Sustainable self-adjusting heating laminate

Abstract

A flat plate electric heater, preferably obtained by co-extrusion or co-lamination, comprising: a plurality of elongate conductors, preferably uniformly spaced from one another and preferably substantially parallel to one another, said conductors being at least partially embedded within and in contact with a semiconductive composition having a positive temperature coefficient (PTC), the semi-conductive composition comprises polyethylene, polypropylene or a mixture thereof, and a conductive filler wherein the semi-conductive composition is preferably contained in an extruded film having a longitudinal direction, and the elongate conductor is preferably parallel to the longitudinal direction of the extruded film comprising the semi-conductive composition; wherein the semiconductive composition has a conductivity [sigma] of 2 to 50 S / m, measured at 40 DEG C according to the "Conductivity Method" described in the "Measurement Method", where 20 DEG C < = TEq < = 50 DEG C and TEq is defined as a temperature at which d [sigma] / dT is at a minimum value.

Description

Technical Field

[0001] The present invention relates to a self-regulating heating laminate, and in particular to a sustainable flat-plate self-regulating heater suitable for close contact with humans or animals, and methods of making such structures. In particular, the present invention relates to the use of co-lamination to make the flat-plate self-regulating heater, or preferably co-extrusion to make the flat-plate self-regulating heater, and thus enables the continuous and inexpensive production of these flat-plate self-regulating heaters. Background Art

[0002] Parallel resistance self-regulating heating cables are known. Such cables typically include two conductors extending longitudinally along the cable. Typically, the conductors are embedded within a resistive polymer heating element which is extruded continuously along the length of the conductors. The cable thus has a parallel resistance form, wherein power is applied via the two conductors to the heating element connected in parallel across the two conductors. The heating element typically has a positive temperature coefficient of resistance. Thus, as the temperature of the heating element increases, the resistance of the electrical connection material between the conductors increases, thereby reducing the power output. Such heating cables, where the power output varies with temperature, are said to be self-regulating or self-limiting.

[0003] Therefore, to avoid overheating and potential damage to the object, they are self-limiting and require no regulating electronics.

[0004] Self-regulation exploits the conversion of electrical energy into thermal energy by allowing an electric current to pass through a semiconductor medium with a positive temperature coefficient (PTC) property, which raises the temperature of an object above that of its surroundings until a steady state (self-regulation) is reached. The resistance of a material with a PTC increases with increasing temperature, so that at a certain temperature, the heating power is balanced with the heat loss of the object, resulting in a stable temperature and explaining the mechanism behind the self-regulating function. These PTC cables are often used for floor heating or are wrapped around pipes for, for example, antifreeze purposes. However, the heating area of ​​the cable is not large, so a large amount of cable is required to provide, for example, floor heating.

[0005] Therefore, the inventors seek to provide a flat plate heater that is different from a cable. The cross section of such a flat plate may be rectangular or square, rather than a cable.

[0006] However, there are documents that disclose flat panel heaters. In WO2014 / 188190, an electric heater is described, which includes a conductor and a heating element arranged between the conductors, wherein the heating element includes a conductive material distributed in a first electrically insulating material. The insulating material separates the conductor from the conductive material. However, such a complex arrangement is not necessary.

[0007] US6512203 describes a device for electrically heating a glass substrate, wherein a conductor is adhered to the surface and a resistive film is adhered to the surface.

[0008] US7250586 describes a surface heating system for automobile seats and the like, which comprises a support and a heating layer comprising a conductive plastic, and is characterized in that the heating layer is formed of a flexible film and the support is flexible.

[0009] US4247756 describes a heating mat in which two inner conductive layers sandwich conductors. These conductors are adhered to the inner layers.

[0010] US7053344 describes a flexible heater for a fabric. This structure cannot be produced by coextrusion.

[0011] EP0731623 describes a PTC cable in which PVC and conductive fillers are present. The cable is surrounded by a microcrystalline silica product to improve performance.

[0012] US5451747 describes a heating mat having a PTC material surrounded by an insulating material. The mat contains two conductors surrounded by a medium density, highly flexible PTC material.

[0013] US2010 / 0038357 describes a plate-shaped heating element having a PTC composition, the PTC composition comprising a resin and at least two different conductive materials. The resin has a cross-linked structure to ensure that the temperature and PTC characteristics are more stable.

[0014] EP3015360 describes a floor for an aircraft comprising a heater layer. The heater layer is formed as a PTC layer with electrical conductor paths which are interconnected by PTC resistor paths. The PTC resistor paths are transverse to the conductor elements to produce a smooth, uniform heat distribution.

[0015] US 2014 / 0166638 describes a flexible homogeneous carbon polymer heating element comprising an elongated mesh of conductive plastic into which a bus conductor is embedded.

[0016] WO2008 / 133562 describes a heating device having two electrodes within a PTC heating material, wherein the PTC material comprises an interconnection of electrodes of a low resistivity PTC material relative to the rest of the heating material. The distance between the electrodes in '562 is 380 mm. Such a large gap can cause problems with heating the device due to the slow heating process. Furthermore, in order to ensure that there is sufficient heat in the device, a high voltage is required, for example from the mains supply. Therefore, the device in '562 is suitable for a limited number of applications, such as floor heating, but due to the high voltage required, such products have inherent safety hazards, such as the possibility of serious electric shock if accidentally drilled into the product.

[0017] Furthermore, most of the flat panel heaters disclosed in the prior art include multiple layers and / or include a combination of many different materials.

[0018] Considering sustainable development, it is crucial to design materials with sustainable performance and focus on the possibility of facilitating their disposal when the product reaches its end of life (EOL) to promote a circular economy. Sustainable development is defined as "meeting the needs of the present without compromising the ability of future generations to meet their own needs" and is an important topic globally.

[0019] The present inventors have realised that a sustainable, simple, flexible and inexpensive heater suitable for close contact with humans or animals can be prepared wherein a conductor and a polymer composition in which the conductor is at least partially embedded are co-laminated or co-extruded to form the target material.

[0020] The present invention enables the use of a "simpler" flat self-regulating heater design, thereby reducing material consumption and improving the sustainability performance of the heater design. At the same time, eliminating different layers and / or eliminating different materials also facilitates the handling of the heater at the end of its service life, further improving sustainability performance.

[0021] In the latter embodiment, this means that a continuous sheet can be prepared with a plurality of conductors which are preferably parallel and preferably equally spaced. In particular, the conductors are preferably kept close together, for example 20 to 150 mm apart. The resulting device heats very quickly and lower voltages can be used in the product, thus avoiding the risk of electric shock, further improving suitability for use in close contact with humans or animals. The device can be used in a wider range of applications, such as heating clothing or car seats, as battery power or low risk voltages are sufficient to heat the material. Furthermore, due to the inherent self-regulating properties, the need for control electronics is eliminated / reduced. Summary of the invention

[0022] From one aspect, the present invention provides a flat electric heater, preferably obtained by coextrusion or colamination, comprising:

[0023] A plurality of elongated conductors,

[0024] The conductor is at least partially embedded in and in contact with a semiconductive composition having a positive temperature coefficient (PTC), the semiconductive composition comprising at least one polyolefin component such as polyethylene, polypropylene or a mixture thereof and a conductive filler,

[0025] wherein the semiconductive composition is preferably contained in an extruded film having a longitudinal direction, and the conductor is preferably parallel to the longitudinal direction of the extruded film containing the semiconductive composition;

[0026] wherein the semiconductive composition has an electrical conductivity σ of 2 to 50 S / m measured at 40° C. according to the “Electrical Conductivity Method” described in the “Determination Methods”,

[0027] Where 20℃≤T Eq ≤50℃ and T Eq Defined as the temperature at which dσ / dT is at a minimum.

[0028] From another aspect, the present invention provides a multi-layer flat electric heater, which is obtained by co-lamination or co-extrusion, preferably co-lamination, and comprises in sequence:

[0029] a first layer comprising a semiconductive composition having a positive temperature coefficient, the semiconductive composition comprising at least one polyolefin component, such as polyethylene, polypropylene or a mixture thereof, and a conductive filler;

[0030] a conductor layer comprising a plurality of elongated conductors,

[0031] a second layer comprising a semiconductive composition having a positive temperature coefficient, the semiconductive composition comprising at least one polyolefin component, such as polyethylene, polypropylene, or a mixture thereof, and a conductive filler, such that the conductor layer is sandwiched between and in contact with the first and second layers;

[0032] wherein the layer of the semiconductive composition is preferably contained in an extruded film having a longitudinal direction, and the conductor is preferably parallel to the longitudinal direction of the extruded film containing the layer of the semiconductive composition;

[0033] wherein the semiconductive composition has an electrical conductivity σ of 2 to 50 S / m measured at 40° C. according to the “Electrical Conductivity Method” described in the “Determination Methods”,

[0034] Where 20℃≤T Eq ≤50℃ and T Eq Defined as the temperature at which dσ / dT is at a minimum.

[0035] From another aspect, the present invention provides a multi-layer flat electric heater, which is obtained by co-lamination or co-extrusion, preferably co-lamination, and comprises in sequence:

[0036] a first layer comprising a semiconductive composition having a positive temperature coefficient, the semiconductive composition comprising at least one polyolefin component, such as polyethylene, polypropylene or a mixture thereof, and a conductive filler;

[0037] a conductor layer comprising a plurality of elongated conductors;

[0038] a second layer comprising a semiconductive composition having a positive temperature coefficient, the semiconductive composition comprising at least one polyolefin component, such as polyethylene, polypropylene, or a mixture thereof, and a conductive filler, such that the conductor layer is sandwiched between and in contact with the first and second layers;

[0039] wherein the layer of the semiconductive composition is preferably contained in an extruded film having a longitudinal direction, and the conductor is preferably parallel to the longitudinal direction of the extruded film containing the layer of the semiconductive composition;

[0040] wherein the semiconductive composition has an electrical conductivity σ of 2 to 50 S / m measured at 40° C. according to the “Electrical Conductivity Method” described in the “Determination Methods”,

[0041] Where 20℃≤T Eq ≤50℃ and T Eq is defined as the temperature at which dσ / dT is at a minimum; and

[0042] There is no adhesive between the layers of the heater.

[0043] From another aspect, the present invention provides a method for preparing a multilayer flat electric heater, which comprises the steps of (a)

[0044] - providing and melt mixing in an extruder a first semiconductive composition comprising at least one polyolefin component such as polyethylene, polypropylene or a mixture thereof, and a conductive filler,

[0045] - providing and melt mixing in an extruder a second semiconductive composition comprising at least one polyolefin component such as polyethylene, polypropylene or a mixture thereof, and a conductive filler,

[0046] (b) applied by coextrusion onto a plurality of preferably uniformly spaced elongated conductors,

[0047] - a molten mixture of the first semiconductive composition obtained from step (a),

[0048] - a molten mixture of the second semiconducting composition obtained from step (a),

[0049] To form a multi-layer flat panel heater having three layers, the core layer comprises a plurality of preferably parallel uniformly spaced elongated conductors at least partially embedded in and in contact with the first and second semiconductive composition layers, wherein the average distance between the elongated conductors is preferably between 20 and 2000 mm;

[0050] wherein the layer of the semiconductive composition is preferably contained in an extruded film having a longitudinal direction, and the conductor is preferably parallel to the longitudinal direction of the extruded film containing the layer of the semiconductive composition;

[0051] wherein the semiconductive composition has an electrical conductivity σ of 2 to 50 S / m measured at 40° C. according to the “Electrical Conductivity Method” described in the “Determination Methods”,

[0052] Where 20℃≤T Eq ≤50℃ and T Eq Defined as the temperature at which dσ / dT is at a minimum.

[0053] From another aspect, the present invention provides a method for preparing a multilayer flat electric heater, which comprises the steps of (a)

[0054] - providing and melt mixing a first semiconductive composition in an extruder, and extruding the first semiconductive composition to form a first layer, the first semiconductive composition comprising at least one polyolefin component such as polyethylene, polypropylene or a mixture thereof, and a conductive filler,

[0055] - providing and melt mixing in an extruder a second semiconductive composition, and extruding the second semiconductive composition to form a second layer, the second semiconductive composition comprising at least one polyolefin component such as polyethylene, polypropylene or a mixture thereof, and a conductive filler,

[0056] (b) co-laminating the first and second layers with a plurality of preferably uniformly spaced elongated conductors, wherein the average distance between the elongated conductors is preferably between 20 and 2000 mm, to form a multilayer flat panel heater having three layers, the core layer comprising a plurality of preferably uniformly spaced elongated conductors sandwiched between and in contact with the first and second layers of the semiconductive composition;

[0057] wherein the layer of the semiconductive composition is preferably contained in an extruded film having a longitudinal direction, and the conductor is preferably parallel to the longitudinal direction of the extruded film containing the layer of the semiconductive composition;

[0058] wherein the semiconductive composition has an electrical conductivity σ of 2 to 50 S / m measured at 40° C. according to the “Electrical Conductivity Method” described in the “Determination Methods”,

[0059] Where 20℃≤T Eq ≤50℃ and T Eq Defined as the temperature at which dσ / dT is at a minimum.

[0060] Detailed description of the invention

[0061] The present invention relates to a sustainable flat panel electric heater that can be used for a wide variety of objects, particularly objects that come into close contact with humans or animals, to provide heat in a sustainable, safe, inexpensive and simple manner. The flat panel electric heater of the present invention uses the positive temperature coefficient (PTC) principle. To avoid overheating and potential damage to the object, the heater is self-regulating or self-limiting and does not require regulating electronics. Therefore, in one embodiment, the flat panel heater of the present invention does not include regulating electronics, such as a thermal cut-off device to prevent overheating.

[0062] Semiconducting composition components

[0063] The semiconducting composition does not overheat and does not require overheat protection. The technical solution of this particular invention is to use electric current through a semiconductor medium with PTC characteristics to convert electrical energy into thermal energy, thereby raising the temperature of the object above the temperature of its surroundings until a steady state (self-regulation) is reached.

[0064] Preferably the conductor is substantially parallel to the longitudinal direction of the semiconductive composition. The longitudinal direction is the direction in which the extruded film passes through the extruder or laminator. When heated, the film shrinks more in the longitudinal direction than in the transverse direction, so even in the final article, the orientation can be determined.

[0065] The semiconductive composition comprises a polyolefin and a conductive filler (e.g. carbon black). The self-regulating or self-limiting thermal phenomenon occurs due to two parallel opposing processes:

[0066] a. Poor conduction of electrons through semiconductor media produces electrical losses, which manifests as heat.

[0067] b. Thermal expansion of the non-conductive portions of the material leads to a further reduction in conductivity through separation of the conductive filler particles.

[0068] Once the two processes reach equilibrium, a stable high temperature plateau or self-regulating temperature is reached.

[0069] The present inventors have found that when a semiconductive composition having an electrical conductivity σ of 2 to 50 S / m measured at 40°C according to the "Electrical Conductivity Method" described in the "Determination Methods" is selected and the following equation is satisfied: 20°C ≤ T Eq ≤50℃, and T Eq Defined as the temperature at which dσ / dT is at a minimum, the flat panel heater is particularly suitable for close contact with humans or animals.

[0070] Preferably, the electrical conductivity σ of the semiconductive composition used in the flat heater of the present invention is equal to or higher than 4 S / m, preferably equal to or higher than 5 S / m or equal to or higher than 6 S / m, measured at 40°C according to the "Electrical Conductivity Method" described in the "Determination Methods", and preferably, the electrical conductivity σ is equal to or lower than 40 S / m, more preferably equal to or lower than 30 S / m, even more preferably equal to or lower than 25 S / m, even more preferably equal to or lower than 10 S / m, and most preferably equal to or lower than 14 S / m.

[0071] The higher the conductivity, the higher the heating power P H The inventors have found that good results are obtained when the conductivity measured at 40° C. according to the “Conductivity Method” described in the “Determination Methods” is between 4 and 40 S / m.

[0072] The relationship between the heating power and conductivity of the PTC material is derived below:

[0073] Heating power P of the object H It is equal to the applied direct current (DC) voltage "U" multiplied by the current "I":

[0074] P H =U×I (Equation 1)

[0075] The current "I" is equal to the voltage "U" divided by the resistance "R" of the object (Ohm's law):

[0076] I = U / R (Equation 2)

[0077] Therefore, the heating power P H It is equal to the voltage "U" squared divided by the resistance "R":

[0078] P H =U 2 / R (Equation 3)

[0079] The resistance "R" of a PTC object is proportional to its volume resistivity "VR", and therefore:

[0080] P H ∝1 / VR (Equation 4)

[0081] Now, the inverse of the volume resistivity "VR" is equal to the conductivity "σ" of the material, and therefore:

[0082] P H ∝σ(Equation 5)

[0083] The conductivity "σ" is a function of the temperature T, which means that the heating power P H (for a given applied voltage) also follows the same function.

[0084] P H (T)∝σ(T) (Equation 6)

[0085] If the heating power P H Higher than the heat loss P L , the temperature of the object will rise. H Relative to P L The higher it is, the faster the temperature rises.

[0086] The slope of σ(T) versus temperature T, i.e., the first derivative below the self-regulating temperature or dσ / dT, reflects the heating rate.

[0087] It should be understood that the flat panel heater preferably reaches a stable high temperature plateau quickly and therefore also has a high heating speed. Preferably, the first derivative or dσ / dT of the semiconductive composition used in the flat panel heater of the present invention between 23°C and 40°C is equal to or higher than -0.7S / (m·°C), preferably equal to or higher than -0.6S / (m·°C) or equal to or higher than -0.5S / (m·°C), and preferably equal to or lower than -0.05S / (m·°C), more preferably equal to or lower than -0.10S / (m·°C), even more preferably equal to or lower than -0.15S / (m·°C), wherein σ is measured according to the "Electrical Conductivity Method" described in the "Determination Methods".

[0088] As described above, the conductivity σ is a function of the temperature T. Therefore, the ratio of the conductivity σ measured at 23°C to the conductivity σ measured at 40°C according to the "Conductivity Method" described in the "Determination Methods" (σ(23°C) / σ(40°C)) will also reflect the heating rate. Therefore, preferably, the ratio σ(23°C) / σ(40°C) of the semiconductive composition used in the flat heater of the present invention is equal to or higher than 1.1, more preferably equal to or higher than 1.2, even more preferably equal to or higher than 1.3, still even more preferably equal to or higher than 1.4, and preferably equal to or lower than 3, more preferably equal to or lower than 2.5, more preferably equal to or lower than 2, more preferably equal to or lower than 1.8.

[0089] The inventors believe that the temperature at which the minimum dσ / dT occurs is equal to P H The fastest approach to P L The inventors further believe that the temperature at which dσ / dT is at a minimum is the optimum or equilibrium self-regulating temperature of the PTC material, further referred to as T Eq It should be understood that the minimum value here refers to the absolute minimum value of dσ / dT. For use in close contact with humans or animals, T Eq Should meet 20℃ <T Eq <50℃, where T EqDefined as the temperature at which dσ / dT is at a minimum.

[0090] Preferably, T Eq is equal to or higher than 25°C, more preferably equal to or higher than 28°C, even more preferably equal to or higher than 30°C, still even more preferably equal to or higher than 32°C, even more preferably equal to or higher than 34°C, most preferably equal to or higher than 35°C, and preferably, T Eq The inventors have found that when T Eq Meet 35℃≤T Eq Good results can be obtained at ≤40℃.

[0091] It should also be understood that the flat panel heater preferably has a certain self-regulating shut-down capability (i.e., reflected by a significant drop in heating power above 40°C). This shut-down capability is also reflected by the minimum value of dσ / dT (hereinafter referred to as min.dσ / dT) (i.e., the maximum drop in heating power with temperature). Preferably, the semiconductive composition used in the flat panel heater of the present invention has a min.dσ / dT equal to or higher than -0.7S / (m·°C), preferably equal to or higher than -0.6S / (m·°C) or equal to or higher than -0.5S / (m·°C), and preferably equal to or lower than -0.1S / (m·°C), more preferably equal to or lower than -0.2S / (m·°C), even more preferably equal to or lower than -0.3S / (m·°C), wherein σ is measured according to the "Electrical Conductivity Method" described in the "Determination Methods".

[0092] The ratio of the conductivity σ measured at 60°C to the conductivity σ measured at 40°C according to the "Conductivity Method" described in the "Determination Methods" (σ(60°C) / σ(40°C)) will also reflect the shutdown capability, that is, a lower ratio reflects improved shutdown capability. Therefore, preferably, the ratio σ(60°C) / σ(40°C) of the semiconductive composition used in the flat heater of the present invention is preferably equal to or lower than 0.9, more preferably equal to or lower than 0.7, more preferably equal to or lower than 0.6. The lower limit is not particularly limited, but is preferably equal to or higher than 0.1, more preferably equal to or higher than 0.2, and even more preferably equal to or higher than 0.3.

[0093] Polyolefin components

[0094] The semiconductive composition comprises at least one polyolefin component, such as polyethylene, polypropylene or a mixture thereof.

[0095] It should be understood that the origin of these materials is not particularly limited, meaning that virgin polyolefin components as well as recycled polyolefins or polyolefins produced from renewable resources may be used.

[0096] Suitable polyethylenes include high density polyethylene (density 940 kg / m 3 or higher), medium density polyethylene (density 930 to 940 kg / m 3 ) and low density or linear low density polyethylene (density 910 to 930 kg / m 3 ).

[0097] Suitable polypropylenes include homopolymers and copolymers of polypropylene. Suitable comonomers include ethylene.

[0098] Preferably polyethylene is used. If the heater comprises a plurality of semiconducting layers, preferably polyethylene, preferably the same polyethylene, is used in all these layers.

[0099] It is further preferred if the polyethylene is a polyethylene produced in an autoclave or tubular process, such as an LDPE homopolymer or copolymer.

[0100] In a preferred embodiment, the semiconductive composition used in the present invention comprises only one polyolefin component, preferably a LDPE homopolymer or copolymer. The inventors believe that the use of only one polyolefin component is beneficial because no reactants need to be included, which is better from a health safety and environmental (HSE) perspective and significantly reduces the risk of premature crosslinking (i.e., scorching) during extrusion. In addition, considering sustainable development, the design of materials also needs to take into account sustainable performance and focus on the possibility of facilitating its disposal when the final application reaches its service life (EOL) to promote a circular economy. The use of a single polyolefin component can achieve a "simpler" laminate heater design, which facilitates the disposal of the laminate heater when it reaches its service life, thereby improving sustainability performance.

[0101] Although the term LDPE is an abbreviation for low-density polyethylene, the term should be understood not to limit the density range, but to cover high-pressure (HP) polyethylene similar to LDPE. Compared with polyethylene produced in the presence of olefin polymerization catalysts, the term "LDPE" only describes and distinguishes the properties of HP polyethylene with typical characteristics, such as a different branching structure.

[0102] LDPE as the polyolefin refers to a low density homopolymer of ethylene (referred to herein as LDPE homopolymer) or a low density copolymer of ethylene and one or more comonomers (referred to herein as LDPE copolymer).

[0103] Preferably, the semiconductive composition comprises a LDPE copolymer. The one or more comonomers of the LDPE copolymer are preferably selected from polar comonomers, non-polar comonomers or mixtures of polar comonomers and non-polar comonomers. Furthermore, the LDPE homopolymer or LDPE copolymer may optionally be unsaturated.

[0104] As polar comonomers of the LDPE copolymer, comonomers containing carboxyl groups and / or ester groups are used as said polar comonomers. Still more preferably, the polar comonomers of the LDPE copolymer are selected from acrylates, methacrylates or acetates, or any mixtures thereof.

[0105] If present in the LDPE copolymer, the polar comonomer is preferably selected from alkyl acrylates, alkyl methacrylates or vinyl acetate, or mixtures thereof.

[0106] Further preferably, the polar comonomer is selected from C1- to C6-alkyl acrylates, C1- to C6-alkyl methacrylates or vinyl acetate. Still more preferably, the LDPE copolymer is a copolymer of ethylene and C1- to C4-alkyl acrylates, such as methyl acrylate, ethyl acrylate, propyl acrylate or butyl acrylate, or vinyl acetate, or any mixture thereof. Preferably, ethylene methyl acrylate (EMA), ethylene ethyl acrylate (EEA), ethylene butyl acrylate (EBA) or ethylene vinyl acetate (EVA) are used.

[0107] As nonpolar comonomers of the LDPE copolymer, preferred choices are polyunsaturated comonomers containing only C and H atoms. In a preferred embodiment, the polyunsaturated comonomer consists of a straight carbon chain having at least 8 carbon atoms and at least 4 carbon atoms between non-conjugated double bonds, at least one of which is terminal.

[0108] Preferred diene compounds are 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene or mixtures thereof. In addition, dienes such as 7-methyl-1,6-octadiene, 9-methyl-1,8-decadiene or mixtures thereof may also be mentioned.

[0109] If the LDPE polymer is a copolymer, it preferably comprises 0.001 to 40 wt%, more preferably 0.05 to 40 wt%, still more preferably 1 to 30 wt% of one or more comonomers. When polar comonomers are present, the comonomer content is preferably 5 to 30 wt%, such as 7.5 to 20 wt%.

[0110] The polyolefin may optionally be unsaturated, for example a LDPE polymer may contain carbon-carbon double bonds. The term "unsaturated" herein means that the polyolefin contains a total amount of at least 0.2 / 1000 carbon atoms, for example at least 0.4 / 1000 carbon atoms, of carbon-carbon double bonds / 1000 carbon atoms.

[0111] The polyolefin may be unimodal or multimodal, such as bimodal.

[0112] Preferably, the polyolefin has a melt flow rate MFR2.16 / 190°C of 0.1 to 50 g / 10 min, more preferably 0.3 to 20 g / 10 min, even more preferably 1.0 to 15 g / 10 min, and most preferably 2.0 to 10 g / 10 min.

[0113] Any LDPE homopolymer or copolymer may have a weight of 905 to 935 kg / m 3 , for example 910 to 925 kg / m 3 density.

[0114] The polyolefin may be produced by any conventional polymerization process. Preferably, it is LDPE and is produced by free radical polymerization such as high pressure free radical polymerization. The high pressure polymerization may be carried out in a tubular reactor or an autoclave reactor. Preferably, it is a tubular reactor. In general, the pressure may be in the range of 1200-3500 bar and the temperature may be in the range of 150° C.-350° C. Further details on high pressure free radical polymerization are given in WO93 / 08222, which is incorporated herein by reference. The polymers of the semiconductive composition are well known and commercially available.

[0115] The semiconductive composition may comprise at least 50 wt% polyethylene, polypropylene or a mixture thereof, such as at least 60 wt%. Any layer in which the semiconductive composition is present may consist of the semiconductive composition. Any layer in which the semiconductive composition is present may comprise at least 50 wt% polyethylene, polypropylene or a mixture thereof, such as at least 60 wt%. Once all other components are determined, polyethylene and / or polypropylene will form the balance of the semiconductive composition.

[0116] Conductive filler

[0117] According to the present invention, the semiconductive composition further comprises a conductive filler such as carbon black.

[0118] Suitable conductive fillers include graphite, graphene, carbon fibers, carbon nanotubes, metal powders, metal wires or carbon black. Preferably, carbon black is used.

[0119] In a preferred embodiment, the semiconductive composition used in the present invention comprises only one conductive filler, preferably carbon black, and preferably all semiconductive compositions in the multilayer flat panel heater comprise the same conductive filler.

[0120] It should be understood that "only one conductive filler" means only one type, for example when carbon black is used as the conductive filler, no other types of conductive fillers, such as graphite, graphene, etc., are present in the semiconductive composition.

[0121] The inventors believe that the use of only one conductive filler enables a "simpler" and therefore more economical laminate heater design which works surprisingly well.

[0122] The semiconductor properties are due to the added conductive filler. Therefore, the amount of conductive filler is at least such that a semiconductor composition is obtained. Depending on the desired use and conductivity of the composition, the amount of conductive filler can vary. It should be understood that different filler levels allow the heat generated to be adjusted. However, preferably, the semiconductive composition contains 5-50% by weight of conductive filler. In other preferred embodiments, the amount of conductive filler is 5-48% by weight, 10-45% by weight, 20-45% by weight, 25-45% by weight or 30-41% by weight, based on the weight of the semiconductive composition.

[0123] Any conductive carbon black may be used. Examples of suitable carbon blacks include furnace black, channel black, gas black, lamp black, thermal black and acetylene black. In addition, graphitized furnace black (produced by Imerys) and high structure carbon black (known as Ketjenblack produced by Nouryon) may also be used. Mixtures may also be used. When a carbon black mixture is used, the percentage refers to the sum of the carbon blacks present.

[0124] The carbon black may have a carbon content of 5 to 1500 m when measured according to ASTM D3037-93. 2 / g, for example 10 to 300 m 2 / g, for example 30 to 200 m 2 / g nitrogen surface area (BET). In addition, the carbon black may have one or more of the following properties:

[0125] i) a primary particle size of at least 5 nm, which is defined as the number average particle size according to ASTM D3849-95a,

[0126] ii) an iodine absorption number (IAN) of at least 10 mg / g, such as 10 to 300 mg / g, such as 30 to 200 mg / g, when determined according to ASTM D-1510; and / or

[0127] iii) a DBP (dibutyl phthalate) absorption value (= oil absorption value) of at least 30 cm when determined according to ASTM D 2414 3 / 100g, e.g. 60 to 300cm 3 / 100g, e.g. 70 to 250cm 3 / 100g, e.g. 80 to 200cm 3 / 100g, e.g. 90 to 180cm 3 / 100g.

[0128] In addition, carbon black may have one or more of the following properties:

[0129] a) a primary particle size of at least 15 nm, defined as the number average particle size according to ASTM D3849-95a;

[0130] b) an iodine value of at least 30 mg / g according to ASTM D1510;

[0131] c) an oil absorption value of at least 30 ml / 100 g as determined in accordance with ASTM D2414.

[0132] Furnace black is preferred. This is a generally accepted term for a well-known type of carbon black produced continuously in a furnace reactor. As examples of carbon black, its preparation method and reactor, reference may be made to EP-A-0629222, US 4,391,789, US 3,922,335 and US 3,401,020 to Cabot. As an example of a commercial furnace black grade described in ASTM D 1765-98b are N351, N293 and N550.

[0133] Other components

[0134] The composition can be crosslinked using peroxide or silane moisture cure systems. Radiation can also be used to crosslink, thus avoiding the use of crosslinking agents.

[0135] Preferably, cross-linking is avoided and the resulting sheet is a more recyclable product.The semiconductive composition of the present invention is preferably not cross-linked.

[0136] The inventors have found that it is advantageous not to crosslink the semiconductive composition of the invention as this reduces the risk of premature crosslinking (i.e. scorching) during extrusion, there are no decomposition products from the crosslinking reaction and no need to initiate crosslinking, e.g. by increasing the temperature, which is advantageous in many respects, including reduced environmental impact and significant improvements from a health safety and environment (HSE) perspective as well as from an economic perspective. Furthermore, the non-crosslinked composition can be easily recycled by remelting, which again contributes to improved sustainability performance.

[0137] Antioxidants

[0138] The semiconductive composition may contain an antioxidant. As antioxidants, mention may be made of sterically hindered or semi-hindered phenols, aromatic amines, aliphatic sterically hindered amines, organic phosphates, thio compounds, polymeric 2,2,4-trimethyl-1,2-dihydroquinoline, and mixtures thereof.

[0139] More preferably, the antioxidant is selected from 4,4'-bis(1,1'-dimethylbenzyl)diphenylamine, para-styrenated diphenylamine, 4,4'-thiobis(2-tert-butyl-5-methylphenol), polymerized 2,2,4-trimethyl-1,2-dihydroquinoline, 4-(1-methyl-1-phenylethyl)N-[4-(1-methyl-1-phenylethyl)phenyl]aniline or its derivatives.

[0140] More preferably, the antioxidant is selected from (but not limited to) 4,4'-bis(1,1'-dimethylbenzyl)diphenylamine, para-styrenated diphenylamine, 4,4'-thiobis(2-tert-butyl-5-methylphenol), 2,2'-thiobis(6-tert-butyl-4-methylphenol), distearylthiodipropionate, 2,2'-thiodiethyl-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, polymerized 2,2,4-trimethyl-1,2-dihydroquinoline or its derivatives. Of course, not only one of the above antioxidants can be used, but also any mixture thereof.

[0141] The amount of the antioxidant, optionally a mixture of two or more antioxidants, may be 0.005 to 2.5 wt%, for example 0.01 to 2.5 wt%, preferably 0.01 to 2.0 wt%, more preferably 0.03 to 2.0 wt%, especially 0.03 to 1.5 wt%, more especially 0.05 to 1.5 wt%, or 0.1 to 1.5 wt%, based on the weight of the semiconductor composition.

[0142] The semiconducting composition may comprise further additives. As possible additives, mention may be made of stabilizers, processing aids, flame retardant additives, acid scavengers, inorganic fillers, voltage stabilizers or mixtures thereof.

[0143] Preferably, the semiconductive composition has a volume resistivity measured at 90° C. of less than 500,000 Ohm·cm, more preferably less than 100,000 Ohm·cm, even more preferably less than 50,000 Ohm·cm.

[0144] conductor

[0145] The heater of the present invention comprises a plurality of conductors. The term "plurality" is used herein to mean at least 2, for example at least 4 conductors. Ideally, the sheet of the present invention comprises an even number of conductors. Ideally, in use, the conductors preferably have alternating polarity.

[0146] The elongated conductor can be made of any suitable conductive metal, typically copper or aluminum. The conductor can be in the form of a strip, foil or wire. The conductor can have a diameter or thickness of 0.05 to 2.0 mm. The conductor can have a width of 0.5 to 20 mm, such as 0.5 to 15 mm, 1.0 to 12 mm or 1.0 to 10 mm. The length of the elongated conductor is determined by the size of the plate. The elongated conductor should pass through most of the plate, such as the entire plate. Each conductor can be provided with electrodes to allow multiple conductors to be connected to each other, and to allow an external power supply to be applied to form a circuit and thus generate heat. The conductor can be designed to be directly weldable for easy installation.

[0147] The flat panel heater may comprise a minimum of 4 independent conductors, but it may comprise more conductors. The conductors are spaced apart from each other and therefore do not touch. Preferably, the conductors are substantially parallel to each other. Preferably, all conductors are evenly spaced apart from each other. Evenly distributed means that the distance between adjacent conductors is always substantially the same. The conductors are preferably linear and preferably oriented in a longitudinal direction relative to the semiconductor composition. However, in theory, the conductors may be curved (e.g. SS shape) so that they always remain equidistant from each other. We consider this to be "parallel".

[0148] The elongated conductors are preferably spaced an average distance of 20 to 2000 mm. In one embodiment, the average distance between the conductors is 20 to 1000 mm, such as 20 to 600 mm or 25 to 250 mm, preferably 30 to 200 mm, more preferably 35 to 150 mm, even more preferably 40 to 100 mm, even more preferably 40 to 90 mm and most preferably 40 to 80 mm.

[0149] In one embodiment of the invention, when the voltage is below 48 V, for example 12 V, the elongated conductors are preferably spaced an average distance of 20 to 150 mm, for example 25 to 130 mm, preferably 30 to 120 mm, more preferably 35 to 110 mm, even more preferably 40 to 100 mm, still even more preferably 40 to 90 mm, and most preferably 40 to 80 mm.

[0150] In an alternative embodiment of the invention, when the voltage is above 48V, for example 220 or 230V or 400V, the elongated conductors are preferably spaced an average distance of 20 to 1000mm, for example 25 to 130mm, preferably 30 to 120mm, more preferably 35 to 110mm, even more preferably 40 to 100mm, still even more preferably 40 to 90mm and most preferably 40 to 80mm.

[0151] These gaps between the conductors are very important to ensure that heat is generated quickly within the PTC material. If the conductors are too far apart, the PTC material takes a long time to warm up. Bringing the conductors closer together also allows lower voltages to be used in the device. This is important because the heaters can generate heat without the risk of electric shock, which makes them very suitable for close contact with humans or animals. Where higher voltages are used, such as where the heater is plugged into the main current, the risk of electric shock is greater. When the gaps between the conductors are reduced, for example a battery can generate sufficient heat. Therefore, in one embodiment, direct current is supplied to the heater. This forms another aspect of the invention. It is particularly preferred that the heater is supplied with direct current by a battery.

[0152] The conductors are in direct contact with the semiconductive composition. There should therefore be no layer separating the semiconductive composition from the conductors. The conductors must also be at least partially embedded in the semiconductive composition, i.e. they should not be located on top of or below the semiconductive composition, but at least partially surrounded by it.

[0153] In a preferred embodiment of the invention, the conductors are completely embedded in the semiconductive composition, i.e. they are completely surrounded by the semiconductive composition. This can be achieved when the conductors are coextruded with the semiconductive composition. It can also be achieved by sandwiching the conductors between two layers of the semiconductive composition.

[0154] When conductors are embedded in semiconducting compositions, we can avoid hot spots or localized overheating in the material.

[0155] The conductors are preferably parallel to the longitudinal direction of the semiconductor composition.

[0156] It should be understood that the conductor layer is not continuous and is formed by a plurality of discrete conductors, preferably parallel and preferably evenly spaced. The gaps between these discrete conductors are filled with a semiconductive composition, such as Figure 1 As shown, in a co-lamination or co-extrusion process.

[0157] Production

[0158] It will be appreciated that a flat panel self-regulating heater according to the present invention may be produced with thicknesses, customized conductor spacing and varying filler levels to allow customization of the heat generated.

[0159] The temperature rise in the semiconducting composition is mainly controlled by the distance between the parallel conductors, the thickness of the semiconducting composition, the amount of conductive filler present, and the applied voltage. Closer conductors increase the temperature at which a stable high temperature plateau is reached. Thicker semiconductor compositions in the slab increase the temperature at which a stable high temperature plateau is reached.

[0160] The increase in the conductive filler content increases the temperature at which a stable high temperature plateau is reached.

[0161] An increase in the applied voltage increases the temperature at which a stable high temperature plateau is reached.

[0162] The claimed flat panel heater may be prepared by co-lamination. In such a process, the two semiconductive layers may be prepared, for example, by extrusion. They may be allowed to cool before co-lamination occurs. The layers may be identical or different. Ideally, they are identical. The layers preferably have the same thickness.

[0163] These layers can then be used to sandwich the conductor layers. Thus, one layer is placed above the conductors and one layer is placed below the conductors, and the whole is pressed together. Thus, the gaps between the conductors are filled with the semiconducting layers. It should be understood that the conductor layers are typically very thin compared to the semiconducting layers.

[0164] One surface of one or both semiconductive layers may be heated prior to co-lamination so that when co-laminated together, the semiconductive layer adheres to the conductor and to the other semiconductive layer without the use of a separate adhesive. In this way, the conductor layer is at least partially embedded in the semiconductive composition.

[0165] In a particularly preferred embodiment, lamination between layers occurs only in the vicinity of the conductors. For example, a strip on either side of each conductor may be melted to allow the two layers to adhere to each other. For example, a strip of 5 mm on either side of the conductor location in a flat heater may be melted in one or both layers to allow the layers to adhere. The width of the melted strip may be 5 to 20 mm, for example 10 to 20 mm, on either side of the conductor location. The width of the melted strip may be adjusted depending on the gap between the conductors.

[0166] The area on the sheet where the conductor is located may also be melted to allow the conductor to adhere to the flat heater during the lamination process. Therefore, the total thickness of the strip to be melted may take into account the diameter of the conductor itself. Thus, for a 2mm diameter conductor, 5mm is melted on each side of the conductor for lamination, and the total width of the melted strip is 12mm.

[0167] Outside these fused strips, the two layers are not laminated together and are therefore able to move independently. This provides the flat heater with enhanced flexibility, which is very important for applications such as heating clothing where the heater must be flexible. In this regard, it is conceivable that it is also advantageous when the semiconducting film used in the heater according to the invention is perforated so as to "breathe".

[0168] Figure 3 The proposed method is described in which a conductor is placed on a layer of a flat heater and strips on either side of the conductor are melted to adhere the second sheet to the first. Conveniently, the conductor adheres to the sheet during the lamination process so the area beneath the conductor location is also melted.

[0169] It should be understood that the fused strips may be located on one or both layers of the laminate.

[0170] From another aspect, the present invention provides a method for preparing a multilayer flat electric heater, which comprises the steps of (a)

[0171] - providing and melt mixing in an extruder a first semiconductive composition and extruding the first semiconductive composition to form a first layer, the first semiconductive composition comprising at least one polyolefin component such as polyethylene, polypropylene or a mixture thereof, and a conductive filler,

[0172] - providing and melt mixing in an extruder a second semiconductive composition, and extruding the second semiconductive composition to form a second layer, the second semiconductive composition comprising at least one polyolefin component such as polyethylene, polypropylene or a mixture thereof, and a conductive filler,

[0173] (b) co-laminating the first and second layers with a plurality of uniformly spaced elongated conductors, wherein the average distance between the elongated conductors is preferably between 20 and 150 mm, to form a multilayer flat panel heater having three layers, the core layer comprising a plurality of preferably uniformly spaced elongated conductors sandwiched between and in contact with the first and second layers of the semiconductive composition;

[0174] wherein the first and second layers are bonded only by strips extending from 50 to 200 cm on either side of each conductor;

[0175] wherein the semiconductive composition has an electrical conductivity σ of 2 to 50 S / m measured at 40° C. according to the “Electrical Conductivity Method” described in the “Determination Methods”,

[0176] Where 20℃≤T Eq ≤50℃ and T Eq Defined as the temperature at which dσ / dT is at a minimum.

[0177] As explained, the claimed flat panel heater can be prepared using coextrusion or colamination. However, the heater of the present invention is preferably not a typical laminate, where the layers are prepared separately and laminated together using an adhesive. Our product does not require an adhesive to form the desired heater.

[0178] Therefore, the heater of the present invention can be produced continuously.

[0179] Importantly, the semiconductor composition can be extruded onto the conductors and thus the conductors are at least partially embedded in the semiconductor composition during the extrusion process rather than being separately adhered to the semiconductor composition. Thus, the semiconductor composition forming a layer above and below a plurality of conductors can be continuously extruded onto the conductors.

[0180] Thus, the process described herein is one that can be operated continuously to maximize the value of the product formed. The heater of the present invention is inexpensive. It is thin and flexible.

[0181] Therefore, if Figure 3 As shown, two semiconducting layers are preferably coextruded together to surround the center conductor.

[0182] In a preferred embodiment of the present invention, the method comprises the step (a):

[0183] - providing and melt mixing in an extruder a first semiconductive composition comprising at least one polyolefin component such as polyethylene, polypropylene or a mixture thereof, and a conductive filler,

[0184] providing and melt mixing in an extruder a second semiconductive composition comprising at least one polyolefin component such as polyethylene, polypropylene or a mixture thereof, and a conductive filler,

[0185] (b) applied by coextrusion onto a plurality of preferably uniformly spaced elongated conductors,

[0186] - a molten mixture of the first semiconductive composition obtained from step (a),

[0187] - a molten mixture of the second semiconducting composition obtained from step (a),

[0188] To form a flat panel heater having three layers, the core layer comprises a plurality of preferably parallel uniformly spaced elongated conductors at least partially embedded within and in contact with said first and second conductive layers, said first and second conductive layers comprising said semiconductive composition;

[0189] wherein the layer of the semiconductive composition is preferably contained in an extruded film having a longitudinal direction, and the conductor is preferably parallel to the longitudinal direction of the extruded film containing the layer of the semiconductive composition;

[0190] wherein the semiconductive composition has an electrical conductivity σ of 2 to 50 S / m measured at 40° C. according to the “Electrical Conductivity Method” described in the “Determination Methods”,

[0191] Where 20℃≤T Eq ≤50℃ and T Eq Defined as the temperature at which dσ / dT is at a minimum.

[0192] The process can be adjusted at any time to add more layers above or below the semiconductor layer.

[0193] In one embodiment, cross-linking conditions may then be applied to induce a cross-linking reaction.

[0194] Melt mixing refers to mixing above the melting point of at least the major polymer components in the mixture, and is usually carried out at a temperature at least 10-15°C higher than the melting point or softening point of the polymer components.

[0195] The term coextrusion herein refers to extruding two or more layers in the same extrusion step. The term "coextrusion" refers to using one or more extrusion heads to form all or part of the layers at the same time. For example, three extrusions can be used to form three layers.

[0196] Thus, the heater of the present invention may be considered as a multi-layer flat-panel heater, which comprises, in order, a first layer comprising a semiconductive composition having a positive temperature coefficient, the semiconductive composition comprising at least one polyolefin component, such as polyethylene or polypropylene, and a conductive filler;

[0197] a conductor layer comprising a plurality of spaced apart conductors;

[0198] a second layer comprising a semiconductive composition having a positive temperature coefficient, the semiconductive composition comprising at least one polyolefin component, such as polyethylene, polypropylene, or a mixture thereof, and a conductive filler, such that the conductor layer is at least partially embedded within and in contact with the first and second layers;

[0199] wherein the semiconductive composition has an electrical conductivity σ of 2 to 50 S / m measured at 40° C. according to the “Electrical Conductivity Method” described in the “Determination Methods”,

[0200] Where 20℃≤T Eq ≤50℃ and T Eq Defined as the temperature at which dσ / dT is at a minimum.

[0201] The electrode is at least partially embedded in the semiconducting layer and preferably parallel to the longitudinal direction of the polymer layer.The two semiconducting compositions may be the same or different, preferably the same.

[0202] Once coextrusion is complete, the material can be subjected to well known crosslinking conditions to crosslink the formed flat sheet, if desired.

[0203] Plate heater

[0204] The heater is in the form of a flat plate, which is sustainable, flexible, light and cheap. The heater may be provided with one or more additional layers to protect the semiconducting composition from damage. For example, the aesthetic top layer may be a textile, non-woven fabric or a solid sheet material (rubber, plastic, paper, wood, metal, etc.). The top layer may be extrudable, such as a polyolefin layer. In view of sustainability (recycling), it is preferred that no top layer is used or that the top layer comprises the same material as the semiconducting composition.

[0205] In one embodiment, the heater is provided with an isolating layer or a heat reflecting layer at the bottom of the heater. Such an isolating layer may be electrically isolating, thermally isolating or both. Such a layer improves the efficiency of the heater. Such a layer may comprise a polyolefin, such as polyethylene, especially LDPE, such as LDPE homopolymer. A preferred isolating layer uses LDPE as the only polymer component. Such a layer is preferably a co-extruded layer, although lamination of the layer is also an option.

[0206] Most preferably, any additional layers are also coextruded. In one embodiment, the heater comprises a five-layer structure, with the conductor forming the central layer, embedded in two semiconductive layers, which in turn are protected by further layers. This is an ABCDE type structure. Layers A / E and B / D need not be identical.

[0207] Preferably, the semiconducting layers have substantially the same thickness.

[0208] Preferably, an insulating layer and / or a heat reflecting layer may be located below the semiconductor composition. This layer may reduce heat loss. It may also provide mechanical protection for the semiconductor layer and provide strength to the plate.

[0209] In a particularly preferred embodiment, the use of an additional insulating layer is avoided. This makes the heater cheaper. Since the conductors in the claimed invention are close together and allow the voltage required to power the heater to be reduced, there is no need to use an insulating layer. In the case of using higher voltages, the insulating layer is used to protect the PTC material and to protect the user from possible electric shock. In our device, depending on the application and the applied voltage, there is no need to use such a layer. Therefore, the heater of the present invention can be composed of the required conductor layer and semiconductor layer.

[0210] In use, an electric current is applied to the heater through a conductor to generate heat. Typically, the voltage is 10 to 70 V, such as 10 to 55 V, preferably 10 to 40 V, such as 12 to 30 V. Application of electricity to the flat heater results in almost instantaneous heating. As the voltage used does not need to be very high, there is no risk of electric shock, which makes it ideal for use in close contact with humans or animals. The heater may be powered by batteries or directly from the mains via a suitable adapter.

[0211] The heater itself can achieve self-regulation within 300 seconds after power is applied. Preferably, the heater will reach its self-regulating temperature between 50 and 250 seconds after power is applied. Therefore, the heater achieves self-regulation at an extremely fast speed.

[0212] The thickness of the heater itself is preferably at most 20 mm, preferably at most 10 mm, for example 0.25 to 5 mm. The thickness of the key semiconducting composition layer may be 100 to 900 μm, for example 125 to 800 μm.

[0213] The width of the heater can be easily adjusted to any possible use. The width can be determined by the coextrusion or co-layer lamination device and sheets from 3cm to 5 meters can be easily produced.

[0214] As mentioned previously, the heating power of a panel heater can be controlled by the thickness of the sheet, the spacing of the conductors, the amount of conductive filler, and the voltage applied. Moving the conductors closer together increases the wattage, which increases the heat generated. The relationship can be expressed as Power = [Voltage] 2 / resistance.

[0215] Because the layer of the semiconducting composition is so thin, the flat panel heater of the present invention is very flexible, making it very useful in environments where flexibility is critical. Such environments include heating clothing or heating car seats, where the flat panel heater needs to bend to operate effectively.

[0216] Thicker plates tend to increase power output.

[0217] The simplicity of the claimed flat panel heater is also important as this makes it very cheap to manufacture. The whole device can be manufactured using co-extrusion or co-lamination. No adhesives etc are required.

[0218] application

[0219] The flat panel heater of the present invention can be used in many fields, but is particularly suitable for close contact with humans or animals. Therefore, the application of the technology described herein is wide.

[0220] We often provide winter thermal comfort by heating the entire air volume in a room or building. In earlier times, our ancestors had a more local concept of heating: heating people, not places. They used radiant heat sources to heat only certain parts of a room to create comfortable microclimates. These people dealt with large temperature differences with insulated furniture, such as hooded chairs and folding screens, and they utilized additional personal heating sources to warm specific body parts. With sustainable living in mind, reviving this ancient way of warming makes a lot of sense, especially as modern technology has made it more practical, safe, and efficient.

[0221] Therefore, the heater of the present invention can be used in furniture items such as screens, chairs or sofas.

[0222] In one embodiment, the heater of the present invention can be used in heated clothing. Today's heated clothing has small wires built into it (usually made of brittle carbon fiber). When a low voltage current passes through them, they will heat up. There are two main types of heated clothing, battery powered or vehicle powered (such as heated gloves on motorcycles). The heater of the present invention is very suitable for both applications.

[0223] The heater can also be used in blankets. One of the main problems with electric blankets currently on the market is the risk of fire. These blankets easily overheat. Using the heater of the present invention eliminates this risk.

[0224] Radiators are bulky, immovable and often unsightly. In many parts of the world, radiators are hidden behind more aesthetically pleasing covers of various designs. These covers can also reduce noise or prevent contact with an overheated radiator. But hiding a radiator is not efficient because adding a radiator cover slows down the rate at which heat flows out of the radiator and into the room. The rate of heat loss through the building's exterior may increase.

[0225] The panels of the invention can replace radiators or be used as heaters in walls, under floors, ceilings. The heaters can even be incorporated into carpets or rugs or other floor coverings.

[0226] Electric vehicles generate almost no heat compared to conventional passenger cars, which generate enough engine heat to heat the interior. Therefore, electric vehicles require additional electric heaters to heat the interior.

[0227] The power for this heater is provided by the same battery that powers the engine. This can significantly reduce the maximum possible driving range.

[0228] Therefore, it is necessary to heat electric vehicles as efficiently as possible. The invention can be used to heat interior contact surfaces in the vehicle, such as steering wheels, armrests, door panels, seats. Compared with heating the entire interior of the car, more efficient heating can be envisaged, especially for short trips.

[0229] The heater of the present invention can be used to prevent the accumulation of ice or snow on critical surfaces such as solar panels. Therefore, the heater may be useful in de-icing operations. Other surfaces may be rearview mirrors.

[0230] The heater is also flexible and can be wrapped around pipes to prevent the liquid in them from freezing. In addition, the heater can also be used to keep liquids heated, such as those in swimming pools or liquid containers. BRIEF DESCRIPTION OF THE DRAWINGS

[0231] Figure 1 is a theoretical diagram of the flat heater of the present invention. Semiconductor layers A and B sandwich conductors uniformly distributed in the plate. The top layer and the bottom layer sandwich the semiconductor layer. The top layer is aesthetically pleasing, and the bottom layer acts as an isolation layer or a heat reflective layer. In some embodiments, the top layer and / or the bottom layer can be removed. Therefore, a particularly preferred structure is simply semiconductor layers A and B with a conductor layer. It is further preferred that the semiconductor layer materials in layers A and B are the same and the thickness of layers A and B is the same.

[0232] Figure 2Seen from above Figure 1 A cross-sectional view of a flat panel heater of the present invention. A plurality of conductors are embedded in the semiconductive layers. These layers are formed by co-lamination or co-extrusion of the semiconductor composition and the conductors. They have alternating polarity.

[0233] Figure 3 is a schematic diagram of the manufacturing process. Figure 3 The arrangement in results in a 5-layer structure with an aesthetically pleasing top layer, a first semiconducting layer, a conductor layer, a second semiconducting layer and a barrier layer. The conductor is distributed as a metal electrode strip to form a center layer in a coextruded or colaminated sheet. The semiconducting composition is coextruded or colaminated to form a layer on either side of the conductor, wherein the top and bottom layers are coextruded or colaminated on the upper and lower surfaces of the semiconducting layer. In the case of coextrusion, the relevant polymers are melted and coextruded through a die to a nip roll and then passed through another roll to form a multilayer flat sheet. The nip roll may be heated and / or coated to prevent the polymer melt from adhering to the roll.

[0234] The bottom layer is usually in contact with the heated roller for a quarter turn, while the other layers are in direct contact with the layer below. Most of the heat reaches the lower layer. At the beginning of the rotation, the two rollers are separated by a distance of, for example, 0.3 mm. The three layers are then aligned with the second roller for half a turn and then passed over the third roller for a quarter turn.

[0235] Current can then be applied by connecting the conductor to a power source.

[0236] Figure 4 A cross section of one layer of a flat panel heater is shown where the strips on either side of the conductor are melted to allow co-lamination with a second sheet.

[0237] Figures 5 to 7 The conductivity σ and the normalized conductivity are shown as a function of temperature T as well as the first derivative of the conductivity dσ / dT. Tables 1 and 2 summarize the data. DETAILED DESCRIPTION

[0238] Example

[0239] Manufacturing method

[0240] Self-regulating heating laminates are made in a continuous process.

[0241] A semiconductive composition was prepared containing about 61.2 wt% of a copolymer of ethylene and vinyl acetate (MFR2 at 190°C of about 7.0 g / 10 min), 0.4 wt% of an antioxidant, 0.4 wt% of an acid scavenger and about 38 wt% of carbon black. This will be used in the following examples.

[0242] Determination method

[0243] Conductivity method

[0244] Samples with a width (w) of 25 mm and a length of 160 mm are punched out of the extruded film. The samples are dried at 60° C. for about 5 hours and then stored in a desiccator for a minimum of 16 hours. For the actual volume resistivity (VR) determination, the electrodes are connected to the sample with a gap of 130 mm. In order to compensate for the so-called contact resistance, two additional electrodes are connected at a distance of 10 mm from the measuring electrode. The electrodes are connected to a device (such as a multimeter or VOM device) that can provide the resistance (R) between the electrodes. The resistance R is measured in ohms. The volume resistivity (VR) is calculated by multiplying the resistance (R) by the cross-sectional area (A) of the sample, where A=h*w (3*25 mm) of the sample, divided by the length (L) between the electrodes (130 mm) or VR=R*A / L / . The conductivity σ is then calculated as σ=1 / VR.

[0245] Example 1 - Conductivity of Semiconductor Compositions

[0246] Table 1 below lists the relationship between conductivity σ and temperature T. In addition, Table 2 calculates the first-order derivative of conductivity, revealing the equilibrium temperature T Eq , at which the conductivity versus temperature has the steepest negative slope, i.e., dσ / dT is at its minimum. As mentioned earlier, this can be considered the optimum or equilibrium self-regulating temperature of the material. Eq At temperatures between 20 and 50°C, such as 37.5°C as shown in Table 2, the material is well suited for applications involving close contact with humans and / or animals.

[0247] Table 1 - Measured volume resistivity, conductivity and normalized conductivity

[0248]

[0249] Table 2 - Slope of conductivity as a function of temperature, i.e. calculated first-order derivative of conductivity

[0250]

[0251] 1 (T2+T1) / 2

[0252] 2 dσ / dT is calculated from (σ2–σ1) / (T2–T1).

Claims

1. A flat electric heater, preferably obtained by coextrusion or colamination, comprising: a plurality of elongated conductors, which are preferably evenly spaced apart from one another and are preferably substantially parallel to one another, The conductor is at least partially embedded in and in contact with a semiconductive composition having a positive temperature coefficient (PTC), the semiconductive composition comprising at least one polyolefin component such as polyethylene, polypropylene or a mixture thereof, and a conductive filler, wherein the semiconductive composition is preferably contained in an extruded film having a longitudinal direction, and the conductor is preferably parallel to the longitudinal direction of the extruded film containing the semiconductive composition; wherein the semiconductive composition has an electrical conductivity σ of 2 to 50 S / m measured at 40° C. according to the “Electrical Conductivity Method” described in the “Determination Methods”, and Where 20℃≤T Eq ≤50℃ and T Eq Defined as the temperature at which dσ / dT is at a minimum.

2. The multilayer flat electric heater according to claim 1, preferably obtained by co-extrusion or co-lamination, more preferably obtained by co-lamination, which comprises in sequence: a first layer comprising a semiconductive composition having a positive temperature coefficient, the semiconductive composition comprising at least one polyolefin component such as polyethylene, polypropylene or a mixture thereof, and a conductive filler; a conductor layer comprising a plurality of elongated conductors uniformly spaced apart from each other and substantially parallel to each other, wherein the distance between the elongated conductors is 20 to 2000 mm; a second layer comprising a semiconductive composition having a positive temperature coefficient, the semiconductive composition comprising polyethylene, polypropylene or a mixture thereof, and a conductive filler, such that the conductor layer is sandwiched between and in contact with the first and second layers; wherein the layer of the semiconductive composition is preferably contained in an extruded film having a longitudinal direction, and the conductor is preferably parallel to the longitudinal direction of the extruded film containing the layer of the semiconductive composition; wherein the semiconductive composition has an electrical conductivity σ of 2 to 50 S / m measured at 40° C. according to the “Electrical Conductivity Method” described in the “Determination Methods”, Where 20℃≤T Eq ≤50℃ and T Eq Defined as the temperature at which dσ / dT is at a minimum.

3. The multilayer flat electric heater according to claim 2, wherein the flat electric heater is provided with at least one further layer above the first layer and / or at least one further layer below the second layer, preferably an insulating layer, such as a thermal insulating layer.

4. A flat electric heater according to any one of the preceding claims, wherein the semiconductive composition comprises a LDPE homopolymer or a LDPE copolymer, preferably an ethylene alkyl acrylate or ethylene vinyl acetate polymer, and / or wherein the semiconductive composition of the invention is not crosslinked.

5. A flat electric heater according to any one of the preceding claims, wherein: The conductive filler comprises carbon black, and wherein the semiconductive composition preferably comprises only one conductive filler.

6. A flat electric heater according to any one of the preceding claims, wherein: The semiconductor composition has an electrical conductivity σ of 4S / m to 40S / m, preferably 5S / m to 30S / m, more preferably 6S / m to 25S / m, even more preferably 6S / m to 10S / m, and / or an electrical conductivity of 23°C to 40°C measured according to the "Electrical Conductivity Method" described in the "Determination Methods". First order derivative or dσ / dT, Equal to or higher than -0.7S / (m·℃), preferably equal to or higher than -0.6S / (m·℃) or equal to or higher than -0.5S / (m·℃), and preferably, equal to or lower than -0.05S / (m·℃), more preferably equal to or lower than -0.10S / (m·℃), even more preferably equal to or lower than -0.15S / (m·℃), and / or wherein the minimum value of the first-order derivative dσ / dT, further referred to as min.dσ / dT is equal to or higher than -0.7S / (m·℃), preferably equal to or higher than -0.6S / (m·℃) or equal to or higher than -0.5S / (m·℃), and preferably, equal to or lower than -0.1S / (m·℃), more preferably equal to or lower than -0.2S / (m·℃), even more preferably equal to or lower than -0.3S / (m·℃).

7. A flat electric heater according to any one of the preceding claims, wherein: T Eq is equal to or higher than 25°C, more preferably equal to or higher than 28°C, even more preferably equal to or higher than 30°C, still even more preferably equal to or higher than 32°C, even more preferably equal to or higher than 34°C, most preferably equal to or higher than 35°C, and preferably, T Eq Equal to or lower than 48°C, more preferably equal to or lower than 46°C, even more preferably equal to or lower than 44°C, still even more preferably equal to or lower than 42°C and most preferably equal to or lower than 40°C.

8. A flat electric heater according to any one of the preceding claims, comprising more than 6 conductors and / or the conductors are fully embedded in and fully surrounded by the semiconductive composition.

9. A flat electric heater according to any one of the preceding claims, wherein: The thickness of the semiconductor composition layer may be from 100 to 900 μm, for example from 125 to 800 μm, and / or wherein the heater has a thickness of from 0.25 to 20 mm.

10. A flat panel heater as claimed in any preceding claim which is free of adhesive.

11. A method for preparing a multilayer flat electric heater, comprising the steps of: (a) - providing and melt mixing in an extruder a first semiconductive composition comprising polyethylene, polypropylene or a mixture thereof, and a conductive filler, - providing and melt mixing in an extruder a second semiconductive composition, said second semiconductive composition comprising polyethylene, polypropylene or a mixture thereof, and a conductive filler, (b) applied by coextrusion onto a plurality of uniformly spaced elongated conductors, - a molten mixture of the first semiconductive composition obtained from step (a), - a molten mixture of the second semiconducting composition obtained from step (a), To form a multi-layer flat panel heater having three layers, the core layer includes a plurality of parallel uniformly spaced elongated conductors at least partially embedded within and in contact with the first and second semiconductive composition layers; The semiconductive composition layer is preferably contained in an extruded film having a longitudinal direction, and the conductor is preferably parallel to the longitudinal direction of the extruded film containing the semiconductive composition layer.

12. A method for preparing a multilayer flat electric heater, comprising the steps of: (a) - providing and melt mixing in an extruder a first semiconductive composition and extruding the first semiconductive composition to form a first layer, the first semiconductive composition comprising polyethylene, polypropylene or a mixture thereof, and a conductive filler, - providing and melt mixing in an extruder a second semiconductive composition and extruding the second semiconductive composition to form a second layer, the second semiconductive composition comprising polyethylene, polypropylene or a mixture thereof, and a conductive filler, (b) laminating the first and second layers with a plurality of uniformly spaced elongated conductors, wherein the elongated conductors The distance between the first and second semiconductive composition layers is 20 to 1000 mm to form a multilayer flat panel heater having three layers, the core layer comprising a plurality of uniformly spaced elongated conductors sandwiched between and in contact with the first and second semiconductive composition layers; The first and second layers are bonded only by strips extending 50 to 200 cm on either side of each conductor.

13. An article of manufacture comprising a flat electric heater as claimed in claims 1 to 12, such as heated clothing or a car seat.

14. A method of heating an article comprising supplying an electric current to the article, the article comprising a flat electric heater according to claims 1 to 12, wherein the conductors have alternating polarity.

15. Use of a flat electric heater according to claims 1 to 12 for heating an object (e.g. heating clothing or heating a car seat) or heating an environment (e.g. a room), wherein the voltage supplied to the flat electric heater is 10 to 70 V, e.g. 12 to 40 V, and / or wherein the heater is powered by direct current.

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