Patent Application
20130260078
The present invention relates to a core material for a vacuum insulation panel that is formed with a cured phenolic resin foam, a vacuum insulation panel using the core material, and a method for manufacturing the vacuum insulation panel. More particularly, the present invention relates to a technology for manufacturing a vacuum insulation panel with high thermal insulation performance and good long-term durability at reduced cost by using a cured phenolic resin foam having a closed cell content of 20% or less as a core material.
A general vacuum insulation panel is manufactured by accommodating a core material, such as an open cell hard plastic foam or an inorganic material, in an encapsulation material composed of a composite plastic laminate film having superior gas barrier properties, reducing the internal pressure of the encapsulation material, and heat sealing the circumferential edges of the laminated gas barrier films.
An inorganic compound with low thermal conductivity and outgassing is suitably used as a core material for a vacuum insulation panel. Particularly, a vacuum insulation panel using a glass fiber laminate as a core material is known to have high thermal insulation performance.
In a conventional vacuum insulation panel, glass fiber wool or a glass fiber board is used alone as a core material. Glass fiber wool is produced by collecting a bulky glass fiber, followed by thermal pressing. The use of glass fiber wool as the core material can ensure thermal insulation performance of the vacuum insulation panel at a level of 0.45 W/mK.
The use of glass fiber wool as a core material for a vacuum insulation panel can ensure high initial thermal performance of the vacuum insulation panel, but gases permeate the vacuum insulation panel through a shell film during long-term use to increase the thermal conductivity of the vacuum insulation panel, resulting in deterioration of long-term durability.
In contrast, the use of a glass fiber board as a core material for a vacuum insulation panel can minimize the thermal conduction of gases permeating the vacuum insulation panel due to the small diameter of pores of the glass fiber board despite long-term use. The vacuum insulation panel has the advantage of good long-term durability but is disadvantageous in terms of initial thermal insulation performance.
In conclusion, the vacuum insulation panel using glass fiber wool as a core material has a relatively short service life due to its poor long-term durability. This causes a problem of low reliability when the vacuum insulation panel is applied to home appliances as well as construction materials where a long service life of at least 10 years is required.
Problems encountered in the use of a glass fiber board as a core material are high manufacturing cost and inferior molding properties, which limit the application of the vacuum insulation panel to a thermal insulation material.
An aspect of the present invention is to provide a core material that is formed with a cured phenolic resin foam having a closed cell content of 20% or less, achieving low production cost, high thermal insulation performance and good long-term durability.
Another aspect of the present invention is to provide a vacuum insulation panel including a core material formed with a cured phenolic resin foam wherein the core material includes cells having an average diameter of 50 to 500 nm and the cells have fine holes with an average diameter of 0.5 to 30 nm on the outer circumferential surfaces thereof to allow the cured phenolic resin foam to have a void content (which is defined as a percent of portions other than the solid in the foam) of at least 50%, thereby achieving improved structural strength and light weight, which enables its utilization in various applications.
In accordance with one aspect of the present invention, a core material for a vacuum insulation panel is formed with a cured phenolic resin foam having a closed cell content of 20% or less.
Preferably, the cured phenolic resin foam includes cells having an average diameter of 50 to 500 μm, and the cells have fine holes with an average diameter of 0.5 to 30 μm on the outer circumferential surfaces thereof to allow the cured phenolic resin foam to have a void content of at least 50%.
In accordance with another aspect of the present invention, a vacuum insulation panel includes a core material formed with a cured phenolic resin foam and a shell material surrounding the core material wherein the core material is packaged within the shell material under vacuum.
Preferably, the vacuum insulation panel further includes at least one getter material attached to or inserted into the core material and having a moisture absorption of at least 25%.
In accordance with another aspect of the present invention, a method for manufacturing a vacuum insulation panel includes producing a core material formed with a cured phenolic resin foam, applying a pressure of 0.5 to 10 Pa to the core material at a temperature of 50 to 250° C. for 10 to 200 minutes to remove remnants from the core material, and surrounding the core material with a shell material, followed by vacuum packaging.
The production cost of the core material of the present invention using a cured phenolic resin foam can be reduced to half or less that of a general core material using glass fiber wool.
In addition, the core material of the present invention uses a cured phenolic resin foam having a thermal conductivity of 0.03 W/mK or less. The high thermal insulation performance of the cured phenolic resin foam can maximally prevent deterioration of the performance of the core material resulting from thermal conduction.
Furthermore, the amount of organic compounds released from the cured phenolic resin foam is minimized, which prevents the degree of vacuum of the vacuum insulation panel from dropping and the overall thermal insulation performance of the vacuum insulation panel from deteriorating. Therefore, the thermal insulation performance of the vacuum insulation panel can be maintained for a long time of at least 10 years.
The above and other aspects, features, and advantages of the invention will become apparent from the detailed description of the following embodiments in conjunction with the accompanying drawings. It should be understood that the present invention is not limited to the following embodiments and may be embodied in different ways, and that the embodiments are given to provide complete disclosure of the invention and a thorough understanding of the invention to those skilled in the art. The scope of the invention is defined only by the claims. Like reference numerals indicate like elements throughout the specification and drawings.
Now, a core material for a vacuum insulation panel formed with a cured phenolic resin foam and a method for producing the core material according to preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
First, the core material and the method of the present invention will be discussed.
The closed cell content is defined as a fraction of closed cells in all cells formed per unit area. If the closed cell content exceeds 20%, the time for subsequent vacuum processing may be increased and gases may remain in the cured phenolic resin foam, causing outgassing in a final vacuum insulation panel.
Meanwhile, a closed cell content of 0% represents a physically impossible state that has a volume but no shape. Accordingly, the lower limit of the closed cell content is adjusted to greater than 0%.
The closed cell content is particularly preferably in the range of 1 to 10%. Within this range, the initial thermal insulation value of the core material is maintained at a low level and an increment in the thermal insulation value of the core material over time is considerably small.
The cured phenolic resin foam used in the core material of the present invention should meet requirements in terms of structural strength and closed cell content. To this end, the cured phenolic resin foam preferably includes cells 110 having an average diameter of 50 to 500 μm and the cells have fine holes with an average diameter of 0.5 to 30 μm on the outer circumferential surfaces thereof.
Referring to
Referring next to
The fine holes 120 serve to adjust the closed cell content to 20% or less while maintaining the structural strength of the core material despite the low closed cell content of the cured phenolic resin foam.
If the average diameter d of the fine holes 120 is less than 0.5 μm, the closed cell content of the cured phenolic resin foam exceeds 20%, and as a result, the core material 100 suffers from outgassing, which may deteriorate the long-term durability of a vacuum insulation panel. Meanwhile, if the average diameter d of the fine holes 120 is greater than 30 μm, the closed cell content approaches 0%, which may deteriorate the structural strength of the core material 100.
A vacuum insulation panel of the present invention includes a core material formed with a cured phenolic resin foam and a shell material surrounding the core material wherein the core material is packaged within the shell material under vacuum. The vacuum insulation panel may further include at least one getter material attached to or inserted into the core material.
The getter material functions to prevent the generation of gases and moisture within the shell material due to changes in external temperature. The getter material will be explained below.
Referring to
The cured phenolic resin foam used in the core material is produced by mixing a phenolic resin, a curing agent, a foaming agent, and one or more additives at a high stirring rate, and curing the mixture at room temperature or above. Water may be generated as a reaction product and monomers may remain unreacted. The reaction product and the unreacted monomers increase the probability of outgassing during vacuum packaging or after manufacture of the vacuum insulation panel.
In the present invention, it is preferred to apply a pressure of 0.5 to 100 Pa to the core material at a temperature of 50 to 250° C. for 10 to 200 minutes before vacuum packaging to remove remaining monomers (formaldehyde, remaining phenol, water) from the core material.
Such pressurization can minimize the generation of gases and moisture in the core material, thus eliminating the need to use the getter material. Moreover, the void content of the cured phenolic resin foam used in the core material of the present invention can be maintained at a high level (at least 50%) due to the low shrinkage of the cured phenolic resin foam (less than 20%), leading to high performance.
Next, the shell material serves as an encapsulation material surrounding the core material. A detailed explanation will be given concerning the shape and production method of the shell material.
The shell material 300 illustrated in
The adhesive layer 330 or 440 is thermally welded to the core material by heat sealing and functions to maintain the vacuum state of the vacuum insulation panel. For this function, the adhesive layer 330 or 440 is formed of at least one thermoplastic plastic film selected among high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), cast polypropylene (CPP), oriented polypropylene (OPP), polyvinylidene chloride (PVDC), polyvinyl chloride (PVC), ethylene-vinyl acetate copolymer (EVA) and ethylene-vinyl alcohol copolymer (EVOH) films, all of which are easily thermally welded to the core material. The thickness of the adhesive layer is preferably in the range of 1 to 100 μm. Within this range, sufficient sealing properties are provided.
Next, the barrier layer 320 or 430 formed on the adhesive layer 330 or 440 functions to block gases and protect the core material. The barrier layer 320 or 430 is formed of a metal thin film having a thickness of 6 to 7 μm. The most general material for the metal barrier layer 320 or 430 is an aluminum foil. Aluminum foil is used because no thin films are known to have superior characteristics to aluminum foil. Aluminum is apt to crack when folded due to material traits thereof. The surface protective layer 310 formed on the metal barrier layer 320 or 430 functions to prevent the occurrence of cracks.
Preferably, the surface protective layer of the shell material has a laminate structure of a 10 to 14 μm thick polyethylene terephthalate (PET) film 410 and a 20 to 30 μm thick nylon film 420.
Severe cracks may occur in the metal barrier layer 430, causing damage to the polyethylene terephthalate film 410/nylon film 420. In the present invention, a vinyl resin layer is coated on the polyethylene terephthalate layer to protect the polyethylene terephthalate film 410/nylon film 420 against damage.
The vinyl resin layer is preferably formed using at least one vinyl resin selected among polyvinyl chloride (PVC), polyvinyl acetate (PVA), polyvinyl alcohol (PVAL), polyvinyl butyral (PVB), and polyvinylidene chloride (PVDC) resins.
The surface protective layer 310, the metal barrier layer 320 or 430, and the adhesive layer 330 or 440 are preferably adhered to one another using polyurethane (PU) resins to further improve the air-tightness of the shell material.
The formation of the shell material 300 or 400 allows the vacuum insulation panel of the present invention to have optimal air-tightness and good long-term durability.
The vacuum insulation panel illustrated in
The vacuum insulation panel structures exhibit high thermal insulation performance and good long-term durability, and will be explained in detail with reference to the following examples.
First, a cured phenolic resin foam having the structure explained with reference to
Next, a shell material was prepared. Specifically, the shell material had a structure consisting of a 12 μm thick polyvinylidene chloride (PVDC)/polyethylene terephthalate film (PET), a 25 μm thick nylon film, a 7 μm thick aluminum foil, and a 50 μm thick linear low density polyethylene (LLDPE) film.
Then, two getter materials were prepared. Specifically, each of the getter materials was produced by putting 25 g of unslaked lime (CaO) having a purity of 95% in a pouch. The getter materials were inserted into the surface of the core material, as illustrated in
Then, a pressure of 5 Pa was applied to the core material at a temperature of 150° C. for 120 min to release all remaining gases from the core material.
Thereafter, the core material was inserted into the encapsulation material and sealed at a degree of vacuum of 10 Pa, completing the manufacture of a vacuum insulation panel.
A vacuum insulation panel was manufactured in the same manner as in Example 1, except that a cured phenolic resin foam including cells whose average diameter was 100 μm and having a closed cell content of 5%, a void content of 93% and a size of 8 mm (thickness)×190 mm (width)×250 mm (length) was used as a core material.
A vacuum insulation panel was manufactured in the same manner as in Example 1, except that a cured phenolic resin foam including cells whose average diameter was 100 μm and having a closed cell content of 10%, a void content of 90% and a size of 8 mm (thickness)×190 mm (width)×250 mm (length) was used as a core material.
A vacuum insulation panel was manufactured in the same manner as in Example 1, except that a cured phenolic resin foam including cells whose average diameter was 100 μm and having a closed cell content of 20%, a void content of 90% and a size of 8 mm (thickness)×190 mm (width)×250 mm (length) was used as a core material.
A vacuum insulation panel was manufactured in the same manner as in Example 1, except that a glass fiber board having a size of 8 mm (thickness)×190 mm (width)×250 mm (length) was used as a core material.
A vacuum insulation panel was manufactured in the same manner as in Example 1, except that a polyurethane foam including cells whose average diameter was 150 μm and having a closed cell content of 2%, a void content of 95% and a size of 8 mm (thickness)×190 mm (width)×250 mm (length) was used as a core material.
A vacuum insulation panel was manufactured in the same manner as in Example 1, except that a cured phenolic resin foam including cells whose average diameter was 100 μm and having a closed cell content of 50%, a void content of 90% and a size of 8 mm (thickness)×190 mm (width)×250 mm (length) was used as a core material.
A vacuum insulation panel was manufactured in the same manner as in Example 1, except that a cured phenolic resin foam including cells whose average diameter was 200 μm and having a closed cell content of 80%, a void content of 60% and a size of 8 mm (thickness)×190 mm (width)×250 mm (length) was used as a core material.
[Performance Testing and Evaluation]
Each of the vacuum insulation panels manufactured in Examples 1-4 and Comparative Examples 1-4 was placed in a thermostatic chamber at 85° C. and allowed to stand for 3 months. The thermal conductivities of the vacuum insulation panels were compared with those of unheated specimens. The thermal conductivities were measured using a thermal conductivity tester (HC-074-200, EKO). Next, an acceleration factor was applied to predict the thermal conductivities of the vacuum insulation panels after 0-10 years. The results were expressed in W/mK and are shown in Table 1.
The vacuum insulation panels of Examples 1-4 had lower initial thermal conductivities and showed smaller increments over time than the vacuum insulation panels of Comparative Examples 1-4. Particularly, the vacuum insulation panel of Example 1, which was manufactured using the cured phenolic resin foam having a closed cell content of 1%, showed much smaller increments over time than the vacuum insulation panels of the other examples.
Therefore, the vacuum insulation panels of Examples 1-4, each of which was manufactured using the cured phenolic resin foam, had superior initial thermal insulation performance and good long-term durability.
Although the present invention has been described herein with reference to the foregoing embodiments, it is not limited to the embodiments and may be embodied in various different forms. Those skilled in the art will appreciate that the present invention may be practiced otherwise than as specifically described herein without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the embodiments are to be considered illustrative in all aspects and are not to be considered as limiting the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2010-0134982 | Dec 2010 | KR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/KR2011/009481 | 12/8/2011 | WO | 00 | 6/12/2013 |
