Title of Invention

"METHOD FOR FABRICATING VACUUM INSULATION MATERIAL CORE"

Abstract

Method for fabricating a vacuum insulation material core, including the steps of (1) injecting a foaming liquid into molds at required temperatures, (2) physically compressing the injected foaming liquid at a time point in a period during which a polyurethane formation reaction proceeds, whereby microcells formed by the polyurethane formation reaction are altered into open type cells, whereby saving a fabricstion cost, and improving a property of the insulating material because enclosed type cells can be opened into homogeneous open type cells by a physical force, that dispense with expensive cell opener.

Full Text

Field of the invention The present invention relates to a method for fabricating a vacuum insulation material core, and more particularly, to a method for fabricating a vacuum insulation material core, which can save a production cost and improve properties of an insulating material. Background of the Related Art In order to make a fresh storage of food for a long time, an inner temperature should be maintained below a certain temperature. Therefore, in order to conserve cold air formed in the refrigerator and cut off infiltration of an external heat into the refrigerator, insulating material is placed between an inner case and an outer case of the refrigerator during fabrication of the refrigerator. In general, polyurethane foam is used as an insulating material for the refrigerator. The polyurethane foam is a thermosetting resin formed by causing polyester or polyether type polyhydric alcohol and diisocyanic acid ester to make reaction under presence of catalyst, such as water to form polyurethane fiber, when the polyurethane become porous consisting of micrometer unit cells of carbon dioxide freed during the reaction process. In this instance, in order to accelerate foaming of the polyurethane foam, a foaming agent is added. Accordingly, the pores of the polyurethane foam are filled with the foaming agent gas, and the carbon dioxide. In general CFC, HCFC, and cyclopentane, the foaming agent gases, and the carbon dioxide have a high heat conductivity that deteriorates an insulating property the polyurethane insulating material. Therefore, the cells in the polyurethane insulating material are opened and the filled foaming agent gas and the carbon dioxide are removed for preparing a vacuum insulating material that has a high insulating property. However, the vacuum insulating material cost high due to a complicated forming process. Therefore, in fabrication of the refrigerator, the vacuum insulating material is inserted between the inner case ant the outer case as a core, and the spaces around the core is filled with a general polyethane foam. FIG.1 illustrates a related art method for fabricating a vacuum insulating material core. Referring to FIG.1, the related art method for fabricating a vacuum insulating material core is as follows. First foaming liquid, a mixture of polyol, cell opener foaming agent, silicon foam surfactant catalyst, and other additives and isocyanate, second foaming liquid are injected into an injector 1 and mixed. Foaming liquid B, which is a mixture of the first foaming liquid and the second foaming liquid, is made to flow down onto a heated conveyor CB through an opening at a bottom of the injector. Then the third foaming liquid 'B' is converted into the polyurethane insulating material 'PI' by reaction between the first foaming liquid and the second foaming liquid. In this instance, the foaming liquid 'B' is heated and compressed into panel type of polyurethane insulating material'PI' by upper and lower heater belts 3 of the conveyer CB moved in one direction by a plurality of upper and lower rollers 2.The panel type polythrane insulating material 'PI' formed thus is cut by a cutter 4 on one side of the conveyer CB into the vacuum insulating material core. In the meantime, as shown in FIG.2, as explained, the first foaming liquid and the second foaming liquid are mixed, and caused to make reaction, to form polyurethane fiber with a plurality to of enclosed type cells 'C' of micrometer units filled with foaming agent gas 'C' and carbon dioxide gas 'G'. And, as shown in FIG.3, the enclosed type cells 'C' (see FIG.2) are opened by the cell opener, a chemical mixed in the first foaming liquid, after elapse of a certain time period, to form opened type cells 'C'. The cell opener is activated at an elevated temperature. However, while the cell opener is activated effectively in an inner portion of the foaming liquid due to a high reaction temperature of the foaming liquid, the cell opener shows poor activation in upper and lower portions of the foaming liquid due to a low temperature conning from contact with an external air. In this instance, the heated heater belt 3 (see FIG.1) helps to compensate foe the low temperature in the surface portions of the foaming liquid. However, since the heat compensation by means of the heater belt 3 has nothing but a limitation, there is still a temperature difference between the inner portion and the surface portion of the foaming liquid. A detailed explanation of the action of the cell opener in the opening the enclosed type cells will be omitted as the action is known and not directly related to the present Invention. In the meantime, in order to complete the polyurethane insulating material 'PI' (see FIG.1) into a vacuum insulating material gaseous components 'G' in the insulating material should be removed. To do this, at first, a getter having zeolite, activated carbon, or chemical adsorbent attached to a surface thereof is inserted into the polyurethane insulating material 'PI'. Since the getter is gas absorptive, remained gas is removed from the polyurethane insulating material 'PI' then, After the polyurethane insulating material 'PI' (see FIG.1) is put into a envelope 10b of stacked films of metal and plastic, the envelope 10b is placed in a vacuum gas extraction apparatus 10, and the gas components in the opened cells 'C' in the polyurethane insulating material 'PI' is extracted to a certain level of vacuum through a discharge opening 10.Then, the entire envelope 10b is sealed, to complete formation of the vacuum insulating material core 5. Thus, the vacuum insulating material can compensate for the low insulating efficiency of the general polyurethane insulating material. That is, since the vacuum insulating material has gone through cell 'C' opening to increase a porosity and removal of foaming agent gas and the like in the cell. Which have low insulating properties, if the vacuum insulating material is buried with the general polyurethane insulating material in the refrigerator, an insulating performance of the refrigerator can be improved, significantly. However, there are the following problems in fabricating the vacuum insulating material having the enclosed type cells 'C' according to the related art method. First, the cell opener material required additionally for forming the open type cells, and high quality polyol and special isocyaanate reaction liquid additionally required for homogeneous formation of the micro cells uniformly all over the insulating material cost high and in the related art, in order to lead the foaming liquid to make an appropriate reaction on the conveyor to harden into a polyurethane insulating material having open type cells, an adequate length of the conveyor should be secure.., that requires a complicated, and large sized production equipment, which results in a high production cost. Second, the open type cells in the core of the related art vacuum insulating material is not homogeneous, because the cell opening is dependent on the chemical reaction, of which reaction condition may vary. As explained, there is a temperature difference between the inner and surface portions of the foaming liquid when the foaming liquid makes a chemical reaction on the conveyor as well as in the compression force between the upper and lower heater belts. Accordingly, the inner portion of the foaming liquid with a higher temperature and smaller compression force forms the open type cells well, while the surface portion of the foaming liquid with a lower temperature and greater compression force forms the open type cells poorly. At the end, in order to obtain a vacuum insulating material core with homogeneous cells formed therein, 30-70% of upper and lower portions of the insulating material formed in a panel form should be cut away, with a substantial scrap loss. SUMMARY OF THE INVENTION Accordingly, the present invention is directed to a method for fabricating a vacuum insulation material core that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. An object of the present invention is to provide a method for fabricating a vacuum insulation material core, which permits to fabricate a vacuum insulation material core having open type cells by using low cost equipment. Other object of the present invention is to provide a method for fabricating a vacuum insulation material core, which can improve an insulating property of an insulating material, such as homogeneous distribution of the open type cell, and the like. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantage of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the method for fabricating a vacuum insulation material core includes the steps of (1) injecting a foaming liquid into molds at a required temperatures, and (2) physically compressing the injected foaming liquid at a time point in a period during which a polyurethane formation reaction proceeds, whereby micro cells formed by the polyurethane formation reaction are altered are into open type cells, thereby permitting to dispense with expensive cell opener required for forming opener open type cells in the polyurethane insulating material, and the large scale related art production equipment, whereby saving a production cost. The compression during the polyurethane formation reaction is carried out by press, whereby permitting fabrication of the vacuum insulating material core by using simple production equipment. The time point of the compression is after a gel time, whereby preventing a build up of foaming pressure even after the compression, which leads to formation of thick surface layers, that impedes formation of the cell. The time point of the compression is a time point between a gel time and a tact free time, thereby permitting uniform opening of the cells before finish of hardening of the vacuum insulating material, whereby making a strength of the insulating material uniform. That is, the compression after the tact free time at which the polyurethane formation reaction is almost completed when the foaming liquid has almost no adhesive force is a compression after the polyurethane fiber is hardened, the compression is not uniform, that impedes formation of the open type cells, and strength of the insulating material is not uniform. The time point of the compression is the tact free time, thereby obtaining the most homogeneous open type layer. A compression ratio in the compression is 40~80%, thereby permitting to fabricate a vacuum insulating material core, which has a high insulating property and low production cost. That is, the compression ratio below 40% causes to have a low insulating property due to less open type cells, and he compression higher than 80% causes to have a higher density of the vacuum insulating material core, to increase consumption of the foaming liquid, that in turn increases a production cost. A compression rate in the compression 0.5~2mm/sec, thereby permitting to uniform compression of the vacuum insulating material core, to reduce a deviation of the strength of the core. In other aspect of the present invention, there is provided a method for fabricating a vacuum insulation material core, comprising the steps of (1) setting temperatures of upper and lower molds and an initial thickness H1 of the core, (2) injecting a foaming liquid into the molds at the set temperatures, (3) compressing the foaming liquid at a time point between a gel time and a tact free time by a press, to form a vacuum insulating material core (4) taking the vacuum insulating material core formed by compression out of the molds, (5) inserting an adsorbent into a surface of the vacuum insulting material core, (6) inserting the vacuum insulting material core into an envelope of stacked films of metal and plastic,(7) extracting gas in the envelope by a vacuum gas extracting equipment down to a preset vacuum, and (8) sealing the envelope of the vacuum insulting material core, thereby preventing a loss caused by scrap because homogeneous open type cells can be formed in the polyurethane insulting material by compressing the foaming liquid, and permitting to increase compression strength and a bending strength because the gas in the open type cells are extracted to form a vacuum insulating material core, whereby preventing shrinkage of the vacuum insulating material core and generation of less gas therein, to permitting to maintain the insulting properly for a long time. The temperature of the upper mold is set higher than the temperature of the lower mold, thereby suppressing formation of the high density insulting material surfaces, which impedes extraction of the gas from the insulting material by means of vacuum. a tact free time by apres for the first time to 30-35 % of the initial thickness H1 of the vacuum insulating material core, (4) compressing the vacuum insulating material core compressed for the first time at a time point between the gel time and.the tact free time or within one hour since the tact free time for the second time to a final thickness H2, (5) taking the vacuum insulating material core compressed for the second time out of the molds, (6) inserting adsorbent into surfaces of the taken out vacuum insulating material core, (7) inserting the vacuum insulating material core into an envelope of stacked films of metal and plastic, (8) extracting gas in the envelope by a vacuum gas extracting equipment down to a preset vacuum, and (9) sealing the envelope of the vacuum insulating material core, thereby saving time and efforts required for taking out the insulating material for two time as the first and second compressions are carried out in the same molds in situ. It is to be understood that the forgoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. STATEMENT OF THE INVENTION: This invention relates to : • A method for fabricating a vacuum insulation material core, comprising the steps of: a) setting temperatures of upper mold 50 ~ 70°C, lower mold 40- 60°C and an initial thickness H1 of the core; b) injecting a foaming liquid into the molds at the set temperatures; c) compressing the foaming liquid by compression rate 0.5- 2 mm/ sec and compression ratio 40 - 80% at a time point between a gel time and a tact free time by a press, to form a vacuum insulating material core; d) taking the vacuum insulating material core formed by compression out of the molds; e) inserting an adsorbent into a surface of the vacuum insulating material core; f) inserting the vacuum insulating material core into an envelope of stacked films of metal and plastic; g) extracting gas in the envelope by a vacuum gas extracting equipment down to a preset vacuum; and h) sealing the envelope of the vacuum insulating material core. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principle s of the invention in the drawings: FIG 1 illustrates related art method for fabricating a vacuum insulating material core. FIG 2 illustrates a section of enclosed type cells in the related art Polyurethane core. FIG 3 explains gas extraction process from open type cells in the related art method for fabricating a vacuum insulating material core FIG.4A illustrates a state foaming liquid is injected in a mold in a method for fabricating a vacuum material core in accordance with a preferred embodiment of the present invention; FIG.4B explain foaming liquid is pressed by a compression press in a method for fabricating a vacuum insulating material core in accordance with a preferred embodiments of the present invention; FIG.5A illustrates a flow chart for explaining the steps of a method for fabricating a vacuum-insulating core in accordance with a first preferred embodiment of the present inventions; FIG.5B illustrates a flow chart for explaining the steps of a method for fabricating a vacuum insulating core in accordance with a second preferred embodiments of the present invention; and, FIG.5C illustrates a flow chart explaining the steps of a method for fabricating a vacuum insulating core in accordance with a third preferred embodiments of the present invention. DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings FIG4A illustrates a state foaming liquid is injected in a mold in a method for fabricating a vacuum insulating material core in accordance with a preferred embodiments of the present invention, and FIG.4B explains foaming liquid is pressed by a compression press in a method for fabricating a vacuum insulating material core in accordance with a preferred embodiments of the present invention. Referring to FIGS. 4A and 4B, the method for fabricating a vacuum insulating material core has two steps, of which first one is the step of injecting a foaming liquid 'B' into a lower mold 20 with a rectangular sectional groove, which is at an elevated temperature of 40~70°C. In this instance, a gap between lower mold 20 mold 20 with a rectangular sectional groove, which is at an elevated temperature of 40~70°C. In this instance, a gap between lower mold 20 and an upper mold 22 is fixed as an initial thickness H1 of the vacuum insulating material core. The second one is a step of pressing the foaming liquid at a fixed rate until the polyurethane insulating material reaches to a final thickness H2 by means of the compression press 24 in contact with the upper mold after a gel time which is a time the foaming liquid 'B' injected in the mold starts reaction to form the polyurethane fiber. By doing so. The micro enclosed type cells formed by the polyurethane reaction are bursted, to form open type cells. Then, the polyurethane insulating material is taken out of space between the upper mold 22 and the lower mold 24,and corner portions of four surfaces and surface layers are removed, to complete fabrication of a vacuum insulating material core. The aforementioned method for fabricating a vacuum insulating material core of the present invention requires no addition of the cell opener for opening the cells by causing the polyurethane liquid to make a chemical reaction, because the enclose type cells formed during the foaming process is physically bursted into open type cells. In formation of the open type cells in the present invention, temperatures of the upper and lower molds, a time to start pressing, a compression ratio and rate are important factors. Particularly, the temperatures of the upper and lower molds vary formation of high density layers on surfaces, which impede extraction of gas from inside of the insulating material by means of vacuum. And, it is preferable that the temperature of the upper mold is set higher than the temperature of the lower mold for suppressing formation of the high density layers in the lower mold. According to a result of experiments, it is known that 50-70° C of the upper mold temperature and 40-60° C of the lower mold temperature yield the most homogenous open type cells. The time to start pressing should be set after the gel time at which the injected foaming liquid starts to make reaction to form the polyurethane fiber, and, preferably, should be at the tact free time when the reaction is almost completed and the foaming liquid loses an adhesive force, for obtaining the best open type cells. If the time to start pressing is set to be before the gel time, formation of the cells are impeded as a foaming pressure increases even after the compression, to form a thicker surface layer. And, if the polyurethane is pressed after the tact free time, the pressed state is not homogeneous as it is the same with pressing the polyurethane after the reaction is completed, that also impedes formation of the open type cells and results in failure in obtaining an insulating material of uniform strength. The compression ratio can be expressed as an equation shown below, which is in arrange of 40~80% of the initial thickness H1. Compression ratio (%) = (1-H2) (1.) Where, H1 denotes an initial thickness of a vacuum insulating material core set for injecting a foaming liquid into the lower mold, and H2 denotes a final thickness of the vacuum insulating material core compressed by a compression press. In this case too, a compression ratio below 40% yields less open type cells are formed to be closer to true spheres, which deteriorate insulating property due to a higher heat transfer caused by radiation. Opposite to this, a compression ratio higher than 80% yields a final vacuum insulating material core with very high density, resulting in consumption of much foaming liquid that leads to a high production cost. The method for fabricating a vacuum insulating material core will be explained through specific embodiments of the present invention. FIG. 5A illustrates a flow chart for explaining the steps of a method for fabricating a vacuum insulating core in accordance with a first preferred embodiment of the present invention. Referring to FIG. 5A, the method for fabricating a vacuum insulating core in accordance with a first preferred embodiment of the present invention starts with setting temperatures of a lower mold 20(seeFIG.4A) and an upper mold 22(seeFIG.4A), and an initial thickness H1 (step 50), and injecting a foaming liquid between the lower molds 20 and the upper mold 22 (step 52). In this instance, the temperatures of the upper and lower molds are preferably set within a range of 40-70° C, which are important factors for suppressing formation of high density layers on surfaces of the polyurethane foam, that impedes vacuum extraction. Preferably, the temperatures of upper mold 22 is set to be 50-70° C, and the temperature of the lower mold 20 is set to be 40~60°C, and the temperature of the lower mold 20 is set to be 40~60°C to be lower then the temperature of upper mold 22 for obtaining the most homogeneous open type cells. Then, the foaming liquid is pressed at a fixed rate (step54) until the foaming liquid reaches to a preset final thickness H2 by using a compression press 24(seeFIG.4A) mounted in contact with the upper mold 22 at a time point between a gel time and a tact free time for physically bursting enclose type cells formed during formation of polyurethane fiber, to form open type cells. The compression ratio is preferably within a range of 40-80%, and the compression rate is preferably at 0.5~2.0mm/sec. Though the compression rate give not so much influence to the formation of the open type cells, a uniform compression of the insulating material can reduce deviation of the strength. After the insulating material is left for a time period in the molds for hardening the insulating material, the insulating material is removed (step 56). The leaving time period of insulating material is set to be 5to 15 minutes, which should be longer than the same in the related art. The water used as a foaming agent for foaming the vacuum insulating material core in the present invention causes to require a longer leaving time period due to much reaction heat, otherwise the hardening is not complete when the vacuum insulating material core is liable to deform, that deteriorates a dimensional stability of the vacuum insulating material core. Than, four corners and surface layers of the insulating material are removed by approx.5% of below (step58), to complete fabrication to a final vacuum insulating material core or the surface layers may not be removed. Because the cells are bursted by physical compression, a foaming liquid with /without the cell opener can be used in the present invention, that can save a production cost. The vacuum insulating material core fabricated thus has zeolite, activated carbon, or chemical adsorbent inserted into surface thereof, is put into an envelop of stacked films of metal-plastic, and placed in a vacuum gas extraction equipment for extraction of all gases in the open type cell in the core to a certain degree of vacuum and sealing the entire envelope, to complete fabrication of the vacuum insulating material core. A second embodiment of the present invention will be explained with references to FIGS. 4A.4B and 5B. The method for fabricating a vacuum insulating core in accordance with the second preferred embodiment of the present invention is identical to the first embodiment of the first present invention in view of the steps of setting mold temperatures and an initial temperatures (step 50), injecting a foaming liquid into the molds (step52), primary pressing (step54), leaving the insulating material for hardening (step56), and removing surface layers and corner portions of the insulating material (step 58), except that, in the second embodiment, the insulating material, once subjected to the primary compression and left for hardening, is subjected to secondary compression at a ratio of 10 to 15% in the mold again after removal of the surface layers and four corners of the insulating material (step59). By doing so, the incomplete opened cells in the primary compression can be opened by 100%. The secondary compression should be conducted within 12-24 hours after the primary compression is finished. This is for bursting the cells not opened in the primary compression once again before stabilization of an inner temperature generated from the foaming reaction of this insulating material, which is after 24 hours since the primary compression. A third embodiment of the present invention will be explained with reference to FIG.5C. In the third embodiment the compression step in the first embodiment is divided into two steps. That is, a first compression is conducted at a compression rate of 0.5~2.0 mm/sec until the initial thickness H1 is compressed down to 30~50% of the initial thickness starting at the gel time or a time point between the gel time and the tact free time. And, the second compression is conducted at compression of 0.5~ 2.0 mm/sec until the thickness reaches to a final thickness at a point between the gel time and the tact free time or within one hour since the tact free time, for obtaining 100% opened cell (step 55). In this instance, different from the compression rate in the first compression, the compression rate in the second compression may be faster than the 2.0 mm/sec. Since the fabrication process is identical to the first embodiment, a detailed explanation will be omitted. The conduction of the compression of the foaming liquid with the steps divided in to two sub steps, not only permits formation of the opened cells to the maximum, but also saves the time and efforts required for leaving for hardening and removing the insulating material from the molds for two times, different from the second embodiment, because the first compression the second compression are done in the same molds. As has been explained the method for fabricating a vacuum insulation material core of the present invention has the following advantages. First, the cell opening by physical force, which can dispense with the costly cell opener and the large sized fabrication equipment required for maximizing the cell opener reaction, permits to save the production cost. Second, different from the related art the method for fabricating a vacuum insulation material core of the present invention opens the cell, not by chemical reaction, but by physical force. That is, the compression of the foaming liquid at an appropriate time and a fixed rate permits to form homogenous open type cells in the polyurethane insulating material, which improves properties of the vacuum insulating material, which improves properties of the vacuum insulating material, that prevents a loss of the polyurethane insulating material caused by much scrap. The production cost can be reduced because the high quality polyol and the special iscoyinate reaction liquid can be dispensed with in the formation of homogenous open type cells. Third, the compression of the foaming liquid and extraction of gas in the open type cells in the formation of the vacuum insulating material core strengthen compression and bending strengths of the vacuum insulating material core. Accordingly, the vacuum insulating material applied as a core in the refrigerator exhibits no shrinkage or deformation, and the less gas generated from inside of the core, that permits of maintain an insulating performance for a long time. It will be apparent to those skilled in the art that various modifications and variations can be made in the method for fabricating a vacuum insulation material core of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modification and variation of this invention provided they come within the scope of the appended claims and there equivalent. We claim: 1. A method for fabricating a vacuum insulation material core, comprising the steps of: a) setting temperatures of upper mold 50 ~ 70°C, lower mold 40~ 60°C and an initial thickness H1 of the core; b) injecting a foaming liquid into the molds at the set temperatures; c) compressing the foaming liquid by compression rate 0.5~ 2 mm/ sec and compression ratio 40 ~ 80% at a time point between a gel time and a tact free time by a press, to form a vacuum insulating material core; d) taking the vacuum insulating material core formed by compression out of the molds; e) inserting an adsorbent into a surface of the vacuum insulating material core; f) inserting the vacuum insulating material core into an envelope of stacked films of metal and plastic; g) extracting gas in the envelope by a vacuum gas extracting equipment down to a preset vacuum; and h) sealing the envelope of the vacuum insulating material core. 2. A method as claimed in claim 1, wherein the temperature of the upper mold is set higher than the temperature of the lower mold in the step (a). 3. A method as claimed in claim 1, wherein the time point of compression is the tact free time in the step (c). 4. A method as claimed in claim 1, wherein the vacuum insulating material core is left for 5~15 minutes before taking the vacuum insulating material core out of the molds in the step (d). 5. A method as claimed in claim 1, wherein the adsorbent in the step (e) is zeolite or activated carbon. 6. A method as claimed in claim 1, wherein there is a step of removing four corner portions and surface layers of the vacuum insulating material core by below 5% between the steps (d) and (e).

Documents:

518-del-2000-abstract.pdf

518-del-2000-claims.pdf

518-del-2000-correspondence-others.pdf

518-del-2000-correspondence-po.pdf

518-del-2000-description (complete).pdf

518-del-2000-drawings.pdf

518-del-2000-form-1.pdf

518-del-2000-form-19.pdf

518-del-2000-form-2.pdf

518-del-2000-form-26.pdf

518-del-2000-form-3.pdf

518-del-2000-form-4.pdf

518-del-2000-form-5.pdf