Radiation imagery chemistry: process – composition – or product th – Thermographic process – Heat applied before imaging
Reexamination Certificate
2002-10-24
2004-05-18
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Thermographic process
Heat applied before imaging
C430S496000, C430S533000, C264S173150, C264S173160, C264S210700, C428S480000
Reexamination Certificate
active
06737226
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for making a polyester photographic film base having improved properties. More particularly, the invention relates to a process involving heat-setting a biaxially stretched CHDM-containing PET-based photographic film base having improved properties with regard to cutting, chopping, and perforating.
BACKGROUND OF THE INVENTION
Poly(ethylene terephthalate) (PET) films exhibit excellent properties for use as photographic film base with regard to transparency, dimensional stability, mechanical strength, and resistance to thermal deformation. However, PET films are extremely tough and not well suited for finishing operations, i.e., slitting, chopping, and perforating processes, which are required in the preparation of photographic films. Moreover, such films are not well suited for cutting processes in various photofinishing steps such as notching, splicing, and sleeving.
Several polyester-based materials with improved cutting characteristics were proposed for use as photographic film base materials in commonly assigned copending U.S. Ser. No. 10/036,668, now U.S. Pat. No. 6,558,884, and U.S. Ser. No. 10/027,023, now U.S. Pat. No. 6,555,303, hereby incorporated by reference in their entirety. This improvement was accomplished through incorporation of 1,4-cyclohexane dimethanol (CHDM) either by copolymerization as a glycol comonomer or by blending with CHDM-containing copolyesters. Although significant improvement in cutting performance has been shown with these PET-modified polyesters, further improvement may be needed to meet the stringent requirements of certain cutting steps in photofinishing operations.
The process for making a polyester-based photographic film base typically comprises the steps of casting a molten polyester resin in a machine direction onto a casting surface to form a continuous sheet, drafting the sheet by stretching in the machine direction, tentering the sheet by stretching in the transverse direction, heat-setting the drafted and tentered sheet, and cooling the heat-set sheet to form a stretched, heat-set film, such as described in, e.g., U.S. Pat. No. 4,141,735, the disclosure of which is incorporated by reference herein. U.S. Pat. Nos. 5,385,704 and 5,607,826 disclose a method for improving the finishing characteristics of photographic materials employing a PET film base involving lowering the planar birefringence of the film base to below 0.150 by performing a detentering step which allows the tentered film to shrink in width by 2 to 20% (pref. 10-18%) after the heat-setting step during film manufacturing. Improvement in finishing characteristics of PET-based photographic film, as manifested by decrease in dirt and debris generated during finishing operations, is also disclosed in U.S. Pat. No. 6,228,569 and U.S. Ser. No. 09/223,876 hereby incorporated by reference in their entirety. These latter inventions disclose a method utilizing relatively high heat-set temperatures (>220° C.) applied during the film manufacturing process, which substantially improves the finishing and cutting characteristics of PET-based photographic supports. However, even with the demonstrated improvements in finishability, the PET-based film is still difficult to cut in various steps of the photofinishing process. Furthermore, applying this method to the manufacture of high-CHDM PET-based photographic film base does not provide the desired improvement in cutting and finishing characteristics. Therefore, a clear need exists to further improve the cutting characteristics of high-CHDM PET-based photographic supports.
U.S. Pat. No. 5,034,263 to Maier et al. disclosed a laminated film comprising a PET core and, on at least one surface thereof, an overcoat of a poly(1,4-cyclohexylene dimethylene terephthalate) polyester, in order to allow the laminated film to be readily slit and perforated using techniques commonly employed with consumer photographic film. Maier et al. states that the CHDM component should comprise at least 70 mol % of the glycol component of the polyester. However, such laminates have been found prone to delamination.
U.S. Pat. No. 5,925,507 to Massa et al. discloses a PET film-base material having less tendency to core set, comprising polyester containing at least 30 weight % CHDM, which polyester is blended with a polycarbonate that contains bisphenol. U.S. Pat. No. 4,141,735 to Schrader et al. discloses a polyester film base having improved core-set curl, involving the use of heat tempering, in one example using poly(1,4-cyclohexylene dimethylene terephthalate). However, this polymer crystallizes rapidly, therefore, the making of its oriented film is difficult. Also, the polymer becomes opaque or hazy and useless for photographic applications where transparency is required.
The blending or copolymerizing of conventional polyester with other polyester constituents, in order to improve the cutting performance of a film, has also been proposed for poly(ethylene naphthalate) (PEN)-based polyester films, as disclosed in U.S. Pat. No. 6,232,054 B1 to Okutu et al. However, PEN is generally considerably more costly and more difficult to manufacture than PET, so a clear need exists for improving the cuttability of PET-based polyester supports.
Outside the photographic field, PET and PEN are valuable commercial semi-crystalline polyesters, which are widely used for packaging materials due to the combination of desirable properties that they possess. The high oxygen barrier properties of these polyesters render them particularly valuable for packaging oxygen-sensitive food and other goods and materials. PEN has advantages over PET due to its higher Tg and higher oxygen barrier properties, although PEN, as mentioned above, is considerably more costly and is somewhat harder to process than PET.
The toughness and cutting difficulty of PET and similar polyesters is generally attributed to the crystal structure and molecular orientation of the film. It is known that changes in these factors, driven either by formulary changes or by modified process conditions, can be used to lower the toughness and improve the cutting performance of PET. Generally, the crystallinity of PET can be lowered or altogether eliminated by adding suitable crystallization modifiers. Crystallization modifiers like isophthalic acid (IPA) and CHDM are often copolymerized into PET and PEN polyesters to form copolyesters that have better processing properties. Modest levels of IPA slow down crystallization and raise the oxygen barrier properties. Higher levels of IPA break up crystallinity and lead to amorphous copolyesters with good barrier properties, but these copolyesters, are known to those skilled in the art, to possess poor impact and other mechanical properties. Modest levels of CHDM also slow down crystallization, but decrease oxygen barrier properties. Higher levels of CHDM are well known to form families of amorphous copolyesters, which are widely used in commerce in a multitude of applications including heavy gauge sheet, signage, medical packages, etc. These copolyesters have excellent impact resistance and other mechanical properties, but have lower oxygen barrier properties than IPA-modified copolyesters and lower oxygen barrier properties than PET.
Photographic film requires a strict control of the thickness uniformity and surface flatness. One method of control is through stretching of a polymer sheet into a semi-crystalline state. For CHDM-modified polyester, only when the concentration of CHDM-comonomer units relative to total glycol content is less than about 30 mol % or greater than about 65 mol % is the resulting polyester crystalline. For materials in which the content is less than about 30 mol %, however, the material does not become sufficiently crystalline for dimensional stability and thickness uniformity until the concentration of CHDM comonomer relative to total glycol content is less than 25 mol %. Amorphous polyester film or insufficiently crystalline film presents dimensional stability and thickness uniformity pro
Brickey Michael R.
Greener Jehuda
Rao Yuanqiao
Eastman Kodak Company
Konkol Chris P.
Schilling Richard L.
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