EP0181369B1

EP0181369B1 - Process for dyeing a continuous polymeric flexible substrate and products produced from said process

Info

Publication number: EP0181369B1
Application number: EP85902282A
Authority: EP
Inventors: James Louis Joyce, Jr.
Original assignee: AMP Inc
Current assignee: TE Connectivity Corp
Priority date: 1984-05-11
Filing date: 1985-04-15
Publication date: 1988-10-26
Also published as: EP0181369A1; ES8703672A1; DE3565799D1; JPS61502109A; WO1985005324A1; ES543010A0

Abstract

The process for dyeing a continuous polymeric flexible substrate (12) such as a film, uses a strip of transfer paper (18) having sublimable dyes deposited on one surface. The substrate (12) and transfer paper (18) are fed simultaneously into a heat transfer apparatus (10) comprised of a heating means (30) and substrate retaining means (32). The layers are fed into the apparatus (10) so the uncoated side of the transfer paper (18) is proximate the heating means (30) and substrate is proximate the retaining means (32). The layers are held against the heating means (30) while sufficient heat is applied to the transfer paper (18) to cause the dye to sublime from the paper (18) and diffuse into the interstices of the substrate (12).

Description

This invention relates to the manufacture of conductor cables and in particular to the manufacture of multiconductor flat flexible cables.
There is increasing use of flexible conductor cables in electrical and electronic equipment such as business machines, communication systems and computers. Concomitant with the increased use is the increased need by equipment manufacturers for cable that is color coordinated with the equipment particularly when the cable is visible to anyone viewing or using the equipment. Furthermore, it is desirable that this cable have a matte finish to eliminate glare from any exposed surface.
Conductor cables typically are comprised of a number of longitudinally extended spaced-apart conductor elements encapsulated within an insulating sheath. The conductor elements may be composed of any suitable electroconductive material that exhibits the required qualities of flexibility and strength, such as copper and the like. The insulating material is usually polyester, polyvinyl chloride or other plastic material. The insulating materials used are generally manufactured as a transparent or translucent matte film. Generally these films must be heat stabilized to control shrinkage prior to being made into cable. The cable is made by sandwiching the conductor elements between webs of adhesive coated insulating material and laminating the layers by applying heat and pressure to the sandwich. Typical methods and apparatus for making flexible cables are disclosed in US-A-3 513 045 and 4 351 689, the latter disclosing methods of making flat multi-conductor cable using polyester film.
Standard methods for coloring the plastic film prior to making flexible cable are unsatisfactory. Although it is possible to add pigment to the raw materials prior to extruding or forming the insulating film of material, this method is economically feasible only for very high volume production. Applying color to the surface of the film by means of dipping, spraying, or otherwise coating at least one surface of the film with a pigmented solution is also unsatisfactory. The colored coating is not sufficiently adhered to the surface or heat resistant to remain on the surfaces during the cable manufacturing process, particularly during lamination.
Applying color to the finished cable by dipping, spraying, or other coating means is also unsatisfactory. The different coefficients of expansion of the insulating material and the conductive elements cause the cable layers to separate under the conditions required for the coloring process. Furthermore, a colored coating on the surface of the cable is subject to wear by abrasion and to attack by cleaning solvents.
Flexible cable can also be colored by adding dye to the adhesive layers or by adding a layer of colored insulating material between the outer dielectric web and the conducting elements. While these methods eliminate the problems associated with surface coating, they produce true vivid colors only when used with transparent film. These methods are generally unsatisfactory for coloring translucent film because true vivid colors are unattainable due to the diffusion and refraction properties of the matte film. Furthermore, these methods increase the number of manufacturing steps required to make a finished product.
It is known from VDI-Nachrichten, Vol, 30 No. 35 1976, B. D. Bahr, Kostengunstiger Transfer- druck, page 12 to provide a process for dyeing a flexible polymeric substrate comprising the steps of:

selecting transfer paper comprised of a continuous strip of paper having at least one sublimable dye on one side thereof;
feeding the transfer paper into a heat transfer apparatus, said apparatus having heating means and substrate retaining means so that the uncoated side of the transfer paper is proximate the heating means;
simultaneously feeding the continuous substrate into the heat transfer apparatus so that one surface of the substrate is proximate the coated surface of the transfer paper and the other surface of the substrate is proximate the substrate retaining means;
pressing said substrate by said retaining means against said heating means with said transfer paper thereby held between said substrate and said heating means;
applying sufficient heat to the transfer paper by said heating means so that the dye sublimes from the transfer paper and diffuses into the flexible polymeric substrate;
removing the colored substrate from the heat transfer apparatus.

It is an object to eliminate the aforementioned problems and to provide for the desired color or colors to be imparted to the insulating film by means of sublimation dyeing.
A processing for making a flat ribbon-like flexible electrical cable comprised of one or more spaced apart longitudinal extending conductor elements encapsulated between two layers of flexible insulating film according to the present invention includes the steps of:

selecting transfer paper comprised of a continuous strip of paper having at least one sublimable dye on one surface thereof;
feeding said transfer paper into a heat transfer apparatus, said apparatus having heating means and film retaining means so that the uncoated side of the transfer paper is proximate the heating means;
simultaneously feeding a layer of flexible insulating film into the heat transfer apparatus so that one surface of the film is proximate the coated surface of the transfer paper and the other surface of the film is proximate the film retaining means;
pressing said film by said retaining means against said heating means with said transfer paper thereby held between said film and said heating means;
applying sufficient heat to the transfer paper by said heating means so that the dye sublimes from the transfer paper and diffuses into and colors the flexible insulating film;
removing the colored film from the heat transfer apparatus;
applying adhesive to one surface of said colored film;
feeding said adhesive coated colored film into a laminating means;
simultaneously feeding at least one conductor element and another layer of adhesive coated insulating film into said laminating means such that said at least one conductor element extends longitudinally between the adhesive coated surfaces of the film layers; and
laminating said at least one conductor element between said two film layers thus encapsulating and surrounding said at least one conductor element with insulating film.

This process allows for provision of means to impart a multicolored design and alphanumeric characters as well as solid color to the film.
The process for dyeing a continuous flexible polymeric substrate such as a film, uses a strip of transfer paper having one or more sublimable dyes deposited on one surface. The substrate and transfer paper are fed simultaneously into a heat transfer apparatus comprised of a heating means and a substrate retaining means. The layers are fed into the apparatus so that the uncoated side of the transfer paper is proximate the heating means, the coated side of the transfer paper is proximate one surface of the substrate and the other surface of the substrate is proximate the substrate retaining means.
The substrate retaining means is used to hold the transfer paper securely between the substrate and the heating means. Sufficient heat is applied to the transfer paper to cause the dye to sublime from the paper and diffuse into the interstices of the substrate as it is swelled during the heating process. The colored substrate is removed from the heat transfer apparatus.
Since the color is diffused into the interstices of the substrate by this process, it becomes an integral part of the substrate and is not merely a coating. The color remains stable during subsequent processing and is not affected by cleaning solvents or abrasion.
Products such as a flat ribbon-like flexible electrical cable dyed in accordance with this method are also disclosed. The cable is comprised of one or more spaced apart, longitudinally extending conductor elements encapsulated between two layers of flexible insulating film wherein at least one of the film layers has been dyed in accordance with the process disclosed herein. The process for making the cable is comprised of the steps of applying adhesive to one surface of the film colored in accordance with the invention; simultaneously feeding said adhesive coated film, at least one conductor element and a second layer of adhesive coated insulating film into a laminating means such that said at least one conductor element lies between the adhesive coated surfaces of the film layers and laminating said at least one conductor element between said two film layers thus encapsulating said at least one conductor with insulating film.
The textile industry has used sublimation dyeing of fabric for a number of years. Apparatus and methods for sublimation dyeing are disclosed in patents such as U.S. Patents 2,911,280, 3,966,396, 4,163,642, 4,226,594 and 4,419,102. Sublimation dyeing has also been used to print graphics on keyboards and the like for membrane switches. The printing takes place just prior to final assembly of the keyboard.
It is new, however, to use sublimation dyeing to impart color to a continuous strip of flexible plastic film that is used for manufacturing flexible cable. Further, it is new to use sublimation dyeing as one of the initial steps in a cable manufacturing process. Using the method as disclosed herein also eliminates the necessity of prestabilizing film prior to making the cable. Sublimation dyeing requires a higher temperature than that normally used for stabilizing the material. Thus, the film can be stabilized and colored at the same time. Furthermore, tests show that flexible cable that has been colored by sublimation dyeing in accordance with the herein disclosed process surprisingly and unexpectedly exhibits greater resistance to being peeled apart than cable that has not been colored by this process.
The invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 is a schematic view of the apparatus used to transfer color to a continuous flexible polymeric substrate.
Figure 2 is an enlarged cross-sectional view taken at circle A of Figure 1.
Figure 3 is a flow chart giving a schematic method for making flexible conductor cables in accordance with the invention.

Figure 1 shows a schematic view of the apparatus used for sublimating dyeing in the disclosed method. Apparatus 10 is comprised of a rotating heatable drum 30 and a continuous belt 32 which is held against the rotating drum 30. a continuous strip of dyed transfer paper 18 and a continuous polymeric substrate 12 are passed between the rotating drum 30 and belt 32. Figure 1 also shows the use of blotting paper 24 which may be used between the polymeric substrate 12 and the belt 32 to absorb any excess dye that penetrates through the substrate during the sublimation process. The transfer paper 18, the polymeric substrate 12 and the blotting paper 24 are fed into the apparatus 10 by use of supply reels 20, 14 and 26 respectively. The spent transfer paper 18', the colored film 12' and the spent blotting paper 24' are wound on take-up reels 22, 16 and 28 respectively.
Figure 2 is an enlarged cross-sectional view of a portion of apparatus 10, showing the drum 30 and the belt 32 with the transfer paper 18, the film 12 and the optional blotting paper 24 situated between the drum 30 and the belt 32. During the sublimation dyeing process the belt 32 and the layers of paper 18, 24 and film 12 are held securely against the drum 30 by the tension means 34 as shown in Figure 1.
Figure 3 is a schematic representation of the steps used in producing flexible cable in accordance with the disclosed method. The polymeric substrate is a plastic film commonly used for electrical cables. The insulating film is dyed by sublimation and coated with an appropriate adhesive. Flexible cable is made by laminating conductor elements between two layers of adhesive coated film. Figure 3 also shows the use of a slitter which can be used to slit a wide strip of colored film into multiple strips. The film can be slit before or after adhesive is applied.
The transfer paper is made by printing sublimable dye having the desired color and in the desired design onto transfer paper. The dye or ink and transfer paper used are the same as those used by the fabric industry. Paper can be obtained from commercial printing paper suppliers such as Crown Zeller Corp., San Francisco, California, 94104. Sublimable dyestuffs are available from manufacturers such as Ciba-Geigy, Ardsley, New York 10502 and Gotham Ink and Color Co., Inc., Long Island City, New York 11101.
The blotting paper, if used, is also standard paper available and commonly used by the fabric industry. Blotting paper is necessary if the apparatus is operated under conditions that cause the dye to be sublimed through the film and onto the belt. The belt is a seamless fiber belt as is used in the fabric industry.
In the preferred embodiment, cable is made from biaxially oriented polyester film. Biaxially oriented film has greater dielectric strength, physical strength and flex life than non-oriented film. In order to have cable that is dimensionally stable the film must be normally stabilized by heating prior to being made into cable. Biaxially oriented film can be obtained from companies such as E. I. DuPont de Nemours & Co. Inc., Wilmington, Delaware 19898; ICI Americas Inc., Wilmington, Delaware 19897 and American Hoechst Corp., Somerville, New Jersey 08876.
The apparatus used is a modification of standard equipment commonly used by the textile industry. Additional heaters and temperature control devices were added so that uniform heat could be maintined throughout the drum. The temperature necessary for dyeing the film depends upon factors such as the dyestuff used, the speed of the drum and the thickness of the paper and film layers. It was found that polyester film dyed best when subjected to temperatures in the range of 350-450°F (177-232°C). The temperature and time relationship is extremely important. The time required for the dye to sublime and penetrate the plastic film is significantly longer than the time required to dye textile.
Furthermore, the tension on the film must be carefully controlled at all stages of the dyeing process, as the film is fed into the heat transfer apparatus, during the time the film remains in contact with the heat and after the film exits the apparatus. The tension on the continuous belt must be controlled.
The take-up drive was also modified so that a contant tension could be maintained on the film despite the number of layers on the take-up reel. The film begins to cool as soon as it is no longer in contact with the drum. If the tension on the exiting film is not controlled precisely, the film will buckle, wrinkle and have varying degrees of shrinkage across the web as the film cools.
Colored cable was made in accordance with the invention. Continuous strips of transfer paper and film were fed from reels onto the rotating drum. The drum was kept at a constant temperature throughout the dyeing process. By carefully controlling the temperature and speed of the drum the amount of dye sublimed into the film was optimized and the amount of wasted dye was minimized. The majority of the sublimed dye thus became part of the structure of the film. The film was maintained under constant tension as it exited from the drum and was wound onto the take-up reel. Adhesive was then applied to one surface of the colored film. In the preferred embodiment adhesive was applied to the surface of film that was against the transfer paper to ensure that any dye on that surface of the film was encased within the laminated cable. The film was then slit into the desired widths. In the preferred cable embodiment, conductor elements were sandwiched between two layers of the colored film and laminated.
The sublimation method can be used to impart a solid color a plurality of colors, alphanumeric characters, and designs to flexible polymeric substrate. The design on the transfer paper is imparted to the substrate. Thus, otherwise solidly colored substrate when used for electrical cables can be color coded to indicate specific conductors. If color coding is desired this method can be used to color code the film, the cable can be made with one color coded layer of film and one uncoded layer of film.
It is thought that the method of coloring continuous flexible polymeric substrate of the present invention and many of its attendant advantages will be understood from the foregoing description.
It will be apparent that various changes may be made in the heat transfer apparatus, the types of substrate, the design and color imparted to the substrate, and the types of cable and other products made therefrom without parting from the scope of the invention or sacrificing all its material advantages.

Claims

1. A process for making a flat ribbon-like flexible electrical cable comprised of one or more spaced apart, longitudinally extending conductor elements encapsulated between two layers of flexible insulating film including the steps of:

selecting transfer paper (18) comprised of a continuous strip of paper having at least one sublimable dye on one surface thereof;

feeding said transfer paper into a heat transfer apparatus (10), said apparatus (10) having heating means (30) and film retaining means so that the uncoated side of the transfer paper (18) is proximate the heating means (30);

simultaneously feeding a layer of flexible insulating film into the heat transfer apparatus (10) so that one surface of the film is proximate the coated surface of the transfer paper (18) and the other surface of the film is proximate the film retaining means (32);

pressing said film by said retaining means (32) against said heating means (30) with said transfer paper (18) thereby held between said film and said heating means (30);

applying sufficient heat to the transfer paper (18) by said heating means (30) so that the dye sublimes from the transfer paper and diffuses into and colors the flexible insulating film;

removing the colored film from the heat transfer apparatus (10);

applying adhesive to one surface of said colored film;

feeding said adhesive coated colored film into a laminating means;

simultaneously feeding at least one conductor element and another layer of adhesive coated insulating film into said laminating means such that said at least one conductor element extends longitudinally between the adhesive coated surfaces of the film layers; and

laminating said at least one conductor element between said two film layers thus encapsulating and surrounding said at least one conductor element with insulating film.

2. The process as recited in claim 1, further including the step of simultaneously feeding a continuous strip of blotting paper (24) with the layeroftheflexible insulating film (12) and transfer paper (18) into the heat transfer apparatus between said layer of flexible insulating film (12) and said retaining means (32), thus sandwiching said layer of flexible insulating film (12) between said transfer paper (18) and said blotting paper (24).

3. The process recited in claim 1, wherein the one or more sublimable dyes are applied to form a design on the surface of the transfer paper (18).

4. A flat ribbon-like flexible electrical cable made by the process of claim 1, wherein at least one of said film layers (12) has been dyed in a pattern selected from the group consisting of a solid color, a multicolored design and a color coded design delineating specific conductor elements.

5. A flat ribbon-like flexible electrical cable as made by the process of claim 1 or as claimed in claim 4, wherein said film layers (12) are selected from the group comprised of matte textured polyester, matte textured polymeric films and essentially transparent polymeric films.