I confess that I snickered when I read the various answers. Considering I do not view my studio as a play room, and do not view my tools as "toys," I was less than impressed with the answers.
Rotary cutters got a lot of votes, as did rulers, irons and other gizmos and doodads. As far as I was concerned, nobody got the only truly correct answer.
Because, if you haven't got a "magical" tool, you can use your noodle, your little grey cells, your thinking cap, your brain, to solve any problem. Very versatile tool, that. And we all have one!
So when I got home tonight and looked at the blocks on my design wall and considered how I might rearrange them to get the effect I wanted with the least amount of effort, (translation: how could I play with the blocks without climbing up and down the ladder to move 117 blocks), in the end I decided not to touch them at all.
Did I "settle?" Certainly not. This is the design that's up there now, with the colors rearranged slightly (without the contrasting strip in the center of each block):
That yellow 6x8 block is in the center, where I wanted it. But what if I made the colors change direction a bit?
This isn't to scale, and I've got the color of the contrasting strips wrong (the yellow has a green strip, not an orange one; the orange has a yellow strip, and so on down the line), but damn, this is looking interesting.
Now I am fairly sure that a lot of you have one of those fussy quilt design programs, but I do not, because I don't make quilts that use a lot of the same block over and over again. Years ago one of my readers commented "You have the best fabrics."
"No," I replied. "But I know how to get the most out of the fabrics that I do have." It's the same thing with tools. You don't need lots of gizmos and gadgets (and trust me, I have a lot of them), but you can get a lot of proverbial "bang" for your "buck" if you can make them do what you want.
Instead of painting your self into a corner or getting to the "I'll just put them in a drawer" stage, you used your brain.
I have always used PowerPoint for my quilt designing. You can make blocks color, group, resize, copy, paste, rotate... I could go on forever.
Well I had a stall yesterday at a local craft fair. It’s been a while because of ill health and I was really looking forward to it! So what happened? The usual of course! Intermittant trickle of visitors admiring and in some cases buying – but usually only for the cheapest item I was selling. Not a lot of change from when I started a couple of years ago!
Yesterday I was selling my goddess/fairy/angel/chakra gifts and jewellery hoping to clear these out as I am now making handmade fabric creations using my sewing and knitting skills and it’s these I hope to start selling in the future. Will I ever make a profit from selling hand made goods? not by going to craft fairs I think….. I’d love to know if anyone has any tips or insights to make it more profitable. One thing I do love about these fairs though is meeting the other stall holders (usually!) and seeing all the amazing creations that are on offer. I think it’s this which keeps me going.
I’ve been doing a lot of reading of other blogs, facebook etc and craft publications as I love my sewing and knitting and crochet and it would be wonderful to turn it into a profitable business instead of hobby – if only to fund the purchase of more fabric or beautiful paper or wool! I have all of these in large quantities which I look at and stroke frequently…I just need the energy and health to make more things with them all!
So today I thought I’d add a link to the Handmade Harbour – after all – meeting other crafters and perusing their creations is my favourite thing!
Fimo spider I made to go with Pebble People which DD said wasn’t up to standard – so it lives on my craft room window ledge instead!
An illumination device includes a plurality of linear light sources disposed with a prescribed spacing therebetween, a light guide means disposed between or among the linear light sources, and a reflection means disposed behind the light guide means so that light issued from the linear light sources ...
An illumination device includes a light source member, a flexible wired board the light source member mounted thereon and a wiring provided thereon, and a structure to be stuck to the wired hoard via sticking members at a plurality of sticking surfaces, wherein one end of the wiring provided on the ...
An object of the invention is to provide an illumination device that can make it easy to detect a disorder of a light emitting element, and a liquid crystal display apparatus including the illumination device. Each light emitting element array (S) is constituted by light emitting elements (T) which ...
An illumination device comprising: a wired board having flexibility and including a light source member mounted on one of principal planes; a light-shielding member disposed so as to cover at least part of the other principal plane of the wired board on the opposite side from the one principal plane ...
A light-emitting diode illumination circuit includes light-emitting diodes connected in series and compensating elements connected in parallel with the light-emitting diodes. Each of the compensating elements includes positive and negative terminals and at least one conductor having a predetermined ...
An illumination device includes: a linear light source; first reflection means disposed opposite to and with a spacing from the linear light source; a light guide means disposed between the linear light source and the first reflection means; and a second reflection means disposed behind the light gu ...
[en] An illuminating device (10) comprises a pair of light sources (12) and a rod-like photoconductor (14). The rod-like photoconductor (14) includes a pair of planes of incidence (16) entered by the light from the light sources (12), a reflection surface (20) having a plurality of prisms (18) and a ...
A method of fabrication of one or more ultra-miniature piezoresistive pressure sensors on silicon wafers is provided. The diaphragm of the piezoresistive pressure sensors is formed by fusion bonding. The piezoresistive pressure sensors can be formed by silicon deposition, photolithography and etching processes.
This application is a continuation of U.S. patent application Ser. No. 14/187,221, filed on Feb. 22, 2014, which claims benefit of U.S. provisional patent application Ser. No. 61/768,018, filed on Feb. 22, 2013. The disclosure of all of the above-referenced US patent applications is herein incorporated by reference.
1. A device, comprising: a first silicon-on-insulator structure comprising a first silicon layer deposited on a first oxide layer over a first bulk silicon layer; a second silicon-on-insulator structure comprising a second silicon layer deposited on a second oxide layer over a second bulk silicon layer, wherein the first silicon layer and the second silicon layer are bonded together with the first silicon layer and the second silicon layer facing each other after the second bulk silicon layer and the second oxide layer are removed to leave the second silicon layer of the second silicon-on-insulator structure overlying the first silicon layer; one or more openings of predetermined shape and dimension formed to expose a portion of the second silicon layer; one or more piezoresistors formed on the one or more openings of the second silicon layer; a patterned trench formed within the second silicon layer and the first silicon layer, stopping at the first oxide layer; a piezoresistor pressure sensor formed within the patterned trench after the first bulk silicon layer is removed.
2. The device of claim 1, wherein the first silicon layer has a thickness of between about 5 .mu.m and about 100 .mu.m.
3. The device of claim 1, wherein the second silicon layer has a thickness of between about 0.5 .mu.m and about 5 .mu.m.
4. The device of claim 1, wherein the first silicon-on-insulator structure is provided with a patterned cavity already formed within the first silicon layer.
5. The device of claim 1, further comprising: a patterned cavity formed on the surface of the first silicon layer of the silicon-on-insulator structure.
6. The device of claim 1, wherein the patterned trench within the second silicon layer and the first silicon layer are positioned to partially enclose a patterned cavity within the first silicon layer, thereby leaving an area, the area having a shape on the surface of the second silicon layer, where an inner edge of the area on the surface facing the patterned cavity is narrower than an outer edge of the area facing away from the patterned cavity.
7. The device of claim 6, wherein a ratio of a first width of the inner edge of the area to a second width of the outer edge of the area is less than or equal to 0.75.
8. The device of claim 1, wherein the patterned trench within the second silicon layer and the first silicon layer are positioned to completely enclose a patterned cavity within the first silicon layer.
9. The device of claim 1, wherein the one or more piezoresistors are formed within the openings of the second silicon layer by diffusion.
10. The device of claim 1, wherein the one or more piezoresistors are formed within the openings of the second silicon layer by ion implantation.
11. The device of claim 1, further comprising: a silicon oxide insulation layer formed on the second silicon layer after the second oxide layer is removed.
16. The device of claim 1, wherein the second oxide layer is removed after the first bulk silicon layer is removed.
17. A pressure sensor, comprising: a first silicon-on-insulator structure comprising a first silicon layer deposited on a first oxide layer over a first bulk silicon layer; a patterned cavity formed on the surface of the first silicon layer of the silicon-on-insulator structure; a second silicon-on-insulator structure comprising a second silicon layer deposited on a second oxide layer over a second bulk silicon layer, wherein the first silicon layer and the second silicon layer are bonded together with the first silicon layer and the second silicon layer facing each other, and the second bulk silicon layer and the second oxide layer are removed to leave the second silicon layer of the second silicon-on-insulator structure overlying the first silicon layer; one or more openings of predetermined shape and dimension formed to expose a portion of the second silicon layer; one or more piezoresistors formed on the one or more openings of the second silicon layer; a patterned trench formed within the second silicon layer and the first silicon layer, stopping at the first oxide layer, wherein the first bulk silicon layer is removed, thereby forming the pressure sensor within the patterned trench.
18. The pressure sensor of claim 17, wherein the first silicon layer has a thickness of between about 5 .mu.m and about 100 .mu.m.
19. The pressure sensor of claim 17, wherein the second silicon layer has a thickness of between about 0.5 .mu.m and about 5 .mu.m.
20. A device, comprising: a first silicon-on-insulator structure comprising a patterned cavity formed on a surface of a first silicon layer deposited on a first oxide layer over a first bulk silicon layer; a second silicon-on-insulator structure comprising a second silicon layer deposited on a second oxide layer over a second bulk silicon layer, wherein the first silicon layer and the second silicon layer are bonded together with the first silicon layer and the second silicon layer facing each other, and wherein the second bulk silicon layer and the second oxide layer are removed to leave the second silicon layer of the second silicon-on-insulator structure overlying the first silicon layer; a silicon oxide insulation layer formed on the second silicon layer after the second oxide layer is removed; one or more openings of predetermined shape and dimension formed to expose a portion of the second silicon layer; one or more piezoresistors formed on the one or more openings of the second silicon layer; a patterned trench formed within the second silicon layer and the first silicon layer, stopping at the first oxide layer, wherein the first bulk silicon layer is removed to form a piezoresistor pressure sensor within the patterned trench.
This invention generally relates to micromachined piezoresistive pressure sensor and more particularly to a method of fabricating micromachined ultra-miniature piezoresistive pressure sensor for low pressure applications by applying wafer-bonding technology to form silicon diaphragms over etched cavities and deep silicon etching approach to define the outlines of the fabricated sensors.
It is well know that monitoring physiological parameters in situ and in vivo within a blood vessel of a human subject being diagnosed or treated during a medical procedure can provide medical professionals critical information as to the status and condition of the human subject. One particular important and beneficial physiological parameter is the blood pressure within the coronary vessel. Study has shown that the blood pressure in situ and in vivo within the coronary vessel can be applied to calculate Fractional Flow Reserve (FFR) which represents the potential decrease in coronary flow distal to the coronary stenosis. More than a decade long clinic study has shown that FFR can provide a quantitative assessment of the functional severity of a coronary artery stenosis identified during coronary angiography and cardiac catheterization, hence, helping the physician to make a quantitative decision on which kind of further treatment is required.
Due to the small diameter of the coronary vessel, which can be as small as less than 1 mm in diameter, it is crucial to have a very small diagnosis device to measure the blood pressure in situ so the blood pressure is not distorted by the diagnosis device itself. In such case, an ultra small pressure sensor is mounted at the distal end of an ultra small delivering device such as a guide wire to form a sensor guide wire assembly. By advancing the distal end of the sensor guide wire assembly to the desired location within the coronary vessel, the ultra miniature pressure sensor mounted at the distal end of the guide wire can perform the measurement of the blood pressure of the coronary vessel in situ and in vivo. The Outside Diameter (OD) of the sensor guide wire assembly is typically 0.35 mm. Hence an ultra small sensor is required so the sensor can be mounted at the distal end of the sensor guide wire assembly.
Therefore it is apparent that there is a need to manufacture miniature pressure sensors which can be mounted at the distal end of delivering devices such as guide wires. In order to mount the pressure sensor on a guide wire whose typical Outside Diameter (OD) is about 0.35 mm, the size of the sensor needs to be smaller than 0.3 mm in width and 0.1 mm in height. To fabricate pressure sensors with this small dimension presents a challenge for mass production.
This application generally discloses a method of fabrication piezoresistive pressure sensors. More specifically, it discloses an improved MEMS process for fabricating piezoresistive pressure sensors which include a thin film diaphragm overlying a cavity with enhanced processes to provide improved sensitivity of ultra miniature pressure sensors which can be mounted on the distal end of a guide wire.
One embodiment provides a piezoresistive pressure sensor fabricating method which can precisely define the dimensions of the pressure sensors by employing photolithography technology and etching trenches partially enclosing the sensors to define the dimensions of the sensors and the sensors can be released by applying mechanical force without dicing.
Another embodiment provides a peiozoresistive pressure sensor fabricating method which can precisely define the dimensions of the pressure sensors by employing photolithography technology and etching trenches completely enclosing the sensors to define the dimensions of the sensors and the sensors can be released using standard MEMS process without dicing.
FIG. 1B illustrates the cross-sectional side view of the pressure sensor shown in FIG. 1A. The cross-sectional view section is along line 1A-1A' of FIG. 1A.
FIG. 2A and FIG. 2B illustrates the cross-sectional view of the first silicon-on-insulator (SOI) wafer working as a carrier wafer where the cavity is formed on the silicon layer.
FIG. 3 illustrates the cross-sectional view of the second SOI wafer whose silicon layer is used to form the diaphragm in according to one embodiment of the present invention.
FIG. 4 illustrates the structure after the first and the second SOI wafers are bonded together according to one embodiment of the present invention.
FIG. 5 illustrates the structure after the supporting silicon wafer and insulation layer of the second SOI wafer has been removed according to one of the embodiment of the present invention.
FIG. 6A illustrates the top view of the piezoresistive sensor after the formation of the piezoresistors according to one embodiment of the present invention.
FIG. 6B illustrates the cross-sectional view of the piezoresistive sensor after the formation of the piezoresistors. The cross-sectional view is along line 6A-6A' of FIG. 6A.
FIG. 9A through FIG. 10 illustrate the steps of forming the trench according to one or more embodiments of the present invention.
FIGS. 11A and 11B illustrate the steps of removing a bulk silicon layer and an insulation layer of the carrier SOI wafer and release the piezoresistive sensor according to one or more embodiments of the present invention.
FIG. 1A and FIG. 1B illustrate a method of manufacturing a miniature pressure sensor and fabricating one or more piezoresistive pressure sensors 10 using Micro-Electro-Mechanical Systems (MEMS) technology. FIG. 1A illustrates the top view of a piezoresistive pressure sensor. FIG. 1B illustrates the cross-sectional view of the piezoresistive pressure sensor in FIG. 1A. The cross-sectional view in FIG. 1B is along line 1A-1A' of FIG. 1A.
The pressure sensor 10 is formed by a thin film diaphragm 13 overlying a cavity 11. The dotted line in FIG. 1A represents the edge 16 of the cavity 11 and hence defines the region of the cavity 11. Piezoresistors 12 are formed on top of the diaphragm 13 within the cavity 11 region by either diffusion or ion implantation. When pressure is applied on top of the diaphragm 13, the diaphragm 13 will deform and bend into the cavity 11, resulting in stress on the piezoresistors 12 hence changing the resistances of the piezoresistors 12.
One important parameter to characterize a pressure sensor is the sensitivity of the sensor. For a given pressure change, the larger the resistance change is, the higher the sensitivity is. The major goal of the pressure sensor design is to achieve as high sensitivity as possible.
The sensitivity of the piezoresistive pressure sensor described above is affected by the thickness of the diaphragm 13. The thinner is the diaphragm 13, the more sensitive is the pressure sensor. However, the thickness of the diaphragm 13 also affects the pressure range the sensor can measure. The thinner is the diaphragm 13, the lower pressure the sensor can measure before the change of the resistance of the piezoresistor 12 becomes nonlinear. It is beneficial is to choose a diaphragm 13 with smallest thickness but large enough for the given dimensions of the cavity 11 so the change of the resistance of the piezoresistor 12 is linear within all the pressure range the device is designed to measure.
The sensitivity of the piezoresistive pressure sensor 10 is also affected by the dimension of the cavity 11. The larger the cavity 11 is, the more sensitive the pressure sensor 10 is. When the space is not a limiting factor, it is beneficial to design the dimension of the piezoresistive sensor, hence the dimension of the cavity 11, to be large enough to satisfy the sensitivity requirement. When the space is a limiting factor, such as the case for intra cardiac and intra vascular applications, the dimension of the piezoresistive sensor, hence the dimension of the cavity 11, is designed to be maximum allowable by the limited space to achieve maximum achievable sensitivity.
For intra cardiac, intra vascular, and Percutaneous Coronary Intervention (PCI) applications, it's preferable to mount the pressure sensor on a guide wire with a Outer Diameter (OD) of about 0.35 mm so no extra device is required to perform the blood pressure measurement in situ and in vivo. In order to mount the above described piezoresistive pressure sensor on a guide wire, the width of the pressure sensor needs to be smaller than 0.3 mm. This small dimension presents a challenge for manufacturing the above described piezoresistive pressure sensor with traditionally available MEMS processes which includes a wafer dicing process to separate the fabricated devices. The first challenge is that the dimension is too small for standard semiconductor dicing equipment to handle. A semiconductor dicing equipment is only designed to handle devices with lateral dimensions not smaller than 1 mm in any direction. Hence special equipment is required, resulting in increased manufacture cost. The second challenge is caused by the dicing error, which is 0.05 mm for most of the commercially available dicing saws. In order to guaranty the finished width is smaller than 0.3 mm, the width of the device needs to be smaller than 0.2 mm so after the dicing error its width will still be smaller than 0.3 mm. Reducing the width from 0.3 mm to 0.2 mm will result in 33% of sensor area reduction, hence 33% of sensitivity reduction.
One intention of this invention is to provide a fabrication method of fabricating piezoresistive pressure sensor whose dimension can be precisely defined, hence to eliminate above mentioned problem of reduction of sensitivity for ultra small piezoresistive pressure sensor due to the uncertainty of the dimension of the finished device. Another intention of this invention is to provide a fabrication method of fabricating piezoresistive pressure sensor with increased sensitivity. Another intention of this invention is to provide a fabrication method which only uses semiconductor compatible processes to fabricate piezoresistive pressure sensor. Yet another intention of this invention is to provide a MEMS process flow which can be used to manufacture piezoresistive pressure sensor in mass production with high yield and low cost.
The method of fabrication of piezoresistive pressure sensor whose diaphragm 13 is formed by employing wafer bonding and whose dimension is precisely defined by employing photolithographic and etching process is described in detail along with the FIGs, in which like parts are generally denoted with like reference numbers and letters. The FIGs are for illustration only and are not to scale.
The steps of fabricating of piezoresistive pressure sensor in accordance with the present invention employ fusion wafer bonding under vacuum and etching process to define the dimension of the finished pressure sensors are illustrated and described with reference to FIG. 1 through FIG. 11. The fabrication process starts with two wafers with silicon-on-insulator (SOI) structures thereon.
During fabrication of the pressure sensor 10, first, the cavity 111 of the pressure sensor is formed on a carrier wafer, such as the first SOI wafer 210. The silicon layer 114 is relatively thick, as it is where the cavity 111 is going to be formed. In one embodiment, the thickness of the silicon layer 114 on the first SOI wafer 210 is between about 5 .mu.m and about 100 .mu.m. While the thickness of the silicon layer 114 of this SOI wafer 210 is not critical to the performance of the piezoresistive pressure sensor 10, the thickness of the silicon layer 114 needs to be shorter than the height limit, if there is any, of the finished sensor 10. The thickness of the silicon layer 114 also affects the limit of the height of the cavity 111 since the cavity 111 needs to be formed within the silicon layer 114 of the first SOI wafer 210.
For low pressure applications, such as blood pressure measurement, the cavity 111 does not need to be high. A height of between about 2 .mu.m and about 50 .mu.m in the cavity 111 is typically sufficient. Hence a thickness of between about 5 .mu.m and about 100 .mu.m in the silicon layer 114 on the first SOI wafer 210 can be used.
As shown in FIG. 2B, a pattern of the cavity 111 can be formed in the silicon layer 114. In general, a mask with openings is used to form and define the shape and pattern of the cavity 111 using photolithography techniques. The shape of the cavity 111 determines the shape of the area where one or more piezoresistors 112 is going to be formed. The most widely used shape is square while rectangular shapes, circular shapes and other shapes are also used.
After the photolithograph, plasma etching technique can be used to form the cavity 111. The time duration and the energy of the plasma etching define the height of the cavity 111. The height of the cavity 111 needs to be much shorter than the thickness of the silicon layer 114, for example, less than half of the thickness of the silicon layer 114. The detailed steps of forming the cavity 111 on the first SOI wafer 210 is well known to those skilled in the art of the MEMS processes. In some cases, it is possible to directly use a silicon-on-insulator wafer which has the cavity 111 already built-in.
The thickness of the silicon layer 113 of the second SOI wafer 220 defines the thickness of the diaphragm 13. For a given cavity dimension, the thinner the diaphragm 13 is, the more sensitive the pressure sensor 10 is to a change in pressure. On the other hand, for the same given cavity dimension, the thinner the diaphragm 13 of the pressure sensor 10 is, the smaller the maximum pressure it can tolerate. In general, a thickness of the silicon layer and the thickness of the diaphragm 13 are thick enough to be able to tolerate the maximum pressure the pressure sensor 10 is going to be exposed to, resulting in maximum sensitivity within the designed pressure range for a given cavity dimension. For miniature small-scale pressure sensor, such as those suitable for intravascular pressure monitoring where sensitive blood pressure change is measured, the silicon layer 113 can have a thickness of between about 0.5 .mu.m and about 5 .mu.m. Since the silicon layer 113 is provided for forming the diaphragm 13, the type of a silicon material for the silicon layer 113 is chosen to be opposite to the type of a silicon material for one or more piezoresistors, such as the piezoresistors 12 or one or more piezoresistors 112, as described below.
Next, as shown in FIG. 4, the second SOI wafer 220 can be placed over the first SOI wafer 210 with the silicon layer 113 facing the silicon layer 114, where the cavity 111 of the carrier wafer 210 is. The first SOI 210 and the second SOI wafers 220 are then bonded together by employing suitable techniques, for example, fusion wafer bonding under vacuum. If the bonding is done under very low pressure, the formed cavities are vacuum-sealed. In addition, other bonding methods such as eutectic bonding can be applied to bond the first silicon-on-insulator wafer and the second silicon-on-insulator wafer together.
After bonding and sealing, the bulk silicon layer 223 and the oxide layer 222 of the second SOI wafer 220 are removed by a grinding process and an etching process, respectively. Accordingly, as illustrated in FIG. 5, only the silicon layer 113 is remained over the surface of the first SOI wafer 210, atop the surfaces of the cavity 111 and the silicon layer 114. The detailed processed to bond the first and the second SOI wafers 210, 220 together using fusion bonding under vacuum and removing the silicon support wafer 223 and oxide layer 222 is well known to those skilled in the art of MEMS process. Reference still to FIG. 5, in some cases, the oxide layer 222 doesn't have to be removed. It can be utilized for future processes if it is desired to do so.
As illustrated in FIG. 7, first, a thin layer of a silicon dioxide insulation layer 261 is deposited on top of the silicon layer 113. The silicon dioxide insulation layer may have a thickness of around about 1 .mu.m. Second, a mask with openings is used to form and define the pattern and shape of the one or more piezoresistors 112 using photolithography techniques.
After photolithography, as illustrated in FIG. 8, a portion of the silicon dioxide insulation layer 261 in the opening areas is removed, thereby exposing a portion of the silicon layer 113. Then, one or more piezoresistors 112 are formed on the exposed surfaces of the silicon layer 113, using diffusion or ion implantation processing techniques. Accordingly, the locations of the piezoresistors 112 are defined by the opening areas in the silicon dioxide insulation layer 261 and should be within an edge 116 of the cavity 111 to maximize the sensitivity of the pressure sensor 10. The edge 116 of the cavity 111 is represented by the dotted line 116 in FIG. 6A. In the case where an ion implantation process is employed to form the piezoresistors 112, the ion implantation process is followed by a high temperature annealing process with typical temperature of 800 to 1100 degree Celsius to drive the implanted ions into the silicon and to repair the damage on the silicon crystals created by the implantation process.
Reference still to FIG. 6A, it should be apparent that the number of the piezoresistors 112 don't have to be four, even though four piezoresistors are illustrated in the figure. In fact, the number of piezoresistors 112 can be from one to any number.
Next, one or more trenches 281 are formed to define the boundary of the pressure sensor 10. FIG. 9A illustrates the top view of a sensor 280 on the first SOI wafer 210, after forming the trenches 281 enclosing one or more piezoresistors 112. FIG. 9B illustrates the cross-sectional view of the wafer 280 after the formation of the trench 281. The cross-sectional view in FIG. 9B is along line 9B-9B' of FIG. 9A. FIG. 9C illustrates another cross-sectional view of the wafer 280 after the formation of the trench 281. The cross-sectional view in FIG. 9C is along line 9A-9A' of FIG. 9A.
First, a mask with openings is used to define the trenches 281, using photolithography techniques. The width of the trench 281 can be several micrometers to several hundred micrometers and is not critical, as long as the trenches 281 are etched completely through the oxide layer 261, the silicon layer 113, and the silicon layer 114. The boundary of the trench 281 is outside of the edge 116 of the cavity 111, leaving some space 285 between the cavity 111 and the trench 281, so that the cavity 111 is not affected. The silicon material within the space 285 is going to support the diaphragm area in the silicon layer 113 after the trench 281 has been formed. The width of the space 285 is designed so that the silicon material remained within the space 285 is strong enough to tolerate any stress during the handling a device of the pressure sensor 10. The width of the space 285 is typically from 5 .mu.m to 50 .mu.m.
Reference still to FIG. 9A, FIG. 9B and FIG. 9C, in one embodiment, the trench 281 does not completely enclose the inner sensor area so the sensor 280 is still partially connected across its surface through an area 282, which may include a thin portion of the silicon dioxide layer 261, the silicon layer 113 and the silicon layer 114, as shown in FIG. 9A and FIG. 9B. In another embodiment, as shown in FIG. 10, the trench 281 can completely enclose the piezoresistive sensor area on the sensor 280.
The shape of the area 282, which connects the inner portion of the pressure sensor with the outer surrounding portion of the sensor 280, is designed to be in a shape that can be easily broken at the edge close to the center of the sensor so as to define the dimension of the finished sensor. One way is to design the shape of the area 282 as a trapezoid shape, whose narrower base is facing the center of the sensor 280 while the wider base is facing away from the center of the sensor 280. The ratio of the width of the narrow side to the width of the wider side is preferably smaller or equal to 0.75. In such a design, when force is applied on the later steps to release the sensor 280 from the first SOI wafer 210, the narrower side is going to break first, hence a well defined sensor dimension can be achieved.
The width of the narrower side of the area 282 is not critical as long as it is narrow enough so the area 282 can be easily broken to release the sensor 280 from the first SOI wafer 210 at later steps. A typical design width of the narrower side of the area 282 is 10 .mu.m to 50 .mu.m. The shape of the area 282 does not need to be trapezoid, but any shape whose width of the side facing the center of the sensor is smaller than the width of the side facing away from the sensor. In addition, the number of the area 282 is not critical and can be any number, for example, there may be two, as shown in FIG. 9A as an example, or four of the area 282 on the two or four sides of the wafer 280. Further, the locations of the area 282 are not critical, even though the preferable locations of the area 282 is in the middle of the sides of the wafer sensor 280, as shown as an example in FIG. 9A.
After the photolithography, a portion of the silicon dioxide insulation layer 261, the silicon layer 113, and the silicon layer 114 in the opening area are removed, for example, by an etching process, to form the trenches 281, stopping at the silicon dioxide layer 212 of the first SOI wafer 210. Once, a pattern of the trenches 281 is formed, the silicon dioxide insulation layer 261 can be completely removed, for example, by an etching process. In some cases, the silicon dioxide insulation layer 261 is not removed and can also be used for future processing steps.
The next steps are to release the sensors 280 from the first SOI wafer 210. In one example, as shown in FIG. 11A, where the trench 281 completely encloses the cavity 111 without forming the area 282, the sensor side of the first SOI wafer 210, having one or more sensors 280, is attached to a holding material 290 through glue or other material. The holding material 290 holds the one or more sensors 280 fabricated on the first SOI wafer 210 in place. Then, the bulk silicon layer 213 of the first SOI wafer 210 is removed.
As shown in FIG. 11B, next, the dioxide layer 212 of the first SOI wafer 210 is removed. After removing the dioxide layer 212, the sensors 280 are only connected with the holding material 290 by glue or other material. The glue, which holds the sensors 280 can be removed, for example, under ultraviolet (UV) light curing, as glue materials become non-adhesive after being exposed to UV light for a certain time.
The holding material 290 can be a transparent material such as glass or plastic materials. After the bulk silicon layer 230 and the dioxide layer 212 are removed, the sensor device can be exposed to UV light and released from the holding material 290. Accordingly, pressure sensors thus fabricated can be easily released from the holding material 290 without dicing.
In the example where the trench 281 does not not completely enclose the inner sensor area where the piezoresistors 112 are located, the area 282 may remain near the trench 281 after, the bulk silicon layer 213 and the oxide layer 212 of the first SOI wafer 210 are etched away. The only material holding the sensors in one piece is the area 282, which is narrow at the inner edge closer to the center of the sensor. Thus, a force can be applied by a sharp tool such as a knife to break the connection and the sensors can be released one by one. Since the inner side edge of the area 282 facing the center of the sensor is smaller compared to the outer side edge of the area 282 facing away from the sensor, the inner side facing the center of the sensor is going to break first when a mechanical force is applied, accomplishing a well defined boundary for the sensor.
From the foregoing, it can be seen that there has been provided a method to manufacture an ultra-miniature pressure sensor whose dimensions are precisely defined. In addition, there has been provided a method which uses only silicon compatible process to manufacture a pressure sensor. Compared with conventional method of fabricating a silicon diaphragm piezoresistive sensor, the present invention has at least the advantages of: (1) The dimensions of the finished sensors are precisely defined. The sensitivity of the sensor can hence be optimized. (2) The height of the finished sensor is precisely defined. (3) No dicing process is required. The sensor can be released by all semiconductor compatible processes.
An intermediate transfer member for use in a transfer-type image recording method including the steps of applying an ink to an intermediate transfer member to form an intermediate image and transferring the intermediate image to a recording medium. The intermediate transfer member includes a surface layer part onto which an ink is applied, the surface layer part containing an organic siloxane compound having a siloxane bond and a polyalkylene oxide unit.
1. An intermediate transfer member for use in a transfer-type image recording method including applying an ink to the intermediate transfer member to form an intermediate image and transferring the intermediate image to a recording medium, wherein a surface layer part of the intermediate transfer member comprises an organic siloxane compound having a siloxane bond and a polyalkylene oxide unit.
2. The intermediate transfer member according to claim 1, wherein the organic siloxane compound is a condensation product of at least one hydrolyzable siloxane compound, and the at least one hydrolyzable siloxane compound includes at least one organic silicon compound represented by general formula (1) or (2): ##STR00017## where X.sup.1 is a polyalkylene oxide unit containing (X.sup.2).sub.n; X.sup.2 is an alkylene oxide group having 2 to 4 carbon atoms; n is an integer of 3 to 50; each of R.sup.1 and R.sup.5 is independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; each of R.sup.2 and R.sup.6 is independently a monovalent group having an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, a carboxyl group, a vinyl group or a cyclic ether group; each of a and c is independently an integer of 1 to 3; each of b and d is independently an integer of 0 to 2; a+b=3; c+d=3; and each of R.sup.3 and R.sup.4 is independently a divalent group containing an alkylene group having 1 to 20 carbon atoms, a urethane bond or a carbonyl group; ##STR00018## where X.sup.3 is a polyalkylene oxide unit containing (X.sup.4).sub.m; X.sup.4 is an alkylene oxide group having 2 to 4 carbon atoms; m is an integer of 3 or 50; R.sup.21 is an alkyl group having 1 to 4 carbon atoms or a hydrogen atom; R.sup.22 is a monovalent group having an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, a carboxyl group, a vinyl group or a cyclic ether group, q is an integer of 1 to 3; r is an integer of 0 to 2; q+r=3; R.sup.23 is a divalent group containing an alkylene group having 1 to 20 carbon atoms, a urethane bond or a carbonyl group; and R.sup.24 is a monovalent group having a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, a carboxyl group, an ester group, a vinyl group or a cyclic ether group.
3. The intermediate transfer member according to claim 2, wherein the condensation product has a ratio of a number of alkylene oxide units to a number of siloxane bonds of 0.1 to 1.2.
6. The intermediate transfer member according to claim 1, wherein the polyalkylene oxide unit is a polyethylene oxide unit.
7. The intermediate transfer member according to claim 1, wherein a thickness of the surface layer part is 0.1 .mu.m to 10.0 .mu.m.
8. A transfer-type image recording method comprising: applying an ink to an intermediate transfer member to form an intermediate image; and transferring the intermediate image to a recording medium, wherein a surface layer part of the intermediate transfer member contains an organic siloxane compound having a siloxane bond and a polyalkylene oxide unit.
9. The transfer-type image recording method according to claim 8, wherein the applying of the ink to the intermediate transfer member is performed by an ink jet method.
10. The intermediate transfer member according to claim 1, wherein the polyalkylene oxide unit has 6 to 100 carbon atoms.
11. The transfer-type image recording method according to claim 8, further comprising applying an aggregation liquid to the intermediate transfer member before the applying of the ink.
13. The transfer-type image recording method according to claim 8, wherein the organic siloxane compound is a condensation product of at least one hydrolyzable siloxane compound, and the at least one hydrolyzable siloxane compound includes at least one organic silicon compound represented by general formula (1) or (2): ##STR00020## where X.sup.1 is a polyalkylene oxide unit containing (X.sup.2).sub.n; X.sup.2 is an alkylene oxide group having 2 to 4 carbon atoms; n is an integer of 3 to 50; each of R.sup.1 and R.sup.5 is independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; each of R.sup.2 and R.sup.6 is independently a monovalent group having an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, a carboxyl group, a vinyl group or a cyclic ether group; each of a and c is independently an integer of 1 to 3; each of b and d is independently an integer of 0 to 2; a+b=3; c+d=3; and each of R.sup.3 and R.sup.4 is independently a divalent group containing an alkylene group having 1 to 20 carbon atoms, a urethane bond or a carbonyl group; ##STR00021## where X.sup.3 is a polyalkylene oxide unit containing (X.sup.4).sub.m; X.sup.4 is an alkylene oxide group having 2 to 4 carbon atoms; m is an integer of 3 to 50; R.sup.21 is an alkyl group having 1 to 4 carbon atoms or a hydrogen atom; R.sup.22 is a monovalent group having an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, a carboxyl group, a vinyl group or a cyclic ether group; q is an integer of 1 to 3; r is an integer of 0 to 2; q+r=3; R.sup.23 is a divalent group containing an alkylene group having 1 to 20 carbon atoms, a urethane bond or a carbonyl group; and R.sup.24 is a monovalent group having a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, a carboxyl group, an ester group, a vinyl group or a cyclic ether group.
14. The transfer-type image recording method according to claim 13, wherein the condensation product has a ratio of a number of alkylene oxide units to a number of siloxane bonds of 0.1 to 1.2.
17. The transfer-type image recording method according to claim 8, wherein the polyalkylene oxide unit is a polyethylene oxide unit.
18. The transfer-type image recording method according to claim 8, wherein a thickness of the surface layer part is 0.1 .mu.m to 10.0 .mu.m.
19. The transfer-type image recording method according to claim 8, wherein the polyalkylene oxide unit has 6 to 100 carbon atoms.
20. A transfer-type image recording apparatus comprising: an intermediate transfer member; an ink applying unit for applying an ink to the intermediate transfer member to form an intermediate image; and a transfer unit for transferring the intermediate image to a recording medium, wherein a surface layer part of the intermediate transfer member contains an organic siloxane compound having a siloxane bond and a polyalkylene oxide unit.
The present invention relates to an intermediate transfer member for transfer-type image recording and a transfer-type image recording apparatus and a transfer-type image recording method using the intermediate transfer member.
As an image recording method using an ink, a transfer-type image recording method is known. In the method, an ink is applied to an image forming surface of an intermediate transfer member to form an intermediate image, then the formed intermediate image is transferred to a recording medium, and an image is formed on the recording medium. The intermediate transfer member used in the image recording method preferably has such a characteristic that the surface thereof easily releases an intermediate image, i.e. good transferability of an intermediate image.
To achieve good transferability of an intermediate image from an intermediate transfer member to a recording medium, it has been considered to be important to reduce a surface free energy of the intermediate transfer member. On this account, the surface (surface layer part) of an intermediate transfer member has been typically made of a material having a low surface free energy, i.e. a highly water-repellent material, such as fluorine resins and silicon resins (see Japanese Patent Application Laid-Open No. 2003-182064). The intermediate transfer member surface formed of such a material has a surface free energy of about 110 degrees in terms of "contact angle for pure water", which is a typical index of the surface free energy.
While, to achieve holding properties and transferability of an intermediate image on an intermediate transfer member, another transfer-type image recording method is disclosed. In the method, an ultraviolet curable solution layer having ink affinity and fixability is previously formed on an intermediate transfer member (see Japanese Patent Application Laid-Open No. 2010-228193). In this image recording method, an ink is applied to the curable solution layer on an intermediate transfer member to form an intermediate image, then the ultraviolet curable solution layer holding the intermediate image is transferred from the intermediate transfer member to a recording medium, and the recording medium is irradiated with ultraviolet rays to form an image.
An intermediate transfer member for transfer-type image recording of the present invention is used in a transfer-type image recording method that includes the steps of applying an ink to an intermediate transfer member to form an intermediate image and transferring the intermediate image to a recording medium. The intermediate transfer member has a surface layer part onto which an ink is applied, and the surface layer part contains an organic siloxane compound having a siloxane bond and a polyalkylene oxide unit.
A transfer-type image recording method of the present invention includes the steps of applying an ink to an intermediate transfer member to form an intermediate image and transferring the intermediate image to a recording medium. In the transfer-type image recording method, the intermediate transfer member is the intermediate transfer member having the above-mentioned structure of the present invention.
A transfer-type image recording apparatus of the present invention includes an intermediate transfer member, an ink applying unit for applying an ink to the intermediate transfer member to form an intermediate image, and a transfer unit for transferring the intermediate image to a recording medium. In the transfer-type image recording apparatus, the intermediate transfer member is the intermediate transfer member having the above-mentioned structure of the present invention.
According to the present invention, an intermediate transfer member having good image formability obtained by using an ink and an aggregation liquid used as needed and having an image forming surface of which the hydrophilicity is unlikely to be changed even by repeated transfer as well as a transfer-type image recording apparatus and a transfer-type image recording method using the intermediate transfer member can be provided.
FIGS. 1A, 1B, 1C, and 1D are schematic views of the structures of intermediate transfer members of the present invention.
FIG. 2 is a schematic view of the structure of an ink jet recording apparatus usable in a transfer-type image recording method of the present invention.
By applying, onto an image forming surface of an intermediate transfer member, an ink and an aggregation liquid that has a function of aggregating ink components and is used as needed, an intermediate image can be formed. During such image formation, in order to further improve image formability and transferability of an intermediate image on the image forming surface of an intermediate transfer member, it is required that an intermediate image be satisfactory transferred to a recording medium while the image forming surface maintain appropriate wettability with an ink and an aggregation liquid.
However, the study by the inventors of the present invention has revealed that the intermediate transfer member described in Japanese Patent Application Laid-Open No. 2003-182064 may be required to have an image forming surface with higher wettability with respect to an ink and an aggregation liquid in some cases to achieve the above requirements for the intermediate transfer member.
When the intermediate transfer member described in Japanese Patent Application Laid-Open No. 2010-228193 is used, the curable solution layer can absorb and fix an ink to achieve image holding properties. However, the curable solution layer itself is transferred together with the ink onto a recording medium side, and thus the formation of the curable solution layer on the intermediate transfer member and the release thereof from the intermediate transfer member are repeated when the intermediate transfer member is repeatedly used. This causes the intermediate transfer member to have lower hydrophilicity with respect to the curable solution layer and thus impairs good formation of the curable solution layer in some cases. In addition, in image formation using the intermediate transfer member described in Japanese Patent Application Laid-Open No. 2010-228193, materials for the curable solution layer are consumed every image formation, the number of image formation steps increases, and the cost for forming images rises in some cases.
The present invention therefore intends to provide an intermediate transfer member for transfer-type image recording having good image formability obtained by using an ink and an aggregation liquid used as needed and having surface hydrophilicity that is unlikely to be changed even by repeated transfer. The present invention also intends to provide an image recording apparatus and an image recording method using the intermediate transfer member.
Intermediate transfer member for transfer-type image recording (intermediate transfer member for transfer-type ink jet recording)
Schematic views of the structures of intermediate transfer members for transfer-type ink jet recording as embodiments of the present invention are shown in FIGS. 1A to 1D.
The intermediate transfer member 1 shown in FIG. 1A has a surface layer part 2. The image forming surface of the intermediate transfer member 1 is on the surface layer part 2 (surface side). Onto the image forming surface, an ink is applied by using an ink jet device to form an intermediate image.
The intermediate transfer member of the present invention preferably has appropriate elasticity because an intermediate image is transferred by pressing the intermediate image against a recording medium such as paper. On this account, for example, if a plain paper is used as the recording medium, the intermediate transfer member is preferably, at least partly formed of an elastic material. The part formed of the elastic material preferably has a durometer type A hardness (in accordance with JIS K6253) of 10 degrees or more to 100 degrees or less. The lower limit thereof is more preferably 20 degrees or more, and the upper limit is more preferably 60 degrees or less.
The intermediate transfer member may have a single layer structure or a multilayer structure composed of a plurality of layers.
The single layer structure is exemplified by a structure using the surface of a base layer 3 as the surface layer part 2 as shown in the schematic cross-sectional view in FIG. 1B. The multilayer structure is exemplified by structures in which a surface layer 2 is provided on a base layer 3 having a single layer structure or a double layer structure (3a, 3b) and the surface layer 2 is the surface layer part 2 constituting the image forming surface, as shown in the schematic cross-sectional views in FIGS. 1C and 1D. The base layer 3 may have a multilayer structure including three or more layers.
The intermediate transfer member may have a compressible elastic layer having such an elasticity that the layer can be compressed by pressing and can be returned to the original shape upon release of the pressure, in order to uniformize the pressure when the intermediate transfer member is pressed against a recording medium for transfer.
The intermediate transfer member may further include a resin layer, a base fabric layer, a metal layer, and the like, in order to have elastic properties, strength, and thermal properties, for example.
As the material for forming the elastic layer, various rubber materials or various elastomer materials can be used in terms of process characteristics or the like. The elastic layer can be provided in the form of a continuous layer or a porous layer.
The size of the intermediate transfer member 1 can be freely set according to the size of an intended print image. FIGS. 1A to 1D exemplify sheet-shaped intermediate transfer members 1, but the whole shape of the intermediate transfer member is not limited to them and is exemplified by, in addition to the sheet shape, a roller shape, a drum shape, a belt shape, and an endless web shape.
In the present invention, "surface layer part" means a part of the surface side on an intermediate transfer member. In the present invention, it is important that the surface layer part, which is the surface layer part of an intermediate transfer member onto which an ink is applied, contains an organic siloxane compound having a siloxane bond and a polyalkylene oxide (PAO) unit (PAO-modified polysiloxane compound). The material constituting the surface layer part is formed of at least a PAO-modified polysiloxane compound, and this organic siloxane compound is fixed to the surface layer part.
It is an essential requirement for exhibiting the advantageous effects of the invention that siloxane bonds and polyalkylene oxide units are fixed to the surface layer part of an image forming surface as described above. Hence, the surface layer part can be any portion that is exposed to the surface of an intermediate transfer member, and is not necessarily provided as a layer distinguished from a base. The surface layer part may be a surface region of an intermediate transfer member having a single layer (one layer) in which the surface region is formed as the surface layer part composed of a material containing the above organic siloxane compound. If an intermediate transfer member has a single layer structure, the whole of the intermediate transfer member may be formed of a material containing the PAO-modified polysiloxane compound, or only the surface layer part of the base may be formed of a material containing the PAO-modified polysiloxane compound. The method for forming a layer constituting the surface layer part that is provided as a layer is preferably a method of applying a coating solution containing the PAO-modified polysiloxane compound or a method of applying a coating solution that contains components of the PAO-modified polysiloxane compound and can form the PAO-modified polysiloxane compound after coating.
The surface layer part may have any thickness, but the thickness of the surface layer part is preferably 0.01 .mu.m or more to 10.00 .mu.m or less, more preferably 0.1 .mu.m or more to 10.0 .mu.m or less, and even more preferably 1.0 .mu.m or more to 5.0 .mu.m or less. In particular, if the surface layer part is formed by applying a coating solution, the surface layer part having a thickness within the above range can obtain more sufficient film strength, and this can suppress cracks on the surface layer part, delamination, or other defects caused by stress due to elastic deformation of the whole intermediate transfer member at the time of the transfer step of an intermediate image. In addition, the surface layer part can obtain appropriate elastic deformation and can follow the surface shape of a recording medium, resulting in better transferability.
If the surface layer part is provided as a layer on a base, the surface layer part preferably has sufficient adhesiveness to a base adjacent to the surface layer part, in addition to the thickness requirements of the surface layer part, in order to suppress generation of cracks, delamination, and reduction in transferability. In order to improve the adhesiveness, the surface of a base adjacent to the surface layer part (the area on which the surface layer part is provided) is preferably subjected to surface treatment.
The surface treatment is exemplified by flame treatment, corona treatment, plasma treatment, polishing treatment, roughening treatment, active-energy-ray-irradiation treatment (UV, IR, RF, for example), ozone treatment, and surfactant treatment. These treatments may be combined to perform the surface treatment. In order to further improve the adhesiveness and the coatability, a coating solution to form the surface layer part preferably contains a silane coupling agent, a sulfur-containing compound, or the like. The coating solution to form the surface layer part can be applied by conventionally known various coating methods. Examples of the coating method include die coating, blade coating, gravure coating, and methods combining such a coating method with offset roller coating.
To achieve good transferability, it is typically required to reduce the surface energy of an image forming surface of an intermediate transfer member, i.e. to increase the water repellency. However, such an image forming surface has lower holding properties of an aggregation liquid or an ink, resulting in deterioration of image qualities unfortunately.
As a result of intensive studies, the inventors of the present invention have found that the surface energy of an intermediate transfer member is not necessarily reduced, i.e. the water repellency is not necessarily increased. In other word, the inventors have found that if the surface layer part of an intermediate transfer member contains the above PAO-modified polysiloxane compound, good transferability can be achieved while image qualities are maintained due to appropriate hydrophilicity.
The image forming surface of the intermediate transfer member of the present invention preferably has a contact angle for pure water of 105 degrees or less, which varies depending on characteristics of an aggregation liquid or an ink. The contact angle for pure water is more preferably 80 degrees or less. If an image forming surface has a smaller contact angle for pure water, an aggregation liquid or an ink applied can be prevented from being repelled on the intermediate transfer member. The contact angle for a liquid such as pure water can be determined by using a common contact angle meter.
If the surface layer part is provided as a surface layer as described above to impart flexibility to the surface layer, generation of cracks on the surface layer and delamination are prevented to suppress the deterioration of transferability, and the performance following to a recording medium is increased to result in an improvement of the transferability. Such a structure is thus preferred. In the present invention, the PAO-modified polysiloxane compound contained in a surface layer contains a long chain functional group containing a polyalkylene oxide unit, and thus the surface layer can obtain flexibility. This is supposed to be because molecular chains in the skeleton have higher mobility to promote the relaxation of internal stress. However, if such a structure as a common long-chain alkyl group is used, an excess carbon number results in higher hydrophobicity, and this makes uniform hydrolysis or condensation reaction difficult. The carbon number is thus preferably 20 or less, and process conditions and the like are limited in some cases when such a structure is used. In contrast, in the present invention, an alkylene oxide group having higher polarity is introduced as the long chain structure, and thus the flexibility can be imparted while an appropriate hydrophilicity is maintained even with a group having a larger carbon number. In addition, by adjusting the type and the content of an alkylene oxide group according to characteristics of an ink or an aggregation liquid, the hydrophilicity of the surface layer can be controlled to achieve optimum image qualities. However, in order to achieve good transferability due to moderately low surface tackiness even if a polyalkylene oxide unit is used, the polyalkylene oxide unit preferably has a carbon number of 120 or less. The polyalkylene oxide unit more preferably has a carbon number of 6 to 100.
When an intermediate transfer member is repeatedly used, the hydrophilicity of the image forming surface may change. If the hydrophilicity of the image forming surface changes, conditions of an aggregation liquid or an ink applied change, and the qualities of images formed may change between transfer in the early stages and transfer after repetition. It is thus important for an intermediate transfer member to suppress the change in hydrophilicity of the image forming surface of the intermediate transfer member when the intermediate transfer member is used repeatedly.
The organic siloxane compound contained in the surface layer part of the present invention preferably has a siloxane bond in the molecular skeleton thereof and also preferably contains a polyalkylene oxide unit in the molecular skeleton. In the present invention, "in a skeleton" means a state in which a siloxane bond and a polyalkylene oxide unit form covalent bonds with other components, as components of the surface layer part of the intermediate transfer member and are immobilized, and differs from the state in which a siloxane bond and a polyalkylene oxide unit are simply attached to, adsorbed to, or infiltrated into the surface layer.
In this manner, the siloxane bond and the polyalkylene oxide unit are fixed to the surface layer part. In addition, both components are immobilized "in the skeleton". This prevents surface layer components from transferring to a recording medium and from disappearing at the time of transfer of an intermediate image, prevents surface layer components from bleeding due to change over time, and prevents surface layer components from disappearing by migration toward an aggregation liquid or toward an ink, for example. Accordingly, the change in hydrophilicity when the intermediate transfer member is used repeatedly can be suppressed.
Whether a siloxane bond and a polyalkylene oxide unit are integrated and immobilized in the molecular structure of an organic siloxane compound can be determined as follows: For example, a surface layer part of an intermediate transfer member is formed as a layer on a base; then the layer is released from the base and immersed in a good solvent such as methanol and benzene; the change in weight of the layer before and after the immersion is calculated; and a .sup.1H-NMR spectrum after immersion is measured. As for the .sup.1H-NMR, for example, a compound having a dimethylsiloxane component and a polyethylene oxide unit can be identified by the presence or absence of the peak of an ethylene oxide group (--CH.sub.2--CH.sub.2--O--, .sigma.=3.5 to 4.5 ppm) and the peak of the terminal structure of a siloxane bond (--O--Si--CH.sub.3, .sigma.=0.0 to 0.2).
The PAO-modified polysiloxane compound as the constituent material of the surface layer part of the intermediate transfer member is preferably a condensation product of at least one of an organic silicon compound represented by General Formula (1) and an organic silicon compound represented by General Formula (2) which are hydrolyzable siloxane compounds to which a polyalkylene oxide (PAO) unit is introduced.
##STR00001## (In the formula, X.sup.1 is a polyalkylene oxide unit containing (X.sup.2).sub.n; X.sup.2 is an alkylene oxide group having 2 to 4 carbon atoms; n is an integer of 3 to 50; each of R.sup.1 and R.sup.5 is independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; each of R.sup.2 and R.sup.6 is independently a monovalent group having an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, a carboxyl group, a vinyl group or a cyclic ether group; each of a and c is independently an integer of 1 to 3; each of b and d is independently an integer of 0 to 2; a+b=3; c+d=3; and each of R.sup.3 and R.sup.4 is independently a divalent group containing an alkylene group having 1 to 20 carbon atoms, a urethane bond or a carbonyl group)
##STR00002## (In the formula, X.sup.3 is a polyalkylene oxide unit containing (X.sup.4).sub.m; X.sup.4 is an alkylene oxide group having 2 to 4 carbon atoms; m is an integer of 3 to 50; R.sup.21 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R.sup.22 is a monovalent group having an alkyl group having 1 to carbon atoms, a hydroxyl group, a carboxyl group, a vinyl group or a cyclic ether group; q is an integer of 1 to 3; r is an integer of 0 to 2; q+r=3; R.sup.23 is a divalent group containing an alkylene group having 1 to 20 carbon atoms, a urethane bond or a carbonyl group; and R.sup.24 is a monovalent group having a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, a carboxyl group, an ester group, a vinyl group or a cyclic ether group)
The organic silicon compounds represented by General Formulae (1) and (2) have at least one structure in which a hydroxy group or an alkyloxy group is bonded to Si.
The hydroxy group or alkyloxy group substituted with Si can form a siloxane bond by dehydration condensation reaction. If an alkyloxy group is bonded to Si, hydrolysis reaction proceeds. Hence, the organic silicon compound having at least one structure in which a hydroxy group or an alkyloxy group is bonded to Si is an organic silicon compound capable of forming a siloxane bond.
In the present invention, such a group allows at least one of the organic silicon compounds represented by General Formulae (1) and (2) to undergo condensation reaction, and consequently a compound having a siloxane bond in the skeleton thereof can be obtained.
R.sup.1, R.sup.5, and R.sup.21 are specifically preferably any of a hydrogen atom, a methyl group, and an ethyl group from the viewpoint of reactivity.
The alkyl groups of R.sup.1, R.sup.2, R.sup.5, R.sup.6, R.sup.21, and R.sup.22 are substituted or unsubstituted alkyl groups, and the substituent of the substituted alkyl groups can be exemplified by a phenyl group.
The organic silicon compounds of General Formulae (1) and (2) have a polyalkylene oxide unit represented by X.sup.1 or X.sup.3.
The polyalkylene oxide unit (X.sup.1) in General Formula (1) can be exemplified by the following units: (A) a unit having one polyalkylene oxide group in which 3 to 50 alkylene oxide groups are bonded; and (B) a unit containing a structure in which a plurality of polyalkylene oxide groups in each of which 3 to 50 alkylene oxide groups are bonded are linked through linker groups (L).
The polyalkylene oxide unit (X.sup.3) in General Formula (2) can be exemplified by the following unit: (C) a unit having one polyalkylene oxide group in which 3 to 50 alkylene oxide groups are bonded.
The alkylene oxide group is specifically preferably an ethylene oxide group or a propylene oxide group from the viewpoint of hydrophilicity and reactivity. The polyethylene oxide group in which a plurality of alkylene oxide groups are bonded may be formed of a single type of alkylene oxide groups or may be formed of two or more types of alkylene oxide groups, such as a copolymerized unit of an ethylene oxide group and a propylene oxide group. It is preferable that the numbers of repeating units of alkylene oxide groups (n, m) are each independently 5 to 30 from the viewpoint of flexibility.
The polyalkylene oxide unit in (A) can be exemplified by units represented by --(O-Alk)-O-- or --O-(Alk-O).sub.n-- (where Alk is an alkylene group having 2 to 4 carbon atoms).
The polyalkylene oxide unit in (C) can also be exemplified by units represented by --(O-Alk)-O-- or --O-(Alk-O).sub.m-- (where Alk is an alkylene group having 2 to 4 carbon atoms).
The linker group (L) in the structure in (B) can be exemplified by linker groups containing an alkylene group which may be substituted. Such a linker can be exemplified by a propylene group substituted with a methyl group at the 2-position. The polyalkylene oxide unit formed by using the propylene group as the linker group has the following structure. --O-(Alk-O)--CH.sub.2--C(.dbd.C)--CH.sub.2--(O-Alk).sub.n''-O-- (each of n' and n'' is independently an integer of 3 to 50)
R.sup.2, R.sup.6, and R.sup.22 in General Formulae (1) and (2) may be a monovalent substituent having a vinyl group or a cyclic ether group. In this case, vinyl groups or cyclic ether groups can be bonded to each other by polymerization reaction among a plurality of organic silicon compound molecules. If both the condensation and the polymerization are performed, the order of the reactions is not limited. By performing polymerization in addition to condensation, the organic skeleton of a compound obtained by condensation of at least one of the organic silicon compounds represented by General Formulae (1) and (2) is developed, and thus the condensation product can obtain higher alkali resistance (ink resistance). Such conditions are thus preferred. A compound formed by polymerization of a vinyl group moiety or a cyclic ether group moiety is also preferred because such a compound suppresses the change in hydrophilicity of the image forming surface when the intermediate transfer member is repeatedly used.
Specific examples of the monovalent substituent having a vinyl group or a cyclic ether group as R.sup.2, R.sup.6, R.sup.22, and R.sup.24 include an acryloxy group, a methacryloxy group, a glycidoxy group, and a 2-epoxycyclohexyl group.
R.sup.3, R.sup.4, and R.sup.23 are a linking chain between a substituted silicon atom and a polyalkylene oxide unit (X.sup.1 or X.sup.3) and are composed of a divalent group containing an alkylene group, a urethane bond or a carbonyl group. The alkylene group as R.sup.3 or R.sup.4 may be substituted, and the substituent of the alkylene group can be exemplified by a hydroxy group.
The divalent group containing an alkylene group can be exemplified by alkylene groups, alkyleneoxy groups (-Alk1-O--), alkyleneoxyalkylene groups (-Alk1-O-Alk2-), alkyleneoxyalkyleneoxy groups (-Alk1-O-Alk2-O--), groups formed by linking an alkylene group and an aminocarbonyl group (-Alk3-NH--CO--), and groups formed by linking an alkylene group and a urethane bond group (-Alk4-NH--CO--O--). Each of Alk1 to Alk4 is independently an alkylene group having 1 to 20 carbon atoms which may be substituted.
The divalent group containing a urethane bond group or a carbonyl group can be exemplified by the above-mentioned groups formed by linking an alkylene group and an aminocarbonyl group (-Alk3-NH--O--) and the above-mentioned groups formed by linking an alkylene group and a urethane bond group (-Alk4-NH--CO--O--).
In General Formula (1), R.sup.1 and R.sup.5 are preferably the same substituent, R.sup.2 and R.sup.6 are preferably the same substituent, R.sup.3 and R.sup.4 are preferably the same substituent, a and c are preferably the same number, and b and d are preferably the same number.
The monovalent substituent as R.sup.24 can also be appropriately selected depending on the position of an oxygen atom at the terminal of a polyalkylene oxide unit. For example, when the R.sup.24 side terminal of a polyoxyalkylene oxide unit is --CH.sub.2--, a group having an oxygen atom that forms a bond with the terminal methylene group of the polyoxyalkylene oxide unit, such as a hydroxyl group, an acetyl group as an ester group, and alkyloxy groups, can be selected. When the R.sup.24 side terminal of a polyoxyalkylene oxide unit is --O--, a hydrogen atom or an alkyl group can be selected, for example. Examples of the organic siloxane compound represented by General Formula (1) and (2) include SIT8192.0, SIH6188, SIB1824.2, SIB1824.84, SIB1824.82 (manufactured by Gelest Inc.), SP-1P-2-006, SP-1P-2-007, and SP-1P-2-013 (manufactured by Specific Polymers Inc.).
By condensation of at least one of the compound of General Formula (1) and the compound of General Formula (2) having the above polyalkylene oxide unit, a resulting compound has siloxane bonds and polyalkylene oxide units in the skeleton thereof.
In the present invention, the number of groups capable of forming a siloxane bond onto the same silicon atom is defined as the number of functional groups per silicon atom of a compound. In other words, each of a, c, and q in General Formulae (1) and (2) represents the number of functional groups per silicon atom. The number of groups capable of forming a siloxane bond in a molecule is defined as the total number of functional groups of a compound. In other words, a+c or q in General Formulae (1) and (2) represents the total number of functional groups. A larger total number of functional groups gives higher crosslinking density after bonding, resulting in lower flexibility. A smaller total number of functional groups results in higher flexibility. On this account, a smaller total number of functional groups is preferred in consideration of only crack resistance. An organic silicon compound having a total number of functional groups of 1 has a terminal of a siloxane skeleton, and thus results in a reduction in crosslinking density, or an improvement in crack resistance, but is unlikely to form an intended skeletal structure to thereby affect coatability and film formability in some cases. Hence, the total number of functional groups of a siloxane skeleton is preferably set in consideration of crack resistance, coating properties, film formability, and the like. In the present invention, a+c.gtoreq.2 or q.gtoreq.2 is preferred.
In the reaction of an organic silicon compound capable of forming a siloxane bond, the number of siloxane bonds, i.e. the progress degree of condensation, is important. In the present invention, the progress degree of condensation is called degree of condensation, hereinafter.
In the present invention, heating the organic silicon compound in the presence of water allows as-needed hydrolysis and condensation reaction to proceed, thereby performing the condensation reaction. As a result, siloxane bonds are formed. The as-needed hydrolysis and the condensation reaction are appropriately controlled by temperature, time, pH, and other conditions, and an intended degree of condensation can be achieved. An acid catalyst or an alkali catalyst can be used, for example. The progress degree of the condensation reaction (degree of condensation) can be defined by the ratio of the number of condensed functional groups to the number of functional groups capable of condensation, and can be estimated by Si-NMR measurement in practice. For example, for an organic silicon compound having a total number of functional groups of 3, the degree of condensation is calculated by the following method. T0-body: a silicon atom that forms no bond with any other silicon atom through oxygen. T1-body: a silicon atom that forms a bond with one silicon atom through oxygen. T2-body: a silicon atom that forms bonds with two silicon atoms through oxygen. T3-body: a silicon atom that forms bonds with three silicon atoms through oxygen.
For an organic silicon compound having a total number of functional groups of 2, the degree of condensation is calculated by the following method. D0-body: a silicon atom that forms no bond with any other silicon atom through oxygen. D1-body: a silicon atom that forms a bond with one silicon atom through oxygen. D2-body: a silicon atom that forms bonds with two silicon atoms through oxygen.
The degree of condensation varies depending on the type of an organic silicon compound and synthetic conditions, but an excessively low degree of condensation may affect coating properties and film formability, for example. The degree of condensation is thus preferably 20% or more and more preferably 30% or more.
For hydrolysis reaction, an organometallic compound containing a central metal selected from silicon, titanium, zirconium, and aluminum can be used as a hydrolysis catalyst to control the degree of condensation. Examples of such a catalyst include titanium alkoxides, zirconium alkoxides, aluminum alkoxides, and complexes thereof (such as an acetyl acetonate complex). Such an organometallic compound can be added during the condensation reaction of an organic silicon compound or can be added to the condensation product of an organic silicon compound.
The organic silicon compound of General Formula (1) is preferably a compound of General Formula (1A).
##STR00003## (In the formula, Xa is a polyalkylene oxide unit represented by --(O-Alk).sub.n-O-- or --(O-Alk).sub.n'--CH.sub.2C(.dbd.CH.sub.2)CH.sub.2--(O-Alk).sub.n''--O-- (where Alk is an alkylene group having 2 to 4 carbon atoms; and each of n, n', and n'' is independently an integer of 3 to 50); each of R.sup.1 and R.sup.5 is independently an alkyl group having 1 to 4 carbon atoms or a hydrogen atom; each of R.sup.2 and R.sup.6 is independently an alkyl group having 1 to 4 carbon atoms; each of a and c is independently 2 or 3; each of b and d is independently 0 or 1; a+b=3; c+d=3; each of R.sup.3 and R.sup.4 is independently an alkylene group having 1 to 4 carbon atoms, --(CH.sub.2).sub.w--O--(CH.sub.2CH(OH)CH.sub.2)--, or --(CH.sub.2).sub.w--NH--CO--; and w is an integer of 1 to 4).
The organic silicon compound of General Formula (2) is preferably a compound of General Formula (2A).
##STR00004## (In the formula, Xa is an alkylene oxide group having 2 to 4 carbon atoms; m is an integer of 3 to 50; R.sup.21 is an alkyl group having 1 to 4 carbon atoms or a hydrogen atom; R.sup.22 is an alkyl group having 1 to 4 carbon atoms; q is an integer of 2 or 3; r is 0 or 1; q+r=3; R.sup.23 is an alkylene group having 1 to 4 carbon atoms or --(CH.sub.2).sub.z--NH--CO--; z is an integer of 1 to 4; and R.sup.24 is a hydrogen atom, an alkylene group having 1 to 4 carbon atoms, or a methylcarbonyl group)
One kind of the organic silicon compounds represented by General Formulae (1) and (2) may be condensed or two or more kinds of the organic silicon compounds may be co-condensed. Alternatively, the organic silicon compound may be co-condensed with at least one organic silicon compound that can form a siloxane bond but is neither of the organic silicon compounds of General Formulae (1) and (2). In particular, if the organic silicon compound is co-condensed with another polymerizable organic silicon compound that has a vinyl group or a cyclic ether group and can form a siloxane bond, substantially the same effect as that described above can be achieved in terms of alkaline resistance and maintenance of hydrophilicity, and thus such conditions are preferred.
The other organic silicon compound capable of undergoing co-condensation may be any organic silicon compound that has a hydrolyzable group capable of forming a siloxane bond, is not modified with PAO, and can give an intended condensation product together with at least one of the organic silicon compounds of General Formulae (1) and (2).
The other hydrolyzable organic compound can be exemplified by hydrolyzable organic compounds that have a nonhydrolyzable alkyl group and are not modified with PAO and hydrolyzable organic compounds that have a nonhydrolyzable polymerizable group and are not modified with PAO.
The nonhydrolyzable alkyl group can be exemplified by alkyl groups having 1 to 10 carbon atoms. The hydrolyzable group can be exemplified by alkyloxy groups, and the alkyl group of the alkyloxy group can be exemplified by a methyl group and an ethyl group.
Examples of the hydrolyzable silane compound that has a nonhydrolyzable polymerizable group and is not modified with PAO include the following compound of General Formula (4).
The nonhydrolyzable polymerizable group can be exemplified by groups having a vinyl group and groups having a cyclic ether group such as an epoxy group and an oxetanyl group.
When at least one compound of General Formulae (3) and (4) is used, the mixing ratio is preferably selected from Compound of General Formula (3):Compound of General Formula (4)=0:100 to 90:10 (molar ratio).
The ratio of at least one of the compounds of General Formulae (3) and (4), (C2), to at least one of the organic silicon compounds of General Formulae (1) and (2), (C1), is preferably selected from C1:C2=1:99 to 20:80 (molar ratio).
In the surface layer part of the intermediate transfer member of the present invention, the content of a condensation product formed by using at least one of the organic silicon compounds represented by General Formulae (1) and (2) varies depending on the type of a polyalkylene oxide and the structures of R.sup.3, R.sup.4, and the like, but can be 0.1% by mass or more. The surface layer part may be formed of the condensation product alone. When the surface layer part is formed of the condensation product and other materials, the content of the condensation product can be selected from, for example, 0.5% by mass or more to 80% by mass or less, and furthermore from 1% by mass or more to 50% by mass or less.
In the present invention, an ethylene oxide unit is preferably included as the alkylene oxide unit especially from the viewpoint of hydrophilicity. By using the ethylene oxide unit, the hydrophilicity is unlikely to be reduced even if the alkylene oxide unit has a larger carbon number, and thus the number of alkylene oxide units can be increased. Accordingly, a longer chain structure can be introduced, and thus a more flexible intermediate transfer member having excellent transferability can be produced.
In the present invention, a compound prepared by at least condensation of the organic silicon compound of General Formula (1) is preferably included. The reason thereof is supposed as follows: in the case of the organic silicon compound of General Formula (1), functional groups capable of forming a siloxane bond are positioned at both sides of the polyalkylene oxide unit; and thus, a compound prepared by condensation of the organic silicon compound can have a molecular structure in which the polyalkylene oxide unit is introduced between siloxane bonds through covalent bonds, i.e. a molecular structure in which the polyalkylene oxide unit is introduced into the main chain of a siloxane skeleton.
Generally, when a long chain structure is introduced to a side chain, the steric hindrance due to a bulkiness of the side chain partially prevents the main chain from bonding to suppress an excessively high crosslinking density, and thus flexibility can be expressed. However, a moiety prevented from bonding remains as an unreacted moiety and thus may lead to characteristic changes such as a change over time due to long-term storage, a change in orientation due to humidity, and reaction progress due to temperature. On this account, a higher degree of condensation is desired in order to suppress such changes in characteristics. In this case, however, the main chain has a very high crosslinking density, and this reduces the effect of increasing flexibility. In addition, a side chain having a long chain structure has high flexibility in the molecule, and thus surface characteristics may change when the orientation near the surface changes. In contrast, when a long chain structure is introduced to a main chain, the long chain structure is introduced between a bonding point and another bonding point of the main chain. On this account, the bond distance of the main chain can be surely widened even at a high degree of condensation, and a moiety having a low crosslinking density can be maintained. The effect of increasing flexibility is thus sufficiently achieved, and such conditions are preferred. In addition, the both sides of a long chain structure are immobilized, thus the change of orientation near the surface is also suppressed, and a surface layer having more stable characteristics can be obtained accordingly. As described above, it is important for the intermediate transfer member of the present invention to appropriately keep the balance between degree of condensation and crosslinking density. In the present invention, the polyalkylene oxide unit is included as the long chain structure. In particular, in the case of the organic silicon compound of General Formula (1), the long chain structure is introduced to the main chain, and such a structure is preferred. A longer chain structure is likely to be developed, and such a structure is more preferred.
The type of the polyalkylene oxide unit and the total number of functional groups are preferably, appropriately set depending on the types and quantity ratios of other compounds, physical properties of an aggregation liquid and an ink, and process conditions, for example.
In the surface layer part of the intermediate transfer member of the present invention, the ratio of the number of alkylene oxide groups (number of alkylene oxide units) to the number of siloxane bonds is preferably 0.1 to 1.2. By adjusting the ratio within this range, a more sufficient number of alkylene oxide units for making the surface layer part have sufficient flexibility, for preventing generation of cracks and delamination, and for giving good transferability of an intermediate transfer member can be supplied to the surface layer part. In addition, the surface of the surface layer part can be formed as a face having a tackiness more suitable for giving good transferability. If the ratio is less than 0.1, it is difficult to give a surface layer part having sufficient flexibility, and cracks are difficult to effectively suppress in some cases. If the ratio is more than 1.2, the flexibility is improved, and the surface tackiness concurrently increases. This reduces the transferability of an ink aggregate in some cases.
The ratio of the number of alkylene oxide groups to the number of siloxane bonds can be estimated by .sup.1H-NMR spectra. As for the .sup.1H-NMR, for example, the ratio of a compound having a dimethylsiloxane component and a polyethylene oxide unit can be expressed by the ratio of the peak intensity of an ethylene oxide group (--CH.sub.2--CH.sub.2--O--, .sigma.=3.5 to 4.5 ppm) and the peak intensity of the terminal structure of a siloxane bond (--O--Si--CH.sub.3, .sigma.=0.0 to 0.2) as described above.
The surface layer part of the intermediate transfer member in the present invention preferably contains a compound prepared by condensation of the organic silicon compound as described above, and the compound is also preferably polymerized at a polymerizable group moiety thereof such as a vinyl group or a cyclic ether group.
The polymerization initiator used when cationic polymerization is performed as polymerization can be exemplified by photocationic polymerization initiators that generate a cationic species or a Bronsted acid by photoirradiation and thermal cationic polymerization initiators that generate a cationic species or a Bronsted acid by heat.
Specific examples of the cationic initiator include onium salts, borate salts, triazine compounds, azo compounds, and peroxides. Aromatic sulfonium salts and aromatic iodonium salts are preferably used in terms of sensitivity, stability, reactivity, and solubility. The cationic polymerization initiators can be used singly or in combination of two or more of them.
As the polymerization initiator used when radical polymerization is performed as polymerization, a photoradical polymerization initiator that generates a radical species by photoirradiation or a thermal radical initiator that generates a radical species by heat can be used. Examples of the radical polymerization initiator include organic peroxides such as dialkyl peroxides, diacyl peroxides, ketone peroxides, peroxyketals, hydroperoxides, and peroxyesters; azo compounds; carbonyl compounds such as benzophenone and benzophenone compounds, acetophenone compounds, benzoin and benzoin ether compounds, aminocarbonyl compounds, and thioxanthones; sulfides; and peroxides. The radical polymerization initiators can be used singly or in combination of two or more of them.
When at least the organic silicon compound having a polymerizable group is used to form a condensation product, a cationic polymerizable resin and/or a radical polymerizable resin can be used as the other material that contains no Si and is usable to form the surface layer part in combination with the condensation product.
The cationic polymerizable resin as the material containing no Si is a resin containing a compound having a cationic polymerizable group such as a vinyl group and a cyclic ether group. Specifically, resins having an epoxy group or an oxetanyl group are preferably used. If an oxetane compound or an oxetane resin is used in combination with an epoxy resin, curing reaction is accelerated. Specific examples of the epoxy resin include bisphenol epoxy resins prepared from a monomer or an oligomer having a bisphenol skeleton, such as bisphenol-A-diglycidyl ether and bisphenol-F-diglycidyl ether; phenol novolac epoxy resins, cresol novolac epoxy resins, and trisphenolmethane epoxy resins; and resins having an alicyclic epoxy structure, such as 3,4-epoxycyclohexenylmethyl-3',4'-epoxycyclohexene carboxylate.
The radical polymerizable resin as the material containing no Si is a resin containing a compound having a radical polymerizable group such as a vinyl group. Specifically, resins having an acryloyl group, a methacryloyl group, or a styryl group are preferably used. Examples of the radical polymerizable resin include polymers of a polymerizable monomer shown below, mixtures of homopolymers of polymerizable monomers, and copolymers of two or more types of polymerizable monomers.
Examples of the styrenic monomer include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, .alpha.-methylstyrene, vinylnaphthalene, 2-ethylstyrene, 3-ethylstyrene, and 4-ethylstyrene.
When a cationic polymerizable resin and/or a radical polymerizable resin is contained as the material containing no Si, a resin having a large functional group equivalent or a known resin having a linear skeleton is preferably used in order to impart sufficient flexibility to the surface layer part. The content of such a resin is preferably 5% by mass or more to 50% by mass or less relative to the surface layer part. In addition to structures best suited for a wide variety of recording medium types, image holding properties on the intermediate transfer member, image transfer efficiency to a recording medium at the time of transfer, image qualities of transfer images, and the like, the thickness, hardness, elastic modulus, and other properties of each layer are appropriately set from the viewpoint of durable stability.
To form the surface layer part of the intermediate transfer member by using a polymerizable material, curing by irradiation of active energy rays or thermal curing enables the formation of a thin and uniform surface layer part having excellent mechanical strength. This also results in good transferability. In addition, the adhesiveness to a layer adjacent to the surface layer part is excellent, resulting in excellent durability. As the active energy rays, electron beams, X-rays, and the like can be used, but ultraviolet rays are preferably used from the viewpoint of workability, for example.
When a coating solution is applied to form the surface layer part, the coating solution also preferably contains appropriate additives such as a surfactant and an auxiliary catalyst for accelerating curing in order to improve the coatability. A coating solution containing no solvent may be applied and the whole coating film may be cured.
In the transfer-type ink jet recording method, an ink or an aggregation liquid used as needed typically has a surface energy of 20 mN/m or more to 50 mN/m or less. In the present invention, it is important for the surface design of the intermediate transfer member to moderately satisfy both wettability and transferability in order to appropriately apply each liquid onto the surface of the intermediate transfer member.
In order to form a good intermediate image on the image forming surface on the surface layer part of the intermediate transfer member and to improve the holding properties of an intermediate image on the intermediate transfer member, the image forming surface preferably has an average surface roughness Ra of 0.001 .mu.m or more to 3.00 .mu.m or less.
An embodiment of the transfer-type image recording apparatus (transfer-type ink jet recording apparatus) of the present invention is shown in FIG. 2. The apparatus includes an intermediate transfer member 11 having an image forming surface, an ink jet device 15 as an ink applying unit, coating rollers 14 as an aggregation liquid coating unit, and a pressure roller 18. The pressure roller 18 constitutes, together with the intermediate transfer member 11, a transfer unit of an intermediate image. The ink jet device 15 has a structure of ejecting inks from ink jet recording heads.
Image recording (image formation) with the apparatus can be performed by the following operations. To the image forming surface on the intermediate transfer member 11 to which an aggregation liquid has been applied with the coating rollers 14, an ink is applied by using the ink jet device 15 to form an intermediate image. Next, the pressure roller 18 is used to press the intermediate image formed on the intermediate transfer member against a recording medium 17, and the intermediate image is transferred to the recording medium.
The intermediate transfer member of the present invention can be provided on a support member 12. The support member 12 is rotationally driven in the arrow direction around an axis 13 as the center. Each device arranged around the intermediate transfer member works in such a way as to be synchronized with the rotation of the support member. The support member is required to have a certain structural strength from the viewpoint of the transfer accuracy and the durability thereof. As the material of the support member, metals, ceramics, and resins are preferably used, for example. Specifically, the following materials are preferably used in terms of the rigidity capable of withstanding the pressure at the time of transfer, dimensional accuracy, and an improvement of control responsivity by reducing inertia during operation: aluminum, iron, stainless steel, acetal resins, epoxy resins, polyimide, polyethylene, polyethylene terephthalate, nylon, polyurethane, silica ceramics, and alumina ceramics, for example. These materials are also preferably used in combination. As the support member, for example, a roller-type support member and a belt-shaped support member are also preferably used according to the shape of a recording apparatus to be applied or the mode of transfer to a recording medium. When a drum-shaped support member or a belt-shaped endless-web type support member is used, the same intermediate transfer member can be continuously, repeatedly used, and thus such a structure is particularly preferred in terms of productivity.
To the intermediate transfer member 11, an aggregation liquid is applied preferably before an ink is applied. As the method of applying the aggregation liquid, conventionally known various methods can be appropriately used. Examples of the method include die coating, blade coating, gravure coating, and methods combining such a method with offset roller coating. As the method of capable of application at high speed with high accuracy, an ink jet method is also preferably used.
The aggregation liquid contains a component that increases the viscosity of an ink. Such a component reduces the flowability of at least a part of an ink on an intermediate transfer member, and thus has effects of suppressing spreading and mixing of the ink, i.e. bleeding and beading, for example. In other words, when an image is formed by using an ink jet device, a large amount of an ink may be applied to a unit area. In such a case, bleeding or beading is likely to occur. However, if an aggregation liquid is applied onto an intermediate transfer member, the flowability of an ink is reduced when the ink is used to form an image. Thus, bleeding or beading is unlikely occur, and consequently the image is satisfactory formed and held.
The component for increasing the viscosity of an ink is preferably appropriately selected according to the type of an ink used for forming an image. For example, for dye type inks, an aggregation liquid containing a polymer aggregating agent is preferably used. For pigment type inks in which pigment particles are dispersed, an aggregation liquid containing a polyvalent metal ion or an aggregation liquid containing a pH adjuster such as an acid buffer is preferably used. As an example of other ink viscosity increasing components, a compound having a plurality of ionic groups, such as a cation polymer, is also preferably used. Combination use of two or more of these compounds is also effective. Specific examples of the polymer aggregating agent usable as the ink viscosity increasing component include cationic polymer aggregating agents, anionic polymer aggregating agents, nonionic polymer aggregating agents, and amphoteric polymer aggregating agents.
Examples of the metal ion used as the component for increasing the viscosity of an ink include divalent metal ions such as Ca.sup.2+, Cu.sup.2+, Ni.sup.2+, Mg.sup.2+, Sr.sup.2+, Ba.sup.2+, and Zn.sup.2+; and trivalent metal ions such as Fe.sup.3+, Cr.sup.3+, Y.sup.3+, and Al.sup.3+. If the aggregation liquid containing such a metal ion is applied, the aggregation liquid is preferably applied as an aqueous metal salt solution. Examples of the anion of the metal salt include, but are not necessarily limited to, Cl, NO.sub.3, CO.sub.3.sup.2, SO.sub.4.sup.2, I, Br, ClO.sub.3, HCOO, and RCOO.sup.- (R is an alkyl group). The aqueous metal salt solution preferably has a metal salt concentration of 0.01% by mass or more, and more preferably 0.1% by mass or more. The metal salt concentration is preferably 20% by mass or less.
As the pH adjuster used as the component for increasing the viscosity of an ink, an acidic solution having a pH of less than 7.0 is preferably used. Examples include inorganic acids such as hydrochloric acid, phosphoric acid, sulfuric acid, nitric acid, and boric acid; and organic acids such as oxalic acid, polyacrylic acid, acetic acid, glycolic acid, malonic acid, malic acid, maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric acid, lactic acid, pyrrolidone carboxylic acid, pyrone carboxylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, and nicotinic acid. A solution of a derivative of such a compound or a solution of a salt of such a compound can also be preferably used.
An acid buffer having a pH buffering capacity is preferably used because the change in pH is small even when the apparent concentration of an aggregation liquid is reduced by an ink and the reactivity with an ink is unlikely reduced. To obtain the pH buffer capacity, the aggregation liquid preferably contains a buffer agent. As the buffer agent, an acetate such as sodium acetate, potassium acetate, and lithium acetate, a hydrogen phosphate, a hydrogen carbonate, or a hydrogen salt of a polyvalent carboxylic acid, such as sodium hydrogen phthalate and potassium hydrogen phthalate can be used, for example. Examples of the polyvalent carboxylic acid include, in addition to the phthalic acid, malonic acid, maleic acid, succinic acid, fumaric acid, itaconic acid, phthalic acid, isophthalic acid, terephthalic acid, adipic acid, sebacic acid, dimer acid, pyromellitic acid, and trimellitic acid. In addition to the above, any known compound which exhibits a pH buffering action when added can be preferably used.
The aggregation liquid may be prepared by dissolving a component that increases the viscosity of an ink as described above in an aqueous medium. Examples of the aqueous medium include water and mixed solvents of water and a water-soluble organic solvent. In the aggregation liquid, the content of the aqueous medium is not limited to particular values, and can be set according to the type of an active component for aggregation in the aggregation liquid, a coating method, and the type of a recording medium, for example.
As the water-soluble organic solvent, the following solvents are specifically preferably used: alkanediols such as 1,3-butanediol, 1,5-pentanediol, 1,2-hexanediol, and 1,6-hexanediol; glycol ethers such as diethylene glycol monomethyl (or monoethyl) ether and triethylene glycol monoethyl (or monobutyl) ether; alkyl alcohols having 1 to 4 carbon atoms, such as ethanol, isopropanol, n-butanol, isobutanol, sec-butanol, and tert-butanol; carboxylic acid amides such as N,N-dimethylformamide and N,N-dimethylacetamide; ketones and keto alcohols, such as acetone, methyl ethyl ketone, and 2-methyl-2-hydroxypentan-4-one; cyclic ethers such as tetrahydrofuran and dioxane; glycerol; alkylene glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2- or 1,3-propylene glycol, 1,2- or 1,4-butylene glycol, and polyethylene glycol; polyhydric alcohols such as thiodiglycol, 1,2,6-hexanetriol, and acetylene glycol derivatives; sulfur-containing compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and dimethyl sulfoxide. From these compounds, two or more compounds can be also preferably selected and used as a mixture. The aggregation liquid can appropriately contain an antifoaming agent, an antiseptic agent, an antifungal agent, and other additives as needed in addition to the above components in order to obtain desired properties.
To the aggregation liquid, various resins can also be added in order to improve the transferability or to improve the toughness of an image finally formed. By adding a resin, the adhesiveness to a recording medium at the time of transfer can be increased, or the mechanical strength of an intermediate image can be increased. Depending on the type of a resin, the water resistance of a final image on a recording medium can be improved. The resin to be added may be any resin that can be present together with the ink viscosity increasing component. As an example, an organic polymer such as polyvinyl alcohol and polyvinylpyrrolidone is preferably used. A resin that reacts with a component contained in an ink to form crosslinkage is also preferred. Such a resin can be exemplified by polyoxazolines and polycarbodiimides that react with a carboxylic acid generally used for dispersion of a coloring material in an ink to form crosslinkage. Such a resin can be dissolved in a solvent of the aggregation liquid or can be added in an emulsion form or a suspension form. To the aggregation liquid, a surfactant may also be added to appropriately control the surface tension.
The aggregation liquid may be applied before the formation of an intermediate image and/or after the formation of an intermediate image. FIG. 2 shows an example in which the aggregation liquid is applied before the formation of an intermediate image.
To the image forming surface of the intermediate transfer member 11 to which the aggregation liquid has been applied, an ink is applied by using the ink jet device 15. The ink ejection system of the ink jet device include a system in which film boiling of an ink is caused by an electrothermal converter to form bubbles and ejects the ink, a system in which an ink is ejected by an electromechanical converter, and a system in which an ink is ejected by using static electricity, for example. From the viewpoint of high-density printing at high speed, the system using an electrothermal converter is preferably used.
The whole shape of the ink jet device is not limited to particular shapes. The shape of the recording head is not also limited to particular shapes, and either a line-head type head in which ink ejection orifices are arranged in a linear manner in the width direction of the image forming surface of the intermediate transfer member or a shuttle type head that conducts scanning in a predetermined direction on the image forming surface to apply an ink can be preferably used.
As the ink, inks widely used as the ink jet ink can be used. Specifically, various inks prepared by dissolving and/or dispersing a coloring material such as a dye, carbon black, and an organic pigment can be used. Of them, carbon black and organic pigment inks give an image having good weatherability or good color developability and thus are preferred.
As the ink, an aqueous ink containing water is preferred. In particular, an ink containing water in an amount of 45.0% by mass or more in the components is preferred. The content of the coloring material in the ink is preferably 0.1% by mass or more, and more preferably 0.2% by mass or more. The content is preferably 15.0% by mass or less, and more preferably 10.0% by mass or less.
The ink can contain a dye and/or a pigment as the coloring material and a polymer compound and a resin component as the dispersant for a pigment added as needed. As the coloring material, such conventional coloring materials as disclosed in Japanese Patent Application Laid-Open No. 2008-018719 can be used.
In order to improve the toughness and the like of an image finally formed on a recording medium, the ink can contain resin components such as water-soluble resins and water-soluble crosslinking agents. The material to be used may be any material that can be present together with ink components.
When an aqueous ink containing a water-soluble organic solvent is used, volatile components such as water are removed from the ink forming an intermediate image when being transferred to a recording medium, and thus such an intermediate image is formed mainly from a coloring material component and a water-soluble organic solvent. When the ink forming an intermediate image contains a water-soluble organic solvent at the time of transfer of the intermediate image to a recording medium, the ink is more satisfactory released from the image forming surface of the intermediate transfer member, and thus the transferability of the intermediate image can be improved. To achieve the effect of improving the transferability, a water-soluble organic solvent having a high boiling point and a low vapor pressure is preferred. Such a water-soluble organic solvent can be exemplified by the following water-soluble organic solvents: alkanediols such as 1,3-butanediol, 1,5-pentanediol, 1,2-hexanediol, and 1,6-hexanediol; glycol ethers such as diethylene glycol monomethyl (or monoethyl) ether and triethylene glycol monoethyl (or monobutyl) ether; alkyl alcohols having 1 to 4 carbon atoms, such as ethanol, isopropanol, n-butanol, isobutanol, sec-butanol, and tert-butanol; carboxylic acid amides such as N,N-dimethylformamide and N,N-dimethylacetamide; ketones and keto alcohols, such as acetone, methyl ethyl ketone, and 2-methyl-2-hydroxypentan-4-one; cyclic ethers such as tetrahydrofuran and dioxane; glycerol; alkylene glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2- or 1,3-propylene glycol, 1,2- or 1,4-butylene glycol, and polyethylene glycol; polyhydric alcohols such as thiodiglycol and 1,2,6-hexanetriol; heterocycles such as 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and N-methylmorpholine; and sulfur-containing compounds such as dimethyl sulfoxide.
If such a water-soluble organic solvent having a high boiling point and a low vapor pressure is used, the content of the solvent in the ink is preferably selected from a range up to 30% by mass.
The ink may contain various additives such as a pH adjuster, an anticorrosive, an antiseptic agent, an antifungal agent, an antioxidant, a reduction inhibitor, a neutralizer for water-soluble resins, and a salt, as needed. A surfactant may be added as needed to appropriately adjust the surface tension of an ink. The surfactant may be any surfactant that does no greatly affect the storage stability or the like of an ink. Examples of the surfactant include anionic surfactants such as fatty acid salts, higher alcohol sulfuric acid ester salts, liquid fatty oil sulfuric acid ester salts, and alkyl allyl sulfonic acid salts; and nonionic surfactants such as polyoxyethylene alkyl esters, polyoxyethylene sorbitan alkyl esters, acetylene alcohols, and acetylene glycols. Two or more of these surfactants can also be appropriately selected and used.
The mixing ratio of components constituting the ink can be appropriately adjusted so that a resulting ink can be ejected in consideration of the ejection capacity, the nozzle diameter, and the like of a selected ink jet head.
In FIG. 2, a heater 16 is used to reduce a liquid content from an intermediate image. If the liquid content in an intermediate image is excess, the excess liquid may extrude or overflow in the subsequent transfer step. This may deteriorate an intermediate image or reduce the transferability. As the method of reducing the liquid content, any of conventional various methods can be preferably used. Examples of the method include a heating method, a method of sending low-humidity air, a decompression method, a method of bringing an absorber that absorbs liquid into contact, and combination methods of them. The drying can also be performed by air drying.
After the drying step, by pressing an intermediate image against a recording medium, the intermediate image is transferred from the image forming surface of the intermediate transfer member to the recording medium, giving a printed product on which a final image is recorded. The recording medium includes not only plain papers and glossy papers used in common printing but also a wide variety of other printing media such as fabrics, plastics, and films, for example. During the pressing, a pressure roller 18 is preferably used to press an intermediate image from both of the intermediate transfer member side and the recording medium side because the intermediate image is efficiently transferred and formed. Pressing in multiple steps is also preferred because good transferability is achieved.
The intermediate transfer member 11 is repeatedly, continuously used in some cases from the viewpoint of productivity. In such a case, the surface is preferably washed and restored with a washing roller 19 or the like before the next image is formed. As the method of washing and restoring the surface, any of conventional various methods can be preferably used. Examples of the method include a method of applying a shower of a cleaning liquid, a method of bringing a wet molton roller into contact with the surface and wiping the surface, a method of bringing the intermediate transfer member surface into contact with the surface of a cleaning liquid, a method of scraping a residue by using a wiper blade, and a method of applying various energies. These methods may be used in combination.
Intermediate transfer members for transfer-type ink jet recording used as examples and comparative examples in the present invention were prepared by the following method.
In Examples 1, 2, 4, 9, and 13 and Comparative Example 2, compounds for constituent unit A and constituent unit B were mixed so as to give the molar composition of a condensation product shown in Table 1, giving a material for producing a hydrolysis-condensation product. In Examples 3, 5 to 8, 10 to 12, and 14 to 17, compounds for constituent unit A, constituent unit B, and constituent unit C were mixed so as to give the molar composition of a condensation product shown in Table 1, giving a material for producing a hydrolysis-condensation product. In Comparative Example 1, only a compound for constituent unit B was used, giving a material for producing a hydrolysis-condensation product. Each material was heated and refluxed in a water solvent together with hydrochloric acid as a catalyst for 24 hours or more to conduct hydrolytic condensation, giving a solution containing a condensation product.
Next, each solution containing the resulting condensation product was diluted to 15% by mass with methyl isobutyl ketone, and a photocationic polymerization initiator (trade name: SP150, manufactured by ADEKA) was added at 5% by mass relative to the total solid content. In this manner, a coating solution for forming a surface layer part was obtained.
Next, the main body of an intermediate transfer member was prepared by coating a polyethylene terephthalate (PET) film having a thickness of 0.05 mm with a silicone rubber having a rubber hardness of 40 degree and a thickness of 0.2 mm. To the main body, each solution containing the hydrolysis-condensation product was applied by spin coating to form a film, thereby providing a surface layer on the main body as the base layer. After the surface layer was provided, an UV lamp was used to perform irradiation and exposure. The surface layer was then heated at 120.degree. C. for 2 hours to be cured, and a surface layer part constituting the image forming surface was formed, giving each intermediate transfer member.
The surface layer part prepared in this manner had a thickness of 1.0 .mu.m in each intermediate transfer member.
The ratio of the number of alkylene oxide groups and the number of siloxane bonds in the skeleton of the surface layer part was determined by the following method.
Each intermediate transfer member was immersed in 2-methyl-diethyl ketone for 12 hours and then was dried. The surface layer part was released to prepare a sample for measurement. The ratio of the peak intensity of an ethylene oxide group (--CH.sub.2--CH.sub.2--O--, .sigma.=3.5 to 4.5 ppm) and the peak intensity of the terminal structure of a siloxane bond (--O--Si--CH.sub.3, .sigma.=0.0 to 0.2) of each measurement sample was determined by solid .sup.1H-NMR (AV400M manufactured by Bruker). From each intensity ratio obtained, the ratio of the number of alkylene oxide groups and the number of siloxane bonds in the skeleton of the surface layer part was calculated.
Each intermediate transfer member was evaluated by using the transfer-type ink jet recording apparatus shown in FIG. 2. As the support member of each intermediate transfer member, a cylindrical drum made of aluminum alloy was used.
First, to a 13% by mass aqueous solution of calcium chloride (CaCl.sub.2.2H.sub.2O), a surfactant and additives were appropriately added to adjust the surface tension and the viscosity, giving an aggregation liquid. The obtained aggregation liquid was continuously applied to the surface (image forming surface) of the intermediate transfer member by using a roller type coating apparatus. Next, an ink for forming images were ejected from an ink jet device to the image forming surface of the intermediate transfer member to form an intermediate image (mirror-inverted image) on the intermediate transfer member. As the ink jet device, a device including an electrothermal converter for ejecting an ink on demand was used. As the ink, a resin dispersion type pigment ink having the following formulation was used.
Styrene-acrylic acid-ethyl acrylate copolymer (an acid value of 240, a weight average molecular weight of 5,000): 1.0 part by mass
Next, a long rolled PET film with a hydrophilized surface (a thickness of 150 .mu.m) was used as the recording medium, and the intermediate image formed by the above method was pressed against the recording medium, giving a final image. After the transfer of the intermediate image, the image forming surface was restored by washing. The formation and transfer of intermediate images were continuously repeated 50,000 times, and the following evaluations were performed.
Before and after the transfer was repeated 50,000 times on an intermediate transfer member, the uniformity of the aggregation liquid applied to the intermediate transfer member surface was visually evaluated based on the following criteria. A: The aggregation liquid is uniformly applied to the intermediate transfer member surface. B: The aggregation liquid is almost uniformly applied to the intermediate transfer member surface. C: The aggregation liquid is not uniformly applied to the intermediate transfer member surface.
After the transfer was repeated 50,000 times, the crack resistance of the surface layer part of an intermediate transfer member was visually evaluated based on the following criteria. AA: No crack is observed on the surface layer part even after the transfer is repeated 50,000 times. A: No crack is observed on the surface layer part after the transfer is repeated 30,000 times, but cracks are observed on the surface layer part after the transfer is repeated 50,000 times. B: No crack is observed on the surface layer part after the transfer is repeated 20,000 times, but cracks are observed on the surface layer part after the transfer is repeated 30,000 times. C: No crack is observed on the surface layer part after the transfer is repeated 10,000 times, but cracks are observed on the surface layer part after the transfer is repeated 20,000 times. D: Cracks are observed on the surface layer part after the transfer is repeated 10,000 times.
Tables 2 and 3 show the structural formulae of the organic silicon compounds used as the compounds for constituent unit A
As shown in Table 1, the intermediate transfer members of Examples 1 to 17 each including a surface layer part composed of the compound having a siloxane bond and a polyalkylene oxide unit in the skeleton exhibited good aggregation liquid coatability in the initial state and after repeated transfer, and the change of the coatability was small.
In these examples, no crack was generated until the transfer was repeated 10,000 times, and there was no difference in image qualities of the obtained images in the initial state and after repeated transfer. In Examples 1 to 12 and 14 to 17 in which the ratio, number of alkyl oxide groups/number of siloxane bonds, was within the particular range, the results indicated higher effects of suppressing the crack generation.
In contrast, the intermediate transfer member of Comparative Example 1 that did not include a surface layer part composed of the compound having a siloxane bond and a polyalkylene oxide unit in the skeleton gave images that had a difference in image qualities in the initial state and after repeated transfer, and stable image recording was difficult. The intermediate transfer member of Comparative Example 2 repelled the aggregation liquid on the surface, and was consequently unlikely to achieve an even coating state.
This application claims the benefit of Japanese Patent Application No. 2015-148505, filed Jul. 28, 2015, which is hereby incorporated by reference herein in its entirety.