HK1070232B - Resistive heater having a controlled resistivity and method for providing the same - Google Patents

Description

Resistive heater with controlled resistivity and method of making same

Background

The present invention relates to the field of resistive heaters.

Thermal spraying

Thermal spraying is a common technique for depositing coatings on metals or ceramics. It includes systems that use powder as feed (e.g., arc plasma, flame spray, and high velocity oxy-fuel (HVOF) systems) and systems that use wire as feed (e.g., arc wire, HVOF wire, and flame spray systems).

Arc plasma spraying is a method that is capable of depositing materials on a variety of substrates. The DC arc generates an ionized gas (plasma) which is used to spray molten powder material in a similar manner as spray painting.

The operation of an electric arc wire spray system is achieved by melting the heads of two wires (e.g. zinc, copper, aluminum or other metals) and delivering the resulting molten droplets to the surface to be coated by means of a carrier gas (e.g. compressed air). The wire feed is melted by an arc created by the potential difference between the two wires.

In flame spraying, a wire or powder feed is melted by means of a combustion flame, which is usually achieved by igniting a gas mixture of oxygen and another gas (e.g. acetylene).

HVOF uses combustion gases (e.g., propane and oxygen) ignited in a small combustion chamber. The high combustion temperature in the combustion chamber causes a simultaneous increase in gas pressure, which in turn causes the gas to be ejected at high velocity from nozzles in the combustion chamber. This hot high velocity gas is used to melt feed (e.g., wire, powder, or a combination thereof) and deliver molten droplets to the substrate surface at a velocity of 330-. A compressed gas (e.g., compressed air) is used to further accelerate the droplets and cool the HVOF apparatus.

The thermal spray coating has a unique microstructure. During deposition, each particle enters the gas stream, melts and cools into a solid form independent of the other particles. When the molten particles impact the substrate being coated, they impact ("splash") into small flat disks and solidify at a high cooling rate. The coating is built up and thickened on the substrate by repeatedly reciprocating the plasma gun assembly transversely over the substrate to form a further coating on the substrate until the desired coating thickness is achieved. Because the particles solidify as flakes of quenched metal, the resulting microstructure has a layered character with randomly stacked grains approximating small disks on the substrate surface.

Resistance heater

Thermal spray techniques have been used to deposit coatings for use as heaters. The resistive heater generates heat by electrons colliding with atoms of the heater material. The rate of heat generation is power, which depends on the amount of current flowing and the resistance of the material to the application of the current. The resistance of a heater depends on the material properties called "resistivity" and geometrical factors describing the length of the current path and the cross-sectional area through which the current passes.

Previously, thermal spraying has been used to deposit resistive coatings. In one such example, deposited and used as a heater is a metal alloy such as 80% nickel-20% chromium. In another example, a powdered metal alloy is mixed with a powder of an electrical insulator, such as alumina, prior to deposition. The mixed material is then deposited using thermal spraying to form a coating of resistive material. However, when nickel-chromium is deposited as a resistive heater, the bulk resistivity of the coating is still rather low, and therefore, it is more difficult to make such an alloy into a component, since obtaining a sufficiently high resistance requires a long current path. When depositing oxide-metal mixtures, there is often a large discontinuity in the composition of the resistive layer, which causes the power distribution across the substrate to often vary widely.

Molded thermoplastic material

Many plastic and metal parts are made by injecting molten metal or polymer melt into complex cavities formed in steel that is machined, for example, aluminum automobile transmission housings and polycarbonate computer housings. The injection molding machine melts the thermoplastic powder in the heating chamber and feeds it into the mold, causing it to harden. The operation is carried out at a strictly controlled temperature and time. During injection molding, it is important to maintain the material, such as polycarbonate, in a molten state as it flows into and through the mold cavity space. In addition, the shear stress profile of the resin flow must be controlled and adjusted to ensure proper filling of the cavity space. If the molten resin solidifies too quickly when it encounters the cold mold, it will not penetrate the narrow mold cavity and will form a weak network as the junction of the two streams. Therefore, a great deal of effort has been made to improve heat management and flow control during injection molding.

Summary of The Invention

The invention relates to a resistance heater with controlled resistivity, comprising: a substrate layer; a resistive layer having a controlled resistivity, the resistive layer further comprising a metal component and one or more reaction products selected from oxide, nitride, carbide and/or boride derivatives of the metal component, the resistivity of the resistive layer being the combined resistivity of the metal component and the one or more reaction products, the resistivity of the reaction products being controlled by the composition and pressure of the reaction gas and the metal component using a manometer in combination with a controlled reaction gas pressure, thereby forming the resistive layer having a layered structure; and a power source connected to the resistive layer.

The invention features a metallic resistance heater and its use. The resistive heater includes a conductive (i.e., low resistivity) metal component and an insulating (i.e., high resistivity) oxide, nitride, carbide, and/or boride derivative of the metal component. The resistivity is controlled in part by controlling the amount of oxides, nitrides, carbides, and borides formed during the deposition of the metallic components and their derivatives. Resistive heaters have numerous industrial and commercial applications (i.e., the production of molded thermoplastic parts, paper, and semiconductor wafers).

Accordingly, in a first aspect, the invention features a resistive heater that includes a resistive layer connected to a power source. The resistive layer includes a metallic component and one or more oxide, nitride, carbide and/or boride derivatives of the metallic component. The resistivity of the resistive layer is derived from the amount of said oxides, nitrides, carbides and/or borides present in the resistive layer. Desirably, the resistive heater is deposited on a substrate, such as a mold cavity surface.

In one embodiment, the resistive layer has a microstructure similar to a plurality of flat disks or platelets, the outer regions of which are nitride, oxide, carbide and/or boride derivatives of the metallic component and the inner regions of which are the metallic component.

In a second and related aspect, the invention features a resistive heater on a substrate, the heater prepared by a method including the steps of: providing a substrate, a metallic component feed, and a gas comprising oxygen, nitrogen, carbon, and/or boron; melting the feed material to produce a stream of molten droplets; reacting the molten droplets with a gas to form one or more nitride, oxide, carbide or boride derivatives of the metallic component, wherein a portion of the metallic component reacts with the gas to form said nitride, oxide, carbide and/or boride derivatives of the metallic component and a portion of the metallic component is unreacted; depositing unreacted metal component and a nitride, oxide, carbide and/or boride derivative of the metal component on a substrate to form a resistive layer; and connecting the resistive layer to a power source.

In an embodiment of the heater of the second aspect, the melting step and the reacting step are coordinated with each other so that the resistivity of the resistive layer is 0.0001 to 1.0 Ω · cm (e.g., 0.0001 to 0.001 Ω · cm, 0.001 to 0.01 Ω · cm, 0.01 to 0.1 Ω · cm, or 0.1 to 1.0 Ω · cm). In another embodiment, the molten droplets have an average diameter of 5 to 150 μm, 10 to 100 μm, or 20 to 80 μm. In other desirable embodiments, the method includes the additional steps of coating a ceramic or metal layer on a surface of the resistive layer, coating an electrically insulating layer between the substrate and the resistive layer, and/or coating a tie layer between the substrate and the insulating layer.

In a third aspect, the invention features a method of depositing a resistive heater on a substrate. The method comprises the following steps: providing a substrate, a metallic component feed, and a gas comprising oxygen, nitrogen, carbon, and/or boron; melting the feed material to produce a stream of molten droplets; reacting the molten droplets with a gas to form one or more nitride, oxide, carbide or boride derivatives of the metallic component, wherein a portion of the metallic component reacts with the gas to form said nitride, oxide, carbide and/or boride derivatives of the metallic component and a portion of the metallic component is unreacted; depositing unreacted metal component and a nitride, oxide, carbide and/or boride derivative of the metal component on a substrate to form a resistive layer; and connecting the resistive layer to a power source.

In a particular embodiment of any one of the first, second and third aspects, the substrate is an injection mold, a roller or a platen (toten) for semiconductor wafer processing.

In yet another aspect, the invention features an injection mold that includes: (i) a mold cavity surface and (ii) a coating comprising a resistive heater which in turn comprises a resistive layer connected to a power source, said coating being present on at least a portion of said surface. The resistive layer includes a metallic component and one or more oxide, nitride, carbide, or boride derivatives of the metallic component. In one embodiment, the resistivity of the resistive layer is derived from the amount of oxides, nitrides, carbides, and/or borides present in the resistive layer. Desirably, the mold includes a runner (runner), and the coating is deposited on at least a portion of the runner surface.

In yet another aspect, the invention features a method of making a molded product. The method comprises the following steps: providing an injection mould as described above; injecting a thermoplastic melt into a mold; the melt in the mold is cooled to form a molded product. Heated resistance heaters regulate solidification and cooling of the melt. In one embodiment, the resistive heater is prepared using the foregoing method.

In another aspect, the invention features a cylindrical roll including an outer surface, an inner surface surrounding a hollow roll core, and a resistive heater including a resistive layer connected to a power source. The resistive layer includes a metallic component and one or more oxide, nitride, carbide, or boride derivatives of the metallic component deposited on the outer and/or inner surface of the cylindrical roller.

In yet another aspect, the invention features a method of drying paper during manufacture. The method comprises the following steps: providing a paper having a water content greater than about 5% and one or more of the aforementioned cylindrical rolls; heating the roller with a resistance heater; the paper is contacted with the rollers for a suitable time to dry the water content of the paper to less than about 5%.

In another aspect, the invention features a semiconductor wafer processing system that includes an enclosure defining a reaction chamber; a support structure secured within the reaction chamber, the support structure securing a semiconductor wafer to be processed within the reaction chamber; a resistive heater comprising a resistive layer coupled to a power source, said resistive layer comprising a metallic component and one or more oxide, nitride, carbide and/or boride derivatives of the metallic component. In one embodiment, the heater is placed on top of the reaction chamber so that one side of the wafer (which typically has been polished) can be adjacent to or in contact with the heater. In another embodiment, the heater is placed at the bottom of the reaction chamber, so that one side of the wafer (polished or unpolished) can be adjacent to or in contact with the heater. In yet another embodiment, the heater is placed at both the top and bottom of the reaction chamber.

In yet another aspect, the invention features a method of heating a semiconductor wafer, including the steps of: providing a semiconductor wafer and a semiconductor wafer processing system as described above; and heating the wafer with a resistive heater.

In various embodiments of any one of the foregoing aspects, the resistivity of the resistive layer is 0.0001 to 1.0 Ω · cm (e.g., 0.0001 to 0.001 Ω · cm, 0.001 to 0.01 Ω · cm, 0.01 to 0.1 Ω · cm, or 0.1 to 1.0 Ω · cm), and a current applied to the resistive layer from a power supply causes the resistive layer to generate heat. Preferably, the resistive layer is capable of generating a sustainable temperature greater than 200 ° f, 350 ° f, 400 ° f, 500 ° f, 1200 ° f or 2200 ° f. In various other embodiments, the resistive heater includes an electrically insulating layer (e.g., a sheet comprising alumina or silica) between the substrate and the resistive layer, a bonding layer (e.g., a sheet comprising a nickel-chromium alloy or a nickel-chromium-aluminum-yttrium alloy) between the insulating layer and the substrate, a thermally reflective layer (e.g., a sheet comprising zirconia) between the resistive layer and the substrate, a ceramic layer (e.g., a sheet comprising alumina) on a surface of the resistive layer, and/or a metal layer (e.g., a sheet comprising molybdenum or tungsten) on a surface of the resistive layer. Desirably, the metallic component in the resistive heater is titanium (Ti), silicon (Si), aluminum (Al), zirconium (Zr), cobalt (Co), nickel (Ni), or alloys or combinations thereof. Other suitable metal components are described herein.

One particular embodiment of the invention includes the use of an insulating layer above or below the heater to provide electrical insulation between the resistive layer and the adjacent conductive elements. Additional coatings may be added to reflect or dissipate the heat of the heater in a selected pattern. One or more coatings may also be included to improve the thermal matching between the components to prevent bending or cracking of the different coatings that differ in their coefficients of thermal expansion. Coatings that improve the bond between the layers and the substrate may also be used.

By "metallic component" is meant a metal, metalloid (metalloid) or composite thereof capable of reacting with a gas to form an oxide, carbide, nitride and/or boride.

By "metal component feed" is meant a metal component having a physical form suitable for use in thermal spraying. Exemplary physical forms include, without limitation, wire, powder, and ingot.

Exemplary metal components include, without limitation, transition metals such as titanium (Ti), vanadium (V), cobalt (Co), nickel (Ni), and transition metal alloys; highly reactive metals such as magnesium (Mg), zirconium (Zr), hafnium (Hf), and aluminum (Al); refractory metals such as tungsten (W), molybdenum (Mo), and tantalum (Ta); metal composites such as aluminum/alumina and cobalt/tungsten carbide; and metalloids such as silicon (Si).

By "substrate" is meant any object on which a resistive layer is deposited. The substrate may be, for example, bare ceramic, or it may be one or more coatings present on the surface, such as an electrically insulating layer.

By "thermoplastic material" is meant a material that softens or melts when heated and hardens again when cooled. Exemplary thermoplastic materials include metals and thermoplastic organic polymers. A "thermoplastic melt" is a softened or melted thermoplastic material.

By "cycle time" is meant the time interval between a point in one cycle and the same point in the next cycle. For example, the cycle time of injection molding is measured as the time between two operations of injecting a thermoplastic melt into a mold.

The term "runner" refers to a passage for feeding a thermoplastic melt from a die inlet into a die cavity.

Other features and advantages will be apparent from the description of the preferred embodiments, and from the claims.

Brief Description of Drawings

Fig. 1 shows an HVOF wire system 2 that uses a metal wire 4 as feed material, which is melted by burning a fuel gas 6. The reaction gas 8 reacts with the molten feedstock and delivers molten droplets to the substrate 10, producing a coating 12.

Fig. 2 shows a plasma spray system 100 that uses metal powder 110 as a feed and produces an argon 120/hydrogen 130 plasma to melt the powder. Another reactive gas 140 is delivered to the molten droplets through a nozzle 150. The molten droplets are deposited as a coating 160 on a substrate 170.

Fig. 3 shows a resistance heater designed for spray deposition of the inner surface of the roll 200. The resistive layer 210 is deposited in a circular pattern to create a parallel heated resistive heater.

Fig. 4 shows a cross section of an injection mold including a resistance heater. The surface of the metal mold 300 includes several coatings: a bonding layer 310, an electrically insulating and thermally insulating layer 320, a metallic resistive layer 330, an electrically insulating and thermally conductive layer 340, and a metallic layer 350. The terminals 360 are insulated from the mold by terminal insulators 370, which connect the resistive layer to a power source.

Detailed Description

We have discovered a metallic resistive layer (and method of making the same) comprising an electrically conductive metallic component and an electrically insulating oxide, nitride, carbide and/or boride derivative of the metallic component. We further found that: the resistive layer can function as a heater when connected to a power source.

In order to deposit a coating that generates heat when a voltage is applied, the coating must have an electrical resistance determined by the desired power level. The resistance R is calculated from the applied voltage V and the desired power value P according to the following formula:

R＝V²/P

the electrical resistance is related to the geometry of the heater coating-the current path length L and the cross-sectional area a-through which the current passes-and also to the resistivity p of the material. The relation is as follows:

R＝ρL/A

thus, to design a coating that operates at a given voltage at a given power level and a given geometry, the resistivity of the material need only be determined according to the following equation:

ρ＝RA/L＝V²A/PL

in the present invention, resistivity is controlled, in part, by controlling the amount of oxide, nitride, carbide, and boride formation during deposition of the metallic component and its derivatives.

Resistivity is a control variable which is important because it represents an additional degree of freedom for the heater designer. In most cases, the resistivity of the heater material, such as Nichomer Nickel-chromium-Heat alloy (nichrome), is a fixed value. In this case, the heater designer must adjust the heater geometry (L and a) to achieve the required power. For example, if it is desired to heat a tube by winding nichrome wire, the designer must select the correct diameter required to pass the cross-sectional area a of the current and the winding spacing required for the total path length L of the current.

We now describe a resistive layer, its use as a coating component and its use as a resistive heater.

Metallic constituent element and oxides, nitrides, carbides and borides thereof

The metal component of the present invention includes any metal or metalloid capable of reacting with a gas to form an oxide, carbide, nitride, boride or combination thereof. Exemplary metal components include, without limitation, transition metals such as titanium (Ti), vanadium (V), cobalt (Co), nickel (Ni), and transition metal alloys; highly reactive metals such as magnesium (Mg), zirconium (Zr), hafnium (Hf), and aluminum (Al); refractory metals such as tungsten (W), molybdenum (Mo), and tantalum (Ta); metal composites such as aluminum/alumina and cobalt/tungsten carbide; and metalloids such as silicon (Si). The resistivity of these metallic components is typically 1-100 x 10^-8Omega cm. In a coating process (e.g., thermal spraying), a feed of metallic components (e.g., powder, wire, or solid rod) is melted, produced, for example, as droplets, and exposed to a gas containing oxygen, nitrogen, carbon, and/or boron. This exposure causes the molten metallic component to react with the gas to form an oxide, nitride, carbide, or boride derivative, or combinations thereof, on at least a portion of the surface of the droplet.

The nature of the reacted metal species depends on the amount and nature of the gas used in the deposition. For example, the use of pure oxygen results in the formation of oxides of the metallic constituents. In addition, mixtures of oxygen, nitrogen and carbon dioxide result in the formation of mixtures of oxides, nitrides and carbides. The exact proportions of each product depend on the inherent properties of the metal component and the proportions of oxygen, nitrogen and carbon in the gas. The resistivity of the coating prepared by the method is 500-50000-template10^-8Ω·cm。

Exemplary oxide types include TiO₂，TiO，ZrO₂，V₂O₅，V₂O₃，V₂O₄，CoO，Co₂O₃，CoO₂，Co₃O₄，NiO，MgO，HfO₂，Al₂O₃，WO₃，WO₂，MoO₃，MoO₂，Ta₂O₅，TaO₂And SiO₂. Exemplary nitrides include TiN, VN, Ni₃N，Mg₃N₂ZrN, AlN and Si₃N₄. The ideal carbide includes TiC, VC, MgC₂，Mg₂C₃，HfC，Al₄C₃，WC，Mo₂C, TaC and SiC. Exemplary borides include TiB, TiB₂，VB₂，Ni₂B，Ni₃B，AlB₂，TaB，TaB₂SiB and ZrB₂. Other oxides, nitrides, carbides and borides are well known to those skilled in the art.

Gas (es)

In order to obtain oxides, nitrides, carbides or borides of the metallic components, the gas that reacts with said components must contain oxygen, nitrogen, carbon and/or boron. Exemplary gases include oxygen, nitrogen, carbon dioxide, boron trichloride, ammonia, methane, and diborane. Other gases are well known to those skilled in the art.

Thermal spraying

The resistive and other layers in the coatings of the present invention are desirably deposited using a thermal spray device. Exemplary thermal spray devices include, without limitation, arc plasma, flame spray, Rockide systems, arc wire, and high velocity oxy-fuel (HVOF) systems.

A typical HVOF wire system includes a spray gun or spray head where three separate gases are brought together (see fig. 1). Propane gas and oxygen are typically used as fuel gases, with the gases selected as reactant gases to accelerate the molten droplets in the lance and to cool the nozzle. Typically, the latter function is achieved by using air. The gases are fed to the nozzle by flow and pressure regulators or by mass flow controllers, so that the flow of each gas is controllable and independent. If less reactant gas is required to be delivered, it can be mixed with a non-reactive gas such as argon so that the amount and flow of gas is sufficient to enable the lance to be operated at the appropriate speed. This mixing can be accomplished using flow and pressure regulators, mass flow control meters, or by using pre-mixed gas cylinders, each of which is generally known to those skilled in the art. The feed material, in this case wire, is fed to the lance head by a wire feeder which controls the rate at which the material is fed to the lance. The spray gun itself may be connected to a motion control system such as a linear transducer or a multi-axis robot.

Ideally, the thermal spray apparatus is configured to enable the injection of the reactant gas into the spray melt stream. For combustion systems and arc wire systems, such injection may be achieved by using a gas as an accelerator. For plasma systems, if the plasma gas is also not used as a reactive gas, the gas can be injected using an additional nozzle (see fig. 2). The addition of additional nozzles for injecting the reaction gas is also feasible for other systems.

The composition of the deposited layer may be affected by the type of thermal spray device used. For example, HVOF systems can scatter droplets quickly compared to other techniques, and the droplets are then exposed to the reactant for a shorter period of time and, therefore, react to a lesser extent with the gas. Furthermore, the bonding strength of HVOF deposited coatings is higher compared to other system deposited coatings.

The resistive layer may be deposited on the substrate according to a defined pattern. This pattern may be determined, for example, by a removable mask. The application of patterning enables the fabrication of more than one spatially separated resistive layer on one or more substrates. The patterned coating also enables control of the heat generation in localized areas of the substrate.

Microstructure

The characteristic layered microstructure of the thermal spray deposited coating is a direct result of the spraying process. The thermal spray process produces streams of molten droplets from the feed material, which are accelerated and move toward the substrate. The droplets typically travel at a speed of hundreds of meters per second, impact the substrate and cool very rapidly at a speed approaching one million degrees per second. This cooling rate results in very rapid solidification. Furthermore, during the impact, the droplets deform into a platelet shape, and as the spray head reciprocates back and forth over the substrate, the deformed droplets stack on top of each other, thickening the coating. The microstructure thus forms a layered structure, all the flat particles being aligned parallel to the substrate and perpendicular to the deposition line.

The composition of the coating is consistent with the composition of the feed material if the deposited material does not react with the gases present in the melt stream. However, if the molten droplets react with ambient gases during deposition, the composition of the coating differs from that of the feedstock. The droplets can give a surface coating consisting of reaction products, the thickness of which depends, for example, on the reaction speed, the temperature at which it is used and the concentration of the gas. In some cases, the droplets were completely reacted; while in other cases there is a significant amount of unreacted metal in the centre of the droplet. The microstructure of the obtained coating is a layered structure, which is composed of individual particles with a complex composition. Such coatings have a reduced volume fraction of unreacted metal, the remainder being reaction products, which generally surround the unreacted metal in each platelet.

When the gas added to the melt stream is polished to form a reaction product with a much higher resistivity, the resulting coating has a higher bulk resistivity than the pure metal component. In addition, when the concentration of the gas, and thus the reaction products, is controlled, the resistivity of the coating can be proportionally controlled. For example, aluminum sprayed in pure oxygen has a higher resistivity than when sprayed in air due to the higher concentration of alumina in the coating, which is very high.

Spatially variable resistivity

The invention also provides a method of producing a coating whose resistivity varies as a function of position on a substrate, for example, a continuous gradient function or a piecewise function. For example, the resistivity of the coating may be increased or decreased by 50, 100, 200, 500, or 1000% for a distance variation of 1, 10, or 100 cm. The apparatus used included a thermal spray gun and a gas source. The gas source comprises two or more gases which may be mixed arbitrarily. By controlling the gas composition used in the thermal spray gun, the composition of the coating, as well as the electrical resistivity, can be controlled. For example, gradually increasing the reactant (e.g., oxygen) in the gas may result in a gradual increase in the resistivity of the coating. This gradual increase can be used to produce coatings having a gradient of resistivity over the substrate. Similarly, other resistivity patterns, such as piecewise functions, may be formed by appropriate control of the gas mixture. The gas mixture may include more than one reactive species (e.g., nitrogen and oxygen) or one reactive species and one inert species (e.g., oxygen and argon). Computer controlled mixing of gases may also be employed.

Applications of

The coating on the coated substrate may comprise a resistive layer of the present invention. In addition, other layers may be present in the coating to provide additional properties. Examples of additional coatings include, without limitation, a bonding layer (e.g., a nickel-aluminum alloy), an electrically insulating layer (e.g., aluminum oxide, zirconium oxide, or magnesium oxide), an electrical contact layer (e.g., copper), a thermally insulating layer (e.g., zirconium dioxide), a thermally emissive layer (e.g., chromium oxide), a layer that improves thermal matching between coatings having different coefficients of thermal expansion (e.g., nickel between aluminum oxide and aluminum), a thermally conductive layer (e.g., molybdenum), and a thermally reflective layer (e.g., tin). These layers may be located between the resistive layer and the substrate (e.g., an adhesive layer) or on the side of the resistive layer remote from the substrate. The resistive layer may also be deposited on a non-conductive surface without an electrically insulating layer.

The heater resistive layer is made into a resistive heater by connecting a power source to the layer. An electric current is passed through the resistive layer, and resistance heat generation then occurs. The connection between the power source and the resistive layer is for example achieved by soldered joints, solder wires or by physical contact using various mechanical joints. These resistive heaters are particularly advantageous where localized heating is required.

A. Injection molding one application for the resistance heater of the present invention is in injection molding. The injection mould has a cavity into which the melt of the thermoplastic material enters under the action of a force. Once the material has cooled to harden, it can be removed from the mold and the process can be repeated. A coating comprising a resistive heating layer is present on at least part of the cavity surface of the injection mold of the invention. The resistive heating layer may be covered with a metal layer (e.g., molybdenum or tungsten). The purpose of providing heater layers in the cavity of the mould and in the lines leading to the cavity is to better control the solidification process and to shorten the cycle time. Heaters in close proximity to the melt can be used to keep the melt hot for better flow and lower pressure, and also to cool the melt in a controlled manner during the solidification stage.

B. Heated rolls are used in many industries including paper making, printing, laminating, and converting industries for paper, film, and foil. One of the uses of the resistance heater of the present invention is a dryer in papermaking (see fig. 3). Several steps in papermaking include forming, pressing and drying. The drying step typically removes residual water (typically about 30%) from the pressing step, typically reducing the water content to about 5%. The drying step typically involves contacting both sides of the paper with heated cylindrical rolls. Thus, a roll for a paper dryer having a resistance heating layer can be manufactured by the method of the present invention. A coating containing a resistive heater layer is deposited on the inner or outer surface of such a roll. Other coatings such as corrosion resistant layers may also be applied. The heater may be coated in a determined pattern by a mask (mask) during the deposition step. For example, a pattern of concentrated heating zones at the ends of the rollers can provide more uniform heating of the paper because the ends of the rollers cool more rapidly than their central portions. Examples of rollers comprising a heating zone are given in us patent 5,420,395, which is incorporated herein by reference.

The deposited resistance heaters may be used on dryer cans (or rolls) used in papermaking processes to remove water from the pulp. In one example, the heater is coated on the inner surface of a steel roll or can. First, an alumina insulation layer is coated with thermal spray and sealed with an alumina nanophase or some other suitable high temperature dielectric sealant. A resistive heater layer was then deposited using a high-speed oxy-fuel wire spray system, titanium wire, and nitrogen. The terminals are fixed inside the can by welding or bolting and insulated so that the power supply can be connected to the deposited resistive layer. Finally, the entire heater layer is covered with high temperature silicone or another layer of thermally sprayed alumina, which is sealed as before.

Alternatively, the heater layer and the insulating layer may be coated on the outer surface of the dryer can and covered with a thermally sprayed metal layer such as nickel. The nickel is then ground to the desired size. When the heated roller is small, the metal shell may be fixed or baked (shrunk) on the roller coated with the heater.

C. Semiconductor wafer processing system heaters are also used in the processing of semiconductor wafers (see WO 98/51127, incorporated herein by reference). The semiconductor wafer processing system of the present invention includes a process chamber, one or more resistive heaters, and means for holding and manipulating a semiconductor wafer. The system may be used in wafer processing applications such as annealing, sintering, silicidation, and glass reflow. Systems including such heaters are also used to promote reactions of the wafer with reactant gases, such as oxidation and nitridation. Furthermore, the system may be used for epitaxial reactions, where materials such as silicon are deposited in single crystal form on a heated surface. Finally, such a system enables chemical vapor deposition of the product of a vapor phase reaction in the form of nanocrystals on a heated substrate.

Additional applications of the heater of the invention are as follows:

1. the top layer of the surface layer heater on the pipeline is a metal contact layer, and the contact point is an alumina insulator.

2. A heater head for a natural gas igniter for a kitchen stove, oven, water heater or heating system.

3. A free standing sleeve made by spray forming on a removable mandrel.

4. Low pressure heater coating for bathroom deodorizers.

5. Laboratory use: resistance heated coated glass and plastic laboratory containers; a working plate; an anatomical disc; a cell culture vessel; a pipeline; a pipeline; a heat exchanger; a manifold; a surface disinfection cover is used for laboratory; self-disinfecting a work surface; sterilizing the container; the filter may be heated; a filter plate (frit); a packed bed; an autoclave; self-sterilizing medical bacteria and tissue culture tools (e.g., loops and spreaders); an incubator; a benchtop heater; a flameless torch; a laboratory stove; an incinerator; a vacuum furnace; a thermostatic bath; a drying tank; hot pressing plate; a pen for irradiation of rays; a reaction vessel; a reaction chamber; a combustion chamber; the mixer and impeller may be heated; electrophoresis equipment; an anode and a cathode electrode; heating the electrode; electrolysis and gas generation systems; a desalination system; a deionization system; (ii) spectroscopic and mass spectrometry equipment; chromatographic equipment; HPLC; an IR sensor; a high temperature probe; a thermoplastic bag; cap and tube sealers; a thermal cycle control device; a water heater; a steam generation system; heating the nozzle; thermally activating the coaxial valve; a shape memory alloy/conductive ceramic system; a freeze dryer; hot ink pens and printing systems;

6. medical and dental applications: self-disinfecting and self-burning surgical tools (e.g., scalpel blades, forceps); an incubator; warming the bed; warming the plate; the warm blood system; a thermal control fluid system; an amalgum heater; a dialysis system; an electrophoresis system; a steam generator dryer; an ultra-high temperature incineration system; self-disinfecting tables and surfaces; drug delivery systems (e.g., medicated aerosol inhalers, heat activated transdermal patches); a dermatological tool; the tile can be heated; a bath tub; a bathroom floor; a towel rack; a small autoclave; a field heater canvas bed; a body warming system;

7. industrial application: a sparkless ignition system; a sparkless combustion engine; a bar heater; a belt heater; a combustion chamber; a reaction chamber; a chemical treatment line; a nozzle and a conduit; static and active mixers; a catalytic heating stage (e.g., scrubber); chemical processing equipment and machinery; an environmental remediation system; a pulp processing and manufacturing system; glass and ceramic processing systems; hot air/air knife applications; an indoor heater; spark-free welding equipment; inert gas welding equipment; a conductive abrasive; a heater water jet or liquid jet cutting system; a heated impeller and mixing box; a melting and damping lock; super-heated fluorescent bulbs using new inert gas; the valve can be heated; heatable interconnect devices and all types of interface devices; heatable ceramic tiles; self-heating circuit boards (e.g., self-brazing sheets; self-laminating sheets); a fire-fighting heater; food processing equipment (e.g., stoves, vats, steam systems, burning systems, shrink-wrap systems, pressure cookware, boilers, fryers, heat-seal systems); online food processing equipment; programmable temperature grids and platens for selective heating of 2-D or 3-D structures (e.g., thermoplastic welding and sealing systems); a point pulse heater; a battery operated heater; a recorder and labeling system; a static mixer; a steam cleaner; an IC chip heater; an LCD panel heater; a condenser; heated aircraft components (e.g., wings, propellers, flaps, ailerons, vertical tail, rotors); conductive ceramic pens and probes; self-healing glaze; self-baking pottery; a large fireplace; a self-welding gasket; a heat pump;

8. home and office applications: all heatable household appliances; self-cleaning a stove; an igniter; a grill; shallow cooking; a susceptor-based heatable ceramic cauterization system for a microwave oven; a heated mixer; an impeller; a stirrer; a tank; press and pressA force pot; an appliance range cover (electric range top); a refrigerator defogging mechanism; a heated ice cream shovel and an eating spoon; a hand-held heater and warmer that operate; a water heater and a switch; a coffee heater system; a heatable food processor; a toilet seat capable of keeping warm; a towel rack; a garment warmer; a body warmer; a cat bed; an instant iron; a water bed heater; a washing machine; a dryer; a faucet; heated bathtubs and wash basins; a dehumidifier; a hose nozzle for heated rinsing or steam cleaning; a hot plate for heating by wiping water; a bathroom fabric heater; a towel heater; a heated soap dispenser; a heated razor; an evaporative quench system; a self-heating key; outdoor CO for attracting and killing bed bug systems₂And a heat generating system; a heater for the aquarium; bathroom mirrors; a chair warmer; a ceiling fan capable of heating the blades; a floor heater;

9. a full surface geometry heater; a direct contact heater; a pure ceramic heating system; a coated metal heating system; a self-error checking system; plasma spraying thermocouples and sensors; plasma spheroidizing bed systems (e.g., boron gas generation systems for the semiconductor industry; thermally conductive chromatographic layers and bead systems); a pre-heater to warm the surface prior to implementing a less expensive or more efficient heating method; a sensor (e.g., a heater as part of an integrated circuit chip package);

10. microwave and electromagnetic applications: a magnetic receptor coating; a coated cooking appliance; magnetic induction furnaces and stove covers;

11. thermoplastic processing applications: a large working surface for resistance heating and a large heater; a heated injection mold; a tool; a mold; a gate; a nozzle; a pouring channel; a feedstock delivery line; a vat; a chemical reaction mold; a screw; a propeller; a compression system; extruding the die; a thermoforming device; a stove; annealing equipment; welding equipment; a thermal connection device; a water vapor curing oven; vacuum and pressure forming systems; a heat sealing device; a film; laminating the board; a cover; hot stamping equipment; a shrink-wrapping device;

12. automotive applications: a detergent fluid heater; a coaxial heater and a nozzle heater; a windshield wiper heater; an engine block heater; an oil pan heater; a steering wheel heater; a damping base locking system; a micro catalytic converter; an exhaust gas purifier; a seat heater; an air heater; a heated mirror; a heated key lock; a heated outer lamp; an integral heater under the paint surface or in place of paint; edges of the inlet and the outlet; sparkless "spark plugs," engine valves, pistons, and bearings; a tiny exhaust gas catalytic tube;

13. marine applications: an anti-fouling coating; deicing coatings (e.g., balustrades, sidewalks); an electrolysis system; a desalination system; a marine product processing system onboard; can preparation equipment; a drying device; ice drill and coring; a life jacket; a wetsuit heater; a drying and dehumidifying system;

14. application of national defense: high temperature hot target material and false target; an obstacle heater; an MRE heating system; a weapon preheater; a hand-held heater; a cooking device; a battery-driven heatable knife; a non-combustion based gas expansion gun; spray de-icing coatings on wings, etc.; a thermal fusion self-destructive system; an incineration device; a flash heating system; an emergency heating system; an emergency distillation unit; a desalination and sterilization system;

15. the marking application comprises the following steps: a heated pavement marker; a thermally responsive color change marker; inert gas (e.g., neon) filled microspheres that fluoresce in a magnetic field;

16. printing and photographic applications: a copier; a printer; a printer heater; a wax heater; a thermally solidified ink system; a heat conversion system; xerographic and printing heaters; a radiographic and photographic film processing heater; a ceramic printing press;

17. building application: a heated sidewalk mat; a grid; a sewer; a drainage ditch; a drainage groove and a roof edge;

18. sports application: a heated golf club head; a rod; a stick; a handle; a heated skate blade; ski and snowboard blades; a de-icing and re-ice system for a rink; a heated visor; a heated lens; a heated auditorium seat; camping stoves; an electric grill; a heatable food storage container;

in one embodiment, the heater of the present invention is used in an injection molding system to manage and control the flow of molten material throughout the mold cavity space. The heater may be deposited directly on the surface of the mold cavity area as part of the coating to precisely manage the temperature distribution in the moving melt material. For some applications, the heater has a variable resistivity at the surface of the mold cavity region, thereby enabling fine tuning of the temperature gradient of the molten material to achieve precise control of heat flow and constant (or precisely managed) viscosity and velocity of the melt stream. The thermal management and flow control of the mold depends on the particular application and the type of material used.

Ideally, the heater is used with a thermal sensor (e.g., a thermal regulator or thermocouple) and/or a pressure sensor. The direct deposition of the heater-containing coating on the mold cavity area reduces or eliminates air gaps between the heater and the heated surface, allowing intimate, direct contact therebetween, thereby improving temperature transfer between the heater and the heated surface.

In one embodiment, the heater is coated on the cavity of the plastic mold (see fig. 4). First, a high velocity oxy-fuel wire (HVOF) thermal spray system was used to apply a NiCrAlY alloy bond coat of about 0.002 inches thick to the die cavity. Next, a zirconia layer having a thickness of 0.012 inches was applied using an arc plasma spray system. The zirconia layer electrically and thermally insulates the heater from the water-cooled steel mold. Next, a resistive heating layer was applied over the zirconia as a 0.008 inch thick sheet or coating of material. Zirconium was deposited using an HVOF thermal spray system, where propane and oxygen were used as fuel gas to melt the metal wire and pure nitrogen as accelerator. The nitrogen promotes the formation of zirconium nitride in the melt stream, raising the resistivity of the coating from 0.00007 Ω -cm for pure zirconium to 0.003 Ω -cm for the deposited coating. Next, the desired heater element pattern is scribed on the mold using a small abrasive blaster using an alumina media and mounted on a multi-axis machining center. At this stage, the zirconium terminal is inserted into a hole machined in a mold. The embedded terminals should make electrical contact with the heater layer. A second 0.015 inch thick layer of ceramic electrical insulator was then applied to the top of the heater. Alumina is chosen for this layer because it has a higher thermal conductivity than zirconia. The alumina is coated using an arc plasma system and subsequently nano-sealed with an alumina phase. Finally, a layer of 0.040 inch thick tungsten metal was applied by arc plasma spray and machined to the required dimensions. And electroplating a layer of nickel on the top layer of the tungsten to finish the treatment of the die cavity.

Other embodiments

All publications and patents mentioned in the above specification are herein incorporated by reference. Various modifications and alterations of the method and system of the present invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. While the invention has been described in connection with specific preferred embodiments, it should be understood that: the claimed invention should not be unduly limited to such specific embodiments. The real purpose is as follows: various modifications to the thermal spray, coating, thermoplastic, or related aspects of the modes for carrying out the invention that will be apparent to those skilled in the relevant arts are within the scope of the invention.

Other embodiments are within the claims.

Claims (24)

1. A resistive heater having a controlled resistivity, comprising:

a substrate layer;

a resistive layer having a controlled resistivity, said resistive layer further comprising a metal component and one or more reaction products selected from oxide, nitride, carbide and/or boride derivatives of the metal component, the resistivity of said resistive layer being the combined resistivity of said metal component and said one or more reaction products, said resistivity of said reaction products being controlled by the composition and pressure of the reaction gases and said metal component by melting a wire or solid rod feed of said metal component to produce a molten droplet stream and by introducing said reaction gases into the molten droplet stream using a pressure regulator at a controlled reaction gas pressure to form said resistive layer having a layered structure, the resistive layer having a resistivity of from 0.001 Ω -cm to 1.0 Ω -cm; and

a power source connected to the resistive layer.

2. The resistive heater of claim 1, wherein the reactive gas is mixed with a non-reactive gas.

3. The resistive heater of claim 1, wherein said reactant gas comprises a gas of one or more of oxygen, nitrogen, carbon, and boron.

4. The resistive heater of claim 1, further comprising an electrically insulating layer between said substrate and said resistive layer.

5. The resistive heater of claim 4, further comprising a bonding layer between said insulating layer and said substrate.

6. The resistive heater of claim 5, wherein the bonding layer comprises a nickel-chromium alloy or a nickel-chromium-aluminum-yttrium alloy.

7. The resistive heater of claim 1, further comprising a heat reflective layer between said resistive layer and said substrate.

8. The resistive heater of claim 7, wherein the thermally reflective layer comprises zirconia.

9. The resistive heater of claim 1, further comprising a ceramic layer on a surface of said resistive layer.

10. The resistive heater of claim 9, wherein the ceramic layer comprises alumina.

11. The resistive heater of claim 1, further comprising a metal layer on a surface of said resistive layer.

12. The resistive heater of claim 11, wherein the metal layer comprises molybdenum or tungsten.

13. The resistive heater of claim 1, wherein the substrate is an injection mold, a roller, or a platen for semiconductor wafer processing.

14. The resistive heater of claim 1, wherein said metallic component is titanium, silicon, aluminum, zirconium, cobalt, nickel, or alloys thereof.

15. A method of making a resistive heater having a controlled resistivity, the resistive heater having a substrate, a resistive heating layer, and a power source, the method comprising the steps of:

determining a desired resistivity of the resistive heater layer;

selecting a solid metallic component in the physical form of a wire or solid rod and at least one reactive gas comprising one or more of oxygen, nitrogen, carbon and boron and capable of reacting with the solid metallic component to produce one or more oxide, nitride, carbide and/or boride derivatives of the metallic component;

selecting the proportions of said solid metallic component and said at least one reactant gas so as to produce said desired resistivity of said resistive heater layer when they are combined;

promoting reaction of at least a portion of the solid metallic component with the reactant gas by: melting said at least a portion of the solid metallic component in physical form of said wire or solid rod to produce a stream of molten droplets, and providing controlled introduction of said reaction gas to said molten droplets at a selected pressure by use of a pressure regulator to combine said molten droplets and said reaction gas to result in unreacted metal and reaction products;

depositing the combined unreacted metal and reaction product on the substrate to form the resistive heater layer having the desired resistivity, the layer having a layered structure, the resistive heater layer having a resistivity of 0.001 Ω -cm to 1.0 Ω -cm;

and providing power to the resistive heater layer.

16. The method of claim 15, wherein the reactive gas is mixed with a non-reactive gas.

17. The method of claim 15, wherein said reactive gas controlled to be introduced into said molten droplets during said step of promoting reaction of at least a portion of said solid metallic constituents comprises a gas of one or more of oxygen, nitrogen, carbon, and boron.

18. The method of claim 15, further comprising the step of providing an electrically insulating layer between said substrate and said resistive layer.

19. The method of claim 18, further comprising the step of providing a bonding layer between said insulating layer and said substrate.

20. The method of claim 15 further comprising the step of providing a heat reflective layer between said resistive heater layer and said substrate.

21. The method of claim 15, further comprising the step of providing a ceramic layer on a surface of the resistive heater layer.

22. The method of claim 15, further comprising the step of providing a metal layer on a surface of the resistive heating layer.

23. The method of claim 15, wherein the solid metallic component is not oxidized prior to the step of promoting the reaction.

24. The method of claim 15, wherein said solid metallic component is non-reactive with said reactive gas prior to said step of promoting reaction.