Plastic and nonmetallic article shaping or treating: processes – With incorporating dye susceptible material or dyeing workpiece
Reexamination Certificate
2000-06-28
2002-12-17
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With incorporating dye susceptible material or dyeing workpiece
C264S210600, C264S210800, C264S211000
Reexamination Certificate
active
06495079
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to a process to prepare drawn melt-spun polymeric fibers colored during the melt-spinning process. More particularly, the invention relates to a process to form polyamide or polyester based melt-colored fibers, containing novel polyester ionomer additive(s), that exhibit improved color and aesthetics over prior art melt-colored fibers.
BACKGROUND
Coloration of fibers has a long history, and the science of dyeing, initially of natural fibers such as flax, cotton and wool, has been under continuous development since Neolithic times. The appearance of man-made fibers, (e.g. cellulosics, acrylics, polyamides and polyesters), stimulated further developments in dyeing, and this method of coloring of fibers and articles made therefrom continues to be the most-practised technique for the production of colored fiber-based articles of manufacture.
In the case of fibers based on the more recent polymers such as polyamides and polyesters, which are spun from the melt, there exists an alternative method for coloration, i.e. addition of the colorant species into said melt and direct extrusion of colored fibers. While such a process may be carried out with dyes, it is more often carried out with pigments, (although the said process is popularly known in the industry as “solution dyeing”). The major difference between dyes and pigments is that, under prevailing processing conditions, pigments are virtually insoluble in polymers, whereas dyes are soluble, (see definitions in German Standards DIN 55943, 55944 and 55949).
As the technique of melt-pigmentation has been developed, it has been demonstrated that fibers made in this way can exhibit certain advantages over those made by post-spinning dyeing of fibers. Such advantages include—improvements to resistance to degradation and fading in sunlight; lower susceptibility to fading and/or yellowing by polluting gases in the atmosphere, such as ozone and nitrogen oxides; improved resistance to chemicals, either in dry-cleaning processes or due to accidental spillage; less leaching or fading of color during laundering or cleaning process involving water and detergents; no need for post-spinning dyeing, or the other processes involved in applying and fixing said dyes onto/into the fiber.
However, melt-pigmentation is also considered to have some disadvantages in terms of the color and appearance obtained in the final fiber. The fibers are known to those skilled in the art to exhibit degrees of lustre and low brightness which can render the said fibers unsuitable in certain applications.
The color change resulting from the addition of pigments to polymers is based on the wavelength-dependant absorption and scattering of light, the appearance and color of the final product being a combination of these two factors as described in the Kubelka-Munk theory. [Note that a description of this theory, and the general concepts of color and its measurement may be found in “Colour Physics for Industry”, Roderick McDonald (Ed.), The Society of Dyers and Colourists, Bradford, UK, 2
nd
edition (1997)]. Dyes can only absorb light and not scatter it, since the physical prerequisite for scattering—a certain minimum particle size—does not exist in the case of dyes in molecular solution; these colors are therefor transparent. In so far as the transparency is attributable to the dye, complete absorption of the light will result in black shades, selected absorption in colored shades.
The optical effect of pigments may in the same way be based on light absorption. If, however, the refractive index of the pigment differs appreciably from that of the polymer (which is almost always the case) and, if a specific particle size range is present, scattering takes place; the initially transparent polymer becomes white and opaque, or if selective absorption takes place at the same time, colored and opaque.
No scattering occurs when the particle sizes are very small, and none or very little if they are very large. With all colored pigments that selectively absorb, the shade and strength of the final color is thus influenced by particle size. The transparency and thickness of the colored substrate may additionally affect the color strength. While some pigments are available in so-called transparent grades (e.g. red and yellow iron oxides) a complete color range across the spectrum is not readily available. Many such ultra-low particle size colorants are expensive, and difficult to maintain at high dispersion when compounded into a polymer matrix. It is also known that very low particle size additives in polymer melts can exhibit a profound effect on the Theological properties of said melt, resulting in formulations which are difficult to spin using standard equipment and techniques. Use of large particle size pigments is not a viable option either, as such additives will result in blocking of filtration systems and spinneret holes, and tend to lead to filament breaks in fiber production.
In any case, a large number of melt-pigmented fiber products are required to be opaque, and the problem lies in producing opaque colored fibers with levels of color brightness close to those of dyed products. Note that a fundamental difference between dyeing and pigmenting of fibers is that, while dyes are either colored or absorb all wavelengths (i.e. give black shades), pigmentation introduces an extra variable in that white pigments are readily available, whereas there is no such species as a “white dye”.
Another potential problem with particulate colorants in a polymeric melt-extruded product is the phenomenon of dichroism, or optical anisotropy. Pigment particles are not necessarily isotropic in shape, and may be needle-shaped, rod-shaped, or platelets. They may thus become oriented in a particular direction in processing. The apparent color then depends on the direction of observation. The origin of this phenomenon is to be found in the fact that certain pigments crystallise in crystal systems of low symmetry resulting in directionally dependant physical properties. As far as the coloristic properties are concerned, this signifies that the absorption and scattering constants differ in the various principle crystallographic axes, i.e. such crystals are optically anisotropic.
With regard to the final fiber (as opposed to the above comments on the pigments themselves) the appearance of a sample thereof can vary depending on the angle of illumination and/or observation. Fiber samples are normally prepared for color and appearance testing by carefully wrapping the fiber or yarn sample (under conditions of uniform tension and consistent positioning of the said fibers) around a flat “card”, and assessing the color properties, and more importantly any differences between said properties and those of the desired standard sample or data, under standard conditions of illumination and observation. This may be carried out visually, but more usually instrumentally. Methods and apparatus for carrying out the analysis of color and appearance in this manner are well known to those skilled in the art.
During such examinations, there are two additional effects which might be observed if the sample is illuminated or observed at a number of different angles (for an example of multi-angle appearance testing of materials see U.S. Pat. No. 4,479,718, assigned to DuPont). The total amount of light reflected from the sample, per unit area, may change. The perceived color may also change. Unless such effects are specifically desired for particular aesthetic effects in a final article of manufacture, the appearance of either may result in the rejection of the fiber by the prospective customer. Eradication or reduction of such effects thus is important in obtaining first quality product.
There thus exists a need in the industry for a simple method to provide pigmented polymeric articles, especially melt-spun fibers, with improved color and appearance, whilst still using standard grades of pigment currently known to those skilled in the art to be suitable fo
Gallucci Robert R.
Roark Milton Keith
Studholme Matthew B.
Kerins John C.
Miles & Stockbridge P.C.
Prisma Fibers Inc.
Tentoni Leo B.
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