxide (EO) and propylene oxide (PO) in the sizing composition can have a weight average molecular weight of from 500 to 10,000, or, preferably, 1500 or more.

Description

EPOXY RESIN COMPOSITION COMPRISING CARBON FIBER SIZED WITH A BLOCK COPOLYMER OF ETHYLENE OXIDE AND PROPYLENE OXIDE

The present invention relates to epoxy resin compositions comprising one or more epoxy resins and sized carbon fibers treated with from 0.1 to 5 wt.% or, preferably, from 0.2 to 5 wt.%, or, more preferably, from 0.2 to 3 wt.%, or, more preferably, 2 wt.% or less, or, more preferably, 0.35 wt.% or more, based on the total weight of the thus sized carbon fibers, of a sizing composition of from 50 to 100 wt.%, or, preferably, from 80 to 100 wt.%, or, more preferably, from 90 to 100 wt.%, or, even more preferably, from 95 to 100 wt.%, [>98 wt.% ] based on the total solids in the composition, of a block copolymer of ethylene oxide (EO) and propylene oxide (PO).

Carbon fibers are brittle and require sizing materials on their surface as lubricants to enable improved fiber processing and protect the fibers from damage during handling and the fabrication of intermediates, e.g. fabric. Acceptable sizing compositions provide low friction and consistent handling that allow for easy processing and that prevent residual build-up on processing equipment. In addition, carbon fibers are used to reinforce or fill resin matrix materials; thus, the sizing compositions must be compatible with resin matrix materials formulated to contain the sized carbon fibers. In addition, the sizing materials should allow matrix resin infusion into carbon fibers or carbon fiber bundles.

Japan Unexamined publication Kokai no. 2002-138370A to Toray industries discloses sizing agents for carbon fibers in two layers for use in thermoplastic composites. The first sizing layer can comprise ethylene oxide and propylene oxide copolymers and the second sizing layer comprises thermoplastic resins, thereby allowing adequate thermoplastic resin penetration into the carbon fiber bundle and enable fiber dispersion into the thermoplastic resin. Toray fails to disclose thermosetting resin matrices or composites comprising them. Further, Toray fails to provide a resin composition that can comprise more than 50 parts by weight of sized carbon fibers per 100 parts of resin and fiber lest the composition loses adequate fluidity during molding.

The present inventors have endeavored to provide sized carbon fiber containing thermosetting epoxy resin compositions that exhibit good matrix resin infusion into the carbon fibers or carbon fiber bundles and in mold processability at fiber loadings of more than one part carbon fiber to one part matrix resin.

STATEMENT OF THE INVENTION

1 . In accordance with the present invention, epoxy resin compositions comprise from 30 to 50 parts by weight or, preferably, from 35 to 50 parts by weight or, more preferably, from 45 to 50 parts by weight, as solids, of one or more epoxy resins, for example, glycidyl ethers of a polyol, such as bisphenol A or bisphenol F, epoxy novolac resins, or epoxy hybrid resins or epoxy resin blends, and from more than 50 to 70 parts by weight or, preferably, from more than 50 to 65 parts by weight or, more preferably, from 50 to 60 parts by weight sized carbon fibers treated with from 0.1 to 5 wt.% or, preferably, from 0.35 to 5 wt.%, or, more preferably, from 1 to 3 wt.%, or, more preferably, 2 wt.% or less, based on the total weight of the thus sized carbon fibers, of a sizing composition of from 50 to 100 wt.%, or, preferably, from 75 to 100 wt.%, or, more preferably, from 90 to 100 wt.%, or, even more preferably, from 95 to 100 wt.%, based on the total solids in the sizing composition, of a block copolymer of ethylene oxide (EO) and propylene oxide (PO).

2. In accordance with the epoxy resin compositions of the present invention as in item 1 , above, wherein the block copolymer of ethylene oxide (EO) and propylene oxide (PO) in the sizing composition comprises from 2 to 200, or, preferably from 4 to 100, or, more preferably, from 5 to 50 ethylene oxide groups.

3. In accordance with the epoxy resin compositions of the present invention as in any one of items 1 or 2, above, wherein the block copolymer of ethylene oxide (EO) and propylene oxide (PO) in the sizing composition comprises from 2 to 400, or, preferably from 5 to 200, or, more preferably, from 10 to 150 or, most preferably, from 20 to 100 propylene oxide groups. 4. In accordance with the epoxy resin compositions of the present invention as in any one of items 1 , 2, or 3, above, wherein the block copolymer of ethylene oxide (EO) and propylene oxide (PO) in the sizing composition has a weight average molecular weight of from 500 to 10,000, or, preferably, from 1000 to 7,500, or, more preferably, 1 500 or more, or, most preferably, from 2600 to 5000. All molecular weight ranges are combinable so, for example, the molecular weight of the ethylene oxide (EO) and propylene oxide (PO) block copolymer can range from 1500 to 5000, from 1500 to 10,000 and from 1500 to 7,500. 5. In accordance with the epoxy resin compositions of the present invention as in items 1 , 2, 3, or 4, above, wherein the block copolymer of ethylene oxide (EO) and propylene oxide (PO) is a diblock or a triblock copolymer.

6. In accordance with the epoxy resin compositions of the present invention as in any one of items 1 , 2, 3, 4, or 5, above, wherein the compositions comprise a sheet molding compound of chopped carbon or graphite fibers or a woven or non-woven article of continuous carbon or graphite fibers.

7. In accordance with the epoxy resin compositions of the present invention as in any one of items 1 to 6, above, wherein the carbon fibers have a first layer of surface oxidation and as second layer, the sizing composition.

8. In accordance with the epoxy resin compositions of present invention as in any one of items 1 to 7, above, wherein the sizing composition is substantially free of or is free of thermoplastic polymer.

Unless otherwise indicated, conditions of temperature and pressure are room temperature and standard pressure, also referred to herein as "ambient conditions."

The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

The endpoints of all ranges directed to the same component or property are inclusive of the endpoint and independently combinable. Thus, for example, a disclosed range of from 50 to 100 wt.%, or, preferably, from 75 to 100 wt.%, or, more preferably, from 90 to 100 wt.%, or, even more preferably, from 95 to 100 wt.% means any and all of from 50 to 100 wt.%, or, preferably, from 75 to 100 wt.%, or, more preferably, from 90 to 100 wt.%, or, even more preferably, from 95 to 100 wt.%, or from 50 to 75 wt.%, or from 50 to 90 wt.%, or from 50 to 95 wt.%, or, preferably, from 75 to 90 wt.%, or, preferably, from 75 to 95 wt.%, or, more preferably, from 90 to 95 wt.%.

As used herein, the term "aqueous" means water or water mixed with up to 50wt.%, or up to 25 wt.%, or, preferably, up to 10 wt.%, based on the total weight of a mixture of water and solvent, of one or more water miscible solvents which is volatile under ambient conditions, such as a lower alkanol, an ether, or a ketone.

As used herein, the term "phr" means per hundred parts resin, by weight.

Unless otherwise indicated, the resin refers to the total amount of resin in a given composition, including blends and combinations of more than one different resin , as well as curing agents and reactive diluents.

As used herein, the term "solids" or "total solids" excludes organic solvents and refers to the non-volatile content of a composition, wherein volatiles comprise anything that boils or is a gas at 100 °C, such as water, ammonia or methyl ethyl ketone.

As used herein, the term "substantially free of thermoplastic polymer" means that the given composition contains less than 500 ppm, on a solids weight basis, of thermoplastic polymer.

As used herein, unless otherwise indicated, the term "weight average molecular weight" means that amount determined by measuring the weight average molecular weight of a given polymer by gel permeation chromatography (GPC) against poly(ethylene glycol) standards to determine the number of ethylene oxide groups and against poly(propylene glycol) standards to determine the number of propylene oxide groups.

As used herein, the term "wt.%" refers to weight percent.

The present inventors have found that carbon fiber filled epoxy resin

compositions wherein the carbon fibers have on them a layer of a sizing composition of a block copolymer of ethylene oxide (EO) and propylene oxide (PO) exhibit enhanced epoxy matrix resin infusion into the carbon fibers, improved fiber and molding processability, and good interlaminer shear strength (ILSS) in high performance carbon fiber composites. At the same time, the sizing composition provides fiber processability through a reduced coefficient of friction and reduced fluff without a need for epoxy resins in the sizing composition, all the while ensuring compatibility with the epoxy resin compositions used as matrix resins.

Aqueous compositions of the present invention for sizing carbon fibers comprise one or more block copolymers of ethylene oxide (EO) and propylene oxide (PO), the compositions having a solids content of from 0.1 to 5.0 wt.%.

The aqueous sizing compositions of the present invention can be made by simple mixing of one or more block copolymers of ethylene oxide (EO) and propylene oxide (PO) in an aqueous medium. Thus, the aqueous sizing composition of the present invention can be made by simple mixing of the ingredients with or in an aqueous medium. The block copolymers of ethylene oxide (EO) and propylene oxide (PO) of the present invention are conventional and can comprise materials, such as the

PLURONIC block copolymers (BASF SE, Ludwigshafen, DE).

Preferably, the performance of the aqueous sizing compositions in terms of all of fiber processability, interfacial bonding of matrix resin and fiber, reduced carbon fiber fluff, and compatibility with the epoxy resin matrix is best when the aqueous sizing composition aqueous sizing compositions contain 100 wt.%, or 75 wt.% or more, or 90 wt.% or more or 95 wt.% or more of the block copolymer of ethylene oxide (EO) and propylene oxide (PO) of the present invention.

The aqueous sizing compositions of the present invention can include up to 50 wt.% or, up to 25 wt.% or, more preferably, up to 10 wt.%, or, most preferably, 5 wt.% or less wt.% of one or more formulation chemicals. Suitable formulation chemicals can comprise nonionic surfactants, emulsifiers, water dispersible epoxy resins, ethoxylated bisphenol A having a weight average of from 2 to 30, or, preferably, from 3 to 20 ethylene oxide groups, higher (fatty) alcohol ethoxylates, thermoplastic resins and antifoaming agents, such as silicone containing oils. Epoxy resins, and leveling agents can also be combined in the sizing compositions.

The sized carbon fibers of the present invention are treated with from 0.1 to 5 wt.%, or from 0.2 to 3 wt.%, or, preferably, from 0.35 to 2.0 wt.% of the composition solids, for example, chopped carbon fibers.

Suitable carbon fibers in the present invention can be any such as Type I (high modulus - HM) and Type I I (high tensile strength - HT) carbon fiber, and can also include graphite fibers. Carbon fibers can be formed in a conventional fashion from polyacrylonitrile (PAN), pitch or hydrocarbon feedstocks, and Rayon™ cellulosic polymer feedstocks, for example, any such polymers having high strength and high moduli of elasticity. Such carbon fibers can have a tensile modulus of elasticity preferably ranging from 165 GPa to 800 GPa and further preferably ranging from 200 GPa to 800 GPa at room temperature.

Preferably, for increased adhesion of the sizing composition of the present invention to a given carbon fiber, the carbon fibers of the present invention are preferably subject to surface oxidation treatment and thereby have a first layer of surface oxidation. The suitable carbon fibers may be subjected to liquid phase or vapor phase surface oxidization treatment in advance of sizing. Suitable methods for surface oxidization treatment may include subjecting carbon fiber to

electrochemical oxidation using the carbon fiber as the anode, with an electrolyte solution of an oxidant compound having any of a hydroxyl (C-OH) group, carbonyl (C=O) group, carboxyl (COOH) group, an ammonium bicarbonate as the and varied current densities [31 ]. Oxidation treatment in an electrolytic aqueous solution is preferable because of its advantages, including its convenience. Solutions for electrolytic treatment are not particularly limited, and may be a sulfuric acid solution or an ammonium carbonate solution, for example. To minimize damage to the carbon fiber, an appropriate example of electricity for electrolytic treatment ranges from 0 (no treatment) to 1 00 coulombs per gram of carbon fiber.

The carbon fiber sizing methods of the present invention may comprise the surface oxidation treatment and then treating the carbon fibers with a second layer of a sizing composition, for example, in an aqueous bath, followed by drying the thus treated carbon fibers.

The aqueous sizing compositions of the present invention can be applied to the carbon fibers as sizing solution bath at an elevated temperature, e.g. of from 30 to 100 °C. In a sizing bath, the amount of size retained on the carbon fibers and the effectiveness of the bath depend on sizing times, bath temperature, sizing line speeds, and carbon fiber tension.

The drying of the sized carbon fibers of the present invention may comprise drying at room temperature or heating to elevated temperatures to remove water or solvent in air or inert atmosphere.

The sized carbon fibers of the present invention can then be processed by winding, such as around a bobbin, and then chopping to make chopped carbon fibers, by weaving so as to form a fabric or a wound thread, or spreading the fibers such as for use in forming tape.

The sized carbon fibers of the present invention, whether chopped or continuous, can be further processed by contacting them with a matrix resin comprising epoxy resin compositions (as in a prepreg), or by laying chopped random carbon fibers on an epoxy resin composition film, as in sheet molding compounds (SMC), or by extruding the carbon fiber or a spread fiber array with the epoxy resin compositions as in bulk molding compounds (BMC), or by compression molding which comprises placing the sized carbon fiber as a fabric in a mold, injecting the matrix epoxy resin compositions and pressing, or by filament winding of resin infused fibers onto a substrate, such as a pressure vessel. In such further processing, the prepreg, the chopped random fiber or SMC materials are intermediates that can later be cured and yet even further processed. Any of the intermediates can be formed into a specific three dimensional shape for further processing.

The epoxy resin compositions of the present invention may further comprise the sized carbon fibers of the present invention in combination with other reinforcing fibers to provide strength to the polymer matrix for reinforcement. Fibers suitable for epoxy resin matrix reinforcement include, for example, ceramic fibers, synthetic organic fibers, natural fibers, mineral fibers, metal fibers, and other forms of fibers.

Suitable epoxy resins for use in making the epoxy resin compositions of the present invention include any thermosetting epoxy resin compositions, for example, glycidyl ethers of polyols, such as those made from the reaction of a polyol and an epihalohydrin, such as epichlorohydrin, or the bisphenol A or bisphenol F glycidyl ether epoxy resins, or epoxy novolac resins, epoxy hybrid resins, e.g acrylic epoxy hybrids or polyester epoxy hybrids or urethane epoxy hybrids, or epoxy resin blends.

The epoxy resin compositions of the present invention can comprise a prepreg, a sheet molding compound of chopped carbon or graphite fibers, an extruded bulk molding compound of carbon or graphite fibers, a woven or non-woven article of continuous carbon or graphite fibers, or a non-woven article of chopped or random carbon or graphite fibers.

Epoxy resins used in the present invention may be combined with an appropriate curing agent, such as an aromatic or aliphatic amine, internal mold release agent, viscosity modifiers such as diluents or thickeners. Epoxy resins are formulated to achieve desired processing characteristics, such as, for example, infusion epoxy resin formulation into the carbon fiber intermediate, such as chopped fiber or fabric; to achieve desired processing characteristics of epoxy and carbon fiber

intermediates, such as uncured (B-staged) carbon fiber and epoxy mixtures intermediates such as prepregs and sheet molding compounds with appropriate tack for handling and viscosity for molding; or to achieve final desired molded composite article performance attributes, such as glass transition temperature, composite tensile and flextural strength and fiber volume fraction. EXAMPLES

The following examples serve to better illustrate the invention, which is not intended to be limited by the examples.

The following materials were used in the examples:

Unsized carbon fibers 12K A42 carbon fiber (DowAksa, Yalova, Turkey). After a conventional carbon fiber graphitization process, the carbon fiber was treated with a basic electrolyte to provide surface oxidation.

CHEMITYLEN AK-1 is a commercial sizing material of 20 to 30 wt% of unsaturated polyester, 10-20 wt% of liquid bisphenol A diglycidyl ether epoxy resin, and 50-60 wt% of water (Sanyo Chemical Industries, Ltd, Kyoto, Japan).

Ethylene oxide/propylene oxide block copolymer sizing materials used are as indicated in Table 1 , below.

Table 1 : Various Block Copolymers of Ethylene Oxide and Propylene Oxide

Resin infusion studies were conducted with D.E.R. 383 bisphenol A glycidyl ether liquid epoxy resin (Olin Corporation, Clayton, MO).

Unless otherwise indicated, the term "liquid epoxy resin" means D.E.R. 383 bisphenol A glycidyl ether liquid epoxy resin.

Interlaminar shear strength (ILSS) and interfacial shear strength (IFSS) were conducted with a second formulated epoxy matrix resin. The epoxy matrix resin formulation is disclosed, below.

An epoxy matrix resin was formulated from a blend of, in one part, 1 00 wt.% of D.E.R. 383 bisphenol A glycidyl ether liquid epoxy resin, 4 wt.% of LICOLUB™ WE-4 montanic acid (Clariant SE, Germany), and, in a second part, 2.5 wt.% of

TECHNICURE™ NanoDicy™ dicyandiamide curing agent (A &C Catalysts, Inc., Linden, NJ), 3.0 wt.% of CUREZOL™ 2MZA-PW imidazole curing agent (Shikoku Chemicals Corporation, Japan) and 6.0 wt.% of BAXXODUR™ ECX21 0 (a mixture of 1 ,3-Cyclohexanediamine, 4-methyl- and 1 ,3-Cyclohexanediamine, 2-methyl- (BASF CORPORATION, Florham Park, NJ). The following Test Methods were used in the Examples:

Sizing level: The indicated sized fiber was weighed before placing the fiber in a furnace purged with nitrogen. The fiber was then heated to 450 °C and then held at the temperature for 1 5 min. After cooling to room temperature, the pyrolyzed fiber was weighed again. The sizing level was calculated as the weight difference before and after pyrolysis as a percentage of the original fiber weight. An acceptable sizing level result is from 0.2 to 3 wt.%, preferably from 0.35 to 2 wt.%.

Epoxy Resin Infusion into Fiber Bundle (Washburn method): A piece of 75 mm length of the indicated fiber was cut from a fiber tow. The cut fiber was doubled over and inserted into a 2.56 cm (1 inch) long, 1 .5 mm inner diameter (I.D.) clear, semi- flexible plastic tube. The loose ends of the fiber were trimmed. The tube with the fiber was hung on a microbalance (Kruss K12 tensiometer, Kruss GmbH, Hamburg, DE). A container filled with the D.E.R. 383 bisphenol A glycidyl ether liquid epoxy resin pre-heated to 40 °C was placed underneath the trimmed ends of the fiber. To start the measurement, the resin was raised until it touched the bottom of the fiber sample. The weight of resin infused over time by the fiber was recorded to evaluate resin uptake by the fiber bundle. The data recording was stopped when there was no change in weight over a 20 second period. The resin infusion experiment was usually completed in 5 to 15 min.

For each fiber and resin combination, three experiments were carried out to obtain an average of the amount of resin infused into the fibers.

Coefficient of friction (COF): One end of a single 12k carbon fiber tow was clamped in a 100 N load cell installed on an INSTRON device (model #5567A Illinois Tool Works, Inc., Norwood, MA), while the other end was threaded through a zig-zag pattern of five (5) stainless-steel pins (0.635 cm (0.25") in outer diameter) and secured to a 100 g mass, such that the carbon fiber tow was suspended from the load cell, with the mass below all of the metal pins. The total wrap angle of the tow with the pins was 360 degrees. The position of the fiber was adjusted such that the end of the tow connected to the 100 g mass was at least 50 mm below the lowest pin on COF test apparatus. The load cell was then engaged; the initial force on the load cell was recorded; and the fiber was displaced upwards 50 mm at 100 mm/min. Following ASTM D3108 (2013), the coefficient of friction μ was calculated as follows:

Equation I: μ = ln(F/F_.oad)/e where

F is the average measured force during the last 20 mm of vertical displacement of the carbon fiber tow with the 100 g mass connected

Fi_oad is the measured preload due to the 100 g mass connected to the tow Θ is the total contact angle of the tow with the pins, which, for each pin is the angle created by the leg of the tow below the pin and above the pin; here Θ equals 2π radians or 360 deg.

For each fiber, five specimens were tested to obtain an average COF. The metal friction pins of the COF apparatus were cleaned with an alcohol wipe after testing each set of fibers.

Fiber bundle breakup: To measure the bulk density of chopped fiber, sized carbon fibers were chopped to 1 .26 cm (0.5 inch) using a Model 80 Fiber Cutter (Finn and Fram, North Hills, CA). The bulk density of 1 .27 cm (½ inch) chopped carbon fiber was determined by placing 200 ml_ of chopped fiber into a pre-weighed 250 ml_ glass cylinder. The weight of the fiber was recorded. The cylinder was then affixed to a Logan TAP-2S Tap Density Tester (Logan Instruments Corp., Somerset, NJ) and the volume of the fiber was reduced by tapping 1 ,000 times. The weight of the fiber was divided by the resultant volume to give the "tap" bulk density. Lower bulk density is desired to afford higher dispersion of fiber, and thus improved composite performance (e.g. tensile strength).

Interfacial Shear Strength (IFSS): The formulated matrix resin and sized fibers were subject to a microbond test to determined IFSS. The microbond test measures the force required to displace a drop of the indicated cured epoxy resin cured so that it adhered around a single carbon fiber filament sized with the indicated composition. See, for example, J. L. Thomason and L. Yang, "Temperature dependence of the interfacial shear strength in glass-fibre polypropylene composites," Composites Science and Technology, 71 (201 1 ) at 1 600-1605. The sized fiber is glued to a paper tab and the cured resin droplet is adhered on the free end of the sized fiber. The IFSS test fixture is installed in the grips of a tension test instrument (Texture Analyser). The cured resin droplet is suspended from the test fixture, consisting of a metal slit -25 um in width and having approximately parallel edges. The paper tab is clamped; the Texture Analyzer is actuated to displace the cured resin droplet (bead length L) from the sized fiber (fiber diameter D), and the peak force (Fp) is recorded. The IFSS is then calculated using Formula (I), below:

(I) τ =—

Interlaminar Shear Strength (ILSS) : To measure the adhesion of fiber to matrix in a liquid epoxy resin composition, the method of ISO 141 30 (International

Organization for Standardization, Geneva, CH, 1 997) was followed using 2mm thick x 20 mm long x 1 0 mm wide molded unidirectionally (UD) aligned carbon fiber reinforced epoxy resin specimens. In the method, the molded UD composite sample is placed symmetrically onto two cylindrical 2 mm ± 0,2 mm support bars running fully across the sample so that the fibers run perpendicular to the supports; the support bars are placed apart a distance equal to five times the thickness of the specimens. A 5 mm ± 0,2 mm cylindrical load member is placed atop the sample parallel to and halfway between the support bars and the load, in Newtons, is applied uniformly across each specimen until one or more shear (e.g.) lines appear in the specimen. Reported is the average of five sample measurements. The I LSS is then calculated (in MPa) as:

T= 3/4 x F/bh

where F is the failure or maximum load, in newtons; b is the width, in millimetres, of the test specimen; and h is the thickness, in millimetres, of the test specimen.

The test results of the indicated sizing and epoxy resin compositions used in the Examples are shown, respectively, in Tables 2 and 3, below.

Comparative Example A: Unsized carbon fibers were sized with

CHEMITYLEN™ AK-1 sizing material which was diluted with water to obtain a diluted sizing dispersion with 2.5 wt.% solids. The diluted sizing dispersion was then poured into a tank on a carbon fiber sizing line and carbon fiber was passed through the diluted sizing dispersion to achieve a target sizing level of 1 .5 wt.%. After sizing coating, the fiber was passed through a 1 05 °C dryer for 1 -2 min to obtain the dry sized fiber. The sizing level of the sized fiber in this example was 1 .5% by weight determined by the sizing level measurement. Based on three trials with the carbon fiber, the average total amount of resin infused into the fiber bundle was 0.069 g for the epoxy (D.E. R. 383) resin. The sized fiber had a COF of 0.33; and, the sized fiber and cured resin droplet had an IFSS of 62 MPa. The bulk density of chopped fiber in this example was 0.43 g/cm³. Example 1 : Using a continuous process, unsized carbon fiber was pulled by a 5 roller feed Godet set roller unit (model FR-N0.6-SRV, Izumi International, Inc.

Greenville, SC) from the creel stand of the roller unit and was then fed through the bath of the prepared, room temperature (-20 °C), aqueous sizing composition of Example 1 in Table 1 , above, which was dispersed into water to prepare an aqueous dispersion with 0.8 wt.% solids. The sizing application time was 4 seconds. The sized carbon fiber tow is pulled by the tension controlled winder from the sizing bath through the dryer, maintained between 146 - 150 °C via a controller, at a line speed of 3 m/min, for a total drying time of 43 sec to remove the water and produce sized carbon fiber. The dried carbon fiber tow is collected on the spool of the winder. The fiber tension was monitored between the dryer and the winder, using a hand held tension meter (ELECTROMATIC DTMB-1 K, Electromatic Equipment Co., INC), and found to be 570-640 g. Finally, sized fiber was placed in a vacuum oven (vacuum strength of 23 cmHg) for 4 hrs at 1 15 °C. The sizing level of the sized fiber in this example was 0.7% by weight. The COF of the sized fiber in this example was 0.27, which was significantly lower than the COF of the sized fibers in Comparative Example A, suggesting that the sized fiber in this example will have better processability when contacting metal fiber processing equipment.

Further, the average total amount of DER 383 epoxy resin infused into carbon fiber bundles treated with the sizing composition was 0.078 g. The resin infusion amount was comparable to that of the sized fiber in Comparative Example A. The bulk density of the chopped fiber in Example 1 was 0.25 g/cm³. This was a significant decrease in the bulk density of chopped fiber compared to Comparative Example A. The IFSS of the sized fiber and cured resin droplet in this example was 64 MPa, which was similar to that of the sized fibers in Comparative Example A. This indicates that the sized carbon fibers in Example 1 have similar interfacial bonding with the formulated matrix epoxy resin after curing as the fibers using the sizing agents in Comparative Example A.

Example 2: Unsized carbon fibers were sized as in Example 1 with the sizing material of Example 2 in Table 1 , above, which was dispersed into water to prepare an aqueous dispersion with 0.6 wt.% solids. The sizing application time was 4 seconds. The sized carbon fiber tow is pulled by the tension controlled winder from the sizing bath through the dryer, maintained between 150 - 154 °C via a controller, at a line speed of 3 m/min, for a total drying time of 43 sec to remove the water and produce sized carbon fiber. The dried carbon fiber tow is collected on the spool of the winder. The fiber tension was monitored between the dryer and the winder, using a hand held tension meter (ELECTROMATIC DTMB-1 K) and found to be 460-530 g. Finally, sized fiber was placed in a vacuum oven (vacuum strength of 23 cmHg) for 4 hrs at 1 1 5 °C. The sizing level of the sized fiber in this example was 0.8% by weight. The COF of the sized fiber in this example was 0.27, which was significantly lower than the COF of the sized fibers in Comparative Example A, suggesting that the sized fiber in this example will have better processability when contacting metal fiber processing equipment.

Further, the average total amount of DER 383 epoxy resin infused into carbon fiber bundles treated with the sizing composition was 0.086 g. The resin infusion amount was comparable to that of the sized fiber in Comparative Example A. The bulk density of the chopped fiber in Example 1 was 0.22 g/cm³. This was a significant decrease in the bulk density of chopped fiber compared to Comparative Example A. The IFSS of the sized fiber and cured resin droplet in this example was 63 MPa, which was similar to that of the sized fibers in Comparative Example A. This indicates that the sized carbon fibers in Example 2 have similar interfacial bonding with the formulated matrix epoxy resin after curing as the fibers using the sizing agents in Comparative Example A.

Example 3: Unsized carbon fibers were sized as in Example 1 with the sizing material of Example 3 in Table 1 , above, which was dispersed into water to prepare an aqueous dispersion with 0.5 wt.% solids. The sizing application time was 4 seconds. The sized carbon fiber tow is pulled by the tension controlled winder from the sizing bath through the dryer, maintained between 147 - 151 °C via a controller, at a line speed of 3 m/min, for a total drying time of 43 sec to remove the water and produce sized carbon fiber. The dried carbon fiber tow is collected on the spool of the winder. The fiber tension was monitored between the dryer and the winder, using a hand held tension meter (ELECTROMATIC DTMB-1 K) and found to be 510-750 g. Finally, sized fiber was placed in a vacuum oven (vacuum strength of 23 cmHg) for 4 hrs at 1 1 5 °C. The sizing level of the sized fiber in this example was 0.8% by weight. The COF of the sized fiber in this example was 0.26, which was significantly lower than the COF of the sized fibers in Comparative Example A, suggesting that the sized fiber in this example will have better processability when contacting metal fiber processing equipment.

Further, the average total amount of DER 383 epoxy resin infused into carbon fiber bundles treated with the sizing composition was 0.1 01 g. The resin infusion amount was significantly higher than that of the sized fiber in Comparative Example A, indicating that the sizing composition increased the compatibility of the carbon fiber and the formulated matrix epoxy resin. The bulk density of the chopped fiber in Example 3 was 0.20 g/cm³. This was a significant decrease in the bulk density of chopped fiber compared to Comparative Example A. The IFSS of the sized fiber and cured resin droplet in this example was 65 MPa, which was similar to that of the sized fibers in Comparative Example A. This indicates that the sized carbon fibers in Example 3 have similar interfacial bonding with the formulated matrix epoxy resin after curing as the fibers using the sizing agents in Comparative Example A.

Example 4: Unsized carbon fibers were sized as in Example 1 with the sizing material of Example 4 in Table 1 , above, which was dispersed into water to prepare an aqueous dispersion with 0.6 wt.% solids. The sizing application time was 4 seconds. The sized carbon fiber tow is pulled by the tension controlled winder from the sizing bath through the dryer, maintained between 148 - 152 °C via a controller, at a line speed of 3 m/min, for a total drying time of 43 sec to remove the water and produce sized carbon fiber. The dried carbon fiber tow is collected on the spool of the winder. The fiber tension was monitored between the dryer and the winder, using a hand held tension meter (ELECTROMATIC DTMB-1 K) and found to be 410-610 g. Finally, sized fiber was placed in a vacuum oven (vacuum strength of 23 cmHg) for 4 hrs at 1 1 5 °C. The sizing level of the sized fiber in this example was 0.7% by weight. The COF of the sized fiber in this example was 0.27, which was significantly lower than the COF of the sized fibers in Comparative Example A, suggesting that the sized fiber in this example will have better processability when contacting metal fiber processing equipment.

Further, the average total amount of DER 383 epoxy resin infused into carbon fiber bundles treated with the sizing composition was 0.096 g. The resin infusion amount was significantly higher than that of the sized fiber in Comparative Example A, indicating that the sizing composition increased the compatibility of the carbon fiber and the matrix epoxy resin. The bulk density of the chopped fiber in Example 1 was 0.20 g/cm³. This was a significant decrease in the bulk density of chopped fiber compared to Comparative Example A. The IFSS of the sized fiber and cured resin droplet in this example was 59 MPa, which was similar to that of the sized fibers in Comparative Example A. This indicates that the sized carbon fibers in Example 3 have similar interfacial bonding with the formulated matrix epoxy resin after curing as the fibers using the sizing agents in Comparative Example A.

Example 5: Unsized carbon fibers were sized as in Example 1 with the sizing material of Example 5 in Table 1 , above, which was dispersed into water to prepare an aqueous dispersion with 0.7 wt.% solids. The sizing application time was 4 seconds. The sized carbon fiber tow is pulled by the tension controlled winder from the sizing bath through the dryer, maintained between 147 - 151 °C via a controller, at a line speed of 3 m/min, for a total drying time of 43 sec to remove the water and produce sized carbon fiber. The dried carbon fiber tow is collected on the spool of the winder. The fiber tension was monitored between the dryer and the winder, using a hand held tension meter (ELECTROMATIC DTMB-1 K) and found to be 490-660 g. Finally, sized fiber was placed in a vacuum oven (vacuum strength of 23 cmHg) for 4 hrs at 1 1 5 °C. The sizing level of the sized fiber in this example was 0.8% by weight. The COF of the sized fiber in this example was 0.27, which was significantly lower than the COF of the sized fibers in Comparative Example A, suggesting that the sized fiber in this example will have better processability when contacting metal fiber processing equipment.

Further, the average total amount of DER 383 epoxy resin infused into carbon fiber bundles treated with the sizing composition was 0.093 g. The resin infusion amount was significantly higher than that of the sized fiber in Comparative Example A, indicating that the sizing composition increased the compatibility of the carbon fiber and the matrix epoxy resin. The bulk density of the chopped fiber in Example 5 was 0.25 g/cm³. This was a significant decrease in the bulk density of chopped fiber compared to Comparative Example A. The IFSS of the sized fiber and cured resin droplet in this example was 64 MPa, which was similar to that of the sized fibers in Comparative Example A. This indicates that the sized carbon fibers in Example 5 have similar interfacial bonding with the formulated matrix epoxy resin after curing as the fibers using the sizing agents in Comparative Example A. Table 2: Sizing Levels and Properties of Sized Carbon Fibers.

Example 3A: The unsized carbon fibers were sized as in Example 3. Further, the sizing composition had a solids content of 0.5 wt% and the measured sizing level was 0.8 wt.%, as solids. Following application of sizing via sizing bath, drying via drying chamber, the sized fibers were rewound onto spools. Using a belt puller, each of four 12k sized carbon fiber tows were pulled from individual rollers, over spreader bars, through an epoxy bath having the epoxy matrix resin formulation as shown, above, and finally through a die to produce a unidirectional (UD) carbon fiber epoxy tape having a width of 2.5 cm (1 in) and, as solids, 39.5 ± 0.5 wt.% sized carbon fiber. These unidirectional carbon fiber epoxy tapes were cut to cut to 26.4 cm lengths and 16 ply layups stacks were prepared with all fibers oriented parallel to the 0 degree orientation. To mold, the stacked lamina were placed within a 26.67 x 2.54 cm (10.5 x 1 inch) shear-edge compression mold that was preheated to 150°C via electrically heated 254 x 254 cm (12x12") platens of a 15 ton press (model 3893.4DI 1 A03; Carver, Inc. Wabash, IN). The mold tool was closed, vacuum was applied to remove air from the mold, and the UD layup was molded for 3 minutes under an applied pressure of 40 bar (575 psi), such that the resulting molded composites had 59 ± 0.5 wt.%, as solids, carbon fiber. The molded product was then tested for interlaminar shear strength (ILSS).

Comparative Example 3B: An unsized 12k carbon fiber was treated with the CHEMITYLEN AK-1 sizing agent at a sizing level of 1 .5 wt.%. The product was tested for ILSS. Table 3: Test Results From Carbon Fiber Reinforced Molded Specimens

As shown in Table 3, above, the inventive sized carbon fiber reinforced epoxy resin moldings of the present invention gave about the same level of interlaminar shear strength even though less than half, as solids, of the inventive sizing composition of inventive Example 3A was used when compared to the amount of the Comparative Example 3B sizing composition.

Claims

We claim:

1 . An epoxy resin composition comprising from 30 to 50 parts by weight, as solids, of one or more epoxy resins, epoxy hybrid resins or epoxy resin blends, and from more than 50 to 70 parts by weight of sized carbon fibers treated with from 0.1 to 5 wt.%, based on the total weight of the thus sized carbon fibers, of a sizing composition of from 50 to 100 wt.%, based on the total solids in the sizing composition, of a block copolymer of ethylene oxide (EO) and propylene oxide (PO).

2. The epoxy resin composition as claimed in claim 1 , wherein the sizing composition comprises from 75 to 100 wt.%, based on the total solids in the sizing composition, of a block copolymer of ethylene oxide (EO) and propylene oxide (PO).

3. The epoxy resin composition as claimed in claim 1 , wherein the block copolymer of ethylene oxide (EO) and propylene oxide (PO) in the sizing

composition comprises from 4 to 100 ethylene oxide groups.

4. The epoxy resin composition as claimed in claim 1 , wherein block copolymer of ethylene oxide (EO) and propylene oxide (PO) in the sizing composition comprises from 5 to 200 propylene oxide groups.

5. The epoxy resin composition as claimed in claim 1 , wherein the block copolymer of ethylene oxide (EO) and propylene oxide (PO) in the sizing

composition has a weight average molecular weight of from 1500 to 5000.

6. The epoxy resin composition as claimed in claim 1 , wherein the block copolymer of ethylene oxide (EO) and propylene oxide (PO) is a diblock or a triblock copolymer.

7. The epoxy resin composition as claimed in claim 1 , wherein the compositions comprise a sheet molding compound of chopped carbon or graphite fibers or a woven or non-woven article of continuous carbon or graphite fibers.

8. The epoxy resin composition as claimed in claim 1 , wherein the carbon fibers have a first layer of surface oxidation and as second layer, the sizing composition.

9. The epoxy resin composition as claimed in claim 1 , wherein the sizing composition is substantially free of or is free of thermoplastic polymer.