Article coated with cured material

Abstract: An article such as a drawn optical fiber (21) or an array of optical fibers is provided with a curable coating material. The array of optical fibers may be held together with a curable matrix material (45). Included in the coating material or the matrix material is a fluorescent constituent the fluorescence emission of which changes as a function of the degree of cure of the coating or matrix material. After the in-line curing of the coating material or of the matrix material, the fluorescence emission of the fluorescent constituent is monitored to determine the degree of cure of the curable material.

Description: This invention relates to articles coated with cured material. It is important to be able to determine the degree of cure of curable coating for coating articles such as optical fibers. Improperly cured bonded ribbon matrix or optical fiber coating material will inhibit cabling, will emit an undesirable odour, will exhibit poor strippability, poor adhesion and poor reliability relative to a properly cured coating. The modulus of the cured material is a function of the degree of cure. Modulus is important to the mechanical and optical performance of an optical fiber and fiber ribbon. In-line testing for the degree of cure of optical fiber coatings is much more efficient than off-line tests. Curable materials are used in the manufacture of many articles such as floor tiles, furniture, medical syringes, compact discs, computer floppy discs, video and audio tapes and glass fiber composites for automobiles. There is a great need for a method of monitoring the degree of cure of curable coating materials, and especially for use with in-line manufacture of optical fiber transmission media. Chemical Abstracts Vol.109 No. 12, 19th September 1988 page 34, Abstract No. 94125p, Columbus, Ohio, U.S.; R.L. Levy et al: "performance characteristics of the fluorescence optrode cure sensor" and ACS Symp.Ser. 1988, 367 (Cross Linked Polym.) 113-21 *Abstract* disclose the coating of articles with cured material and are concerned with determining the degree of cure of the curable material by monitoring the curing of certain types of materials. According to one aspect of the present invention there is provided an article as defined in claim 1. According to another aspect of the present invention there is provided a method as defined in claim 6. Brief Description of the Drawing FIG. 1 is a schematic view of a manufacturing line which is used to provide one or multiple coating materials for a drawn optical fiber; FIG. 2 is an end view in section of an optical fiber having a coating provided by portions of the apparatus of FIG. 1; FIG. 3 is a schematic view of a manufacturing line which is used to provide a matrix material for a plurality of optical fibers disposed in an array; FIG. 4 is an end view in section of an optical fiber array which is embedded in a matrix material; FIG. 5 is a cross sectional view of an elliptical reflector which is used to cure the optical fiber coating or matrix materials; FIG. 6 depicts the modulus of a curable coating or matrix material as plotted against radiation cure dose; FIG. 7 is a graph which depicts the relationship of viscosity of a curable coating or matrix material to a UV dose which is used to cure the coating or matrix material; FIGS. 8, 9 and 10 are graphs which show relative fluorescence emission of fluorescent materials versus relative viscosity of coating or matrix material in percent of full cure; FIG. 11 is a graph which shows absorption spectra for a coating or matrix material and for a probe and an emission spectrum for the probe; FIG. 12 is another graph which shows an absorption spectra for a coating or matrix material and for a probe and an emission spectrum for the probe; FIGS. 13 and 14 show, respectively, relative coating or matrix material absorption versus radiation dose, and relative absorption versus wavelength as a function of cure for a material the absorption of which increases as a function of the degree of cure; and FIGS. 15 and 16 show, respectively, relative coating or matrix material absorption versus radiation dose, and relative absorption versus wavelength as a function of cure for a material the absorption of which decreases as a function of the degree of cure. Apparatus 20 is used to draw optical fiber 21 from a preform 22, heated in a furnace 23. The fiber diameter is measured by a device 24 and provides an input into a control system for adjusting the fiber draw speed such that the fiber diameter approaches the desired value. A protective coating of material 25 is applied by apparatus 27 to the newly drawn fiber to protect it from the deleterious effects of the atmosphere. The coating apparatus may be as described in US Patent 4,474,830, (C.R.Taylor) and includes a centering gauge 28. After the coating material has been applied to the drawn fiber, the coating material must be cured. Accordingly, the optical fiber having the coating material thereon is passed through a device 30 for curing the coating and a device 32 for measuring the outer diameter of the coated fiber. Afterwards, it is moved through a capstan 34 and is spooled for testing and storage prior to subsequent cable operations. Referring now to FIG. 3, there is shown a schematic view of a manufacturing line which is designated generally the numeral 40. The line 40 is capable of manufacturing a bonded ribbon 42 (see FIG. 4). The ribbon 42 includes a plurality of coated optical fibers 36-36 each of which includes a core, a cladding and one or more layers 25-25 of coating material. As can be seen in FIG. 4, the optical fibers 36-36 may be disposed in a planar array. The fibers are held bonded together in that array by a matrix material 45. It is common to refer to such a structure as a bonded ribbon. In a preferred embodiment, the matrix material is an ultraviolet (UV) curable material. Along the line 40, a plurality of the optical fibers 36-36 are payed out from supplies 46-46, and an ink from a reservoir is applied thereto by an applicator 48. Afterwards, the ink is dried in an oven 49. Then the optical fibers are gathered together and embedded in the curable matrix material in an applicator 52. The applicator 52 may be an extruder, for example. Afterwards, the array in the matrix material is directed past an apparatus 54 which is well known and which is used to cure the curable matrix material and taken up on a spool 58. As mentioned, after the curable coating material has been applied to the drawn optical fiber or the curable matrix material to the array of optical fibers, the coating or the matrix material must be cured. The curing of the bonded ribbon, for example, may be accomplished within apparatus which includes an elliptical reflector 60 (see FIG. 5). In it a lamp 61 is positioned at one of two focal points 63 and 65 and the article at the other. The lamp 61 is such that it emits energy at wavelengths which are suitable to cure the curable material. The modulus of the cured coating material is dependent on the U.V. curing dose (see FIG. 6). In order to cause the modulus of the coating material or the matrix material 45 of the bonded ribbon to be a desired value, the degree of cure is monitored. Although reference hereinafter may be made only to the coating material or to the matrix material, it should be understood that the following applies to both. The methods of this invention facilitate the in-line monitoring of the degree of cure. This is accomplished by including a probe in the coating material or in the matrix material. The probe comprises a material which emits light subsequent to being promoted to an excited electronic state. In the apparatus 20, an in-line cure detector system 57 is included after the curing apparatus 30 whereas in the apparatus 40, an in-line detector system 59 precedes the spool 56. Broadly, the in-line cure detector system includes a light source which emits appropriate wavelengths necessary to promote the probe to an excited electronic state and a detector which is capable of quantitatively measuring the intensity of emission from the probe as it transitions from the excited electronic state to an unexcited electronic state. The curable matrix material, for example, is a material system which comprises a composition comprising an ultraviolet (UV) curable material such as an acrylate and a probe such as, for example, a fluorescent constituent. Hereinafter, the description is couched in terms of a UV curable coating or matrix material and a fluorescent probe. The system is such that its emission of light changes as a function of the degree of cure of the curable material. Emission from the fluorescent material provides a signature or a fingerprint of the probe constituent in the material. This signature or fingerprint remains with the curable material after the curable material has been cured and provides about the same emission level thereafter. The unique excitation and emission spectra of a material system functions as the signature or fingerprint for the curable material system or for the final product subsequent to manufacture. After the UV absorption spectrum of the material system or of the article containing the cured system has been determined, excitation at the longest wavelength of the UV absorption spectrum will yield a fluorescence emission spectrum. Subsequently, determination of the characteristic fluorescence excitation spectrum for the wavelength corresponding to the maximum fluorescence emission will yield the excitation spectrum of the fluorescent probe. The very fact that an emission spectrum results upon excitation of the curable material system or of the article containing the cured material system is indicative of the use of a curable material system which includes a constituent probe. The enclosing material system of the optical fiber or of the fiber array must be one such that under cure, the fluorescence emission of the material system changes with the degree of cure. The fluorescent probe constituent is such that its fluorescence emission is dependent on the degree of cure of the coating or matrix material. Properties of the fluorescent material may change because of the change in the polymer coating material which changes the fluorescence emission of the probe. There are several ways in which the fluorescence emission may change and these are best seen by relating that change to viscosity of the coating or matrix material being cured. The probe is preferably an organic material that has a fluorescent form that may be dependent on its orientation in space. That orientation is dependent on its mobility which changes with the degree of cure of the optical fiber coating or matrix material. As the coating or matrix material cures, its viscosity increases (see FIG. 7) until it becomes a solid. At that time, there is no further increase in viscosity and further change in fluroescence emission does not occur. For those probe materials in which the fluorescence emission is dependent on orientation in space, the emission may increase as a function of viscosity (see FIG.8) or it may decrease (see FIG.9). Further, the curable coating or matrix system may include a fluorescent consituent which is such that it is independent of the viscosity (see FIG.10), however, in that type the fluorescence emission of the system is such that it changes as a function of the absorption of the coating or matrix material which is dependent on the degree of cure of the coating or matrix material. If as the enclosing coating or matrix material is cured and its viscosity increases, the orientation of the probe favours increased fluorescence, then the intensity of emission increases as a function of the degree of cure (see again FIG.8). During cure of the optical fiber coating or matrix material, the motion of the fluorescent probe is restricted to favour the fluorescent form. A system which includes a coating or matrix material and this kind of prove may be referred to as a Type A system. On the other hand, if as the enclosing coating or matrix material is cured and viscosity increases, the orientation favours less fluorescence, then the intensity of emission decreases as a function of cure (see again FIG. 9). A system which includes a coating or a matrix material and this latter kind of probe is referred to herein as a Type B system. For the foregoing two approaches, i.e. types A and B, the absorption wavelength of the fluorescent probe must exceed substantially that of the matrix material. Any overlap of the absorption of the coating or matrix material with the absorption of the probe must be insubstantial. Viewing now FIG. 11, there is shown a graph which depicts absorption of the coating or matrix material and of the probe and fluorescence emission of the probe plotted as a function of wavelength. As can be seen, the wavelength at which the fluorescence emission of the probe is a maximum is displaced from that at which the absorption of the probe reaches a maximum value. This displacement of the emission wavelength from the absorption wavelength is well known and is referred to as the Stokes shift. If this condition be satisfied as in FIG. 11, then any change in the probe emission is due to a change of its orientation in space and hence of its fluorescence as a function of the degree of cure. This arrangement is effective because as the coating or matrix material transitions from a liquid to a solid material, its viscosity increases from about 10000 cps at 23° C to a solid. The more viscous the matrix material, the less mobile is the probe material. As the degree of cure increases, the relative intensity of the emission of the probe increases or decreases, unaffected by the absorption or emission of the coating or of the matrix material. A third approach is to use a fluorescent probe constituent which is independent of the viscosity of the coating or matrix material during cure (see again FIG. 10). A system which includes a coating material and such a probe is referred to herein as a Type C system. Such a system is ideal when the absorption characteristic of the probe is substantially the same as that of the coating or matrix material. If the fluorescence of the probe remains the same as a function of the viscosity of the medium which is dependent on the degree of cure, then reliance must be put on the properties of the coating or matrix material. The transmission of the coating or matrix material changes as a function of the degree of cure. For a Type C system to be a viable one, there are three requirements. First, it must be known that the emission intensity of the probe is not dependent on its orientation in space which is dependent on the viscosity of the coating or matrix material. That is, the fluorescence is independent of the viscosity of the medium. Secondly, it must be known that the excitation spectrum of the probe is coincident with or has somewhat substantial overlap with the absorption spectrum of the curable matrix or coating material (see FIG. 12). Thirdly, the coating or matrix material must have an absorption which is cure dependent. For some UV coating and matrix materials, percent relative absorption of UV radiation increases with respect to the radiation curing dose. For example, viewing FIG. 13, it is seen that a curve 70 increases until it plateaus at about 80% absorption at a given wavelength. Viewing now FIG. 14, there is shown a family of curves 72,73,74 and 76 with the relative absorption in percent being the ordinate and the wavelength of radiation being the abscissa. The curve 72 of FIG. 14 represents a coating or matrix material in liquid form. For curve 73, the cure dose is 0.13 Joule/cm 2 , for curve 74, 0.25 Joule/cm 2 and for curve 76, 0.5 Joule/cm 2 . These curves illustrate that for some materials, the absorption increases with the degree of cure. For other UV coating and matrix materials, the absorption decreases as a function of the degree of cure. Curves exemplary of these kinds of materials are shown in FIGS. 15 and 16. As is seen by a curve 80 in FIG. 15, the relative absorption in percent of a matrix or coating material decreases with increasing radiation curing dose as expressed in Joules per square centimeter. In FIG. 16, a family of curves 82, 83, 84 and 86 represent plots of the relative absorption in percent versus wavelength. The curve 82 represents a liquid as applied as a coating or as a matrix material. As is seen, as the coating or the matrix materials represented by this family of curves undergo an increasing cure dose of radiation energy, the percent absorption decreases. The curve 83 represents a plot of percent absorption versus wavelength for a cure dose of 0.13 Joule/cm 2 , curve 84 for 0.25 Joule/cm 2 and curve 86 for 0.5 Joule/cm 2 . Transmission and absorption are inversely related. If the above-mentioned three mentioned requirements for a Type C system be met and a coating or matrix material as characterized by the graphs of FIGS. 13 and 14 be used, then upon excitation, as the matrix material absorbs more radiation as a function of cure, there is less light which reaches the probe constituent and hence there is less fluorescence emission. The greater the cure of the matrix material, the more its absorption increases. In effect, the arrangement uses the attenuation of light reaching the probe to excite it. Conversely, if a coating or matrix material characterized by the graphs of FIGS. 15 and 16 be used, then upon excitation, as the coating or matrix material absorbs less radiation as a function of cure, more light reaches the probe constituent and hence there is more fluorescence emission. A Type C system is operative independent of the viscosity of the coating or matrix material whereas type A or B includes a viscosity dependent probe. Instead, in a Type C system, reliance is placed on the absorption of the coating or matrix material to attenuate the light which excites the probe. In using the probe characterized by FIG. 10, the fluorescence of the coating or matrix system does not depend on the mobility of the probe, but rather on the light absorption of the coating or matrix material. In this kind of coating system, the absorption of the coating or matrix material changes as it cures. This is not desirable in the types shown in FIGS. 8 and 9, for there, a fluorescent probe, the absorption of which is different from that of the matrix, is chosen. In none of the three techniques described hereinabove does the fluorescent material cure. Rather it is trapped in the matrix or in the optical fiber coating material. In Type A and B systems, the probe mobility becomes restricted as the viscosity of the coating or matrix material increases and the fluorescence changes. In a Type C system, reliance is placed on the absorption of the coating or matrix material because the probe has a fluorescence emission which is viscosity independent. Further, the fluorescence emission of the material system is substantially constant over time, and, following cure of the curable coating or matrix material, functions as a fingerprint for the system at anytime thereafter. There are other kinds of probes which may be used. If a probe is consumed by, for example, a photoreaction, less absorption may occur. One of these other kinds of probes is characterized in that it reacts with itself, whereas another is characterized in that it undergoes a photoreaction with components of the coating or with components of the matrix material. As the material is exposed to radiation, the absorption is decreased because it is consumed by reacting with itself or with the coating or matrix material. It becomes important to choose a probe constituent that on exposure to radiation does not become non-fluorescent and one such that the absorption of the probe constituent does not change with respect to the degree of cure of the coating or matrix material. Desirably, a probe is selected the emission of which increases or decreases. If the probe is consumed by or reacts with the coating or the matrix material, the absorption of the probe decreases and there occurs a decrease in the emission of the material. Systems designated types A, B and C are preferred. For a probe reaction with itself in the concentrations used herein, i.e. ppm, the probability of reacting the probe with itself is low. If the concentration of the probe material is increased, the coating or matrix material is perturbed which affects the properties such as aging and cure speed of the material. As the material cures, viscosity increases which increases the difficulty for one molecule of the probe material to reach another. These other kinds of probes just described are not preferred because of the concentration levels present and because the mobility of the probes is decreased as a result of increasing viscosity during cure. It should be understood that although the preferred embodiment has been described as an article comprising an optical fiber provided with a curable coating system or an array of optical fibers provided with a curable matrix material, that the invention has many other uses. It may be used to monitor the degree of cure of curable materials used to manufacture floor tile, furniture, syringes for medical use, compact audio discs, computer floppy discs, video and audio tapes and glass fiber composites for automobiles and other products. The invention has been described in terms of adding a probe to a coating or matrix material to provide a material system. It should be understood that the coating or matrix material having a component the emission of light from which is dependent upon the degree of cure may be used. Example 1 One half gram of a solution comprising 0.05 gram 1,3-bispyrenylpropane in 25 ml. N-vinylpyrrolidone was blended with 100 grams of Cabelite 3287-9-11, a UV curable acrylate-based material commercially available from DeSoto, Inc., Des Plaines, Illinois. The resulting material system was of Type B. Irradiation of this formulation on release paper with a UV dose of 0.25 Joule/cm 2 provided a 0.05 mm film with a 395 nm fluorescence of 73% on a scale of 0 to 100, i.e. 73% of full scale. The instrument 0% reading was set with no sample in the instrument upon excitation at 350 nm. Irradiation of this formulation on release paper with a UV dose of 0.5 J/cm 2 provided a 0.05 mm film with a 305 nm fluorescence of 49% upon excitation at 350 nm. Irradiation of this formulation at 1.0 J/cm 2 provided a 0.05 mm film with a 305 nm fluorescence of 13% full scale upon excitation at 350 nm. Example 2 One half gram of a solution comprising 0.125 gram 9,10-diphenylanthracene in 25 ml. N-vinylpyrrolidone was blended with 100 grams of Cabelite 3287-9-11, a UV curable material commercially available from DeSoto, Inc., Des Plaines, Illinois. The resulting material system relied on changes in the absorption of the UV constituent to effect changes in fluorescence emission of the probe. As such, this is an example of a Type C material system. Irradiation of this formulation on release paper with a UV dose of 0.25 Joule/ cm 2 provided a 0.05 mm film with 430 nm fluorescence of 57% upon excitation at 380 nm. Irradiation of this formulation on release paper with a UV dose of 1.0 Joule/ cm 2 provided a 0.05 mm film with a 430 nm fluorescence of 25% upon excitation at 380 nm.

Claims: An article, which comprises a substrate material, said article being characterized by a material system which has been applied to said substrate material, said material system comprising at least one U.V. light curable material which has been cured, and photochemical means includes a component which functions as a probe and further comprises a fluorescent constituent for emitting light when in an excited state, the photochemical means having emitted light which spans a range dependent upon the degree of cure of the curable material and further that the degree of overlap of the excitation spectrum of the fluorescent constituent and the curable material being a function of the behaviour of the absorbance of the curable material as the degree of cure changes, and the system being such that its fluorescence emission changes as a function of the degree of cure of said curable material. An article according to claim 1, in the form of an elongated strand material, which comprises a transmission medium, the coating material enclosing said transmission medium. The article of claim 2, wherein the fluorescence emission increases as the degree of cure of the curable material increases. The material of claim 2, wherein the emission decreases as the degree of cure of the curable material increases. The elongated strand material of claim 1, wherein the fluorescence of said probe is independent of the change in viscosity of said curable material. A method of curing a coating on an article, said method comprising applying a curable material system to the article, and curing the said material, said method being characterized in that said material includes a photochemical means including a fluorescent constituent which is such that it emits light upon being promoted to an excited state, and the system being such that emission of light changes as a function of cure of the curable coating material; and in that the method is further characterized by determining the emission of light of the said constituent to measure the degree of cure of the curable coating material. The method of claim 6, wherein the coating material comprises an ultraviolet curable coating material and the step of curing includes the ultraviolet curing of the coating material, and wherein the probe comprises a fluorescent constituent, and the system is such that its fluorescence emission changes as a function of the degree of cure of the curable material.

Inventors: PETISCE JAMES R, PETISCE, JAMES R.
Applicants: AT & T CORP, AT&T CORP.
Application year: 1990
Main classification: C03C25
IPC codes: B29C35, C03C25, G02B6, B01J19, C08J3, G01N21, G01N33