CA2108407A1 - Molds with improved surface properties - Google Patents

Abstract

MOLDS WITH IMPROVED SURFACE
PROPERTIES

Abstract Articles such as molds for thermoplastics, having an insulating layer preferably of resin deposited on the metal core materials, have a second layer of metal suspended in resin deposited on said insulating layer. The second layer may contain metal in platelet form as the inner mold surface, or may contain metal in fiber, whisker or irregular form with a further metal coating deposited thereon to provide resistance to abrasion. In the layer case, the adhesion of the further metal coating to the mold surface is higher than is the case if no metal-containing resin layer is present.

Description

21~ 8 ~ ~ 1 08CT05452 MOLDS WITII IMPRC)V D SURFACE
PROPERTIES

This invention relates to the molding of thermoplastic materials, and more particularly to articles useful as molds for such materials.
Various types of molds haw long baen in use for pr~paring shaped articles from thermoplastic r~sins, in such operations as injection molding, blow moldin~, resin transfer molding, comprsssion moldin~ and castin~. Molds for these purposes are typically manufactursd from metal or a -~imilar material havin~ high thermal conductivity.
For most purposas, hi~h thermal conductivity is desirable since it permits the resin in the mold to cool rapidly, shortening the molding cycle time. At times, however, cooling is so rapid that the resin freez~s instantaneously at the mold surface upon introduction into the mold, forming a thin solid layer which, ~specially if it :
cont~ins a-filler, can create rou~h surfaces, voids and porosity.
There have recently been disclosed multilayer molds in which a metal core has an insulatin~ layer bonded ~hereto, for the purpose of slowing the initial cooling of the ::
r~sin during the molding op~ration. The insulating layer is : ~ -fabricated of material having low thermal conductivity.
thus slowing the cooling of the molded r~sin, and also having ~ood resistaRce to hi~h temperatur~ degradagion, ~ ~:
permitting use in a mold maintained at high tampera~ures.
Said layer is typically made of a resin such as polyimide, polyamideimide, polyethersulfone or polye~h@Yketone, typically applied in uncured form ~e.g., as a po3yamic acid ~ -:
in the cas~ of a polyimide or polyamideimide) and sub~equently cured.

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~ esinous insulating layers have a major disadvantage, however: they are not mechanically stron0 and are easily abraded upon con~act, for example, with filled thermoplastics. Thus, they do not have sufficient 5 m~chanical integrity to produce molded articles having surfaces of high quality.
A solution to this problem is disclosed, for example, in various applications such as copending, commonly owned application Serial No. ~7/784,115. It 10 consists of one or more skin layers of hard material, typically metal, bonded ~o ~he insulating layer. The skin layer may be daposi$ed by such operations as electroless deposition, slectrolytic deposition and combinations ther~of. ::
Such deposition operations introduce their own problems into the mold fabricating process. it is well known, for example, that the adhesion of metal layers to resinous substrates is poor. This fact has dictated that the resin employed in the insulating layer be one which 20 intrinsically has or can be modified to have relatively high adhesion to metal layers deposited thereon. One genus of --resins having this property is the fluorinat~d polyimides, of the type prepared by the reaetion of pyromellitic dianhydride with 2,2-bis~4-(4-aminophPnoxy)phenyl]-25 hexafluoropropane. Such polyimides are available from Ethyl Corporation under the trademark "EYMYD".
Fluorinated polyimides of this type may be --~
subjected to various operations to improv~ th~ir adhesion to metal. Methods for so improving adhesion are disclosed 30 in other copending, commonly owned applications, no~ably Serial Nos. 07/765,801, 07t874,448, 071874,453 and 07t874,458. The major disadvan~age in the ~mployment of such resins and adhesion improving methods is that the resins are considerably more expensive than corresponding ~ .r,~
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08c-ro5452 ~8'~ 3 7 non-fluorinated polyimides and other resins of high thermal conductivity and stability at high temperatures, and the adhesion improving operation is an additional pr~cess step which may be burdensome and inconveniant.
A further problem is ~he difficulties involved in repairing a mold having a metal skin on a resin insulating la~er. To repair even relativaly minor damage such as one ~r more scratches which p~netrate the metal skin, it is necessary to remove the mold from use and deposit a new 10 metal layer thereon by further electroless or electrolytic deposition, often after removing at laast the area of the old skin which surrounds the damage. Thus, the mold is out cf service for a relatively long period, often several weeks.
The present invention is based on the discovery 15 of a highly effective proc~dure for producing a m~tal surface on a layer of low thermal condlJctivity, typically a resin layer. This procedure may comprise one step or two steps, dep~nding on whether the metal surface desired is mer~ly metal-rich or is a "skin". Said metal surfacs has 20 high adhesion to the underiying resin layer. in many instances, the metal surface is also relatively easy to repair without removal of the mold. -Accordingly, the invention is an article comprising:
a substrate having high thermal conductivity;
a first layer of temperature-resistant material having low thermal conductivity, deposited on said substrate; and a second layer deposited on said first layer, 30 comprising a suspension of metal particles in a t~rnperature-resist~nt material having low thermal conductivity .
The articles of this invention find their principal us~ in the molding of thermoplastics, as '- r,~

'i:: . ~ , previously noted. tlowever, they may aiso be used for o~her purposes. For example, they may be fabricated into enclosures which block the passage of electromagnetic and radio fre~uency waves, which may cause interference. They 5 may also be employed as parts for engines operated under high temperature conditions. Because of their predominant use in the molding of thermoplastics, however, such articles will frequently be idcntifi0d as "molds"
hereinafter.
The substrates in the articles of this invention, which are the rnold cores in the preferred molds, are fabricated of material having high thermal conductivity They are typically metal, and any ma~al suitable for molds may be employecl.
The first layer (in a mold, ~he insulating layer~
deposited on the mold core is typically of a resin, i.e., a polymer, having low thermal conductivity and being - ~:
resistant to high temperatures. The aforementioned polyimides, polyamideimides, polyethersuifones and 2 û polyetherketones are illustrative; polyimidss and polyarnideimides are often preferred. The polyimide may be a fluorinated polyimide of the type previously described, - -although the presence of fluorine is not necessary to rnaximize adhesion of deposited meta! since excellent -25 adhesion is provided by the method of this invention.
Said first layer may be deposited by arly of numerous art-recognized methods such as roller coating or : -~
spraying. In the case of a mold, spraying is usually preferred bec~use of its effectiveness to coat an irregular 30 surface uniformly. Many resins, including polyimides and polyamideimides, are oured after deposition. The thickness of the first layer is not critical but is typically in the range of about 1~500 microns.

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The key feature of the articles of the invention is a second, metal~ontaining layer deposited on said first or insulating layer. The continuous phase of the metal-containing layer is a temperature-resistant polymer having 5 low thermal conductivity. Said polymer is most often identical to the one employed as the insulating lay~r.
Suspended in the temperature-resistant polymer of th~ seoond layer are metal particles. The identity of the metal is not critical so long as it is substantially resistant 10 to oxidation under the conditions of use of the mold. Nickel is often preferred.
The shap~ of the metal particles is not critical Howsver, spherical particles are less effectiv~ than those of other shapes in improving adhesion of metal skins;
15 there~ore, non spherical particlcs are strongly preferred.
They may be, for example, in the form of platelets, fibers or whiskers. Typical metal particle sizes are in the range of a~out 1-~0 microns. It is preferred that the bulk density of the metal particles be below about 2 ~./oo. The thickness 20 of the second metal layer is typically in the range of about 10-100 microns, with abou~ 2~5û microns usually being preferred .
Two embodiments of the invention are worth partioular mention. In the first embodiment, the second 25 layer is the inner metal surface layer of the mold, which contacts the resin being molded. This ~mbodirnent is particularly useful when said resin is oharged to the mold at relatively low pressure, as in blow molding and low ~ pressure injection molding, whereby the mold surface 30 eneounters relatively iow friction; and when the de~ree of srnoothness of the surface of the molded part is not critical .
The metal constituent o~ the s~cond layer is most oft~n in platele~ form in this embodiment, so as to .. ,,~,_................................................................. .

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produce a relatively dense, metal-rich surface wh~rein the platelets are substantially parallel to the surface of the rnold. Nickel particles in plateiet form are commercially available as, for example, "Novamet HCA-1~' nickel filler, a 5 product of Novamet Products Corp.
The bulk density o~ the metal in pla~elet form is pr~ferably in the range of about 1.1-1.5 y./cc., and the partiol~s thereof generally have an avera~e width on the order of 10 microns and an average thickncss in ths range of 10 about 0.1-0.5 micron. Said metal is typically suspend~d in the resin at w~ight ratios of metal to resin (excluding solvent) in the range of about 0.5-5.0:1.
Conventional application methods such as those described above with reference to the first layer may also 15 be employed for the second layer, with spraying generally being preferred. When necessary, said layer is cured after :
application. ::
The metal surfaees provided by the first embodimsnt are particularly advantageous because of the 20 ease of repairing scratches and other mincr damage therein.
All that is necessary is to apply further metal-resin suspension, typically by the same appiication method previously employed, and to burnish or polish the resulting surface after curing of the resin if curing is necessary. The -25 repaired surface is then suitable for continued use.
In the second embodim~nt of the invention, a further metal coatin~ is applied over said se~ond layer. The m~tal suspended in the resin for formation of the second .
iayer is usually in fiber, whisker or irr~gular form and has a 3 0 somewhat lower buik density than the platelet-form metal used in the first embodiment, typical bulk densities being in the range of about 0.~1.0 g./cc. Filament l~n~ths in the range of about 10-50 microns are t~pical Products of this type are illustrated by "Novamet ~55", "Novamet 255AC"

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and "Novam~t 287" nickel powders. The metal in the second layer itself is porous as contrasted with the dense m~tal surface provided in the first embodiment. Metal to resin ratios of about 1~:1 are preferred, since optimum adhesion 5 of said further coating is observed in this range.
One advantage of usin~ irregular-shaped or fibrous metal parti~les is that the expos~d surface particles in the second layer are catalytic toward eiectroless deposition of metals such as nickel. It may 10 nevertheless be advantageous und~r some conditions to traat the surface of the second layer to further activ~te it catalytically. Typical treatments of this type may include abrasion to expose a maximum of metal parti~les and/or surfactant treatm0nt to increase their hydrophilicity.
The deposition of the second layer in this embodiment may be effected by the methods describ~d hsr~inabove with respect to the first ernbodiment. Similar ratios of metal ~o r~sin may be employ~d. Following its deposition, the further metal coating may be applied by such 2 0 art-recognized methods as electroless or electrolytic deposition; electroless deposition is usually preferred for large mold surfaces, and electroplating for small surfaces Improved adh~sion of the further metal coating is believed to be provided according to this embodiment by a 2 5 combined mechanical and metallurgical interaction between said coatin~ and the metal in the second layer. The second layer is also electricaily conductive by reason of the metal therein, facilitating the electrodeposition of further metal thereon .
3 0 The invention is illustrat~d by the following examples. All parts and percentages are by weight unless o~herwise indicated. Adhesion was rneasure~ by a test (IPC
method 2.4.8) in which strips of tape, 3.2 mm. wide, are -~
used ~o mask portions of a metallized suffaee after ., ,"~_,.

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21~13 ~1 deposition of electrolytic copper and the exposed copper is etched away with concentrated nitric acid. The substrate is rinsed thoroughly in water, after which the tape is removed and the remaining copper strips subjected to a 90 peel 5 test.

Example 1 A stainless steel plaqu~ was employed to emulate the surface of a mold. It was abraded by ~rit blasting, washed with water and dried. Its surfacs was then sprayed with a 6% solution of "EYMYD" polyimide precursor in a mixture of N-methylpyrrolidone and methyl ethyl ketone comprising 20% by volume N- - -methylpyrrolidone. The polyimide was dried briefly at -:
240C and the process was repeated a sufficient number of times to produce, after curing, a first resin layer 250 microns thick in which the resin was polyimide. The coated 20 plaque was then heated for 2 hours at 240C and 2 hours at 31 5C to fsrm the fully cured polyimide. - -The first resin layer was spray~oated to a thickness of 38 microns with a suspension in the same EYMYD solution of 12% powdered nickel ~NOVAMET Ni-25 25 having an irregular particle shape and a bulk density of about 0.5 ~.lcc. The polyimide in the suspension was cured under the same conditions employed in the previous curing StQp, to form a second layer.
The surface coated with ~he second lay~r was 30 blasted with glass b~ads to expose nickel particles, and the residue was remsv~d by spray rinsing with water. The plaque was then immersed in a commercial electroless nickel plating solution (Enthone ENPLATE 426) and plated for 30 minutes, a~ter which it was water rinsed and dried " ~,AO.-.. -' . , 2 ~ a 7 08CT05452 at 110C for 16 hours. Finally, a 38-micron layer of copper was electroplated on the electroless nickel. It had a peel strength of 66.2 g./mm.

5 Example 2 The procedure of Example 1 was repeated four times, with the addition of 1 0-minute treatments with four different surfactant solutions fnllowing glass bead blas~ing 10 and rinsing, followed by a 10-minute water rinse. The peel strengths of the resulting plaques varied from 119.9 to 193.3 g./mm., demonstrating the advantage of surfactant treatment prior to electroless deposition.

15 Example 3 The proeedure of Exampte 2 was repeated, with the addition of the following steps of treatment with a catalyst for electroiess deposition after the surfactant 2 0 treatment and water rinse:
Shipley CATAPREP 40~1 minute;
Shipley CATAPOSIT 44--5 minutes;
Water rinse 4 minutes;
2 5 Shipley Accelerator 1~5 minu$es;
Water rinsc 5 minut~s.
The peel strength for the resulting plaque was 252.4 g./mm., demonstrating the advantage of treatment with 3 0 catalyst. : ::

Examples 4-8 The procedure of Exarnple 1 was repeated, 35 substituting for the "EYMYD" polyimide a polyamideimide 2 ~ 0~CT054~2 :
precursor sold by DuPont under ths tra~ename "TC)RLON", comprising structural units of the type resultin~ from the reaction of trimellitic anhydride with an arornatic ciiamine.
The polyamideimide coating was cured for 2 hours at 288C
5 after application. The second layer contained various nickel powders from Novamet Produc~s Corp. suspended in the polyamideimide precursor solution at a weight ratio of nickel to resin of 2:1. The poel test resul~s are ~iven in Table 1.

TAsLE I
Example Ni powder:
Product designation Ni-255 Ni-255AC Ni-287 HC~1 Ni-123 Particle shap~ Irreg. Irreg. Irreg.Platelets Spheres E~ulk density, g./cc. 0.5 0.~ 0.9 1.2 2.2 Peel strang~h, g./mm. 161.1 150.4 80.6 26.9 12.5 it is apparent that adhesion is improved to a substantially greater extent when the metal particles are non-spherical than when they are spherical, and also that 20 the particles with irregular shapes and bulk densities in the range of abou~ 0.4-1.0 g./cc. produced substantially better adhesion than the platelet shaped or sphsrical particles having higher bulk densities.

2 5 Example 9 The procedure of Example 4 was repeated, ::
varying the metal to resin ratio in the second layer. The ..
resul~s are given in Table ll.

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l :2 39 4 1 :1 60.9 2:1 1 59.3 4:1 84:1 8:1 25:1 The results in Table ll show that superior adhesi~n is demonstrated when the ratio of metal to resin is in the range of about 1:1~:1, and drops off significantly at ratios above 5:1.

Example 1 0 The procedure of Fxample 7, employing the HCA-1 nickel powder in platelet form, was repeated except 1~ that the article coated was an injection molding insert and no electroless rnetal was deposited, the second layer b~ing ~-:
a 25-50 rnicron resin coating rich in nickel in platelet form at the resin~ontacting surface of the mold. The insert was used in an injection molding trial in which ~0 samples of ~--20 glass-filled bisphenol A polycarbonate resin were molded against the insert at an injection pressure of about 34.5 MPa. No svidenoe of abrasion of the mold surface was noted when the procedure was cornpleted.
The injection pressure was then inar0ased to 69 ~ ;
25l MPa. and 100 more samples were molded, again, the insert was inspscted for wear and none was seen. Finally, the pressure was increased to 138 MPa. and an additional 100 samples ware molded. The in~ert showed slight abrasion in the gate ragion but none elsewhere.

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Similar tests were conducted at metal to resin ratios of û.5-8.0:1. The best results were obtained at a ratio of 4:1.
Results similar to those described above were 5 obtained with the following cornmercially available polyimides: "MATRIMID 5218" of Ciba-Geigy, based on ~-amino-1-(4'-aminophenyl)-1,3-trimethylindane; "P84" from Lenzing USA Corp., prepared from an aromatic diamine and bis-3,4~icarboxybenzophenone dianhydride; and ~'AVIMID-N"
10 from DlJPsnt, based on an arom~tic diamine and 2,2- bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride.

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Claims (23)

1. An article comprising:
a substrate having high thermal conductivity;
a first layer of temperature-resistant material having low thermal conductivity, deposited in said substrate; and a second layer deposited on said first layer, comprising a suspension of metal particles in a temperature-resistant material having low thermal conductivity.

2. An article according to claim 1 wherein the metal particles are non-spherical.

3. An article according to claim 2 wherein the substrate is metal.

4. An article according to claim 3 wherein the temperature-resistant material is a resin.

5. An article according to claim 4 wherein the resin is a polyimide or polyamideimide.

6. An article according to claim 4 wherein the metal particles are nickel.

7. An article according to claim 4 wherein the thickness of the first layer is in the range of about 10-500 microns.

8. An article according to claim 4 wherein the thickness of the second layer is in the range of about 10-100 microns.

9. A article according to claim 4 wherein the bulk density of the metal particles is below about 2 g./cc.

10. An article according to claim 4 wherein the metal is in platelet form and has a bulk density in the range of about 1.1-1.5 g./cc.

11. An article according to claim 10 wherein the weight ratio of metal to resin in the second layer is in the range of about 0.5-5.0:1.

12. An article according to claim 4 which has a further metal coating deposited on said second layer,

13. An article according to claim 12 wherein the metal in the second layer is in fiber, whisker or irregular form and has a bulk density in the range of about 0.4-1.0 g./cc.

14. An article according to claim 13 wherein the weight ratio of metal to resin in the second layer is in the range of about 1-4:1.

15. A multilayer mold for molding thermoplastic into finished parts, comprising:
a metal core;
an insulating layer of temperature-resistant polymer having low thermal conductivity, deposited on said core; and a metal-containing layer comprising a suspension of non-spherical metal particles in a temperature-resistant polymer having low thermal conductivity, deposited on said insulating layer.

16. An article according to claim 15 wherein the polymer is a polyimide or polyamideimide.

17. An article according to claim 15 wherein the metal particles are nickel.

18. An article according to claim 15 wherein the metal is in platelet form and has a bulk density in the range of about 1.5 g./cc.

19. An article according to claim 18 wherein the weight ratio of metal to resin in the metal-containing layer is in the range of about 0.5-5.0:1.

20. An article according to claim 15 which has a further metal coating deposited on said metal-containing layer.

21. An article according to claim 20 wherein the metal in the metal-containing layer is in fiber, whisker or irregular form and has a bulk density in the range of about 0.41.0 g./cc.

22. An article according to claim 21 wherein the weight ratio of metal to resin in the metal-containing layer is in the range of about 1-4:1.

23. The invention as defined in any of the preceding claims including any further features of novelty disclosed.