WO2020057836A1

WO2020057836A1 - A core material compound, a vacuum insulation panel and a cooling device

Info

Publication number: WO2020057836A1
Application number: PCT/EP2019/070634
Authority: WO
Inventors: Tugce ONER; Yusuf YUSUFOGLU; Cahit Can CANAKCI; Orcun YUCEL
Original assignee: Arcelik Anonim Sirketi
Priority date: 2018-09-20
Filing date: 2019-07-31
Publication date: 2020-03-26

Abstract

The present invention relates to a core material (2) comprising at least one silica-based powder compound as core material with improved thermal properties and strength which is homogeneously mixed, to a vacuum insulation panel (1) and to a cooling device (4) comprising said panel (1).

Description

A CORE MATERIAL COMPOUND, A VACUUM INSULATION PANEL AND A COOLING DEVICE

The present invention relates to a core material compound in the vacuum insulation panel applied in cooling systems such as cooling device, etc., to a vacuum insulation panel having said core material and to a cooling device having said panel.

Vacuum insulation panels are panels comprising open-cell core materials in order to have the maximum thermal insulation efficiency. Said materials may provide better performance up to ten times in their application areas such as cooling systems, house insulation, refrigerator insulation, etc. compared to conventional core materials (EPS, fiberglass, polyurethane, etc.). Nowadays vacuum insulation panels are used in various fields since they have better performance with respect to the conventional insulation materials and since they provide better thermal resistance by using the insulating feature of the vacuum.

Basically, a vacuum insulation panel is produced by putting a porous core material into an outer protective envelope exclusively or together with getter material that retains gas and moisture according to the characteristic of the core material, vacuuming and closing it by providing leak-proofing. The insulation performance of the vacuum insulation panels is directly related to the barrier film which is the vacuum sheath, core material and vacuuming process.

Nowadays, in the production of the vacuum insulation panels, especially in order to ensure that the compound in the powder-based panels has an incorruptible structure, chemical components such as fiberglass, polyester, cellulose fiber, etc. which have a suitable adherence surface with respect to the core material. Said components which are used as core material cause, depending on their density, the weight of the panel to increase, and cause, depending on the thermal conductivity values of the materials, the thermal conductivity coefficient of the panel to decrease.

In vacuum insulation panels, various fiber materials, powder-based chemical compounds or resin fibers can be used as core material. The most common of these are compounds such as fiberglass, cellulose fiber materials, silicon-based powders, polyester, etc.

In the insulation panels, in order to reinforce the silicon-based powder materials, fiberglass is used. However, the fiberglass, which is a hard material due to its form, cannot be homogeneously dispersed in the powder, and as a result a different effect is obtained in each region in the insulation panels. This adversely affects the efficiency of the insulation.

When silicon powders with a density of 30-100 kg/m³are mixed with glassfiber with a density of 2500 kg/m³, the thermal and strength performances of the core material are adversely affected due to the thermal conductivity coefficient difference between the two materials in addition to the high density difference.

In the state of the art United States Patent Document No. US2018238605, a vacuum insulation panel having a core material comprising unwoven resin fibers and a cooling device wherein the panel is applied are disclosed.

In the state of the art Chinese Patent Document No. CN104556966, a vacuum insulation panel prepared with the compound of fumed silica and nanocarbon composite material, and the preparation method thereof are disclosed.

The aim of the present invention is the realization of a core material compound with improved strength and base insulation performance, of a vacuum insulation panel comprising said compound as core material, and a cooling device wherein the insulation panel is applied.

The core material compound realized in order to attain the aim of the present invention, explicated in the first claim and the respective claims thereof comprises at least one silicon-based powder compound as core material and microcrystalline cellulose. By means of said compound, the thermal properties and strength of the core material are improved.

In an embodiment of the present invention, the core material comprises microcrystalline cellulose which is obtained by bleaching, hydrolysis, centrifuge and neutralization and drying processes respectively after the amorphous and crystalline structures of the cellulose source raw material are separated by alkali treatment. The crystallinity of the microcrystalline cellulose obtained with said method increases and particles with a certain diameter are obtained.

In an embodiment of the present invention, microcrystalline cellulose in the core material has a diameter between 1 to 10 microns, preferably between 1 to 3 microns. Thus, the homogeneity of the compound is provided and the insulation performance is positively affected. Moreover, since the surface area value is very high at a particle size of 1-3 microns, adherence of the microcrystalline cellulose to the silica is increased. Thus, the rigidity of the core material is improved.

In an embodiment of the present invention, the core material comprises microcrystalline cellulose with a crystallinity between 60% to 90%. The amorphous structures of the microcrystalline cellulose with said crystallinity value are better separated. Thus, the microcrystalline cellulose can better show its material properties such as insulation, etc. in the core material compound. Moreover, by increasing the crystallinity of the microcrystalline cellulose, improvement in terms of failure to retain moisture and water in the core material which may occur due to production is provided. In order to increase the performance of the microcrystalline cellulose above 90%, which may drop under said limit, nano materials should be used.

In an embodiment of the present invention, silica-based powders in the core material are selected from pearlite and/or sepiolite and/or precipitated silica and/or fumed silica and/or vermiculite and/or diatomite and/or zeolite and/or the mixture of said materials. By means of said compounds used, a light core material and hence a light vacuum insulation panel are realized.

In an embodiment of the present invention, the core material comprises at least one compound selected from silicon carbide and/or carbon black and/or titanium dioxide and/or iron oxide opacifiers. Thus, the transfer by radiation value of the core material is minimized, and the thermal conductivity coefficient can be controlled.

In an embodiment of the present invention the core material compound comprises 15% to 30% microcrystalline cellulose and 70% to 55% silica-based powder compound and 15% opacifier by weight. An optimum thermal performance and strength is obtained with said mixture by weight. Moreover, a rigid vacuum insulation panel is realized with said ratios.

In an embodiment of the present invention the core material compound comprises 10% to 15% fiberglass and 10% to 15% opacifier compound and 15% to 20% microcrystalline cellulose and 65% to 50% silica-based powder compound by weight.

In another preferred embodiment of the present invention, the core material compound comprises 15% fiberglass and 15% microcrystalline cellulose and 10% silicon carbide and 60% silica-based material by weight. Said compounds and ratios used provide a compound with high insulation values and strength.

In an embodiment of the present invention, polyester fiber and/or fiberglass is added as reinforcing agent to the microcrystalline cellulose and silica-based powder compound.

By vacuuming the core material with the compound of the present invention between barrier films, vacuum insulation panels are obtained. By means of the improved thermal and mechanical properties of the core material, a vacuum insulation panel with improved thermal and mechanical resistant is obtained.

In an embodiment of the present invention, the barrier film in the vacuum insulation panel comprises layered PE-PA-PET and/or PE-PET-PET and/or PE-PET-EVOH-PET materials. Said materials and layered structure, the insulation of the panel is maintained.

A vacuum insulation panel having the core material of the present invention is used in refrigerators in order to provide a better thermal insulation.

In an embodiment of the present invention, in order to obtain the microcrystalline cellulose to be used in the core material compound, the steps of

- separating amorphous and crystalline structures from the cellulose source material (alkali treatment),

- bleaching the cellulose source wherein the amorphous and crystalline structures are separated and which is subjected to the pulpifying process, and removing the impurities thereof,

- obtaining, by hydrolysis, microcrystalline cellulose from the cellulose which is bleached and cleansed of impurities,

- applying centrifuge and neutralization processes in order increase the pH value which decreases after the hydrolysis process, and

- drying the obtained microcrystalline cellulose

are followed. By means of said method, microcrystalline cellulose with high crystallinity, homogeneous dimensions and high effficiency is obtained.

The model embodiments relating to the vacuum insulation panel and the cooling device comprising said vacuum insulation panel realized in order to attain the aim of the present invention are illustrated in the attached figures, where:

Figure 1 - is the schematic view of the vacuum insulation panel comprising the core material of the present invention.

Figure 2 - is the schematic view of the cooling device having the vacuum insulation panel comprising the core material of the present invention.

The elements illustrated in the figures are numbered as follows:

Vacuum insulation panel
Core material
Barrier film
Cooling device

Core materials (2) are the mixture of powder-based chemical compounds and at least one other compound which has a suitable adhesion surface to said compounds and which improves the thermal insulation performance.

The core material (2) compound of the present invention comprises at least one silica-based powder compound and microcrystalline cellulose in order to increase the thermal resistance and strength.

As the microcrystalline cellulose in the core material (2) compound of the present invention can be easily dispersed in the core material, the problem of homogeneous durability/rigidity in the vacuum insulation panels is solved. By means of the low density of the microcrystalline material, the weight of the vacuum panels used is reduced, which in turn results in the use of less material. Moreover, by using the microcrystalline cellulose which is a biobased material in the insulation panel, the adverse effects of the vacuum insulation panels on environment are decreased.

Said silica-based powder compounds are selected among pearlite and/or sepiolite and/or precipitated silica and/or fumed silica and/or vermiculite and/or diatomite and/or zeolite and/or the mixture of said materials. Depending on the density values of said compounds, a lighter core material (2) can be obtained.

The microcrystalline cellulose in the core material (2) of the present invention is obtained from any cellulose source such as wood, cotton, bleached soft or hard craft paper, ramie, sisal, tunicate and various agricultural wastes, but preferably from cotton linter.

In a preferred embodiment of the present invention, the microcrystalline cellulose in the core material (2) of the present invention is obtained by carrying out the method steps below in that order

Separating amorphous and crystalline structures from the cellulose source material (alkali treatment):

After the percentage humidity value of the cellulose source material is determined by humidity measurement, the material is treated in 5-25% NaOH solution for 12-20 hours in the room temperature with a magnetic stirrer. In this process, the amorphous and crystalline structures in the cellulose source are separated from each other. Thus, the crystallinity of the material is increased. Moreover, impurities in the raw material which are hemicellulose and lignin are broken down.

Bleaching process:

The cellulose source with the amorphous and crystalline structures thereof being separated, which is subjected to pulpifying process, is bleached with a mixture of 1-3% hydrogen peroxide and 3-5% NaOH (sodium hydroxide) in order to give the material a white color and to oxidize the impurities therein. In this process the temperature is preferably between 90 and 100ºC. The process takes 2-5 hours on average and the magnetic stirrer is used.

Hydrolysis:

After the bleaching process with hydrogen peroxide, hydrolysis process can be performed with ultrasonication and sulfuric acid, lauric acid, maleic acid, hydrobromic acid, and phosphotungstic acid. A 40%-60% sulfuric acid solution is prepared and the bleached cellulose source obtained after the bleaching process is hydrolysed, thus realizing the microcrystalline cellulose production process. This process is realized at 40-55°C for 3-5 hours by using magnetic stirrer. The aim of the process is to break down the glycosidic bonds in the cellulose, thus reducing the structure to the desired micro scale. After the process is completed, the reaction is stopped with a 1M NaOH solution, and the solution containing microcrystalline is taken into the sonication device, and the produced material is suspended for 15-60 minutes so as to cool down and to stabilize the reaction.

Centrifuge and neutralization:

After the hydrolysis process, in order to neutralize the pH value which decreases due to the acid, the resulting microcrystalline cellulose is washed with pure water and the centrifuge process is performed. In this process, the washing process is continued until the pH value is between 6 and 7. Moreover, the hydrolysis process can be performed with cellulose dialysis bag for 3-7 days against water instead of washing with centrifuge.

Drying process:

By performing the drying process on the neutralized microcrystalline cellulose, the water retained by the material is removed.

In an exemplary embodiment of the present invention, 25% NaOH solution and 10 grams cotton linter are mixed for 20 hours in the room temperature. Afterwards, the cotton linter with the amorphous structures thereof being broken down is subjected to the bleaching process for 3 hours at 90˚C for cleaning purposes. For hydrolysis process 60% sulfuric acid solution is prepared and the last process for the microcrystalline cellulose production is performed for 5 hours at 55˚C. Washing with centrifuge is performed to stop the hydrolysis process with the diluted NaOH solution and then to adjust the pH value with solution neutralization. When the pH is close to 7, stable value measurements are taken and the process is ended, and the microcrystalline cellulose is placed into the oven for drying purposes. As a result of the process, 70% efficiency is provided with the production of 7 grams material. The diameter of the microcrystalline cellulose is measured to be between 2 and 3 micros.

The microcrystalline cellulose in the core material (2) of the present invention has a diameter between 1 to 10 microns, preferably between 1 to 3 microns. As the effect coefficient (length/diameter ratio) of the microcrystalline cellulose with a diameter of 1-10 microns used in the core material (2) compound is high, the strength of the panels is increased compared to other known reinforcing agents, such as fiberglass. By means of the microcrystalline cellulose which increasing the adherence surface with the main core material, the amount of scrap generated due to breakage during the production of the panels is decreased.

The core material (2) of the present invention further comprises an opacifier compound such as silicon carbide and/or carbon black and/or titanium dioxide and/or iron oxide opacifiers in order to control the thermal conductivity coefficient.

In the preferred embodiment of the present invention, the core material (2) comprises 15% to 30% microcrystalline cellulose and 70% to 55% silica-based powder compound and 15% opacifier by weight. An optimum thermal performance and strength is obtained with said mixture by weight.

In another preferred embodiment of the present invention, the core material (2) comprises 15% fiberglass and 15% microcrystalline cellulose and 10% silicon carbide and 60% silica-based material by weight. Said values used provide a compound with high insulation values and strength.

In an embodiment of the present invention the core material (2) compound comprises 10% to 15% fiberglass and 10% to 15% opacifier compound and 15% to 20% microcrystalline cellulose and 65% to 50% silica-based powder compound by weight. Said value ranges provide improved thermal and mechanical properties for the material compound of the present invention.

The core material (2) of the present invention comprises microcrystalline cellulose with a crystallinity between 60% to 90%. Thus, better insulation properties are provided depending on the crystallinity value.

In a preferred embodiment of the present invention, the core material (2) of the present invention comprises polyester fiber and/or fiberglass. With the addition of said compounds, the core material (2) is reinforced.

The core material (2) of the present invention is used in the vacuum insulation panel (1).

In the preferred embodiment of the present invention, the vacuum insulation panel (1) comprises the core material (2) and a barrier film (3) wherein the core material (2) is placed.

By compressing the core material (2) of the present invention in a barrier film (3) at suitable pressure values, the vacuum insulation panel (1) is formed. The suitable pressure values for said process is between 0.01 and 1 mbar. The barrier film (3) in the vacuum insulation panel (1) wherein the core material (2) of the present invention is used can be any material configured to have a laminated, layered, airtight and moistureproof structure. In a preferred embodiment of the present invention, in order to close the barrier film (3) and to maintain the vacuum environment, the barrier film (3) is produced as a structure comprising a high density and/or low density polyetylene (LDPE/HDPE) layer as the innermost layer, polyethylene terephthalate (PET) which prevents the ingress of air and moisture at the surface which is the outermost layer, ethylene vinyl alcohol (EVOH) copolymer layer and/or layers produced from polymers such as polyamide (PA), etc. in order to increase the strength of the panel.

In an embodiment of the present invention, the barrier film (3) in the vacuum insulation panel (1) is produced from layered PE-PA-PET and/or PE-PET-PET and/or PE-PET-EVOH-PET materials. By means of said structure, vacuum environment is maintained.

The vacuum insulation panel (1) is used in a cooling device (4) to increase the thermal insulation performance.

By means of the present invention, a biobased, environmentally-friendly core material (2) which has improved thermal resistance and strength, decreased fragility and which homogeneous thermal insulation, and a vacuum insulation panel (1) are realized.

Claims

A core material (2) compound characterized by comprising at least one silicon-based powder compound as core material and microcrystalline cellulose in order to improve the thermal properties and strength.
A core material (2) compound as in Claim 1, comprising the microcrystalline cellulose which is obtained by bleaching, hydrolysis, centrifuge and neutralization and drying processes respectively after the amorphous and crystalline structures of the cellulose source raw material are separated by alkali treatment.
A core material (2) compound as in Claim 1 or 2, comprising the microcrystalline cellulose which has a diameter between 1 to 10 microns, preferably between 1 to 3 microns.
A core material (2) compound as in any one of the Claims 1 to 3, comprising the microcrystalline cellulose with a crystallinity value of 60%-90%.
A core material (2) compound as in Claim 1, comprises at least one silica-based powder compound which is selected from pearlite and/or sepiolite and/or precipitated silica and/or fumed silica and/or vermiculite and/or diatomite and/or zeolite and/or the mixture of said materials.
A core material (2) compound as in any one of the Claims 1 to 5, comprising at least one compound selected from silicon carbide and/or carbon black and/or titanium dioxide and/or iron oxide opacifiers in order to control the thermal conductivity coefficient.
A core material (2) compound as in any one of the Claims 1 to 6, comprising 15% to 30% microcrystalline cellulose and 70% to 55% silica-based powder compound and 15% opacifier compound by weight.
A core material (2) compound as in any one of the Claims 1 to 7, comprising polyester fiber and/or fiberglass as reinforcing agent.
A core material (2) compound as in Claim 8, comprising 10% to 15% fiberglass and 10% to 15% opacifier compound and 15% to 20% microcrystalline cellulose and 65% to 50% silica-based powder compound by weight.
A core material (2) compound as in Claim 8 or 9, comprising 15% fiberglass and 15% microcrystalline cellulose and 10% silicon carbide and 60% silica-based material by weight.
A vacuum insulation panel (1) comprising a core material (2) as in any one of the above claims.
A vacuum insulation panel (1) comprising a core material (2) as in Claim 11 and a barrier film (3) wherein the core material (2) is placed.
A vacuum insulation panel (1) as in Claim 12, comprising a barrier film (3) which is composed of layered PE-PA-PET and/or PE-PET-PET and/or PE-PET-EVOH-PET materials in order to maintain the vacuum environment.
A cooling device (4) comprising a vacuum insulation panel (1) as in any one of the Claims 11 to 13.
A microcrystalline cellulose production method for producing microcrystalline cellulose to be used in the core material (2), comprising the steps of

- separating amorphous and crystalline structures from the cellulose source material (alkali treatment),

- bleaching the cellulose source wherein the amorphous and crystalline structures are separated and which is subjected to the pulpifying process, and removing the impurities thereof,

- obtaining, by hydrolysis, microcrystalline cellulose from the cellulose which is bleached and cleansed of impurities,

- applying centrifuge and neutralization processes in order increase the pH value which decreases after the hydrolysis process, and

- drying the obtained microcrystalline cellulose.