US2352725A - Shaped product - Google Patents

Description

Patented July 4, 1944 UNITE-o STATE William H.

smirnn rnonuc'r Markwood, In, Wilmington, DeL, as-

si nor to E. L du Pont de Nemours a Company, Wilmington, Del., a corporation of Delaware No Drawing. Application November 4, 1941,

Serial No. 417,807

13 Claims.

This invention relates to lustrous, opaque sheet material, especially thin, flexible, synthetic polymer film. More particularly it appertains to the treatment of continuous, transparent webs of polyhexamethylene adipamide to engender a pearlescent efl'ect therein.

In U. S. A. Patents Nos. 2,071,251, 2,071,253, 2,130,523 and 2,130,948 to Carothers there is described a new class of fiber-forming materials which are'now commonly referred. to as synthetic linear condensation polymers. ing of such materials int thin, transparent, coherent, self-sustaining films is disclosed in several U. S. A. patents, for example, Nos. 2,141,169 (Catlin), 2,212,770 (Foster), 2,212,772 (Graves). and 2,216,735-6 (Carothers). The preparation of similar sheet having a pearlescent appearance is a deslderatum, inter alia, because of its great decorative value, The common methods of producing this efiect, for example, by incorporating pearl-essence, are not satisfactory for various reasons, including the expense of adding material and the weakening efi'ect of such material on the polymer.

The primary object of this invention was to produce decorative eflects in'polyhexamethylene adipamide and similar synthetic linear polyamide sheet by inexpensive means. Other objects were to produce poiyhexamethylene adipamide and related nylon films with a highly appealing lustrous pearlescent effect, to produce silvery polyhexamethylene adipamide films without incorporating extraneous materials therein, and to process ordinary transparent shaped polyhexamethylene adipamide products, without chemical treatment, in such a way that, although they do not, they appear to contain pearl-essence. A general advance in the art, and other objects which will appear hereinafter, are also contemplated.

It has now been found that transparent sheets oi polyhexamethylene adipamide and the like assume a pearlescent appearance when drawn under certain critical conditions, principally moisture content. An increase in length of about 300% (the product being four times its original length) results when-this drawing is in one direction. The pearlescent effect is remarkably stable. Samples of the sheet soaked for over a week in water are without any alteration in appearance, and samples stored in ordinary atmospheres for over a year show no noticeable change. I

How the foregoing objects and related ends are accomplished will be apparent from the following exposition, in which are disclosed the prin The shap-- ciple and divers, embodiments of the invention, including the best mode contemplated for carrying out the same.

In carrying out the present invention, transparent polyhexamethylene adipamid sheet containing a critical amount of moisture is drawn or stretched in one or more directions at such a rate that a pearlescent eifect develops therein. Such sheet tends to. become brittle when almost completely dry, and-it is therefore necessary that the drawing operation not be carried out under conditions of extreme dryness. Sheet which has been subjected to an atmosphere which is too humid can be dried in any conventional or desired way.

For convenience, the moisture content is stated in terms of the relative humidity of the circumambient atmosphere with which the sheet is in equilibrium. A relative humidity of 10% has been found to be a practical lower limit, and 30% a practical upper limit, for the atmosphere used to condition or equalize the sheet before draw ing. Sheet conditioned at relative humidities between 15% and 25% have been found to-give the most satisfactory results. These relative humidities are based'on ordinary normal room temperature, i. e.. 20. C.

The proper limits (lower and upper) of relative humidity essential are influenced to some extent by the thickness of the sheet being treated, principally because of the time factor involved'in bringing the sheet toan equilibrium.

These limits need not be set forth specifically, since they are easily and more satisfactorily determined empirically.

In one specific embodiment, a strip of polyhexamethylene adipamide was held in such a way that a 3 inch length was subjected to stretching, and it was drawn at a rate which produced a pearlescent effect, in this case Va of an inch of material having a pearlescent appearance being produced per second. This is near the minimum rate of drawing which can be employed for this particular polymer. A drawing rate which produced 1.5 inches of pearlescent effect sheet per second was found to result in too frequent ylene diammonium sebacate, and the interpolymers of hexamethylene diammonium adipate, hexamethylene diammonium sebacate and caprolactam (d-amino-caproic acid) v The rate of drawing or speed of conversion is a subsidiary consideration, but it does depend to some extent upon the composition being drawn, for example, a much more rapid rate is necessary for polyhexamethylene adipamide than for polyhexamethylene sebacamide. To amplify, practically any rate of drawing, regardless of how slow, will produce the desired effect in the latter product, but a very rapid rate is necessary for the former. In all cases the maximum drawing rate is determined by sheet breakage.

The polyamides. generally speaking, comprise the reaction product of a linear polymer forming composition, for example, one consisting essentially of bi-functional reacting material which comprises in substantial amount molecules containing two amide-forming groups, each of which is complementary to an amide-forming group in other molecules in said composition. They can be obtained, by example,- by self-poly-' merization of mono amino mono carboxylic acids or by reacting ,diamines with dibasic carboxylic acids in substantially equimolecular amounts, it being understood that this reference to amino acids. diamines and dibasic carboxylic acids is intended to include the equivalent amideforming derivatives of these reactants or similar products. The average number of carbon atoms separating the amide groups should be at least 2.

Modification of the polymers with minor amounts of resins, for example, phenol formaldehyde resins, does not prevent the production of of drawing, to produce a sheet which a not qui opaque but which is only translucent.

It is often convenient to process sheet according to this invention shortly after its solidificationin melt casting processes such as that de- .scribed in U. S. A. Patent No. 2,212,710. Such sheet need only be allowed to pick up the critical amount of moisture before being drawn.

The invention is not limited to the treatment of sheet material to produce a metallic effect.

Such articles have been made the basis of the description mainly for convenience. Other shaped products such as yarns, and mono articles like bristles, behave similarly when so treated, and give equal or better results. Regardless of the external shape of the product having the pearlescent effect, it contains elongated voids, the presence of which can be shown by microscopic examination, which are substantially uniform in size and shape.

An interesting and unexpected characteristic of the products of this invention is that they may be retransparentized by the application of pressure. This property has numerous useful and ornamental applications, for example, the sheet may be stamped with decorative patterns or indicia of various kinds such as trade-marks, which are transparent as a result of the pressure exerted by the die or stamp utilized. The opaque sheets of this invention may be written on by using a stylus or similar instrument, thereby providing va permanent record which is obliterated only by the application of greater pressure or the pearlescent efiect. In many cases sheets containing 10% to 20% of resins such as p-tertiarybutyi phenol formaldehyde resins, are more susceptible to the production of the pearlescent effect than sheets without the resins (but otherwise identical).

Vinyl polymers which are capable of being cold drawn, for example, polyethylene, interpolymers of unsymmetrical dichlorethylene (with vinyl chloride, vinyl acetate and the like), and to a lesser extent, the interpolymers of polyvinyl chloride and polyvinyl acetate, behave similarly to the polyamides.

The products used in the practice of this invention are of high molecular weight and generally oan be obtained with a crystalline structure, as evidenced by X-ray powder diffraction patterns in the massive state. The high molecular weight required for the best-fiber forming properties is obtained by continuing the polymerization until the intrinsic viscosity (as defined in U. S. A. Patent No. 2,130,948 to Carothers) is at least 0.4. Such polymers can be cold drawn (that is, drawn under tension in the solid state) with permanent and high linear extension from 200% to 500% or more to yield textile fibers showing by X-ray examination molecular orientation along the flber axis. Reference is made to the patents mentioned elsewhere in this specification for further details.

The mechanical features of the drawing operation can be varied as desired, and the stretching procedures of this invention may be described as cold drawing, as defined in U. S. A. Patent No. 2,130,948.

Although the invention has been described in terms of the production of an opaque film, it is possible in most cases, by the control of the rate deterioration of the sheet. As an example of such a use, the preparation of a bank check from such material may be mentioned. The writing on such a check would be exceedingly difllcult to alter without detection.

The shaped products of the present invention may contain minor amounts of a material suchas pigments, delusterants, etc. The finished products may be dyed before or after braiding, weaving, and like operations, with acid and basic dyes and the so-called acetate colors. Amazingly brilliant and highly pleasing products are obtained in this manner. Apparently the high reflectance due to the pearlescent efiect, combined with the color sensation arising from the dye, is in proper balance to give a most pleasing sensation.

Surprisingly, the products of this invention possess as good tenacity as products prepared from the same materials but drawn more slowly or in a manner which does not bring out the pearlescent effect.

Other advantages and uses of the invention will be obvious to those skilled in the art. It is infrequent that a valuable and highly decorative material such as that described herein, can be produced by such an inexpensive process and without the added expense and weakening effect transparent film composed of a synthetic linear polyamide having a moisture content in equilibrium with an atmosphere of 10%-30% relative humidity, whereby to impart a to said film. 1

9. The process which comprises drawing a transparent film composed of a synthetic linear polyamide having a moisturecontent in equilibrium with an atmosphere of 10%-30% relative humidity, whereby to impart a pearlescent eifect to said film, said polyamide comprising essentially the reaction product of a linearpplymeramide, said film having a pearlescent eflect due to the presence therein 01 minute elongated voids, said polyamide comprising essentially the reaction product of a linear polymer-forming composition which comprises a substantial amount of reacting material selected from at least one of the groups consisting of (a) monoamino carboxylic acids and (b) mixtures of diamine with dibasic carboxylic acid.

5. A film composed of polyhexamethylene adipamide, said film having a pearlescent eflect due to the presence therein of minute elongated voids.

,6. The processwhich comprises drawing a transparent shaped body composed of a synthetic linear poiyamide having a moisture content in equilibrium. with an atmosphere of l0%-30% relative humidity, whereby to impart a pearlescent and to said body.

7. The process which comprises drawing a transparent shaped body composed of a synthetic linear poiyamide having a moisture content in equilibrium with an atmosphere of 10%-30% relative humidity. whereby to impart a pearlescent eflect to said body, said polyamide comprising essentially the reaction product of a linear polymer-forming composition which comprises a' substantial amount of reacting material selected irom at least one of the groups consisting of (a) mono-amino carboxylic acids and (in mixtures of diamine withdibasic carboxylic acid. 8. The process which comprises drawing a forming composition which comprises a substantial amount of reacting material selected from at least one of the groups consisting of (a) mono-amino carboxylic acids and (b) mixtures of diamine with dibasic carboxylic acid.

10. The process which comprises drawing a transparent film of polyhexamethylen'e adipamide having a moisture content in equilibrium with an atmosphere of 10%-30%- relative humidity, whereby to impart a pearlescent effect to said film.

11. The process of claim 6 in which said polyamide has a moisture'content in equilibrium with an atmosphere of 15%-25 relative humidity.

12. The process which comprises drawing a transparent shaped body composed of a synthetic linear polyamide having a moisture content in equilibrium with an atmosphere of 10 %-30% relative humidity, wherebyto impart a pearlescent eiiect to said body, and rendering sections of said pearlescent body transparent by application or pressure.

13. The process which comprises drawing a transparent film composed of s synthetic linear polyamidehaving a moisture content in equilibrium with an atmosphere of 10%-30% relative humidity, whereby to impart a pearlescent eflect to said film, and rendering sections oi said pearlescent film transparentby application of pressure.

WILLIAM H. MARKWOOD,

pearlescent eflect I