Patent Publication Number: US-2012026226-A1

Title: Inkjet head and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2010-169692, filed on Jul. 28, 2010, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an inkjet head including a cover which covers a control section. 
     BACKGROUND 
     Inkjet printers use various types of inkjet heads, such as an ink circulating inkjet head which circulates ink between the inside of a head and the outside of the head, and a non-circulating inkjet head which uses up all of the ink supplied in the head. 
     Generally, an inkjet head includes a plurality of nozzles formed on a nozzle plate, a drive element which is provided in an ink chamber and discharges ink from the nozzles, and a drive circuit which is provided outside the ink chamber and on which an electronic component, such as a driver IC, for driving the drive element is mounted. In addition, in many cases, the inkjet head is used in a state where it is fixed to a ceramic base, for example. 
     One idea to protect the drive circuit on which the above-mentioned electronic component is mounted from ink is to arrange a cover made of a synthetic resin which is capable of covering the drive circuit, and bond the cover to a base by an adhesive. However, the ceramic base and the cover made of a synthetic resin have different coefficients of linear expansion. For this reason, when the temperature of the inkjet head becomes high during discharge of the ink, cracks may occur in the adhesive. Thus, the ink may leak inside from the cracked parts and cause a malfunction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view which shows an inkjet head of the present embodiment; 
         FIG. 2  is a top view which shows the inkjet head shown in  FIG. 1 ; 
         FIG. 3  is an exploded perspective view which schematically illustrates a head main body of the inkjet head shown in  FIG. 1 ; and 
         FIG. 4  is a graph which shows test results of an immersion test of an adhesive of the present embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, an inkjet head includes a head main body having a plurality of nozzles and drive elements which discharges ink from the plurality of nozzles, a control section which controls the drive elements, and a ceramic base on which the head main body and the control section are arranged. The inkjet head further includes a cover which is formed of a resin in which ceramic particles are mixed, and fixed to the base to cover the control section and hold the control section inside, and an adhesive which is interposed between the base and the cover, and seals an interior of the cover. 
     A first embodiment of an inkjet head will now be described with reference to drawings. The inkjet head is mounted in a printing device, such as a printer, and while receiving supply of ink from an ink tank, ink droplets are discharged toward a to-be-printed object, thereby forming a character and image on the to-be-printed object. Further, in the present embodiment, an explanation will be given for a case where the present invention is applied to a non-circulating inkjet head in which ink is not circulated between the inside of a head and the outside of the head, as an example. However, needless to say, the present invention can also be applied to an ink circulating inkjet head. 
     As shown in  FIGS. 1 and 2 , an inkjet head  11  comprises a base  12  which is flat-shaped, a head main body  13  and a control section  14  which are arranged on the base  12 , a cover  15  which is fixed on the base  12  to cover the control section  14 , and an adhesive  16  which is interposed between the base  12  and the cover  15 . The inkjet head  11  further comprises a filter  19  for removing dust from the ink which is located near the connection to an ink tank which is not shown. 
     As shown in  FIG. 3 , the head main body  13  comprises, for example, a substrate  17 , a top panel  18  which is bonded to the substrate, and a nozzle plate  21  which is bonded to the substrate  17  and the top panel  18  in such a manner that extends therebetween. The nozzle plate  21  includes a plurality of nozzles  22 . In a state where the nozzle plate  21  is bonded to the substrate  17  and the top panel  18 , the nozzles  22  communicate with pressure chambers  23 , respectively. 
     On the top panel  18 , a supply port  24  for supplying ink inside the head main body  13  is provided. Further, a common fluid chamber  25  is provided inside the top panel  18 , and the common fluid chamber  25  communicates with each of the pressure chambers  23 . 
     The substrate  17  is formed by bonding together two piezolelectric members  26  which are made of lead zirconate titanate (PZT) such that their polarization directions are opposed to each other. The substrate  17  comprises a plurality of pressure chambers  23  which are formed like grooves on one surface of the substrate, struts  27  which are an example of a drive element provided on both sides of the pressure chambers  23 , and electrodes  28  which are formed on a side surface of each of the struts  27  and the bottom of the pressure chambers  23 . Further, on the substrate  17 , a plurality of wiring lines  31  are provided. The wiring lines  31  are connected to the electrodes  28  at one end and connected to a flexible printed wiring board  32  of the control section  14  at the other end. 
     The base  12  is formed of a ceramic material, such as alumina, for example. The coefficient of linear expansion of the base  12  made of alumina is 5×10 −6  to 7×10 −6 , for example. The base  12  includes a temperature adjustment channel  33  which is made inside the base  12 , and an adapter  34  which is connected to the channel  33 . A fluid can be flowed inside the temperature adjustment channel  33 . By making hot water which is controlled to have a constant temperature flow inside the temperature adjustment channel  33 , the temperature of the head main body  13  and a driver IC  35  of the control section  14  can be maintained at a constant level. 
     The control section  14  can directly control the struts  27  of the substrate  17  to discharge ink from the nozzles  22 . The control section  14  comprises the flexible printed circuit board  32  which is connected to the wiring lines  31 , the driver IC  35  which is electrically connected to the flexible printed circuit board  32 , and a drive circuit  36  which is electrically connected to the driver IC  35 . 
     To perform printing processing with a printing device, which is equipped with the head main body  13  and the control section  14  of the inkjet head  11  mentioned above, it is necessary to supply ink to the head main body  13  from the ink tank of the printing device. The supply of the ink is performed via the supply port  24 , and the ink which has flowed out of the ink tank is supplied within each of the pressure chambers  23  through the supply port  24  and the common fluid chamber  25 . 
     In this state, if a user instructs printing to a printer, a main substrate of the printer outputs a signal for printing instruction with respect to the control section  14  of the ink jet head  11 . The driver IC  35  of the control section  14  which received the signal for printing instruction applies a pulse voltage to the struts  27  via the wiring lines  31 . By the application of the pulse voltage, a pair of struts  27  (right and left struts  27 ) is drawn apart in a bending manner as a result of shear mode deformation. Further, by restoring these struts to an initial position and raising a pressure within the pressure chambers  23 , ink droplets are discharged from the nozzles  22  with great force. 
     The cover  15  is formed to have a configuration of a recessed portion for accommodating the control section  14  inside. The cover  15  is formed of a resin material which is made by mixing a ceramic filler into a synthetic resin, such as poly phenylene sulfide resin (PPS) and polybutyleneterephthalate resin (PBT). The ceramic particles comprise inorganic particles, such as SiO 2 . More specifically, the cover  15  is formed by molding a mixture comprising either PPS or PBT and further comprising 30 to 40% by weight of an inorganic substance, such as SiO 2 . 
     The coefficient of linear expansion of the cover  15  is 1×10 −5  to 2×10 −5 . Since the coefficient of linear expansion of PPS without the filler is 7×10 −5  to 10×10 −5 , the coefficient of linear expansion of the cover  15  of the present embodiment is approximately 5 to 10 times smaller than that of PPS without the filler. 
     Accordingly, in the present embodiment, the coefficient of linear expansion of the cover  15  is equal to that of the base  12  or greater than that of the base  12  by not more than 10 times. 
     As shown in  FIG. 2 , the adhesive  16  is applied to the base  12  and the head main body  13  in the form of “C” substantially. The adhesive  16  is interposed between the base  12  and the cover  15 , and can seal the interior of the cover  15 . Further, the adhesive  16  covers both a gap between the cover  15  and the base  12  and a gap between the cover  15  and the head main body  13 . 
     A base compound of the adhesive  16  is formed of a bisphenol A-type epoxy resin or a bisphenol F-type epoxy resin, or a combination of the two. Further, as a curing agent, the adhesive  16  contains a curing agent made of epoxy resin (epoxy resin curing agent), for example. The coefficient of elasticity of the adhesive  16  is within the range of 3 to 3.5 GPa. Since the adhesive  16  of the present embodiment contain the curing agent made of epoxy resin, an ink resistance property is imparted to the adhesive  16 . 
     When the heat cycle test, which varies the temperature within the range of −10 to 60° C., is performed on the inkjet heat  11  structured as stated above, even if such thermal hysteresis is applied to the inkjet head  11 , no cracks occurred in the adhesive  16 . 
     As shown in  FIG. 4 , the inventors carried out an immersion test, which immerses the adhesive  16  to be used in the present embodiment in ink to judge whether the adhesive  16  is resistant to ink. In the immersion test, the adhesive  16  was immersed in ink A, ink B, and ink C for a predetermined number of days (one week, one month, and three months), under the condition of 45° C., to evaluate the ink resistance property of the adhesive  16 . For all of ink A, ink B, and ink C, acrylic UV curable ink was used. When this test was conducted, in all cases, adhesive strength of the adhesive did not fall below 100 kg/cm 2 , which is a reference value, and it has been confirmed that the adhesive  16  has a resistance property to all of ink A, ink B, and ink C. 
     According to the first embodiment, the inkjet head  11  comprises the head main body  13  including the nozzles  22  and the drive element which discharges ink from the nozzles  22 , the control section  14  which controls the drive element, the ceramic base  12  on which the head main body  13  and the control section  14  are mounted, the cover  15  which is formed of a resin in which ceramic particles are mixed, and fixed to the base  12  to cover the control section  14  and hold it inside, and the adhesive  16  which is interposed between the base  12  and the cover  15 , and seals the interior of the cover  15 . 
     Since the ceramic particles are mixed into the resin for forming the cover  15 , the structure as stated above enables to reduce a difference between the coefficient of linear expansion of the cover  15  and that of the base  12 . By this structure, it is possible to prevent cracks from occurring in the adhesive  16 , and prevent ink from leaking inside the cover  15  and affecting the control section  14 . Thus, a highly-reliable inkjet head  11  can be provided. 
     The adhesive  16  is made by adding the curing agent made of epoxy resin to the epoxy resin comprising at least one of a bisphenol A-type epoxy resin and a bisphenol F-type epoxy resin. By adopting this structure, an ink resistance property can be imparted to the adhesive  16 , thereby preventing the swelling of the adhesive  16  and reduction in the adhesive strength of the adhesive  16 . 
     The coefficient of linear expansion of the cover  15  is equal to that of the base  12  or greater than that of the base  12  by not more than 10 times, and the coefficient of elasticity of the adhesive  16  is 3 to 3.5 GPa. If an adhesive has a coefficient of elasticity of 3 GPa or less, gaps are formed between molecules, which causes a problem of damage by partial ink. On the other hand, if the coefficient of elasticity is 3.5 GPa or more, elasticity is not sufficient, and cracks may occur in the adhesive  16  when thermal hysteresis is applied to the inkjet head  11 . With the above-mentioned structure, it is possible to make the adhesive  16  have such elasticity as to allow the adhesive  16  follow the thermal expansion of the cover  15 , and also make the adhesive  16  have a property of not being affected by ink. 
     The inkjet head  11  is not limited to the above embodiment, and may be embodied by modifying constituent features without departing from the spirit when the inkjet head is put into practice. Further, various inventions can be achieved by suitably combining the constituent features disclosed in the above embodiment. For example, some constituent features may be deleted from the entire constituent features shown in the embodiment. Further, constituent features of different embodiments may be combined suitably. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.