Magnetic head assembly and method for reading and/or writing data onto a thin magnetic layer placed on a photographic element

A method and apparatus for reading and/or recording information on a photographic element having a thin magnetic layer. The apparatus includes a magnetic head assembly having a read and/or write head having an outer engaging surface for contacting the magnetic layer. The outer engaging surface has at least one pole for reading or writing information on the magnetic layer and a protective layer and is made of a material having a Vickers hardness equal to or greater than 1000 kg/mm.sup.2. A spring is provided for applying a substantially perpendicular loading force between the photographic element and the magnetic read and/or write head. The substantially perpendicular loading being equal to or greater than about 10 gm/mm.sup.2.

FIELD OF THE INVENTION 
The present invention is directed to a magnetic head assembly and method 
for reading and writing information onto a thin optical transparent 
magnetic recording layer placed on a photographic element. 
BACKGROUND OF THE INVENTION 
It is known from various U.S. Pat. Nos. including, 3,782,947; 4,279,945; 
4,990,276; 5,217,804; 5,147,768; 5,229,259; and others; to include a 
sensitive silver halide photographic element and an optically transparent 
magnetic recording layer. Such photographic elements are advantageous 
because they can be employed to record images by the customary 
photographic process while at the same time information can be recorded 
into and read from the magnetic recording layer using magnetic record/read 
head. The magnetic recording layer is typically coated across the entire 
photographic element, thus, the necessity for maintaining/providing a very 
thin magnetic layer such that it is substantially optically transparent. 
The use of the photographic element to carry magnetic information on a thin 
magnetic layer present may present significant problems with respect to 
reading and writing applications. The presence of the magnetic recording 
layer can not interfere with the primary function of the photographic 
element which is to achieve realistic reproductions of the original images 
recorded thereon. In addition, the magnetic recording layer must be 
capable of accurately recording information applied thereto and reading 
out the information out on demand. This is particularly difficult because 
the loading and distribution of the magnetic particles in the transparent 
layer must be such as to not interfere with the quality of the 
photographic elements. The resultant magnetic field set up by the very 
thin magnetic layer is minimal. To obtain a quality of the read back 
signal required to meet performance specification intimate contact with 
the magnetic head and magnetic layer must be maintained. 
The photographic element, as is typical in prior art, is coated with a 
hydroscopic photographic emulsion, which expands and contracts with the 
presence of moisture in the atmosphere. The effect on the flatness of the 
medium is perceived and known as curl, representing static forces in the 
media which oppose mechanically applied flattening force against the 
magnetic head. In order to avoid degradation of the image area of the 
film, the magnetic information is preferably placed within a zone located 
outside of the printable image area which generally lies in close 
proximity to the film edge. However, this zone is located in an area which 
undergoes planar deformations due to media properties when subjected to 
environmental extremes, curvatures in a film transport path, and film 
tension in the transport path. These deformations resist the flattening of 
the film which is important in order to provide good contact between the 
magnetic layer and the magnetic head. To lessen the effect of the curl on 
the head to film interface, the photographic media is wrapped over a 
radius of curvature of the magnetic head contact face. This bending of the 
photographic media creates static forces at the edge, known as anticlastic 
curl, which tends to lift the film edge from contact with head face. Since 
photographic film is of substantially greater thickness than of typical 
magnetic tapes, the edge deformation or anticlastic curl is substantially 
greater than that which normally occurs in magnetic tape applications. 
Additionally, since the photographic film is of substantially greater 
thickness than of typical magnetic tapes, the photographic film exhibits a 
substantially greater media stiffness which further represents additional 
opposition to flattening of the film. 
Another concern with the use of a thin magnetic layer is the presence of 
small amounts of residue and/or dirt between the head and film interface, 
which can adversely affect the ability of the head to read the information 
from the thin magnetic layer. In order to minimize residue/dirt build up 
on the head it has been suggested the placement of abrasive particle on 
the film element to minimize residue build up on the head. However, this 
can adversely affect the life of the magnetic head. 
The present invention provides a magnetic head assembly and method for 
reading and/or writing information onto a thin magnetic layer placed on a 
photographic element which overcomes the problems of the prior art. 
The detailed features and advantages of the present invention will become 
more apparent than the following description when taken in conjunction 
with the accompanied drawings in which preferred embodiments of the 
present inventions are shown by way of illustrative example. 
SUMMARY OF THE INVENTION 
In one aspect of the invention there is provided a magnetic head assembly 
for reading and/or recording information on a photographic element having 
a thin magnetic layer, the magnetic head assembly comprising: 
a read and/or write head having an outer engaging surface for contacting 
the magnetic layer, the outer engaging surface comprising at least one 
pole for reading or writing information on the magnetic layer and a 
protective layer, the protective layer being made of a material having a 
Vickers hardness equal to or greater than 1000 kg/mm.sup.2 ; and 
means for providing a substantially perpendicular loading force between the 
photographic element and the magnetic read and/or write head, the 
substantially perpendicular loading force being equal to or greater than 
about 10 gm/mm.sup.2. 
In another aspect of the present invention there is provided a magnetic 
head assembly for reading and/or recording information on a photographic 
element having a thin magnetic layer, the magnetic head assembly 
comprising: 
a read and/or write head having an outer engaging surface for contacting 
the magnetic layer, the outer engaging surface comprising at least one 
pole for reading or writing information on the magnetic layer and a 
protective layer, the protective layer being made of a material having a 
Vickers hardness equal to or greater than 1000 kg/mm.sup.2, the protective 
layer completely surrounding the at least one pole. 
In yet another aspect of the present invention there is provided a system 
for reading and/or recording information on a thin magnetic layer, 
comprising: 
a photographic element comprising a support member having a top surface and 
a bottom surface, a light-sensitive emulsion layer provided on the top 
surface, an optically transparent magnetic layer provided on the bottom 
surface and a lubricant is provided on the bottom side, the photographic 
element having a coefficient of friction less than or equal than 0.3; and 
a read and/or write head having an outer engaging surface for contacting 
the magnetic layer, the outer engaging surface comprising at least one 
pole for reading or writing information on the magnetic layer and a 
protective layer, the protective layer being made of a material having a 
Vickers hardness equal to or greater than 1000 kg/mm.sup.2. 
In still another aspect of the present invention there is provided a method 
for reading and/or writing information onto a thin magnetic layer 
comprising the steps of: 
providing a photographic element comprising a support member having a top 
surface and a bottom surface, a light-sensitive emulsion layer provided on 
the top surface and a thin optically transparent magnetic layer provided 
on the bottom surface; 
a read and/or write head having an outer engaging surface for contacting 
the magnetic layer, the outer engaging surface comprising at least one 
pole for reading or writing information on the magnetic layer and a 
protective layer, the protective layer being made of a material having a 
Vickers hardness equal to or greater than 1000 kg/mm.sup.2 ; 
applying a substantially perpendicular load between the photographic film 
and the magnetic read and/or write head, the substantially perpendicular 
load being equal to or greater than 10 gm/mm.sup.2 ; and 
moving the photographic element across the magnetic head while the load is 
being applied to the photographic element. 
In still another aspect of the present invention there is provided 
photographic apparatus for exposing an image onto a photosensitive 
material, the photographic material having a thin magnetic recording 
layer, the apparatus having a magnetic head assembly for reading and/or 
recording information on the photographic material, the magnetic head 
assembly comprising: 
a read and/or write head having an outer engaging surface for contacting 
the magnetic layer, the outer engaging surface comprising at least one 
pole for reading or writing information on the magnetic layer and a 
protective layer, the protective layer being made of a material having a 
Vickers hardness equal to or greater than 1000 kg/mm.sup.2 ; and 
means for providing a substantially perpendicular loading force between the 
photographic element and the magnetic read and/or write head, the 
substantially perpendicular loading force being equal to or greater than 
about 10 gm/mm.sup.2.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIGS. 1 and 2, there is illustrated a magnetic head assembly 
10 made according to the present invention. The magnetic head assembly 10 
is designed to read and/or write information onto a very thin optically 
transparent magnetic layer placed onto a photographic element. In the 
particular embodiment illustrated, the photographic element is a strip of 
film 12, such as a 35 mm as is well known in prior art. It is of course 
understood that the strip of film may be of any desired size. Referring to 
FIGS. 3, 4, and 5, the photographic film 12 comprises a top surface 14 and 
the bottom surface 16. The film 12 includes a support member 18 having a 
thickness t, which in the particular embodiment illustrated, is 
approximately 85 .mu.m and is made of polyethylene naphthalate (PEN). 
However, layer 18 may be made of any desired material, e.g., polyethylene 
terephthalate, a cellulose ester, or cellulose acetate. An emulsion layer 
20 is provided on one side of support member 18 with an outer protective 
layer 22 disposed over the emulsion layer 20. In the particular embodiment 
illustrated the protective and emulsion layers 20,22 have an combined 
thickness t.sub.E of approximately 27 .mu.m or less. However, the 
thickness t.sub.E of layers 20,22 may be any size desired. 
Disposed on the opposite side of support member 18 is a thin optically 
transparent magnetic layer 24. In the particular embodiment illustrated 
the magnetic layer 24 comprises ferro-magnetic particles and abrasive 
particles. The magnetic particles have a surface area greater than 30 
m.sup.2 /g and a coverage of from about 1.times.10.sup.-11 mg/.mu.m.sup.3 
to about 1.times.10.sup.-10 mg/.mu.m.sup.3. The abrasive particles having 
a mean diameter from about 0.04 .mu.m to 0.4 .mu.m. The specific surface 
area of the abrasive particles being greater than 5 m.sup.2 /g and having 
a Mohs hardness of at least 5 and being present in the transparent 
magnetic/abrasive layer 24 in the amount of 30% by weight based on the 
weight of the magnetic particles present. The thin optically transparent 
magnetic layer 24 typically has a thickness t in the range of about 0.9 to 
1.6 microns. In the embodiment illustrated, the layer has a thickness in 
the range of about 1.1 to 1.3 microns. 
A thin lubricant layer 28 is provided on top of layer 24. The lubricant 
layer 28 and magnetic layer 24 have a combined thickness t.sub.m of about 
1.2 .mu.m. It is important that the thickness and physical properties of 
the lubricant layer 28 and magnetic/abrasive layer 24 be such as not to 
interfere with the optical properties of the emulsion layer 20. Thus, 
layers 24,28 are designed to be substantially optically transparent. It 
should be understood that layers 24,28 may be selected and formulated as 
desired. A specific example of the formulation of these layers in the film 
are illustrated in the following co-pending applications, all of which are 
incorporated herein by reference: U.S. Ser. No. 08/173,793, filed Dec. 22, 
1993, entitled PHOTOGRAPHIC ELEMENT HAVING A TRANSENT MAGNETIC LAYER 
AND A PROCESS OF PREING THE SAME, Brick et al now U.S. Pat. No. 
5,395,743; U.S. Ser. No. 08/173,833, filed Dec. 22, 1993, entitled COATING 
COMPOSITION FOR A TRANSENT MAGNETIC RECORDING LAYER, Wexler now U.S. 
Pat. No. 5,397,826; U.S. Ser. No. 08/193,304, filed Feb. 8, 1994, entitled 
PHOTOGRAPHIC ELEMENT, DeCory et al now U.S. Pat. No. 5,427,900; U.S. Ser. 
No. 08/193,349, filed Feb. 8, 1994, entitled PHOTOGRAPHIC ELEMENT, Wexler 
et al now U.S. Pat. No. 5,432,050; U.S. Ser. No. 08/251,883, filed Jun. 1, 
1994, entitled PHOTOGRAPHIC ELEMENT, Wexler et al now U.S. Pat. No. 
5,436,120; and U.S. Ser. No. 08/252,500, filed Jun. 1, 1994, entitled 
PHOTOGRAPHIC ELEMENT, Wexler et al now U.S. Pat. No. 5,434,037. 
While in the particular embodiment illustrated a separate lubricant layer 
28 is provided, a lubricant may be impregnated into the magnetic layer 24 
and avoid providing of a separate layer. Also, the abrasive particles may 
be in a separate layer from the magnetic layer. 
In the particular embodiment illustrated, the lubricant layer 28 comprises 
caranuba wax, waxes, surfactants, and wetting agents. The film is designed 
such that the coefficient of friction between the film and the magnetic 
head is equal to or less than 0.3, preferably less than or equal to 0.2 
and most preferably, less than or equal to 0.15. In the embodiment 
illustrated, the coefficient of friction ranges from about 0.08 to 0.16. 
Referring to FIG. 3, there is illustrated a top plan view of film 12. As is 
typical, on film 12 there is provided image area 30 wherein images 31 are 
formed in the emulsion layer 20. Disposed laterally outside of the image 
area 30 there is provided magnetic recording areas 32, each being disposed 
outside of the image areas 30 and adjacent the edge 34 of the film. The 
magnetic recording area 32 is placed axially outside the image area 30 so 
as to minimize or avoid degradation of the image on the film. However, as 
can be seen from FIG. 4, the magnetic recording areas 32 are placed in the 
areas of the film having the most curl. It is not unusual for the film to 
have a cross web curl equal to or less than 70 1/m, typically in the range 
of 5 to 45 1/m. In addition to the curl exhibited by the film, the overall 
stiffness of the film contributes to making it difficult to read and/or 
write information on the thin magnetic layer 24. In the embodiment 
illustrated, the film 12 has a modulus of elasticity in the range of about 
8.times.10.sup.5 to 1.2.times.10.sup.6 lbs/in.sup.2. As is typical with 
such films, perforations 36 may be provided adjacent the edges 34 for 
assisting with moving of the film within the camera or printer, or for 
identifying the image area 30. 
Referring back to FIGS. 1 and 2, the magnetic head assembly 10 further 
includes a backer plate assembly 40 is provided for engagement with 
magnetic head 42 through any desired means. In the particular embodiment 
illustrated, the magnetic head 42 is secured to a mounting block 44 having 
a pair of openings 46,47 for mounting of the mounting block 44 to an 
apparatus. In the particular embodiment illustrated, the openings 46,47 
are sized so as to receive a pair of threaded screws (not shown) designed 
to be received by threaded openings (not shown). The magnetic head 
assembly 10 is preferably designed to be used in a high speed photographic 
printing apparatus for printing of photographic images onto photosensitive 
material. An example of such a device is illustrated by the Kodak Clas 35 
printer which can produce prints at a rate of about 3 images per second. 
As illustrated in FIG. 2, the back plate assembly 40 is designed to apply 
a loading force against the back of the film 12 such that the magnetic 
layer 24 will be in direct and intimate contact with the head 42. The 
backer assembly 40 includes a frame 48 which defines a cavity 50 designed 
to hold a reed-like backer member (bubble spring) 52 adapted to urge film 
12 in contact with the head 42. An example of a suitable backer plate 
assembly 40 is described in detail in U.S. Pat. No. 5,274,522, which is 
owned by the assignee of the instant application and is hereby 
incorporated by reference. The backer plate assembly 40 is designed such 
that when in the engaged position as illustrated in FIG. 2 a substantially 
perpendicular loading force will be applied to the head 42 so as to apply 
a minimum pressure against the film. Preferably the average contact 
pressure within about 0.85 mm of the gap is greater than about 10 
g/mm.sup.2. In the particular embodiment illustrated, the backer plate 
assembly 40 is designed so as to provide a loading force in the range of 
approximately 20 to 50 g/mm.sup.2. 
The magnetic head assembly 10 is designed for use in minilab and full-lab 
situations where printing can occur at relatively fast velocities. Typical 
velocity in photographic printers is generally equal to or greater than 
about 100 mm/sec. In typical minilab situations, the film can be moved at 
speeds equal to or excess of 250 mm/sec, and in wholesale applications 
film can move at speeds upwards of 400 mm/sec. In order to minimize the 
degree of wear in the head 42, it is important that the head be designed 
to be resistant to the resulting forces from the film sliding along the 
engaging surface of the head. This is of particular importance in view of 
the significant force being applied by the backup plate assembly and the 
abrasive materials present on the film. 
Referring to FIGS. 6, 7, 8, and 9, there is disclosed in more detail the 
magnetic head 42. In particular, the magnetic head 42 has an outer 
engaging surface 60 designed to contact the magnetic record area 32 of the 
film 12. Mounting block 44 is provided with a guide surface 62 designed to 
engage one of the edges 34 of the film such that the film 12 will be 
positioned accurately with respect to the magnetic head 42 such that the 
magnetic information contained in the magnetic recording areas 32 of 
magnetic layer 24 can be properly aligned with the head 42. The magnetic 
head 42 includes at least one pole 64 for reading and writing information 
on the magnetic layer 24. In the particular embodiment illustrated, there 
are two poles 64 which are spaced apart a distance D which in the 
particular embodiment illustrated is about 1.2 mm. Each of the poles 64 
includes a gap 66 at which the magnetic information is either read or 
placed onto the magnetic layer. A protective layer 68 is provided on head 
42 for minimizing wear. The protective layer 68 and poles 64 combine 
together to form the outer engaging surface 60 which actually engages and 
contacts film 12. The protective layer 68 is made out of a hard protective 
material. The hardness of the protective layer 68 is designed so as to 
resist wear caused by the abrasive material in the film. The Vickers 
hardness of layer 68 is equal to or greater than 1000 kg/mm.sup.2, 
preferably greater than about 1700 kg/mm.sup.2. In the embodiment 
illustrated, protective layer 68 is made of ceramic, in particular, the 
protective layer 68 is an inorganic matrix material composed of aluminum 
oxide with titanium carbide particles of about 1.0 .mu.m dispersed through 
out, and optionally with zirconium oxide, the titanium carbide particles 
comprising in the range of about 25 to 40% by weight of the composite. A 
source of suitable ceramic material is sold by Kyocera Corporation under 
the trade name TF400L. However, it should be understood that other 
materials such as zirconium oxide may be used. As can best be seen by 
reference to FIG. 6, the protective layer completely surrounds pole 64 
such that the magnetic layer 24 will contact either the poles 64 or 
protective layer 68. The outer engaging surface 60 is preferably designed 
to have a radius R, such that the film will come in close contact with the 
outer engaging surface 60. Preferably, the radius R may range from 15 mm 
to 50 mm. In the particular embodiment illustrated, the radius R is about 
30 mm. 
In order to ensure that appropriate signals are being obtained from head 
42, each of the poles 64 has a length L in the direction of travel of the 
photographic film 12 equal to or less than about 1.5 mm, preferably less 
than or equal to 1.0 mm. In the particular embodiment illustrated, length 
L is equal to about 0.5 mm. The contact length L.sub.c between the 
photographic film 12 and the outer engaging surface 60 is preferably equal 
to or greater than about 0.5 mm, preferably greater than or equal to 1.0 
mm. In the particular embodiment illustrated, the length L.sub.c is 
approximately 1.0 mm. As illustrated in FIG. 6, the protective layer 68 
completely surrounds the pole 64. 
It is to be understood that various changes and modifications may be made 
without departing from the scope of the present invention. 
Referring to FIG. 10, there is illustrated a modified head 42', which is 
similar to magnetic head 42, like numerals indicating like parts. In this 
embodiment, two poles 64 are provided which are separated by shields 70 
and spacer sections 72, which are typically made of a material softer than 
the protective layer. In this embodiment, the protective layer 68 extends 
on either side of the poles 64 in the direction of travel of the film 12. 
While this embodiment may be somewhat easier to construct, it is not as 
preferable as the embodiment illustrated in FIGS. 1-9. 
In order to more fully understand the present invention, a brief 
description of its use will now be described. Prior to the assembly, the 
backer plate assembly is separated from the magnetic head 42 as 
illustrated in FIG. 1. Once assembled, the head assembly will be as 
illustrated in FIG. 2. The film is slid between the head 42 and plate 
assembly 40. The film 12 is driven by appropriate film drive means (not 
shown) such that the film is wrapped about the head 42 as illustrated in 
FIG. 2. One of the edges 34 of the film 12 is biased against guide surface 
42 such that the poles 64 will be aligned with the magnetic recording area 
32. The backer member 40 causes the surface of the film containing the 
magnetic layer to be pressed against the gap area as it is being moved 
along the head 42. The backer plate assembly 40 maintains the film in 
direct intimate contact with head 42. After the magnetic information has 
been read from or placed onto the magnetic layer 24, the backer plate 
assembly 40 may be disengaged as appropriate. 
It is to be understood that various other changes and modifications may be 
made without departing from the scope of the present invention, the 
present invention being limited by the following claims. 
Parts List 
10 . . . assembly 
12 . . . film 
14 . . . top surface 
16 . . . bottom surface 
18 . . . support member 
20 . . . emulsion layer 
22 . . . outer protective layer 
24 . . . magnetic layer 
28 . . . lubricant layer 
30 . . . image area 
31 . . . images 
32 . . . magnetic recording areas 
34 . . . edges 
36 . . . perforations 
40 . . . backer plate assembly 
42 . . . magnetic head 
42'. . . modified head 
44 . . . mounting block 
46,47 . . . openings 
48 . . . frame 
50 . . . cavity 
52 . . . reed-like backer member 
60 . . . outer engaging surface 
62 . . . guide surface 
64 . . . poles 
66 . . . gap 
68 . . . protective layer 
70 . . . shields 
72 . . . spacer sections