Disclosed herein is a golf ball having a core and a cover comprising a blend of ionomer and plastomer. The golf ball has an impact resistance and cut resistance comparable to a ball having a non-plastomer cover and containing higher quantities of ionomer.

The present invention relates generally to golf balls, and more particularly to golf balls having covers containing blends of ionomer and plastomer.
Traditional golf ball covers were comprised of balata or blends of balata with elastomeric or plastic materials. Balata covered balls provide an experienced golfer with the ability to apply a spin to control the ball in flight. Moreover, the soft balata covers produce a soft xe2x80x98feelxe2x80x9d to the low handicap player. However, despite the benefits of balata, balata-covered golf balls are easily cut and/or damaged if mis-hit; thus, balata and its synthetic substitutes, trans-polybutadiene and trans-polyisoprene have been essentially replaced by covers made of ionomers.
Ionomers are partial metal salts of acid containing polymers, such as ethylene based polymers. These include the partial metal salts of copolymers of ethylene and an ethylene-copolymerizable unsaturated carboxylic acid, such as acrylic acid, methacrylic acid, or maleic acid. Metal ions, such as sodium, zinc, lithium, magnesium, and the like are used to neutralize a portion of the acidic group in the copolymer resulting in a thermoplastically reversible crosslinked polymer exhibiting enhanced properties, i.e. durability, etc., for golf ball cover construction as compared to balata-covered balls.
Several attempts have been made to match or improve the performance of an ionomer golf ball by adding non-ionic and non-ionizable polymers thereto. For example, U.S. Pat. No. 4,567,219 is directed to a cover composition for golf balls with improved impact resistance. The cover comprises a blend of ionomer resin and 1-15 parts by weight of a linear, low-density polyethylene per 100 parts by weight of the ionomer resin. U.S. Pat. No. 5,019,320 discloses a golf ball composition comprising an ionomer resin and a low molecular weight polyethylene wax. This blend also is alleged to provide improved impact resistance. The polyethylene wax is present in a quantity of 0.1 to 6 parts by weight based upon 100 parts by weight of ionomer resin. It would be useful to develop a golf ball cover containing a blend of an ionomer and a non-ionic or non-ionizable polymer in which substantial quantities of the non-ionic and/or non-ionizable polymers can be used while achieving playability properties comparable to those which are obtained using known ionomeric golf ball cover materials.
An object of the invention is to provide a golf ball having the playability properties of an ionomeric covered ball while containing reduced quantities of ionomer.
Another object of the invention is to provide a golf ball having a durable cover.
Yet another object of the invention is to provide a golf ball which can be produced in an efficient and economical manner.
A further object of the invention is to provide a method for making a golf ball having the characteristics described above.
Other objects will be in part obvious and in part pointed out more in detail hereafter.
The invention in a preferred form is a golf ball having a core and one or more cover layers, wherein the cover layer contains a blend of ionomer and plastomer. The plastomer is comprised of catalytically polymerized, random copolymers of ethylene and one or more olefin comonomers characterized by a narrow or controlled composition distribution. The plastomer preferably has a dispersion index (MW/MM), i.e. the ratio of weight average molecular weight to number average molecular weight, of about 1.5 to 4. The olefin comonomer or comonomers are present in amounts of about 10-35 wt % based upon the overall weight of the plastomer.
In a particularly preferred form of the invention, the cover layer contains 10-90, and preferably 20-60, parts of plastomer based upon 100 parts by weight of ionomer. The golf ball has a cut resistance of at least 3 and a Shore D hardness in the range of 40-80.
Another preferred form of the invention is a method of making a golf ball comprising the steps of (1) obtaining a core and (2) forming a cover over the core, the cover comprising a blend of ionomer and plastomer.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others and the article possessing the features, properties, and the relation of elements exemplified in the following detailed disclosure.
The golf balls of the invention have covers which comprise blends of ionomers, thermoplastic elastomers, and non-ionic and/or non-ionizable olefin copolymers which have a uniform, narrow molecular weight, a high comonomer content, and an even distribution of plastomer. The dispersion index of the plastomers generally is about 1.5-4, preferably 1.5-3.5 and more preferably 1.5-2.4. The density is typically in the range of 0.85-0.93 g/cc it unfoamed and 0.10-0.90 g/cc if foamed. The comonomer content typically is in the range of 10-35%, and preferably 15-30%. The melt index (MI) of the plastomer generally is less than 30 with the lower molt index materials providing blends with better low temperature impact. Accordingly a melt index less than about 20 is typical with a melt index of less than 10 being preferred and one of less than 5 being most preferred. The composition distribution breadth index generally is greater than 30%, preferably is at least 45%, and more preferably is at least 50%. Preferably the golf balls also include a curing agent for the plastomer.
The term xe2x80x9ccopolymerxe2x80x9d includes olefin copolymers made from ethylene and one or other olefin monomers. Examples of olefin monomers include propylene, 1-butene, 1-hexene, 1-octene, 4-methyl pentene-1,1,4-hexadiene, norbornene, norbornadiene, vinyl norbornene, ethylidene norbornene, etc. The compositions of the invention further may include additives and fillers as well as a co-agent that can react with the curing agent to aid in crosslinking the plastomer and/or ionomer or to improve processability. Co-agents which have been used for that purpose include triallyl cyanurates, ethylene glycol di(meth)acrylate, tri(meth)acrylates, divinyl benzene and other multifunctional chemicals.
The xe2x80x9ccomposition distribution breadth indexxe2x80x9d (CDBI) is defined as the weight percent of the plastomer molecules which have a comonomer content between 50 percent and 125 percent of the median comonomer content (on a mole basis) of the sample. For example the CDBI of a sample which had a butene content of 8 mole percent would be the weight percent of the molecules which had butene contents between 6 and 10 mole percent.
The plastomers employed are polyolefin copolymers developed using metallocene single-site catalyst technology. Polyethylene plastomers generally have better impact resistance than polyethylenes made with Ziegler-Natta catalysts. Plastomers exhibit both thermoplastic and elastomeric characteristics. In addition to being comprised of a polyolefin such as ethylene, plastomers contain up to about 35 wt % comonomer. Plastomers include but are not limited to ethylene-butene copolymers, ethylene-octene copolymers, ethylene-hexene copolymers, and ethylene-hexene-butene terpolymers, as well as mixtures thereof.
The golf ball covers of the invention contain a blend of plastomer and ionomer in a ratio of 10:90 to 90:10, and more preferably 20:80 to 50:50. The golf ball covers may also include a thermoplastic elastomer such as available from Shell Chemical Company under the designation Kraton(copyright). It has been found that the golf ball cover properties of high impact resistance, good durability and playability are particularly favorable when the ratio of plastomer;ionomer is in the range of 10:90 to 50:50. Other additives such as coloring agents, optical brighteners, processing aids and fillers typically are added in an amount of up to about 10 parts by weight based upon 100 parts by weight of the plastomer-ionomer blend.
The plastomers employed in the invention preferably are formed by a single site metallocene catalyst such as those disclosed in EP 29368, U.S. Pat. Nos. 4,752,597, 4,808,561, and 4,937,299, the teachings of which are incorporated herein by reference. Blends of plastomers can be used. As is known in the art, plastomers can be produced by solution, slurry and gas phase accesses but the preferred materials are produced by metallocene catalysis using a high pressure process by polymerizing ethylene in combination with other olefin monomers, such as butene-1, hexene-1, octene-1 and 4-methyl-1-pentene in the presence of catalyst system comprising a cyclopentadienyl-transition metal compound and an alumoxane.
Plastomers found especially useful in the invention are those sold by Exxon Chemical under the trademark xe2x80x9cEXACTxe2x80x9d and include linear ethylene-butene copolymers such as EXACT 3024 having a density of about 0.905 g/cc (ASTM D-1505) and a melt index of about 4.5 g/10 min. (ASTM D-2839); EXACT 3025 having a density of about 0.910 g/cc (ASTM D-1505) and a melt index of about 1.2 g/10 min. (ASTM D-2839); EXACT 3027 having a density of about 0.900 g/cc (ASTM D-1505) and a melt index of about 3.5 g/10 min. (ASTM D-2839). Other useful plastomers include but are not limited to ethylene-hexene copolymers such as EXACT 3031 having a density of about 0.900 g/cc (ASTM D-1505) and a melt index of about 3.5 g/10 min. (ASTM D-2839) , as well as EXACT 4049, which is an ethylene-butene copolymer having a density of about 0.873 g/cc (ASTM D-1505) and a melt index of about 4.5 g/10 min. (ASTM D-2839). All of the above EXACT series plastomers are available from EXXON Chemical Co.
EXACT plastomers typically have a dispersion index (Mw/Mn where Mw is weight average molecular weight and Mn is number average molecular weight) of about 1.5 to 4.0, preferably 1.5-2.4, a density of about 0.86 to about 0.93 g/cc, preferably about 0.87 g/cc to about 0.91 g/cc, a melting point of about 140-220xc2x0 F., and a melt index (MI) above about 0.5 g/10 mins, preferably about 1-10 g/10 mins as determined by ASTM D-1238, condition E. Plastomers which may be employed in the invention include copolymers of ethylene and at least one C3-C20 xcex1-olefin, preferably a C4-C8 xcex1-olefin present in an amount of about 5 to about 32 wt %, preferably about 7 to about 22 wt %, more preferably about 9-18 wt %. These plastomers are believed to have a composition distribution breadth index of about 45% or more.
Plastomers such as those sold by Dow Chemical Co. under the trade name ENGAGE also may be employed in the invention. These plastomers are believed to be produced in accordance with U.S. Pat. No. 5,272,236, the teachings of which are incorporated herein by reference. These plastomers are substantially linear polymers having a density of about 0.85 g/cc to about 0.93 g/cc measured in accordance with ASTM D-792, a melt index (MI) of less than 30 g/10 minutes, a melt flow ratio (I10/I2) of about 7 to about 20, where I10 is measured in accordance with ASTM D-1238 (190/10) and I2 is measured in accordance with ASTM D-1238 (190/2.16), and a dispersion index Mw/Mn which preferably is less than 5, and more preferably is less than about 3.5 and most preferably is from about 1.5 to about 2.5. These plastomers include homopolymers of C2-C20 olefins such as ethylene, propylene, 4-methyl-1-pentene, and the like, or they can be interpolymers of ethylene with at least one C3-C20 xcex1-olefin and/or C2-C20 acetylenically unsaturated monomer and/or C4-C18 diolefins. These plastomers have a polymer backbone that is either unsubstituted or substituted with up to 3 long chain branches/1000 carbons. As used herein, long chain branching means a chain length of at least about 6 carbons, above which the length cannot be distinguished using 13C nuclear magnetic resonance spectroscopy. The preferred ENGAGE plastomers are characterized by a saturated ethylene-octene backbone and a narrow dispersion index Mw/Mn of about 2.
These plastomers also are compatible with many conventional plasticizers and fillers. The fillers include, but are not limited to, clay, talc, asbestos, graphite, glass, mica, calcium metasilicate, barium sulfate, zinc sulfide, aluminum hydroxide, silicates, diatomaceous earth, carbonates such as calcium carbonate, magnesium carbonate and the like, metals such as titanium, tungsten, aluminum, bismuth, nickel, molybdenum, iron, copper, brass, boron, bronze, cobalt and beryllium, and alloys of the above metals, metal oxides such as zinc oxide, iron oxide, aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide and the like, particulate synthetic plastic such as high molecular weight polyethylene, polystyrene, polyethylene ionomer resins and the like, particulate carbonaceous materials such as carbon black, natural bitumen and the like, as well as cotton flock, cellulose flock, and leather fiber. Dark colored fillers generally are not preferred for use at the outer surface of the ball if a white ball is desired. Thus, a two-layer cover in which a non-white filler is only present in the inner cover layer can be employed. The amount of filler employed is primarily a function of weight restrictions. For example, weight may be removed from the core and placed in the inner and/or outer cover. This added weight will change the moment of inertia of the ball thereby potentially altering performance. Various commercially available plastomers may be useful in the invention, including those manufactured by Mitsui.
The dispersion index Mw/Mn of plastomers made in accordance with U.S. Pat. No. 5,272,236 most preferably is about 2.0. Non-limiting examples of these plastomers include ENGAGE CL 8001 having a density of about 0.868 g/cc, a melt index of about 0.5 g/10 mins, and a Shore A hardness of about 75; ENGAGE CL 8002 having a density of about 0.87 g/cc, a melt index of about 1 gms/10 min, Shore A hardness of about 75; ENGAGE CL 8003 having a density of about 0.885 g/cc, melt index of about 1.0 gms/10 min, and a Shore A hardness of about 86; ENGAGE EG 8100 having a density of about 0.87 g/cc, a melt index of about 1 gms/10 min., and a Shore A hardness of about 87; ENGAGE 8150 having a density of about 0.868 g/cc, a melt index of about 0.5 gms/10 min, and a Shore A hardness of about 75; ENGAGE 8200 having a density of about 0.87 g/cc, a melt index of about 5 g/10 min., and a Shore A hardness of about 75; and ENGAGE EP 8500 having a density of about 0.87 gms/cc, a melt index of about 5 g/10 min., and a Shore A hardness of about 75.
The ionomers which are blended with plastomer preferably are various commercially available ionomers sold under the trade name lotek, such as lotek 8000, lotek 8020, lotek 8030 or lotek 7000, lotek 7010, lotek 7020 or lotek 7030. Blends of ionomers can be used, however hard ionomers are preferred.
Coloring pigments and optical brighteners also may be included in the compositions of the invention. Useful coloring pigments include, for example, titanium dioxide, the presence of which simplifies the surface painting operation of the finished ball. In some cases, coloring pigments eliminate the need for painting, such as, for example, where the ball is intended for use on driving ranges.
The golf balls of the invention have a coefficient of restitution of at least 0.650, and more preferably at least 0.700, a PGA compression of about 60-110 and preferably 80-90, a ball size of 1.68xe2x80x3-1.75xe2x80x3, and a ball weight of 45.93 grams or less.
To form a golf ball according to the invention, a solid, liquid or wound golf ball center is obtained. The center optionally may be covered with one or more non-plastomer inner cover layers prior to application of the plastomer cover layer or layers. If necessary, the center can be surface treated to facilitate adhesion thereof to a cover composition. Surface treatment can be performed by techniques known in the art, such as corona discharge, ozone treatment, sand blasting, grinding and the like. Non-limiting examples of useful non-plastomer cover compositions include blends of ethylene-acrylic acid or ethylene-methacrylic acid, as well as copolymers neutralized with mono-or divalent metals such as sodium, potassium, lithium, calcium, zinc or magnesium. Such compositions are shown in U.S. Pat. No. 5,368,304, the disclosure of which is incorporated herein in its entirety by reference. The plastomer cover layer or layers are then formed over the core using a conventional molding technique, such as compression molding or injection molding. The golf ball is finished by applying an indicia and a thin top coat with or without the use of a primer coat.
The plastomer and ionomer typically are subject to intensive mixing such as in a Banbury mixer, two roll mill, or the like. When the plastomer cover is made by compression molding, the golf ball center is placed between two half-shells and the ball is molded for about 1-3 minutes at 200-300xc2x0 F. and 100 p.s.i. Subsequently, the molded ball is cooled for about 10 minutes. When the plastomer cover is made by injection molding, the cover material is heated to 300-400xc2x0 F. and injection molded into a cold mold where it is maintained for about 20-60 seconds.
Coefficient of restitution (COR) is measured by firing a golf ball from an air cannon at about 125 feet per second against a steel plate positioned 12 feet from the muzzle of the cannon. The rebound velocity then is measured. The rebound velocity is divided by the initial velocity of 125 feet per second to give the COR.
Riehle compression is a measurement of the deformation of a golf ball in inches under a load. Riehle compression can be converted to PGA compression by subtracting Riehle compression values from 160.
The xe2x80x9cGuillotine Cut Testxe2x80x9d employed to measure cut resistance is performed by holding an unfinished ball firmly in a cavity to expose the top half of the ball. A guillotine blade weighing 5 pounds and having inner and outer blade edge angles of 90xc2x0 and 60xc2x0 relative to the horizontal, respectively, and a blunt cutting edge of three sixty-fourths inch radius which is designed to simulate the leading edge of an iron is dropped from a height of three feet to strike the ball at a point one-half inch off the top center point. The guillotine blade is guided during the drop by means of a substantially friction-free vertical track. Optionally, but not necessarily, the test can be repeated on the same or on different sections of the ball. Ball failure is defined as permanent damage evidenced by a crack or by removal of a segment from the ball surface. A rating of 1 is excellent and a rating of 4 is poor. The cut-off for a commercially acceptable ball is a rating of 3.
Having generally described the invention, the following examples are included for purposes of illustration so that the invention may be more readily understood and are in no way intended to limit the scope of the invention unless otherwise specifically indicated. In the examples, Shore C and Shore D hardness values generally were measured in accordance with ASTM D-2240, except that measurements were made on the curved surface of a golf ball.

Golf ball cover containing a blend of ionomer and plastomer, and method of making same


A method has been described for preparing an ultrathin tabular grain emulsion rich in silver bromide, having {111} major faces, wherein tabular grains having a thickness of less than 0.08 xcexcm exhibit an average aspect ratio of more than 5:1 and account for at least 75% by number of hexagonal grains and a coefficient of variation on average equivalent surface area of less than 0.50. The process is characterized in that during formation, (a) pH is maintained from 0.8 to 10; (b) a gelatino-peptizer is present in a concentration of 0 to 50 g per liter of dispersing medium, and (c) pBr having a value of at least 1.8 is maintained during grain nucleation and pBr is maintained at less than 2.4 during growth provided that a gelatin peptizer which is free from calcium ions and has a methionine content of less than 30 micromoles per gram of gelatino-peptizer is present.

The present invention relates to a method of preparing light-sensitive ultrathin tabular grains rich in silver bromide, having {111} major faces.
High aspect ratio tabular grains exhibit several pronounced photographic advantages as is well-known since their introduction into photographic applications in the eighties. Thanks to their particular morphology greater amounts of spectral sensitizers can be adsorbed per mole of silver halide if compared with classical globular (e.g. cubic or octahedral) grains. As a consequence such spectrally sensitized tabular grains show an improved speed-granularity relationship and a wide separation between their blue speed and minus blue speed. Sharpness of photographic images can be improved using tabular grains thanks to their lower light scattering properties, again if compared with conventionally known globular emulsion grains. In color negative materials e.g. the conventional sequence of the light-sensitive layers can be altered and the yellow filter layer can be omitted. In developed black-and-white images high covering power is obtained even at high hardening levels. Alternatively reduced silver halide coverages can be achieved if desired, which again results in improved sharpness. In duplitized radiographic materials the presence of tabular grains reduces the so-called cross-over which is the main factor for sharpness in such materials. Moreover coating amounts of silver can be reduced, further in favor of production cost and ecology.
An emulsion is generally understood to be a xe2x80x9ctabular grain emulsionxe2x80x9d when tabular grains account for at least 50 percent of total grain projected area. A grain is generally considered to be a tabular grain when the ratio of its equivalent circular diameter to its thickness is at least 2. The equivalent circular diameter of a grain is the diameter of a circle having an area equal to the projected area of the grain.
Early patent disclosures on high aspect tabular grains, e.g. U.S. Pat. Nos. 4,434,226; 4,439,520; 4,425,425; 4,425,426; 4,433,048 and Research Disclosure, Vol. 225, January 1983, Item 22534, are concerned with high sensitive silver bromide or silver iodobromide emulsions. In a lot of photographic applications high sensitivity remains important. As nowadays ultrathin tabular grains, in the range of from 0.05 up to 0.10 xcexcm are envisaged as in EP-A""s 0 650 085, 0 667 557, 0 701 164, 0 701 166, 0 706 079, 0 699 945 up to 0 699 951, 0 756 199, 0 758 758 and in U.S. Pat. Nos. 5,470,698; 5,641,618; 5,667,955 it is clear that a major role is dedicated to spectral sensitization of such thin tabular grains, making use of huge sensitizing amounts thereof, in order to provide high speed, high covering power, low cross-over and a low level of residual colour after (rapid) processing. As it remains important to provide a high a percentage of tabular grains as high as possible within the whole emulsion crystal population, in favor of xe2x80x9cchemical homogneityxe2x80x9d, reflected in sensitometric benifits (like desired higher contrast e.g.) as a result of xe2x80x9cphysicalxe2x80x9d or xe2x80x9cmorphological homogeneityxe2x80x9d offered by the said tabular grains, it is clear that every improvement in that direction is highly appreciated. Without taking into account well-defined emulsion preparation parameters when preparing tabular grains, it is well-known by a person skilled in the art of photography that such a method leads to grain populations consisting of a mixture of all shapes of crystals.
As a consequence many attempts have been made in order to improve the degree of homogeneity of the size and shape of the crystals. In this context EP-A""s 0 566 076; 0 506 947; 0 518 066; 0 513 722 and 0 911 687 and U.S. Pat. No. 4,797,354 are related with the preparation of monodisperse hexagonal tabular crystals. In said U.S. Pat. No. 4,797,354 the preparation has been described of tabular emulsions having a high percentage of hexagonal, tabular crystals accounting for 70 to 100% of the total projected area of the said crystals with an average aspect ratio of from 2.5/1 to 20/1. However the examples therein, and in the other references cited, except for the said EP-A 0 911 687 are illustrative for a low yield of silver halide emulsion in the reaction vessel mixture, said yield being defined as amount of silver nitrate precipitated per liter of the said reaction vessel mixture.
For radiographic applications photographic advantages of tabular grains, if compared with normal globular grains, are a high covering power at high forehardening levels as set forth in U.S. Pat. No. 4,414,304. Further a high developability and high sharpness especially in double side coated spectrally sensitized materials can be obtained. The thinner the tabular grains and the lower the number of non-tabular grains in the total grain population the greater these advantages are. To express it in another way: a high degree of homogeneity in grain morphology is desired, leading to a high covering power in order to further offer the possibility to coat lower amounts of silver. Moreover with respect to ecology it is of utmost importance to prepare tabular grains rich in silver bromide having an enhanced covering power. The present invention thus further extends the teachings on thin tabular {111} emulsion grains rich in silver bromide showing a high degree of homogeneity.
It is an object to reduce the amount of silver halide coated in black-and-white materials, and more particularly, those coated on one or both sides of a transparent support as used in radiographic applications, in order to have reduced production costs before selling those materials and environmental load after processing said materials after exposure.
As ultrathin grains having {111} major faces are envisaged to offer a valuable tool to reach the objects of the present invention it was a further object to provide a method to produce said ultrathin grains, preferably having an average grain thickness of less than 0.08 xcexcm and even more preferably of less than 0.06 xcexcm.
It was still a further object of the present invention to add at least one spectral sensitizer in amounts providing high speed, covering power and low cross-over.
Further objects will become apparent from the description hereinafter.
It has been found that the objects of the present invention are attained by a preparation method, within a temperature-controlled reaction vessel, of an ultrathin tabular grain emulsion rich in silver bromide, having {111} major faces, wherein tabular grains having a thickness of less than 0.08 xcexcm exhibit an average aspect ratio of more than 5:1 and account for at least 80 percent of total grain projected area of said grains, said process comprising introducing into a temperature-controlled reaction vessel an aqueous dispersing medium and silver, bromide, and, optionally, iodide and/or chloride, and maintaining pBr values within said reaction vessel during grain nucleation and growth that favors the formation and growth of tabular grains, characterized in that at the time said tabular grains are being formed, (a) pH in said reaction vessel is maintained at a value ranging from 0.8 to 10; (b) a gelatino-peptizer is present in the reaction vessel in a concentration of from 0 to 50 g per liter of said dispersing medium, and pBr within said reaction vessel has a value of at least 1.8 is maintained during grain nucleation, wherein nucleation is performed in a reaction vessel at a temperature in the range from 10-60xc2x0 C., more preferably in the range from 10-50xc2x0 C., and even more preferably in the range from 40-50xc2x0 C., and a pBr value within said reaction vessel is maintained at a value of less than 2.4 during growth, wherein growth is performed in a reaction vessel at a temperature in the range from 40-80xc2x0 C. (in the range from 40-50xc2x0 C. if an average grain thickness of 0.06 xcexcm is envisaged), provided that a gelatino peptizer which is free from calcium ions and has a methionine content of less than 30 micromoles per gram of gelatino-peptizer (oxidized to a degree in order to have a methionine content of at most 4000 ppm) is present in said dispersing medium during grain nucleation and growth.
Moreover a photographic material comprising an emulsion prepared according to the method of the present invention has been claimed. Specific features for preferred embodiments of the invention are set out in the dependent claims.
Further advantages and embodiments of the present invention will become apparent from the following description.
As can be derived from the statement of the present invention set forth above, it is an essential feature that in the temperature-controlled reaction vessel a gelatino peptizer is provided which is free from calcium ions and has a methionine content of less than 30 xcexcmoles per gram of gelatino-peptizer (oxidized to a degree in order to have a methionine content of at most 4000 ppm) and that the gelatino peptizer is present in said dispersing medium during grain nucleation and growth.
The calcium content of most commercial high-quality inert gelatins is about 0.4% or about 100 mmol/kg, measured at the end of the preparation process of inert gelatin. The basis for a high-quality gelatin is preferably formed by pure, degreased hard cattle bones. In a first preparation step the bones are treated with acid in order to remove calcium and magnesium phosphates. This step is followed by an alkaline hydrolysis step, wherein mostly use is made of calcium hydroxide. At the low pH used to remove the phosphates the calcium ions, bound to specific amino acids of the polypeptide, are exchanged with the protons from the used acid. During the alkaline hydrolysis with calcium hydroxide the polypeptide is saturated with calcium ions again. After diafiltration the non-removable calcium concentration in the gelatin is about 0.5% or 125 mmol/kg. When slightly acidifying during washing the calcium content can be reduced to about 0.4% (40 ppm) or 100 mmol/kg. These and other data can be found in the scientific publication xe2x80x9cInfluence of Calcium on the Physical properties of Gelatin Solutions and on Symplex Formation with Macromolecular Polyanionsxe2x80x9d by B. H. Tavernier, J. Phot. Sci., Vol. 40, (1992), p. 168-173. The author concluded that complex-bound calcium ions strongly decrease the electric potential carried by gelatin. The influence of calcium ions on physical characteristics such as viscosity was found to be non-significant. So called xe2x80x9ccalcium free gelatinxe2x80x9d is obtained by cation exchange by means of an ion exchange resin, preferably a so-called mixed-bed resin. Substantially xe2x80x9ccalcium free gelatinxe2x80x9d is thus defined as gelatin with a calcium content at a level below 40 ppm which corresponds with the analytical detection limit.
On the other hand oxidized gelatin is commonly defined as a gelatin having a methionine content of less than 30 xcexcmol/g, which corresponds with an amount of about 4400 ppm or less. So gelatin can e.g. be oxidized by means of e.g. hydrogen peroxide. A publication on the determination of methionine and its oxides in gelatin can be found e.g. in J. Phot. Sci., Vol. 41, (1993), p. 172-175, by S. Tani and T. Tani. A high number of tabular grains rich in silver bromide in the total grain population is obtained if use is made in the preparation method of so-called xe2x80x9coxidized gelatinxe2x80x9d, characterized by the presence in the said gelatin of amounts of methionine of less than 30 xcexcmoles per gram of gelatin as claimed in U.S. Pat. No. 4,713,320. Modification of the methionine content of a gelatino-dispersion medium by means of an oxidizer which should be added to the reaction vessel immediately before nucleation formation can also be applied as has been described in U.S. Pat. No. 5,372,975, wherein seed grains are further added. Seed grains formed in the presence of an oxidizing agent have futher been described in JP-A 05-210187, in JP-A 06-003758 and in JP-A 06-003759. Processing a gelatin solution by means of H202 has e.g. been described in JP-A 05-341415. Other oxidizing agents besides hydrogen peroxide as e.g. ozone, peroxy acid salts, halogens, thiosulphonic acid salts, quinones and organic peroxides can also be used as has been disclosed in U.S. Pat. No. 5,489,504. Oxidation of methionine reduces the complexing ablity of gelatin.
In order to determine the methionine content of gelatin in a quantitative manner many references from literature are available as e.g. in J.Phot.Sc., Vol. 28(1980), p.111-118 wherein as most obvious reducing substances in gelatin methionine residues of the macromolecule are determined in reaction with Au(III)-ions. The so-called xe2x80x9cgold numberxe2x80x9d permits determination of amounts of methionine in the gelatin following the rule that 1 xcexcmole of Au corresponds with 1.6 xcexcmole of methionine. In J.Phot.Sc., Vol. 33(1989), p.10-17 the methionine content was determined making use of the gas chromatographic procedure developed by Apostolatos and Hoff (Anal. Biochem. Vol. 118(1981), p.126) and applied to gelatin by Rose and Kaplan. In this article calorimetry is used in a quantitative procedure for determining methionine (constant over initial pH range examined: 3.0-8.0). In J.Phot.Sc., Vol. 40(1992), p.149-151 amounts of methionine, methionine sulphoxide and methionine sulphone are determined by a chromatographic technique for amino acids (Hitachi Amino Acid Analyser), whereas in J.Phot.Sc., Vol. 41(1993), p.172-175, these compounds are determined by HPLC-techniques. In J.Phot.Sc., Vol. 39(1995), p. 367-372 it has been established that a good correlation between methionine content determined by Rose and Kaplan making use of gas chromatographic techniques (4th IAG Conference, Fribourg 1985, Amman-Brass and Pouradier) and the Scatchard technique (described in J.Phot.Sc., Vol. 42(1994), p.117-119) can be found. In the said technique the interaction at pH=3.0 of Ag+ and gelatin is determined by means of potential measurements of free Ag+-ions.
The method of the present invention, wherein, at the time said tabular grains are being formed in the temperature-controlled reaction vessel,
(a) has a pH in the said reaction vessel, which is maintained at a value ranging from 0.8 to 10.0;
(b) provides a gelatino-peptizer which should be present in the reaction vessel in a concentration of from 0 to 50 g per liter of said dispersing medium, and
(c) has a pBr value within said reaction vessel of at least 1.8, which is maintained at the said value during grain nucleation, wherein nucleation is performed in a reaction vessel at a temperature in the range from 10-60xc2x0 C., more preferably in the range from 10-50xc2x0 C., and still more preferably in the range from 40-50xc2x0 C.,; whereas a pBr value within said reaction vessel is maintained at a value of less than 2.4 during growth, wherein growth is performed in a reaction vessel at a temperature in the range from 40-80xc2x0 C. (in the range from 40-50xc2x0 C. if an average grain thickness of 0.06 xcexcm is envisaged) only leads to the desired thin tabular grains if the gelatino peptizer is free from calcium ions and has a methionine content of less than 30 xcexcmoles per gram of said gelatino-peptizer and when said gelatino-peptizer is present in said dispersing medium during grain nucleation and growth.
Control of those differing, well-defined temperature ranges and pBr values during nucleation and growth unambiguously results in the preparation of ultrathin tabular grains rich in silver bromide having {111} major faces, wherein tabular grains having a thickness of less than 0.08 xcexcm (and at least 0.03 xcexcm), exhibit an average aspect ratio of more than 5:1, and account for at least 80 percent of total grain projected area of said emulsion grains or crystals.
During precipitation into said temperature-controlled reaction vessel in said aqueous dispersing medium silver, bromide, and, optionally, chloride and/or iodide ions are introduced, while maintaining pBr values within said reaction vessel during grain nucleation and growth in order to favour the formation and growth of the desired thin tabular grains under the conditions according to the method of the present invention set forth above.
According to the method of the present invention after preparing in the reaction vessel, the temperature of which is controlled in the range between 10 and 60xc2x0 C., more preferably in the range from 10-50xc2x0 C., and still more preferably in the range from 40-50xc2x0 C., the dispersion medium containing calcium-free gelatin having less than 30 xcexcmoles of methionine per gram in a concentration of from 0 to 50 g per liter, a total amount of silver nitrate of less than 10% by weight, and more preferably 0.5% to 5.0%, is added during the nucleation step which consists of simultaneous addition of silver nitrate and halide (preferably pure bromide, optionally in the presence of very small amountsxe2x80x94less than 1 mole % versus bromidexe2x80x94of iodide) salts at the prescribed pBr value of at least 1.8.
In one embodiment according to the method of the present invention less than 50% of said dispersing medium is present during nucleation, the rest being added before or during growth; wherein said gelatino-peptizer is present in a total amount of less than 5% per liter of dispersing medium, and even more preferably in a total amount of from 0.5% to 2.0% per liter of dispersing medium.
With respect to conditions of pH, in one embodiment according to the present invention pH in said temperature-controlled reaction vessel is maintained at a value ranging from 0.8 to 3.0 during grain nucleation and from 0.8 to 8.0 during grain growth.
With respect to conditions of pBr, in one embodiment according to the present invention, said pBr within said reaction vessel is maintained in the range of 2.3-2.5 during grain nucleation, wherein nucleation is performed in a reaction vessel at a temperature in the range from 10-60xc2x0 C., more preferably in the range from 10-50xc2x0 C., and even more preferably in the range from 40-50xc2x0 C., e.g. 45xc2x0 C. as in most inventive examples given hereinafter.
In another embodiment according to the method of the present invention, growing said silver halide crystal nuclei proceeds by precipitation of silver brom(oiod)ide or silver brom(ochloro)(iod)ide by means of double-jet precipitation of an aqueous silver nitrate solution and an aqueous solution comprising the halide ions, wherein more than 90% and more preferably up to 95% by weight of the total amount of silver nitrate is consumed. It is clear that the method of the present invention is related with thin tabular grains having {111} major faces and which is composed of silver halide crystals rich in silver bromide, i.a. containing more than 90 mole % of silver bromide, more preferably more than 95 mole % of silver bromide and even more preferably at least 99 mole % of silver bromide, whereas the other halides are optionally present: chloride in an amount in the range from 0% up to at most 10 mole % and iodide in an amount of at most 3 mole % and even more preferably in the range from 0.05 mole % up to 1.0 mole %. In one embodiment according to the the method of the present invention, iodide ions, when present, are added after ending growth by iodide providing compounds. In another embodiment according to the method of the present invention said iodide providing compounds are potassium iodide, iodate ions, organic iodide releasing compounds, I3xe2x88x92 or ultrafine AgI microcrystals having an average diameter of less than 0.050 xcexcm.) Information about practical use of such compounds providing iodide ions in emulsion preparation can be found in EP-A""s 0 563 701, 0 563 708, 0 561 415, 0 651 284 and 0 926 133 and in U.S. Pat. Nos. 5,498,516; 5,736,412 and 5,879,874.
The different precipitation steps can be alternated by physical ripening steps or by so called xe2x80x9cneutralization stepsxe2x80x9d, during which the pAg value is changed to a value required in the next growth step by adding an amount of silver nitrate solution or a water soluble halide salt within a well-defined time of addition by means of the single-jet technique. Alternative ways to regulate the pAg to the desired value before continuing the processing are diluting the emulsion present in the reaction vessel, diafiltration or ultrafiltration and even flocculation and washing procedures, the last techniques being preferred to concentrate the emulsion crystals in the reaction vessel. Any combination or any choice of the mentioned techniques may be applied thereto, provided that pBr is controlled during the growth steps at a value of less than 2.4 for a temperature-controlled reaction vessel having a temperature in the range from 40-80xc2x0 C. (and more particularly from 40-50xc2x0 C. if an average grain thickness of 0.06 xcexcm is envisaged).
At least two growth steps are commonly used. The ratio of the second growth step to the first growth step and the pBr in this second growth step is such that the tabular {111} grains rich in silver bromide at the end of the preparation according to the method of the present invention exhibit an average aspect ratio of more than 2:1.
According to the method of the present invention thin {111} tabular grains rich in silver bromide having a thickness of at least 0.03 xcexcm, exhibiting an average aspect ratio of from 5:1 to 50:1 are thus prepared, said tabular grains accounting for at least 75%, and more preferably at least 80%, by number of hexagonal grains and a coefficient of variation on average equivalent surface area of less than 0.50.
During the growth step(s) an increasing flow rate of silver and halide solutions is preferably applied, e.g. a linearly increasing flow rate. Typically the flow rate at the end is about 3 to 10 times greater then at the start of the growth step.
In a preferred embodiment according to the method according of the present invention the molar ratio of reactant flow rates during grain nucleation to reactant flow rates at the start of grain growth ranges from 1.0 to 50.
In another preferred embodiment according to the present invention the ratio of silver bromide precipitated during growth versus during nucleation ranges from 10:1 up to 100:1.
Whereas according to the method of the present invention the whole precipitation reaction, including nucleation, growth, neutralization and Ostwald ripening or physical ripening steps are performed in one temperature-controlled reaction vessel, it is clear that nuclei can be prepared in a separate vessel, whereas growth of the said nuclei may proceed in another vessel, provided that the conditions of pH, pBr and temperature are in accordance with those as described in the statement of the present invention.
According to another embodiment of the method of the present invention, besides performing nuclation in a concentrated reaction vessel, it may be important to concentrate the reaction mixture volume obtained by ultrafiltration during the precipitation growth steps by applying during said ultrafiltration process an ultrafiltration flux equal to (as preferred in steady-state circumstances) or higher than total flow rates of silver salt and halide salt solutions, thereby concentrating silver halide formed in the said reaction vessel to e.g. at least 250 g, expressed as an equivalent amount of silver nitrate, per liter, or even from 300 g up to 450 g per liter. In order to get the preferred volume of the reaction mixture in the reaction vessel it is however possible that a temporary lower ultrafiltration flux is required. The practically applied ultrafiltration or membrane flux further is a function of the total operative surface of the membrane and the trans-membrane pressure. The right choice of the membrane used in order to reach the desired volume of the reaction mixture in the reaction vessel is thus very important. Preferably the ultrafiltration procedure is applied in a continuous way during the precipitation steps, but, if required, it can be interrupted for short periods as e.g. during physical ripening preferably no ultrafiltration is applied. By applying the ultrafiltration procedure the total reaction mixture volume can be lowered during the precipitation. Alternatively the reaction mixture volume can be readjusted, e.g. kept constant by the application of an additional jet of water. By those methods it is possible to reduce the end precipitation volume and to concentrate silver halide to values set forth hereinbefore. This achievement cannot be attained by solely concentrating the silver ion and halide ion jets as in that case a tremendous deviation from the required morphologic homogeneity and homogeneity of the crystal size distribution is observed, but as already set forth hereinbefore, by the presence in low amounts of oxidized gelatin in a low starting volume of the reaction vessel. In a preferred embodiment an ultrafiltration module is conceived in such a way that the total volume of the ultrafiltration module and of its connecting means, is lower than ⅓ of the total precipitation volume. Moreover the circulation flux through the ultrafiltration module is preferably high enough, in order to achieve a delay time in the module of any liquid volume unit of lower than 60 seconds and, most preferably lower than 30 seconds. Even delay times as low as 10 seconds can be achieved.
A preferred ultrafiltration module for the practice of this invention is a ROMICON HF2-20-PM10, provided with a pump. For a typical precipitation (see examples) the flow rate of the silver ion jet during the growth step(s) is linearly increased to an end rate of 25 ml/min per 500 g of silver nitrate to be precipitated and a linearly increasing flux having an end rate of about 50 ml/min is applied. But in the case of more strongly increasing flow rates, e.g. quadratically increasing flow rates, a flux of about 200 ml/min can be established if required.
According to another embodiment of the method of the present invention a variation of the grain size distribution of the equivalent circular diameters of tabular grains having a value of less than 0.50 is obtained, wherein the percentage by number of hexagonal grains is at least 80%. Said xe2x80x9cvariationxe2x80x9d for the thus obtained thin tabular grains is defined as the homogeneity (width) of the distribution, independent on the average grain size.
Preparation of silver bromo(chloro)iodide emulsion crystals can be achieved by mixing a soluble bromide or bromochloride mixture and a soluble iodide salt in one or more of the halide solutions up to the desired concentrations, expressed in mol %, required in each preparation step by double jet or by a triple jet technique by separate addition of an iodide containing aqueous solution. Due to the lower solubility of silver iodide in comparison with silver bromide, said iodide ions are able to displace bromide and chloride ions from the grain, a technique known in the art as conversion. Iodide ions may also be incorporated into the silver halide crystal lattice by the addition of a previously prepared silver iodide micrate emulsion, composed of either pure silver iodide or mixed halide ultrafine crystals, but as has already set forth hereinbefore in a preferred embodiment iodide releasing agents are used, at least partially, e.g. in one or more conversion steps during or at the end of the precipitation. Even bromide releasing agents are not excluded in the precipitation steps according to the method of this invention.
Two or more types of tabular silver halide emulsions that have been prepared differently can be mixed for forming a photographic emulsion for use in photographic materials according to the present invention, depending on the desired specifications. Thin tabular silver halide emulsions rich in silver bromide, prepared by the method of the present invention, can be chemically sensitized as has been described e.g. in xe2x80x9cChimie et Physique Photographiquexe2x80x9d by P. Glafkides, in xe2x80x9cPhotographic Emulsion Chemistryxe2x80x9d by G. F. Duffin, in xe2x80x9cMaking and Coating Photographic Emulsionxe2x80x9d by V. L. Zelikman et al, and in xe2x80x9cDie Grundlagen der Photographischen Prozesse mit Silberhalogeni-denxe2x80x9d edited by H. Frieser and published by Akademische Verlagsgesell-schaft (1968). Chemical sensitization has e.g. also been described in Research Disclosure No 38957 (September 1996), Chapter IV.
As described in said literature chemical sensitization can be carried out by effecting the ripening in the presence of small amounts of compounds containing sulphur e.g. thiosulphate, thiocyanate, thioureas, sulphites, mercapto compounds, and rhodamines. Said compounds containing sulphur can also be, at least partially, replaced by compounds containing selenium and/or tellurium. The emulsions may be sensitized also by means of gold-sulphur, gold-sulphur-selenium, gold-selenium ripeners or by means of reductors as e.g. tin compounds described in GB-Patent 789,823, amines, hydrazine derivatives, formamidine-sulphinic acids, and silane compounds. Useful information about chemical sensitization of tabular grains by means of selenium compounds can be found in EP-A""s 0 404 142, 0 443 453, 0 488 029, 0 585 787 and 0 638 840 and in U.S. Pat. Nos. 5,028,522; 5,112,733; 5,158,892; 5,397,692; 5,348,850; 5,466,571; 5,573,901 and 5,888,717; whereas information about chemical sensitization of tabular grains by means of tellurium compounds can be found in EP-A""s 0 619 515, 0 809 137 and in EP-Application No. 99202439, filed Jul. 23, 1999 and in U.S. Pat. Nos. 5,459,027; 5,395,745; 5,561,033; 5,358,850; 5,654,134; 5,759,760; 5,888,717.
The tabular silver halide emulsions may be spectrally sensitized with methine dyes such as those described by F. M. Hamer in xe2x80x9cThe Cyanine Dyes and Related Compoundsxe2x80x9d, 1964, John Wiley and Sons and in Research Disclosure No 38957 (1994), Chapter V. Dyes that can be used for the purpose of spectral sensitization include cyanine dyes, merocyanine dyes, complex cyanine dyes, complex merocyanine dyes, hemicyanine dyes, styryl dyes and hemioxonol dyes. Particularly valuable dyes are those belonging to the cyanine dyes, merocyanine dyes and complex merocyanine dyes. A survey of useful chemical classes of spectral sensitizing dyes and specific useful examples in connection with tabular grains is given in the already cited Research Disclosure Item 22534. Oxacarbocyanines have been described e.g. in U.S. Pat. No. 5,434,042. Especially preferred green sensitizers in connection with the present invention are anhydro-5,5xe2x80x2-dichloro-3,3xe2x80x2-bis(n.sulfobutyl)-9-ethyloxacarbo-cyanine hydroxide and anhydro-5,5xe2x80x2-dichloro-3,3xe2x80x2-bis(n.sulfopropyl)-9-ethyl-oxacarbo-cyanine hydroxide. Imidacarbocyanines as e.g. those described in Research Disclosure No 37312 (1995) may be useful as well as combinations of oxacarbocyanines and imidacarbocyanines as in EP-A 0 590 593 from the viewpoint of sensitivity as well as from the viewpoint of decolouring properties and stain removal in the processing of materials containing spectrally sensitized tabular grains rich in silver bromide as in this invention.
Useful information about spectral sensitization, applicable to thin tabular grains prepared according to the method of the present invention can be found in EP-A""s 0 487 010, 0 506 584, 0 509 519, 0 514 105, 0 590 715, 0 556 413, 0 608 312, 0 614 542, 0 547 568, 0 634 688, 0 562 476, 0 608 955, 0 712 033, 0 712 034, 0 651 283, 0 699 945, 0 666 497, 0 794 232, 0 844 516, 0 833 195, 0 953 867, 0 809 139 and 0 897 131; in U.S. Pat. Nos. 5,118,600; 5,141,846; 5,348,849; 5,259,016; 5,308,748; 5,391,475; 5,364,755; 5,348,850; 5,536,634; 5,851,752; 5,612,176; 5,614,359; 5,641,618; 5,700,608; 5,851,243; 5,928,854; 5,972,590 and in EP-Application Nos. 999204008, 99204009, and 99204011, filed Nov. 26, 1999. In view of the desired low residual colour after processing of materials coated with emulsions having thin tabular grains and requiring huge amounts of spectral sensitizer the methods with respect to spectrally sensitize said grains as described in EP-A""s 0 953 867 and in EP-Applications Nos. 99201189 and 99201190, both filed Apr. 16, 1999 are particularly recommended.
In classical emulsion preparation spectral sensitization traditionally follows the completion of chemical sensitization. However, in connection with tabular grains, it is specifically considered that spectral sensitization may occur simultaneously with or may even precede completely the chemical sensitization step: the chemical sensitization after spectral sensitization is believed to occur at one or more ordered discrete sites of tabular grains. This may also be done, just as in e.g. EP-A""s 0 556 413 and 0 953 867 with the emulsions prepared according to the present invention, wherein the chemical sensitization proceeds in the presence of one or more phenidone and derivatives, a dihydroxy benzene as hydroquinone, resorcinol, catechol and/or a derivative(s) therefrom, one or more stabilizer(s) or antifoggant(s), one or more spectral sensitizer(s) or combinations of said ingredients. Especially 1-p-carboxyphenyl, 4,4xe2x80x2 dimethyl-pyrazolidine-3-one may be added as a preferred auxiliary agent.
The gelatinous silver halide emulsion rich in silver bromide prepared according to the method of the present invention, characterized by a specific gelatin composition as set forth hereinbefore, is further coated in hydrophilic layer(s) which may, just as non-light-sensitive layers of the photographic material according to this invention, comprise compounds preventing the formation of fog or stabilizing the photographic characteristics during the production or storage of the photographic elements or during the photographic treatment thereof. Many known compounds can be added as fog-inhibiting agent or stabilizer to the silver halide emulsion layer or to other coating layers in water-permeable relationship therewith such as an undercoat or a protective layer. Suitable examples are e.g. the heterocyclic nitrogen-containing compounds such as benzothiazolium or benzselenazolium salts as described e.g. in EP-A 0 488 030 and 0 490 297, nitroimidazoles, nitrobenzimidazoles, chlorobenzimidazoles, bromobenzimidazoles, mercaptothiazoles, mercaptobenzothiazoles, mercaptobenzimidazoles, mercaptothiadiazoles, aminotriazoles, benzotriazoles (preferably 5-methyl-benzotriazole), nitrobenzotria-zoles, mercaptotetrazoles, in particular 1-phenyl-5-mercaptotetrazole, mercaptopyrimidines, mercaptotriazines, benzothiazoline-2-thione, oxazoline-thione, triazaindenes, tetrazaindenes (as in EP-A 0 843 209, wherein azaindenes or tetra-azaindenes have been added between emulsion grain formation and emulsion washing; and in EP-A 0 845 703) and pentazaindenes, especially those described by Birr in Z. Wiss. Phot. 47 (1952), pages 2-58, triazolopyrimidines such as those described in GB 1,203,757, GB 1,209,146, JP-A 75/39537, and GB-A 1,500,278, and 7-hydroxy-s-triazolo-[1,5-a]-pyrimidines as described in U.S. Pat. No. 4,727,017, and other compounds such as benzenethiosulfonic acid, benzenethiosulfinic acid and benzenethiosulfonic acid amide or N-containing heterorings in general as described in EP-A""s 0 547 568 and 0 452 811. Other compounds that can be used as fog-inhibiting compounds are described in EP-A 0 590 620 (masked heterocyclic antifoggants), in EP-A 0 658 803 (alkyne substituted heterocyclic compounds), in EP-A 0 961 164 (amino-substituted cyclopentadiones) and in Research Disclosure No 17643 (1978), Chapter VI and in RD No 38957 (1996), Chapter VII. Many of these fog-inhibiting compounds may have been already added before or during chemical ripening of the tabular silver halide crystals rich in silver bromide.
It is clear that additional gelatin is added in a later stage of the emulsion preparation, e.g. after washing, in order to establish optimal coating conditions and/or to establish the required thickness of the coated emulsion layer. Preferably a gelatin to silver halide ratio ranging from 0.3 to 1.0 is then obtained, wherein extra gelatin added is not required to have a composition as specific as in the preparation step of the grains according to the method of the present invention. Another binder may also be added instead of or in addition to gelatin or gelatin derivatives as e.g. phthalated gelatin. Useful vehicles, vehicle extenders, vehicle-like addenda and vehicle related addenda have been described e.g. in Research Disclosures Nos 36544 (1994) and 38957 (1996), chapter II.
The gelatin binder of the photographic material having at least one gelatinous emulsion according to the present invention can be forehardened with appropriate hardening agents such as those of the epoxide type, those of the ethylenimine type, those of the vinylsulfone type e.g. 1,3-vinylsulphonyl-2-propanol, chromium salts as e.g. chromium acetate and chromium alum, aldehydes e.g. formaldehyde, glyoxal, and glutaraldehyde, N-methylol compounds e.g. dimethylol-urea and methyloldimethylhydantoin, dioxan derivatives e.g. 2,3-dihydroxydioxan, active vinyl compounds e.g. 1,3,5-triacryloyl-hexahydro-s-trizine, active halogen compounds e.g. 2,4-dichloro-6-hydroxy-s-triazine, and mucohalogenic acids e.g. mucochloric acid and mucophenoxychloric acid. These hardeners can be used alone or in combination. The binder can also be hardened with fast-reacting hardeners such as carbamoylpyridinium salts as disclosed in U.S. Pat. No. 4,063,952 and with the onium compounds as disclosed in EP-A 0 408 143.
In a preferred embodiment the hydrophilic layer package of silver halide photographic materials comprising in one or more light-sensitive layers one or more {111} tabular emulsions rich in silver bromide crystals prepared according to the method of the present invention, has a swelling degree of not more than 200%. Said swelling degree is determined by means of the following procedure: a sample of the coated material is incubated at 57xc2x0 C. and 34% RH for 3 days, whereafter the thickness (a) of the layer assemblage is measured. Thereafter the sample is immersed in distilled water at 21xc2x0 C. for 3 minutes and the thickness (b) of the swollen layer is measured. The swelling ratio is then calculated as: (bxe2x88x92a)/axc3x97100(%).
The gelatinous emulsions comprising thin tabular grains rich in silver bromide of the present invention can be used in various types of photographic elements, e.g. black and white silver halide photographic materials, like materials used for X-ray diagnostic purposes, or colour sensitive materials.
According to the present invention a photographic material comprising a support and at least one light-sensitive silver halide emulsion layer on at least one side of said support is thus provided, wherein said emulsion layer(s) comprise(s) one or more emulsion(s) containing {111} tabular silver bromide or bromoiodide (optionally silver chlorobromide or chlorobromiodide) emulsion grains prepared according to the method of the present invention disclosed hereinbefore (silver bromide being present therein in an amount of at least 90 mole %, based on silver).
According to the present invention said photographic material is a single or double side coated X-ray material. In one embodiment according to the present invention said photographic element or material thus comprises a support and on one or on each side thereof one or more silver halide emulsion layer(s) coated from a gelatinous emulsion according to the present invention. More specifically said photographic material is thus a single-side or double-side coated X-ray material.
The single-side coated x-ray material may contain one single emulsion layer, as it is the case for many applications, or it can be built up by two or even more emulsion layers. In X-ray photography a material with a single or a duplitized emulsion layer coated on one or both sides of the support thus contains at least one gelatinous silver halide emulsion according to the present invention. By using duplitized emulsions differing in photographic speed by at least 0.15 log E a gain in cross-over exposure in double side coated materials can be obtained. In the case of colour photography the material contains blue, green and red sensitive layers each of which can be single coated, but merely consists of double or even triple layers. Besides the light sensitive emulsion layer(s) the photographic material may contain several light-insensitive layers, e.g. a protective layer, one or more backing layers, one or more subbing layers, one or more intermediate layers e.g. filter layers and even an afterlayer containing e.g. the hardening agent(s), the antistatic agent(s), filter dyes for safety-light purposes, etc.
The photographic element of the present invention may further comprise various kinds of coating physical property modifying addenda as described in RD""s Nos 36544 (1994) and 38957 (1996), Chapter IX, wherein coating aids, plasticizers and lubricants, antistats and matting agents have been described. Development acceleration can be accomplished by incorporating in the emulsion layer or adjacent layers various compounds, preferably polyalkylene derivatives having a molecular weight of at least 400 such as those described in e.g. U.S. Pat. Nos. 3,038,805; 4,038,075 and 4,292,400 as well as in EP-A""s 0 634 688 and 0 674 215.
The photographic element of the present invention may further comprise various other additives such as e.g. compounds improving the dimensional stability of the photographic element, UV-absorbers, spacing agents and plasticizers.
Suitable UV-absorbers are e.g. aryl-substituted benzotriazole compounds as described in U.S. Pat. No. 3,533,794, 4-thiazolidone compounds as described in U.S. Pat. Nos. 3,314,794 and 3,352,681, benzophenone compounds as described in JP-A 2784/71, cinnamic ester compounds as described in U.S. Pat. Nos. 3,705,805 and 3,707,375, butadiene compounds as described in U.S. Pat. No. 4,045,229, and benzoxazole compounds as described in U.S. Pat. No. 3,700,455 and those described in RD""s Nos. 36544 (1994) and 38957 (1996), Chapter VI, wherein also suitable optical brighteners are mentioned. UV-absorbers are especially useful in colour materials where they prevent the fading by light of the colour images formed after processing.
Spacing agents can be present of which, in general, the average particle size is comprised between 0.2 and 10 xcexcm. Spacing agents can be soluble or insoluble in alkali. Alkali-insoluble spacing agents usually remain permanently in the photographic element, whereas alkali-soluble spacing agents usually are removed therefrom in an alkaline processing bath. Suitable spacing agents can be made e.g. of polymethyl methacrylate, of copolymers of acrylic acid and methyl methacrylate, and of hydroxypropylmethyl cellulose hexahydrophthalate. Other suitable spacing agents have been described in U.S. Pat. No. 4,614,708.
Suitable additives for improving the dimensional stability of the photographic element are e.g. dispersions of a water-soluble or hardly soluble synthetic polymer e.g. polymers of alkyl(meth)acrylates, alkoxy(meth)acrylates, glycidyl(meth)acrylates, (meth)acrylamides, vinyl esters, acrylonitriles, olefins, and styrenes, or copolymers of the above with acrylic acids, methacrylic acids, xcex1,xcex2-unsaturated dicarboxylic acids, hydroxyalkyl(meth)acrylates, sulphoalkyl(meth)acrylates, and styrene sulphonic acids.
The photographic material may contain several non-light sensitive layers, e.g. an antistress topcoat layer, one or more backing layers, and one or more intermediate layers eventually containing filter dyes or antihalation dyes that absorb scattering light and thus promote the image sharpness. Suitable light-absorbing dyes used in these intermediate layers are described in e.g. U.S. Pat. Nos. 4,092,168 and 4,311,787, in DE-A 2,453,217, and in GB-A 7,907,440. Situated in such an intermediate layer between the emulsion layers and the support there will be only a small negligable loss in sensitivity but in rapid processing conditions decolouration of the filter dye layers may form a problem. Therefor it should be recommended to decrease the thickness of the whole coated layer packet resulting in shorter drying times after washing in the processing cycle. Alternatively the use of intermediate layers situated between emulsion layer(s) and support, reflecting the fluorescent light emitted by the screens may bring a solution. As the light emitted from the screens by the phosphors incorporated therein is a very important source of light-scattering the addition of appropriate filter dyes to the screens may be recommended. In the presence in the screens of e.g. green light-emitting phosphors use may be made of specific dyes as MAKROLEX ORANGE G or GG, trademarked products of BAYER AG.
One or more backing layers can be provided at the non-light sensitive side of the support of materials coated with at least one emulsion layer at only one side of the support. These layers which can serve as anti-curl layer can contain e.g. matting agents like silica particles, lubricants, antistatic agents, light absorbing dyes, opacifying agents, e.g. titanium oxide and the usual ingredients like hardeners and wetting agents.
The support of the photographic material may be opaque or transparent, e.g. a paper support or resin support. When a paper support is used preference is given to one coated at one or both sides with an xcex1-olefin polymer, e.g. a polyethylene layer which optionally contains an anti-halation dye or pigment. It is also possible to use an organic resin support e.g. cellulose nitrate film, cellulose acetate film, poly(vinyl acetal) film, polystyrene film, poly(ethylene terephthalate) or poly(ethylene naphthalate) film, polycarbonate film, polyvinylchloride film or poly-xcex1-olefin films such as polyethylene or polypropylene film. The thickness of such organic resin film is preferably comprised between 0.07 and 0.35 mm. These organic resin supports are preferably coated with a subbing layer which can contain water insoluble particles such as silica or titanium dioxide.
The photographic material containing tabular grains prepared according to the present invention can be image-wise exposed by any convenient radiation source in accordance with its specific application.
Of course processing conditions and composition of processing solutions are dependent from the specific type of photographic material in which the tabular grains prepared according to the present invention are applied. For example, in a preferred embodiment of materials for X-ray diagnostic purposes said materials may be adapted to rapid processing conditions. Preferably an automatically operating processing apparatus is used provided with a system for automatic regeneration (replenishment) of the processing solutions.
The forehardened material may be processed using one-part package chemistry or three-part package chemistry, depending on the processing application determining the degree of hardening required in said processing cycle. Applications within total processing times of 30 seconds and lower up to 90 seconds, known as common praxis, are possible. From an ecological point of view it is e.g. possible to use developer and fixer solutions free from hardening agents, wherein, in the developer ascorbic acid, analogues and derivatives thereof can be used instead of the commonly used hydroquinone and wherein, in the fixer, sodium thiosulphate instead of ammonium thiosulphate can be used.
By the method of the present invention it is thus possible to provide a high covering power for different hardening levels of the layer material, wherein the substantially thin hexagonal {111} tabular grains rich in silver bromide are coated in gelatinous emulsion form, accounting for at least 75% , and more preferably at least 80%, by number of hexagonal grains, further having a coefficient of variation on average equivalent surface area of less than 0.50.

Method of preparing ultrathin light-sensitive tabular grain emulsions rich in silver bromide


Soy-based, flaked food products are provided. In one form, the food product includes defatted soy flakes, an exogenous source of protein and isolated starch. The product may further include a cereal grain, wherein the defatted soy flakes are present in the product in greater amounts by weight than the cereal grain. The defatted soy flakes may be pre-toasted to reduce the bittery, beany off-flavors of the soybean. Methods of producing the soy-based, flaked food products are also provided.

The present invention relates generally to soy-based food products. Specifically, the invention relates to soy-based food products that include pre-toasted defatted soy flakes, in combination with selected components that provide for a palatable food composition.
Soybeans are widely recognized by medical and health professionals for their health benefits. [Riaz, (1999) xe2x80x9cHealthy Baking with Soy Ingredientsxe2x80x9d, Cereal Foods World, 44(2):88-92]. Various constituents of soybeans, including soy protein and isoflavones, have been linked to the health benefits of soybeans. As one example, soy protein has been found to reduce the risk of coronary heart disease when consumed at about 6.25 g/serving/day as part of a diet low in saturated fat and cholesterol. Attempts have therefore been made to incorporate various forms of soybean into food products.
For example, soy proteins have been incorporated into cereal food products. Some of these food products include soy protein isolates, soy protein concentrates and soy flour. In order to obtain these sources of protein, the defatted soy flake starting material, obtained after extracting soybean oil from soybeans, must be further processed or otherwise refined, which leads to an increase in the cost of the final product.
A further drawback of soybeans are their beany, bittery off-flavors, caused, in part, by lipid peroxidation catalyzed by lipooxygenase. Attempts to reduce the off-flavors in soybeans have included enzymatic pretreatment of the soy protein, or addition of yeast or sodium bicarboatlo the soy product. However, some of these treatments add to an increased cost of the final product, and may not result in a food product that is optimized with respect to texture, structure and overall palatability. Moreover, certain forms of processed soybeans are relatively unpalatable. For example, inclusion of primarily defatted soy flakes in a food product can lead to a gritty, unpalatable mixture. There is therefore a need in the art for an inexpensive, ready-to-eat food product that takes advantage of the low cost of defatted soy flakes as a starting material, includes all of the advantages of soy products, and has an optimal palatability. The present invention addresses this need.
It has been discovered that defatted soy flakes, which traditionally have a gritty, unacceptable texture, may form the basis of a nutritious, delicious food product having an acceptable texture when combined with selected palatable components. Accordingly, in one form of the invention, a soy-based food product that includes defatted soy flakes, an exogenous source of protein and isolated starch is provided. Soy off-flavors may be advantageously reduced by pre-toasting the defatted soy flakes prior to combining them with the other components of the product. Such pretreatment advantageously substantially inactivates or otherwise denatures enzymes, such as lipooxygenases, present in the soy flakes, the activity of which contributes to the off-flavors. Moreover, soy off-flavors may be further reduced by including sodium bicarbonate in the food product. In yet another form of the invention, the food product may be a soy-based cereal food product and thus include a cereal grain in addition to the other components described above. In further forms of the invention, the food product may also include flavoring agents, as well as a coating that may include flavoring agents and a vitamin and/or mineral mixture. In yet other embodiments, a soy-based flaked food product includes a flaked food product having pre-toasted defatted soy flakes incorporated therein is provided.
In another aspect of the invention, methods for producing the food product are provided and include, in another form of the invention, providing, preferably pre-toasted, defatted soy flakes and incorporating the flakes into a flaked food product. In preferred embodiments, a method includes providing defatted soy flakes, preferably pre-toasted, combining the above-described components and processing the mixture into a flaked food product. The food product produced may include up to 100% of the Recommended Daily Allowance (RDA) for 10 essential vitamins and minerals. The soy-based food product is low in fat, cholesterol free and an excellent source of protein.
It is an object of the invention to provide soy-based food products wherein soy off-flavors are reduced.
It is a further object of the invention to provide low cost, nutritious, palatable soy-based food products, and methods for their production.
These and other objects and advantages of the present invention will be apparent from the following description.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to preferred embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications of the invention, and such further applications of the principles of the invention as illustrated herein, being contemplated as would normally occur to one skilled in the art to which the invention relates.
The present invention provides a soy-based, flaked food product that includes pre-toasted, defatted soy flakes, an exogenous source of protein and isolated starch. It has been unexpectedly discovered that an exogenous source of protein and isolated starch, when combined with defatted soy flakes, masks or otherwise reduces the gritty texture of the soy flakes so that a nutritious, delicious food product is obtained having a desirable texture and taste. A cereal grain is also preferably included to further favorably enhance the texture and taste of the product. Moreover, the beany and bittery off-flavors associated with soy-based products are substantially reduced by a pre-toasting step. As soy flakes are utilized as a starting material, the food product described herein is an inexpensive way to enable consumers to enjoy the nutrition and other benefits of soy products. The preferred food product has a texture that is crisp and crunchy, and is able to hold its structure (i.e, will not fall apart and/or become soggy) in milk longer than flakes made from other products. The food product may be eaten anytime as a snack, with or without milk, or as a breakfast food. The preferred soy-based, flaked food product described herein is an excellent source of protein, a good source of fiber, is low in fat and is cholesterol-free. Methods for producing the soy-based, flaked, food products are also provided.
In one aspect of the invention, a soy-based, flaked food product is provided. The food product includes defatted, desolventized soy flakes (also known as xe2x80x9cwhitexe2x80x9d or xe2x80x9cspentxe2x80x9d flakes), isolated starch and an exogenous source of protein. A cereal grain is also preferably included in the food product. The defatted soy flakes may be obtained as a by-product of soybean oil processing as known in the art and as briefly described below.
In a typical operation, soybeans may first be cleaned and dried. The soybeans are then cracked, dehulled, and treated with steam to facilitate flaking, prior to being extracted with hexane to remove the oil. After lipid extraction, the flakes retain their carbohydrate and fiber components and only trace levels of fat remain. After solvent extraction, the flakes are flash-desolventized by quick heating with superheated hexane vapor as known in the art to remove hexane for safe consumption by humans and may typically be purchased in this form. This flash-desolventization step also denatures, to a certain extent, trypsin inhibitors and enzymes that play a role in contributing to off-flavors, such as lipooxygenase [Hettiarachchy, N. and Kalapathy, U., xe2x80x9cSoybean Protein Productsxe2x80x9d, Ch. 8 in Soybeans: Chemistry, Technology, and Utilization, Liu, K. (Ed.), pp. 379-411, Chapman and Hall, NY (1997)]. Although further denaturation of these enzymes may be accomplished in other steps of forming the final food product, it has been found that a pre-toasting step, defined herein to mean a step that functions to reduce soy off-flavors compared to the commercially obtained defatted soy flakes, typically by substantially inactivating lipooxygenases, or other enzymes that play a role in contributing to soy off-flavors.
The pre-toasting step is typically performed at a temperature and for a time period sufficient to reduce the beany, bitter flavor of the soybeans. As an example, the pre-toasting step may include heating the defatted soy flakes at a temperature of about 100xc2x0 C. to about 300xc2x0 C., preferably at about 150xc2x0 C. to about 300xc2x0 C. and most preferably at about 200xc2x0 to about 300xc2x0 C., for a period of about 3 minutes to 10 minutes. A most preferred pre-toasting step is performed at about 205xc2x0 C. for about 5 minutes. This step advantageously removes residual hexane, in addition to reducing soybean off-flavors and provides a food product having an acceptable or otherwise improved taste. The pre-toasting step also contributes to the toasted brown color of the food product. The pre-toasting step is distinguished from, and is accomplished in addition to, the commercial flash-desolventizing step. It has been found that, if the pre-toasting step is accomplished during the cooking step after all of the components of the food product are mixed together, the amount of further cooking that would be needed to obtain an equivalent reduction in off-flavors results in a burnt, or otherwise darkened or blackened product, which significantly adversely affects the texture, appearance and flavor of the product, thereby making it undesirable for consumption.
The defatted soy flakes obtained commercially may have a thickness in the range of about 0.25 mm to about 0.37 mm, and more preferably have a thickness in the range of about 0.25 mm to about 0.30 mm. The flakes may be variously shaped and the average size of the defatted soy flakes will depend on the source of the flakes. Although the defatted soy flakes are typically no larger than about 10 mesh, the mesh size may range from about 10 mesh to about 80 mesh. The defatted soy flakes are typically included in the food product in an amount of at least about 30%, preferably about 30% to about 70%, and more preferably about 40% to about 60% by weight of the dried food product. The defatted soy flakes contribute to the texture, flavor and nutritional benefits of the food product. The defatted soy flakes alone include about 50% protein by weight of the defatted soy flakes, and thus greatly contribute to the protein content of the food product.
The exogenous source of protein also contributes to the texture, flavor and nutrition of the food product. As used herein, an exogenous source of protein includes a protein that has been isolated from its respective source and that is included the food product in addition to any protein contributed by the other protein-containing components of the food product, including the defatted soy flakes and cereal grain. An exogenous source of protein may also include the source from which the protein was isolated, as long as the source includes at least about 50% by weight protein, and preferably about 80% to about 100% by weight protein and contributes palatable, or otherwise suitable, characteristics. A wide variety of exogenous sources of proteins may be included in the food product. For example, the proteins may be isolated from corn, oat, wheat, rye, barley, rice, sorghum, a combination thereof, or from some other source of protein. Many of these proteins may be obtained commercially, or may be isolated by methods well known to the skilled artisan. It is preferred that the protein be obtained from soybeans. For example, the protein may be a soy protein isolate, a soy protein concentrate or may be contributed by soy flour, although soy protein isolates are preferred exogenous sources of protein. The various soy sources of protein may be obtained commercially, or may be isolated from soybeans by well-known methods in the art. Typically, the exogenous source of protein is included in the product in an amount of at least about 1% by weight, preferably about 1% by weight to about 30% by weight, and more preferably about 10% by weight to about 20% by weight of the dried food product.
Proteins are known to be responsible for a wide variety of functional properties of food systems. Although not being limited by theory, the protein in the food product described herein is believed to provide, for example, solubility, water adsorption and retention, cohesion and adhesion, stabilization and may provide other beneficial properties. Such properties advantageously improve dough handling and the shelf-life of the product. Although a majority of the functional properties of soybeans are attributed to the protein fraction, carbohydrates of the soybeans are also known to be responsible for some of the functional properties. For example, it is known that oligosaccharides in soy can absorb water, causing the system, when extruded, to expand and provide a fibrous, lacy network as described in Wolf, W. J. and Cowan, J. C. (1975) Soybeans as a Food Source, CRC Press, Inc., Cleveland, Ohio, p. 43.
As used herein, isolated starch is starch that is added to the food product in addition to the starch that is present in the starch-containing components of the food product, such as the soy flakes and the cereal grain. Starch may be isolated from a wide variety of sources. For example, starch may be obtained from a variety of plants, including cereals such as corn, oat, wheat, rye, barley, rice, sorghum, as well as from other sources, such as cassava and tubers of potato plants, and combinations of any of these sources. The starch may be isolated from these sources by methods known to the skilled artisan, although many of the starches described herein are available commercially. In preferred embodiments, the starch is corn starch. In more preferred embodiments, the starch is a modified food starch, including modified corn starch.
Modified food starches are well known in the art and are described, for example, by Bemiller, J. N. and Whistler, R. L., xe2x80x9cCarbohydratesxe2x80x9d, Ch. 4 in Food Chemistry, 3rd edition, Fennema, O. R., Marcel Dekker, Inc. (Eds.), pp. 201-204, New York (1996). Briefly, modifications to food starch include, for example, crosslinking of polymer chains, non-cross-linking derivatization, depolymerization and pregelatinization. Chemical reactions most frequently used to produce modified food starches include, for example, esterification with acetic anhydride, succinic anhydride, the mixed anhydride of acetic and adipic acids, 1-octenylsuccinic anhydride, phosphoryl chloride, sodium trimetaphosphate, sodium tripolyphosphate, and monosodium orthophosphate; etherification with propylene oxide; acid modification with hydrochloric and sulfuric acids: bleaching with hydrogen peroxide, peracetic acid, potassium permanganate, and sodium hypochlorite; oxidation with sodium hypochlorite; and various combinations of these reactions. A most preferred modified food starch is corn starch modified by cross-linking or pregelatinization. The modified food starches may be produced by methods known to the art and/or may be purchased commercially.
The food starch advantageously contributes to the flavor and texture of the food product. Moreover, food starch also advantageously improves the shelf-life of the product, acts as a humectant and a binder for oils and fats as known in the art. The food starch may be included in the food product in an amount of from about 0.5% by weight to about 15% by weight, preferably about 0.5% by weight to about 10% by weight, and further preferably about 3% by weight to about 6% by weight of the dried food product.
It is preferable to add cereal grains to the flaked food product to form a soy-based, flaked cereal food product,. as the cereal grains also contribute to the texture, flavor and nutrition of the food product. A wide variety of cereal grains may be utilized. For example, corn, oats, wheat, sorghum, rye, rice and combinations thereof may be incorporated into the food product. The cereal grain may be provided in a variety of forms, including flour, grits and cereal meal. In a preferred form of the invention, the cereal grain is corn meal. Cereal meal, such as corn meal, advantageously improves the texture of the flaked food product and further adds structure to the product. That is, the cereal meal helps the cereal keep its form when placed in a liquid medium, such as milk. Moreover, the cereal grain is incorporated into the food product typically in an amount no more than about 30%, preferably no more than about 20%, and more preferably no more than about 10% by weight. The cereal grain may further be preferably incorporated into the food product in an amount of about 3% to about 20%, and more preferably about 5% to about 10%, based on the weight of the dried food product. A greater amount of defatted soy flakes by weight are preferably included in the food product than the cereal grain. Typically about 5 fold to about 10 fold more defatted soy flakes are included in the food product than the cereal grain by weight.
Other components or agents that may affect flavor, texture and/or may further mask soybean off-flavors may be included in the flaked food product. For example, flavoring agents may be added to enhance the flavor and/or texture of the product. A wide variety of flavoring agents may be used, including dextrose, brown sugar, cereal malt syrup, corn syrup, molasses, honey, sorbitol, sucrose (sugar), salt, honey flavoring, or other natural or synthetic flavors or sweeteners. Sucrose is a preferred flavor enhancer and texturizer. Although any form of sucrose may be added, granular sucrose is most preferred. Sucrose may function in improving extrudability factors of cereals, improving texture profiles of cereals, and may be effective in controlling gelatinization of starch. The flavoring agents, especially those that add a sweet flavor to the product, have also been found to help mask any residual off-flavors. The flavoring agents may be added to the food product in an amount of about 0.2% by weight to about 25% by weight, and preferably about 15% by weight to about 20% by weight of the dried food product.
As mentioned above, salt (sodium chloride) may be added to the product as a flavoring agent. Salt may be added to the food product in relatively small amounts, such as about 1% to about 2% by weight of the dried food product, although more or less may be added depending on the taste desired. Moreover, sodium bicarbonate may be added to further mask any residual off-flavors. Typically, about 0.5% by weight to about 2% by weight, preferably about 1% by weight to about 2% by weight sodium bicarbonate is added to the food product, although more or less may be added depending on the taste desired.
The soy-based food product may also include a coating of vitamins and/or minerals. The coating may further include other flavoring agents, such as sweetening agents, as described above to further mask any residual off-flavors. A wide variety of vitamins may be included in the coating. For example, the vitamin coating may include vitamins A, B1, B2, B3, B6, B12, C, D, E, K, biotin and calcium pantothenate, or other desired vitamins. The coating may include minerals such as iron, zinc oxide, copper gluconate and potassium iodide, or other desired minerals. The vitamin/mineral mix is typically provided as a solid that may be dissolved in a flavoring agent liquid carrier. The flavoring agent liquid carrier may include a combination of the flavoring agents described herein. For example, the liquid carrier may include corn syrup, such as high fructose corn syrup, with honey flavoring. The honey-flavored syrup provides a medium for the vitamin pre-mix to be applied, while protecting temperature sensitive vitamins, such as vitamins A and D, from oxidative degradation caused by contacting them with a hot surface of the food product after the food product is cooked. The vitamin/mineral mix is included in the carrier/flavoring medium in an amount to provide at least about 1%, preferably at least about 5%, further preferably at least about 10%, more preferably at least about 25%, further more preferably at least about 50% and most preferably at least about 100% of the recommended daily allowance (RDA) in a single serving, such as a 30 g serving, after the carrier/flavoring medium is sprayed onto the food product. The flavoring agents that are included in the coating contribute about 0.2% by weight to about 3% by weight of the dried food product. As an example, the corn syrup is included in the coating of the dried food product so that it contributes about 1% by weight to about 3% by weight of the dried food product after the coating is applied and dried. The honey-flavoring is included in the coating in an amount of about 0.3% to about 0.6% by weight of the dried food product.
In yet another aspect of the invention, methods of forming a soy-based, flaked food product are provided. In one form of the invention, defatted soy flakes that have been flash-desolventized as described above are first toasted, according to the pre-toasting step described above, and are then combined with the other dry ingredients and mixed with water, typically in a ratio of dry ingredients to water of about 1:1 to about 1:2.5, preferably 1:1.5 to about 1:2, to form a dough. The dough is kneaded until all the ingredients are thoroughly mixed. Pellets are then typically formed that range in size from about 4 mm to about 8 mm in diameter. The pellets then undergo a tempering process by being exposed to room temperature (i.e., about 20xc2x0 C. to about 30xc2x0 C.) air, for a period of about 1 hour to about 3 hours. The pellets are then flaked utilizing appropriate equipment, such as a manual pasta maker, prior to being cooked, or otherwise baked, at a minimum temperature of about 150xc2x0 C., but may be cooked at about 150xc2x0 C. to about 300xc2x0 C., for a period of about 10 to about 20 minutes. The cooked dough is then cooled at room temperature. The moisture content of the final, dried food product is typically less than about 3% by weight of the dried food product.
The flakes may then be coated with a desired coating that includes a vitamin/mineral composition as described above. The coating is dried, typically at room temperature, and the dried food product is then cooled prior to packaging. Altematively, higher temperatures may be used to dry the coating, such as a temperature of no more than about 35xc2x0 C. Such an elevated temperature facilitates the application of the coating and may prevent the oxidative damage of heat labile vitamins that may occur at a temperature higher than about 35xc2x0 C.
The dried food product may then be packaged. The packaging of the food product generally protects the product from moisture gain that may result in loss of crispness, lipid oxidation that may result in rancidity and off-flavors and loss of vitamins due to oxidation. The food product may be packaged in similar cereal -food product packages known in the art. However, a preferred package may include multi-layer bags, preferably made from oriented polypropylene (OPP) coated with polyvinylidene chloride (PVdc), an adhesive and low-density polyethylene (LDPE). The printing for the packaging may be on the inside of the LDPE layer. This may prevent the printing from being rubbed off during shipping and handling by the consumer since the LDPE will cover the printing. By using multiple layer packaging, the barrier properties of each packaging material can be maximized. The cereal bag can have a zip-lock closure for consumer convenience. Butylated hydroxytoluene (BHT), an antioxidant, may be integrated with the OPP to help prevent oxidative damage of vitamins and any lipids present in the food product. Packaging the food product in plastic bags may reduce the cost of the product compared to the cost of packaging in traditional boxes. Table 1 below discloses preferred properties of the packaging materials.