Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1997-08-25
2002-04-02
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S064000, C347S063000, C347S044000, C347S045000
Reexamination Certificate
active
06364465
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to ink jet print heads and, more preferably, to print heads having improved durability.
BACKGROUND OF THE INVENTION
Ink jet print heads are sandwich structures having top and bottom plates, and a dry film photoresist intermediate layer that defines liquid pathways and discharge orifices. The top plate contains the ink nozzles, and typically is made of a noble metal, glass or plastic. The bottom plate typically is a thermally stable substrate, such as a silicon wafer, that bears microcircuits. Microresistors are mounted on the substrate, projecting into the liquid pathways in the photoresist layer, in alignment with the ink nozzles. At computer command, the resistors superheat nearby ink, creating a steam bubble that forces ink droplets out the nozzles.
The dry film photoresist layer must meet many demanding requirements. It must be capable of being imaged to the fine resolution needed to define the ink passageways. The layer must be dimensionally stable (e.g., not swell) and capable of withstanding chemical attack from the hot aqueous inks, which typically have high pH and contain organic components. Moreover, the layer must remain firmly bonded to the top and bottom plates, which frequently are constructed of materials difficult to bond to (e.g., gold), during millions of firing cycles, despite stresses that tend to cause delamination.
Various photoresist materials have been proposed to meet the demanding requirements of print head construction. For example, Japanese Patent Application 5-278222, published Oct. 26, 1993, discloses a dry photoresist film containing a half acryloyl ester of a bis-phenol A epoxy monomer, a photoinitiator, and a polymeric binder that is said to be particularly useful for this purpose. Vacrel® solder mask material, a photoresist material sold by E. I. du Pont de Nemours and Company that contains acrylic and melamine monomers, photoinitiator, and an acrylic binder with acidic functions for water-based development, also has been used for this purpose.
The inks contained in the print heads contain cosolvents to improve their daytime and water fastness. However, these cosolvents have a tendency to swell known resist layers causing them to delaminate from the top and bottom plates, leading to failure of the print head.
Although known dry film photoresists have proven useful, further improvements are desired to achieve the desired durability for extended use of ink jet print heads.
SUMMARY OF THE INVENTION
It now has been found that the photoresists containing poly(amic acid) will improve durability of the print heads. Accordingly, the present invention provides an ink jet print head having a top plate, an intermediate photoresist layer defining ink passageways, and a bottom plate, wherein the photoresist layer, prior to imaging to form the passageways, contains an ethylenically unsaturated compound, a photoinitiator, and a poly(amic acid) prepared from at least one dianhydride and at least one aliphatic diamine.
The photopolymerizable poly(amic acid) solutions can also be used to make solder masks, photoimageable coverlays, for flexible circuits, optical wave guides and an adhesiveless laminate to make disk drives.
DETAILED DESCRIPTION OF THE INVENTION
While the details of print head design will vary with the manufacturer, the print head
10
(as seen in FIG. 1) generally has a top plate,
11
(which is shown partly sectioned to permit illustration of the ink passageways) an intermediate photoresist layer
12
, and a bottom plate
13
. The intermediate photoresist layer
12
is a dry film that is imaged during the manufacturing process, followed by removal of non-exposed regions of the photoresist, to form ink passageways
14
,
15
. It is critical that the photosensitive or photoresist layer
12
remain firmly bonded to the top
11
and bottom
13
layers of the print head
10
during extended use, and be resistant to chemical attack or swelling by the inks, which are aqueous based and typically contain organic components.
BOTTOM PLATE
The bottom plate serves as a mounting platform for microresistors or other elements used to generate pressure to discharge the ink, such as heat generating or piezo elements. The bottom plate typically is constructed of silicon, glass, ceramic, plastic or metal. Sputter-coated “passivation” layers may be employed to protect circuits mounted on the bottom plate from ink attack. For example, passivation layers of Si
3
N
4
and SiC are shown in U.S. Pat. No. 4,809,428. Other inorganic oxide or inorganic nitride materials useful for this purpose are SiO
2
, Ta
2
O
5
, Al
2
O
3
, glass, BN, etc.
The bottom plate also may be coated with a metal protective layer to impart ink resistance, either with or without a passivation layer. Anti-corrosive metals such as Ti, Cr, Ni, Ta, Mo, W, Nb and the like may be selected for this purpose, or alloys such as stainless steel or noble metals. Noble metals such as gold, palladium or platinum also may be selected, but are more difficult to bond to the photoresist layer.
PHOTORESIST LAYER
The photoresist layer may be applied to the bottom plate either in liquid form, then dried, or preferably as a dry film. The photoresist layer contains an ethylenically unsaturated compound or monomer, a photoinitiator, and a poly(amic acid) prepared from at least one dianhydride and at least one aliphatic diamine in accordance with this invention. Other additives may be present to modify the properties of photopolymer materials. Particularly preferred composites are disclosed in U.S. Pat. No. 4,937,172, and are composed of a monomer that is a half acryloyl ester of bisphenol A epoxy; a photoinitiator system; and a macromolecular elastomeric water-insoluble binder.
Poly(amic acid):
Poly(amic acid) can be easily prepared by reacting a tetracarboxylic dianhydride to at least one aliphatic diamine in an organic solvent.
The tetracarboxylic dianhydride may be represented by the formula:
wherein R
1
is a tetravalent organic group having 2 to 30 carbon atoms, preferably 6-21 carbon atoms. For example, aliphatic or alicyclic tetracarboxylic dianhydrides can be used to practice the invention. Useful examples include but are not limited to butanetetracarboxylic dianhydride, pentane-tetracarboxylic dianhydride, hexanetetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, bicyclohexanetetracarboxylic dianhydride, cyclopropanetetracarboxylic dianhydride, and methylcyclohexanetetracarboxylic dianhydride, ethylene diamine tetraacetic dianhydride, propylene diamine tetraacetic dianhydride and bicyclo octene tetracarboxylic anhydride. The use of an aromatic tetracarboxylic dianhydride can afford a poly(amic acid) which can be converted to a polyimide with superior physical properties. Examples of useful aromatic tetracarboxylic dianhydrides include but are not limited to 2,2′-bis(3,3′,4,4′-biphenyl)-hexaflurorpropane dianhydride (6-FDA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), pyromellitic dianhydride (PMDA), oxydiphthalic anhydride (ODPA), 3,3′,4,4′-biphenyltetracarboxlic dianhydride, 2,2′,3,3′-biphenyltetracarboxlic dianhydride, 2,3,3′,-4′-biphenyltetracarboxylic dianhydride, 2,2-bis[5-(3,3-dicarboxyphenoxy)phenyl]propane dianhydride, 2,2-bis(3,-4-dicarboxy-phenyl)propane dianhydride, 2,2′-bis(3,3′,4,-4′-biphenylpropane dianhydride, bis(3,4′-dicarboxyphenyl) dimethylsilane dianhydride, bis(3,4-dicarboxyphenyl) dimethylsiloxane dianhydride, 4,4′-isophthaloyl diphthalic anhydride, hydroquinone diether anhydride, sulfonyl bis(phthalic anhydride), and ethyleneglycol bis(trimellitic anhydride), 3,4,9,10-perylenetetracarboxylic dianhydride, 4,4′-sulfonyldiphthalic dianhydride, 3,3′4,4′biphenyltetracarboxylic dianhydride (BPDA), 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, and 2,3,5,6-pyri
Barlow John
E. I. du Pont de Nemours and Company
Shah Manish
LandOfFree
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