US3366503A

US3366503A - Process of embedding flock in a polyethylene substrate

Info

Publication number: US3366503A
Application number: US629039A
Authority: US
Inventors: James R Dillhoefer; Jr John R Nelson
Original assignee: Eagle Picher Industries Inc
Current assignee: Eagle Picher Industries Inc
Priority date: 1967-01-23
Filing date: 1967-01-23
Publication date: 1968-01-30
Anticipated expiration: 1985-01-30
Also published as: BE709502A; GB1210554A; FR1553225A

Description

Jan- 30, 1968 J. R. mLLHoEr-ER r-:TAL 3,366,503

PROCESS OF EMBEDDING FLOCK IN A POLYETHYLENE SUBSTRATE Filed Jan. 23. 1967 HEAT T0 BLOW LEVEL VAgUUM REMOVED 00 n n 1:55 I I inw/maf United States Patent O 3,366,503 PROCESS F EMBEDDING FLOCK IW A PGLYETHYLENE SUBSTRATE .lames R. Diilhoefer, Cleveland Heights, and .lohn R. Nelson, Jr., Mentor, Ohio, assignors to Eagle-Picher Industries Inc., Cincinnati, Ohio, a corporation of Ohio Continuation-impart of application Ser. No. 486,358, Sept. 10, 1965. This application Jan. 23, 1967, Ser. No. 629,939

10 Claims. (Cl. 117-17) ABSTRACT 0F THE DISCLSURE A process for making a flocked article including the steps of supporting molten polyethylene or mixtures of polyethylene and other thermoplastic materials against gravity and flocking upwardly into the molten material.

This is a continuation-impart of my copending application Ser. No. 486,358 filed Sept. 10, 1965, now abandoned. This invention relates to a process for manufacturing a flocked article and, more particularly, the invention is directed to the adhering of flock fibers directly to a plastic substrate.

Flocking is the art of depositing and adhering short fibers to the surface of an article to provide the article with a cut pile surface. The present invention is concerned particularly with the flocking of sheets of material as contrasted to threedimensional objects and the invention will be described in that context.

A principal use of flocked sheet material is in the manufacture of automotive floor coverings or similar carpeting. The flocked sheet material has been found to be very satisfactory in such applications because of its unusual resistance to abrasion or wear as -by the heels of the vehicle occupants continually grinding into the surface of the floor covering. Another reason for the interest of the automotive industry in flocked carpeting resides in the ability t0 introduce interesting patterns of multicolored flock into the surface of the carpeting and in the ability to produce a carpeting of rich, luxuriant appearance.

In the evolution of the art of flocking, fibers were first sifted by means of gravity onto an article Whose surface had been first coated with an adhesive. Subsequently, it was found that by establishing a high voltage electrostatic field between the source of flock fibers and the article, the fibers could be driven more efliciently into the article and with a better orientation.

The use of an adhesive for securing the fibers to the sheet introduced a variable into the process for not all adhesives are chemically compatible with the substrate or with the fibers and a reproducible, satisfactory adherence is diflicult to attain. The present invention is concerned with the elimination of the need for an adhesive as well as the elimination of the step required in applying the adhesive to the substrate. More specifically, an objec- 'tive of the invention has been to improve the manufacture of flocked sheets by bringing a plastic sheet to a molten condition and driving the fibers directly into the molten plastic.

A still further objective has been to support the molten layer of plastic facing downwardly and, using an electrostatic field, to drive the flock fibers upwardly into the sur- ICC pendicularly to the surface to which they are driven. However, a certain percentage of the fibers lose that chargeable characteristic which enables them to become oriented in the electrostatic field and, when flocked in the direction of the gravitational force, they fall in a random pattern against the adhesive or fluid plastic. By flocking against gravity, only those fibers susceptible of becoming charged so as to move against gravity through the force of the electrostatic field are driven into the substrate. Thus, only those fibers which are susceptible of perpendicular orientation engage the surface of the substrate, thereby avoiding any measurable random orientation of the fibers.

It has been another objective of the invention to provide a process for flocking a plastic substrate, the process including the final step of post curing the substrate. The post curing step involves the raising of the flocked sub strate to a temperature above its melting point `but below the melting point of the fibers and maintaining the article at that temperature for a limited period of time. Empirically, it has been determined that the post curing step is critically important to the provision of a satisfactory bond between high melting point fibers and a comparatively low melting point substrate as, for example, nylon fibers and a polyolefin substrate. In other combinations as, for example, olefin to olefin, the post curing step has been found to materially' augment bonding of the fibers to the substrate.

These and other objectives of the invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a diagrammatic view illustrating the steps in the process of flocking a molded textured sheet, and

FIG. 2 is a diagrammatic perspective view of a form of flocking apparatus.

As indicated above, the invention has as its essential step the flocking of molten plastic against gravity. There are a number of subsidary conditions which will be discussed below and which must be taken into consideration in the performance of a process which will provide the most satisfactory manufactured article. Prior to the actual flocking step, the plastic material may be brought to that condition of readiness to receive a deposit of flock fibers in any one of several different processes beginning with one of several starting materials. The plastic material may initially be a particulate or powdered plastic which is held on a support and heated until it fuses and flows together to form a single coherent viscous sheet of approximately the consistency of honey. Alternatively, the plastic may be extruded onto a moving belt, for example, and flocked before the temperature of the plastic has been reduced to the point of freezing the plastic or flocked after reheating if the plastic freezes after extruding. In a third alternative, a sheet of thermoplastic material is secured to a mold and brought to a molten condition after which it is flocked against gravity.

Apparatus by which the steps of the process may be carried out are diagrammatically illustrated in FIGS. 1 and 2. Referring to FIG. 1, the apparatus employed is designed to produce a contoured flocked article using a sheet of plastic material as the substrate. The appartus illustrated at step A comprises a support in the form of a mold 10 having a mold surface 11, The mold 10 may be of the type described in copending application Ser. No. 453,937, filed May 7, 1965, now Patent No. 3,337,- 908, in the name of Nelson, et al. The mold is metallic, at least on the surface 11 which receives the sheet to be flocked, so that the mold can function additionally as an electrode in the flocking process. The mold is perforated as indicated at 14 and has a cavity 15 which is adapted to be evacuated through the port 16 having a one-way valve 18. A sheet of plastic material 17 is adapted to be placed on the surface 11 and a vacuum created in the chamber to cause the evacuation of the space between the surface 11 and the sheet 17 to hold the sheet against the surface 11 in general conformity to the contour of the surface.

Following the mounting of the sheet on the mold and evacuation of the space between the mold and the sheet, the next succeeding step of the process indicated at B is performed. In that step, the sheet is heated as by a heat source constituted by infrared lamps 20 until the sheet becomes warm, that is, the sheet is raised to a temperature of approximately 200 F. The heating may be performed in an oven or by any other suitable apparatus. The temperature of the sheet is raised to that minimum temperature which permits the sheet to attain the degree of fiexibility which enables it to conform quite closely to the surface 11 of the mold, but the sheet is not sufiiciently fiuid to permit it to be drawn into the evacuating holes 14.

The mold is then inverted at step C and the source of vacuum is removed. A one-way valve 18 in the port 16 prevents the immediate release of the vacuum between the sheet and the surface 11 in order to prevent the immediate dropping of the sheet from the mold when the vacuum source is removed. At step D in the process, the sheet is heated until it becomes fluid, the surface tension of the fluid plastic maintaining the sheet in position on the mold.

As soon as the sheet has been brought to a fluid condition, the step illustrated at E proceeds and the article is flocked under the conditions which will be more fully described below.

In FIG. 2, there is illustrated an alternative form of apparatus for the continuous production of a flocked web. The apparatus includes a support in the form of a conveyor belt which is wrapped about two drums 31 and 32. Apparatus 33 for applying a thermoplastic material to the belt 30 is located adjacent its upper flight at the upstream end of that flight. The apparatus 33 may simply be a hopper for applying a continuous supply of granules to the -belt or the apparatus may be an extruder for applying a continuous film of plastic to the belt. A doctor roll 34 is located above the belt and is adapted to level the applied plastic material to a predetermined thickness.

A heat source 35 constituted by a bank of infrared lamps 36, for example, mounted in a hood 37 is located downstream of the doctor roll 34 and is adapted to raise the temperature of the plastic material until it attains that condition of fluidity suitable for the flocking process. The surface tension of the fluid plastic causes it to adhere to the belt as the belt passes around the drum 32 and over a supply of ock.

The belt 30 has a lower flight 40 which passes over a first fiock supply belt 41 and a second flock supply belt 42. The supply belt 41 receives a supply of flock fibers of a first color from a hopper 43 of the type described in said copending application Ser. No. 453,937, filed May 7, 1965. Similarly, the belt 42 receives a second supply of ock fibers from a hopper 44, the fibers of the second hopper being of a color different from that of the first hopper. Electrode plates 45 and 46 connected at ground potential are mounted below the respective flock supply belts. Cooperating electrodes 47 and 4S are mounted above the lower flight 40 of the belt 30 and are connected to a source of high potential. The thus cooperating electrode pairs 45, 47 and 46, 48 provide the electrostatic force required for the flocking operation.

A flexible stencil 50 formed as an endless belt passing around drums 51 and 52 has an upper night 53 which passes between the lower flight 40 of belt 30 and the upper flight of the hopper supply belt. The

drums

32 and 51 are connected together by meshing gears 54 and 55 fixed to the

drums

32 and 51 respectively to cause the upper flight of the stencil to move at the same lineal speed and in the same direction as the lower flight 40 of the conveyor belt 30.

In the operation of the apparatus of FIG. 2, the plastic material is deposited on the belt 30 from the supply apparatus 33 and is brought to a predetermined thickness by the doctor roll 34. The plastic material is then melted by the heating apparatus 35 and in that condition adheres to the belt 30. It passes around the drum 32 with the belt and between the electrodes 45 and 47 and immediately above the stencil 50. The electrostatic force provided by voltage between the plates 45 and 47 causes the flock fibers to be driven upwardly through openings 57 and to be embedded into the fluid plastic sheet in a predetermined pattern determined by the openings in the stencil. The duration of any increment of the plastic sheet between the two electrodes 45 and 47 is sufficiently long to permit a complete deposit of flock onto the exposed area of the plastic sheet.`

The sheet thereafter passes over the second supply of flock between eleectrodes 46 and 48. Since there is no stencil for blocking the movement of the ock from the belt 42 to the plastic sheet, the remaining unffocked areas of the sheet receive a deposit of flock.

After completion of the Hocking steps, the temperature of the substrate is maintained (or brought) to a temperature above its melting temperature but below the melting temperature of the fibers for a predetermined period of time. This heat treatment, following flocking, appears to provide a more intimate contact of the substrate with the fibers and hence improves its pull test.

After the post flocking heat step, or after flocking if no post flocking heat is used, the substrate is permitted to cool and is thereafter removed from the supporting belt.

The process of flocking the molten plastic sheets against gravity Ainvolves a number of factors which admit of some variation as will be discused below. The ultimate objective in the variation of any of the `factors is to obtain an adherence or penetration of the ock fibers into the substrate to the extent that each fiber can withstand at least a sixteen pound pull test. The pull test involves an instrument (manufactured by Instron) having means for holding the liocked article and means for clamping a measured group of ock fibers (one inch by 1A; inch) and pulling them out of the `substrate at la constant rate (ten inches per minute). The applied tension is measured and that required to pull the fibers out of the substrate provides a measure of `adherence which is referred to as the pull test. Among the factors contributing to adherence are the following:

(il) Substrate material (2) Fiber material (3) Thickness of substrate (4) Temperature applied to the substrate (5) Time of application of heat (6) Applied voltage (7) Distance between the electrodes (8) Post cure The preferred substrate of the present invention is polyethylene or a mixture of polyethylene and other thermoplastics wherein the major portion of the mixture is polyethylene. Thermoplastic materials which can be mixed with polyethylene and provide a satisfactory substrate are ethylene vinyl acetate and ethylene ethyl acrylate. Polypropylene, rayon, and nylon have proved to 'be satisfactory materials for the fibers. Satisfactory articles have been manufactured in which the nylon tlibers have a `denier of 53 and a length of 0.120 inch and in lwhich the polypropylene fibers have a denier of 30 and a length of 0.160 inc'h. These dimensions are not critical and any fibers properly prepared to receive an electrostatic charge may be used.

The thickness of the substrate should not be less than approximately 0.015 inch, for it has been found that the required depth of penetration of the fibers for a satisfactory tuft pull should be between 0.007 and 0.018 inch. The maximum thickness of the substrate appears to be determined only by the ability of the substrate to maintain itself on the mold against the pull of gravity.

The ltemperature of the melting atmosphere surrounding the plastic will, of course, be determined in part by the material of which the bers and the substrate are formed. Polyethylene, for example, should lbe heated to .a uniform temperature in the range of 375 to 400 F. This temperature within this range is subject to variation, depending upon factors such as the type of flock fiber, thickness of the substrate, and the post cure and t-he ultimate quality of the product desired.

.For example, when flocking with polypropylene fibers, the polyethylene substrate should 'be raised to a temperature of 375-385 F. While this -is well above the melting point of the polypropylene fibers (335 E), the temperature of the substrate is low enough that the polypropylene fibers do not melt completely upon impingement with the hot substrate. Rather, the substrate appears to 'be fluid enough for the `fibers to get good penetration into it and their embedded ends melt `slightly to form a ball Which tends to facilitate the anchorage of the fibers to the substrate.

In ocking with nylon fibers, it is preferable to raise the temperature of the substrate S90-400 F. The higher temperature in the case of the nyl-on fibers appears to be necessary in order to obtain the required penetration of the nylon fibers into the substrate. A temperature substantially higher than 400 F. is undesirable because it causes discoloration or oxidat-ion of the fibers.

The applied voltage and distance between the electrode plates should be selected to assure a satisfactory depth of penetration. `For example, to obtain a satisfactory depth of penetration, the applied voltage should be between 25,000 and 50,000 volts direct current and the spacing between the electrodes should be between three and five inches. The depth of penetration which has proved sat-isfactory -to obtain the minimum tuft pull is between 0.007 and 0.018 inch.

Following flocking, and preferably before the substrate cools to its freezing point, the flocked substrate is subjected to heat (post cure) to maintain vits temperature vabove the melting temperature of the polyethylene (280 F.) and below the melting temperature of the fibers polypropylene 335 F.) (nylon 440 F.). The length o-f time during which the substrate is subjected to heat following flocking will depend upon the temperature of the heat applied and, as indicated, the temperature will depend in part upon the melting point of the fibers which have been flocked into the substrate. By way of example, if the article is docked with polypropylene fibers, the temperature of the substrate should be maintained at about 300 F. for approximately ten minutes. If the ,article is flocked with nylon fibers, the temperature of the substrate should be maintained at approximately 375 F. for three to five minutes.

Example 1 Ninety parts by Weight of polyethylene (800 E by Eastman Kodak) were intimately mixed with ten parts 'by weight of ethylene ethyl acrylate (6169 by lUnion Carbide) and raised to a temperature of 380 F. While held at this temperature and supported lon a flat plate, the plate was inverted so that the molten plastic mixture faced downwardly. Using the plate as one electrode, the pl-astic mixture was flocked at 40,000 volts DC. With a spacing of approximately four inches between electrodes. The substrate was ocked with nylon fibers having a denier of 53 and a length of 0.120 inch.

The flocked article Was subjected to a post flocking heat treatment of 375 for five minutes. After cooling, the article responded 'satisfactorily to a tuft pull test.

Example 2 The steps of Example 1 were performed as set forth yin Example 1 except that 85 parts of polyethylene and 15 parts of ethylene ethyl acrylate were mixed together to form the substrate. The flocked substrate responded satisfactorily to a tuft pull test.

Example 3 The steps of Example 1 were performed as set forth in Example 1 except that four different substrates were formed. The first was 100% polyethylene. The second, third, and fourth were 80%, and 70% polyethylene, respectively, with the remainder being ethylene vinyl acetate. In a-ll four cases, the substrate responded satis factorily to a tuft pull test.

Example 4 The steps of Examples 1-3 were performed as set forth in Examples 1-3 except that the flock fibers employed were polypropylene having a denier of 30 and a length of 0.160 and except that in the post flock treatment, a flocked substrate was subjected to a temperature of 300 F. for approximately ten minutes. The articles responded satisfactorily to tuft pull tests.

We claim:

1. The process of embedding yflock fibers in a polyethylene substrate comprising the steps of subjecting the polyethylene to an elecated temperature until it becomes a viscous fluid, said polyethylene being on a support in the form of a sheet which is at least 0.015 inch thick, positioning the support over a supply of flock fibers with the polyethylene in a viscous fluid state facing down- Wardly,

applying a voltage between the support and the supply of the fibers to drive the ends of the fibers into the viscous fluid polyethylene,

cooling the sheet below its melting point, and

removing the sheet from the support.

2. The process of embedding flock fibers in a polyethylene substrate comprising the steps of subjecting the polyethylene to an elevated temperature until it becomes a viscous fiuid, said polyethylene being on a support in the form of a sheet which is at least 0.015 inch thick.

positioning the support over a supply of flock fibers with the polyethylene in a viscous fluid state facing downwardly,

applying a voltage between the support and the supply of fibers to drive the ends of the fibers into the viscous uid polyethylene,

subjecting the sheet to an elevated temperature above the melting point of the polyethylene and below the melting point of the fibers for a limited period of time to increase the adherence of the fibers to the polyethylene,

cooling the sheet below its melting point, and

removing the sheet from the support.

3. The process according to claim 2 in which said fibers are selected from the group consisting of nylon and polypropylene.

4. The process according to claim 2 in which, following flocking, the sheet is maintained at a temperature of approximately 300-375 F. for three to ten minutes.

5. 'Ihe process of embedding flock fibers in a polyethylene substrate comprising the steps of subjecting the polyethylene to an elevated temperature until it becomes a viscous fluid, said polyethylene being on a support in the form of a sheet which is at least 0.015 inch thick,

applying a voltage between the support and the supply of bers to drive the ends of the bers into the viscous fluid polyethylene to a depth of at least approximately 0.007 inch,

cooling the sheet below its melting point, and

removing the sheet from the support.

6. The process of embedding flock bers in a substrate consisting of at least predominantly polyethylene,

subjecting the substrate to an elevated temperature until it becomes a viscous lhuid, said substrate being on a support in the form of a sheet which is at least 0.015 inch thick,

positioning the support over a supply of -lock bers with the substrate in a viscous tiuid state facing downwardly,

applying a voltage between the support and the supply of bers to drive the ends of the bers into the viscous lfluid substrate to a Vdepth of at least approximately 0.007 inch,

cooling the substrate below its melting point, and

removing the sheet from the support.

7. The process according to claim 6 in which said substrate is a mixture of polyethylene and another thermoplastic material.

8. The process according to claim 6 in which said substrate is a mixture of polyethylene and a substance selected from the group consisting of ethylene ethyl acrylate and ethylene vinyl acetate.

9. The process according to claim 8 in which the substrate is at least 70 parts by weight polyethylene.

10. The process of embedding flock fibers in a substrate consisting of at least predominantly polyethylene,

subjecting the substrate to an elevated temperature until it becomes a viscous Huid, said substrate being on a support in the form of a sheet which is at least 0.015 inch thick,

positioning the support over a supply of flock Atibers with the substrate in a Viscous uid state facing downwardly,

applying a voltage between the support and the supply of bers to drive the ends of the fibers into the viscous iiuid substrate,

cooling the substrate below its melting point, and removing the sheet from the support, Y

References Cited UNITED STATES PATENTS 2,087,260 7/1937 Miner 117-17 2,222,539 11/1940 Meeren 156-246 2,290,238 7/1942 Hiekek 117-25 15 2,308,624 1/1943 Peveeh 117-33 2,472,551 6/1949 smith 264-131 2,553,259 8/1951 Miner 117-33 2,567,186 9/1951 Cross et al 117-16 2,686,733 8/1954 Burridge etal 117-17 2 2,689,801 9/1954 DAnelie 117-16 2,784,630 3/1957 Keprew et a1. 117-17 2,844,489 7/1958 Gemmer 117-21 2,907,671 10/1959 Duviver 117-16 3,099,572 7/1963 Rien et a1. 117-16 3,168,603 2/1965 seefluth 264-69 3,212,137 10/1965 Lememe 264-25 3,215,584 11/1965 Mccenneuer a1 117-33 3,257,743 6/ 1966 Closson et al. 117--16 Y 3,275,487 9/1966 Lemelson 156-72 FOREIGN PATENTS 453,234 9/ 1936 Great Britain.

NILLLM D. MARTIN, Primary Examiner.

E. I. CABIC,-Assstan\t Examiner.