JP7611425B2 - Thermal printhead substrate with composite lead-free protective layer and method of manufacture thereof - Google Patents

Description

The embodiments of the present application relate to the technical field of thermal printhead manufacturing, for example, a composite lead-free protective layer thermal printhead substrate having lead-free, wear-resistant, and corrosion-resistant properties, and a method for manufacturing the same.

As is well known, a thermal printhead comprises a substrate made of an insulating heat-resistant material, on which a base glaze layer for heat storage is provided, lead electrodes are provided on the surface of the base glaze layer and the substrate, a heating resistor layer is provided on the surface of the electrodes, and the heating resistor layer is covered with a protective layer.

The manufacturing process of the protective layer of the related thermal printhead is to select a protective layer slurry prepared by a lead-containing silicate material, and apply it uniformly to the surface of the heating resistor layer and the electrode layer by using a thick film process such as printing or spray coating, and then sinter it by using a belt-type sintering furnace or a box-type sintering furnace to form a dense film layer after sintering. The wear-resistant protective layer of the related thermal printhead often uses a sintering flux containing PbO, which can reduce the glass softening point and realize a glass glaze that is fired at a low temperature. The glass glaze with lead oxide as the sintering flux has a wide firing temperature range and excellent sintering film quality, has excellent comprehensive performance, and is widely used. However, lead is an element that is not friendly to humans and the environment, and is not good for the environment. As people's awareness of environmental protection gradually increases, the poisoning of humans and pollution of the environment caused by lead is increasingly being paid attention to from all quarters, and lead-containing substances are being eliminated from electronic products.

In order to reduce the sintering temperature, metal electrode slurries for thick-film thermal printheads generally contain some flux, and the firing temperature range of thick-film protective layer slurries commonly used in related thermal printheads is about 600-850°C. Ordinary lead-free silicate protective layers often have poor PbO melting promotion effect, and their firing temperatures are generally above 850°C, making the related thick-film conductor slurries incompatible with the related lead-free glass processes, which has created a great need for the development of low-melting point lead-free silicate glass.

Related lead-free glass systems are generally widely studied and popular because phosphate-based low-melting lead-free glass is complex and its linear expansion coefficient is inconsistent with its chemical stability, vanadate glass has a layered structure and is prone to absorbing moisture and forming bubbles, and boron oxide in low-melting borosilicate-based lead-free glass increases the thermal stability and chemical stability of glass, reduces the high-temperature viscosity during sintering, has excellent high-temperature fluidity, and can form a dense film layer.

The glass of the related lead-free protective layer is generally prepared by using borosilicate glass material, and uses boron oxide and silicon oxide as the glass skeleton, and has excellent chemical stability, but borosilicate glass often uses alkali metal oxides such as _Li2O , _Na2O , and _K2O as flux, which has high high-temperature viscosity, so that the flowability of the glass after melting is poor, and the film surface after firing is rough, and furthermore, its hardness is insufficient and its wear resistance is weak, so that it cannot cope with the wear of thermal paper. In order to increase the physical hardness of lead-free silicate glass, aluminum oxide or other high-hardness material filler is often added into the borosilicate matrix glass, but the aluminum oxide or other high-hardness material filler does not enter the glass mesh, so that the internal mesh structure of the silicate protective layer becomes coarse, its chemical stability is reduced, and its acid-alkali and water-corrosion resistance is poor, which has a negative effect on the requirement of the corrosion resistance of the thermal printhead protective layer being difficult to meet. In application No. 201910933628.X, the content of _{Al2O3 filler} is reduced and the content of _SiO2 is increased, that is, the ratio of the composition of the glass skeleton _SiO2 to the content of the _{filler Al2O3} is increased, thereby increasing its density and improving its insulation and corrosion resistance. However, when applied to the _{field of thermal printhead protective layers, the proportion of the high hardness filler Al2O3 inside is often lower than the glass skeleton SiO2 and B2O3 , etc. , resulting} in insufficient wear resistance, and there is a great need for lead-free protective layer materials and structures that solve wear resistance and corrosion resistance.

The following is a brief overview of the subject matter discussed in detail in this paper. This overview is not intended to limit the scope of protection of the patent claims.

The embodiments of the present application present a thermal printhead substrate having a composite lead-free protective layer that can effectively increase the corrosion resistance and wear resistance of the insulating substrate and ensure the service life of the thermal printhead, and a method for manufacturing the same.

The embodiment of the present application is achieved by the following measures:

an insulating substrate is provided on its surface, on which a heat storage and heat retention base glaze layer, an electrode layer made of a metal material, a heating resistor layer made of a semiconductor material, and a corrosion-resistant and abrasion-resistant protective layer are sequentially provided from bottom to top, said protective layer comprises at least two sub-protective layers, of which the sub-protective layer closest to the insulating substrate is a first protective layer, and a second protective layer is combined with the outside of the first protective layer, the thermal expansion coefficients of the first protective layer and the second protective layer are 50×10 ^-7 /°C to 70×10 ^-7 /°C, and the expansion coefficient of the second protective layer is equal to or less than that of the first protective layer,
The first protective layer has a Webster hardness of 600 to 900 HV, and the glass glaze composition of the first protective layer includes, calculated by mass percentage, 5 to 15% B ₂ O ₃ , 25 to 50% Al ₂ O _{3 ,} 5 to 30% SiO ₂ , and 10 to 30% glass flux, and the glass flux is BaO, ZnO, and CaO.

The glass glaze composition of the first protective layer described in the examples of this application has a B ₂ O ₃ content of 8-13%, Al ₂ O ₃ content of 40-45%, and SiO ₂ content range of 21-30%, calculated as a total mass percentage of the composition.

In the glass glaze composition for forming the first protective layer in the embodiment of the present application, the glass flux has a BaO content range of 3-8%, a ZnO content range of 2-6%, and a CaO content range of 5-20%, calculated as a total mass percentage of the composition.

In the embodiments of the present application, in order to increase the hardness and wear resistance of the glass film layer, a certain amount of Al ₂ O ₃ is often added as an internal filler, and the Al ₂ O ₃ is spherical or flake-shaped Al ₂ O ₃ with a particle size of about 0.1-1 μm. If the content of Al ₂ O ₃ is too high, the surface roughness of the film layer is high and the bonding strength of the film layer is poor; if the content of Al ₂ O ₃ is too low, the hardness is insufficient and the wear resistance is weak.

The glass glaze composition of the second protective layer described in the examples of the present application contains, calculated by mass percentage, the following components: B ₂ O ₃ content 10-30%, Al ₂ O ₃ content 20-50%, SiO ₂ content range 30-50%, and glass glaze flux content 1-5%, and the glass glaze flux is Na ₂ O and K ₂ O.

Furthermore, the glass glaze composition of the second protective layer described in the examples of the present application has a boron oxide B ₂ O ₃ content of 10-30%, an aluminum oxide Al ₂ O ₃ content of 25-40%, a silicon dioxide SiO ₂ content range of 40-45%, a Na ₂ O content of 2.5-5% and a K ₂ O content of 0-5% in the glass glaze flux, calculated in terms of the total mass percentage of the composition.

In the embodiment of the present application, a third protective layer is further provided, which is an ultra-hard protective layer formed of carbide, nitride or silicide and has a physical characteristic of Vickers hardness ≧1200 Hv, and is compounded on the outside of the second protective layer.

The first and third protective layers described in the examples of this application cover the active area of the electrode layer locally or entirely.

The embodiment of the present application further provides a method for manufacturing a thermal printhead substrate having the above-mentioned composite lead-free protective layer, in which the first protective layer in the composite protective layer is subjected to a surface flattening treatment after sintering is completed, and the surface roughness after the treatment is ≦0.2 μm, and the surface flattening treatment is performed by using a polishing sand belt made of aluminum oxide or silicon carbide material with a mesh number of 500 to 3000 and a particle size of <50 μm, and the surface of the product after the polishing treatment is washed and dried to complete the preparation of the first protective layer, and then the glass glaze composition slurry of the second protective layer is printed and sintered on the outside of the first protective layer to form the second protective layer.

The embodiment of the present application further includes employing magnetron sputtering or other processes to prepare high hardness carbides or nitrides in the effective area of the third protective layer outside the second protective layer to form the third protective layer.

The method for manufacturing a thermal printhead substrate having a composite lead-free protective layer described in the embodiments of the present application specifically includes:
Step 1: preparing a heat storage underglaze layer, a metal electrode layer, and a heating resistor layer on the surface of an insulating substrate in this order, and then printing a first protective layer slurry on the heating resistor area, drying, and then sintering to form a first protective layer;
Step 2: using a surface smoothing process, i.e. using an aluminum oxide or silicon carbide polishing sand belt with a mesh number of 3000 and a particle size of about 5 μm to polish the product back and forth; then, the product after the polishing process is subjected to a surface cleaning process, and anhydrous ethanol is used as the cleaning medium to perform ultrasonic cleaning; and the product after the cleaning is subjected to a drying process at 80 to 120 ° C.;
The method includes step 3 of printing a second protective layer on the processed substrate, drying and sintering the second protective layer, printing the second protective layer slurry on the electrode-coverable area, and forming a corrosion-resistant protective layer as the second protective layer.

Compared to the related art, the present application has a first lead-free protective layer prepared by using abrasion-resistant silicate glass with high Webster hardness, a second lead-free protective layer prepared by using lead-free silicate glass with excellent water resistance and moisture corrosion resistance, and a third protective layer that is an ultra-high hardness protective layer, so that the present application can effectively deal with corrosion damage caused by a corrosive or highly humid environment, and the three protective layers with different functions respectively provide abrasion protection, corrosion resistance, and scratch resistance, thereby improving the reliability of the product.

Other aspects can be understood after reading and understanding the drawings and detailed description.

The drawings are intended to provide further understanding of the technical solutions of the present paper, constitute a part of the specification, and are used to interpret the technical solutions of the present paper together with the examples of the present application, and are not intended to limit the technical solutions of the present paper.

FIG. 2 is a structural cross-sectional view of one embodiment of the present application. FIG. 2 is a structural cross-sectional view of another embodiment of the present application. FIG. 11 is a cross-sectional view of a third structure according to an embodiment of the present application. 1 is a comparison of the preservation performance of corrosion resistance of different lead-free protective layers in Example 1. 1 is a comparison of the wear resistance of different lead-free protective layers in Example 3. FIG. 11 is a comparison of protective layer wear at equal distances for different protective layers in Example 3.

1: Aluminum oxide ceramic substrate, 2: Bottom heat-insulating glaze layer, 3: Metal electrode layer, 4: Heating resistor layer, 5A: First protective layer, 5B: Second protective layer, 5C: Third protective layer.

The present application will be further described below with reference to the drawings and examples.

As shown in FIG. 1 and FIG. 2, the present application provides a thermal printhead substrate having a composite lead-free protective layer provided with an insulating substrate, the surface of the insulating substrate is provided with a heat storage and heat retention underglaze layer, an electrode layer made of a metal material, a heating resistor layer made of a semiconductor material, and a corrosion-resistant and wear-resistant protective layer in this order from bottom to top, the protective layer has at least two sub-protective layers, the sub-protective layer close to the insulating substrate is a first protective layer, and a second protective layer is combined with the outer side of the first protective layer, the thermal expansion coefficients of the first protective layer and the second protective layer are 50×10 ⁻⁷ /°C to 70×10 ⁻⁷ /°C, and the thermal expansion coefficient of the second protective layer is equal to or lower than that of the first protective layer,
The reason for the above setting is that thermal printheads usually use an aluminum oxide ceramic substrate as the base insulating substrate, which has a thermal expansion coefficient of 68×10 ⁻⁷ /°C to 78×10 ⁻⁷ /°C, and in order to adapt to the thermal expansion coefficient of the bottom insulating substrate and reduce stress caused by thermal shock resulting from repeated heating and cooling, its thermal expansion coefficient is slightly lower than that of the substrate, at 50×10 ⁻⁷ /°C to 70×10 ⁻⁷ /°C.

Related lead-free borosilicate glasses are often polarized because they have difficulty combining excellent chemical stability, such as acid-alkali and water-corrosion resistance, with excellent abrasion resistance, while silicate glasses used as thermal printhead protective layers often deal with high humidity, ionized environments, and the abrasion of large particulate matter on thermal paper.
In the present application, a certain amount of boron oxide in borosilicate glass is used to form a stable and dense glass network, thereby improving its chemical stability. However, this often results in low physical hardness and poor wear resistance. The present application utilizes this strong chemical stability to form a second protective layer with corrosion resistance, in which CaO, BaO, ZnO and aluminum oxide fillers are added to the borosilicate glass to fully utilize the ceramic glass phase with CaO-B ₂ O ₃ -SiO ₂ as the main crystal phase (abbreviated as CBS ceramic glass phase) and the ceramic glass phase with BaO-B ₂ O ₃ -SiO ₂ as the main crystal phase, and fine crystal particles are precipitated on the surface to increase the strength and physical hardness, thereby improving its wear resistance. However, the addition of Al ₂ O ₃ increases the physical hardness and wear resistance of the second protective layer. ³⁺ has a larger nuclear charge number and preferentially bonds with free oxygen, which results in fewer boron-oxygen tetrahedra and more boron-oxygen triangles, making the glass network structure coarse and causing a decrease in its chemical stability; and the addition _{of Al2O3} increases its high-temperature viscosity and reduces its fluidity, making it difficult to form a dense, highly smooth film layer. The present application utilizes the high physical hardness and strength of the film layer to provide the first protective layer with wear resistance.

The Webster hardness of the first protective layer described in the present application is 600-900HV, and the glass glaze composition of the first protective layer, calculated by mass percentage, includes B ₂ O ₃ 5-15%, Al ₂ O ₃ 25-50%, SiO ₂ content range 5-30%, glass flux BaO, ZnO, CaO content 10-30%, and the Al ₂ O ₃ adopts spherical or flake aluminum oxide Al ₂ O ₃ as wear-resistant filler in the first protective layer, with a particle size of about 0.1-1 μm. In order to increase the hardness and wear resistance of the glass film layer, aluminum oxide is often added as an internal filler, but if the content of aluminum oxide is too high, the surface roughness of the film layer is high and the bonding force of the film layer is poor, and if the content of aluminum oxide is too low, the hardness and wear resistance are insufficient.

As shown in Table 1 below, a certain amount of aluminum oxide is added as an internal filler to increase the hardness and wear resistance of the glass film layer. If the aluminum oxide content is too high, the film layer has high surface roughness and poor bonding strength, and if the aluminum oxide content is too low, the hardness and wear resistance are insufficient. If the aluminum oxide content is in the range of 25-50%, it has a relatively low surface roughness, usually <0.4 μm, and a high Vickers hardness, usually >600 Hv.

As shown in Table 2 below, CaO and BaO are doped to form a CaO-B ₂ O ₃ -SiO ₂ ceramic glass phase (abbreviated as CBS glass) and a BaO-B ₂ O ₃ -SiO ₂ ceramic glass phase (abbreviated as BBS glass), and within the addition range of 1 to 30%, it has good two-phase eutectic and can precipitate fine crystal grains of CaSiO ₃ and BaSiO ₃ , thereby enhancing the strength of the film layer.

Table 1 Comparison of hardness, surface roughness, and wear volume of different compositions

Table 2 Comparison of hardness, surface roughness, and wear amount for different CaO contents in the first protective layer of the present invention

The glass glaze composition of the second protective layer contains, in mass percentage, 10-30% boron oxide B ₂ O ₃ , 20-50% aluminum oxide Al ₂ O ₃ , 30-50% silicon dioxide SiO ₂ , and 1-5% glass glaze flux, and the glass glaze flux is Na ₂ O and K ₂ O;
As shown in Table 3 below, Na ₂ O and K ₂ O, as fluxes, provide liberated oxygen to convert boron oxygen triangles into boron oxygen tetrahedra, thereby converting the boron structure from layered to shelf-like, creating conditions for the formation of a dense and uniform glass framework. When the content of boron oxide is 10-30%, the protective film layer has excellent chemical stability, and is excellent in acid-alkali resistance and water corrosion resistance. When the content of boron oxide is too much or too little, excessive boron oxygen triangles are formed therein, destroying the glass network architecture and reducing its chemical stability.

Table 3 Comparison of weight loss due to acid-alkali and water-corrosion resistance of different compositions

In the present application, a third protective layer is further provided, and the third protective layer is combined with the outside of the second protective layer. The third protective layer is an ultra-high hardness protective layer formed of carbide, nitride or silicide, and has a physical characteristic of Vickers hardness ≧1200 Hv. The first protective layer and the third protective layer may cover the upper part of the heating resistor, and may also cover the effective area of the electrode layer locally or entirely.

The present application further presents a method for manufacturing a thermal printhead substrate having the above-mentioned composite lead-free protective layer, characterized in that the first protective layer in the composite protective layer is subjected to a surface planarization treatment after sintering is completed, and the surface roughness after the smoothing treatment is ≦0.2 μm, and the surface planarization treatment is performed by using a polishing sand belt made of aluminum oxide material with a mesh number of 500 to 3000 and a particle size of <50 μm, and the product after the polishing treatment is subjected to a surface cleaning treatment, and ultrasonic cleaning is performed using anhydrous ethanol or pure water as a cleaning medium, and the cleaned product is subjected to a drying treatment, thereby completing a substrate after the first protective layer has been smoothed, and then printing and sintering a glass glaze composition slurry for the second protective layer to form the second protective layer.

The method for manufacturing a thermal printhead substrate having a composite lead-free protective layer described in the present application specifically includes the steps of:
Step 1: preparing a heat storage underglaze layer, a metal electrode layer, and a heating resistor layer on the surface of an insulating substrate in this order, and then printing a first protective layer slurry on the heating resistor area, drying, and then sintering to form a first protective layer;
Step 2: using a surface smoothing process, i.e. using an aluminum oxide polishing sand belt with a mesh number of 3000 and a particle size of about 5 μm to polish the product back and forth; then cleaning the surface of the product after polishing; using anhydrous ethanol as the cleaning medium to perform ultrasonic cleaning; and drying the product after cleaning at 80-120°C;
The method includes step 3 of printing a second protective layer on the processed substrate, drying and sintering the second protective layer, printing the second protective layer slurry on the electrode-coverable area, and forming a corrosion-resistant protective layer as the second protective layer.

The present application further includes step 4 of preparing a high hardness carbide or nitride in the effective area of the third protective layer outside the second protective layer by employing magnetron sputtering or other processes to form the third protective layer.

Compared to the related art, the present application has a first lead-free protective layer prepared by using abrasion-resistant silicate glass with high Vickers hardness, a second lead-free protective layer prepared by using lead-free silicate glass with excellent water resistance and moisture corrosion resistance, and a third protective layer that is an ultra-high hardness protective layer, so that the present application can effectively deal with corrosion damage caused by a corrosive or highly humid environment, and the three protective layers with different functions respectively provide abrasion resistance protection, corrosion resistance protection, and scratch resistance protection, thereby improving the reliability of the product.

Example 1
This example provides a thermal printhead, which comprises a substrate 1, a base glaze layer 2, an electrode layer 3, a heating resistor layer 4, and a protective layer 5. The substrate 1 is heat-resistant and insulating, and is generally an aluminum oxide ceramic substrate. The base glaze layer 2 mainly serves the functions of heat storage and heat retention, isolating the heating resistor 4, which is a resistor, from the substrate 1 and providing a smooth surface. The surface of the heating resistor layer is coated with a wear-resistant protective layer 5, which is a composite protective layer made of lead-free silicate glass with a different function. The structures of the above components and the interconnection relationships between them are the same as those in the related art, and will not be described again here.

As shown in FIG. 1, a base glaze slurry containing one or more components such as aluminum oxide, silicon oxide, magnesium oxide, etc. is printed on the surface of an insulating substrate 1 by using screen printing or other thick-film processes, and then sintered at a high temperature of 1100-1200°C to form a heat storage base glaze layer 2 for a heating resistor. On the surface of the base glaze layer 2, a screen printer is used to print a metal slurry on the surface of the heat storage base glaze layer, which is then fired in a belt-type sintering furnace to metallize the surface of the substrate, and photoengraving technology is used to pattern the metal electrodes.

Screen printing is used to print the heating resistor slurry on the effective area, and after sintering, a heating resistor layer 4 is formed; thick-film process is used to print the lead-free glass glaze composition for preparing the first protective layer on the heating resistor area; after drying, the electrode area that needs to be sintered to the heating resistor forms a wear-resistant first protective layer;
The lead-free glass glaze composition of the first protective layer contains, in mass fraction, 13% _B2O3 , 21% _SiO2 , 50% _Al2O3 , 6% BaO, 4% CaO, and 6 _% ZnO. Among them, the _{spherical Al2O3} added as a filler has a particle diameter D50 of 0.5 _μm .
The prepared lead-free first protective layer has a high Vickers hardness of about 650Hv. As shown in FIG. 4, the first lead-free protective layer is treated by a surface smoothing process after sintering is completed, that is, the polishing sandpaper belt made of aluminum oxide material with 800 mesh number and particle size of about 30 μm is used to polish and polish the polished product, and the surface is washed and cleaned with pure water. The washed product is dried at 120° C., and the second lead-free protective layer is printed on the processed substrate, followed by the process of drying and sintering.
Wherein, the first protective layer after surface planarization has high surface smoothness, its surface roughness is about 0.15μm; the second lead-free protective layer slurry is printed on the electrode-coverable area to form the second protective layer, which is a corrosion-resistant protective layer; wherein, the lead-free protective layer glass glaze composition for preparing the second protective layer, calculated by mass fraction, has a _B2O3 content of 20%, _{an Al2O3} content of 30%, a _SiO2 content range of 45%, a _Na2O content of 2.5% and a _K2O content of _2.5 %; the prepared lead-free second protective layer has good acid-alkali corrosion resistance, and the lead-free second protective layer is formed on a surface with high smoothness, has good film-forming quality and strong bonding strength of the film layer.

After drying and sintering, the thermal printhead of Example 1 of the present patent is completed.

This embodiment provides a heat generating substrate with high surface smoothness and excellent resistance to wear and corrosion, effectively guaranteeing the product's service life in high humidity and corrosive environments.

Example 2
As shown in FIG. 2, a base glaze slurry containing one or more components of aluminum oxide, silicon oxide, magnesium oxide, etc. is printed on the surface of an insulating substrate 1 by screen printing or other thick-film process, and then sintered at a high temperature of 1100-1200°C to form a heat storage base glaze layer 2 of a heating resistor. On the surface of the base glaze layer 2, a screen printer is used to print a metal slurry on the surface of the heat storage base glaze layer, and a belt-type sintering furnace is used for firing to metallize the substrate, and photoengraving technology is used to pattern the metal electrodes. The heating resistor slurry is printed on the effective area by using a screen printing or drawing process, and the heating resistor layer 4 is formed after sintering. The lead-free first protective layer slurry is printed on the heating resistor area by using a thick film process, and then dried and sintered. The lead-free glass glaze composition of the first protective layer, i.e., the first protective layer, is, in terms of mass _fraction , composed of 5% _B2O3 , 30% _SiO2 , 45% _Al2O3 , 8% _BaO , 6% CaO, and 6% ZnO, among which, the spherical _Al2O3 added as a _filler has a particle diameter D50 of 0.5 μm. The lead-free first protective layer prepared by this composition has a high Vickers hardness of about 700 Hv.
Then, the lead-free slurry of the second protective layer is printed on the electrode-coverable area to form a corrosion-resistant second protective layer, where the lead-free glass glaze composition of the second protective layer is, in mass fraction, _B2O3 content 10%, _Al2O3 content 35%, _SiO2 content range 50%, and _Na2O content about _{5 %} , the lead-free protective layer prepared by this composition has excellent acid-alkali corrosion resistance, and high hardness carbide or nitride is prepared in the effective area of the third protective layer by magnetron sputtering or other process. Thus, the thermal printhead of the second embodiment of the present application is completed.

Example 3
As shown in Fig. 3, a base glaze slurry containing one or more components of aluminum oxide, silicon oxide, magnesium oxide, etc. is printed on the surface of an insulating substrate 1 by screen printing or other thick film process, and then sintered at a high temperature of 1100-1200°C to form a heat storage base glaze layer 2 of a heating resistor, and a screen printer is used to print a metal slurry on the surface of the base glaze layer 2, and a belt-type sintering furnace 8 is used for firing to metallize the surface of the substrate, and a photolithography technique is used to pattern a metal electrode. The heating resistor slurry is printed on the effective area by screen printing or a drawing process, and a heating resistor layer 4 is formed after sintering, and a thick film process is used to print a first protective layer slurry on the electrode-coverable area, and then sintered after drying. Then, the second protective layer slurry is printed on the electrode-coverable area to form a corrosion-resistant second protective layer, and the composition of the glass glaze of the first and second protective layers is the same as that of Example 1, which will not be described again, and high-hardness carbide or nitride is prepared on the effective area of the third protective layer by magnetron sputtering or other processes. Thus, the thermal printhead of Example 3 of the present application is completed.

As shown in Figure 5, humidity and ion resistance tests were performed on Example 1 and Example 2, and the storage time in a 90% humidity, Na, and K ion environment was compared. The storage time in a corrosive environment when the first protective layer was used alone was 1/5B (H), the storage time in a corrosive environment when the second protective layer was used alone was 2B (H), and the storage period when the composite structure lead-free protective layer was used was 2B (H). The corrosion resistance of the composite structure protective layer is equivalent to that of the second protective layer used alone, and the corrosion resistance is about 10 times that of the first protective layer used alone. When converted according to the relevant acceleration coefficient, the two-layer protective layer and the three-layer protective layer using the composite structure can both guarantee normal use of the product life of 1 to 3 years.

As shown in Figure 6, the wear of the protective layer was compared when the same paper was used and the car was run over the same distance. When the first protective layer was used alone, the wear was A (μm/km), when the second protective layer was used alone, the wear was 2A (μm/km), and when the composite structure lead-free protective layer was used, the wear was about 1.5A (μm/km). When the ultra-hard protective layer, which is the composite structure protective layer (including the third protective layer), was used, the wear was about 1/4A (μm/km) over the same distance. Converted according to the product's service life, the two-layer protective layer and the three-layer protective layer using the composite structure protective layer can guarantee a product service life of about 40-50KM and 100-150KM, respectively.

The present application is prepared by adopting a composite structure with lead-free protective layers with different functions, the first protective layer has high physical hardness and excellent smoothness to ensure the wear resistance of the product, the first protective layer provides excellent wear resistance after undergoing a surface flattening treatment, and at the same time provides a smooth base for the second protective layer, thereby ensuring that the second protective layer, which is the corrosion-resistant protective layer, can generate excellent binding and adhesion, thereby improving the wear resistance of the second protective layer, and the third protective layer can achieve ultra-high hardness protection by dealing with large particulate matter, such as pebbles, sandstone, etc., in poor printing environments, thereby ensuring the service life of the product and increasing its reliability.

Claims (10)

an insulating substrate is provided on its surface, on which a heat storage and heat retention base glaze layer, an electrode layer made of a metal material, a heating resistor layer made of a semiconductor material, and a protective layer are sequentially provided from bottom to top, the protective layer comprises at least two sub-protective layers, the sub-protective layer closest to the insulating substrate is a first protective layer, and a second protective layer is combined on the outside of the first protective layer, the thermal expansion coefficients of the first protective layer and the second protective layer are 50×10 ^-7 /°C to 70×10 ^-7 /°C, and the expansion coefficient of the second protective layer is equal to or less than the expansion coefficient of the first protective layer,
The Webster hardness of the first protective layer is 600 to 900 HV, and the glass glaze composition of the first protective layer includes, calculated by mass percentage, 5 to 15% boron oxide B ₂ O ₃ , 25 to 50% aluminum oxide Al ₂ O ₃ , 5 to 30% silicon oxide SiO ₂ , and 10 to 30% glass flux, and the glass flux is barium oxide BaO, zinc oxide ZnO, and calcium oxide CaO.
A thermal printhead substrate having a composite lead-free protective layer. The glass glaze composition of the first protective layer contains boron _{oxide B2O3} in an amount of 8-13%, aluminum oxide _Al2O3 in an amount of 40-45%, and silicon oxide _SiO2 in an amount of 21-30%, calculated as a total mass percentage of the _composition .
A thermal printhead substrate having the composite lead-free protective layer of claim 1. The glass flux in the glass glaze composition of the first protective layer has a barium oxide (BaO) content range of 3 to 8%, a zinc oxide (ZnO) content range of 2 to 6%, and a calcium oxide (CaO) content range of 5 to 20%, calculated as a total mass percentage of the composition.
A thermal printhead substrate having the composite lead-free protective layer of claim 1. The aluminum oxide Al ₂ O ₃ adopts spherical or flake-shaped aluminum oxide Al ₂ O ₃ as the wear-resistant filler in the first protective layer, and the particle size is about 0.1-1 μm;
A thermal printhead substrate having the composite lead-free protective layer of claim 1. The glass glaze composition of the second protective layer includes, calculated by mass percentage, boron oxide B ₂ O ₃ content of 10-30%, aluminum oxide Al ₂ O ₃ content of 20-50%, silicon dioxide SiO ₂ content range of 30-50%, and glass glaze flux content of 1-5%, and the glass glaze flux is Na ₂ O, K ₂ O;
A thermal printhead substrate having the composite lead-free protective layer of claim 1. The glass glaze composition of the second protective layer has a boron oxide B ₂ O ₃ content of 10-30%, an aluminum oxide Al ₂ O ₃ content of 25-40%, a silicon dioxide SiO ₂ content range of 40-45%, a Na ₂ O content of 2.5-5% and a K ₂ O content of 0-5% in the glass glaze flux, calculated in terms of the total mass percentage of the composition;
A thermal printhead substrate having the composite lead-free protective layer of claim 5. A third protective layer is further provided, which is an ultra-hard protective layer formed of carbide, nitride or silicide and has a physical characteristic of Vickers hardness ≧1200Hv, and is compounded on the outside of the second protective layer.
A thermal printhead substrate having the composite lead-free protective layer of claim 1. The first protective layer and the third protective layer locally or entirely cover an effective area of the electrode layer.
A thermal printhead substrate having the composite lead-free protective layer of claim 7. The first protective layer of the composite protective layer is subjected to surface flattening treatment after sintering, and the surface roughness of the first protective layer is ≦0.2μm after smoothing treatment, and the surface flattening treatment is performed by using a polishing sand belt made of aluminum oxide material with a mesh number of 500-3000 and a particle size of <50μm to polish the product after polishing treatment, and the product is washed and dried, and then the glass glaze composition slurry of the second protective layer is printed and sintered on the outside of the first protective layer to form the second protective layer.
A method for manufacturing a thermal printhead substrate having the composite lead-free protective layer according to any one of claims 1 to 8. Step 1: preparing a heat storage underglaze layer, a metal electrode layer, and a heating resistor layer on the surface of an insulating substrate in this order, and then printing a first protective layer slurry on the heating resistor area, drying, and then sintering to form a first protective layer;
Step 2: using a surface smoothing process, i.e. using an aluminum oxide polishing sand belt with a mesh number of 3000 and a particle size of about 5 μm to polish the product back and forth; then cleaning the surface of the product after polishing; using anhydrous ethanol as the cleaning medium to perform ultrasonic cleaning; and then drying the product at 80-120°C after cleaning;
and step 3 of printing a second protective layer on the processed substrate, drying and sintering the second protective layer slurry to print the electrode-coverable area to form a corrosion-resistant protective layer, which is the second protective layer.
A method for manufacturing a thermal printhead substrate having the composite lead-free protective layer of claim 9.