WO2001043967A2

WO2001043967A2 - One side matte multilayer coversheet

Info

Publication number: WO2001043967A2
Application number: PCT/US2000/042554
Authority: WO
Inventors: Rickey J. Seyler
Original assignee: Tredegar Film Products Corporation
Priority date: 1999-12-10
Filing date: 2000-12-05
Publication date: 2001-06-21
Also published as: WO2001043967A3; AU4516101A

Abstract

A one side matte conversheet is formed of a multi-layer laminate which is matte embossed and features improved smoothness and reduced micropitting on the non-matte side which makes this article particularly suitable for use as a photopolymer coversheet. A method of producing the coversheet involving the melt casting of a coextruded polymeric continuous web having at least two layers and using polymers which exhibit differences in melting temperature and/or crystallization temperature, is also shown. According to the method, sufficient quenching or cooling of the higher melting temperature or higher crystallization temperature resin on the smooth side is accomplished to set this layer prior to entering a nip roll arrangement to rubber roll emboss the lower melting temperature or lower crystallization temperature matte side resin. It is the setting or crystallization of the smooth side resin prior to embossing which affords greater control of the web in the embossing step as well as improved smoothness with significantly reduced micropits on the smooth side of the resulting coversheet.

Description

ONE SIDE MATTE COVERSHEET

FIELD OF THE INVENTION

The present invention pertains to a one side matte coversheet and a method of manufacture therefor. Specifically, the coversheet of the present invention is a multilayer laminate which is matte embossed and features improved smoothness and reduced micropitting on the non-matte side which makes this article particularly suitable for use as a photopolymer coversheet.

BACKGROUND OF THE INVENTION

Photopolymer films are frequently used in the production of electronic devices, especially integrated circuits. Photopolymer films are laminate structures of various polymers which are placed over a substrate like a circuit board and used to control chemical etching and deposition processes. In view of the small scale environment in which these films must function, even the smallest of defects in the surface of the photopolymer film may have a profound effect on performance. It is critical to protect the photopolymer film from dirt, dust, scratches, and surface irregularities such as wrinkles and gels which can damage the smooth surface of the photopolymer.

Accordingly, these photopolymer films are typically provided with a coversheet formed of a thermoplastic film which serves to protect the photopolymer film during shipping, storage and handling. A preferred design for a photopolymer coversheet is a one side matte (OSM), one side smooth polymer film which is capable of adhering to the photopolymer via intimate contact and surface interactions between the smooth side of the coversheet film and the smooth surface of the photopolymer film.

As noted earlier, the photopolymer film may be damaged if dirt or other debris becomes trapped between the photopolymer film and the coversheet which is designed to protect it. Similarly, it is possible to damage the photopolymer film if the coversheet contains an excessive amount of microscopic surface irregularities, or mircopits, on the smooth contact surface as the photopolymer film may conform to and pick up the negative image of these micropits. It is also desirable in a coversheet to have a matte surface, opposite to the smooth surface facing the photopolymer, capable of preventing blocking or self-adhesion of the coversheet/photopolymer combination to itself when taken up on or removed from a roll. Although prior art OSM-type films in both single and multi-layer embodiments are known to be useful in masking applications for protecting fairly smooth and rigid substrates like polycarbonate or acrylic sheets, as generally set forth and described in U.S. Patent 4,895,760 issued to Barger and U.S. Patent 5,100,709 issued to Barger et al, there remains a need for improved masking films specifically designed for use with photopolymers or other substrates which are sensitive to even the slightest surface irregularity such as micropits. U.S. Patent 4,631 ,246 issued to Bennett discloses a single-layer OSM polymer coversheet for use with photopolymers, and discusses the benefits which may be obtained by use of a coversheet having a matte exterior surface opposite the smooth contact surface. As a practical matter, however, it has remained difficult to obtain the proper amount of roughening or embossing on one exterior surface while obtaining the desired amount of smoothness on the opposite exterior surface. Accordingly, there is a need for a multi-layer or laminate structure coversheet, suitable for use with photopolymer substrates, which is capable of providing improved smoothness and reduced micropitting on the non-matte side while also providing a uniformly roughened surface on the embossed side.

SUMMARY OF THE INVENTION

The present invention discloses a coextruded laminate particularly adapted for use as a photopolymer coversheet and having at least two layers in which one external surface is roughened, textured, or patterned by matte embossing and the other external surface features improved smoothness and reduced micropitting. A method for producing the coversheet of the present invention involves melt casting a coextruded polymeric continuous web having at least two layers and using resins which exhibit differences in melting temperature and/or crystallization temperature between the matte side and the smooth side of the laminate. According to the method of the present invention, sufficient quenching or cooling of the higher melting temperature or higher crystallization temperature resin on the smooth side is accomplished to set this layer prior to entering a nip roll arrangement to rubber roll emboss the lower melting temperature or lower crystallization temperature matte side resin. It is the setting or crystallization of the smooth side resin prior to embossing which affords greater control of the web in the embossing step as well as improved smoothness with significantly reduced micropits on the smooth side. Similarly, because the resin of the matte side layer is still relatively molten, it is possible to obtain the desired amount of surface roughening to prevent blocking and self-adhesion by rubber roll matte embossing.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding of the method and apparatus of the present invention may be obtained by reference to the following Detailed Description when taken in conjunction with the accompanying Drawings wherein:

Figure 1 is a cutaway view of a multi-layer photopolymer coversheet, according to the present invention. Figure 2 is a side elevational view of a conventional rubber roll matte embossing arrangement in which the vertical and horizontal distances between the coextrusion die and the nip rolls may be adjusted.

Figure 3 is a side elevational view of a modified rubber roll matte embossing apparatus in which the rubber roll may be repositioned relative to the polished chrome casting roll.

DETAILED DESCRIPTION OF THE INVENTION

With reference now to Figure 1, a multi-layer photopolymer coversheet 100 according to the present invention is depicted in a cutaway side view. The photopolymer coversheet 100 generally includes a first layer 10 and a second layer 20. As illustrated in Figure 1 , the coversheet 100 includes one or more core layers or tie layers 30 disposed between the first layer 10 and the second layer 20. However, the present invention also contemplates a coversheet 100 having no core or tie layers 30.

The first layer 10 of the coversheet 100 has a smooth outer surface 11 for contact with, and engaging a substrate, not shown, such as a photopolymer sheet. The second layer 20 of the cover sheet 100 includes a roughened outer surface 21. When the coversheet 100 is wound up onto a roll for later usage, the roughened surface 21 of the second layer 20 inhibits adhesion with the smooth surface 11 on an adjacent first layer

10 of the coversheet 100.

As used herein, the terms polymer and polymeric material shall be understood to refer to homopolymers, copolymers, and blends thereof and may also include various additives to affect nucleation of crystal structures, opacity, color, and other characteristics.

The first layer 10 of the coversheet 100 is formed from a first polymeric material, comprising one or more individual components, and having a specific melting temperature (T_ml) and crystallization temperature (T_cl). The second layer 20 of the coversheet 100 is formed from a second polymeric material, comprising one or more individual components, and having a specific melting temperature (T,^) and crystallization temperature (T_c2). The difference in the crystallization temperatures (ΔT_C) for these two materials may be computed as follows: ΔT_C = T_cl - T_c2. With reference now to Figure 2, an apparatus for coextruding and matte embossing the photopolymer coversheet 100 of the present invention is illustrated. According to the present invention, various thermoplastic polymeric compounds including the first polymeric material and the second polymeric material are fed into extruders, not shown, which in turn supply the polymeric materials in molten form to a coextrusion die 110. The coextrusion die 110 is generally known in the art and has a parallel, slotted design so as to extrude two or more thin film sheets parallel to each other to form a laminate 100 suitable for casting. A molten multi-layer web 100' is extruded from the coextrusion die 110. The molten multilayer web 100' includes both the first layer 10 and the second layer 20, as shown in Figure 1, in a molten form. The molten multi-layered web 100' is allowed to cool or is quenched for a brief period of time prior to entering a nip roller arrangement, generally referred to by the numeral 120. The nip roller arrangement 120 includes a polished chrome casting roll 130 and a rubber embossing roll 140. The polished chrome casting roll 130 has a casting roll surface 131 with a surface roughness average (RJ of less than about 5 microinches. The rubber embossing roll 140 has an embossing surface 141 with a surface roughness average (RJ of about 20 to 70 microinches.

Preferably, the molten multi-layer web 100' contacts the casting roll surface 131 prior to engaging the embossing surface 141 of the rubber roll 140. After engaging the casting roll surface 131 of the casting roll 130, the molten multi-layer web reduces its temperature to a temperature below the crystallization temperature (T_cl) of the first layer

10, thereby creating the multi-layer web 100" having the first layer 10 in a crystallized condition, and the second layer 20 in a molten form. After the multi-layer film 100" is formed with the first layer 10 in contact with the casting roll surface 131 of the casting roll 130, the multi-layer web 100" engages the rubber embossing roll 140. The multilayer web 100" engages the rubber embossing roll 140 with the molten second layer 20 contacting the embossing surface 141. The embossing surface 141 of the rubber embossing roll 140 imparts the roughened surface 21 to the second layer 20 in the molten condition in the multi-layer film 100". Subsequent to, or concurrent with, engagement of the multi-layer film 100" with the rubber embossing roll 140, the temperature of the multi-layer film is reduced to below the crystallization temperature (T_c2) of the polymeric material in the second layer 20, thereby forming the coextruded laminate coversheet 100. After passing through the nip roll apparatus 120, the coextruded laminate 100 is then wound around a take-up roll, not shown, as known in the art. By varying the speed of the take-up roll it is also possible to vary the speed of the coextruded laminate through the nip roll apparatus 120 and to further orient the polymer of the coversheet 100 laminate in the machine direction, if desired. By using the apparatus described above and depicted in Figure 2, it is possible to coextrude a multi-layer polymer film laminate 100 having the smooth surface 11 corresponding to the smooth casting roll surface 131 of the casting roll 130 and a matte surface 21 corresponding to the embossing surface 141 of the embossing roll 140. As used herein, a matte surface is understood to mean a surface having a roughened texture which may be either random or patterned. As illustrated, the smooth surface 11 of the laminate 100 is formed of the first polymer material in the first layer 10 and the matte surface 21 of the laminate 100 is formed of the second polymer material in the second layer 20. Each of the polymer materials has a melting temperature (T-J and a crystallization temperature (T_c). The crystallization temperature of a particular polymeric material may be determined by various techniques as known in the art including differential scanning calorimetry (DSC). In a preferred embodiment of the present invention, the first polymer used to create the smooth surface layer 10 of the laminate 100 will have a higher melting temperature and/or crystallization temperature than the second polymer used to create the matte surface layer 20 of the laminate 100. This is of particular importance as it is necessary to have the first polymer begin to crystallize or set before entering the nip roll while having the second polymer layer reach its crystallization temperature after embossing in the nip roll. By processing the coextruded laminate in this manner, it is possible to create a smoother surface for contacting the photopolymer film substrate when applied as a protective coversheet. It is believed that this is possible because, if the first polymer layer 10 is allowed to crystallize prior to entering the nip roller apparatus 120, it will resist permanent deformation caused by entrapped air bubbles or blisters, thus creating a smooth surface 11 with less micropitting. This is particularly important as each micropit in the coversheet may subsequently transfer as a negative image to the photopolymer film to which the coversheet is applied.

Additionally, by selecting a second polymer material for the second layer 20 which does not crystallize until after the nip roller arrangement 120, it is possible to rubber roll emboss a uniform and continuous matte surface onto the laminate which will prevent blocking or self-adhesion of one layer of the film to another when wound up on or removed from a take-up roll.

In one preferred embodiment of the present invention, the first layer 10 of the coversheet 100 is formed of a polypropylene (PP) and the second layer 20 of the cover sheet 100 is formed of polyethylene (PE). The polypropylene material of the first layer 10 has a higher melting temperature and a higher crystallization temperature than the polyethylene material of the second layer 20. It should also be noted that other polymer combinations may be used to form the laminate provided that the polymer used for the smooth surface 1 1 has a higher crystallization temperature than the polymer used for the matte surface 21. Examples of other polymer combinations which may be suitable for use in forming a laminate according to the present invention would be: high density polyethylene (HDPE) / low density polyethylene (LDPE), ethylene propylene rubber (EP) / low density polyethylene (LDPE), polyethylene terephthalate (PET) / polybutylene terephthalate (PBT), and polyethylene naphthalate / polyethylene terephthalate (PET).

While it is desirable that these polymer combinations are sufficiently compatible or miscible with each other to avoid delamination in the laminate film, it is possible to make a multilayer laminate film of smooth and embossed layers which are incompatible by using the one or more core or tie layers 30 to bond the two outer layers together. While different polymers have different melting temperatures and also different crystallization temperatures, it is not always possible to predict which combinations will be useful based entirely on a difference in melt temperature. For example, it may be possible to have a difference in melt temperatures between polymers of over 45 °C while having a difference in crystallization temperatures between the two polymers of only 7° to 10°C. In the context of the present invention, it would be preferable to have a difference in crystallization temperatures between the first polymer material at the smooth surface 11 and the second polymer material at the rough surface 21 of about

10°C, with a difference of crystallization temperature of 10° to 30 °C being more preferred, and a difference of greater than 30 °C being the most preferred. It is also possible to create the desired difference in crystallization temperature by adding nucleating agents, or other additives which can effectively bring about spherulite crystallization at higher temperatures, to the first polymer layer 10. One form of nucleating agents, by way of example only, are clarifying agents such as Millad 3905, 3940 or 3988, produced by Milliken Chemical of Spartanburg, South Carolina, or Amfine NA- 11 or NA-2, produced by Amfine Chemical of Allendale, New Jersey. Thus, it is possible to raise the crystallization temperature of the first polymer and to significantly increase the difference in crystallization temperature, ΔT_C, between the two polymers comprising the laminate 100.

Referring back now to Figure 2, it is possible to adjust various processing conditions and variables to alter the resulting laminate film 100. The first of these variables is designated by the letter V which indicates the distance from the lip of the die 110 to the point at which the laminate film 100' impinges on the polished chrome casting roll 130. This distance, V, is also known as the draw length and in conjunction with the line speed will determine the amount of time which the film will experience air cooling prior to entering the nip roll apparatus 120. The distance designated by the letter H represents the horizontal displacement from the center of the casting roll 130 to the die 110 thereby influencing the cooling time, the angle at which the laminate enters the nip roll apparatus 120, and the point at which the smooth side of the laminate 100' will first impinge the casting roll 130. Other variables which may be altered in the manufacturing process to control the properties of the resulting laminate include the speed of the take-up roll, which is expressed in feet per minute, and the pressure between the rubber roll 140 and the polished chrome casting roll 130 known as the nip pressure, which is expressed in pounds per square inch (psi).

It is also possible to use a vacuum box 150 or an electrostatic pinning bar, not shown, to create better pinning of the smooth side of the laminate film 100' to the polished chrome casting roll 130 and to reduce necking out of the die 1 10. The vacuum box 150 is essentially a vacuum and nozzle arrangement which may be directed at the film between the die 110 and the casting roll 130 to cause the laminate 100' to be drawn toward and impinge upon the casting roll at a position higher up such as a 1 O'clock or

2 O'clock position on the casting roll with the nip fixed at about a 3 O'clock position. Alternatively, an electrostatic pinning bar may be positioned on the side of the laminate 100' opposite to the casting roll 130 and push the laminate 100' toward the casting roll 130 using a static charge which is similar to that which tends to build up on the laminate, and again causes the laminate 100' to impinge the casting roll 130 sooner. By either method, good pinning of the laminate 100' to the casting roll 130 seems to reduce the amount of air entrapped prior to entering the nip. Also, by having the polymer impinge on the polished chrome casting roll 130 earlier, it resides on the roll for a longer period of time prior to entering the nip for embossment. The chrome casting roll 130 is typically chilled and runs at an operating temperature between about 65° and 150°F, with an operating temperature range of about 67° to 70 °F being more preferred. By having the laminate 100' on the roll 130 for a longer period of time prior to entering the nip, it further sets or crystallizes the polymer used in the smooth layer 10 resulting in a smoother laminate film 100. It has been noticed, however, that as the impingement point is moved toward 3 O'clock, which is understood to be 12 O'clock for a horizontal die configuration, or precisely tangent to the chrome casting roll 130 faster processing is achievable, but the film will not be as thoroughly set or crystalline. One way in which to impinge the chrome casting roll 130 at the 3 O'clock position while still getting sufficient residence time to set the film prior to embossing is to move the rubber roll 140 relative to the chrome roll 130 at an angle. This is best illustrated by reference to Figure

3 in which the rubber roll 140 is shown offset to the polished chrome casting roll 130 by an angle A. By moving the embossing roll 140 to the 4 O'clock or 5 O'clock position, it is possible to maximize line speed while optimizing casting roll residence time .

The level of roughness on the matte side of the film is evaluated by measuring the air bleed in units known as Bekk seconds. This measurement is made by placing the matte side of the laminate film on a glass disk with a metal orifice in its center and drawing a vacuum on the metal orifice. The vacuum is then turned off and the time required for atmospheric air pressure to break the vacuum between the matte side of the film and the orifice is then measured in seconds. The air bleed for the coversheet film of the present invention is preferably less than 1,500 Bekk seconds. Lower air bleed values are generally preferred in that entrapped air will distribute itself more quickly and uniformly as the coversheet is taken up with the photopolymer to form a master roll. As the entrapped air is able to redistribute itself more rapidly, it will result in a more uniform air cushion between adjacent layers of the photopolymer/coversheet combination on the master roll and better storage properties.

Micropitting of the smooth surface of the laminate films is measured in two ways. The first measure of micropitting is an average micropit size in micrometers squared (μ²).

The second way in which micropitting is measured is in a percent area of the total surface. Accordingly, in a preferred embodiment of the present invention, it would be desirable to have an average micropit size of less than 3,000 μ² and a total micropit area of less than 10%. It is more preferred to have an average micropit size of less than 600 μ² and a total micropit area of less than 5%. It is most preferred to have an average micropit size of less than 33 μ² and a total micropit area of less than 0.3%. This most preferred smooth surface for a film would be regarded as an ideal condition and, according to current industry standards, would be regarded as having no micropitting. It has also been observed that micropit size appears to be more critical than the micropit area. Accordingly, by way of example only, a coversheet with micropit size of about 250 μ² and a total micropit area of less than 5% would be more preferred than a coversheet with micropit size of about 500 μ² and a total micropit area of less than 2.5%.

Another processing variable which must be considered is the surface roughness of the rubber roll. The roughness of the rubber embossing roll may be expressed in Ra or a roughness average which is measured in units of microinches. It has been noted that rubber rolls having a surface roughness of about 20 to 70 Ra emboss quite effectively with a roughness of about 40 to 55 Ra being preferred.

A more complete understanding of the one side matte coversheet of the present invention may be obtained by reference to the following Examples of several two-layer coversheets which have been produced under various processing conditions. Also, please note that the Melt Index (MI) or Melt Flow of a particular polymer may be determined according to the testing procedures set forth in ASTM D-1238, which is incorporated in its entirety herein by specific reference thereto, and that test conditions for polyethylene (PE) should be a temperature of 190° C and a load of 2.16 kg and test conditions for polypropylene (PP) should be a temperature of 230°C and a load of 2.16 kg- Example 1

A layer of low density polyethylene (LDPE) with a Melt Index of 4.20 g/ 10 min. and density of 0.922 g/cm³, and a layer of polypropylene (PP) with a Melt Index of 9.0 g/10 min. and density of 0.905 g/cm³, were coextruded to form a two-layer LDPE/PP coversheet with a 60/40 layer thickness ratio. The polymers had a difference in crystallization temperature of about 7 °C. The coextruded laminate was then fed at a line speed of 200 feet per minute to a nip roll apparatus displaced a short distance from the die (V = 13.875 in, H = 16.125 in) and having a nip pressure of 70 psi. A vacuum fan operating at 5 Hz was used to assist in pinning the smooth PP layer of the film to the chrome casting roll of the nip roll apparatus. The resulting one side matte coversheet had the following surface characteristics:

Smooth surface - micropit mean size = 705 μ² , micropit area = 8.0% Matte surface - air bleed > 1500 Bekk seconds Example 2

A layer of LDPE with a Melt Index of 3.00 g/ 10 min. and density of 0.921 g/cm³, and a layer PP with a Melt Index of 8.0 g/10 min. and density of 0.900 g/cm³, were coextruded to form a two- layer LDPE/PP coversheet with a 70/30 layer thickness ratio. The polymers had a difference in crystallization temperature of about 17 °C.

The coextruded laminate was then fed at a line speed of 200 feet per minute to a nip roll apparatus displaced a short distance from the die (V = 15.000 in, H = 16.125 in) and having a nip pressure of 35 psi. A vacuum fan operating at 7.5 Hz was used to assist in pinning the smooth PP layer of the film to the chrome casting roll of the nip roll apparatus.

The resulting one side matte coversheet had the following surface characteristics: Smooth surface - micropit mean size = 764 μ² , micropit area = 5.0% Matte surface - air bleed > 423 Bekk seconds Example 3

As in Example 2, a layer of LDPE with a Melt Index of 3.00 g/ 10 min. and density of 0.921 g/cm³, and a layer PP with a Melt Index of 8.0 g/10 min. and density of 0.900 g/cm³, were coextruded to form a two-layer LDPE/PP coversheet with a 70/30 layer thickness ratio. In this Example, however, the polypropylene material further contains about 500 ppm of Amfine NA-11 nucleating agent. The polymers had a difference in crystallization temperature of about 35 °C.

The coextruded laminate was then fed at a line speed of 100 feet per minute to a nip roll apparatus displaced a short distance from the die (V = 16.000 in, H = 16.125 in) and having a nip pressure of 60 psi. A vacuum fan operating at 6.0 Hz was used to assist in pinning the smooth PP layer of the film to the chrome casting roll of the nip roll apparatus.

The resulting one side matte coversheet had the following surface characteristics: Smooth surface - micropit mean size = 230 μ , micropit area = 4.9% Matte surface - air bleed > 704 Bekk seconds

Example 4

As in Example 3, a layer of LDPE with a Melt Index of 3.00 g/ 10 min. and density of 0.921 g/cm³, and a layer PP with a Melt Index of 8.0 g/10 min. and density of 0.900 g/cm³, were coextruded to form a two-layer LDPE/PP coversheet with a 70/30 layer thickness ratio. Again, the polypropylene material further contains about 500 ppm of Amfine NA-11 nucleating agent. The polymers had a difference in crystallization temperature of about 35 °C.

The coextruded laminate was then fed at a line speed of 100 feet per minute to a nip roll apparatus displaced a short distance from the die (V = 16.000 in, H = 15.375 in) and having a nip pressure of 60 psi. A vacuum fan operating at 3.0 Hz was used to assist in pinning the smooth PP layer of the film to the chrome casting roll of the nip roll apparatus.

The resulting one side matte coversheet had the following surface characteristics: Smooth surface - micropit mean size = 517 μ , micropit area = 2.4% Matte surface - air bleed __ 266 Bekk seconds

By way of comparison to the above Examples, a typical monolithic coversheet formed of an LDPE having comparable melt index and density properties would generally have the following surface characteristics:

Smooth surface - micropit mean size = 3500 μ² , micropit area = 15% Matte surface - air bleed < 2000 Bekk seconds Although preferred embodiments of the invention have been described in the Examples and foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements and modifications of parts and elements without departing from the spirit of the invention as defined in the following claims. Therefore, the spirit and the scope of the appended claims should not be limited to the description of the preferred embodiments contained herein.

Claims

WHAT IS CLAIMED IS:

1. A coversheet comprising: a first layer having a smooth exterior surface; said first layer being a first polymer having a first polymer crystallization temperature; a second layer laminated to the first layer and having a matte exterior surface; said second layer being a second polymer having a second polymer crystallization temperature; and wherein said first polymer crystallization temperature of said first layer is higher than said second polymer crystallization temperature of said second layer.

2. The coversheet of claim 1, wherein said first polymer further comprises a nucleating agent.

3. The coversheet of claim 1, wherein said first polymer comprises polypropylene.

4. The coversheet of claim 3, wherein said second polymer comprises polyethylene.

5. The coversheet of claim 1, wherein said second polymer comprises polyethylene.

6. The coversheet of claim 1 , wherein said exterior smooth surface has micropit dimensions of less than 3,000 micrometers squared and a micropit area of less than 10% of the total area.

7. The coversheet of claim 1, wherein said exterior smooth surface has micropit dimensions of less than 600 micrometers squared and a micropit area of less than 5% of the total area.

8. The coversheet of claim 1, wherein said exterior smooth surface has micropit dimensions of less than 33 micrometers squared and a micropit area of less than 0.3% of the total area.

9. The coversheet of claim 1, wherein said exterior matte surface exhibits an air bleed value less than about 1,500 Bekk seconds.

10. A coversheet comprising: a first layer having a smooth exterior surface; said first layer being a first polymer having a first polymer crystallization temperature; a second layer having a matte exterior surface; said second layer being a second polymer having a second polymer crystallization temperature; at least one tie layer bonding said first layer to said second layer; wherein said first polymer crystallization temperature of said first layer is higher than said second polymer crystallization temperature of said second layer.

11. The coversheet of claim 10, wherein said first polymer further comprises a nucleating agent.

12. The coversheet of claim 10, wherein said first polymer comprises polypropylene.

13. The coversheet of claim 12, wherein said second polymer comprises polyethylene.

14. The coversheet of claim 10, wherein said second polymer comprises polyethylene.

15. The coversheet of claim 10, wherein said exterior smooth surface has micropit dimensions of less than 3,000 micrometers squared and a micropit area of less than 10%) of the total area.

16. The coversheet of claim 10, wherein said exterior smooth surface has micropit dimensions of less than 600 micrometers squared and a micropit area of less than 5% of the total area.

17. The coversheet of claim 10, wherein said exterior smooth surface has micropit dimensions of less than 33 micrometers squared and a micropit area of less than 0.3% of the total area.

18. The coversheet of claim 10, wherein said exterior matte surface exhibits an air bleed value less than about 1,500 Bekk seconds.

19. A method of manufacturing a coversheet comprising the steps of: preselecting a first polymer having a crystallization temperature and adapted for use as a smooth layer; preselecting a second polymer having a lower crystallization temperature than said first polymer and adapted for use as a matte layer; coextruding a first polymer layer of said first polymer and a second polymer layer of said second polymer to form a laminate structure; quenching said laminate for sufficient time as to permit said first polymer to crystallize; and matte embossing said second polymer matte layer to create a roughened surface.

20. The method of manufacturing a coversheet of claim 17 wherein the step of preselecting a first polymer further comprises selecting said first polymer with a nucleating agent.

21. The method of manufacturing a coversheet of claim 17 wherein the step of coextruding a first polymer layer and a second polymer layer to form a laminate structure further comprises coxtruding at least one tie layer disposed between said first layer and said second layer.