Pregnancy in animals such as the pig usually does not continue to term when there are only a few embryos in the uterus. Currently available technology for maintaining pregnancy involves a series of hormone injections, and the failure rate is high. It has now been discovered that pregnancy can be maintained by complementing fertile embryos in the uterus with additional embryos that aren""t expected to survive the full term of the pregnancy. Particularly suitable are parthenogenetic embryos, formed by activating and diploidizing unfertilized oocytes. The carrier embryos are engrafted into the uterus of a surrogate female, and the pregnancy continues to term without further interventionxe2x80x94even if the number of fertile embryos are below the minimum litter size. This provides valuable biological material that can be used for transplantation, the production of pharmaceuticals, and for agricultural use.

This application claims priority under 35 USC xc2xa7119(a) to an application with the same title filed in the UK Patent Office on Mar. 24, 2000.
This invention relates generally to the field of embryo transfer. More particularly, it relates to factors that allow pregnancy to reach term following artificial engraftment of a fertile embryo in animal species such as ungulates.
There are now a variety of powerful techniques for developing new artificial strains of animals. These strains hold considerable promise for producing biological material for use in human and veterinary medicine, research, and agriculture.
Many of these techniques involve embryo transfer, in which a fertile embryo is engrafted into the uterus of a surrogate host. Pregnancy is a complex physiological transformation involving a number of signaling events, some of which emanate from the embryos in utero. In some species, a plurality of embryos must be present in order for pregnancy to be maintained. If less than the critical number of embryos is present, the corpora lutea regress and the embryos are not carried to term. When artificial embryo transfer is employed to initiate pregnancy in these species, it is often too difficult or too costly to transfer enough embryos for the pregnancy to be viable.
The estrous cycle of the sow is reviewed in the following publications: I. Gordon, pp. 60-76 in xe2x80x9cControlled Reproduction in Pigsxe2x80x9d Vol. 3, CAB International, 1997; P. Dziuk et al., pp. 471-489 in xe2x80x9cReproduction in Domestic Animalsxe2x80x9d, 4th ed. P. T. Cupps, Academic Press Inc., 1991; R. D. Geisert et al., J. Reprod. Fert., Suppl. 40:293-305, 1990; and W. W. Thatcher et al., J. Animal Sci. 62 (suppl. 2):25-46, 1986.
Pigs normally deliver a litter of about 11 piglets. Following fertilization, a dialogue between endometrial epithelium and trophectoderm of the developing conceptus is important for pregnancy to be maintained. The normal reproductive cycle lasts 21 days, and unless specific signals are received the uterus secretes prostaglandin into the circulation 15 days after ovulation. This causes the corpora lutea (formed from follicles after they have ovulated) to regress, allowing the development of another group of follicles that grow to a pre-ovulatory size by day 21. The follicles release estrogen, which causes a surge in luteonizing hormone, triggering ovulation and starting the whole cycle over again.
If the eggs released by the follicles are successfully fertilized, they migrate around the uterus of the pig, and by 10-11 days are evenly spaced throughout the tract. The growing embryos provide signals that act locally or systemically. One such signal (thought to be mediated by estrogen) redirects secretion of prostaglandin from uterine cells to within the lumen of the uterus. This prevents regression of the corpora lutea, which in turn maintains raised levels of progesterone, preventing resumption of the estrus cycle and allowing the pregnancy to continue.
If there are not embryos occupying about 50% of the uterus before day 10 of the cycle, then the corpora lutea regresses and the estrus cycle is resumed. The critical number of embryos for maintaining pregnancy in the pig is about 3-4. However, if all the embryos are removed from one of the two horns after day 15, pregnancy is still successfully maintained to term (Dziuk et al., supra).
Current methods for artificially maintaining pregnancy typically rely on administering hormones that mimic the signals released by embryos or artificially maintain progesterone levels, preventing resumption of the estrous cycle.
Spies et al. (J. Anim. Sci. 19:114, 1960) conducted studies to determine the hormonal requirements for maintaining pregnancy in swine. Subcutaneous injections of progesterone and estrone were started 72 hours after breeding with a fertile bore. The percentages of embryo survival and the numbers of live embryos per pregnant gilt were significantly less for the treated animals than for the untreated controls.
Ellicott et al. (Biol. Reprod. 9:300, 1973a) conducted studies to measure the minimum quantity of estrogen and progesterone necessary to maintain pregnancy. Gilts were bred artificially or naturally on the first day of estrus, and ovariectomized under halothane anesthesia. Hormone was administered by inserting silicone capsules in the abdominal cavity. Pregnancy was maintained at a progesterone dose as low as 28.6 mg/day, and there was no added benefit of including 5 xcexcg estradiol. No ovarian estrogen was necessary after day 10. A concentration of 4 ng/mL of progesterone in peripheral plasma appeared to be the minimum to maintain pregnancy.
Ellicott et al. (J. Animal Sci. 37:971, 1973b) studied the effects of various hormone combinations on the induction of an accessory set of corpora lutea for maintaining pregnancy. A significantly higher proportion of inseminated gilts were pregnant at day 30 when treated with estrogen-progestogen combinations. Oral administration of 200 xcexcg melengestrol acetate and 1 mg estradiol on day 12 resulted in pregnancy in 4 out of 10 inseminated gilts. Five gilts pregnant at day 60 were removed from treatment, and two of these farrowed 5-6 piglets to term.
Christenson et al. (J. Animal Sci. 32:282, 1971) studied the maintenance of unilateral pregnancy in the pig with induced corpora lutea. The gilts were injected with pregnant mare serum and human chorionic gonadotrophin prior to the 11th day of pregnancy to induce a second set of corpora lutea. This increased the percentage of gilts with a non-pregnant uterine horn that maintained pregnancy to 25-37 days of gestation.
U.S. Pat. No. 5,366,888 reports enhanced maintenance of pregnancy using leukemia inhibitory factor (LIF) in embryo culturing. Following introduction into foster mothers of embryos cultured in vitro in the presence of LIF, the maintenance of pregnancy is enhanced relative to that seen following introduction of embryos that had not been cultured with LIF. Embryos cultured in a medium optimally containing 1000-5000 units/mL of LIF is proposed to help maintain pregnancy in sheep.
In practice, administering hormones to a surrogate mother has a sub-optimal success rate in maintaining pregnancy in animals that have received an embryo transfer. In the laboratory where the present invention was made, the best treatment regime involving hormones alone was found to maintain pregnancy in only 26% of treated pigs. Embryos were also transferred into pigs that have already been mated. In these experiments, 37% of the pigs carried the transferred embryos. However, ultrasound at day 35 is unable to distinguish the transferred embryos from the embryos resulting from inseminationxe2x80x94so it was not possible to determine which of the females were carrying the high value transferred embryos.
In view of the limitations of currently available technology, there is a pressing need to develop new artificial methods to maintain pregnancy.
This invention provides a technique for maintaining pregnancy in a female to which a fertile embryo has been transferred. The technique involves placing additional infertile embryos into the uterus, which have the effect of generating signals that allow the pregnancy to continue. The additional embryos typically maintain pregnancy through the early critical period, and then are reabsorbed or otherwise eliminated before the end of term. This allows viability of the engrafted fertile embryos to be monitored later in pregnancy, and helps avoid overcrowding of the uterus.
Embodiments of this invention include methods for maintaining pregnancy in a female pregnant with one or more fertile embryos, by engrafting into the uterus of the female one or more infertile embryos, thereby allowing the pregnancy to reach term, or at least until the fertile embryo is at a stage that it is viable ex utero. Also embodied in the invention are pregnant animals and birthed animals that result from the application of such methods.
The female is treated according to the invention generally because she is at risk of not carrying the fertile embryo to term due to potential lack of a signal that is usually required to maintain pregnancy. This can be caused, for example, because a signal produced by the embryo for maintaining pregnancy is missing or defective, because there is a problem in signal transduction, or because there is an insufficient number of embryos to provide adequate signal. In certain species, the viability of the pregnancy depends on the number of embryos in the uterus, such as an ungulate like the domestic swine.
The fertile embryo can be present in the uterus of the pregnant animal as a result of mating or embryo transfer. The infertile embryos can be engrafted simultaneously with the fertile embryo, or at an earlier or later time, typically early enough during the pregnancy to prevent regression of the corpora lutea. Depending on the period of pregnancy for the species being treated, the infertile embryos continue to develop in utero until at least about the 15th day of gestation. They are typically eliminated before the pregnancy reaches term, which may help prevent overcrowding. Progress of fertile and infertile embryos can be monitored if desired by diagnostic techniques such as ultrasound.
Exemplary infertile embryos are parthenogenetic embryos made, for example, by diploidizing and activating an oocyte of the same species as the female. Other infertile embryos suitable for use in this invention are cells with abnormal ploidy, such as polyspermic embryos. Sometimes, at least five, ten, twenty, or even more infertile embryos are engrafted into the uterus so that a high enough number will last through the critical period.
In particular embodiments of this invention, at least one of the fertile embryos has grown from a cell produced by transfer of a cell nucleus obtained from a first individual to an oocyte of a second individual with a different genotype from that of the first. The fertile embryos can be grown from a cell produced by transfer of a cell nucleus containing DNA that has been genetically altered into an oocyte. In some embodiments, chromosomal DNA in the embryonic cell has been genetically altered to express a heterologous gene, and/or altered to prevent expression of a gene that would otherwise be expressed.
Particular embodiments of this invention are methods for maintaining pregnancy in a pig, comprising engrafting the pig with one or more fertile embryos containing chromosomal DNA that has been genetically altered, plus one or more parthenogenetic embryos, whereby the number of fertile embryos and parthenogenetic embryos is sufficient to prevent regression of the corpora lutea, thereby allowing the pregnancy to reach term. Also embodied is a pig pregnant with one or more fertile embryos containing chromosomal DNA that has been genetically altered, plus one or more parthenogenetic embryos.
Further embodiments of this invention are methods for producing a mammal with chromosomal DNA that has been genetically altered by artificially engrafting into the uterus of a female a fertile embryo containing nuclear DNA that has been genetically altered, so that the female becomes pregnant with the embryo; artificially engralting into the uterus of the female one or more infertile embryo(s) before, after or at the same time as the fertile embryo; and then birthing a mammal from said female that results from intrauterine development of the fertile embryo. Also embodied is a mammal having chromosomal DNA that has been genetically altered, produced according to a method of this invention.
Yet another embodiment of this invention is a method for producing a protein (optionally a human protein), which involves maintaining pregnancy in a female according to a method of this invention, wherein a fertile embryo in the female comprises an expressible gene encoding the protein; harvesting biological material from the birthed animal or its progeny (either solid tissue or a biological fluid, such as milk); and using the material to purify the protein. Another embodiment of the invention is a method for producing tissue suitable for transplantation (for example, into a human), which involves maintaining pregnancy in a female, wherein the chromosomal DNA of a fertile embryo has been genetically altered to inactivate a gene that encodes an antigen or encodes a protein that creates an antigen that is xenogeneic to the transplant recipient (such as Galxcex1(1,3)Gal); and harvesting tissue from the birthed animal or its progeny. Also embodied in the invention are proteins, biological material, and tissues obtained according to such methods.
These and other embodiments of the invention will be apparent from the description that follows.
It has been discovered that pregnancy can be maintained by complementing fertile embryos in the uterus with additional embryos that usually do not survive the full term of the pregnancy. Using this technique, valuable embryos can be reliably developed in utero, in litters that are below the usual minimum size for the species being used.
Particularly suitable as infertile carrier embryos are parthenogenetic embryos, formed from an oocyte without fertilization by a male. For example, matured pig oocytes are activated using electrical pulses, and then diploidized using cytochalasin B. The carrier embryos are then placed in the uterus of a synchronized female along with the fertile embryo, and the pregnancy continues to term without the necessity for further intervention. This provides biological tissue that can be used for a number of valuable purposes, including agriculture and veterinary use, transplantation, and the production of pharmaceuticals on a commercial scale.
The term xe2x80x9cembryoxe2x80x9d as it is used in this disclosure refers to an organism developing in the uterus of a species of interest at any time after fertilization or intrauterine transfer, not limited to a particular developmental period.
A xe2x80x9cfertile embryoxe2x80x9d is an embryo with a diploid genotype that is capable of producing a viable neonate of the respective animal species.
An xe2x80x9cinfertile embryoxe2x80x9d or xe2x80x9ccarrier embryoxe2x80x9d is an embryo that is typically incapable of surviving the full term of pregnancy without intervention. Exemplary is a parthenogenetic embryo, usually (but not necessarily) of diploid genotype, produced from a female gamete without any genetic contribution from a male gamete. Other types of embryos that can meet this definition comprise cells that are haploid, triploid, tetraploid, or have any other abnormal ploidy. This includes embryos that are mosaic of different ploidy, such as a mosaic of diploid and tetraploid cells.
An xe2x80x9cembryonic cellxe2x80x9d is either a single cell or a particular member of a group of cells, wherein either the single cell or the group of cells as a whole is capable of developing into an embryo in utero. The term includes but is not limited to a fertilized oocyte, a chimeric cell created by transfer of a nucleus from a donor cell into an enucleated oocyte or other embryonic cell, a particular cell present in a developing embryo, or a particular cell present in a mass of cells cultured in vitro for engraftment in utero.
The terms xe2x80x9cengraftingxe2x80x9d or xe2x80x9ctransplantingxe2x80x9d, in reference to embryo manipulation, refer to any process known in the art for artificially introducing one or more embryos into the uterus (including the uterine horns) of a female animal. The engrafted embryo or blastocyst can be fertile or infertile; it may or may not become implanted to the endometrium, and may or may not give rise to a viable neonate.
A cell is said to be xe2x80x9cgenetically alteredxe2x80x9d when genetic material such as a polynucleotide has been introduced into it. The definition also includes the progeny of a cell so altered that has inherited the introduced polynucleotide, or a copy thereof. The polynucleotide may contain a sequence that is exogenous to the cell, it may contain native sequences in an artificial arrangement (e.g., an encoding region linked to a different promoter), or it may provide additional copies of a native encoding sequence. The polynucleotide can be introduced by transfection using electroporation or liposome-mediated transfer, homologous recombination, transduction using a viral vector, any combination thereof, or any other technique known in the art. The polynucleotide will often comprise a transcribable sequence encoding a protein of interest, which enables the cell to express the protein at an elevated level. In the context of the present application, a xe2x80x9cgenetically altered cellxe2x80x9d has a genetic alteration that is inheritable by progeny of the cell. For example, an embryo having genetically altered DNA, if carried to term, will give rise to a neonate that has cells containing the genetic alteration.
xe2x80x9cBiological materialxe2x80x9d refers to any material obtained from a biological organism. Biological material obtained from a mammal can include biological fluids, such as milk, plasma, serum, lymph, saliva, and urine. It can also include solid material, such as cells in a particular organ, and fluid extracts of such material.
An xe2x80x9cexpressible genexe2x80x9d is a nucleotide sequence in chromosomal DNA operatively liked to transcription control elements that permit it to be transcribed into RNA in a particular cell or organism. Genes that encode a protein sequence of interest are also typically linked to translation control elements, such that the RNA transcription can be translated inside the cell into the protein.
xe2x80x9cOperatively linkedxe2x80x9d refers to relationship between genetic elements in which the function of one element influences the function of another element. For example, an expressible encoding sequence is operatively linked to control elements such as promoters and enhancers that permit transcription, and typically to control elements such as translation initiation sequences, stop codons, and signals for polyadenylation.
Unless otherwise noted, the practice of this invention can be carried out by employing standard techniques of genetic engineering, protein manipulation, and cell culture. Textbooks that describe standard laboratory techniques include xe2x80x9cMolecular Cloning: A Laboratory Manualxe2x80x9d, 2nd Ed. (Sambrook et al., 1989); xe2x80x9cOligonucleotide Synthesisxe2x80x9d (M. J. Gait, ed., 1984); xe2x80x9cAnimal Cell Culturexe2x80x9d (R. I. Freshney, ed., 1987); the series xe2x80x9cMethods in Enzymologyxe2x80x9d (Academic Press, Inc.); xe2x80x9cGene Transfer Vectors for Mammalian Cellsxe2x80x9d (J. M. Miller and M. P. Calos, eds., 1987); xe2x80x9cCurrent Protocols in Molecular Biologyxe2x80x9d and xe2x80x9cShort Protocols in Molecular Biology, 3rd Editionxe2x80x9d (F. M. Ausubel et al., eds., 1987 and 1995); and xe2x80x9cRecombinant DNA Methodology IIxe2x80x9d (R. Wu ed., Academic Press 1995).
Texts that describe reproductive techniques and embryo transfer in animals include xe2x80x9cControlled Reproduction in Pigsxe2x80x9d Vol. 3 (I. Gordon, CAB International, 1997); xe2x80x9cManual of the International Embryo Transfer Society: A procedural guide and general information for the use of embryo transfer technology emphasizing sanitary proceduresxe2x80x9d, 3rd ed. (Stringfellow et al., Savoy, Ill.: International Embryo Transfer Society, Savoy Ill.); xe2x80x9cEmbryo transfer in farm animals: A review of techniques and applicationsxe2x80x9d (K. J. Betteridge, ed., Agriculture Canada Monographs No. 16, Ottawa, 1977).
This invention provides for the maintenance of pregnancy in any species wherein the viability of pregnancy depends in part on one or more signals provided by the embryoxe2x80x94either a molecular signal, such as the secretion of a hormone, or a physical signal, such as a volume or mass change detectable by the pregnant female. The invention can be implemented, when the embryo(s) which it is desired to carry to term are believed to be inadequate in providing such signals.
In one illustration, an embryo is somehow defective in providing adequate signal that is usually provided by embryos of the species in question, perhaps because of a genetic abnormality or some other disturbance that interferes with generation of the signal, or transduction of the signal into the host. In another illustration, ongoing pregnancy requires signal to be provided by a plurality of embryos in the uterus, and maintenance of pregnancy is positively correlated with the number of embryos in the uterus. Where the number of fertile embryos present is less than what is usually required, then the probability of maintaining pregnancy can be enhanced by implementing the techniques of this invention. In general terms, the invention is applicable to all mammals without limitation. The strategy can be employed in human and veterinary medicine, and for research purposes. In particular embodiments, the invention is practiced on ungulates including but not limited to Artiodactyla, including ruminants and suids, which in turn are exemplified by Suidae, particularly the domestic swine. In another embodiment, the invention is practiced on rodents (including mice and rats) that also give birth to large litters, and generally require a minimum number of embryos to maintain pregnancy.
The technique involves engrafting a female with one or more infertile embryo(s) at a time when the female is pregnant with one or more fertile embryo(s) of about the same age, from which it is desired to produce viable neonates. The combination of fertile and infertile embryos provides a situation in which sufficient signals are provided to promote maintenance of the pregnancy, and maturation of a valuable embryo. Typically, the combined signals prevent regression of the corpora lutea, which would otherwise indicate termination of the pregnancy and resumption of the estrous cycle.
The infertile embryos are generally selected to remain viable at least through the critical period for maintaining the corpora lutea in the species of interest (about the 15th day of pregnancy in the pig), but then to be reabsorbed or expelled before the pregnancy reaches term, which may help prevent overcrowding. In the pig, it is typically preferable for the infertile embryos to be reabsorbed, expelled, or otherwise eliminated by about the 30th day, in order to avoid the risk of overcrowding of the uterus as the embryos grow. For many large animal agricultural species, the infertile embryos remain in the female for 10, 15, 20, or 25 days, selected at least to exceed the critical period, and are eliminated by the 5th, 4th, 3rd or 2nd month, in order of increasing preference. It will be recognized that species that have substantially shorter gestation periods will require scaling down of this time frame appropriately. More generally, the infertile embryos remain in the female for 5%, 10%, or 15% of the full term of pregnancy, but are eliminated before 80%, 60%, or 40% of term, as appropriate.
An exemplary type of infertile embryo is the parthenogenetic embryo. Mammalian oocytes can be parthenogenetically activated by a variety of physical and chemical stimuli, reviewed in D. C. Whittingham, pp. 205-231 of xe2x80x9cParthenogenesis in mammalsxe2x80x9d, ed. C. A. Finn, Oxford Rev. Reprod. Biol. Vol. 2, Clarendon Press, Oxford, 1980. Any technique in the art for activating oocytes may be suitable, providing the oocytes are activated to divide without fertilization.
Effective physical stimuli include mechanical manipulation, thermal changes, or electrical stimulation. Effective chemical stimuli include osmotic or ionic changes (divalent cations or calcium ionophores), or enzymatic challenge (Wang et al., Biol. Reprod. 58:1357, 1998). U.S. Pat. No. 5,496,720 outlines a process for parthenogenetic activation of bovine oocytes by increasing intracellular levels of divalent cations, and reducing phosphorylation of cellular proteins, for example a serine-threonine kinase inhibitor. Protein synthesis inhibitors, such as puromycin and cyclohexamide can be effective (Siracusa et al., J. Embryol. Exp. Morphol. 43:157, 1978). Chemicals that stimulate the G protein/phospholipase C cascade (IP3, GTP-G-S) have also successfully activated oocytes (Machaty et al., Biol. Reprod. 52:753, 1995; Busa et al., J. Cell Biol. 101:677, 1984). Oocytes can also be activated by electrical pulses. Factors affecting electrical activation in vitro are reported by Liu et al. (Anim. Reprod. Sci. 48:67, 1997).
Loi et al. (Biol. Reprod. 58:1177, 1998) compare different activation protocols and the subsequent rates of embryonic development in the sheep. Combinations of chemical activators induced pronuclear development at a slightly higher rate than physical activation. lonomycin plus 6-dimethylaminopurine (6-DMAP) were used to produce parthenogenetic blastocysts that were transferred into previously synchronized ewes. Over 70% of the parthenogenotes were viable on day 21 of pregnancy, but dead by day 25.
Joliff et al. (Biol. Reprod. 56:544, 1997) report the development of parthenogenetically activated oocytes from the pig. Oocytes were matured in vitro, and then stimulated with an electric pulse at 36-48 hours. Electrically stimulated oocytes were transferred to the oviduct of a synchronous gilt and developed the to the filamentous stage (containing an intact embryonic disc, 10% development beyond the blastocyst stage) at 14 days after activation.
Parthenogenetic embryos for use in this invention can be produced using oocytes from whole ovaries. Follicular fluid is aspirated, and used as a source of cumulus-oocyte complexes. The complexes are typically matured for about 2 days in a suitable maturation medium, such as Waymoth""s medium, typically supplemented with eCG and/or hCG and other factors that enhance maturation (Jolliff et al., supra). Also suitable are recently ovulated oocytes obtained from females by surgical or mechanical extraction of their oviducts (Loi et al., supra). Ovulated oocytes typically do not need to be matured in the same fashion as complexes extracted from ovaries. Oocytes prepared by either method are then activated and diploidized by appropriate methods.
An exemplary method for maturing oocytes in vivo is conducted as follows. Follicles about 3-8 mm in size are selected from ovaries of recently killed animals, and an oocyte complex is aspirated from a selected follicle. The oocyte complex is cultured for about 36-48 hours in a suitable medium, such as described by Wang et al. (J. Reprod. Fertil. 111:101, 1997). Oocytes matured in vitro are denuded of cumulus (either manually, or by treating with a suitable protease, such as 600 IU/mL hyluronidase). Oocytes matured under these conditions have improved competence for development into parthenogenetic embryos.
Oocytes can also be collected from live donors by surgical procedures or flushing the fallopian tubes with medium. The developmental competence can be improved by harvesting the oocytes about 42-50 hours after injecting gonadotropin in a sufficient dose to induce superovulation. Effective hormones with gonadotrophic activity include pregnant mares serum gonadotropin (PMSG), hCG, equine chorionic gonadotropin (eCG), and gonadotropin releasing hormone. Optionally, two separate administrations can be performed. For example, PMSG is injected first towards the end of the diurnal rhythm of the animal to recruit follicles to be ovulated, and hCG is injected xcx9c88 hours later to induce ovulation and maturation of the oocyte. The mature oocyte is then harvested xcx9c46 hours later to prepare infertile embryos for use in this invention. Further information on the maturation of oocytes both in vitro and in vivo can be obtained from International Patent Application PCT/GB99/03384.
An exemplary method for producing parthenogenetic embryos from domestic swine proceeds as follows: Oocytes are optimally matured in vitro or in vivo, according to the procedures just described. They are then activated electrically by an optimized protocol. For example, matured pig oocytes are activated by pulses of 5 secxc3x975 Volts AC, 3xc3x9780 xcexcsec pulses of 1 kiloVolts/cm (20 Volts/200 xcexcm) DC in 0.3 M mannitol, 50 xcexcM CaCl2, 100 xcexcM MgCl2. The activated oocytes are then diploidized by culturing in 7.5 xcexcg/mL cytochalasin B in NCSU23 medium for 6-8 h at 38.5xc2x0 C., 5% CO2 in air. The oocytes are then cultured overnight in NCSU23 until transfer the next day.
In a variation of this method, cyclohexamide is added to the medium to a concentration of 10 xcexcg/mL, and the period of treatment after activation is reduced to 4 hours. After pulsing in mannitol buffer as before, the activated oocytes are diploidized by culturing in NCSU medium containing both 7.5 xcexcg/mL cytochalasin B and 10 xcexcg/mL cyclohexamide in NCSU23 medium at 38.5xc2x0 C., 5% CO2 in air, for only 4 hours. The oocytes are then cultured overnight in NCSU23 until transfer the next day.
Other types of infertile embryos are also suitable for use in this invention. Included are embryos that have a euploid genotype and have somehow been adapted so that the usual course is for it to be expelled or absorbed before the end of term. For example, an embryo may be genetically altered to not survive beyond a certain number of cell divisions, or to render them susceptible to a toxic drug that could be administered in utero. Another type of infertile embryo are embryos that have abnormal ploidy, and which, as a consequence, are unlikely to survive the full length of pregnancy. This includes embryos comprising cells that are haploid, triploid, or tetraploid, including mosaics. Such embryos can be obtained from poly-pronuclear eggs. See Han et al. (Biol. Reprod. 60:1110, 1999a) and Han et al. (Biol. Reprod. 61:1340, 1999b) regarding polyspermic pig embryos produced in vitro. Briefly, oocytes are matured if necessary, and fertilized in vitro. About 10 h after fertilization, the eggs were centrifuged at xcx9c12,000xc3x97g for xcx9c10 min, and then classified individually as to whether they are two-pronuclear (2PN) or poly-pronuclear (PPN, 3 pronuclei or more). About 53% of 2PN and 40% of PPN develop to the blastocyst stage in vitro. PPN eggs are more likely to produce fetuses that are not strictly diploid, and therefore less likely to survive the full term of pregnancy.
Suitable infertile embryos are typically maintained in culture until required for engrafting into the surrogate female.
Infertile embryos are typically engrafted in a female also engrafted with a fertile embryo, in order to increase the number of embryos in the uterus and thereby improve the probability that the fertile embryo will reach term and produce a neonate.
Fertile embryo of many different origins can be used for engrafting into the female host. Included are fertilized embryos obtained from females or inseminated as part of an in vitro fertilization technique. Using the technology of this invention, embryos from superior matings can be prepared in advance and stored frozen, then raised to term in low-numbered litters whenever desired. Also contemplated is maintaining the pregnancy of one or more fertile embryos present in the uterus through other means. For example, the female may have been made pregnant through the natural process of insemination, optionally facilitated by sildenafil citrate, or other medication, device, or environmental condition that enhances the frequency of an efficacious fertilization event.
This invention is particularly useful for the maturation of embryos that are produced in vitro by artificial manipulation of embryonic cells. For example, U.S. Pat. Nos. 5,905,042 and 5,994,619 relate to production of chimeric bovine and porcine animals using cultured inner cell masses. Of interest are embryos produced by transfer of a donor nucleus of one individual to an oocyte of another individual. International Patent Application WO 97/07669 (Roslin Institute) describes quiescent cell populations for nuclear transfer. International Patent Application WO 97/07668 (Roslin Institute) describes inactivated oocytes as cytoplast recipients for nuclear transfer. WO 99/01164 (University of Massachusetts) relates to cloning pigs using donor nuclei from differentiated cells.
Donor nuclei are obtained from a suitable donor cell, such as an in vitro manipulated embryonic cell, or an adult cell in germ-line configuration. Nuclear transfer is particularly effective if the nucleus of the donor cell is quiescent, which can be achieved by culturing the donor cell in a serum-free medium (WO 97/07669). In an exemplary method, the nucleus of a donor cell is transferred into an oocyte that is arrested in the metaphase of the second meiotic division, and subsequently activating the reconstituted cell. Briefly, unfertilized metaphase II oocytes are collected as follows: Female animals are synchronized using progestagen sponges for xcx9c14 days, and induced to superovulate with single injections of follicle-stimulating hormone on two successive days. Ovulation is induced with a suitable dose of gonadotrophin-releasing hormone or an analog thereof (e.g., xcx9c8 mg GnRH Receptal(trademark), Hoechst, UK) on the following day. The oocytes are recovered by flushing from the oviduct one day later, washed, and enucleated by treating with cytochalasin B and aspirating the nucleus using a glass pipette. Enucleated oocytes are then placed into contact with a single cell which acts as the nucleus donor.
Fusion of the donor nucleus into the enucleated recipient cell is effected by placing the couplet in a fusion chamber and aligning it between the electrodes. Electrical pulses are then applied to induce fusion, typically a low-voltage AC pulse for several seconds, followed by a plurality of very short high-voltage DC pulses. Following an incubation period, activation is induced by application of an additional electrical pulse. The reconstructed zygote is then cultured for a time before engrafting into a surrogate female. Further details and alternative procedures are described in the patent publications cited above.
In certain embodiments of the invention, the chromosomal DNA is genetically altered to express a transgene, such as a heterologous gene construct. The transgene can be inserted into the genome of the nuclear donor cell by any suitable method in the art, including (but not limited to) homologous recombination and transduction using a virus that integrates into the genome as part of its replicative cycle. U.S. Pat. No. 5,591,625 relates to the preparation stem cells capable of augmented expression of certain gene products, signal transduction molecules, and cell surface proteins for therapeutic applications. U.S. Pat. Nos. 5,573,933 and 5,942,435 report methods for preparing transgenic pigs. International Patent Application WO 97/25413 reports the use of primordial germ cells from porcine or bovine embryos for obtaining chimeric ungulates that produce pharmaceutical products.
In some of these embodiments the transgene is an expressible gene comprising a nucleotide sequence that encodes a human protein that can be recovered from a tissue sample or bodily fluid, exemplified by but not limited to plasma and milk. Optimally, the encoding region will be operatively linked to control elements that specifically permit biosynthesis and secretion of the encoded protein into the bodily fluid. Suitable are control elements for other proteins naturally secreted into milk, such as lactoferrin, casein, and whey acidic protein. U.S. Pat. No. 5,565,362 provides DNA constructs with a casein promoter and a casein enhancer region. The protein product includes a signal peptide that is functional in mammary secretory cells to facilitate translocation of the protein across the Golgi membrane and secretion of the peptide into the milk. U.S. Pat. No. 5,700,671 claims methods for making transgenic animals producing oligosaccharides or glycoproteins in the milk, wherein the transgene comprises an encoding region for a heterologous glycosyltransferase. U.S. Pat. No. 5,880,327 claims transgenic mammals that produce milk containing human Factor VIII protein.
To obtain animals producing the desired human protein, a fertile embryo containing the transgene is then engrafted into a female in estrus. For production of protein from milk, the fertile embryo is optionally preselected to be an XX genotype; alternatively, female neonates are selected after birth. The pregnancy is maintained by engrafting one or more infertile embryos, and the fertile embryo matures and is birthed from the surrogate mother. After the neonate has grown to sufficient age, the tissue or body fluid containing the protein of interest is harvested. The protein can then be purified by a suitable combination of standard protein separation techniques, including but not limited to salt precipitation, ion exchange chromatography, gel exclusion chromatography, and affinity separation. Proteins that have therapeutic value can then be formulated into a medicament, in accordance with generally accepted procedures for the preparation of pharmaceutical preparations. See Remington""s Pharmaceutical Sciences 18th Edition (1990), E. W. Martin ed., Mack Publishing Co., Pa.
In certain embodiments of the invention, the chromosomal DNA is genetically altered to prevent expression of a gene that would otherwise be expressed. For example, it is sometimes desirable to prevent expression of a histocompatibility marker or other antigen in an animal so that its tissues are transplantable to an allogeneic or xenogeneic recipient. Knock-out animals can be prepared by inactivating a gene of interest so that it is not expressed in the birthed animal. The gene can be inactivated by a number of different strategies, including altering or removing a control element (such as a promoter or a start signal for transcription or translation), or a critical part of the encoding sequence (such as the active site of an enzyme), or placing the encoding region out of phase, or by altering the specificity of the encoded protein. Any method in the art for accomplishing such disruption may be used, including but not limited to homologous recombination or directed point mutation.
In one illustration, animal tissue can be prepared without the Galxcex1(1,3)Gal xenoantigen that causes hyperacute rejection when transplanted into human recipients. The Galxcex1(1,3)Gal determinant is synthesized by a xcex1(1,3)galactosyltransferase that places galactose onto a Galxcex2(1,4)GlcNAc (N-acetyl lactosamine) acceptor present on the surface of a number of different cell types, including endothelial cells that line the vasculature of transplant tissues. Targeting constructs are designed to delete or replace one or more of the six separate exons that typically make up the xcex1(1,3)galactosyltransferase encoding region (Katayama et al., Glycoconj. J. 15:583, 1998). The constructs are used to genetically alter embryonic cells, and then cells are selected for successful targeting. To prevent formation of the Galxcex1(1,3)Gal epitope in the adult animal, it is usually necessary for the animal to be homozygous for inactivated xcex1(1,3)galactosyltransferase. This can be accomplished either by selecting for homozygous knock-outs in the embryonic cells, or by mating two animals that have inactivated xcex1(1,3)galactosyltransferase in one haplotype. See U.S. Pat. Nos. 5,849,991 and 5,821,117. The genetically altered embryonic cell is then prepared for transfer in utero as a fertile embryo.
To improve the probability that the fertile embryo will reach term and produce a neonate in an individual in need of the techniques of this invention, the surrogate female is engrafted with one or more fertile embryos, and one or more infertile embryos. The total number of embryos is chosen so as to provide an adequate signal between both the fertile embryos and the infertile embryos for the pregnancy to be maintained. Typically, it is more convenient to introduce both the fertile embryos and the infertile embryos into the uterus at the same time. On some occasions, it may be desirable to engraft the fertile embryos before the infertile embryos, or vice versa. The number of infertile embryos used depends on the signal required for maintaining pregnancy in the animal species being employed.
Estrus in the surrogate female is typically synchronized artificially using a suitable combination of inducing agents. Cameron et al. (Aust. Vet. J. 66:314, 1989) discuss synchronization methods and other practical aspects for commercial embryo transfer in pigs. Blum-Reckow et al. (J. Anim. Sci. 69:3335, 1991) report experiments relating to transfer of pig embryos after long-term in vitro culture. Replacing medium every 12 h during culture improved survival, and pregnancy rate improved if the sexual cycle of recipients was 24 h behind that of the donor.
Fertile or infertile embryos can be introduced into the uterus of the recipient female using any suitable technique, including surgical methods. For example, U.S. Pat. No. 4,326,505 describes surgical procedures for embryo transplants in animals, in which the uterine horn is positioned in the peritoneal cavity proximate to the vaginal wall, a cannula is inserted through the vaginal wall and into the uterine horn, and the embryo is introduced through the cannula. Also included are non-surgical methods, using a suitable device to manipulate the injection port through the folds of the cervix to the bifurcation of the uterus. For example, devices and techniques for porcine non-surgical embryo transfer are reported by Li et al. (J. Anim. Sci. 74:2263, 1996). Wallenhorst et al. (J. Anim. Sci. 77:2327, 1999) describe the effect of transferring pig embryos to different uterine sites.
The number of infertile embryos that are engrafted will depend on several considerations. One consideration is the manner in which the pregnancy of the fertile embryo is at risk. In species where pregnancies of a single embryo can be carried to term, but the signal for maintaining pregnancy is somehow missing from the fertile embryo, then it may be sufficient to engraft just a single infertile embryo to overcome the deficiency. Another consideration is the number of embryos typically required to maintain pregnancy in the species, which can be predicted based on the typical smallest observed litter size. In this case, the number of infertile embryos should be chosen so that the total number of embryos exceeds the minimum number. Another consideration is the nature of the infertile embryos, and the probability that they will survive through the critical period and prevent regression of the corpora lutea. The number of embryos should be adjusted to compensate for the embryos that will be lost by the end of the period. A countervailing consideration is the risk that the uterus will become overcrowded when embryos are more developed. This caps the number of infertile embryos that should be engrafted. Where the infertile embryos are not expected to last until the point where overcrowding becomes a problem, then there is more latitude for engrafting a larger number. Even where pregnancy can be maintained by a single embryo, additional infertile embryos can be engrafted to improve the probability that the valuable fertile embryo will reach term.
By way of illustration, parthenogenetic embryos generated from pig oocytes have about a 40% to 60% chance of surviving to day 7 in culture, and probably even less of surviving past day 15. To implement this invention in a female pig, at least about 3-5 infertile embryos are typically engrafted where the purpose is to support pregnancy when just a single fertile embryo, since the minimum litter size is about 4 neonates. Accommodating the expected loss before the end of the critical period, the number of infertile embryos engrafted will frequently be at least 10. Since parthenogenetic embryos generally do not survive to the point where overcrowding becomes an issue, it is acceptable to engraft an even larger number of infertile embryos to improve the probability of success. Thus, it may be suitable to engraft 20, 40, 60, or even more infertile embryos to maintain the pregnancy. An alternative strategy is to improve the probability that parthenogenetic embryos will survive the critical period. In one approach, activated oocytes are grown in culture for 7 days, and those still surviving are then be engrafted into the uterus in support of the fertile embryo, which may or may not have been cultured in vitro for a similar period.
Once the fertile and infertile embryos have been engrafted, the pregnancy is then allowed to continue to term, or at least until at least one valuable fetus is viable outside the womb. It is permissible to treat the surrogate female during the pregnancy to further improve the chances that the pregnancy will reach term: for example, with hormone injections. However, such intervention is generally not required.


The invention relates to a photographic element comprising nacreous pigment.

This invention relates to imaging materials. In a preferred form, it relates to nacreous photographic reflective paper.
Prior art reflective imaging output materials such as silver halide reflective images or ink jet reflective images typically comprise imaging layers applied to a white reflective base material. The white reflective base reflects ambient light back to the observer""s eye to form the image in the brain. Prior art base materials typically utilize white reflecting pigments such as TiO2 or barium sulfate in a polymer matrix to form a white reflective base material. Prior art reflective photographic papers also contain white pigments in the support just below the silver halide imaging layers to obtain image whiteness and sharpness during image exposure, as the white pigment reduces the amount exposure light energy scattered by the cellulose paper core. Details on the use of white pigments in highly loaded coextruded layers to obtain silver halide image sharpness and whiteness are recorded in U.S. Pat. No. 5,466,519.
It has been proposed in U.S. Pat No. 5,866,282 (Bourdelais et al) to utilize a composite support material with laminated biaxially oriented polyolefin sheets as a photographic imaging material. 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 in U.S. Pat. No. 5,866,282 have a microvoided layer in combination with coextruded layers that contain white pigments such as TiO2 above and below the microvoided layer. The composite imaging support structure described in U.S. Pat. No. 5,866,282 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.
It has been proposed in U.S. Pat. No. 6,071,680 (Bourdelais et al) to utilize a voided polyester sheet coated with light sensitive silver halide imaging layers for use as photographic output material. The voided layer in U.S. Pat. No. 6,071,680 improves opacity, image lightness, and image brightness compared to prior art polyethylene melt extrusion coated cellulose paper base materials. The image base proposed in U.S. Pat. No. 6,071,680 also contains an integral polyolefin skin layer to facilitate imaging layer adhesion at the time of manufacture and during the processing of silver halide imaging layers.
There, however, remains a continuing need for improvements to the appearance of imaging output materials. It has been shown that consumers, in addition to reflective output material, also prefer nacreous images. Nacreous images exhibit a pearly or nacreous luster, an iridescent play of colors, and a brilliant luster that appears in three dimensions. Nacreous appearance can be found in nature if one examines a pearl or the polished shell of Turbo marmoratus.
A nacreous photographic element with a microvoided sheet of opalescence is described in U.S. Pat. No. 5,888,681 (Gula et al). In U.S. Pat. No. 5,888,681 microvoided polymer sheets with microvoided polymer layer located between a cellulose paper base and developed silver halide imaging provide an image with an opalescence appearance. The nacreous appearance is created in U.S. Pat. No. 5,888,681 by providing multiple internal reflections in the voided layer of the polymer sheet. While the opalescence appearance is present in the image, the image suffers from a loss of image sharpness or acutance, a higher density minimum position, and a decrease in printing speed compared to a typical photographic image formed on a white, reflecting base. It would be desirable if the opalescent look of the image could be maintained while improving printing speed, increasing sharpness, and decreasing density minimum. Also, while the voided polymer does provide an excellent nacreous image, the voided layer, because it is pre-fractured, is subjected to permanent deformation, thus reducing the quality of the image.
In addition to the use of white pigments in reflective consumer photographs, white pigments are also utilized in photographic display materials for diffusion of illumination light source. While the use of white pigments in display materials does provide the desired diffusion and reflection properties, the white pigments tend to change the hue angle of the color dyes in a developed photographic display image. Dye hue angle is a measure in CIElab color space of that aspect of color vision that can be related to regions of the color spectrum. For color photographic systems there is a perceptual preferred dye hue angle for the yellow, magenta, and cyan dyes. It has been found that when photographic dyes are coated on support containing white pigments, the hue angle of the developed image changes compared to the hue angle of the dyes coated onto a transparent support. The hue angle change of photographic dyes caused by the presence of white pigments often reduces the perceived quality of the dyes compared to the dye set coated on a transparent base that is substantially free of white pigments. It would be desirable if a developed photographic dye set coated on a reflective support material had a dye hue angle that was not significantly different than the same dye set coated on a transparent support.
Nacreous pigments added to a matrix, such as paint or plastic, have been known to exhibit a nacreous appearance. The prior art use of the nacreous pigments have been for pigmenting paints, printing inks, plastics, cosmetics, and glazes for ceramics and glass. Nacreous pigments are dispersed in a matrix and then painted or printed onto a substrate. Pearl luster pigments containing titanium dioxide have been successfully employed for many years. They are constructed in accordance with the layer substrate principle, with mica being employed virtually without exception as substrate.
Mica pigments are used widely in the printing and coating industries, in cosmetology, and in polymer processing. They are distinguished by interference colors and a high luster. For the formation of extremely thin layers, however, mica pigments are not suitable, since the mica itself, as a substrate for the metal-oxide layers of the pigment, has a thickness of from 200 to 1200 nm. A further disadvantage is that the thickness of the mica platelets within a certain fraction defined by the platelet size in some cases varies markedly about a mean value. Moreover, mica is a naturally occurring mineral which is contaminated by foreign ions. Furthermore, technically highly complex and time-consuming processing steps are required including, in particular, grinding and classifying.
Pearl luster pigments based on thick mica platelets and coated with metal oxides have, owing to the thickness of the edge, a marked scatter fraction, especially in the case of relatively fine particle-size distributions below 20 micrometers. As a substitute for mica, it has been proposed to use thin glass flakes which are obtained by rolling a glass melt with subsequent grinding. Indeed, interference pigments based on such materials exhibit color effects superior to those of conventional, mica-based pigments. Disadvantages, however, are that the glass flakes have a very large mean thickness of about 10-15 micrometers and a very broad thickness distribution (typically between 4 and 20 micrometers), whereas the thickness of interference pigments is typically not more than 3 micrometers.
In U.S. Pat. No. 5,340,692 (Vermeulen et al) an imaging receiving material with nacreous pigment for producing contone images according to the silver salt diffusion process is disclosed. According to the process disclosed in U.S. Pat. No. 5,340,692, contone images with an antique look can be obtained utilizing the silver salt diffusion transfer process without the need of special processing liquids using a nacreous pigment in the imaging receiving layer or located between the support and the image receiving layer. The silver halide imaging layers used are created with retained silver and, therefore, are not semitransparent. Because the nacreous pigments used are contained in the imaging receiving layer and not silver halide imaging layer, the image form will not have a uniform nacreous appearance, as the density of the transferred silver halide image block the multiple reflections from the nacreous pigments. Further, the nacreous pigments utilized are too large and in too great a concentration to be included in the silver halide imaging layer as a rough surface would result, reducing the desired nacreous appearance of the image. The gold flakes used in the example in U.S. Pat. No. 5,340,692 are an attempt to simulate prior art black-and-white photographic xe2x80x9cSepatonexe2x80x9d appearance produced during a post process treatment of the imaging layers. While the image in the example does have an antique appearance, the image does not have a nacreous appearance.
In U.S. Pat. No. 4,269,916 (Bilofsky et al) and related patents U.S. Pat. No. 4,288,524 and U.S. Pat. No. 4,216,018, instant photographic products having reflective layers which comprise lemellar interference pigments are disclosed. The intended use of the lemellar pigments is to create a pleasing white reflective appearance for the base material without the need for blue tints. It has been proposed that flat particles of metal oxides created by coating salts with metal oxides and later dissolving the salts leaving a thin flake of metal oxide as a substitute for spherical TiO2 particles. Titanium dioxide particles typically are utilized in photographic art to create a white reflective surface for the viewing of print materials. The intent of U.S. Pat. No. 4,269,916 is to provide a white reflecting surface that does not have an angular viewing appearance and a consistent L*, thus the invention materials do not exhibit a nacreous appearance. Examples in U.S. Pat. No. 4,269,916 show high reflectivity at a variety of collection angles which is opposite of a nacreous appearance where reflectivity changes as a function of collection angle. Further, the lemellar pigments are not present in the silver halide imaging layers or in the base materials used in the invention.
In U.S. Pat. No. 5,858,078 (Andes et al), a process for the production platelet like, substrate free TiO2 pigment is disclosed for use in printing inks, plastics, cosmetics and foodstuffs is.
In U.S. Pat. No. 5,733,658 (Schmid et al) luster pigments obtainable by treating titania coated silicate based platelets from 400xc2x0 C. to 900xc2x0 C. with a gas mixture comprising a vaporized organic compound and ammonia are described as useful for coloring paints, inks, plastics, glasses, ceramic products, and decorative cosmetic preparations.
When imaging supports are subject to variations in ambient conditions over long periods of time, the image-containing layers and resin layers tend to deteriorate into a mass of cracks which are aesthetically undesirable and which, in extreme cases, extend over the entire print completely destroying the image. All polymers are inherently prone to chemical degradation that leads to loss of mechanical properties. They undergo thermal degradation during processing such as extrusion of thin films, and photooxidative degradation with long-term exposure to light. The TiO2 utilized in U.S. Pat. No. 5,858,078 and U.S. Pat. No. 5,733,658 catalyzes and accelerates both thermal and photooxidative degradation. In the art of resin coating imaging papers, the melt polymers are extruded at high temperatures and are also subjected to high shear forces. These conditions may degrade the polymer, resulting in discoloration and charring, formation of polymer slugs or xe2x80x9cgelsxe2x80x9d, and formation of lines and streaks in the extruded film from degraded material deposits on die surfaces. Also, thermally degraded polymer is less robust than non-degraded polymer for long-term stability, and may thereby shorten the life of the print.
It has been shown that when imaging layers (silver halide, ink jet, flexography, laser toner, and the like) are applied to nacreous base materials, the nacreous appearance of the image is optimized when the image forming layers contain semitransparent dyes. The use of pigmented inks and dyes in the imaging layers tend to reduce the nacreous appearance of the image. In U.S. Pat. No. 6,071,654 (Camp et al) silver halide imaging layers that are semitransparent are coated on a nacreous support containing a voided polymer layer. The voided polymer layers create flat platelets oriented parallel to each other. The reflection which reaches the eye is primarily specular. It arises in depth, since each transparent polymer platelet reflects some of the incident light and reflects the remainder. The images in U.S. Pat. No. 6,071,654 exhibit a nacreous appearance.
There is a need for a reflective imaging material that provides a nacreous or pearlescent appearance without having to have a special base while, at the same time, maintains photographic sharpness or printing.
It is an object of the invention to provide improved photographic materials.
It is another object to improved image appearance compared to prior art voided base photographic materials.
It is a further object to provide photographic materials that have a nacreous appearance independent of the base material.
These and other objects of the invention are accomplished by a photographic element comprising nacreous pigment.
The invention provides brighter, snappy images that sparkle while having exceptional photographic sharpness and exposure speed. Further the images have a desirable nacreous appearance that does not require a special base.
The invention has numerous advantages over prior art photographic reflective materials. The reflective materials of the invention provide an image with a nacreous appearance while maintaining efficient reflection of light, sharpness, and photographic speed. Maintaining image sharpness and whiteness is important, as consumers expect silver halide images to be high in quality. Further, maintaining printing speed is critical for efficient photographic processing, as a significant loss in printer speed could increase the cost of consumer silver halide images.
The nacreous imaging materials of the invention provide an eye-catching appearance that make them particularly desirable in imaging applications that require obtaining the attention of the consumer. One example includes display materials that are intended to communicate an advertising message to people in a public setting such as a bus stop, train station, or airport. The nacreous images are differentiated in look from prior art materials and, thus, provide the pop and sizzle that can catch the consumer""s attention. By providing the nacreous image with a pressure sensitive adhesive, the tough, durable nacreous image can be applied to various surfaces, which is particularly desirable for the youth market.
Photographic nacreous labels of the invention utilized in packaging markets enable a differentiated look and consumer appeal on store shelf. The utilization of the thin, flexible, and tough silver halide materials results in a packaging material having many superior properties. The packaging materials of the invention have a depth of image unsurpassed by existing packaging materials. The packaging materials of the invention may be utilized with a variety of packaging materials that are suitable pressure sensitive labeling, such as shampoo bottles, perfume bottles, and film boxes. The packaging materials of the invention, while having the advantage of superior image, are available on thin base materials which are low in cost while providing superior opacity and strength. The packaging materials of the invention, as they may be imaged by flash optical exposure or digital printing, have the ability to be formed in short runs and to be rapidly switched from one image to the next without delay.
The term xe2x80x9cnacreousxe2x80x9d refers to a pearly, luster, and nacreous appearance. This may include a metallic, lustrous, and somewhat iridescent effect. The nacreous effect is the result of interference pigments that are platelet-like in their structure. Typically these are elongated platelet-like structures of silicate-based materials such as mica, feldspar, and quartz. These pigments tend to cause specular and diffuse reflection, and they also transmit some light. The use of nacreous pigments in the paint and printing industry are typically designed to create a variety of eye-popping colors. These materials are typically coated over dark black backgrounds to help accentuate the eye-popping optical effects. Special metal oxide coatings are applied to mica particles in very thin layers. This allows for some light to be refracted, while other light will transmit through to the near transparent layers of the mica particle to be refracted at a slightly different angle. Since these pigments are suspended in a binder polymer of yet another refractive index, there are multiple light refractions that create a lustrous appearance. In addition, the chemistry of the coating that is applied to the mica particles may be varied to create various colors. Metal oxide coatings that may be used in an embodiment of this invention include titanium, iron, chromium, barium, aluminum, zinc, zirconium, bismuth vanadate, nickel titanate, chromium titanate, lead, and others. While these produce some exciting colors in the field of photography and imaging, traditional print materials have a white background. Additionally, it should be noted that the thickness of the metal oxide coating on the mica may also impact the color. In a preferred embodiment of this invention the metal oxide coating on the mica particles may comprise titanium, aluminum, and/or barium. These materials are preferred because it is desirable to have a more traditional white background that can be achieved with these materials. The most preferred metal oxide is titanium because of its superior whiteness. Typically it is important to control the thickness of the metal oxide coating to less than 120 nanometers to achieve a blue white appearance.
With nacreous pigments used in imaging application, it may be desirable to have non-uniform platelet thickness and small particles to create a white nacreous appearance. In imaging application where a different look is desirable, the use of thicker particles and more uniform spacing of platelets to each other creates a color interference that is more characteristic of mother-of-pearl. In general, the lustrous pigments referred to in this invention are pigments that consist of flat mica platelets coated with titanium dioxide or other metal oxides. They are irregular in shape and may vary in thickness from 0.1 to 0.5 micrometers, although some individual particles may be thicker. The particles may have a length of up to 500 micrometers. The coating applied to the mica particles should be controlled in thickness, but the overall thickness is one parameter that controls the overall color appearance. Each transparent coating helps to create the lustrous or pearlescent effect. The particle of these pigments influences the perceived texture of the pearl luster effect and adds a new dimension of beauty and quality to the image. The coating may be colored with other compatible transparent pigments and dyestuffs. Metallic effects can be simulated by adding small amounts of carbon black with some silvery white pigments. The color seen is different than color pigments and dyes in that the color and lustrous iridescence is produced by light interference and not absorption or reflection of light. This is a surprisingly unique attribute to the field of silver halide photography and imaging. With the use of nacreous pigments there are many refractive interface that can produce a unique appearance to an imaging element. A light ray striking a layer containing nacreous platelets must pass through a substantially transparent layer of relatively lower refractive index binder polymer surrounding the platelet, and then the ray is then partially reflected by the metal oxide coating on the surface. The remaining part passes into the metal oxide coating layer and is again reflected as it exits the layer at the interface with the mica particle. Since the coating is very thin and the mica platelets are substantially transparent, the remaining light has many opportunities to be reflected at different angles. This helps to provide the luster nacreous appearance, as well as to add a three-dimensional quality to the image. The resulting color effect that is produced depends on the light reflection from the interfaces, as well as the type of coating on the mica particles. The multiple interfaces cause the reflected light to be slightly out of phase. It should also be noted that the color varies based on the angle of illumination and that an iridescence effect can be seen. Control of this effect is desirable depending on the effect that needs to be conveyed by the image. As noted above the thickness and type of the coating on the mica particles are factors that need to be considered. In addition the particle size can also be used to control the effect. For use in a photographic element it is desirable to have a smooth surface. To achieve this, a small particle is best but the layer thickness of the binder polymer in which the pigments are suspended may also be increased as well as applying clear overcoats. Larger particles are desirable when a bold effect with visual impact is desired. The nacreous effect can be changed by adjusting the particle size, metal oxide coating thickness and type, as well as the concentration of the pigment. In general, low pigmentation levels are better at producing a three-dimensional effect. This effect may be enhanced by applying a thick clear layer over the top of the nacreous pigments. When a more metallic sheen is desired, higher pigmentation levels are best. It should also be noted that different effects may be achieved by adding other transparent pigments and dyes in the layers. Since light sensitive photographic layers produce dye couplers that are semitransparent and typically do not contain pigment particles; they are uniquely positioned to be able to create synergistic effects with the nacreous pigments.
The nacreous pigments are relatively stable and generally resistant to alkali and acids, as well as high temperature. They can be dispersed in most carrying (binder polymer) media. Since the particles are substantially transparent, the use of a carrying media that is also transparent provides the maximum effect. If a more translucent carrying media is used, more nacreous pigment may be needed to achieve the same level of nacreous appearance.
In some applications it may be desirable to also have a nacreous pigment that is also conductive. This has some unique advantages in the area of photography that uses light sensitive layers. Static accumulation and discharge can result in a fogged layer. Being able to provide a conductive path that helps to prevent the charge from building up is an important element for imaging media. This not only helps prevent light fogging of light sensitive layer, but also allows sheets to slide over each other and various equipment parts without static buildup or cling of one sheet to another. This type of pigment is also a means of adding conductivity to the emulsion side of a photographic element. Conductive nacreous pigments consist of an inter core of platelet mica that is coated with materials such as TiO2, SiO2 and further coated with an outer layer of dense layer of conductive, inorganic mixed metal oxide. A typical material is antimony-doped tin dioxide. The elongated particles of mica are useful in providing a conductive pathway when particles are touching.
The origin of the beauty of a genuine pearl has been well documented. It is known that its luster and color come from the multiple smooth concentric layers of nacre, i.e., calcium carbonate layer, organic constituent (conchiolin) layer. Each of these layers partially reflects and transmits light. Hence, a sense of depth and luster is observed in the reflection. Pigments that try to simulate the visual effect of a pearl are called as pearlescent or nacreous pigments. The first nacreous pigment was the natural pearl. The commercial grades of nacreous pigments are made of thin transparent platelets of high refractive index. These pigments are so designed that multiple reflections and transmissions occur and, as a result, a sense of depth is obtained in the overall reflected image. The characteristics of the pigment determine whether color is produced by light interference (specifically called as interference pigments) or no color is produced (called as white nacreous pigments).
Some of the earliest pearlescent pigments were the plate-like bismuth oxychloride crystals, and basic lead carbonate. These pigments reflect light similar to a pearl essence crystal. Due to toxicity of lead, bismuth oxychloride (BiOCl) crystals have seen an increased use in the marketplace. BiOCl is generally crystallized from solution into smooth, thin platelets which has a particle size ranging from 5 xcexcm and 15 xcexcm.
The other commonly used pearlescent pigments are those made from mica coated with either titanium dioxide (U.S. Pat. No. 4,040,859), iron oxide (U.S. Pat. No. 3,087,829), zirconium dioxide (U.S. Pat. No. 3,087,828), or other high refractive index materials. Mica is used because it is transparent to light and can be cleaved into extremely thin flakes. Examples of mica suitable for pearlescent pigments are muscovite, paragonite, phlogopite, biotite, and lepidolite. The mica platelets are then coated with a thin single layer or multiple layers of high refractive index inorganic oxide. The reflection efficiency depends to a large extent on the refractive index difference between the mica platelet and the inorganic oxide coating. This layered structure enables it to function like a pearlescent pigment. The oxide coating provides the optical effects like luster, interference reflection color (if oxide coating is sufficiently thick) and absorption color (if the oxide contains color material). The size of the mica particle also plays an important role in determining the final reflected image. The weight of the mica in the pigment usually lies between 40% and 90% and most usually in the range of 60% and 80%. If titanium dioxide is used as the coating and its coating thickness is increased, then an iridescence effect (color) is observed. The dimensions of pearlescent pigments used in this invention may be between 5 xcexcm and 400 xcexcm and preferably between 5 xcexcm and 100 xcexcm because particles less than 5 xcexcm are not very efficient in creating the nacreous appearance, while particles greater than 100 xcexcm progressively get rougher. Excessive roughness on the surface tends to shut down the nacreous appearance. The thickness of the pigment is preferably between 0.1 xcexcm and 0.6 xcexcm and more preferably between 0.2 xcexcm and 0.4 xcexcm. Particles less than 5 xcexcm or less than 0.2 xcexcm typically do not have sufficiently higher nacreous appearance, while particles greater than 400 xcexcm in length or 0.6 xcexcm in width typically are very large and tend to create roughness which starts to shut down the nacreous effect.
Other optically variable pigments that are suitably used are silicon oxide coated with thin layers of aluminum (5 nm and 10 nm) or titanium dioxide, and magnesium fluoride crystals coated with chromium have also been used. These pigment structures have been highlighted in U.S. Pat. No. 3,438,796. New optically variable pigment structures based on coated platelet like metallic substrates have been disclosed in U.S. Pat. No. 5,364,467 and U.S. Pat. No. 5,662,738. U.S. Pat. No. 5,976,511 discloses pigments composed of barium sulfate particles and coated with zinc oxide, cerium oxide, or titanium dioxide which have a pearly luster.
The photographic elements of this invention may utilize an integral emulsion bonding layer that allows the emulsion to adhere to the support materials during manufacturing and wet processing of images without the need for expensive subbing coatings.
The terms as used herein, xe2x80x9ctopxe2x80x9d, xe2x80x9cupperxe2x80x9d, xe2x80x9cemulsion sidexe2x80x9d, and xe2x80x9cfacexe2x80x9d mean the side or toward the side of a photographic member bearing the imaging layers. The terms xe2x80x9cbottomxe2x80x9d, xe2x80x9clower sidexe2x80x9d, and xe2x80x9cbackxe2x80x9d mean the side or toward the side of the photographic member opposite from the side bearing the photosensitive imaging layers or developed image. Nacreous appearance is a pearly, luster, iridescent, metallic sheen. A characteristic property of a nacreous appearance is an angular dependence of viewing angle.
For the imaging element of this invention, imaging layers are generally applied to a white reflective base, and the image layers comprise nacreous materials. In the invention a photographic element comprises nacreous pigments. This embodiment is preferred because said photographic element that comprises nacreous pigment has a unique pearly luster appearance. Such a photographic element has a unique capability to preserve images with special luster sheen that is not available in traditional photographs or commercial displays. A preferred embodiment of this invention comprises nacreous material in a photographic layer which is on a white reflective base. The white reflective base provides an excellent surface and background while viewing prints. In particular, it is desirable to have a white reflective base that has an L* of greater than 92. L* greater than 92 are desirable because they provide good contrast to the image and are pleasing to the viewer. Highly reflective whites are highly desirable from a final consumer standpoint. L* or lightness and opacity were measured for using a Spectrogard spectrophotometer, CIE system, using illuminant D6500.
In a further embodiment of this invention it is desirable to have a base with a surface smoothness of less than 0.8 micrometers. Having a base that is smooth is desirable in providing an image surface that is relatively free of orange peel and has a high level of gloss. Most consumers desire a smooth base because the high level of gloss helps to accent the nacreous appearance.
For the purpose of this invention the photographic element comprises silver halide emulsion. Said silver halide emulsion may comprise more than one layer. It should also be noted that some layers may comprise light sensitive silver halide materials, and other layers may not contain light sensitive materials.
In this invention the photographic element comprises nacreous pigments. The element may have nacreous pigment in a layer that comprises silver halide emulsion; that is, the nacreous pigment is in the same layer or layers that have the light sensitive silver halide emulsion. After the silver halide is exposed and processed, the nacreous pigment provides a source of additional spectral reflection that provides a unique appearance to the image. Since the silver halide emulsion has more than one layer, and in the case of color emulsions there may be at least three or more layers each capable of capturing light of a different wavelength, said nacreous pigment may be in one or more layers. This will allow only certain colors or all colors to demonstrate the nacreous appearance.
In a preferred additional embodiment the nacreous pigment may be in a layer of the photographic element that is free of silver halide emulsion. It is common knowledge that photographic emulsions have multiple layers in which the light sensitive layers are separated by an interlayer and furthermore have a size overcoat in the topmost position that are not light sensitive. In this embodiment the nacreous material is located above or below a layer or layers that further comprise silver halide. This embodiment is preferred because the nacreous pigments do not have to be fully compatible with the silver halide emulsion and are, therefore, less likely to interfere with image development or keeping. The nacreous appearance is still present after the image is formed and developed. In an additional embodiment the nacreous pigment is in a layer on the surface or adjacent to the surface of said photographic element. In this embodiment the reflected light of the exposed and developed image creates a nacreous appearance to the image. In yet another preferred embodiment of said photographic element, said nacreous pigment is in a layer below said bottommost layer comprising silver halide. This embodiment is preferred because light is allowed to expose the silver halide as it passes through the layers, but the secondary light that bounces back from the base is impacted by the nacreous pigments. This provides a very soft nacreous appearance to the image.
In a preferred embodiment of this invention the nacreous pigments comprises mica. Coated mica is preferred because it has a platelet structure that, when coated with metal oxides, has a nacreous appearance that provides a very unique look to an image which is appealing. Furthermore, said mica may be easily dispersed and coated in a layer or layers that comprise silver halide emulsion, as well as layers that are free of or at least substantially free of silver halide emulsion. For the purpose of this invention the term xe2x80x9cmicaxe2x80x9d refers to nacreous materials and includes mica, feldspar, quartz, silicates, modified mica, and mica that has been coated with a metal oxide, mica coated with materials that have a difference in refractive index greater than 0.2. The mica material may be a translucent organic and/or inorganic materials and may have a nacreous effect when viewed from different angles.
In other suitable embodiments of this invention, nacreous pigments may be incorporated in either or both the light sensitive emulsion layers and the size overcoat. Nacreous pigments have been shown to be an effective means to filter UV radiation. This has significant advantage to minimize photographic dye fade.
In an additional embodiment of this invention, said photographic element comprising a nacreous pigment further comprises electrical resistant of less than 1013 log ohms per square. Electrical resistance less than 1013 is desirable to prevent static buildup and discharge that can cause the light sensitive layer to fog.
In yet an additional embodiment of this invention, said photographic element that comprises said nacreous pigment has a mean particle size between 0.5 and 50 micrometers. Particles less than 0.5 micrometer in size tend not to have a sufficient platelet structure to create a strong nacreous appearance. It should be noted that small particle sizes in the preferred range have less of a scattering impact on the light sensitive layers and, therefore, have minimal interference with the exposure of the silver halide and sharpness. The smaller particle sizes are further desirable with the relatively thin layer of a photographic emulsion to minimize roughness that can cause excessive light scattering. Larger particles are desirable to get more efficient nacreous appearance, but particles greater than 50 micrometers are very rough and difficult to incorporate in or around light sensitive layers. Typically the large particles should be coated in layers several times thicker than the particle.
In a preferred embodiment of this invention said photographic element has a b* less than 10. A b* less than 10 is desirable for photographic print material because of the customer traditional expectation of a white appearing print. Furthermore, b* less than 10 provides excellent contrast to other colors. There are many color shades of white. Blue whites are desirable to make the whites look whiter, while less blue or more yellow whites are desirable for warmer tones images. Other color tints may be used for other shades of white, while optical brighteners may be used in conjunction with the nacreous pigments to make the whites more blue appearing. Nacreous pigments with colors other than white may be used to create special effects or color schemes.
In this invention the nacreous pigments may comprises between 0.5 and 1000 mg/m2 of the photographic element. Nacreous pigment levels below 0.5 mg/m2 are difficult to detect and generally do not have a nacreous impact. Nacreous pigment levels above 1000 mg/m2 do not have a proportional improved nacreous appearance for the additional expense. Furthermore, if the level is above 1000 mg/m2, the nacreous pigments tend to stack more vertically and their impact is decreased. In a preferred embodiment of this invention, said nacreous pigments are present in the amount between 7 and 250 mg/m2. Below 7 mg/m2 the nacreous appearance is more difficult to see, while levels above 250 mg/m2 do not have a significantly improved nacreous appearance for the additional expense. When nacreous pigments are incorporated in and/or above silver halide layers, the amount of the nacreous pigment should be kept low to minimize interference with the image exposure. Higher level in the preferred range tend to have a stronger nacreous appearance which is desirable in certain applications for display or youth markets where a different look is valued. In the preferred embodiment of this invention, the nacreous pigment should comprise between 0.1 to 9% by volume of the photographic emulsion. Levels below 0.1% have minimal nacreous appearance, while levels above 9% cause excessive stacking of the platelets which tends to interfere with the nacreous appearance. Additionally it is desirable to have the nacreous pigments as the only pigment in a substantial clear polymer. The inclusion of other solid particles tends to cause more light scattering and, therefore, reduces the nacreous effect.
Nacreous or pearlescence appearing media has shown to be highly desirous from a commercial standpoint. Incorporation of nacreous pigments in a substantially transparent substrate or construction of composite materials containing localized voiding of a specific geometry, orientation, and formulation can produce both xe2x80x9ccoloredxe2x80x9d nacreous and xe2x80x9cwhitexe2x80x9d nacreous media. For both types, this nacrescence results in perceived depth, luster, and a metallic appearance. Correct measurement of these materials is required for robust design.
For both pigment and voiding methods, xe2x80x9cwhitexe2x80x9d nacreous luster is a function of the orientation, as well as the spacing and composition of the materials. The luster and depth appearance of the media are mainly due to the reflected light that reaches the eye. Both pigments and voids that provide a nacreous appearance function as substantially transparent platelets oriented parallel to each other. This results in depth as each platelet reflects some of the incident light while transmitting the rest. Any imperfections due to surface defects or platelet or void orientation misalignments will cause the light to be scattered in a non-specular direction, and will degrade the nacreous appearance of the material.
In addition, the natural tendency for randomness in regards to platelet or void alignment and spacing will render the media incapable of producing color by light interference. Any color produced by one alignment and spacing will have a tendency to be counteracted by other encountered alignments and spacing. However, gross geometric misalignments of the platelets or voids will also result in less than desirable functionality, and a method of measuring this defect is required as well.
FLOP is a test method used to measure the nacreous quality of materials of interest. 45-degree incident light is collected at 10, 45, and 110 degrees from the specular reflection angle. The spectrophotometric output, e.g., CIE L* (L1*, L2*, L3* respectively) is used as follows:
FLOP=15(L1*xe2x88x92L3*)1.11/L2*0.86
whereby FLOP values between less than 10 have no nacreous appearance and FLOP values greater than 10 are indicative of a nacrescent appearance.
Furthermore, quality monitoring of these nacreous materials, when combined with one or more semitransparent color forming dyes layers, places limitations on the usefulness of measurements taken with typically found reflection densitometers having 0/45 geometry. This is due to the angular dependency of these media. This angular viewing dependency of the media and the inherent randomness of the structure will result in errors xe2x80x9creading outxe2x80x9d the dye formed due to the variability of the media at any one collection angle. These highly specular and translucent materials will reflect some light in angular dependent non-specular directions as well. It has been found that although incident light and collection at 0/45 will allow for a prediction of density minimum versus FLOP, these values are no longer predictive, as density increases from density minimum to density maximum as color dye forming layers are added to the media.
This can be explained as a function of the dye density. As density increases, the ability for multiple reflections through the media decreases. As the reflection passes approach one, the nacreous look will no longer be apparent.
Spectrogoniometric measurements can be employed to measure the media at various angles, but spectrogoniometric readings are tedious and the apparatus is expensive. An alternative for quality monitoring purposes to assess the amount of color forming layers coated and subsequently processed would be useful. During a color photographic coating operation, the need to reduce inherent manufacturing variability of color forming coupler levels is required and this data collection by conventional reflection 0/45 densitometry is impeded by the natural variability found in the nacreous media. Slight changes in the reflective properties of the base media will result in more or less light reaching the densitometer which, in turn, can result in an erroneous readout of the formed dye.
One such method to provide correct assessment during a coating operation would be to remove the nacreous properties of the media. This can be accomplished by collecting light from the prepared sample at a grazing angle that would minimize the nacreous layer contributions. Diffuse 8 degree sphere optical geometry handheld spectrophotometers have been shown to meet this need.
In a preferred embodiment of this invention, said photographic element comprising nacreous pigments wherein said element has a flop measurement of between 2 and 65. Flop measurements below 2 have little or no nacreous appearance, while flop measurements above 65 are difficult to achieve with nacreous pigments.
In a further embodiment of this invention, the photographic element further comprises a white reflective base that further comprises a surface roughness of less than 0.8 micrometer. Reflective bases greater than 0.8 micrometers tend to exhibit a roughness frequency that greatly reduces the nacreous appearance. Bases with a roughness of less than 0.8 micrometers are generally glossy in overall appearance which tends to maximize the nacreous appearance in an imaging print.
In a preferred embodiment of this invention, the photographic element comprising a nacreous pigment further comprises at least two exposed and developed images that are folded with the image sides out, and the non-image bearing sides are adhesively joined to form an album page. This embodiment is preferred because it allows the nacreous appearance to be utilized with album pages. Multiple images may be exposed and developed on one sheet of photographic element that contains nacreous pigment and then folded and joined to form a convenient display. The page can then be punched and used as part of an album page. In an additional embodiment, the exposed and developed photographic element may be folded using an apparatus for making an album leaf from an image-bearing sheet. The sheet has an image bearing side and a non-image bearing side, comprising:
a first roller about which said image bearing sheet is driven;
a second roller positioned adjacent said first roller so as to form a first nip there between, said second roller is used for driving an adhesive sheet into said first nip against said image bearing sheet that is driven by said first roller; and
a third roller positioned adjacent said first roller so as to form a second nip there between, said third and said first roller moving in a direction which caused said image bearing sheet to be folded firmly about said adhesive sheet and move through said second nip so as to form an album leaf.
The imaging elements of this invention are photographic elements, such as photographic display films, photographic paper, or photographic glass plates, in which the image-forming layer is a radiation-sensitive silver halide emulsion layer. Such emulsion layers typically comprise a film-forming hydrophilic colloid. The most commonly used of these is gelatin, and gelatin is a particularly preferred material for use in this invention. Most of the nacreous pigments useful in this invention are easily dispersed in gelatin. Additional dispersing aids may be used with gelatin or other hydrophilic colloids. Most any aqueous dispersing aid known in the art of pigments and paints may be useful. Useful gelatins include alkali-treated gelatin (cattle bone or hide gelatin), acid-treated gelatin (pigskin gelatin), and gelatin derivatives such as acetylated gelatin, phthalated gelatin, and the like. Other hydrophilic colloids that can be utilized alone or in combination with gelatin include dextran, gum arabic, zein, casein, pectin, collagen derivatives, collodion, agar-agar, arrowroot, albumin, and the like. Still other useful hydrophilic colloids are water-soluble polyvinyl compounds such as polyvinyl alcohol, polyacrylamide, poly(vinylpyrrolidone), and the like.
The photographic elements of the present invention can be simple black-and-white or monochrome elements comprising a support bearing a layer of light-sensitive silver halide emulsion, or they can be multilayer and/or multicolor elements.
Color photographic elements of this invention typically contain dye image-forming units sensitive to each of the three primary regions of the spectrum. Each unit can be comprised of a single silver halide emulsion layer or of multiple emulsion layers sensitive to a given region of the spectrum. The layers of the element, including the layers of the image-forming units, can be arranged in various orders as is well known in the art.
In addition to emulsion layers, the photographic layer can contain auxiliary layers conventional in photographic elements, such as overcoat layers, spacer layers, filter layers, interlayers, antihalation layers, pH lowering layers (sometimes referred to as acid layers and neutralizing layers), timing layers, opaque reflecting layers, opaque light-absorbing layers, and the like. The support can be any suitable support as described in this invention. Typical supports include polymeric films, polymeric film laminated to other polymeric, glass, and the like. The important thing is to have translucent support that is both reflective and diffusive. The light-sensitive silver halide emulsions employed in the photographic elements of this invention can include coarse, regular, or fine grain silver halide crystals or mixtures thereof and can be comprised of such silver halides as silver chloride, silver bromide, silver bromoiodide, silver chlorobromide, silver chloroiodide, silver chorobromoiodide, and mixtures thereof. The emulsions can be, for example, tabular grain light-sensitive silver halide emulsions. The emulsions can be negative-working or direct positive emulsions. They can form latent images predominantly on the surface of the silver halide grains or in the interior of the silver halide grains. They can be chemically and spectrally sensitized in accordance with usual practices. The emulsions typically will be gelatin emulsions, although other hydrophilic colloids can be used in accordance with usual practice. Details regarding the silver halide emulsions are contained in and described in Research Disclosure, September 1994, Item 36544, Section I, published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire PO10 7DQ, ENGLAND as well as Research Disclosure, Item 36544, September 1994, and the references listed therein, as well as Research Disclosure, September 2000, Item 437013, published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire PO10 7DQ, ENGLAND.
The photographic silver halide emulsions utilized in this invention can contain other addenda conventional in the photographic art. Useful addenda are described, for example, in Research Disclosure, Item 36544, September 1994, and Research Disclosure, September 2000, Item 437013, published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire PO10 7DQ, ENGLAND. Useful addenda include spectral sensitizing dyes, desensitizers, antifoggants, masking couplers, DIR couplers, DIR compounds, antistain agents, image dye stabilizers, absorbing materials such as filter dyes and UV absorbers, light-scattering materials, coating aids, plasticizers and lubricants, and the like.
Depending upon the dye-image-providing material employed in the photographic element, it can be incorporated in the silver halide emulsion layer or in a separate layer associated with the emulsion layer. The dye-image-providing material can be any of a number known in the art, such as dye-forming couplers, bleachable dyes, dye developers and redox dye-releasers, and the particular one employed will depend on the nature of the element, and the type of image desired.
Dye-image-providing materials employed with conventional color materials designed for processing with separate solutions are preferably dye-forming couplers; i.e., compounds which couple with oxidized developing agent to form a dye. Preferred couplers which form cyan dye images are phenols and naphthols. Preferred couplers which form magenta dye images are pyrazolones and pyrazolotriazoles. Preferred couplers which form yellow dye images are benzoylacetanilides and pivalylacetanilides.
Below in Table 1 is a typical photographic element which includes a size overcoat, three light sensitive silver halide emulsion units with a color dye forming, and interlayers to separate the various light sensitive layers. For the purpose of this invention, the nacreous comprising materials may be added individually to each light sensitive emulsion and interlayer of Table 1 or in more than one layer in any combination. Additionally the nacreous materials may be added to a layer under the emulsion such as in the gel sub or primer layer or as a separate additional layer.
These and other advantages will be apparent from the detailed description below.
The following examples illustrate the practice of this invention. They are not intended to be exhaustive of all possible variations of the invention. Parts and percentages are by weight unless otherwise indicated.