CA1098675A

CA1098675A - Thermoplastic resin molding of complex decorative relief

Info

Publication number: CA1098675A
Application number: CA275,704A
Authority: CA
Inventors: Eugene H. Bergh
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1976-04-19
Filing date: 1977-04-06
Publication date: 1981-04-07
Also published as: GB1561525A; US4097634A; MX146611A; NZ183887A; FR2348801A1; DE2717529C2; FR2348801B1; AU2437577A; JPS52127966A; JPS5420226B2; DE2717529A1; ZA772334B; BR7702450A; IT1086571B; AU510361B2

Abstract

ABSTRACT

Essentially continuous thermoplastic resin molding of complex decorative relief is produced by continuously extruding molten resin into a rotating forming wheel and cooling and removing the molded resin from the wheel. A doctor wheel cooperates with the forming wheel to provide a flat surface to which a pressure-sensitive adhesive layer may be applied for bonding the resin molding to an intended substrate. A
removable backing member protects the adhesive layer during storage and handling.

Description

~rl 9.-1.2,76'7 ~ 3~

T~IE.RMOPLASTIC RESIN MOLDING OF
COMPLEX DECORATIVE RELIEF

This invention concerns the production of elongate thermoplastic resln moldings such as may be cut to short lengths and applied to the side of an automobile for protective ancl-decorative purposes.
. 5 Such moldings, upon emerging from the extruder~ may be embossed by-patterned squeeze rollers, e.g.~ t~o provide a leather-grain pattern-. That procedure has not been useful for producing-an extruded thermoplastic resin strip of complex decorative relief,-because deeply embossed squeeze rollers-would introduce internal strains that-would tend to distort the moldings. Also, : the deep-embossing would make it difficult to control khe flash which necessarily would be quite exten~ive in-order to~-insure-a complete pattern.
- Because of such problems 3 elongate-thermo-plastic resin-moldings of complex decorative relief have:been-generally formed by pouring or in~ecting .
molten plastic into open or closed molds. Not only are such t.echniques slow, but the length of the molding is-limited-by the size of the-moldO

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~ The-present invention-permits the-production -of thermoplastic resin-molding of complex decorative -relief on a continuousj economical-basis and is -adapted to-convenient application of a functional : : 25 -adhesive lcLyer to the molding-during its-production.

The resultant resin molding is essentially free:from -- external defects-and-internal strains and is characterlzed : ~ :
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by uniformity over its entire, essentially continllous length. The novel resin molding is Eormed on a continuously rotating forming wheel having a complex intaglio in its circumferen-tial surface and doctor means providing an orifice tangential to the forming wheel and a pair of interstices at the sides of the orifice. It is produced by:
1) heating thermoplastic resin to a molten state,

2) providing a bank of the molten resin in contact with the forming wheel at the leading edge of the orifice sufficient to fill the intaglio as the forming wheel rotates and to flow through said interstices to provide a pair of resin flashes,

3) cooling the resin deposited in the intaglio while the forming wheel continues to rotate until the resin develops tenacity at least at its surface contacting the intaglio, and

4) continuously removing the cooled resin molding from the intaglio.
The continuous rotation of the forming wheel past the bank of resin carries enough resin past the orifice to fill the intaglio to the height of the orifice. By virture of th0 complex intaglio in the surface of the forming wheel, the molding takes on a complex decorative relief such as was hereto-fore available on a practical commercial basis only on an individual strip basis. By "complex" decorative relief is meant a relief having both differ-ing longitudinal cross-sections and differing transverse cross-sections~as opposed to rubber timing belts which have differing cross-sections only in the transverse direction).

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~ he only strains introduced into the moldlng are caused by the-cooling and are of a minimal nature so that the molding is essentially distortion-free. By using an orifice which gives the molding an essentially ~lat open surface, an adhesive layer may be applied conveniently by rolling-a transfer tape into contact with that surface, preferably before the molding is removed from the forming wheel. The temporary backing member of the transfer tape may remain in place to keep the adhesive clean, being removed irnmediàtely prior to applicatlon of the molding to an intended substrate, Such protection is especially desirable when the adhesive is pressure-sensitive.
Preferably the transfer tape incorporates a foam cushioning layer between two pressure-sensitive -15 adhesive layers, one of which bonds to the plastic molding, the other bonding the resin molding to the intended substrate.
-~y virtue of the-continuous rotation of the forming wheel, very high rates of production are feasibleO
The-continuous rotation simplifies application of adhesive transfer tape and the winding of the adhesive-bearing resin molding upon itself into roll-form for convenient storage-and shipment Thermoplastic resins which can be used ln the 25 -present invention include polyethylene, plasticized polyvinyl chloride,-blends of polyvinyl chloride with nitrile rubber or with-other elastomers~ styrene-terminated b~ock copolymers-and-polyolefin rubbers. The thermoplastic resins may--be blended with materials with which they are common~y use, for example, pigments and ,, ~ .. . .. . ~ _ , . . .

s other ultraviolet-inhibitin~ materlals~ antloxidants~
lubricants and inert ~illers.
In the drawing~
Figure 1 is a schematic elevation o~ apparatus for producing adhesive bearing resin molding in the practice-of the invention;
Figure 2 is an enlarged sche~atic cross-section along line 2-2 of Figure l;
Figure 3 illustrates the face of the resin molding produced on the apparatus of ~igures-l and 2; and Figure 4 is a schematic cross-section along line-4-4 of ~igure 3.
Referring to-Figure 1, molten thermoplastic resin is extruded through the nozæle 10 of a screw-type extruder 12 to form a bank or nip of molten-resin 14 at an orifice between an aluminum forming wheel 16 and a steel doctor wheel-18 which rotate at the same uniform speed in the direction of the arrows. The forming wheel 16 has a complex intaglio in its circumferential surface consisting of a continuous series o~ symmetrical depressions 20, The molten resin 14 fills the depressions 20 and is -solidified as it-is cooled by water circulated-throu~h a network of channels ~not shown-) in the forming wheel 16 immediately beneath its depressions 20, After cooling -25 to dèvelop tenacity at-least at its surface contacting -the intaglio depressions, the resin-molding-is carried around an internally water-cooled roll 22 to cool the resin-further.
A pressure-sensitive adhesive tape 24 is drawn by the doctor wheel 18 which presses the adhesive layer s 26 of' the tape agalnst the molten resin 1ll. The tape remalnsfirmly bonded to the solidified resin to provide an adhesive-bearing resin molding 27 having a backing mernber 28 to protect the pressure~sensitive layer 260 The backing member 28 has a low-adhesion surface facing the adhesive so that it can readily be pulled away and discarded to permit lengths of the adhesive-bearing resin molding 27 to be applied to an intended substrate. Preferably, the pressure-sensitive adhesive layer 26 has a foam construction, as seen in ~igure 4, consisting of a central foam 30 bearing pressure-sensitive adhesive coatings 32 and 34 on both sides.
As seen in Figure 2, the circumference of the doctor wheel 18 has a crown shape to aid in achieving a flat adhesive-bearing surface. Bolted to the sides of the doctor wheel are a pair of hardened steel cylindrical anvils 38 and-40 which cooperate with a pair of steel cylindrical knives-42 and 44 bolted to the forming wheel 16. The knives may be spaced from the anvils-38 and 40 by about 0.125 mm to provide a-pair of interstices through which excess resin ? ~lows to form resin flash at 46 and 48. The flash-cools and-hardens quickly and cooperates with the knives 42 and 44 which act as tenters to inhibit lateral shrinkage of the~resin as it cools in contact with the-forming wheel 16. By-cooling the resin against the sli~htly crowned 25- surface of the roll-22, its adhesive-bearing surface ;~ ~develops-the~desired flatness~ This tends to control the - shrinkage of the resin~so that only the-decorative-surfaces are affected; The resultant slight concavities-at 50 and-52 of Figure 4 provide an attractive-highlighting.

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~a~ s The resln ~lash is slit awa;y prior to windup to provide the adhesive bearing resin molding 27 illustratecl in ~igures 3 and 4.
~ ~le The adhesive-bearing resin molding 27 has been made as schematically illustrated in Figures 1 and 2 using the following-thermoplastic resln composition:
Parts bv wei~ht __ _ Polyvinyl chloride . 0 . . , . . . 100 10 Polymeric-polyester plasticizer. . 60 Calcium carbonate . . . . . 0 ~ . 18.5 Metal salt stabilizers 0 . 0 . , . 3 Epoxidized soybean oil . . 0 . . . 5 Brown color-concentrate containing -aluminum flakes ~or metallic effect 2 The pressure-sensitive adhesive layer-26-consisted of a thin neoprene foam having on each side a-coating of pressure-sensitive-adhesive consisting o~ a copolymer -of-9~ parts-isooctyl acrylate and 10 parts by weight o~
acrylic-acid.-~-The-neoprene foam was closed cell, 80o kg/m3 and 0075 mm in thickness-. The low-adhesion backing member~28 was a thin polyethylene--film.
The thermoplastic-resin-composltion at a temperature o~ 185C was extruded through-a nozzle 10 , .
of l.3-cm-lnside~-dlameter while the rolls 16 and 18 25--were rotated-at the constant-speed of eight revolutions per minute.- The flnished adheslve-bearing resin-mo~ding 27 was-approsimately 0,5 cm in thickness and~ a~ter slltting~off the~resin flash~ 302 cm in widtho- It was ~ - :
wound upon itself for storage-and shipment.--Subseq~ently~
-30 the-polyethylene~f~lm was peeled away from--strips~o~ the .: ~ ; :

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resin molding to permlt each strip to be bonded by its exposed adhesive-layers to the complete periphery of a ~uneral casket as a decorative molding a~ordin~ bump protection.
Another pressure-sensitive adhesive layer 26 which has been used success~ully in place o~ the above-described pressure sensitive adhesive layer consisted of a thin neoprene foam having a coatlng o~ pressure-sensitive adhesive-on one side as described above and a thermoplastic coating on the other side. The thermoplastic coating was selected to .~orm a strong bond upon contacting the molten resin 14. If the foam were o~ a material which wouldrstrongly bond to the molten-resin, there would be no need rOr any coating between the ~oam and the thermo-plastic resin.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Process for forming essentially continuous thermoplastic resin molding on a continuously rotating forming wheel having a complex intaglio in its circumferential surface and doctor means providing an orifice tan-gential to the forming wheel and a pair of interstices at the sides of the orifice comprising the steps of (1) heating the thermoplastic resin to a molten state, (2) providing a bank of the molten resin in contact with the forming wheel at the leading edge of the orifice sufficient to fill the intaglio as the forming wheel rotates and to flow through said interstices to provide a pair of resin flashes, (3) cooling the resin deposited in the intaglio while the forming wheel continues to rotate until the resin develops tenacity at least at its surface contacting the intaglio, and (4) continuously removing from the intaglio a cooled resin molding which has complex decorative relief and yet is essentially free from external defects and internal strains.

2. Process as defined in claim 1 wherein a transfer tape comprising a pressure-sensitive adhesive layer and a removable, low-adhesion backing member is drawn by the doctor means with its adhesive layer in contact with the bank of heated resin to provide an adhesive-bearing resin molding.

3. Process as defined in claim 2 wherein said pressure-sensitive adhesive layer comprises a cushioning foam having a pressure-sensitive adhesive coating on the side which does not contact the molten thermoplastic resin.

4. Essentially continuous thermoplastic resin molding of complex relief made by the process defined in claim 1.

5. Essentially continuous pressure-sensitive adhesive-bearing thermo-plastic resin molding of complex relief made by the process defined in

claim 2.