Semi-preg material with a property-enhancing surface film for improved properties

Abstract

Semi-preg material is disclosed adapted for use in composite material comprising a) a first resin layer, b) covered on both side by layers of fibrous reinforcements whereby c) one of the two fabric layers is coated with a second resin layer and d) wherein said second resin layer has a tack level of not more than 100 N. Such semi-preg material has improved handling properties and contributes to the superior mechanical properties of the composite material formed therewith.

Claims

1. A semi-preg material that is composed of a semi-preg having a first outer side and a second outer side where the tack of said first outer side varies from 20 to 38 N and where the tack of said first outer side is controlled by a property enhancing film that has a more consistent and reduced tack of from 10 to 15 N, said semi-preg material comprising: A) a semi-preg comprising: a) a first resin layer comprising an uncured thermosetting resin and a curing agent for said uncured thermosetting resin; b) a first layer of fibrous reinforcement located on one side of said first resin layer, said first layer of fibrous reinforcement, comprising an inner side adjacent to said first resin layer and an outer side that forms said first outer side of the semipreg, wherein a portion of said uncured thermosetting resin from said first resin layer has travelled through portions of said first layer of fibrous reinforcement from said inner side to said first outer side of the semipreg such that said first outer side of the semipreg has a tack that varies from 20 to 38 N; c) a second layer of fibrous reinforcement that is located on the other side of said first resin layer, said second layer of fibrous reinforcement having an inner side adjacent to said first resin layer and an outer side that forms said second outer side of the semipreg; and B) a property enhancing film comprising a mixture of uncured thermosetting resin and a rubber toughening component, said property enhancing film being in the form of a solid film that has an outer surface and an inside surface, said inside surface contacting and covering said first outer side of the semipreg, wherein said solid film weighs from 10 to 60 gsm and wherein the outer surface of said solid film has a tack level of 10 to 15 N to thereby control the tack level of the first outer side of said semi-preg to be more consistent and reduced.

2. Semi-preg material according to claim 1 wherein the first resin layer is present in an amount of 100 to 800 g/m.sup.2 of the semi-preg material.

3. Semi-preg material according to claim 2 wherein the first resin layer is present in an amount of 350 to 650 g/m.sup.2 of the semi-preg material.

4. Semi-preg material according to claim 1 wherein the fibres of said first layer of fibrous reinforcement are in +30 to +45 orientation.

5. Semi-preg material according to claim 4 wherein the fibres of said second layer of fibrous reinforcement are in 30 to 45 orientation.

6. Semi-preg material according to claim 1 wherein the first layer of fibrous reinforcement and the second layer of fibrous reinforcement are stitched together.

7. Semi-preg material according to claim 1 wherein said property enhancing film has a tack level that varies from 10 to 12 N.

8. Semi-preg material according to claim 1 wherein said first resin layer comprises an uncured thermosetting resin selected from the group consisting of phenol formaldehyde resins, epoxy, polyester, vinylester, polyimide, cyanate ester, phenolic and bismaleimide resins and mixtures thereof.

9. Semi-preg material according to claim 1 wherein said property enhancing film comprises uncured solid bis enol-epoxy resin, a rubber toughening component and polyamide particles.

10. A method for making a composite material comprising the steps of placing a semi-preg material according to claim 1 into a mold and curing said first resin layer and said property enhancing film to form a cured composite material.

11. A method for making a composite material according to claim 10 wherein said composite material forms at least part of a large load bearing structure.

12. A method for making a composite material according to claim 11 wherein said large load beating structure is a wind turbine blade.

13. A method for making a composite material according to claim 11 wherein said large load bearing structure is an aerospace structure.

14. A roll of semi-preg material comprising a semi-preg material according to claim 1 that has been formed into a roll wherein said property enhancing film is located adjacent to and in contact with said second layer of fiber reinforcement.

15. Semi-preg material according to claim 1 wherein said property enhancing film comprises uncured solid bisphenol-epoxy resin, a rubber toughening component and nano sized core/shell rubber particles.

16. A method for making a semi-preg material that composed of a semi-preg having a first outer side and a second outer side Where the tack of said first outer side varies from 20 to 38 N and where the tack of said first outer side is controlled by a property enhancing film that has a more consistent and reduced tack of from 10 to 15 N, said method comprising the steps of: A) providing outside of the mold a semi-preg comprising: a) a first resin layer comprising an uncured liquid thermosetting resin and a curing agent for said uncured thermosetting resin; b) a first layer of fibrous reinforcement on one side of said first resin layer, said first layer of fibrous reinforcement comprising an inner side adjacent to said first resin layer and an outer side that forms said first outer side of the semipreg, wherein a portion of said uncured thermosetting resin from said first resin layer travels through portions of said first layer of fibrous reinforcement from said inner side to said first outer side of the semi-preg such that said first outer side of the semi-preg has a tack that varies from 20 to 38 N; c) a second layer of fibrous reinforcement that is located on the other side of said first resin layer, said second layer of fibrous reinforcement having an inner side adjacent to said first resin layer and an outer side that forms said second outer side of the semipreg; and B) forming a property enhancing film on the outer side of said first layer of fibrous reinforcement, said property enhancing film comprising a mixture of uncured thermosetting resin and a rubber toughening component, said property enhancing film being in the form of a solid film that has an outer surface and an inside surface, said inside surface contacting and covering said first outer side of the semipreg, wherein said solid film weighs from 10 to 60 gsm and wherein the outer surface of said solid film has a tack level of 10 to 15 N to thereby control the tack level of the first outer side of said semi-preg to be more consistent and reduced.

17. A method for making a semi-preg material according to claim 16 wherein the first resin layer is present in an amount of 100 to 800 g/m.sup.2 of the semi-preg material.

18. A method for making a semi-preg material according to claim 16 which includes the additional step of form said semi-preg material into a roll wherein said property enhancing film is located adjacent to and in contact with said second layer of fiber reinforcement.

19. A method for making as semi-preg material according to claim 16 wherein said property enhancing film comprises uncured solid bisphenol-epoxy resin, a rubber toughening component and nano sized core/shell rubber particles.

20. A method for making a semi-preg material according to claim 16 wherein said property enhancing film comprises uncured solid bisphenol-epoxy resin, a rubber toughening component and polyamide particles.

Description

4. DESCRIPTION OF THE DRAWINGS

(1) The foregoing and other advantages and features of the invention and the manner in which the same are accomplished will become more readily apparent upon consideration of the following examples taken in conjunction with the accompanying drawings which illustrate preferred and exemplary embodiments.

(2) FIG. 1 shows a preferred embodiment of the semi-preg of the present invention. The central resin layer is covered on both sides by fabric layers whereby the orientation of the fibres in the fabric layer above the central resin layer is +45 to the warp direction and the orientation in the fabric layer below the central resin layer is 45 to the warp direction. On top of the upper fabric layers there is the second resin layer prepared by a dry to touch/tack control film applied in an amount between 10 to 60 gsm, preferably 20 to 60 gsm.

(3) FIG. 2 shows the improvement of the fracture toughness G1c obtainable by the semi-preg of the present invention. The graph shows on the left-hand side a standard semi-preg without the second resin layer. In the middle the semi-preg according to the invention with a second layer having 20 gsm is show whereby on the right-hand side a semi-preg according to the present invention with a second resin layer of 60 gsm is shown.

(4) FIG. 3 shows the improvement of the interlaminar shear strength (ILSS) obtainable with the prepreg according to the present invention. On the left-hand side the prepreg without the second resin layer is shown, the sample in the middle contains a second resin layer with 20 gsm and on the right a semi-preg according to the invention with a second layer of 60 gsm is shown.

(5) FIG. 4 shows how the tack properties of the semi-preg of the invention are improved by the second resin layer. Without the second resin layer the tack values range from about 20 to 38 whereas by using the second resin layer the tack is reduced to below 15 N.

(6) By comparing FIGS. 2 and 3 it becomes evident that by changing the amount of resin in the second resin layer from 20 gsm to 60 gsm the advantageous properties of the composite material prepared from the semi-preg of the present invention can be influenced. On the other hand, FIGS. 2 and 3 show that a substantial portion of the advantages possible with 60 gsm layers are already achieved with 20 gsm layers. This can be important in situations where weight is at a premium, e.g., aerospace components.

(7) The following examples illustrate the invention and serve for illustrative purposes.

EXAMPLE 1

(8) Standard semi-preg materials typically comprise a film of formulated resin to which a dry fibrous reinforcement is attached to one or both sides of the film usually by means of the inherent tack of the resin film.

(9) The semi-preg material of the invention was constructed from a 340 gsm film layer of M9.6-LT, M9.6F-LT or M9.7 (an epoxy resin based on a blend of liquid, semi-solid and solid bisphenol-A epoxies, dicyandiamide and a urone) resin to which a layer of glass UD fibrous reinforcement is attached to either side of the film. One reinforcement layer typically possesses unidirectional fibres running at +45 or +30 to the warp (i.e. 0) direction of the resin film and the other layer possesses the same unidirectional reinforcement fibres running at 45 or 30 to the warp direction. The reinforcement fibres for each layer are typically bundled into tows. These tows are stitched together in order to hold the fabric layer together.

(10) To the above semi-preg material a tack controlling, property enhancing resin film was applied which was prepared by blending at greater than 80 C. a mixture of molten solid bisphenol-A epoxy resin, such as Epikote 1001 (manufactured by Hexion Speciality Chemicals B.V., The Netherlands) at 75 parts per hundred and a rubber adducted liquid bisphenol-A epoxy resin, such as Struktol Polydis 3614 (manufactured by Schill and Seilacher, Germany) at 25 parts per hundred. This resin blend is referred to by Hexcel as DLS1765 and is then transferred on to the outer surface of the semi-preg as a film at 20-60 gsm or is first converted into a film supported on a silicone release paper before heat transferring to a surface of the semi-preg. The overall material structure is depicted in FIG. 1.

(11) The DLS1765 can be modified by the addition of thermoplastic polyamide particles such as Orgasol 1002 DNAT 1 (manufactured by Arkema Inc, Philadelphia, US) at 10-15 parts per hundred. An alternative to DLS1765 resin blend is to substitute part or all of the Epikote 1001 with a solid bisphenol A epoxy resin containing nano sized core shell rubber particles, such as Kaneace MX181 (manufactured by Kaneka, Tex., US).

EXAMPLE 2

(12) Fracture Toughness (G.sub.1c) Improvement:

(13) Eight ply laminates were constructed from standard semi-preg material and semi-preg material with the property enhancing film attached using +/45 unidirectional fabrics. The laminates were constructed such that the two adjacent inner plies were orientated with fibres running in the 0 (i.e. test) direction. The rest of the laminate was constructed symmetrically with the plane of symmetry being between the two inner plies with the fibre directions (with respect to the test direction) as follows: 90, 0, 90, 0, 90, 0, 90, 0, 0, 90 0, 90 0, 90 0, 90. At one end of the construction a piece of non porous peel ply was inserted to act as a crack initiator for the fracture toughness test. The construction is then cured in a standard vacuum bag assembly and a standard cure cycle of 1 hour at 120 C.

(14) The laminates were then prepared and tested to measure G.sub.1c performance according to AITM (Airbus Industrie Test Method) 1-0005 using an Instron 5569 test machine. Results showed that G.sub.1 performance was improved from an average of 757 J/m.sup.2 using standard semi-preg to >900 J/m.sup.2 using semi-preg with the property enhancing film (represented by box plots in FIG. 2.

EXAMPLE 3

(15) Interlaminar Shear Strength

(16) ILSS testing according to BS (British Standard) EN 2563 using a Zwick 1445 test machine was performed on samples taken from the above laminates such that the inner 0 fibres ran lengthwise along the test specimens. Results showed that ILSS performance was improved from an average of 36.4 MPa using standard semi-preg to 43.8 MPa using semi-preg with a 20 gsm layer of property enhancing film to 45.3 MPa using semi-preg with a 60 gsm layer of property enhancing film (represented by box plots in FIG. 3).

EXAMPLE 4

(17) Improved Tack Control

(18) A proprietary test method was developed using a Texture Analyser XT Plus system which employed a load cell fitted to a probe which is allowed to come into contact with the test sample. The probe is a piece of machined aluminium, cylindrical in shape (referred to as P/36R). The flat circular surface which comes into contact with the test sample has a diameter of 36 mm to allow for the test area to be representative. The load cell measures any force that is required to remove the probe from the sample. Small square samples measuring approximately 4 cm by 4 cm of semi-preg were attached to a plate using double-sided adhesive tape. The probe is then allowed to come into contact with the sample and a small force of 10 N is applied for 30 seconds to ensure full contact. The probe is then pulled away from the sample at a rate of 0.5 mm/sec. The peak force required to detach the probe from the sample is then recorded. The results show that the semi-preg using the property enhancing film exhibited a lower, more consistent tack of 11.3 N with a standard deviation of 0.83 N compared to the standard semi-preg which exhibited a less consistent and higher tack level of 31.1 N with a standard deviation of 8.6 N (represented by box plots in FIG. 4).