DE3051228C2 - Ink jet printing head mfg. method - Google Patents

Abstract

The mfg. process is for an ink-jet type printing head.The latter ejects fine droplets of ink from a jet coupled to a working chamber holding the ink. Part of this jet is deposited on the printing material surface to produce the printed copy desired.In one stage a part is produced having a through bore. This forms the working chamber. In another stage this bore is connected to an aperture of another part that forms an intermediate supply chamber for the ink. In yet another stage one other part is brought close to another so that a slit is formed near the other aperture of the through bore. In the first stage a number of plate-like components can be integrally joined together

Description

The invention relates to a recording head according to the Ober Concept of claim 1.

Such a recording head is equipped with a variety of heat generating resistors and electrodes for power supply the resistors and a protective layer for the resistors and the electrodes equipped.

From the various non-stop recording ver the inks have been driving in recent years beam recording due to various advantages of most vividly evolved. These advantages are for example wise a very low noise or noise level the recording and the possibility of a high speed record and a record ordinary paper without special fixing.  

In the ink jet recording method, a generally referred to as ink recording liquid ejected. Accordingly, to carry out the Ver a recording head is required, which is an off Shock nozzle, the recording liquid in one droplet-like state ejects and the flight of the Droplet causes, as well as has an inlet through which the Recording liquid is introduced. The record head can ent in various constructions ent speaking the basic principles of droplet ejection will be realized.

For example, a recording head is known, where the ink comes from an external ink supply tank into a nozzle-shaped liquid chamber under one Pressure is replenished, no ink ejection causes the nozzle. In this recording head becomes a Voltage applied to the ink in the liquid chamber; an electrode is arranged in front of the nozzle to a electrostatic discharge of the ink from the nozzle to be Act.

Although this recording head has a simple Rationale, disadvantageous in him, however, is that a complicated detailed construction of the entire system as well a sophisticated accurate electrical control for the generation and direction of the droplets needed is. In addition, the production of a high-speed Auf Drawing device difficult: The production of a Multi-head with a high density nozzle assembly, the indispensable for high-speed recording is, is with the above-explained basic principle difficult.

Accordingly, most of the known ones are on drawing heads with unsolved problems in the Konstruk  tion, in the production, while achieving high speed records and / or at the time of the meeting tion of the overall system.

In addition, the various items of Auf drawing head have a consistent quality level. In fact, it is not easy to handle these items to produce a satisfactory yield.

These technical difficulties in the production increase in the case of as a Mehrfachkopfanord constructed recording heads, where each Item is smaller and he has an increased accuracy calls.

A suitably designed ink jet recording Head is for example from DE-OS 26 49 970 known. In this known case, the energy is on the pressure fluid with the help of Kompressi applied onskammern, which each have a membrane and a ceramic oscillator is assigned to short-term To realize pressure increases at the compression chamber. The write head is constructed in sandwich construction and has pairs of oppositely arranged Kom press chambers, between which an approximately equal and not liquid-filled, as well as with Off the compression systems not fluidly connected is arranged equal chamber. If to the ceramics vibrating voltage pulses are applied, deform These and lead to a reduction of the Kom pressionsräume. The resulting pressure waves propagate towards the ejection nozzle to open expel drawing fluid.

It has been shown that it is with such a structure of the recording head becomes difficult, the ejection nozzle high density, especially as the body parts  the known recording head in the welding process be connected to each other.

To improve the quality of the printed image and in the In the course of an increase in the number of nozzles per area is in DE-OS 28 43 064 already an ink jet Aufzeich head, in which the recording liquid ink, namely ink, from an outer ink ver supply tank into a nozzle-shaped liquid chamber redone under pressure that does not yet Ink ejection from the nozzle causes. In front of the nozzle is an electrode arranged with the after applying a Voltage an electrostatic discharge of Aufzeich tion liquid can be effected from the nozzle. With this structure succeeds, the liquid channels and the connection to an ink supply chamber to close rem room to accommodate, using a micro-Schnei ders or -Fräsers grooves in a carrier plate with incorporated a very small pitch who the. By means of a glued lid these Nu Then closed to channels.

To further increase the nozzle density is in the eige NEN older patent application P 30 05 394 a method for producing an ink-jet recording head proposed in which a first plate on which a for energy intended for ink ejection ment in the form of an electrothermal or electrome chanical converter with associated power electrodes is applied, to form a working chamber block is glued to a second plate in one predetermined distance equal to the distance of the energy giewandlerelemente is groove-shaped recesses points, so that the recesses of the second plate in Connection to the first plate an ink channel he enter, in the course of which the energy converter element is brought, wherein the ink channel an ejection opening  and an ink supply port provided with a Ink supply chamber communicates. Also in In this case, therefore, the production of the individual Recording head functional areas by separate Be Working different layers or substrates, the then with the help of evaluable adhesive to egg a complete inkjet recording head together be joined.

In ink jet recording heads of the above be typed design is to ensure that a direct contact one in the area of the elektrothermi rule converter element provided heating or cons stand layer or an electrode layer with the up drawing liquid or ink is avoided. Because such a contact would lead to oxidation the resistance layer or the electrode layer or lead to a decomposition of the ink.

The invention is therefore based on the object, a Ink jet recording head with an electrothermi converter according to the preamble of the claim 1 to create with the despite high nozzle density oxidation problems or a Influence the ink quality even with longer Ein Set the inkjet recording head reliable can be excluded, at the same time the thermal responses of droplet ejection and the recording energy efficiency as high ge to be kept.

This object is with respect to the ink jet on Drawing head by the features of claim 1 solved.  

According to the invention it has been found that by means of the built up from the at least two special layers Protective layer a contact of the electrodes layer or the resistance layer with the ink or a reaction caused thereby in the ink verhin be changed then.

The measures of the invention allow a Tin Ten-beam recording head with extremely high nozzles make dense. This can be a Inkjet recording head with simple and at the same time ensuring a high precision Ver make steps.

The inventive structure of the recording head he allows the production of ink channels extremely smaller Width while ensuring a great manufacturing accuracy. By erfindungsgeinäße design The protective layer can be the protective layer reduce thickness very far, without the shielding function in any way impair. It can the Rated specification for the specific resistance inserted to hold.  

The invention will be described below with reference to embodiment Examples with reference to the drawing closer be wrote. Show it:

Fig. 1A, 1B and 1C in the connection shown in Fig. 1 flow diagrams for a suitable method for producing the recording head.

Fig. 2 to 7 are schematic views of the recording head in different process steps, and

FIGS. 8A and 8B, 9 and 10 are partial schematic views of the recording head for explaining the steps of the method according to the invention.

In the following, an embodiment for the assembly of a multiple head will first be explained with reference to FIG. 1.

In Fig. 1A, A and B denote parts constituting the working chamber of the recording head.

Fig. 2 shows that the item A is obtained from a flat plate 1 , which may be made of, for example, glass, quartz, ceramics, plastic, metal, etc. in the following manner: After washing, the flat plate becomes the first coated on one side with an anchoring layer 2 , which consists essentially of an epoxy resin. Subsequently, it is subjected to a heat treatment at 100 ° C. for 20 minutes, and the anchoring layer 2 is coated with an adhesive layer 3 having a thickness of 0.5 to 10 μm, preferably from 1 to 5 μm. The adhesive layer 3 may, for example, have the following composition:

parts by weight Epicote 1007 (trade name) 100 aromatic amino curing agent 5 Silane coupling agent 5 methyl ethyl ketone 300

After the adhesive layer is half hardened by pre-drying at 100 ° C for 5 minutes, a certain number of elongated grooves 4 are coated on the thus coated surface with a diamond cutting tool, for example Disco 2H / 5 (trade name) of Disco Corporation cut. Subsequently, the flat plate is cut to produce the item A to the predetermined dimensions.

In general, the grooves 4 have a cross section in the range of 10 × 10 microns to 150 × 150 microns and a Tei ment in the range of 30 to 200 microns. As the adhesive, not only the composition given above is possible, but also other adhesives which exhibit adhesive effect during a heat treatment. Such adhesives are, for example, organic compounds such as epoxy resin adhesives, phenolic resin adhesives, urethane resin adhesives, silicone resin adhesives, triazine or BT adhesives, and inorganic compounds, for example, liquid silver salts (see US Patent No. 3,089,799) or low melting glasses. These inorganic compounds are more frequently used in powder form than in the liquid state.

Fig. 3 shows the separately produced another one-piece B. From the cross-section in the line XY of Fig. 3 facing Fig. 4 it can be seen that the item B is obtained in that on one surface of a substrate 5 , the one Thickness of about 0.6 mm and made of alumina, monocrystalline silicon or a metal such as aluminum, iron or the like, a heat-storing layer (sprayed SiO ₂ layer having a thickness of 2 to 3 μm), a heat-generating resistance layer 7 (sprayed Hfβ ₂ layer having a thickness of 50 to 100 nm), an electrode layer 8 (vapor-deposited aluminum layer having a thickness of 70 to 80 nm), a first protective layer 9 (sputtered SiO layer having a thickness of 1 micron) and a second protective layer 10 (a parylene or silicone sputtered layer) is applied one after the other and then the substrate is trimmed to the desired dimensions approx.

In the above-explained procedure, the electrode layer 8 is subjected to a pattern etching step to form individual lead electrodes 11 and a common lead electrode 12 as shown in Fig. 3 and to set the resistance layer 7 in a desired pattern 13 in a certain one Expose number. The resistance pattern 13 preferably has a dimension which is approximately equal to the width of the grooves 4 .

The thus manufactured parts A and B are aligned against each other so that the grooves 4 and the resistor pattern 13 are opposite. The parts A and B are held in this inclined in Fig. 5 position.

Subsequently, the adhesive layer 3 is first half-hardened in a further 10 minutes of heat treatment at about 100 ° C and in a control ge checks that there are no alignment errors, nor the grooves 4 are added. If the result is negative (case no) items A and B are separated and item B is washed for reuse while item A is discarded. If no error occurs (Yes case), the adhesive layer 3 is cured completely by 50 minutes at a temperature of Tempe 100 ° C and two hours at a temperature of 180 ° C lasting heat treatment. Subsequently, the control step is repeated again to confirm that none of the grooves 4 is too close. If no errors occur, the complete working chamber - block C is forwarded to further production steps.

In the described method, in which several Parts for making a particular construction with a hardenable resin are glued together, is the Use of the above-described adhesive method Particularly advantageous, the one step in which a curable resin layer on at least one of the parts applied and in an intermediate state of curing process, a step in which a Ril lenmuster on a surface of the resin layer provided component, and a step in which several components by curing the Glued together resin layer.  

In this way it becomes possible, the components without damage to the very small groove patterns thereby to assemble one on the component on which the Grooved patterns are to be formed, applied hardenable resin layer is semi-hardened, then ßend the groove patterns on the component with the half hardened resin layer are formed and last the Resin layer after the component with the other construction has been merged, completely out is hardened.

Especially in the production of a recording head, which droplets a recording liquid shaped mold ejected from a nozzle allows the method explained above, the preparation of a Variety of nozzles with the same diameter and the same Shape, which are arranged with a high density.

To further illustrate this bonding method is to the content of the published patent application DE 30 11 919 directed.  

In the following, the first protective layer 9 shown in Fig. 4 and the second protective layer 10 will be explained. These layers are designed to prevent a direct contact of the resistive layer 7 or the electrode layer 8 with the recording liquid or the ink, which would lead to an oxidation of the resistive layer or the electrode layer or to a decomposition of the ink. In the recording head described, the thickness of the first protective layer 9 and the second protective layer 10 has a marked influence on the thermal response of the droplet ejection and the recording energy efficiency, since the thermal energy generated by the resistive layer 7 passes through the two layers. In these embodiments, the thinner the first protection layer 9 and the second protection layer 10 are, the better the thermal response and the lower the required write energy, since the heat conduction is improved. However, a protective layer prepared by vapor deposition or spraying, which is normally used in the production of thermal recording heads, tends to cause uncovered portions on the land between the electrode layer 8 and the resist layer 7 or holes in the layer itself when the thickness the layer is reduced. For these reasons, a certain thickness has heretofore been considered necessary so as not to expose the electrode layer 8 or the resistive layer 7 to harmful influences, even if the thermal conductivity conditions are thereby deteriorated.

According to the invention, however, it has been found that even with an extremely thin protective layer, contact of the electrode layer 8 or resistive layer 7 with the ink or a reaction in the ink caused thereby can be prevented.

After the desired pattern in the electrode layer 8 and the resistive layer 7 have been formed, it is on a first protective layer 9 with a thickness of 0.01 to 1 micron by electron beam evaporation or spraying applied, optionally of silica, magnesium oxide, alumina, Tantalum oxide or zirconium oxide, a carbide such as beryllium carbide, a boride such as beryllium boride, a sulfide such as lanthanum sulfide, praseodymium sulfide, neodymium sulfide or ytterbium sulfide, amorphous silicon or selenium.

The first protective layer 9 may also be made by spray coating, spin coating, or dipping coating of a thickness of 0.01 to 1 μm from a heat-resistant resin selected from silicone resin, fluorinated resins, polyimide resin (for example, aromatic polyamides and addition-polymerized polyimides ), Epoxy resins, p-vinyl phenolic resins and BT resins (addition polymerization resins of triazine resins and bismaleimide).

The first protective layer 9 is not necessarily a single layer, it may also be composed of several layers. The presence of holes in the protective layers 9 has not been the major problem with the thermal recording related thermal recording heads. In the case of the ink jet recording, however, in which the protective layer comes into direct contact with the liquid, the prevention of holes in the first protective layer 9 becomes more important with respect to the life of the recording apparatus.

In the illustrated method, voids, such as the holes present in the first protective layer 9 , are almost completely filled by a second protective layer (or filling layer) 10 applied over the first protective layer 9 . Thus, the second protective layer acts as a filling layer for the first protective layer 9 . The resin used for producing the second protective layer 10 preferably has the following characteristics: (1) sufficient film formation, (2) bubble-free structure with little hole formation, (3) no swelling or dissolution in the ink used, (4) sufficient adhesion to the first protective layer and (5) high thermal resistance. The resins usable in the present invention are silicone resins, fluorinated resins, aromatic polyamides, addition polymerization type polyimides, polybenzimidazole, epoxy resins, p-vinylphenol resins, triazine resins or BT resins (addition polymerization resins of triazine resin and bismaleimide).

In the use of the above-mentioned heat-resistant resins, a protective layer can also be prepared by dissolving such a resin in a solvent and applying the solution thus obtained by spin coating, spray coating or dip coating on the first protective layer 9 , followed by drying.

The second protective layer 10 should be as thin as possible, as it directly affects the thermal response of the droplet ejection or energy efficiency. According to the described method, after drying, the thickness is in the range of 0.01 to 10 μm, preferably 0.01 to 5 μm, and more preferably 0.1 to 3 μm.

When a recording head is used in conjunction with an electroconductive ink using water as a solvent, the first protective layer 9 and / or the second protective layer 10 should preferably have a thickness of about 0.1 to 5 μm for a specific resist of 5 × 10 ⁵ Ωcm or larger is achieved to prevent short-circuiting of the ink.

As stated above, the protective layer should preferably made thinner to the thermal Responsibility of droplet ejection or energy increase efficiency. Taking this into account Fact and the required isolation should be the Thickness preferably in the range of 0.2 to 3 microns.

Such an iso Lier protective layer is Herge by known methods provides. The materials for such layers are chosen so that they  a high cons stood in film formation by means of sputtering, CVD method, Vapor deposition, coating after reactions in the gas phase or coating from the liquid, even if they have a low resistance as a normal solid to have. The thickness of these films is generally in the Range of 0.1 to 5 microns, preferably from 0.2 to 3 microns.  

The effect of the protective layers explained above is explained below by experimental examples.

Experimental Examples 1 to 9

A substrate with heat-generating elements, as shown in an enlarged perspective view in Fig. 8A, was prepared in the following manner:
On an alumina substrate 212, the number of a heat-storing ZrB were after a Heat reserving SiO ₂ layer 213 (several microns), ₂ -Widerstandsschicht 214 (80 nm) and an aluminum electrode layer 215 (500 nm) is applied. By selective etching heating resistors 214 'were made with a width of 60 microns and a length of 75 microns. By similar etching control electrodes 215 a and a common electrode 215 b were formed. As shown in FIG. 8B, a first SiO ₂ protective layer 216 (0.01 μm) was subsequently applied to the electrode layer 215 . On the protective layer 216 , a heat-resistant resin from the liquid state was applied as shown in Table 1 to the second protective layer, dried under vacuum, and subjected to heat treatment under the conditions also shown in Table 1 to prepare the substrate for Experimental Examples 1 to 9 manufacture.

Separately, a groove plate 220 shown in Fig. 9 was prepared by cutting a plurality of grooves 218 having a width of 70 μm and a depth of 60 μm and another groove 219 forming the common ink chamber with a micro-cutter.

The above-explained substrate with the heat generating elements and the groove plate were bonded together after the heat generating elements and the grooves were aligned. By attaching an ink supply piping 221 for supplying ink from an ink tank, not shown, the recording head block 222 shown in Fig. 10 was completed. Further, the block 222 was connected to a printed circuit board, which provided the electrical connection to the control electrodes and the common electrode forth.

The ink droplet ejection was with write pulses with a pulse width of 10 μsec, and a pulse frequency of 10 KHz.

The composition of the ink was:

percentages by weight water 70 diethylene glycol 29 Black dye 1

In the under the above conditions durchge led droplet ejection test showed the write head, as summarized in Table 1, is excellent Life together with a sufficient writing quality.

In these examples, the life was evaluated by the number of electrical pulses applied to the write head one by one as follows:

A: ≧ 10 ⁹
B: 10 ⁸ -10 ⁹
C: ≦ 10 ⁵ .

Table 1

Experimental Examples 10 to 23

The SiO ₂ protective layer 216 in the above Examples 1 to 9 can be replaced by the materials listed in Table 2 which are covered by the heat-resistant cured resins just listed in Table 2, in a manner similar to the experimental examples To obtain 1 to 9 prepared substrates.

The obtained recording heads were set to a tested the same way, the results are the same in Table 2

Table 2

The results of the above experimental Examples clearly show that the presence of the Protective layers the life of the recording head significantly increased.

The attachment of an intermediate chamber block D for the ink supply, as shown in Fig. 6, it follows then to the assembly of the working chamber block C shown in Fig. 5 .

In this assembly, crosspieces E and E ', respectively, are coated with an adhesive of the composition below, then aligned with the working chamber block C, as shown in Fig. 6, and heat treated at about 60 ° C for one minute to form the adhesive into a semi-hardened state:
Adhesive: Epikote # 828 (Shell Chemical) 100 parts by weight
Epomate Epomate B-002 (Ajinomoto Co.) 40 parts by weight.

While the adhesive is in this state, a control step is performed to check that there are neither assembly errors, nor that adhesive mistakenly flowed into other parts. Is this Result negative (case no) the parts E and E ' again separated from the block C and for a Wiederver cleaned. If there is no defect (case yes) is heat treated at 60 ° C for about 30 minutes performed to cure the adhesive.

Subsequently, the rear end part F with adhesive coated, oriented in a similar way and heat treatment for one minute at 60 ° C pulled to half cure the adhesive. In similar A check step is performed, and at negative result (case no) the part as explained above cleaned, while if no error occurs (case yes) a 30-minute heat treatment at 60 ° performed  is used to cure the adhesive.

Next, a cover part G with adhesive coated, similarly oriented and for heat treated for one minute at 60 ° C, to semi-cure the adhesive. Again, a control Step performed. Is the result negative (case no) is explained as explained above, the part while, if no error occurs (case yes) a 30-minute Heat treatment is carried out at 60 ° C and then another 10 minutes heat treatment at about 100 ° C, to complete the curing of the adhesive.

Subsequently, the tube parts H and H 'in the predetermined locations of the block thus produced set, the gap around the tube parts is covered with glue refilled. Hardening progresses slowly in this case continued. Subsequently, a control step is carried out, to check that no adhesive in the parts H, H ' or has penetrated into the intermediate chamber. Is this Result negative (case no) the parts are ge again disconnects and for reuse, as explained above, cleaned. In the case that no defect occurs (case yes), is a 30-minute heat treatment at 60 ° C and at followed by a 10 minute heat treatment at 100 ° C is performed to complete the curing.

In this way, the connection of the intermediate chamber block D to the rear portion of the working chamber blocks C is completed. Subsequently, the front surface 15 of the working chamber block C, on which the ejection nozzles are located, smoothed with abrasive sand (# 1000 or higher). After grinding, the assembly is cleaned to remove abrasive sand and other debris that has entered the grooves 4 through nozzles 14 during grinding. It is then checked in a control step whether the front surface 15 is completely flat and the grooves 4 are cleaned, and if the grinding is not yet complete, the grinding and cleaning steps are repeated. The control step is repeated again, and in the case of a negative result (case no) the previous step is repeated. If, on the other hand, there is no defect, (case yes), the arrangement consisting of blocks C and D is dried. In the following manufacturing step, a slit block I with nozzles on the front surface 15 is introduced .

Fig. 7 shows that the slot block I has a bottom part J, side parts K and K 'and a front part L.

These parts are included in certain sections. Adhesive coated, then appropriately aligned and subjected to a heat treatment at 60 ° C for one minute to convert the adhesive into a semi-cured state. After a control step, in which the correct assembly is checked, the parts J, K, K 'and L are separated again in case of negative result (case no) and cleaned for reuse. On the other hand, if there is no error (case yes), a 30-minute heat treatment at about 60 ° C and another 10-minute heat treatment at 100 ° C is performed to complete the curing process of the adhesive. Subsequently, the blocks I and C are respectively coated with adhesive, and then aligned as shown by the arrows in Fig. 7, aligned. They are then allowed to stand at room temperature for 30 minutes to achieve a semi-cured state of the adhesive. In a subsequent control step it is checked that no adhesive has flowed into the nozzles 14 or into the slots 16 of the block I. If the result is negative (case no), the blocks are again separated and cleaned for reuse as explained above. On the other hand, if there is no error, (case yes), so a 30-minute heat treatment at 60 ° C and another 10-minute heat treatment at 100 ° C is performed to complete the curing process of the adhesive.

Subsequently, a tube N in a certain Place inserted, the gap around them as above at the part H filled with adhesive and the arrangement allowed to stand at room temperature for about 30 minutes. In one following check step it is checked that no Adhesive is leaked, and, if the result is negative is (case no) the parts separated again and again use cleaned. If no error occurs (case yes) is a 30 minute heat treatment at 60 ° C and for a further 10-minute heat treatment at 100 ° C Completion of the curing process of the adhesive carried out. In this way, a complete up Drawing head made.

The thus completed recording head is opened an aluminum plate glued on, and the line electrodes connected to a flexible printed circuit.

An example of an ink jet recording with the recording head thus completed and shown in Fig. 7 will be explained below. Although Fig. 7 shows the various blocks of the recording head in an exploded view, it goes without saying that these blocks are firmly connected to each other in the use of the recording head.

First, the recording ink is introduced into each working chamber 4 through the parts H, H '. When a pulsed voltage is applied, the heating resistor, not shown, generates a thermal pulse which causes a sudden change of state of the ink.

This state change exerts a force on the ink due to the pressure wave. As a result, ink is ejected in a droplet-shaped state from the working chamber 4 with the associated nozzle 14 . This droplet is knocked down on the recording medium, not shown, and accomplishes the recording. The ink discharged from the nozzle 14 tends to flow on the walls around the nozzle 14 . This results in the formation of an ink film near the nozzle 14 , which may hinder droplet ejection. In the present embodiment, this phenomenon is prevented by providing a slit 16 in the vicinity of the nozzle 14 . This slot serves to eliminate the ink film due to its suction effect. In this way, the size and speed of the ejected droplets remain extremely stable.

The above comments dealt with a thermi energy using inkjet recording system. Of course, the described method is just as applicable in other ink jet recording systems in which the thermally acting part, for example by a mechanical vibrator such as a piezoelectric Vibration layer is replaced. Next is the recording Do not go for the designs shown in the drawing limited. An example of the ink is a two percent Dispersion of a black dye in a solution agent which is essentially composed of ethyl alcohol is set.

Claims (1)

A recording head for an ink jet recording apparatus having a plurality of heat generating resistors ( 7 ) and electrodes ( 11 , 12 ) for supplying the resistors ( 7 ), a protective layer ( 9 , 10 ) for the resistors ( 7 ) and the electrodes ( 11 , 12 ) therethrough characterized in that

• - The protective layer ( 9 , 10 ) consists of at least two layers, wherein
• the first layer optionally of SiO ₂ , Ta ₂ O ₅ , magnesia, alumina, zirconia, carbides, borides, sulfides, amorphous silicon or selenium or heat resistant resins, the heat resistant resins being silicone resin, fluorinated resin, polyamide resin, polyimide resin, Epoxy resin, BT resin (addition polymerization resin of triazine resin and bismaleimide) and p-vinylphenol resin group, and
• the second layer consists of silicone resins, fluorinated resins, aromatic polyamides, addition polymerization type polyimides, polybenzimidazole, epoxy resins, p-vinylphenol resins, triazine resins or BT resins (addition polymerization resins of triazine resins and bismaleimide).