US3625788A

US3625788A - Method of manufacturing a unitary composite article comprised of a core and lining

Info

Publication number: US3625788A
Application number: US860150A
Authority: US
Inventors: Bernard I Bartner
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-09-04
Filing date: 1969-09-04
Publication date: 1971-12-07
Anticipated expiration: 1988-12-07
Also published as: GB1262221A

Abstract

A method of manufacturing a writing implement having an inner body portion of unfoamed resin. The method consists of inserting a heated probe into the inner body portion so as to cause the foamed resin to become molten, withdrawing the probe and simultaneously inserting a writing core into the cavity, and allowing the body to cool whereby foamed resin adheres and bonds to the writing core.

Description

United States Patent inventor Bernard 1. Bar-tner 229-07 58th Ave., Bayside, N.Y. 11364 Sept. 4, 1969 Dec. 7, 1971 Continuation-impart 01 application Ser. No. 631,652, Apr. 18, 1967. Thk application Sept. 4, 1969, Ser. No. 860,150

App]. No. Filed Patented METHOD OF MANUFACTURING A UNITARY COMPOSITE ARTICLE COMPRISED OF A CORE AND LINING [56] References Cited UNITED STATES PATENTS 3,340,] 15 9/l967 Rubenstein 156/294 X 3,500,819 3/1970 Silverman l56/294 X Primary Examiner-Carl D. Quarforth Assistant ExaminerStephen J. Lechert, Jr Attorney-Jerome Bauer ABSTRACT: A method of manufacturing a writing implement having an inner body portion of unfoamed resin. The method consists of inserting a heated probe into the inner body portion so as to cause the foamed resin to become molten, withdrawing the probe and simultaneously inserting a writing core into the cavity, and allowing the body to cool whereby foamed resin adheres and bonds to the writing core.

PATENTEI] DEC 7 I971 SHEET 1 OF 2 R E HN m N BA VB WI D R A N R E B BY i ATTORNEY PATENTEDuEc 719?: 3625788 sum 2 OF 2 INVENTOR. BERNARD I. BARTNER ATTORNEY METHOD OF MANUFACTURING A UNITARY COMPOSITE ARTICLE COMPRISED OF A CORE AND LINING This application is a continuation-in-part of my copending application Ser. No. 63 I ,652,filed Apr. 18, I967.

BACKGROUND OF THE INVENTION The present invention relates to unitary composite articles, such as writing instruments and the like, and methods of manufacturing such articles.

In the manufacture of a unitary composite article such as a lead pencil, it had been customary to provide a pair of complementary shaped elongated wooden members each of which is formed with a groove for receiving part of a lead core. The lead core is received in the bore formed by the grooves of the pair of elongated wooden members which are thereafier joined to each other by a suitable adhesive or the like, so that in this way lead pencils are conventionally manufactured. As a result of these procedures, it is necessary to carry out a multiplicity of steps in order to manufacture lead pencils, undesirably increasing the cost thereof, and because of problems encountered with respect to the joining of the wooden bodies to each other and to the lead core, a reliable bond between these components is not always achieved.

SUMMARY OF THE INVENTION It is accordingly a primary object of the present invention to provide a unitary composite article and method of manufacturing the same which will avoid the aforementioned problems.

In particular, it is an object of the present invention to provide a unitary composite article such as a writing instrument that may take the form of a crayon pencil or lead pencil which obviates the cumbersome prior art practice of joining separate casing components to each other surrounding the core of the writing instrument and the use of a bonding adhesive therebetween.

In particular, it is an object of the invention to provide a unitary composite article where an inner elongated member is encased within a one-piece exterior casing so that the problems encountered with the conventional constructions can be avoided.

Further, it is an object of the present invention to provide a method according to which an elongated member, such as a marking or writing member, as the core of a lead pencil, is in troduced into the interior of a one-piece body which encases the core or elongated member while also becoming firmly bonded thereto, so that it becomes possible with the method of the invention to manufacture articles such as writing instruments or the like at a far lower cost than conventional articles of this type while at the same time eliminating the problems encountered with the finished article, such as the reliable holding together or adhesion of the components thereof.

In accordance with the method of the invention, an elongated member is introduced to the interior of an elongated body of a foam thermoplastic while the body is in a plastic condition. By the method of the invention, the elongated member directly engages the inner surface of the elongated body so that during subsequent cooling and setting of the body, its inner surface becomes securely and permanently bonded with the elongated member, thereby resulting in the unitary composite article. The elongated body of foam thermoplastic can be extruded in a conventional manner and an elongated heated probe may be axially passed through the body of foam plastic for providing it with its heated inner surface which subsequently engages the elongated member. This latter member may be introduced into the plastic body substantially simultaneously with withdrawal of the probe therefrom. The heated probe has been used to form a bore in the body the dimension of which is determined by the size of the outer surface of the probe. However, it has been found that the body may be initially extruded with a bore so that when the probe is introduced into the bore the surface which defines the bore will become heated, softened and plastic. The elongated member itself may have a diameter slightly greater than that of the inner surface of the bore which is in the heated plastic condition, so that this bore becomes expanded slightly during the introduction thereinto of the elongated member and thus forms a secure bond therewith. During its extrusion, the plastic body is provided at its outer surface with a nonfoamed plastic at least partially covering the outer surface of the plastic body, so thatthe rigidity of the body is increased without adversely affecting its machine-ability characteristics. Thus, it becomes possible to machine the resulting unitary composite article in a conventional pencil sharpener.

The foamed inner body may have two foamed concentric layers, with the outer layer having been foamed in the extruder and the inner layer subsequently foamed in situ as a consequence of contact with the heated probe.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated by way of example in the accompanying drawings-which form part of this application and in which:

FIG. I is a schematic illustration of one possible manner in which elongated plastic bodies may be formed;

FIG. 2 is a transverse section, taken along line 22 of FIG. 5 in the direction of the arrows, of a plastic body extruded with the structure of FIG. I; I

FIG. 3 is a transverse section of the plastic body taken along line 3-3 of FIG. 7, in the direction of the arrows;

FIG. 4 is a schematic side elevation, partly in longitudinal section, of an enlarged heating structure used in the method of the invention;

FIG. 5 illustrates on stage in the manufacture of an article according to the method of the invention;

FIG. 6 shows a stage in the method subsequent to that of FIG. 5;

FIG. 7 illustrates a stage in the method of manufacture of the invention subsequent to that of FIG. 6;

FIG. 8 shows, in side elevation, one possible article of the present invention manufactured according to the method of the invention;

FIG. 9 is a schematic illustration of a manner of forming another embodiment of the elongated plastic bodies of this invention;

FIG. I0 is a transverse section, taken along line l0-10 of FIG. 9 in the direction of the arrows, of a plastic body extruded with the structure of FIG. 9;

FIG. 11 illustrates one stage in the manufacture of an article according to the method of the invention; and

FIG. 12 illustrates a stage in the method of manufacture of the invention subsequent to that of FIG. I 1.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, and first to FIGS. 1-8, with initial reference to FIG. 8, the unitary composite article, generally identified by the numeral 10, is illustrated therein as a lead or a coloring pencil, having a writing core I2 which at one end projects beyond a casing or body 14 which surrounds the core I2. The core 12 thus forms an elongated member capable of making a mark on paper so that the article 10 may be said to be a writing instrument. The casing generally identified by the numeral 14 encases the elongated core member 12 and has, in the illustrated sample, an outer shell 16 of a relatively rigid nonfoamed plastic. This shell 16 of the elongated body 14 surrounds and is integrally extruded with a foam plastic inner lining or portion 18 which extends longitudinally through and for the length of the shell 16. The plastic body 14 is made of any suitable thermoplastic, as referred to in greater detail below. It is a one-piece body which finnly adheres and is permanently bonded at its inner surface to the exterior surface of the elongated member 12, the result of which is an inseparable unitary composite structure.

The cellular structure of the foam plastic inner lining 18 approximate the structure and characteristic of wood, thereby enabling it to be machined with the same ease as wood in a conventional pencil sharpener. If the whole body 14 were of such porous or cellular structure as the inner lining 18, it would be too flexible and, therefore, it would not sufiiciently protect the soft core 12 therewithin. Hence, the added protection of the harder, less porous and more rigid outer shell 16. When this thin outer shell 16 is applied to the inner lining 18, it adds sufficient rigidity to the body that limits flexing or bending of the body that might damage its inner core 12.

In order to manufacture the article 10, in accordance with the method of the invention, the body 14 thereof is extruded in a conventional extruder 20 shown in FIG. l.This extruder contains the foam plastic mass 22 which is urged outwardly through the extruder outlet 24 in any suitable way, such as by a plunger or piston 26 which is acted upon in a conventional manner. If desired, a screw-type of material feeder can be provided for the extruder to urge the plasticized mass 22 out of the latter. This mass 22 is a thermoplastic material which contains a suitable foaming agent so that the resultant extrusion will be composed primarily of a foamed plastic porous in structure and having a multiplicity of cells therein which may be either of the open or closed type.

Positioned about and in the region of the outlet 24, the extruder 20 has an annular chamber 28. The chamber 28 surrounds the outlet opening 24 through which the mass 22 issues and communicates with a mass of nonfoamed plastic 30 which is compatible with the material 22 so as to form an integral and indistinguishable body therewith. Because the channel 28 surrounds the outlet 24 through which the extruded mass 22 issues, the material 30 forms the outer shell covering 16 of the body 14. It is this nonfoamed plastic coating 16 that gives the cellular foamed body 18 added rigidity. The mass of plasticized nonfoamed material 30 is urged out of the chamber 32 by a plunger 34 acted upon in a conventional way, or in this case also a screw-type of material feeder may be used.

If desired, the channel 28 need not form a continuous circle around the bore through which the material 22 issued, and instead it can be interrupted by ribs extending across the channel 28 in the direction of the axis of the outlet 24 through which the material 22 issues. These ribs may be uniformly or nonuniformly distributed about the axis of the channel 28 to interrupt the flow and extrusion of the material 30 about the prior extruded material 22. By controlling the design of the ribbing of the outlet channel 28, it has been found possible to apply reinforcing rigidifying ribs to the extruded material 22 rather than to apply a full and complete shell covering 16. In this way it is also possible to achieve many different types of decorative effects on the outer surface of the body 14.

Thus, it will be recognized that as the foam plastic material 22 is extruded through the outlet 24, its outer cellular surface is almost immediately impregnated with the nonfoaming plastic material 30. As the material 30 is extruded, it flows into the porous, cellular structure of the material 22, fusing therewith and becoming indivisible and inseparable therefrom. For all purposes, the two

materials

22 and 30 become one whole, unitary extruded body. The inner portion or lining 22 becomes the part in the article identified as the lining 18, while the outer covering 30 is the shell 16.

Upon issuing from the extruder 20, the composite extrusion passes through a cooling bath 36 of any conventional construction, and is transported by means 38, which may be driven in any suitable way, to a cutter unit 40, also of any conventional construction. This unit 40 cuts the extruded rod into bodies 14, of preselected lengths, collected in any suitable receptacle, as schematically indicated at the lower right portion of FIG. 1. The extruded bodies will have in cross section the construction indicated in FIG. 2 which illustrates the inner cellular body 18 of foam thermoplastic surrounded by the indivisibly and integrally fused outer shell 16 of nonfoamed plastic that is polymerized therewith.

After each body 14 is formed it is worked upon by a heated probe 42 indicated in FIG. 4. This probe may take the form, for example, of a nichrome wire 44 encased within a suitable casing 46 with an end 48 of the wire 44 exposed and electrically joined, as by silver solder 50 to an outer stainless steel casing 52. This casing 52 and the wire 44 are electrically connected with a pair of conductors of a lead 54 joined to any power source 56, so that when the latter is energized the probe 42 will be heated.

Referring now to FIG. 5, the body 14 and the probe 42 are initially situated at opposite ends of the body 14 and with respect to each other substantially in the manner shown in FIG. 5. While the body 14 is held in any suitable holding structure (not shown), the heated probe 42 is guided into and through the body 14 so that the outer shell 52 of the probe, which is at an elevated temperature, pierces at its leading pointed end the body 14 to produce or form an axial hollow or bore therein. During the time the probe 42 pierces through the body 14 to form the latter with an axial bore, the elongated member 12, in the form of a lead core in the illustrated example, is maintained in readiness of any suitable support to be pushed into the body 14 at its opposite end.

In the event the body 14 is extruded as a solid rod, as shown in cross section in FIG. 2, it will be necessary to form the same by the probe 42 with a central axial bore 43 therethrough to enable it to subsequently receive the member 12 therein. On the other hand, it has been found convenient to initially extrude the body 14 with a central hollow or axial bore 43 as in FIG. 3. If the bore 43 is initially extruded therein, its size will be smaller than that of the heated probe 42 which, in turn, is smaller than that of the insert 12. Thus, while the body 14 is held in any suitable holder (not shown) the heated probe 42 will enter the bore 43 to be guided thereby to penetrate the length of the body. As the heated probe 42 quickly penetrates the length of the bore 43 or forms the same, the cellular lining l8 breaks down and melts rapidly under its heat, thereby enlarging the bore size. Hence, it is important that the operation of the probe be performed rapidly. Its insertion into and removal from the body 14 should be no longer than is necessary to form the bore 43 of the size opening that is just sufficient to accommodate the receipt of the insert member 12 therein. If the probe 42 remains in the body too long, its heat will form an increasingly larger bore by causing the adjacent cellular structure of the lining 18 to melt and break down. Thus, to facilitate the rapid and also accurate insertion of the probe 42 into the body, it is convenient if the body is initially extruded with the bore 43. The terms melt, melts" and "molten" herein refer to a heated condition of the foamed thermoplastic material sufficient to cause material flow under the prevailing conditions of heat and pressure. Molten or melt or melts state is often referred to as being plastic.

Consequently, it will be clear that the heated probe 42 will form the central bore 43 if none previously existed, or if one was there initially, it will enlarge the same. The longer it remains in the bore 43, more cells of the foam lining will be melted and, therefore, the larger will be the resultant bore 43. For this reason, it is a good practice to attempt to insert the core 12 into the body bore 43 almost simultaneously or as soon as possible after the removal of the probe 42 after it has reached its end position of FIG. 6. Therefore, substantially simultaneously with the removal of the probe 42 from the bore 43, and while the inner surface of the bore is still in its molten state, the core 12 is forced thereinto as shown in FIG. 7. This may be accomplished by the use of any desired pusher structure 58.

As the core 12 is forced into the bore 43 formed by the probe 42, it disturbs the molten cellular structure of the foam plastic in which the bore exists. This results in surface to surface contact and engagement between the outer surface of the core 12 and the bordering cells of the bore 43. If the insertion of the core 12 is performed while the foam thermoplastic is in its heated plastic condition, the engaging cellular surfaces of the bore adheres and becomes securely and permanently bonded to the core 12 as the thermoplastic hardens and sets.

, Furthermore, if the plastic is sufficiently molten when the core is inserted, the plastic will flow into whatever cells, pores or crevices may be present in the core so as to form a locking bond therewith. The resultant structure is a core so permanently bonded to the interior of the body that they form a unitary combined article.

As has been indicated above, the body 14 is composed primarily of a foam thermoplastic material. As a result, when the inner surface of the body is heated and placed in a plastic condition, cells of the body break and flow so that the material of the body 14 spreads and flows along the exterior surface of the elongated member 12. During heating and setting of the body 14 at its inner surface it forms with the exterior surface of the member 12 a bond which has proved to be of the greatest strength, a highly intimate and secure connection being provided in this way. It is to be noted that in dealing with a lead core 12, in particular, because of the slippery, somewhat greasy nature of this lead core, problems have been encountered in the prior art in joining the half casings of a wood pencil to such lead cores, whereas with the structure of this invention, without the use of any adhesive, solvent, or the like, the inner surface of the body 14 directly adheres and permanently bonds to the exterior surface of the member 12, forming an exceedingly secure connection therewith in a very simple way.

The foaming of the plastic body 14 is achieved by the use of a foaming agent, as is well known in the art. In accordance with a further feature of the invention, this foaming agent may be activated when the inner surface of the bore 43 of the body 14 is heated and engages the exterior surface of the member 12. As a result of the heat derived from the heated inner surface of the bore 43 of the plastic body, the foaming agent continues to function and tends to expand the cells of the body inward toward the core 12 so that not only does it press the plastic cells into tighter frictional engagement and connection with the member 12, but it mechanically grips and squeezes the member 12, thus increasing the security of the adhesion and bond of the connection.

Another embodiment of the invention is illustrated in FIGS. 9-11 depicting the manufacture of a composite article having the inner core 12 surrounded by an inwardly directed foam cylindrical body 86 (See FIG. 12). Cylindrical body 86 is encased within and integral with intermediate foam cylindrical body 62 which is surrounded by nonfoam shell 60. Shell 60 and intermediate body 62 correspond to shell 16 and body 14 respectively.

The composite article illustrated in FIG. 12, in the last stages of being manufactured, is first an extrusion product of extruder 66. This extruder 66 contains the nonfoam plastic mass C in the chamber 68. The plastic mass C is urged outwardly by plunger 70 through the inner annular chamber 72 about the tube 73 to form an inner cylindrical nonfoam body 64 which is extruded with an inner bore 65, that may be maintained open by a gas discharged thereinto by way of the tube 73. Chamber 74 contains foam plastic mass B. The foam plastic mass B is urged outwardly by plunger 76 through the intermediate annular chamber 78 to form the intermediate foam cylindrical body 62. The chamber 80 contains nonfoam plastic mass A. Plastic mass A is urged outwardly by plunger 82 through the outer annular chamber 84 to form the nonfoam shell 60.

Nonfoam shell 60 and intermediate foam body 62 are integral in the same fashion as described hereinbefore in connection with shell 16 and body 14. Similarly, the inner nonfoam cylindrical body 64 is also integral with the intermediate foam body 62.

The composite extrusion illustrated in FIG. is cut into segments of specified length and then worked upon by a heated probe 52 as indicated in FIG. 11. The point of the heated probe 52 is inserted through the length of bore 65. Mass C which forms the inner nonfoam cylindrical body 64 is a thermoplastic material containing a foaming agent which does not decompose or vaporize at the extrusion temperatures for mass C existent in extruder 66. The surface 52 of the probe is heated to a temperature higher than the extrusion temperature in extruder 66 and sufficiently high to decompose or otherwise vaporize the foaming agent in body 64. This causes a foaming reaction and transfonns tenaciously body 64 into inner foam cylindrical body 86. The foaming reaction causes an expansion in the mass of body 64 as it transforms and expands into foam body 86. As probe 52 is withdrawn, this expansion tends to be inward in the direction of the axis of the cylindrical body. The core 12 is inserted into the composite body as probe 52 is withdrawn, as illustrated in FIG. 12, substantially simultaneously therewith and is tenaciously engaged by hot foam body 84.

The preparation of composite articles such as that illustrated in FIG. 8, in accordance with the process schematically illustrated in FIG. 1, follows:

Polystyrene having a density of about 10 lbs. per cubic foot was used for body 14 and outer shell 6. The polystyrene=used to form the inner core member 12 was admixed with a foaming agent such as dichloroethane which vaporizes at a temperature of about Il90 F. The polystyrene used for the outer shell 16 did not contain a foaming agent. Both polystyrenes were heated and extruded at a temperature of about 325 F. An elongated heated probe having a surface temperature of about 500 F. was inserted through the body 14 to form the latter with an axial bore. The elongated probe was then removed while concomitantly inserting the elongated member 12 from the opposite end of the body 14 which had been pierced.

The production of the composite article illustrated in FIGS. 9-12 in intermediate stages of manufacture follows:

The outer shell 60 and the intermediate foam body 62 correspond to the outer shell 16 and the body 14 described in the preceding paragraph. The same polystyrene materials are used. The inner nonfoam body 64 is also prepared from a nonfoam polystyrene having a density of about 10 lbs. per cubic foot. This material (plastic mass C) contains a foaming agent which does not decompose under the conditions present in the extruder but which will decompose at a higher temperature. Polystyrene admixed with an azobisforrnamide (decomposition temperature 360-400 F.) was admixed with the polystyrene. All the extrusions were at a temperature of about 300 F. The extrusion formed a'stiff composite material containing a nonfoam outer shell 60, an intermediate foam body 62 and an inner nonfoam shell 64 surrounding a central bore 65. The elongated heated probe 52 is then inserted into and through bore 65. The elongated heated probe 52 was at a temperature of 500-600 F. and caused the inner body 64 to foam and expand into foam body 86. The elongated probe 52 was then withdrawn while concomitantly inserting the elongated core 12 as illustrated in FIG. 12 from the opposite side. The expansion resultant from the foaming reaction together with the effect of heat at the interface of the body 86 and the core 12 caused an adherent bond. Although the outer shell 60, the intermediate foam body 62, and the inner foam body 86 are referred to herein separately, it is to be understood that by virtue of their formation as a common extrusion the three shells form an integral composite. The integrity of the composite is illustrated by the difficulty in delineating a sharp boundary between adjacent bodies 60-62 or 62-86 when the completed product is cross sectioned.

The composites of this invention have been made of numerous thermoplastics. Thus, polystyrene with a suitable foaming agent has been successfully used for the

inner foam portions

18, 62 and 64 while nonfoamed polystyrene is used for the outer shells I6 and 60, although any other compatible plastic which is not foamed could also be used for this purpose. In addition, polypropylene has been used with a suitable foaming agent for the

interior portions

18 and 62, while nonfoamed polypropylene is used for the outer shells l6 and 60. Polystyrene; high impact polystyrene, i.e., rubber modified polystyrene such as poIybutadiene-styrene (e.g., 5-15 percent butadiene); polypropylene; and rigid polyvinylchloride are the preferred thermoplastic resinous materials. Other resinous thermoplastics are generally less preferred because of their higher cost. These include the cellulosics, the acrylonitrile-butadiene-styrenes, the acrylic resins such as methacrylate, polyethylene and the polyamids, e.g., nylon. All thermoplastic materials, which may be hardened to a degree of rigidity compatible with the intended use and which may be extruded and foamed of which the aforespecified are illustrative, may be used. Although the difierent cylindrical shells for bodies may be formed of different thermoplastic materials, it is preferred that-they be of the same material. This preference follows from the ability to utilize such scrap from the process as a raw 1 material.

The foaming agents utilized are the conventional foaming agents which decompose or vaporize at the process condition specified. These include inorganic carbonates, such as sodium bicarbonate; alkanes such as pentane and hexane; halogenated alkanes such dichloroethane; aromatics such as benzene; ethers such as the aliphatic and petroleum ethers, etc. These are illustrative of foaming agents having decomposition temperatures below about 300 F. Foaming agents having higher decomposition or vaporization temperatures are particularly useful for foaming in situ after extrusion, such as the azonitriles such as azobisformamide. Suitable foaming agents are readily selected from those listed in conventional references as on pages 380 to 387 of Modern Plastics Encyclopedia, 1968-4969 Edition, published by McGraw-Hill Incorporated, New York, N.Y. The foam mixture in the extruder may also be formed by direct injection of gas, e.g., nitrogen or pentane, at a temperature of about 100 F. into

chambers

22 and 74.

The density of the thermoplastic used for the foamed portion or portions of the body can be varied. In the case of polystyrene, it has been found that this density may range from the neighborhood of 6 pounds per cubic foot up to approximately 16 pounds per cubic foot. The particular choice will depend on the results which are to be achieved. For example, solid polystyrene is far too brittle to be machined in a conventional pencil sharpener and will tend to shatter, creating considerable difficulties in the sharpening. However, at relatively low densities, lower than approximately 6 pounds per cubic foot, the foamed inner portion of the body 10 becomes much too flexible, while at densities greater than 16 pounds per cubic foot it becomes too tough. By reason of the outer shell 16, or at least by reason of partially covering the foam portion with an outer portion of nonfoamed plastic, it is possible to provide a very easily machinable body, capable of being handled without any difficulty whatsoever in a conventional pencil sharpener, at the same time providing the body with the required rigidity. The same considerations will, of course, apply to any thermoplastic, and depending upon the desired properties of the final unitary composite article, it is possible to choose suitable densities and a suitable extent of foaming.

While the above-described method and article of the invention refer to a lead pencil, the invention is applicable to many other types of articles. Many different types of elongated members can be encased within the

body

14 or 86 according to the method of the invention. For example, instead of black lead, the elongated core member 12 may take the form of crayon of any desired color. The elongated member 12 may also form a ballpoint pen filler which is enclosed at its exterior surface within the plastic body and with the writing end of the pen projecting beyond the plastic body.

During the practice of the invention, it has been found that instead of using a heated probe 42 (52), it is possible to heat the elongated core member 12 just prior to insertion thereof into the body 14, so that this core member 12 itself will form its own conforming bore. in the case where the body is extruded with a preformed axial bore insert 43 or 65, it will serve as guide for the rapid insertion of the heated core 12 thereby assuring its exact central location within the body. During such insertion, the heated core member 12 will heat the adjacent cells of the thermoplastic material to a molten condition. As the heat dissipates, the plastic hardens and firmly adheres and bonds to the surrounded wall of the core member.

One of the advantages achieved by using the foam form of the elongated body is that the thermoplastic material can be used to a far greater extent for a greater number of articles because of the lesser amount of the thermoplastic used for any one article. Furthermore, when using foam plastics, there are limitations on the coloring which may be provided for the article, since it is difficult to obtain dark shades for foam plastics. Also, the feel of the article is not as comfortable as the tactile qualities of a solid nonfoamed plastic. Thus, by providing an outer shell 16, or at least a partial exterior covering of a nonfoamed plastic, it becomes possible to produce an article which is more comfortable to handle and which can be provided in a far easier manner with any desired coloration or even with any desired printed matter, advertising matter, or the like.

Thus, with the method of the invention, it is possible to produce unitary combined articles of the invention which have a very pleasing exterior appearance and which are pleasant to handle while at the same time, in the case of lead pencils, being easy to machine. The coloration can take many different forms, including swirls of different colors and when using elongated striations of solid nonfoamed plastic at the exterior of the body, extending longitudinally thereof, leaving portions of the foam plastic uncovered, particularly pleasing effects have been achieved. One of the further advantages which is derived from the use of an outer nonfoamed plastic is that the tendency of the foamed plastic to have an exterior surface which is formed with longitudinal scratches or grooves as it issues from the extruder is avoided because the nonfoamed plastic gives to the exterior of the article a smooth outer surface which is free of such defects. The use of the outer, harder shell 16 of nonfoamed plastic limits the extent to which the body 10 can be bent, so that in this way the inner core member 12 is protected. Without an outer, at least partial, covering of nonfoamed plastic, the flexible foam will permit easy bending of the article, which may be desirable in some uses but will result in breaking a brittle core 12 when the latter takes the form of the lead of a lead pencil.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that the various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention. lt is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

What is claimed is:

1. ln a method of manufacturing a writing implement having a body portion of foamed thermoplastic resinous material provided with an outer lining of unfoamed resin selected from the group consisting of polystyrene, polypropylene, polyethylene and rigid polyvinylchloride and the body portion of foamed resin selected from the group consisting of polystyrene, polypropylene, polyethylene and rigid polyvinylchloride, said method comprising inserting a heated probe into the body portion so as to cause the foamed thermoplastic in the area about the probe to become molten and to form a core receiving cavity, withdrawing the heated probe and simultaneously inserting a writing core into the cavity, and allowing the body to cool whereby the foamed thermoplastic portion adheres and bonds firmly to the writing core.

2. In a method of manufacturing a unitary composite article having a body of foam thermoplastic resinous material and a core, the steps comprising making the body with a lining of foam thermoplastic material, inserting the core into the lining of thermoplastic material while at least a portion of the lining is in a plastic condition, by treating the portion of the lining of the thermoplastic material into which the core is inserted to place the lining in its plastic condition while the core is inserted thereinto, so that upon subsequent changing of the lining from its plastic to its set condition, it engages said body to form a unitary composite article.

3. In a method of manufacturing an elongated unitary composite article of a core member and a preformed plastic body in which the interior of the plastic body has a foam thermoplastic material lining of cellular structure that melts and breaks down rapidly under heat, the steps comprising inserting the core member into the interior of the cellular lining of foam thermoplastic material while such material is in a heated molten condition, so that the core engages the plastic material while the same is in its heated molten condition, allowing the plastic material to cool and upon the cooling and setting of the material, the same adheres to the core to bond the body and core together to form the unitary composite article.

4. In a method as recited in claim 3,

the steps of inserting a heated probe into said cellular lining prior to insertion of said core member into the cellular lining to provide said cellular lining with a heated inner surface which is in molten condition, withdrawing said probe from said cellular lining while said inner surface thereof is in said molten condition, and inserting said core member into said cellular lining into engagement with said heated inner surface thereof substantially immediately upon withdrawal of said probe from said cellular lining so that said cellular lining will have said inner surface thereof still in said molten condition to engage said exterior surface of said member and become joined thereto upon cooling and setting of said cellular lining at said inner surface thereof.

5. In a method as recited in claim 4,

wherein said cellular lining is elongated and said probe is directed longitudinally through said elongated cellular lining from one end to the other end thereof so that said heated surface of said cellular lining defines an axial bore passing therethrough,

and introducing said core member into said cellular lining from said other end toward said one end thereof substantially simultaneously with the withdrawal of said probe from said cellular lining through said one end thereof so that as said probe is displaced out of said cellular lining said core member is substantially simultaneously introduced into the latter to engage said inner surface while the latter is still in a heated molten condition.

6. In a method as recited in claim 4, wherein said resinous thermoplastic material is at least one material selected from the group consisting of polystyrene, high impact polystyrene, polypropylene and rigid polyvinylchloride.

7. In a method of manufacturing an elongated unitary composite article of a core member and a preformed thermoplastic resinous body, the steps comprising forming an elongated composite having a cylindrical foam thermoplastic resinous body surrounding an inner axially hollow cylindrical nonfoam thennoplastic resinous body containing admixed therewith a foaming agent, heating said inner nonfoam body to a temperature sufficient to cause a foaming reaction whereby said inner nonfoam body is transformed into a cellular body and inserting the core member into the axial hollow whereby it is tight bonded to said cellular body.

8. In a method as recited in claim 7, wherein said probe is withdrawn while said inner surface is in a molten condition, and inserting said core member into said body into engagement with the inner surface thereof substantially immediately upon withdrawal of said probe from said body.

9. In a method as recited in claim 8, wherein said resinous themioplastic material is at least one material selected from the group consisting of polystyrene, high impact polystyrene, polypropylene, rigid polyvinylchloride and polyethylene.

10. In a method of manufacturing a writing implement having a body portion of foamed thermoplastic resinous material provided with an outer lining of unfoamed resin selected from the rou consistin of ol st rene, l ro lene, polye iyle e and rigid golyvinyl hlbride and th bzii iy g rtion of foamed resin selected from the group consisting of polystyrene, polypropylene, polethylene and rigid polyvinylchloride and in which said body portion has an axial bore, said method comprising inserting a core having a dimension larger than said axial bore in a heated condition into said axial bore to form an enlarged bore therein to the size and shape of said core, allowing the core and body to cool so that after said core and body cool and said body sets, its inner surface will adhere to and be joined with said core. I

Claims

2. In a method of manufacturing a unitary composite article having a body of foam thermoplastic resinous material and a core, the steps comprising making the body with a lining of foam thermoplastic material, inserting the core into the lining of thermoplastic material while at least a portion of the lining is in a plastic condition, by treating the portion of the lining of the thermoplastic material into which the core is inserted to place the lining in its plastic condition while the core is inserted thereinto, so that upon subsequent changing of the lining from its plastic to its set condition, it engages said body to form a unitary composite article.
3. In a method of manufacturing an elongated unitary composite article of a core member and a preformed plastic body in which the interior of the plastic body has a foam thermoplastic material lining of cellular structure that melts and breaks down rapidly under heat, the steps comprising inserting the core member into the interior of the cellular lining of foam thermoplastic material while such material is in a heated molten condition, so that the core engages the plastic material while the same is in its heated molten condition, allowing the plastic material to cool and upon the cooling and setting of the material, the same adheres to the core to bond the body and core together to form the unitary composite article.
4. In a method as recited in claim 3, the steps of inserting a heated probe into said cellular lining prior to insertion of said core member into the cellular lining to provide said cellular lining with a heated inner surface which is in molten condition, withdrawing said probe from said cellular lining while said inner surface thereof is in said molten condition, and inserting said core member into said cellular lining into engagement with said heated inner surface thereof substantially Immediately upon withdrawal of said probe from said cellular lining so that said cellular lining will have said inner surface thereof still in said molten condition to engage said exterior surface of said member and become joined thereto upon cooling and setting of said cellular lining at said inner surface thereof.
5. In a method as recited in claim 4, wherein said cellular lining is elongated and said probe is directed longitudinally through said elongated cellular lining from one end to the other end thereof so that said heated surface of said cellular lining defines an axial bore passing therethrough, and introducing said core member into said cellular lining from said other end toward said one end thereof substantially simultaneously with the withdrawal of said probe from said cellular lining through said one end thereof so that as said probe is displaced out of said cellular lining said core member is substantially simultaneously introduced into the latter to engage said inner surface while the latter is still in a heated molten condition.
6. In a method as recited in claim 4, wherein said resinous thermoplastic material is at least one material selected from the group consisting of polystyrene, high impact polystyrene, polypropylene and rigid polyvinylchloride.
7. In a method of manufacturing an elongated unitary composite article of a core member and a preformed thermoplastic resinous body, the steps comprising forming an elongated composite having a cylindrical foam thermoplastic resinous body surrounding an inner axially hollow cylindrical nonfoam thermoplastic resinous body containing admixed therewith a foaming agent, heating said inner nonfoam body to a temperature sufficient to cause a foaming reaction whereby said inner nonfoam body is transformed into a cellular body and inserting the core member into the axial hollow whereby it is tight bonded to said cellular body.
8. In a method as recited in claim 7, wherein said probe is withdrawn while said inner surface is in a molten condition, and inserting said core member into said body into engagement with the inner surface thereof substantially immediately upon withdrawal of said probe from said body.
9. In a method as recited in claim 8, wherein said resinous thermoplastic material is at least one material selected from the group consisting of polystyrene, high impact polystyrene, polypropylene, rigid polyvinylchloride and polyethylene.
10. In a method of manufacturing a writing implement having a body portion of foamed thermoplastic resinous material provided with an outer lining of unfoamed resin selected from the group consisting of polystyrene, polypropylene, polyethylene and rigid polyvinylchloride and the body portion of foamed resin selected from the group consisting of polystyrene, polypropylene, polethylene and rigid polyvinylchloride and in which said body portion has an axial bore, said method comprising inserting a core having a dimension larger than said axial bore in a heated condition into said axial bore to form an enlarged bore therein to the size and shape of said core, allowing the core and body to cool so that after said core and body cool and said body sets, its inner surface will adhere to and be joined with said core.