Patent Application
20150174800
1. Field of the Invention
The present invention relates to a resin molding method and a liquid ejection head manufacturing method.
2. Description of the Related Art
Some parts of liquid ejection heads such as base plates that require a high degree of dimensional accuracy are formed by means of metal or ceramic (e.g., alumina) in certain instances. Parts can be formed to represent a high degree of dimensional accuracy with ease by means of ceramic materials such as alumina, which are additionally highly resistant to liquids such as ink. However, alumina is expensive and hence raises the manufacturing cost of the products that are formed by using alumina.
Thus, Japanese Patent Application Laid-Open No. 2009-155370 proposes a technique of molding parts of motors to be used for driving vehicles by using an epoxy resin molding material containing epoxy resin, an epoxy resin curing agent, a curing accelerator, an inorganic filler, silicon resin, thermosetting resin, and a silane coupling agent.
The epoxy resin molding material described in Japanese Patent Application Laid-Open No. 2009-155370 is less expensive than alumina and represents a small linear expansion coefficient because the proposed material contains a filter to a large extent. Therefore, the material is less likely to significantly expand to give rise to stress and deformation in a state where the material is bonded to some other member. Like other thermosetting resin materials, the epoxy resin molding material is injected into the cavity of a metal mold apparatus for molding and, when the mold is opened in a later step, the material has already been cured to represent a high elastic modulus. Such molded product may adhere to the inner surface of the mold so that the mold may not be opened smoothly with ease in some instances because of the high elastic modulus they represent. If the molded product cannot smoothly and soundly be released from the mold (for mold releasing) after the molding process, the molded product may be cracked and rejected as defective molded product particularly when the molded product has a micro structure.
In view of the above-identified problem, therefore, the object of the present invention is to provide a resin molding method that can produce molded products that are inexpensive and can smoothly and soundly be released from the mold (for mold releasing) and a liquid ejection head manufacturing method that utilizes the resin molding method.
In an aspect of the present invention, the above object is achieved by providing a resin molding method including: a step of plasticizing thermosetting resin and injecting the plasticized thermosetting resin into the cavity of a metal mold apparatus; a step of curing the thermosetting resin in the cavity; and a step of opening the mold.
The step of opening the mold is executed when the mold having the cavity is at a temperature not lower than the glass transition point of the thermosetting resin.
With this method, since the mold is opened at a temperature not lower than the glass transition point of the thermosetting resin and hence in a state where the molded product can easily be elastically deformed, the molded product is made to come off from the mold little by little while the product is elastically deformed. Therefore, if compared with an instance where a part of a molded product having a broad surface comes off from a mold at a time, the method of the present invention provides an improved mold releasing effect.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Now, the present invention will be described further by referring to the accompanying drawings that illustrate embodiments of the invention.
An exemplary embodiment of thermosetting resin molding method according to the present invention employs a metal mold apparatus 100 as illustrated in
With this embodiment, the metal mold apparatus 100 is employed for transfer molding, using thermosetting resin, which may typically be epoxy resin, as molding material. As illustrated in the flowchart of
Glass transition point Tg is the temperature found between the solid elasticity area and the rubber elasticity area of resin, which is the temperature range in which resin is in a dynamic viscoelasticity state, and at which the loss coefficient tan 5, which is the ratio of the storage elastic modulus E′ to the loss elastic modulus E″, represents the peak value.
Epoxy resin represents an excellent heat resistant property and an excellent chemical resistant property and hence is hardly eluted if brought into contact with liquid such as ink. Additionally, epoxy resin has an advantage of representing a relatively small linear expansion coefficient and hence has a small cure contraction coefficient. Furthermore, epoxy resin is a highly adhesive material and hence is mainly used in adhesive agents. Since materials representing a small linear expansion coefficient normally have a high glass transition point, such a material is conventionally molded in a condition where the mold temperature is lower than the glass transition temperature. Then, therefore, the mold is opened and the molded product is taken out in the solid elasticity area. At this time, namely after the molding process, however, the molded product cannot satisfactorily be released from the mold (mold releasing) because of the high adhesiveness and the high elastic modulus of epoxy resin. In other words, the molded product adheres to the mold at the time of opening the mold and hence cannot be taken out smoothly and soundly from the mold. Then, in certain instances, the molded product can be cracked or otherwise become defective.
To the contrary, with this embodiment, the timing of opening the mold is ingeniously planned, while maintaining the advantages of epoxy resin including that epoxy resin is hardly eluted and represents a high elastic modulus and a small linear expansion coefficient. More specifically, after the molding process, the molds 100A and 100B are opened in a state where the molds 100A and 100B are held to a temperature not lower than the glass transition point Tg so that the molded product 104 can be released from the mold smoothly and soundly (mold releasing). Additionally, a molded product that represents a high degree of dimensional accuracy can be produced highly efficiently with ease. The storage elastic modulus E′ of epoxy resin or some other similar resin material at the glass transition point Tg is generally not greater than about ½ to 1/10 of the storage elastic modulus E″ of the resin at room temperature. In other words, the resin material is in a state of being elastically deformed with ease at the glass transition point Tg. Therefore, when the mold is opened at a temperature not lower than the glass transition point, any part of the molded product 104 that has a relatively broad surface would not come off from the mold at a time but comes off gradually step by step while the molded product is deformed to a certain extent. In other words, the linear part comes off from the mold gradually and sequentially so that consequently the molded product can be released from the mold with ease. When the mold is opened at a higher temperature where the molded product is in the rubber elasticity area and the storage elastic modulus E′ is at the lowest level, the resin is more easily elastically deformed to further improve the mold releasing effect. Then, as a result, the degradation, if any, of the dimensional accuracy of the molded product 104 is effectively suppressed.
Now, a mode of application of a molded product molded by the above-described resin molding method, where the molded product is employed for a liquid ejection head for ejecting liquid such as ink, will be described below. As illustrated in
As illustrated in
As an electric signal transmitted from a control circuit (not illustrated) to the element substrates 3 by way of the connecting sections 4b of the electric wiring substrate 4 is supplied to the heat generating resistors 13 by way of electric wiring (not illustrated), the heat generating resistors 13 are driven to generate heat. Then, the liquid in the pressure chambers 11 to which heat is applied as ejection energy bubbles and is ejected to the outside from the ejection ports 12 under the pressure of bubbles. If, for example, the liquid is ink, the ink ejected from the ejection ports 12 as described above adheres to the recording medium (not illustrated) placed at a position that faces the liquid ejection head 1 to form one or more than one characters and/or images on the recording medium. The liquid ejection head 1 illustrated in
In general, the element substrates 3 of a liquid ejection head 1 having the above-described configuration are formed by applying a micro machining technique, which may typically be the so-called Micro Electro Mechanical (MEM) Technology onto a silicon-made substrate. Minute ejection ports 12 are highly densely arranged in liquid ejection heads 1 including those that have been fabricated in recent years and those that are being fabricated currently for the purpose of high speed and high definition recording. Therefore, the element substrates 3 and the base plate 2 that is a support member for supporting the element substrates 3 are required to represent a high degree of dimensional accuracy and also a high degree of flatness in order to realize high quality recording.
Particularly, in the case of a long liquid ejection head 1 having a length that corresponds to the length of the recording mediums to be used for the liquid ejection head 1 as illustrated in
From this point of view, epoxy resin is highly suitable as the material of the base plate 2 of the liquid ejection head 1 because epoxy resin represents a high degree of heat resistance and chemical resistance and has a small linear expansion coefficient. Note, however, epoxy resin is a material that is highly adhesive and hence cannot be released from the mold with ease after a molded product is produced, as pointed out earlier. For this reason, to date, the use of epoxy resin for producing molded products can entail a poor efficiency of molding operations and a low degree of dimensional accuracy.
To eliminate the above-identified problem, the liquid ejection head manufacturing method of this embodiment includes forming a base plate 2 by means of the above-described resin molding method and bonding a plurality of element substrates 3 onto the base plate 2. More specifically, with this embodiment, the timing of opening the mold is ingeniously planned for molding a base plate 2 in order to improve the mold releasability after the molding process, while maintaining the above-listed advantages of epoxy resin. In other words, the mold is opened before the molded product is fully cooled after the molding operation, more specifically, in a state where the epoxy resin in the mold is at a temperature not lower than the glass transition point and hence before the epoxy resin gets into the solid elasticity area. Then, as a result, the molded product can be released from the mold with ease, while the product is being elastically deformed. Thus, the efficiency of the molding operation is improved and a molded product that represents a high degree of dimensional accuracy can be obtained.
Now, the present invention will be described further by way of specific examples and comparative examples, the latter being set forth for the purpose of comparison.
The composition of the molding material 104 used in Examples and Comparative Examples in this specification is represented below.
The molding material (epoxy resin) 104 does not contain any internal mold releasing agents such as wax and/or fatty acid metal salt. Instead, a mold releasing agent for secondary processing (MS-600: trade name, available from Daikin Industries, Ltd.) is blown onto the inner surface of the cavity 101 of the molds 100A and 100B of the metal mold apparatus 100 and wiped so as to eliminate unevenness of the blown agent.
The molding material 104 was heated at 150° C. for 4 hours and further at 180° C. for 1.5 hours for thermosetting. Then, that no reaction heat had been generated and the cross linking reaction had been completed was confirmed by differential scanning calorimetry (DSC). Thereafter, the dynamic viscoelasticity of the molding material 104 was measured by means of a dynamic viscoelasticity measuring instrument (DMS6100: trade name, available from SII Nanotechnology Inc.). As a result, the molding material 104 proved that the storage elastic modulus E′ thereof abruptly falls from about 140° C. while the glass transition point Tg thereof (the temperature at which tang δ is at the peak) is 170° C. and the material gets into the rubber elasticity area at 190° C. and higher.
The molding material 104 was mixed and kneaded in a planetary mixer to bring the material into a clay-like state. Then, the molding material that is in a clay-like state is arranged in a heating chamber as illustrated in
With the above-described molding method, the molds were opened in a state where both of the molds 100A and 100B were at 190° C. in Example 1 and the molds were opened in a state where the mold 100A was at 200° C. and the mold 100B was at 190° C. in Example 2, while the molds were opened in a state where both of the molds 100A and 100B were at 170° C. in Example 3. As a result, the molded product was released in an excellent manner (to represent an excellent mold releasing effect) in each of Examples 1 through 3 and the molded products 104 were free from degradation of dimensional accuracy (Table 1). This was because, when the molding material (epoxy resin) 104 was at a temperature not lower than the glass transition point Tg of the material, the molding material 104 represents a low elastic modulus so that the molding material 104 is easily elastically deformed at the time of being released from the mold 100A and hence the force trying to move the molding material 104 away from the mold 100A was localized and hence acted efficiently. Particularly, the molds were opened in a state where the molding material 104 was in the rubber elasticity area in each of Examples 1 and 2 so that the molding material 104 was easily elastically deformed to further improve the effect of being released from the mold.
As described above, the molds are preferably opened in a state where the molding material 104 is at a temperature not lower than the glass transition point Tg of the material (more preferably at a temperature where the molding material is put into the rubber elasticity area) to realize the advantages of the present invention. Note, however, that it is difficult to measure the temperature of the molding material 104 itself when the molding process is in progress and immediately after the molding process. However, this problem can be eliminated by measuring the temperature of the molds 100A and 100B for the molding operation because the measured temperature of the molds 100A and 100B can safely be regarded to be substantially equal to the temperature of the molding material 104 in the molds. The temperature of the molds 100A and 100B is preferably measured at or near the inner surface of the cavity 101.
To the contrary, no injection start standby time period, or no heating time for plasticizing the molding material 104, was provided prior to the actual operation of injecting the molding material 104 in Comparative Example 1. In other words, the molding material 104 was injected into the cavity 101 before the fluidity of the molding material 104 was improved. Then, the molding material 104 was heated for 75 seconds for thermosetting and the molds 100A and 100B were opened in a state where both the molds 100A and 100B were at 150° C., which is lower than the glass transition point Tg of the molding material 104 (epoxy resin), and the molded product 104 was taken out. Since the molding material 104 was pushed into the cavity 101 in a state where the molding material 104 showed a poor fluidity in Comparative Example 1, the soft mold releasing agent on the surfaces of the molds 100A and 100B was scraped and forced to come off by the filler in the molding material 104. Then, the molding material 104 that was adhering to the surfaces of the molds 100A and 100B from which the mold releasing agent had been lost would not be separated from the surfaces of the molds 100A and 100B and hence the molded product 104 could not be released from the molds.
In Comparative Example 2, an injection start standby time period of 5 seconds was provided prior to the injection of the molding material and the molding material was injected into the cavity and heated for 75 seconds for thermosetting. Subsequently, the molds 100A and 100B were opened in a state where the molding material was at 150° C., which was lower than the glass transition point Tg of the molding material, and the molded product was taken out. In each of Comparative Examples 3 through 5, an injection start standby time period of 10 seconds was provided for injection and the molding material 104 was injected into the cavity 101 and heated for 75 seconds for thermosetting as in Examples 1 through 3. Thereafter, the molds 100A and 100B were opened in a state where both of the molds 100A and 100B were at 150° C. in Comparative Example 3, in a state where both of the molds 100A and 100B were at 160° C. in Comparative Example 4 and in a state where both of the molds 100A and 100B were at 165° C. in Comparative Example 5 and then the molded products 104 were taken out. In each of Comparative Examples 2 through 5, the mold releasing agent on the surfaces of the molds 100A and 100B did not come off but a situation where the molded product 104 was gradually released from the molds 100A and 100B, while being deformed to a certain extent, could not be realized because the elastic modulus of the molding material 104 was high at the time of opening the molds and hence the molded product 104 could hardly be elastically deformed. In other words, because the molded product 104 could hardly be elastically deformed, the part of the molded product having a relatively broad surface area had to be separated from the molds 100A and 100B at a time and hence the molded product 104 could not be smoothly released from the mold 100B when the molded product 104 was pushed by the eject pins 105.
When compared with Comparative Examples 1 through 5, the molding material 104 of Examples 1 through 3 showed a small elastic modulus and hence could be elastically deformed so that the molded product 104 could be gradually separated from the molds 100A and 100B, while being deformed to a certain extent, to realize a smooth mold releasing effect.
The molding time is desirably short from the viewpoint of productivity. However, when the molding time is made too short, the reaction ratio of the molding material 104 itself falls and the molded product 104 can be plastically deformed and broken at the time of opening the molds so that a too short molding time is not desirable from the viewpoint of molding performance. Stated differently, the reaction ratio is preferably not less than 90%, more preferably not less than 93%, at the time of opening the molds. The reaction ratio was about 93% in Examples and Comparative Examples, which were described above. The reaction ratio is expressed by the formula represent below.
Reaction Ratio=(calorific value of material before molding−calorific value of material after molding)/(calorific value of material before molding)×100
In Examples and Comparative Examples, the calorific values were measured by means of a differential scanning calorimeter (DSC822: trade name, available from Mettler Toledo International Inc.).
When the surface area of the molded product 104 that is in contact with the mold 100A differs from the surface area of the product 104 that is in contact with mold 100B, the molded product 104 can adhere to the mold with which the lager surface area of the product is in contact to give rise to a problem of imperfect mold releasing. To prevent such an imperfect mold releasing problem from taking place, preferably the draft angle (draft taper) of the mold having a larger contact area is made large and the draft angle of the mold having a smaller contact area is made small. For example, when the upper mold 100A has a contact area of being in contact with the molded product that is larger than the contact area of the lower mold 100B as schematically illustrated in
The composition of molding material that can be used for the purpose of the present invention is not limited to the above-described one. In other words, various different epoxy resin molding materials can be used for the present invention so long as the material represents a small linear expansion coefficient and a small cure contraction coefficient. Furthermore, thermosetting resin molding materials other than epoxy resin molding materials can also be used for the purpose of the present invention. Thermosetting resin molding materials that can be used for the present invention may contain one or more than one internal mold releasing agents of any types (e.g., wax) that do not give rise to elution if contained to a large content ratio.
The present invention can be applied not only to molding of parts of liquid ejection heads 1 (including base plates 2 and element substrates 3) but also to production of any molded products. The present invention is particularly very effective when it is utilized to form parts that should maximally prevent elution of the material into liquid such as parts of water purification apparatus and water purification systems, food manufacturing apparatus, medical apparatus, etc.
According to the present invention, as described above, molded products of materials representing a small linear expansion coefficient and also a small cure contraction coefficient can be released from the mold with ease after the molding process. Even molded products of thermosetting materials that do not contain any mold releasing agent can be released from the mold with ease when the molds are subjected to a mold releasing treatment.
Thus, according to the present invention, the mold releasing effect can be improved for molded products by specifying the timing of opening the molds after the completion of the molding process so that the operation of opening the molds does not entail any degradation of the dimensional accuracy of the molded product. Therefore, a molded product that represents a high degree of dimensional accuracy can be produced efficiently with ease. Thus, the present invention is very effective particularly for forming members such as base plates of liquid ejection heads that require a high degree of dimensional accuracy and, at the same time, satisfying various requirements including a requirement of a low linear expansion coefficient and a requirement of hardly allowing elution.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2013-263908, filed Dec. 20, 2013, and Japanese Patent Application No. 2014-226868, filed Nov. 7, 2014 which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-263908 | Dec 2013 | JP | national |
| 2014-226868 | Nov 2014 | JP | national |
