Imaging member with amorphous hydrocarbon resin Number:6,762,003 from the United States Patent and Trademark Office (PTO) owispatent

Title: Imaging member with amorphous hydrocarbon resin

Abstract: The present invention relates to an imaging member comprising an imaging layer and at least one stiffening layer comprising a blend of polyolefin polymer and amorphous hydrocarbon resin. The invention further describes a method for making the imaging member, comprising extruding a foam polymer sheet, orienting the foam polymer sheet, bringing a stiffening layer comprising a blend of polyolefin polymer and amorphous hydrocarbon resin into contact with the oriented foam polymer sheet, and applying an imaging layer above the stiffening layer. A second method of forming an imaging member comprises extruding a foam polymer sheet, bringing at least one stiffening layer comprising a blend of polyolefin polymer and amorphous hydrocarbon resin into contact with the foam polymer sheet, orienting said foam polymer sheet and said stiffening layer and applying an imaging layer above said stiffening layer. Another method describes the formation of an imaging member comprising making a cellulosic sheet, bringing at least one stiffening layer comprising a blend of polyolefin polymer and amorphous hydrocarbon resin into contact with the cellulosic sheet and applying an imaging layer above the stiffening layer.

Patent Number: 6,762,003 Issued on 07/13/2004 to Sunderrajan,   et al.

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Inventors:	Sunderrajan; Suresh (Rochester, NY), Dontula; Narasimharao (Rochester, NY), Aylward; Peter T. (Hilton, NY), Phippen; Nicholas I. (Great Missenden, GB)
Assignee:	Eastman Kodak Company (Rochester, NY)
Appl. No.:	10/154,887
Filed:	May 24, 2002

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Current U.S. Class:	430/60 ; 347/105; 428/483; 428/497; 428/498; 428/513; 428/523; 430/201; 430/536; 430/538; 430/56
Current International Class:	B41M 5/50 (20060101); B41M 5/40 (20060101); B41M 5/41 (20060101); B41M 5/52 (20060101); C08L 23/00 (20060101); C08L 23/02 (20060101); G03C 1/775 (20060101); G03C 1/79 (20060101); G03G 7/00 (20060101); B41M 5/00 (20060101); G03C 1/93 (20060101); G03C 1/91 (20060101); C08L 57/00 (20060101)
Field of Search:	430/56,60,201,536,538 347/105 428/483,497,498,513,523

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References Cited [Referenced By]

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U.S. Patent Documents

	3148059		September 1964		Brunson et al.
	3874880		April 1975		Venor et al.
	4365044		December 1982		Liu
	4378404		March 1983		Liu
	4514452		April 1985		Tanaka et al.
	4832775		May 1989		Park et al.
	4921749		May 1990		Bossaert et al.
	4939063		July 1990		Tamagawa et al.
	5188875		February 1993		Yamaoka et al.
	5213744		May 1993		Bossaert
	5462788		October 1995		Ohashi et al.
	5466519		November 1995		Shirakura et al.
	5851651		December 1998		Chao
	5866282		February 1999		Bourdelais et al.
	5888643		March 1999		Aylward et al.
	6030742		February 2000		Bourdelais et al.
	6281290		August 2001		Klosiewicz
	6447976		September 2002		Dontula et al.
	6514659		February 2003		Dontula et al.
	6531214		March 2003		Carter et al.
	6537656		March 2003		Dontula et al.

Foreign Patent Documents

	0 247 898		Dec., 1987		EP
	1003226		Sep., 1965		GB
	1035165		Jul., 1966		GB
	3-197940		Aug., 1991		JP
	97106038		Apr., 1997		JP
	97127648		May., 1997		JP
	97179241		Jul., 1997		JP
	2839905		Dec., 1998		JP

Other References

Japanese Patent Abstract 04181243 (Jun. 29, 1992). . Japanese Patent Abstract XP-002246524 (Aug. 29, 1991). . Co-pending USSN 10/154,894, Aylward et al., Imaging Element With Improved Surface And Stiffness (D-83848)..

Primary Examiner: Schilling; Richard L.
Attorney, Agent or Firm: Blank; Lynne M.

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Parent Case Text

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CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly assigned, co-pending U.S. patent application Ser. No. 10/154,894 by Aylward et al. filed of even date herewith entitled "Imaging Element With Improved Surface And Stiffness", the disclosures of which are incorporated herein.

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Claims

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What is claimed is:

1. An imaging member comprising an imaging layer and at least one stiffening layer on a support, wherein said stiffening layer comprises a blend of polyolefin polymer and amorphous hydrocarbon resin, and wherein said hydrocarbon resin comprises a resin having carbon backbone units of from 8 to 24.

2. The imaging member of claim 1 wherein said amorphous hydrocarbon resin has a softening temperature of greater than 30 degrees Centigrade.

3. The imaging member of claim 2 wherein said amorphous hydrocarbon resin has a softening temperature from 70 degrees to 180 degrees Centigrade.

4. The imaging member of claim 1, wherein said hydrocarbon resin comprises rosin.

5. The imaging member of claim 1, wherein said amorphous hydrocarbon resin is present in an amount of from 2 to 50% by weight of said blend.

6. The imaging member of claim 1, wherein said amorphous hydrocarbon resin is present in an amount of from 10 to 20% by weight of said blend.

7. The imaging member of claim 1, wherein said amorphous hydrocarbon resin comprises hydrogenated cyclopentadiene.

8. The imaging member of claim 1, wherein said amorphous hydrocarbon resin is at least one member selected from the group consisting of pure monomer hydrocarbon resins, physical blends of hydrogenated hydrocarbon resins, partially hydrogenated hydrocarbon resins, fully hydrogenated hydrocarbon resins, and polyterpenes.

9. The imaging member of claim 1, wherein said polyolefin polymer comprises polypropylene.

10. The imaging member of claim 1 wherein said stiffening layer is extruded.

11. The imaging member of claim 1, wherein said stiffening layer further comprises pigment.

12. The imaging member of claim 1, wherein said stiffening layer further comprises talc.

13. The imaging member of claim 1, wherein said stiffening layer further comprises titanium dioxide pigment.

14. The imaging member of claim 1, wherein said stiffening layer comprises an unoriented layer.

15. The imaging member of claim 1, wherein said stiffening layer comprises an oriented layer.

16. The imaging member of claim 15, wherein said oriented layer is bonded to a polymer foam layer.

17. The imaging member of claim 15, wherein said oriented layer is bonded to paper.

18. The imaging member of claim 15, wherein said oriented layer is bonded to a fabric.

19. The imaging member of claim 15, wherein said oriented layer is bonded to a polymer sheet having a light transmission of greater than 20%.

20. The imaging member of claim 1, wherein said stiffening layer is bonded to paper.

21. The imaging member of claim 20 wherein said paper comprises less than 75 weight % of said imaging member.

22. The imaging member of claim 20, wherein said stiffening layer is bonded to inorganic coated paper.

23. The imaging member of claim 1 wherein said imaging member is extruded.

24. The imaging member of claim 1 wherein said support comprises a modulus less than the modulus of said stiffening layer.

25. The imaging member of claim 1, wherein said support comprises a polymer sheet having a light transmission of greater than 20%.

26. The imaging member of claim 1, wherein said support comprises a polymer foam layer.

27. The imaging member of claim 1 wherein said at least one stiffening layer comprises a modulus from 700 MPa to 10500 MPa.

28. The imaging member of claim 1, wherein said support comprises paper.

29. The imaging member of claim 1, wherein said support comprises a fabric.

30. The imaging member of claim 1, further comprising a polyethylene layer between said stiffening layer and said imaging layer.

31. The imaging member of claim 1, further comprising a subbing layer between said stiffening layer and said imaging layer.

32. The imaging member of claim 1, wherein said imaging layer comprises at least one layer comprising photosensitive silver halide.

33. The imaging member of claim 1, wherein said imaging layer comprises at least one layer comprising inkjet receiving material.

34. The imaging member of claim 1, wherein said imaging layer comprises at least one layer comprising thermosensitive imaging material.

35. The imaging member of claim 1, wherein said imaging layer comprises at least one layer comprising electrophotographic imaging material.

36. The imaging member of claim 1 wherein said at least one stiffening layer has a modulus greater than said imaging layer.

37. The imaging member of claim 1 wherein said imaging member comprises less than 75 weight % paper.

38. A method of forming an imaging member comprising extruding a foam polymer sheet; orienting said foam polymer sheet; bringing at least one stiffening layer into contact with the oriented foam polymer sheet, wherein said stiffening member comprises a blend of polyolefin polymer and amorphous hydrocarbon resin; and applying an imaging layer above said stiffening layer, and wherein said hydrocarbon resin comprises a resin having carbon backbone units of from 8 to 24.

39. The method of claim 38 wherein said amorphous hydrocarbon resin has a softening temperature of greater than 30 degrees Centigrade.

40. The method of claim 39 wherein said amorphous hydrocarbon resin has a softening temperature from 70 degrees Centigrade to 180 degrees Centigrade.

41. The method of claim 38 wherein said bringing at least one stiffening layer into contact comprises extrusion coating said blend onto said foam polymer sheet.

42. The method of claim 38 wherein said bringing at least one stiffening layer into contact comprises adhesively connecting said stiffening layer to said foam polymer sheet.

43. The method of claim 38, wherein said stiffening layer comprises an oriented layer.

44. The method of claim 38, wherein said amorphous hydrocarbon resin is at least one member selected from the group consisting of pure monomer hydrocarbon resins, physical blends of hydrogenated hydrocarbon resins, partially hydrogenated hydrocarbon resins, fully hydrogenated hydrocarbon resins, and polyterpenes.

45. The method of claim 38, wherein said amorphous hydrocarbon resin is present in an amount of from 2 to 50% by weight of said blend.

46. The method of claim 38, wherein said amorphous hydrocarbon resin is present in an amount of from 10 to 20% by weight of said blend.

47. The method of claim 38, wherein said stiffening layer further comprises talc.

48. The method of claim 38, wherein said stiffening layer further comprises titanium dioxide pigment.

49. The method of claim 38, wherein said at least one stiffening layer comprises a modulus from 700 MPa to 10500 MPa.

50. The method of claim 38, wherein said polyolefin polymer comprises polypropylene.

51. The method of claim 38, further comprising a polyethylene layer between said stiffening layer and said imaging layer.

52. The method of claim 38, further comprising a subbing layer between said stiffening layer and said imaging layer.

53. The method of claim 38 wherein said foam polymer sheet comprises a modulus less than the modulus of said stiffening layer.

54. The method of claim 38, wherein said imaging layer comprises at least one layer comprising photosensitive silver halide.

55. The method of claim 38, wherein said imaging layer comprises at least one layer comprising inkjet receiving material.

56. The method of claim 38, wherein said imaging layer comprises at least one layer comprising thermosensitive imaging material.

57. The method of claim 38, wherein said imaging layer comprises at least one layer comprising electrophotographic imaging material.

58. The method of claim 38 wherein said imaging member comprises less than 75 weight % paper.

59. A method of forming an imaging member comprising extruding a foam polymer sheet; bringing at least one stiffening layer into contact with the foam polymer sheet, wherein said stiffening layer comprises a blend of polyolefin polymer and amorphous hydrocarbon resin; orienting said foam polymer sheet and said stiffening layer; and applying an imaging layer above said stiffening layer, and wherein said hydrocarbon resin comprises a resin having carbon backbone units of from 8 to 24.

60. The method of claim 59 wherein said amorphous hydrocarbon resin has a softening temperature of greater than 30 degrees Centigrade.

61. The method of claim 60 wherein said amorphous hydrocarbon resin has a softening temperature from 70 degrees to 180 degrees Centigrade.

62. The method of claim 59, wherein said amorphous hydrocarbon resin is at least one member selected from the group consisting of pure monomer hydrocarbon resins, physical blends of hydrogenated hydrocarbon resins, partially hydrogenated hydrocarbon resins, fully hydrogenated hydrocarbon resins, and polyterpenes.

63. The method of claim 59, wherein said amorphous hydrocarbon resin is present in an amount of from 2 to 50% by weight of said blend.

64. The method of claim 59, wherein said amorphous hydrocarbon resin is present in an amount of from 10 to 20% by weight of said blend.

65. The method of claim 59, wherein said stiffening layer further comprises talc.

66. The method of claim 59, wherein said stiffening layer further comprises titanium dioxide pigment.

67. The method of claim 59 wherein said bringing at least one stiffening layer into contact comprises extrusion coating said blend onto said foam polymer sheet.

68. The method of claim 59 wherein said bringing at least one stiffening layer into contact comprises adhesively connecting said stiffening layer to said foam polymer sheet.

69. The method of claim 59 wherein said at least one stiffening layer comprises a modulus from 700 MPa to 10500 MPa.

70. The method of claim 59, wherein said polyolefin polymer comprises polypropylene.

71. The method of claim 59, further comprising a polyethylene layer between said stiffening layer and said imaging layer.

72. The method of claim 59, further comprising a subbing layer between said stiffening layer and said imaging layer.

73. A method of forming an imaging member comprising providing a cellulosic sheet; bringing at least one stiffening layer into contact with said cellulosic sheet, wherein said stiffening layer comprises a blend of polyolefin polymer and amorphous hydrocarbon resin; and applying an imaging layer above said stiffening layer, and wherein said hydrocarbon resin comprises a resin having carbon backbone units of from 8 to 24.

74. The method of claim 73 wherein said imaging member comprises less than 75 weight % paper.

75. The method of claim 73 wherein said cellulosic sheet comprises coated paper.

76. The method of claim 73 wherein said amorphous hydrocarbon resin has a softening temperature of greater than 30 degrees Centigrade.

77. The method of claim 74 wherein said stiffening layer has a softening temperature of from 70 degrees to 180 degrees Ccntigrade.

78. The method of claim 73, wherein said amorphous hydrocarbon resin is at least one member selected from the group consisting of pure monomer hydrocarbon resins, physical blends of hydrogenated hydrocarbon resins, partially hydrogenated hydrocarbon resins, fully hydrogenated hydrocarbon resins, and polyterpenes.

79. The method of claim 73, wherein said stiffening layer further comprises talc.

80. The method of claim 73, wherein said stiffening layer further comprises titanium dioxide pigment.

81. The method of claim 73, wherein said polyolefin polymer comprises polypropylene.

82. The method of claim 73, further comprising a polyethylene layer between said stiffening layer and said imaging layer.

83. The method of claim 73, further comprising a subbing layer between said stiffening layer and said imaging layer.

84. An imaging member comprising an imaging layer and at least one stiffening layer on a support, wherein said stiffening layer comprises a blend of polyolefin polymer and amorphous hydrocarbon resin, wherein said hydrocarbon resin comprises a resin having carbon backbone units of from 8 to 24, and wherein said support comprises a modulus less than the modulus of said stiffening layer.

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Description

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FIELD OF THE INVENTION

This invention relates to imaging media. In a preferred form, it relates to supports for photographic, inkjet, thermal, and electrophotographic media.

BACKGROUND OF THE INVENTION

In order for a print imaging support to be widely accepted by the consumer for imaging applications, it has to meet requirements for preferred basis weight, caliper, stiffness, smoothness, gloss, whiteness, and opacity. Supports with properties outside the typical range for imaging media suffer low consumer acceptance.

In addition to these fundamental requirements, imaging supports are also subject to other specific requirements depending upon the mode of image formation onto the support. For example, in the formation of photographic paper, it is important that the photographic paper be resistant to penetration by liquid processing chemicals, failing which, there is a stain present on the print border accompanied by a severe loss in image quality. In the formation of photo quality inkjet paper, it is important that the paper is readily wetted by ink and that it exhibits the ability to absorb high concentrations of ink and dry quickly. If the ink is not absorbed quickly, the elements block or stick together when stacked against subsequent prints and exhibit smudging and uneven print density. For thermal media, it is important that the support contain an insulative layer in order to maximize the transfer of dye from the donor which results in a higher color saturation.

It is important, therefore, for an imaging media to simultaneously satisfy several requirements. One commonly used technique in the art for simultaneously satisfying multiple requirements is through the use of composite structures comprising multiple layers wherein each of the layers, either individually or synergistically, serves distinct functions. For example, it is known that a conventional photographic paper comprises a cellulose paper base that has applied thereto a layer of polyolefin resin, typically polyethylene, on each side, which serves to provide waterproofing to the paper and also provides a smooth surface on which the photosensitive layers are formed. In another imaging material, as in U.S. Pat. No. 5,866,282, biaxially oriented polyolefin sheets are extrusion laminated to cellulose paper to create a support for silver halide imaging layers. The biaxially oriented sheets described therein have a microvoided layer in combination with coextruded layers that contain white pigments such as TiO.sub.2 above and below the microvoided layer. The composite imaging support structure described has been found to be more durable, sharper, and brighter than prior art photographic paper imaging supports that use cast melt extruded polyethylene layers coated on cellulose paper. In U.S. Pat. No. 5,851,651, porous coatings comprising inorganic pigments and anionic, organic binders are blade coated to cellulose paper to create photo quality inkjet paper.

In all of the above imaging supports, multiple operations are required to manufacture and assemble all of the individual layers. For example, photographic paper typically requires a paper-making operation followed by a polyethylene extrusion coating operation, or, as disclosed in U.S. Pat. No. 5,866,282, a paper making operation is followed by a lamination operation for which the laminates are made in yet another extrusion casting operation. There is a need for imaging supports that can be manufactured in a single in-line manufacturing process while still meeting the stringent features and quality requirements of imaging bases.

It is also well known in the art that traditional imaging bases consist of raw paper base. For example, in typical photographic paper as currently made, approximately 75% of the weight of the photographic paper comprises the raw paper base. Although raw paper base is typically a high modulus, low cost material, there exist significant environmental issues with the paper manufacturing process. There is a need for alternate raw materials and manufacturing processes that are more environmentally friendly. Additionally to minimize environmental impact, it is important to reduce the raw paper base content, where possible, without sacrificing the imaging base features that are valued by the customer, i.e., strength, stiffness, surface properties, and the like, of the imaging support.

An important corollary of the above is the ability to recycle photographic paper. Current photographic papers cannot be recycled because they are composites of polyethylene and raw paper base and, as such, cannot be recycled using polymer recovery processes or paper recovery processes. A photographic paper that comprises significantly higher contents of polymer lends itself to recycling using polymer recovery processes.

Existing composite color paper structures are typically subject to curl through the manufacturing, finishing, and processing operations. This curl is primarily due to internal stresses that are built into the various layers of the composite structure during manufacturing and drying operations, as well as during storage operations (core-set curl). Additionally, since the different layers of the composite structure exhibit different susceptibility to humidity, the curl of the imaging base changes as a function of the humidity of its immediate environment. There is a need for an imaging support that minimizes curl sensitivity as a function of humidity, or ideally, does not exhibit curl sensitivity.

The stringent and varied requirements of imaging media, therefore, demand a constant evolution of material and processing technology. One such technology known in the art as polymer foams has previously found significant application in food and drink containers, packaging, furniture, appliances, and the like. Polymer foams have also been referred to as cellular polymers, foamed plastic, or expanded plastic. Polymer foams are multiple phase systems comprising a solid polymer matrix that is continuous and a gas phase. For example, U.S. Pat. No. 4,832,775 discloses a composite foam/film structure which comprises a polystyrene foam substrate, oriented polypropylene film applied to at least one major surface of the polystyrene foam substrate, and an acrylic adhesive component securing the polypropylene film to said major surface of the polystyrene foam substrate. The foregoing composite foam/film structure can be shaped by conventional processes as thermoforming to provide numerous types of useful articles including cups, bowls, and plates, as well as cartons and containers that exhibit excellent levels of puncture, flex-crack, grease and abrasion resistance, moisture barrier properties, and resiliency.

Foams have also found limited application in imaging media. For example, JP 2839905 B2 discloses a 3-layer structure comprising a foamed polyolefin layer on the image-receiving side, raw paper base, and a polyethylene resin coat on the backside. The foamed resin layer was created by extruding a mixture of 20 weight % titanium dioxide master batch in low density polyethylene, 78 weight % polypropylene, and 2 weight % of Daiblow PE-M20 (AL)NK blowing agent through a T-die. This foamed sheet was then laminated to the paper base using a hot melt adhesive. The disclosure JP 09127648 A highlights a variation of the JP 2839905 B2 structure, in which the resin on the backside of the paper base is foamed, while the image receiving side resin layer is unfoamed. Another variation is a 4-layer structure highlighted in JP 09106038 A. In this, the image receiving resin layer comprises 2 layers, an unfoamed resin layer which is in contact with the emulsion, and a foamed resin layer which is adhered to the paper base. There are several problems with this, however. Structures described in the foregoing patents need to use foamed layers as thin as 10 .mu.m to 45 .mu.m, since the foamed resin layers are being used to replace existing resin coated layers to the paper base. The thickness restriction is further needed to maintain the structural integrity of the photographic paper base since the raw paper base is providing the stiffness. It is known by those versed in the art of foaming that it is very difficult to make thin uniform foamed films with substantial reduction in density especially in the thickness range noted above.

Another key feature of imaging media is bending stiffness. It is well known that stiffness of an imaging element is a function of the modulus of the various layers of the imaging element, the location of the various layers (particularly in terms of the distance from the bending axis) and the overall caliper of the imaging element. Improvements that can be made to the modulus of the various layers comprising the imaging element can increase the overall bending stiffness of the element thus, in turn, increasing its value as an imaging support.

Organic additives that have the potential to enhance the modulus of a polyolefin film are known in the art. The composition of the organic additive, which is typically a hydrocarbon resin, must be such that it exhibits a higher glass transition temperature (Tg) than polyolefin, for example, propylene. It must also be compatible with polyolefins such as propylene. It is believed that the addition of the organic additive increases the Tg of the amorphous polyolefin, leading to a densification of the amorphous phase over time, which leads to increased stress transfer between crystalline regions (also called a pseudonetwork effect) that, in turn, leads to increasing stiffness. For example, Bossaert et al. in U.S. Pat. No. 4,921,749 claim a polyolefin film comprising a base layer of 70% to 97% polypropylene and 30% to 3% hydrogenated resin. The addition of about 20% hydrogenated resin is shown to result in an increase in modulus of about 10-20%. Klosiewicz, in U.S. Pat. No. 6,281,290 claims a process for producing a master batch for a polypropylene article (film, fiber, sheet, or bottle) comprising a mixture of polypropylene, high density polyethylene and hydrocarbon resin having a Ring and Ball softening point of at least 70 degrees Centigrade. The addition of low levels of hydrocarbon resin and high density polyethylene (HDPE) are reported to increase the tensile modulus of extrusion cast polypropylene films by 15% to 70%. C-S Liu, in U.S. Pat. No. 4,365,044, discloses an extrusion-coatable polypropylene composition comprising a hydrogenated copolymer of vinyl toluene, alpha-methyl styrene, and low density polyethylene. Extrusion coatability at speeds up to about 900 feet per minute (274 meters/min.) and good adhesion to cellulose substrates is claimed.

PROBLEM TO BE SOLVED BY THE INVENTION

There is a need for a composite material that can be manufactured in a single in-line operation and that meets all the requirements of an imaging base, especially the bending stiffness requirements. There is also a need for an imaging base that reduces the amount of raw paper base that is used and can be effectively recycled. There is also a need for an imaging base that resists the tendency to curl as a function of ambient humidity.

SUMMARY OF THE INVENTION

These and other objects of the invention are accomplished by an imaging member comprising an imaging layer and at least one stiffening layer comprising a blend of polyolefin polymer and amorphous hydrocarbon resin having a softening temperature of greater than 30 degrees Centigrade. The invention further describes a method for making the imaging member, comprising extruding a foam polymer sheet, orienting the foam polymer sheet, bringing a stiffening layer comprising a blend of polyolefin polymer and amorphous hydrocarbon resin into contact with the oriented foam polymer sheet, and applying an imaging layer above the stiffening layer. A second method of forming an imaging member comprises extruding a foam polymer sheet, bringing at least one stiffening layer comprising a blend of polyolefin polymer and amorphous hydrocarbon resin into contact with the foam polymer sheet, orienting said foam polymer sheet and said stiffening layer and applying an imaging layer above said stiffening layer. Another method describes the formation of an imaging member comprising making a cellulosic sheet, bringing at least one stiffening layer comprising a blend of polyolefin polymer and amorphous hydrocarbon resin into contact with the cellulosic sheet and applying an imaging layer above the stiffening layer.

This invention provides a superior imaging support. Specifically, it provides an imaging support of high stiffness, excellent smoothness, high opacity, and excellent humidity curl resistance. In one embodiment, it also provides an imaging support that can be manufactured using a single in-line operation that can be effectively recycled.

The present invention offers several advantages. The invention produces an element or member that has much less tendency to curl when exposed to extremes in humidity. In one embodiment, the ability to manufacture the element or member in a single in-line operation significantly lowers element manufacturing costs and may eliminate disadvantages in the manufacturing of the current generation of imaging supports, such as very tight moisture specifications in the raw base and specifications to minimize pits during resin coating. In one embodiment, the element or member can also be recycled to recover and reuse polyolefin instead of being discarded into landfills.

DETAILED DESCRIPTION OF THE INVENTION

This invention teaches the use of a higher modulus stiffening flange layers that provide the needed stiffness for an imaging support, especially when surrounding a core on one or both sides. The high modulus stiffening flange layers may, in turn, comprise organic stiffness enhancing materials. Using this approach, many new features of the imaging base may be exploited and restrictions in manufacturing eliminated. High modulus materials or layers are defined herein as having a modulus of greater than 100,000 psi or 689 MPa.

The prior art is primarily limited to teaching the application of organic stiffening additives to extrusion cast film applications. There is no prior art in the application of such stiffening additives to imaging elements. Traditional imaging elements derive a predominant fraction of their bending stiffness from the cellulose paper substrate and as such do not require the use of organic stiffening additives. However, in the case of foam core imaging elements, there is potentially a significant application of such technology if it is shown to be viable for polyolefin foam elements and for extrusion coating processes. C-S Liu, in U.S. Pat. No. 4,365,044, discloses an extrusion-coatable polypropylene composition comprising a hydrogenated copolymer of vinyl toluene, alpha-methyl styrene, and low density polyethylene. Extrusion coatability at speeds up to about 900 feet per minute (274 m/min.) and good adhesion to cellulose substrates is claimed. However, such a composition is not suitable for use in an imaging element.

The present invention describes an imaging member comprising an imaging layer and at least one stiffening layer comprising a blend of polyolefin polymer and amorphous hydrocarbon resin, preferably having a softening temperature of greater than 30 degrees Centigrade. In a preferred embodiment, the stiffening layer is affixed to a support to form a composite comprising a core layer, at least one stiffening flange layer with an imaging layer applied thereon. The invention further describes methods for making the imaging member. It should also be noted that the cellulosic sheet described in one method may also be a inorganic coated cellulosic sheet or even fabric. Additionally, this method and the other methods described herein may also contain hydrocarbon resin having carbon backbone units of between 8 and 24. This resin may be a pure monomer hydrocarbon resin, physical blends of hydrogenated hydrocarbon resins, partially hydrogenated hydrocarbon resins, fully hydrogenated hydrocarbon resins, or polyterpenes. Furthermore, the stiffening layer of this method may also contain talc and or TiO.sub.2 to enhance the overall opacity. It should be noted that almost any white pigment known in the art may be useful in this invention. Additionally, in the formation of this imaging element by this method, there may be a polyethylene and/or subbing layer between the stiffening layer and the image layer.

Imaging element or members are constrained to a range in stiffness and caliper. At stiffness below a certain minimum stiffness, there is a problem with the element in print stackability and print conveyance during transport through photofinishing equipment, particularly high speed photoprocessors. It is believed that there is a minimum cross direction stiffness of 60 mN required for effective transport through photofinishing equipment. At stiffness above a certain maximum, there is a problem with the element in cutting, punching, slitting, and chopping during transport through photofinishing equipment. It is believed that there is a maximum machine direction stiffness of 300 mN for effective transport through photofinishing equipment. It is also important for the same transport reasons through photofinishing equipment that the caliper of the imaging element be constrained between 75 .mu.m and 350 .mu.m.

Imaging elements are also constrained by consumer performance and present processing machine restrictions to a stiffness range of between approximately 50 mN and 250 mN and a caliper range of between approximately 100 .mu.m and 400 .mu.m. In the design of the element or member of the invention, there exists a relationship between stiffness of the imaging element and the caliper and modulus of the core and modulus of the stiffening flange layers, i.e., for a given core thickness, the stiffness of the element can be altered by changing the caliper of the stiffening flange elements and/or changing the modulus of the stiffening flange elements and/or changing the modulus of the core. The stiffening effect of the present invention may occur as a result of increasing modulus which, in turn, increases stiffness. When the present invention is applied to a conventional paper core, a thinner paper core may be used to produce a support or base having the same stiffness as conventional paper support. Further, base or support layers may be made from materials which were previously lacking the necessary stiffness to be useful as the core of an imaging element or member.

If the target overall stiffness and caliper of the imaging element or member are specified then for a given core thickness and core material, the target caliper and modulus of the stiffening flange elements are implicitly constrained. Conversely, given a target stiffness and caliper of the imaging element for a given caliper and modulus of the stiffening flange layers, the core thickness and core modulus are implicitly constrained.

The stiffening flange layers of the composite sheet can be made of a homopolymer such as a polyolefin, polystyrene, polyvinylchloride or other typical thermoplastic polymers, their copolymers or their blends thereof, or other polymeric systems like polyurethanes, and polyisocyanurates. The composite sheet can be made with stiffening flange(s) of the same polymeric material as the core matrix, or it can be made with stiffening flange(s) of different polymeric composition than the core matrix.

Other solid phases may be present in the core in the form of fillers that are of organic (polymeric, fibrous) or inorganic (glass, ceramic, metal) origin. The fillers may be used for physical, optical (lightness, whiteness, and opacity), chemical, or processing property enhancements of the core.

In a preferred lamination embodiment of this invention, the stiffening or flange layers used comprise high modulus polymers, preferably having a modulus between 700 MPa to 10500 MPa, such as low density polyethylene, high density polyethylene, polypropylene, or polystyrene, their blends or their copolymers, that have been stretched and oriented. They may be filled with suitable filler materials to increase the modulus of the polymer and/or to enhance other properties such as opacity and smoothness. In a preferred extrusion coating embodiment of this invention, the stiffening flange layers used comprise high modulus extrusion-coatable polymer compositions such as high density polyethylene, polypropylene, or polystyrene, their blends or their copolymers, filled with suitable filler materials. Some of the commonly used inorganic filler materials are talc, clays, calcium carbonate, magnesium carbonate, barium sulfate, mica, aluminum hydroxide (trihydrate), wollastonite, glass fibers and spheres, silica, various silicates, and carbon black. Some of the organic fillers used are wood flour, jute fibers, sisal fibers, polyester fibers, and the like. The preferred fillers are talc, mica, and calcium carbonate because they provide excellent modulus enhancing properties. Extrusion coating thicknesses useful to this invention are of caliper between about 10 .mu.m and about 150 .mu.m, preferably between about 25 .mu.m and about 75 .mu.m.

Another key additive to lamination polymer sheets/layers or extrusion coatable compositions to enhance physical properties such as modulus and stiffness of the imaging element or member is a low molecular weight substantially amorphous resin or rosin additive. The low molecular weight resin or rosin additive, preferably hydrogenated, has a number average molecular weight below that of the polyolefin to which it is added. The additive resin or rosin may be natural or it may be synthetic. Examples of suitable resins are amorphous petroleum hydrocarbons, coal or petroleum derivatives, substituted hydrocarbons or hydrocarbon derivatives such as polyterpene resins, rosins, rosin derivatives, and styrene resins. These materials may be characterized using the Ring and Ball softening point test and typically have a softening temperature in the range from about 30 degrees Centigrade to about 200 degrees Centigrade, and more typically in the range from about 70 degrees Centigrade to about 180 degrees Centigrade. The additive resin must exhibit a higher glass transition temperature (Tg) than the matrix polymer and must be, at least to a limited extent, compatible with the matrix polymer. For example, if the matrix polymer is polypropylene, then the additive resin must have a higher glass transition temperature than polypropylene. It must also be compatible with polypropylene. Compatibility with the matrix polymer may be manipulated by reducing the average molecular weight of the resin additive or functionalizing the resin additive. For example, the resin additive may be functionalized with a polar functional group for use with a polar matrix polymer.

The resin additive is typically added from about 2% concentration by weight to about 50% concentration by weight. Preferably, it is added from about 10% concentration by weight to about 20% concentration by weight. At an addition level of less than 2%, there is little change in the desired modulus. At addition levels greater than about 50%, processability becomes a concern due to poor chill roll release. Examples of resin additives include, but are not limited to, master batched materials, for example, cyclopentadiene derivatives such as a hydrogenated cyclopentadiene master batched with polypropylene such as PA-609 made by Exxon Mobil, or pure monomer hydrocarbon resins master batched with a polyolefin such as Plastolyn.RTM. P2539 made by Eastman Chemical Co., physical blends of hydrogenated hydrocarbon resins and polymer such as Res.RTM. P2567, partially hydrogenated aliphatic hydrocarbon resins such as Res.RTM. A2661, or fully hydrogenated aliphatic hydrocarbon resins such as the Regalite.RTM. R1125 or Regalite.RTM. V3140, or hydrogenated pure aromatic resins such as Regalrez.RTM. 1139, or polyterpenes such as Piccolyte.RTM. C135, and the like. Preferred hydrocarbon resins may contain carbon backbone units of between 8 and 24.

In the most preferred embodiment, the imaging member of the invention comprises a polymer foam core that has adhered thereto an upper and a lower flange or stiffening layer. The polymer foams of this core are true foams, and have also been referred to as cellular polymers, foamed plastic, or expanded plastic. Polymer foams are multiple phase systems comprising a solid polymer matrix that is continuous and a gas phase. These closed cell foams are not synonymous with voided polymers or voided polymer layers, which are created through the addition of an incompatible phase or void-initiating particle to a polymer matrix, followed by orientation in which voids are created in the matrix polymer as it is stretched around the void-initiating particles, leaving the void-initiating particles to remain in the voids of the finished sheet. These foams have been created by the use of a blowing agent.

The polymer foam useful in this invention may comprise a homopolymer such as a polyolefin, polystyrene, polyvinylchloride or other typical thermoplastic polymers, their copolymers or their blends thereof, or other polymeric systems like polyurethanes, polyisocyanurates that has been expanded through the use of a blowing agent to consist of two phases, a solid polymer matrix, and a gaseous phase. Other solid phases may be present in the foams in the form of fillers that are of organic (polymeric, fibrous) or inorganic (glass, ceramic, metal) origin. The fillers may be used for physical, optical (lightness, whiteness, and opacity), chemical, or processing property enhancements of the foam.

Other solid phases may be present in the foams in the form of fillers that are of organic (polymeric, fibrous) or inorganic (glass, ceramic, metal) origin. The fillers may be used for physical, optical (lightness, whiteness, and opacity), chemical, or processing property enhancements of the foam.

The foaming of these polymers may be carried out through several mechanical, chemical, or physical means. Mechanical methods include whipping a gas into a polymer melt, solution, or suspension, which then hardens either by catalytic action or heat or both, thus entrapping the gas bubbles in the matrix. Chemical methods include such techniques as the thermal decomposition of chemical blowing agents generating gases such as nitrogen or carbon dioxide by the application of heat or through exothermic heat of reaction during polymerization. Physical methods include such techniques as the expansion of a gas dissolved in a polymer mass upon reduction of system pressure, the volatilization of low-boiling liquids such as fluorocarbons or methylene chloride, or the incorporation of hollow microspheres in a polymer matrix. The choice of foaming technique is dictated by desired foam density reduction, desired properties, and manufacturing process.

In a preferred embodiment of this invention polyolelins such as polyethylene and polypropylene, their blends and their copolymers are used as the matrix polymer in the foam core along with a chemical blowing agent such as sodium bicarbonate and its mixture with citric acid, organic acid salts, azodicarbonamide, azobisformamide, azobisisobutyrolnitrile, diazoaminobenzene, 4,4'-oxybis(benzene sulfonyl hydrazide) (OBSH), N,N'-dinitrosopentamethyltetramine (DNPA), sodium borohydride, and other blowing agents well known in the art. Polyethylene and polypropylene, their blends and their copolymers are preferred due to their ready availability, common usage, low cost and excellent adherence to the stiffening flange of the present invention. The preferred chemical blowing agents would be sodium bicarbonate/citric acid mixtures, azodicarbonamide, though others can also be used. If necessary, these foaming agents may be used together with an auxiliary foaming agent, nucleating agent, and a cross-linking agent.

The stiffening flange layers with the core of this invention are chosen to satisfy specific requirements of flexural modulus, caliper, surface roughness, and optical properties such as colorimetry and opacity. The stiffening flange members may be formed integral with a core by manufacturing the core with a stiffening flange skin layer or extrusion coating the stiffening flange onto the core materials or the stiffening flange may be laminated to the core material. The integral extrusion of stiffening flange members with the core is preferred for cost. The layers may be either preformed and adhered to each other or coextruded. The lamination technique allows a wider range of properties and materials to be used for the skin materials.

The preferred range in caliper of the core is from 25 .mu.m to 350 .mu.m. The most preferred caliper range is between 75 .mu.m and 350 .mu.m. The preferred modulus of the core varies from 30 MPa to 10500 MPa. The preferred range in caliper of the flange layer is between 5 .mu.m and 175 .mu.m and modulus of 100 MPa to 10500 MPa. These ranges are preferred across the range of non-foam, such as paper based, and foam based cores because of the preferred overall caliper range of the element which lies between 100 .mu.m and 400 .mu.m with a stiffness of between 50 and 250 mN.

Preferred ranges of non-foam based core caliper and modulus and stiffening flange caliper and modulus follow: the preferred caliper of the core of the invention ranges between 25 .mu.m and 300 .mu.m, the preferred caliper of the stiffening flange layers of the invention ranges between 5 .mu.m and 75 .mu.m, the preferred modulus of the core of the invention ranges between 3000 MPa and 10500 MPa, and the preferred modulus of the stiffening flange layers of the invention ranges from 100 MPa to 3500 MPa. In each case, the above range is preferred because of (a) consumer preference, (b) manufacturability, and (c) materials selection. It is noted that the final choice of stiffening flange and core materials, modulus, and caliper will be a subject of the target overall element stiffness and caliper.

Preferred ranges of foam core caliper and modulus and stiffening flange caliper and modulus follow: the preferred caliper of the foam core of the invention ranges between 200 .mu.m and 350 .mu.m, the preferred caliper of the stiffening flange layers of the invention ranges between 10 .mu.m and 175 .mu.m, the preferred modulus of the foam core of the invention ranges between 30 MPa and 1000 MPa, and the preferred modulus of the stiffening flange layers of the invention ranges from 700 MPa to 10500 MPa. The range in density reduction of the foam core is from 20% to 95%. The preferred range in density reduction is between 40% and 70%. This is because it is difficult to manufacture a uniform foam product with very high density reduction (over 70%). Density reduction is the percent difference between solid polymer and a particular foam sample. It is also not economical to manufacture a product with density reduction less than 40%.

The selection of core material, the extent of density reduction (foaming) and the use of any additives/treatments determine the core modulus. The selection of stiffening flange materials and treatments (for example, the use of inorganic fillers such as talc for polymeric stiffening flange materials) determines the stiffening flange modulus. In the preferred embodiment, the modulus of the core will be lower than the modulus of the stiffening flange layer or layers.

For example, at the low end of target stiffness (50 mN) and caliper (100 .mu.m), given a typical non-foam based core of caliper 50 .mu.m and modulus 4826 MPa, the stiffening flange layer caliper is then constrained to 62.5 .mu.m on each side of the core, and the stiffening flange modulus required is 1700 MPa. Also, for example, at the high end of target stiffness (250 mN) and caliper (350 .mu.m), given a typical non-foam based core of caliper 200 .mu.m and modulus 4136 MPa, the stiffening flange layer caliper is constrained to 75 .mu.m on each side and the stiffening flange modulus required is 140 MPa.

For example, at the low end of target stiffness (50 mN) and caliper (100 .mu.m), given a typical polyolefin foam of caliper 50 .mu.m and modulus 137.9 MPa, the stiffening flange layer caliper is then constrained to 25 .mu.m on each side of the core, and the stiffening flange modulus required is 10343 MPa. Also, for example, at the high end of target stiffness (250 mN) and caliper (400 .mu.m), given a typical polyolefin foam of caliper 300 .mu.m and modulus 137.9 MPa, the stiffening flange layer caliper is constrained to 50 .mu.m on each side and the stiffening flange modulus required is 1034 MPa. It is seen from the above explanation that the higher the modulus of the stiffening flange layers, the lower the necessary caliper to achieve a target stiffness.

The element or members of the invention can be made using several different manufacturing methods. In a preferred embodiment comprising oriented sheets, the coextrusion, quenching, orienting, and heat setting of the element may be effected by any process which is known in the art for producing oriented sheet, such as by a flat sheet process or a bubble or tubular process. The flat sheet process involves extruding the blend through a slit die and rapidly quenching the extruded web upon a chilled casting drum so that the core component of the element, especially foam, and the polymeric integral stiffening flange components are quenched below their solidification temperature. The stiffening flange components may be extruded through a multiple stream die. In a preferred embodiment utilizing a foam core, the outer stiffening flange forming polymer streams may not contain foaming agent or, alternatively, the surface of the foaming agent containing polymer may be cooled to prevent surface foaming and form a stiffening flange. The quenched sheet is then biaxially oriented by stretching in mutually perpendicular directions at a temperature above the glass transition temperature and below the melting temperature of the matrix polymers. The sheet may be stretched in one direction and then in a second direction or may be simultaneously stretched in both directions. After the sheet has been stretched, it is heat set by heating to a temperature sufficient to crystallize or anneal the polymers while restraining, to some degree, the sheet against retraction in both directions of stretching.

The element or member of the invention may also be manufactured through a three-stage process that may, but is not limited to, be in a single, in-line manufacturing process. In the case of a foam core, the first stage of this process involves the creation of a foamed sheet at a density reduction of between 1% and 30% or, alternatively, percent of solid density of between 99% and 70%. The next stage of this process involves the orientation and voiding of this foamed sheet to further reduce the density of the sheet. After the second stage the density reduction achieved is between 30% and 70% or, alternatively, percent of solid density of between 70% and 30% of the original formulation. The final stage of this process involves the addition of stiffening flange layers to the reduced density sheet. This may be done through extrusion coating or through extrusion lamination operations. In addition, surface skin layers for smoothness, primer coats for adhesion, and the like, may be used as needed.

If voiding is part of the manufacturing process a necessary component of the core materials is an incompatible phase that may be of inorganic (glass, ceramic, mineral, metal salt) or organic (polymeric, fibrous) origin. This component is important for further density reduction through voiding during the orientation process. Other solid phases may also be present in the core in the form of fillers that are of organic (polymeric, fibrous) or inorganic (glass, ceramic, metal) origin. This material is a void initiator. The void-initiating particles which remain in the finished packaging sheet core should be from 0.1 to 10 .mu.m in diameter, preferably round in shape, to produce voids of the desired shape and size. The size of the void is also dependent on the degree of orientation in the machine and transverse directions. Ideally, the void would assume a shape which is defined by two opposed and edge contacting concave disks. In other words, the voids tend to have a lens-like or biconvex shape. The voids are oriented so that the two major dimensions are aligned with the machine and transverse directions of the sheet. The Z-direction axis is a minor dimension and is roughly the size of the cross diameter of the voiding particle. The voids generally tend to be closed cells, and thus there is virtually no path open from one side of the voided-core to the other side through which gas or liquid can traverse. The voids can be tailored to favor open cells for imaging techniques where a porous element or member is desired. During the orientation process, it is also likely that cells that may have been formed during an optional foaming process are further stretched, increasing the density reduction, or alternatively, further reducing percent of solid density.

The void-initiating material may be selected from a variety of materials, and should be present in an amount of about 5-70% by weight based on the weight of the core matrix polymer. Preferably, the void-initiating material comprises a polymeric material. When a polymeric material is used, it may be a polymer that can be melt-mixed with the polymer from which the core matrix is made and be able to form dispersed spherical particles as the suspension is cooled down. Examples of this would include nylon dispersed in polypropylene, polybutylene terephthalate in polypropylene, polystyrene in polypropylene, or polypropylene dispersed in polyethylene terephthalate.

If the polymer is preshaped and blended into the matrix polymer, the important characteristic is the size and shape of the particles. Spheres are preferred and they can be hollow or solid. These spheres may be made from cross-linked polymers which are members selected from the group consisting of an alkenyl aromatic compound having the general formula Ar--C(R).dbd.CH.sub.2, wherein Ar represents an aromatic hydrocarbon radical, or an aromatic halohydrocarbon radical of the benzene series and R is hydrogen or the methyl radical, acrylate-type monomers include monomers of the formula CH.sub.2.dbd.C(R')--C(O)(OR) wherein R is selected from the group consisting of hydrogen and an alkyl radical containing from about 1 to 12 carbon atoms and R' is selected from the group consisting of hydrogen and methyl, copolymers of vinyl chloride and vinylidene chloride, acrylonitrile and vinyl chloride, vinyl bromide, vinyl esters having formula CH.sub.2.dbd.CH(O)COR, wherein R is an alkyl radical containing from 2 to 18 carbon atoms, acrylic acid, methacrylic acid, itaconic acid, citraconic acid, maleic acid, fumaric acid, oleic acid, vinylbenzoic acid, the synthetic polyester resins which are prepared by reacting terephthalic acid and dialkyl terephthalics or ester-forming derivatives thereof, with a glycol of the series HO(CH.sub.2).sub.n OH wherein n is a whole number within the range of 2-10 and having reactive olefinic linkages within the polymer molecule, the above described polyesters which include copolymerized therein up to 20 percent by weight of a second acid or ester thereof having reactive olefinic unsaturation and mixtures thereof, and a cross-linking agent selected from the group consisting of divinylbenzene, diethylene glycol dimethacrylate, diallyl fumarate, diallyl phthalate and mixtures thereof.

Examples of typical monomers for making the crosslinked polymer include styrene, butyl acrylate, acrylamide, acrylonitrile, methyl methacrylate, ethylene glycol dimethacrylate, vinyl pyridine, vinyl acetate, methyl acrylate, vinylbenzyl chloride, vinylidene chloride, acrylic acid, divinylbenzene, acrylamidomethylpropane sulfonic acid, vinyl toluene, and the like. Preferably, the