US4898754A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Poly(amide-imide) prepreg and composite processing
Assignee: Boeing Co
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Filing: 1988-05-05
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Granted: 1990-02-06
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Expires: 2008-05-05
Abstract
Abstract A method is disclosed for forming poly(amide-imide) prepregs that permits forming void-free composites having residual solvent contents of less than 0.2% by weight. Such composite have improved glass transition temperatures near those of the pure polymer. In a preferred method, a poly(amide-imide) prepreg containing a residual N-methyl-2-pyrrolidone solvent is rapidly heated to about 650° F. to evaporate residual solvent to less than 1.0% by weight. The prepreg is rapidly cooled before the thermoplastic poly(amide-imide) polymer begins to significantly advance in molecular weight. The prepreg may then be layed up to form composite articles that are consolidatable by application of further heat and pressure.
Inventors
- 👤 Stephen Christensen
- 👤 Jay O. Rakel
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 22:06
CPC Classifications
C; C08; C08J; C08J5/00; C08J5/24; C08J5/241; C08J5/243; C08J5/249; C08J2379/00; C08J2379/04; C08J2379/08; Y; Y10; Y10T; Y10T428/00; Y10T428/31504; Y10T428/31721
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
203 words
A method of making and treating a pre-impregnated fiber reinforced poly(amide-imide) material, comprising the steps of: impregnating a fibrous reinforcing material with a poly(amide-imide) resin dissolved in an organic solvent to form a prepreg, said poly(amide-imide) resin being heat fusible at an elevated temperature that is above the boiling point of said solvent; drying the prepreg at a temperature of less than 550°-650° F. until approximately 4%, by weight, of the solvent remains; elevating the temperature of said prepreg to an elevated temperature in the range of about 550°-650° F., said elevated temperature being substantially above the boiling point of the solvent and being approximately equal to the temperature where said resin begins to advance in molecular weight; maintaining said elevated temperature for approximately 1 to 5 minutes such that said solvent substantially completely evaporates from said prepreg; and reducing the temperature of said prepreg before the resin advances in molecular weight sufficiently to cause a substantial adverse effect on consolidatability, wherein after the step of reducing the temperature of the prepreg, the prepreg has a substantially reduced solvent content, and is heat fusible to form a composite article having a glass transition temperature that is about that of the pure poly(amide-imide) resin.
Claim 2
Independent Claim
203 words
A method of making and treating a pre-impregnated fiber reinforced poly(amide-imide) material, comprising the steps of: impregnating a fibrous reinforcing material with a poly(amide-imide) resin dissolved in an organic solvent to form a prepreg, said poly(amide-imide) resin being heat fusible at an elevated temperature that is above the boiling point of said solvent; drying the prepreg at a temperature of less than 550°-650° F. until approximately 4%, by weight, of the solvent remains; elevating the temperature of said prepreg to an elevated temperature in the range of about 550°-650° F., said elevated temperature being substantially above the boiling point of the solvent and being approximately equal to the temperature where said resin begins to advance in molecular weight; maintaining said elevated temperature for approximately 1 to 5 minutes such that said solvent substantially completely evaporates from said prepreg; and reducing the temperature of said prepreg before the resin advances in molecular weight sufficiently to cause a substantial adverse effect on consolidatability, wherein after the step of reducing the temperature of the prepreg, the prepreg has a substantially reduced solvent content, and is heat fusible to form a composite article having a glass transition temperature that is about that of the pure poly(amide-imide) resin.
Claim 3
Dependent Claim
32 words
The method of claim 1 wherein after the step of reducing the temperature of the prepreg, the solvent remaining in the prepreg is less than about 1%, by weight, of said prepreg.
Claim 4
Dependent Claim
90 words
The method of claim 2 further comprising the steps of: forming a composite article from said prepreg; elevating the temperature of said article such that further residual solvent is evaporated and said poly(amide-imide) resin viscosity is minimized; applying a pressure differential to said article while the resin is at a minimum viscosity which pressure squeezes said article and causes said resin to flow and fully impregnate said article; and cooling said article while maintaining said elevated pressure on said article, whereby said resin hardens and a substantially void-free composite results.
Claim 5
Dependent Claim
29 words
The method of claim 3 wherein after the step of cooling said article, solvent remaining in said composite article is less than about 0.2%, by weight, of said article.
Claim 6
Dependent Claim
37 words
The method of claim 3 wherein the solvent is N-methyl-2-pyrrolidone, and composite articles which are formed of said prepreg and are fully hardened are characterized by a glass transition temperature of about 470-500 degrees F. (243-260degrees C.).
Claim 7
Dependent Claim
15 words
The method of claim 1 wherein said elevated temperature is about 650° F. (343° C.).
Claim 8
Independent Claim
181 words
A method of treating a prepreg made of fiber pre-impregnated with poly(amide-imide) resin, said prepreg having a solvent content of about 4%, by weight, and said prepreg being suitable for use in making a composite article, comprising the steps of: elevating the temperature of the prepreg to an elevated temperature in the range of about 550°-650° F., said elevated temperature being substantially above the boiling point of the solvent and approximately equal to the temperature where the poly(amide-imide) resin begins to advance in molecular weight; maintaining the elevated temperature for approximately 1 to 5 minutes so that substantially all the solvent evaporates from the prepreg; and reducing the temperature of the prepreg before the poly(amide-imide) resin advances in molecular weight sufficiently to cause a substantial adverse effect on consolidatability, wherein the steps of elevating the temperature, maintaining the elevated temperature, and reducing the temperature are accomplished before the prepreg is used to make a composite article, and wherein after the step of reducing the temperature of the prepreg, the solvent content of the prepreg is less than about 1%, by weight.
Claim 9
Independent Claim
181 words
A method of treating a prepreg made of fiber pre-impregnated with poly(amide-imide) resin, said prepreg having a solvent content of about 4%, by weight, and said prepreg being suitable for use in making a composite article, comprising the steps of: elevating the temperature of the prepreg to an elevated temperature in the range of about 550°-650° F., said elevated temperature being substantially above the boiling point of the solvent and approximately equal to the temperature where the poly(amide-imide) resin begins to advance in molecular weight; maintaining the elevated temperature for approximately 1 to 5 minutes so that substantially all the solvent evaporates from the prepreg; and reducing the temperature of the prepreg before the poly(amide-imide) resin advances in molecular weight sufficiently to cause a substantial adverse effect on consolidatability, wherein the steps of elevating the temperature, maintaining the elevated temperature, and reducing the temperature are accomplished before the prepreg is used to make a composite article, and wherein after the step of reducing the temperature of the prepreg, the solvent content of the prepreg is less than about 1%, by weight.
Claim 10
Dependent Claim
15 words
The method of claim 7 wherein said elevated temperature is approximately 650° F. (343° C.).
Claim 11
Dependent Claim
31 words
The method of claim 7 wherein after the step of reducing the temperature of the prepreg, the prepreg is characterized by a glass transition temperature of about 470°-500° F. (243°-260° C.).
Claim 12
Dependent Claim
99 words
The method of claim 7 further comprising the steps of: forming a composite article from the prepreg; elevating the temperature of the article such that substantially all residual solvent in the prepreg is evaporated and the resin viscosity of the poly(amide-imide) resin is minimized; applying a pressure differential to the article while the resin is at minimum viscosity, where the pressure squeezes the article together and causes the resin to flow and fully impregnate the article; and cooling the article while maintaining a pressure differential on the article, whereby the resin hardens to form a substantially void-free composite article.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1993-02-05 | 1993-08-07 | 1994-02-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-02-05 | 1997-08-07 | 1998-02-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2001-02-05 | 2001-08-07 | 2002-02-06 | $7700.00 | Window Closed / Lapsed |