CA1243176A

CA1243176A - Screen fabrication

Info

Publication number: CA1243176A
Application number: CA000463185A
Authority: CA
Inventors: Dean M. Spear; Garland E. Raley
Original assignee: Ethyl Corp
Current assignee: Tredegar Film Products LLC
Priority date: 1983-09-21
Filing date: 1984-09-14
Publication date: 1988-10-18
Also published as: ES296810Y; BE905121Q; JPH0240501B2; DE3484298D1; ES296810U; EP0147013A2; EP0147013B1; EP0147013A3; JPS60155436A; US4543299A

Abstract

ABSTRACT
SCREEN FABRICATION

A laminated, cylindrical, metal screen or molding element for vacuum perforation of plastic film or sheets, comprising two or more relatively thin cylin-drical metal screens, each having a predetermined inside and outside diameter and each having a plurality of openings or holes therein of a predetermined size and geometrical shape, and said relatively thin screens stacked and bonded together, diametrically one inside the other thereby providing a screen of a desired thick-ness and a desired hole geometry wherein the holes in the screen have substantially straight walls perpen-dicular to the surface of the screen.
A method of producing a relatively thick cylin-drical metal screen for vacuum perforation of plastic film or sheets wherein the holes or openings in the screen have substantially straight walls perpendicular to the surface of the screen, comprising stacking and bonding together two or more matched relatively thin metal screens diametrically one inside the other.

Description

3 ~

Case V~5222 _REEN FABRICATION

The present invention is in the general field of perforated plastic film and especially relates to vacuum perforating of plastic film. The invention par-ticularly relates to metal screens or molding elementsused in the vacuum perforation of plastic film and to a method of fabricating such screens.
Perforated plastic film has many useful appli-cations. It is used in gardening and farming to prevent the growth of grass and weeds ~7hile permitting moisture to be transmitted through the film to the soil beneath.
Perforated film is also used for making disposable diapers, for example, see U.S. 3,814,101.
One of the earlier methods for vacuum perfora-1~ tion of plastic film is disclosed in U.S. 3,054,148.The patentee describes a stationary drum having a molding element or screen mounted around the outer surface of the drum and adapted to freely rotate thereon. A vacuum chamber is employed beneath the screen to create a pressure differential between the respective surfaces of the thermoplastic sheet to be perforated to cause the plasticized sheet to flow into openings provided in the screen and thereby cause a series of openings, holes or perforations to be formed in the plastic sheet or film.

~Z~3~

A variety of methods and apparatuses including particular types of perforating screens or rotatable molding elements have been developed over the years for particular perforation operations. Examples of these are U.S. 4,155,693, U.S. 4,252,516, U.S. 3,709,647, U.S.
4,151,240, U.S. 4,319,868 and U.S. 4,388,056. In U.S.
4,155,693, the screen is comprised of a series of per-forated metal strips preferably welded together to form a cylinder. U.S. 4,252,516 provides a screen having a series of hexagonal depressions with elliptical holes centered therein. U.S. 3,709,647 provides for a rotating vacuum-forming roll having a circulating cooling medium therein.
U.S. 4,151,240 provides a means for cooling the film after it has been perforated and debossed. U.S.
4,319,868 sets forth an apparatus for making a thermo-plastic film having raised bosses with perforated tips.
A particularly constructed embossing roll for effecting the desired film pattern is disclosed. U.S. 4,388,056 ~0 discloses an apparatus for continuously forming an air-laid fibrous web having oppositely phased, cylindrically undulating side edges and a predetermined basis weight distribution. An air-laying drum has a honeycomb type annular-shape frame including circumferentially extending ribs and transverse plates. A stationary adjustable air flow modulating means is disposed adjacent the radially ~Z(~3~76 inwardly disposed boundary of an arcuate portion of a circumferentially segmented annular-shape plenum, circumferentially spanning a plurality of plenum segments for adjusting a pressure drop across particular areas of the surface of the air-laying drum.
Vacuum perforation of thin plastic films involves the extrusion of molten polymeric materials such as polyethylene and other plastic polymers though a slot die. The hot melt web of film or plastic sheet exiting the die impinges on a rotating cylindrical screen which is mounted on a stationary vacuum drum or roll.
The vacuum roll has an axial slot and a set of seals extending longitudinally the length of its outside sur-face, beneath the area where the web of plastic impinges lS on the screen or molding element. A high vacuum from inside the screen is directed through the slot in the vacuum roll. The vacuum present within the slot forms or molds the plastic film or sheet to the screen and perforates it through the holes of the screen. At the same time, an airflow is produced which cools the film.
The most important component of the vacuum processing equipment is the cylindrical screen. This molding element defines aesthetic and mechanical proper-ties of the film as well as the geometric pattern of the perforated film. In a preferred screen fabrication technique, the desired screen pattern is nickel plated 3~7 on a specially prepared cylindrical mandrel. A seamless cylindrical nickel screen of any predetermined or desired pattern can be produced. Other metals, such as copper may also be used.
Some film products require the use of relatively thick screens, i.e., from 0.020 to 0.100 inches thick, and also require that the walls of the patterned holes are straight and perpendicular to the screen surface.
Present screen fabrication techniques as heretofore 10 described are not capable of producing a screen meeting these requirements. The patterned holes on screens produced by nickel plating a prepared cylindrical mandrel, even with the application of specialized plating and post etching techniques, take the shape of inverted, 15 truncated, concaved cones. The thicker the screen, the more exaggerated the effect becomes.
A relatively thick, laminated, cylindrical metal screen or molding element for vacuum perforation of plastic film or sheets is provided which comprises 20 two or more relatively thin, cyclindrical metal screens, each of which has predetermined inside and outside diameters and a plurality of openings or holes therein of predetermined size and geometrical shape, which screens have been stacked and bonded together dia-25 metrically one inside the other, and having a desiredthickness and a desired hole geometry wherein the holes ~2~3~'76 ` have substantially straight walls ~hich are perpendicular to the surface of the screen.
A method of making a relatively thick cylindrical metal screen for vacuum perforation of plastic film is provided wherein the holes in the screen have substantially straight walls perpendicular to the surface of the screen, comprising stacking and bonding together two or more matched relatively thin cylindrical metal screens diametrically one inside the other, each of the relatively thin metal screens having a plurality of holes therein which have substantially straight walls and which are perpendicular to the surface of their respective relatively thin cylindrical metal screen.
A method is also provided for producing the screens wherein matched sets of relatively thin, seamless, cylindrical metal screens are overplated with a -thin layer of a bonding metal within specified tolerances wherein the inside diameter of the largest screen fits the outside diameter of the next largest screen. Each screen fits similarly inside the next largest screen and has a common reference mark on each end thereof for alignment. Two relatively thicker seamless metal sleeves of didfferent diameters are prepared wherein the inside surface of the larger diameter sleeve is chrome plated and the outside surface of the smaller diameter sleeve is chrome plated. The inside diameter of the larger sleeve fits the outside diameter of the largest diameter matched screen within specified tolerances. The outside diame-ter of the smaller sleeve fits the inside diameter of the smallest diameter matched screen within specified tolerances. The entire inside surfaces and the matched screens are coated with ~n ~ppropriate flux. The largest cylindrical sleeve i5 cradled and clamped so as to retain its cylindrical shape.
The largest diameter screen is malformed, slid inside the cradled sleeve and then reformed into its cylindrical shape.
The next largest screen is then rn/~c lZ'~3~L76 malformed and slid inside thre reformed screen. The reference marks of the two screens are aligned and the screens are then pinned or otherwise fastened together.
The smaller screen is then reformed into its cylindrical 5 shape. The remaining screens of the matched set are similarly assembled. The smaller diameter sleeve is installed similarly to the matched screens. The final assembly of sleeves and screens is then heated in an oven to a suitable bonding temperature, cooled to near 10 ambient temperature and then removed from the oven.
Thereafter, the outside sleeve is care~ully cut axially and removed. Any remaining flux is removed with an appropriate agent and the inside sleeve is removed thereby leaving a finished laminated screen product of 15 desired specifications.
Figure 1 is a schematic view illustration of an apparatus and method for vacuum perforation of thermo-plastic film;
Figure 2 is a side elevational view of a sleeve 20 mounted in a cradle with a screen partially inserted therein;
Figure 3 is an end view of the assembly of Figure 2 with the wall thickness of the screen and sleeve enlarged to show detail Figure 4 is an end view similar to that of Figure 3, but illustrates a complete assembly of screens and sleeves;

3~'76 Figure 5 is a perspective view of a laminated screen of the invention;
Figure 6 is an enlarged view of a segment of the screen of Figure 5;
Figure 7 is a sectional view of the screen seg-ment of Figure 6 taken along line 7-7;
Figure 8 is a sectional view of a screen seg-ment similar to that of Figure 7 illustrating an alter-nate hole radial cross-section;
Figure 9 is a sectional view of a screen segment similar to that of Figure 7 illustrating another alter-nate hole radial cross-section; and Figure 10 is a sectional view of a screen seg-ment similar to that of Figure 7 illustrating still another alternate hole radial cross-section.
Referring now to Figure 1 of the drawings, vacuum process equipment and method for perforating plastic film or sheet therewith are schematically illustrated. A plastic polymer such as polyethylene is heated to a melt and extruded from an extruder E through a die D where a film web 10 is formed. The web 10 is directed onto a rotating cylindrical screen 11 having a desired pattern of holes which is turning clockwise as indicated by arrow A around a stationary vacuum roll or drum 12. A vacuum chamber 13 within the roll 12, longi-tudinal air slot 14 and seals 15 are employed to create a ~Z~L7~

pressure differential betwee^n the respective surfaces of the thermoplastic sheet or web 10 to cause the plasti-cized sheet to flow into the holes in the screen in the direction indicated by the arrow B and therefore per-forate the web 10. The perforated film web 10' travelsonto a guide roll 16 and continues onto a wind-up roll 17. Additional guide rolls or tensioning rolls can be employed as desired as well as various film treating equipment.
Seamless cylindrical nickel screens produced by plating are made by two principal methods. In one method, a mandrel is ground to a dimension corresponding to the desired dimension of the finished screen. The desired screen hole pattern is engraved on the mandrel either by spiral engraving or malett indexing techniques.
A plating resist medium is applied to the surface of the mandrel, fill ng the pattern produced by the engraving.
A finish grinding operation is employed to remove the plating resist medium from the land areas between the ~0 engraved pattern, so that only the land area will be subject to plating. Subsequent nickel plating of the mandrel forms the screen. The mandrel is cooled and the finished screen is removed therefrom.
The other method of producing a seamless cylin-drical nickel screen is similar to the foregoing method, except that instead of engraving the pattern on the mandrel, a special photograp~hic negative of the pattern is created and wrapped around the mandrel. Exposing of the negative transfers the pattern to the mandrel in the form of a plating resist, leaving only the land areas of the screen available for plating. The mandrel is then plated, forming the screen which is then removed from the mandrel to obtain the finished product.
Either of these screen manufacturing methods are satisfactory to produce thin screens for lamination however, the latter method is preferred. Using a photo-graphic negative permits relative ease in transferring a pattern from one diameter screen to an identical one on another diameter screen by reduction of the photographic negative.
In preparing a matched set of screens for lami-nation, several requirements must be met. First, each successive screen of the set must fit diametrically inside the next larger diameter screen, with sufficient space allowed for the metal or tin-lead alloy plating of ~ each screen. Secondly, each screen of the set must be geometrically identical. This means that each screen has the same number of holes, both axially and circum-ferentially, and that the radial centerlines of each hole of any one screen match identically the radial centerlines of the corresponding holes in all other screens in the set. Finally,-the individual hole ~ ~ z~3~

geometry of all the aligned ~oles in all the screens must be nearly identical.
The inside diameter of each individual thin screen to be laminated may be calculated by the Eollowing formula:
Dn = D + 2tp + (n-l) (2tL + 4tp) wherein Dn = Inside diameter of each individual thin screen n;
D = Inside diameter of the finished laminated screen;
n = The number of individual thin screens, counting from inside out, n = 1, 2, 3, . . . N;
tL = The individual thin screen thickness (assumed constant for each screen of the set);
and, tp = The thickness of the metal plating to be applied (assumed constant for each screen of the set).
The inside diameter of the outer solid metal sleeve may be calculated by the following formula:
Do.S = DN + 2tL + 2tp + 2tc wherein Do.s = Inside diameter of the outer sleeve DN = Inside diameter of the Nth thin screen, and, tc = The thickness of the chrome plating to be applied.

The inside diameter^of the inner solid metal sleeve may be calculated by the following formula:
DI.s = D - 2ts - 2tc wherein ts = The thickness of the solid metal sleeves (assumed to ~e same for each sleeve) Using the foregoing procedures and formulas, matched sets of seamless, cylindrical metal tnickel) screens may be produced as follows:
1. Grind a mandrel to a dimension corres-ponding to the finished sleeve inside diameter of Do.s, produce the outer cylindrical metal sleeve thereon, and plate the sleeve to a thickness of ts.

2. Grind the same mandrel to a dimension corresponding to the finished inside diameter of the Nth screen. Apply a desired screen pattern using the photo-negative resist method including a reference alignment mark at each end of the screen. Plate the mandrel to a thickness of tLr forming the largest, "Nth", screen of the matched set.
~0 3. Grind the same mandrel to a dimension corresponding to the finished inside diameter of the (N-l)th screen. Reduce the photographic negative in the circumferential direction only to equal the circumference of the reground mandrel, and apply the pattern to the mandrel as before. Plate the mandrel to a thickness of tL forming the next largest, (N-l)th, screen of the :1 Z~3:~76 matched set. The photographic negative reduction and transfer operation may be a computerized operation.
4. ~epeat Step 3 for each of the remaining screens of the matched set.
5. Grind the same mandrel to a dimension corresponding to the finished sleeve inside diameter of DI.s., produce the inner cylindrical sleeve thereon, and plate the sleeve to a thickness of ts.
Since screens are generally prepared for par-ticular film perforating operations, the use of the same mandrel is preferable. Should a number of laminated screens of the same pattern be produced, a number of mandrels may be used, as appropriate.
In the preferred form of the invention, a matched set of thin, seamless, cylindrical, nickel screens are prepared as set forth in detail hereinafter.
The length and diameter of the screens is selected on the basis of the type of vacuum perforating equipment and the number of screens to be laminated. The thick-ness of each screen is determined on the basis of the type of hole wall shape desired. A screen thickness of approximately 0.005 inches (0.0127 centimeters) provides hole walls that are substantially straight and perpen-dicular to the surface of the screen.
Each screen of the matched set is overplated with a thin layer of a bonding material, preferably a

3 ~'~6 tin-lead alloy. An alloy of~63 weight percent tin and 37 percent lead is especially preferred. An alloy layer of about 0.00025 inches (O.OOOÇ35 centimeters) thick is most preferred. Each screen of the matched set i5 designed and produced so that after plating, the inside diameter of the largest screen fits, within a specified tolerance, the outside diameter of the next largest screen. In turn, each screen of the set fits similarly inside the next largest screen. Each screen of the set is designed and produced with a common reference or aligning mark at each end ~hereof. Alignment of the reference marks during assembly produces proper pattern hole alignment.
Two seamless cylindrical nickel sleeves of lS different diameters are also required. The sleeves are about the same length of the thin screens. The thick-ness of the sleeves may be varied, but a thickness of approximately 0.010 inches ~0.0254 centimeters) is especially preferred. The inside surface of the larger ~ diameter sleeve, and the outside surface of the smaller diameter sleeve are chrome plated. A plating thickness of about 0.0005 inches (0.00127 centimeters) is most pre-ferred. The sleeves are designed and produced so that after chrome plating, the inside diameter of the larger ~5 sleeve fits, within a specified tolerance, the autside diameter of the largest diameter thin screen, after the 3L2~3~76 .

screen has been plated. Also, after chrome plating, the outside diameter of the smaller sleeve is designed and produced to fit the inside diameter of the smallest diameter thin screen of the matched set of screens, after the screen has been plated. The two sleeves are used as fixtures during the assembly and bonding operations as explained hereinafter.
The tin-lead alloy plating applied to each screen provides the bonding medium for laminationO The chrome plating applied to the sleeves acts as a resist to prevent the tin screens being laminated from bonding to the sleeves.
After the matched set of thin screens and the two sleeves have been prepared in the manner described, the assembly and bonding operations can be completed.
Referring now to Figs. 2-4 of the drawings, the larger cylindrical sleeve 20 is mounted in a cradle 21 and restrained therein so as to retain its cylindrical shape by two stiff outside diameter ring clamps 22 and ~ 23. Any other suitable restraining or clamping means may be used. The largest diameter thin screen 30 of the matched set of screens is malformed or otherwise dis-torted and slid or positioned inside the larger diameter sleeve 20. The screen 30 is then reformed into its cylindrical shape.
The next largest screen 31 is similarly mal-formed and slid inside the largest screen 30 of the 3:~76 assembly 40. Reference marks 32 on the ends of the two screens are aligned and the screens are pinned or other-wise fastened together.
If more than two thin screens are to be lami-nated or assembled, the remaining thin screens are similarly installed with the next largest thin screen being positioned inside the second thin screen 31 and so on, until each thin screen of the matched set of thin screens has been assembled.
Once all the thin screens have been assembled, the smaller sleeve 24 is positioned within the smallest diameter thin screen in the same manner as the various thin screens were installed. Prior to the installation of the smaller sleeve, the entire inside surface of the assembly is thoroughly coated with an appropriate flux, for example, a liquid solder flux having a pure resin base or a soldering paste containing zinc chloride, both manufactured by CG Electronics. Any other suitable flux may be used.
Once the assembly 40 is completed, it is trans-ferred to an oven and uniformly heated to a temperature of about 400F + 10F (204.4C + 5.56C) or 390F to 410F (or 198.84C to 209.96C). During the bonding cycle, the cylindrical nickel sleeves remain on the assembled screens. The sleeves act to uniformly restrain the screen laminates while permitting growth and shrink-age during heating and cooling cycles as they are -~ lZl.~3'~'7~

pre~erably o~ the same material as the thin screens.
The assembly is then allowed to cool in the oven to nearly room ox ambient temperature. It is then removed from the oven for final operations.
After the assembly has been cooled and removed from the oven, the outside sleeve is carefully axially cut and removed. Remaining flux residue is removed from the screen assembly with a suitable agent, for example, by washing with a degreasing liquid followed by a neutralizing wash of a 2 percent solution of muriatic acid. Any other suitable flux removing agent may be used. The inside sleeve is then removed, leaving a finished laminated screen of a desired thickness.
Although other bonding mediums may be used, the specific one of 63% tin-37% lead, plated to a thickness of 0.00025 inches ~0.000635 centimeters) particularly meets the requirements of the fabricating system. Pure, plated nickel initiates embrittlement at approximately 425F (218.3C). Any bonding system selected must 2~ there- fore cure or flow at a temperature below the embrittle- ment temperature of the nickel plating. The tin-lead alloy preferred is the eutectic formulation of the two elements. The alloy melts and solidifies at 361F (182.3C). The instant bonding system is unique, in that, by plating each individual thin screen prior to assembly, difficult and messy applications of bonding mediums during assembly are avoided. ~he tin-lead alloy plating thickness of 0 00025 inches (0.000635 centi-meters) is the optimum thickness to produce good bonding with minimum excess alloy.
Referring no~ to Fig. 5, a laminated screen 50 of the invention is seen which comprises four thin screens 51, 52, 53 and 54 which have been stacked and bonded together in accordance with the foregoing pro-cedure.
As seen in Fig. 6, the screen 50 has a pluarlity of openings or holes 50a therein. The holes 50a have walls 50b which are substantially straight as best seen in Fig. 7. In the latter figure, it is readily seen that the walls 50b are formed from the individual walls 15 51b, 52b, 53b and 54b of each of the tin screens 51, 52, 53 and 54, respectively. For purposes of illustration, the truncated holes of the thin screens have been exag-gerated. The effect of the multiscreen lamination provides hole walls which are substantially straight.
While the invention is particularly directed to a method of producing relatively thick seamless cylin-drical metal screens, especially nickel screens, with holes or openings which are essentially straight and perpendicular to the screen surface, the method can also be utilized to provide thick screens with an expanded variety of hole radial cross-sections. It is only L?~ 3 ~

essential that the basic holé radial centerlines of each screen laminate be the same.
Although for simplification, the invention is illustrated with screens having round holes, other hole configurations or patterns are suitable. Such holes may be oval, rectangular, pentagonal, hexagonal or any other desired geometric shape.
Figs. 8-lO illustrate some of the screen arrangements that can be achieved by using thin screens of different hole sizes. It can readily be appreciated that a wide variety of hole shapes and sizes can be obtained for providing a particular hole effect in a thermoplastic film or sheet.
Although the invention is particularly suited for perforating thermoplastic sheets or film made from polyolefins, especially polyethylene and polypropylene, it can be used with other types of thermoplastic films as desired.

Claims

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

1. A laminated, cylindrical metal screen or molding element for vacuum perforation of plastic film or sheets, comprising two or more thin cylindrical metal screens, each of said thin screens having a plurality of openings or holes therein, said thin screens stacked and bonded together diametrically one inside the other to provide the laminated cylindrical metal screen, the holes of each screens being substantially aligned with the holes of the other screens and having substantially straight walls perpendicular to the surface of the laminated cylindrical metal screen.

2. The laminated, cylindrical metal screen of claim 1 wherein each of said thin scrrens has a thickness of about 0.005 inches.

3. The laminated, cylindrical metal screen of claim 1, wherein said screen has a total thickness of about 0.020 to 0.100 inches.

4. The laminated, cylindrical metal screen of claim 1 wherein the metal is nickel.

5. The laminated, cylindrical metal screen of claim 1 wherein the metal is copper.

6. The laminated, cylindrical metal screen of claim 1 wherein each of the thin screens is overplated with a tin-lead plating.

7. The laminated, cylindrical metal screen of claim 6 wherein the tin-lead plating is about 63 weight percent tin and 37 weight percent lead.

8. The laminated, cylindrical metal screen of claim 1 wherein each of said thin screens has substantially the same number of holes, both axially and circumferentially and that each of said holes in one of said screens has a radial centerline matching a radial center line in each of said holes of said other thin screens.

9. The laminated, cylindrical metal screen of claim 1 wherein the individual geometry of each of said holes in each of said thin screens is substantially identical.

10. The laminated, cylindrical metal screen of claim 9 wherein said individual geometry of said holes in each of said thin screens is a square.

11. The laminated, cylindrical metal screen of claim 9, wherein said individual geometry of said holes in each of said thin screens is a pentagon.

12. The laminated, cylindrical metal screen of claim 9, wherein said individual geometry of said holes in each of said thin screens is a hexagon.

13. The laminated, cylindrical metal screen of claim 1, wherein there are about 100 to 20,000 holes per square inch of screen surfaces.

14. The laminated, cylindrical metal screen of claim 13 wherein each of said holes has a diameter of about 0.015 to 0.020 inches.

15. A method of fabricating a laminated, cylindrical metal screen or molding element for vacuum perforation of plastic film or sheets, comprising the steps of:

a. preparing at least two matched thin seamless, cylindrical metal screens, each of a predetermined size;
b. overplating each of said matched thin screens with a thin plate of a bonding metal whereby after plating, the inside diameter of the largest screen fits, within a specified tolerance, the outside diameter of the next largest screen;
c. preparing two seamless, cylindrical metal sleeves, each of a predetermined size with one being larger than the other;
d. chrome plating the inside surface of the larger diameter sleeve and the outside surface of the smaller diameter sleeve whereby after plating, the inside diameter of the larger sleeve fits, within a specified tolerance, the outside diameter of the largest diameter metal plated matched screen and the outside diameter of the smaller sleeve fits within a specified tolerance the inside diameter of the smallest diameter plated matched screen;
e. coating the entire inside surfaces of each of the matched screens with a flux;
f. mounting the larger sleeve in a cradle and so restraining it as to retain its cylindrical shape;
g. malforming the largest diameter matched screen, sliding it inside the larger sleeve and then reforming it to its cylindrical shape;
h. malforming the next largest diameter matched screen, sliding it inside the largest diameter matched screen, aligning the two screens and fastening them together, and then reforming said next largest diameter matched screen to its cylindrical shape;
i. successively installing any remaining screens in a manner similar to that of step h;
j. after all of the matched screens have been installed, installing the smaller cylindrical sleeve in a manner similar to that of the matched screens thereby completing the assembly;
k. after assembly is completed, uniformly heating it in an oven to a predetermined temperature to bond each matched screen to the other matched screens;
l. cooling the assembly to near ambient temperature, and then removing it from the oven;
m. carefully axially cutting the larger diameter sleeve and removing it from the assembly; and n. removing the smaller diameter sleeve from the assembly, thereby providing the desired laminated cylindrical metal screen.

16. The method of Claim 15, wherein the matched metal screens are nickel screens.

17. The method of Claim 15, wherein each matched metal screens are copper screens.

18. The method of Claim 15, wherein each matched screen is about 0.005 inches thick.

19. The method of Claim 15, wherein said bonding metal is a tin-lead alloy.

20. The method of Claim 19, wherein said tin-lead alloy is about 63 weight percent tin and about 37 weight percent lead.

21. The method of Claim 15 wherein said bonding metal overplated on the matched screens is about 0.0025 inches thick.

22. The method of Claim 15, wherein the metal sleeves are nickel sleeves.

23. The method of Claim 15, wherein the chrome plating on the metal sleeves is about 0.0005 inches thick.

24. The method of Claim 15, wherein the temperature in step k. is about 390°F-420°F.

25. The method of Claim 15, wherein each matched screen has a patterned hole geometry wherein the walls of the holes are substantially straight and perpendicular to the surface of the screen.

26. The method of Claim 15, wherein each matched screen has a patterned hole geometry wherein the holes are round, oval, rectangular, pentagonal, hexagonal, or other desired geometrical shape.

27. The method of Claim 15, wherein each matched screen is of a diameter wherein each screen of the matched set fits diametrically inside the next larger diameter screen with sufficient space being allowed for the metal plating of each screen.

28. The method of Claim 15, wherein each screen of the matched set has a geometrical pattern substantially identical to each of the other screens of the matched set.

29. The method of Claim 15, wherein each screen of the matched set has substantially the same number of holes, both axially and circumferentially and the radial centerlines of the holes in one screen substantially matches the radial centerlines of the holes in each of the other screens.

30. The method of Claim 15, wherein the hole geometry of one of said matched screens is substantially identical to the hole geometry of each of the other of said matched screens.

31. The method of Claim 15, wherein two matched thin, seamless cylindrical screens are laminated to each other.

32. The method of Claim 15, wherein three matched thin, seamless cylindrical screens are laminated together.

33. The method of claim 15, wherein four matched thin, seamless cylindrical screens are laminated together.

34. A method of making a cylindrical metal screen for vacuum perforation of plastic film wherein the holes in the screen have substantially straight walls perpendicular to the surface of the screen, comprising stacking and bonding together two or more matched thin cylindrical metal screens diametrically one inside the other, each of said thin metal screens having a plurality of holes therein which have substantially straight walls and which are perpendicular to the surface of their respective thin cylindrical metal screen.

35. The method of claim 34, wherein the matched metal screens are nickel metal screens.

36. The method of claim 34, wherein the matched metal screens are overplated with a bonding metal alloy.

37. The method of claim 36, wherein the metal alloy is tin-lead.

38. The method of claim 37, wherein the tin-lead alloy is about 63 weight percent tin and about 37 weight percent lead.

39. The method of claim 36, wherein the bonding is accomplished by coating the entire inner surface of the matched screen with a flux and heating the stacked screens in an oven to a temperature sufficient to effect the bonding.

40. The method of Claim 34, wherein each of the matched thin screens have the same geometrical hole pattern and the same number of holes both axially and circumferentially, with the radial cetnerlines of each hole of one thin screen matching the radial centerlines of each hole of the other tin screen.

41. The method of Claim 40, wherein the geometrical hole pattern of each screen is round, oval, rectangular, pentagonal, hexagonal or other geometric shape.