JP2006283817A - Vacuum insulation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vacuum heat insulating material that has an extremely low environmental load at the time of manufacture and at the time of recycling, is excellent in handleability / workability and production efficiency, and maintains good heat insulation over a long period of time.
A vacuum heat insulating material is characterized in that an inner packaging material containing a core material containing polyester fiber is accommodated in an outer packaging material in a reduced pressure state.
[Selection figure] None

Description

The present invention relates to a vacuum heat insulating material used as a heat insulating material for a refrigerator, a vending machine, a cold box, a cold car, and the like.

  Conventionally, heat insulating materials having various structures and performances are used in refrigerators, vending machines, cold storage boxes, cold cars, and the like. In recent years, a vacuum heat insulating material having a very excellent heat insulating property has been used in many applications. The vacuum heat insulating material generally has a structure in which a core material is filled in an outer packaging material made of a gas barrier metal deposition film or the like, and the inside thereof is decompressed and sealed. The heat insulating properties, productivity, and handling performance of such a vacuum heat insulating material greatly depend on the core material, but as a core material that is currently widely used, open cell polyurethane foam (Patent Document 1), the average fiber diameter is Examples thereof include a glass fiber aggregate (Patent Document 2) of about 0.5 to 8 μm and a composite of a glass fiber aggregate and other thermoplastic resin fibers (Patent Document 3).

However, the general-purpose core for vacuum heat insulating material has the following problems.
Although the core material using the open-cell polyurethane foam is very excellent in workability, handleability, lightness and the like, it has a poor heat insulating property as compared with a fibrous material such as glass fiber.

  Although the core material using the glass fiber aggregate having an average fiber diameter of about 0.5 to 8 μm has no outgas (gas component volatilized from the core material) and has excellent heat insulation properties, the glass fiber The material itself has great difficulty in handling and workability. In order to improve handling, some improvements have been made to the work of inserting the core material into the outer packaging material by applying needle punch to the laminated glass fiber, but the handling and workability difficulties derived from the material itself are difficult. Is not something that can be solved. In particular, the problems of working environment and handling at the time of recycling the core material remain. For example, if the outer packaging material is opened at the time of recycling, the glass fiber aggregate core material scatters, which causes problems not only in handling and workability but also in terms of environmental burden.

  A core material using a composite of glass fiber aggregates and other thermoplastic resin fibers is not satisfactory, although a slight improvement in handleability is observed. Similar to thermoplastic resin fibers, some composites of rock wool, pulp, and other fibers are also seen, but because glass fibers are used, the difficulties in handling and workability derived from the glass fibers themselves and the environmental burden are Still remains.

  A vacuum heat insulating material using only organic fibers such as thermoplastic resin fibers as a core material is also conceivable, but no example is realized due to the problem of outgas generated from organic fibers. In particular, an example in which a 0.75d polyester fiber collection is used as a core material can be seen (Patent Document 4), but if used in a wrinkled form, handling properties are extremely poor and cannot be considered as a practical product. Therefore, it is possible to make the cotton collection into a sheet for the purpose of improving the handleability. However, when using ultrafine fibers as described above, the needle punch method is difficult to use, so a binder is used by the chemical bond method. And there is a problem that outgas is generated, the change with time is large, and the heat insulation is greatly deteriorated with time.

In addition, any of the vacuum heat insulating materials described above is manufactured by directly storing the core material in the outer packaging material and sealing the outer packaging material opening while maintaining the inside of the outer packaging material in a reduced pressure state. Production efficiency was a problem. That is, when the core material is directly accommodated in the outer packaging material, the outer packaging material is easily scratched, so that the yield of the vacuum heat insulating material is reduced. Further, when the core material is directly accommodated in the outer packaging material, the core material is likely to adhere to the finally sealed outer packaging material opening due to static electricity or the like, and it is difficult to sufficiently remove the adhered core material. The opening of the adhering core material was formed between the inside and outside of the outer packaging material by the seal of the opening, and the yield of the vacuum heat insulating material was lowered. Such a problem of yield reduction is remarkable when a wrinkle-shaped core material that is difficult to handle is used. Moreover, in the case where the wrapping core material is directly accommodated in the outer packaging material, as described above, the accommodating operation is limited from the viewpoint of scratches on the outer packaging material, so that it can be accommodated to have a uniform thickness. It was difficult. As a result, the heat insulating property decreased.
JP-A-6-213561 JP-A-8-28776 JP 2003-155651 A JP 2002-188791 A

  The present invention has been made to solve the above-described problems, and has an extremely low environmental load during manufacturing and recycling, and is excellent in handleability, workability and production efficiency, and has good heat insulation over a long period of time. It aims at providing the vacuum heat insulating material to maintain.

  The present invention relates to a vacuum heat insulating material characterized in that an inner packaging material containing a core material containing polyester fiber is accommodated in an outer packaging material in a reduced pressure state.

In the vacuum heat insulating material of the present invention, since the core material is made of polyester fiber, the environmental load is small, and the recyclability after use is very excellent. Moreover, the vacuum heat insulating material of the present invention exhibits a heat insulating property that exceeds the vacuum heat insulating material using the open-cell urethane foam employed in refrigerators and the like over a long period of time, and is easier to handle and work than glass fiber. Excellent.
Further, in the vacuum heat insulating material of the present invention, since the core material is accommodated in the outer packaging material in a state of being accommodated in the inner packaging material, the outer packaging material is hardly scratched, and the core material is hardly attached to the opening of the outer packaging material. Accordingly, the yield of the vacuum heat insulating material is improved and the production efficiency is increased.

  The vacuum heat insulating material of the present invention is configured such that an inner packaging material containing a core material is accommodated in an outer packaging material in a reduced pressure state.

  In the present invention, the core material is composed of a fiber assembly containing polyester fibers. The core material is preferably a fiber assembly made only of polyester fibers from the viewpoints of environmental load, handleability / workability, recyclability and heat insulation. When the core material does not contain polyester fibers and is made of other organic fibers such as polyethylene fibers, the heat insulating property is lowered over time due to outgassing.

  In the present invention, the term “polyester fiber” means a fiber made of a polymer in which chemical structural units are bonded mainly by ester bonds, and the production method is not particularly limited. For example, it may be a polyester fiber obtained by a reaction between a dicarboxylic acid component and a diol component, or a polyester fiber obtained by a reaction between hydroxycarboxylic acid components having a hydroxyl group and a carboxyl group in one molecule. May be.

  Specific examples of the polyester fiber include polyethylene terephthalate (PET) fiber, polybutylene terephthalate (PBT) fiber, polypropylene terephthalate fiber, and polyarylate fiber. For example, PET fiber is obtained by a reaction of dimethyl terephthalate (DMT) and ethylene glycol (EG) or terephthalic acid (TPA) and EG, and PBT fiber is DMT and tetramethylene glycol (TMG) or TPA and TMG. It can be obtained by the reaction of Considering mass productivity and cost, polyethylene terephthalate fiber is preferable. Of course, there is no problem even if recycled PET fibers are used.

  The fiber thickness of the polyester fiber is not particularly limited as long as the object of the present invention can be achieved. For example, it is preferably 1 to 6 denier, particularly preferably 1 to 3 denier. The average fiber diameters of the polyester fibers having the fiber thickness correspond to 9 to 25 μm and 9 to 17 μm, respectively. The average fiber diameter was measured by processing two diameters per 10 fibers with a CCD camera image for 10 fibers, and calculating the average value of the diameters at a total of 20 positions as the average fiber diameter value.

  A polyester fiber having a softening point of about 200 to 260 ° C. and a strength of about 0.3 to 1.2 GPa is preferable from the viewpoint of easy fiber production.

  Examples of the method for fiberizing polyester include a melt spinning method, a wet spinning method, and a dry spinning method. In the present invention, the melt spinning method is preferable. The melt spinning method is a system in which a polymer melt is discharged into the air from a pore nozzle, cooled and solidified with air while thinning the discharged molten yarn, and then taken up at a constant speed. In this method, the polyester fiber having the fiber thickness can be easily produced.

  The form of the fiber assembly containing the polyester fiber is not particularly limited, and may be, for example, a sheet shape or a wicker shape. By making it into a sheet form, the handling property and workability of the core material are further improved, the environmental load during manufacturing and recycling can be further reduced, and the heat insulating property of the vacuum heat insulating material is further improved. By using the wrinkled shape, the object of the present invention can be achieved more effectively. Conventionally, when a cotton-like fiber assembly is used, the inside of the outer packaging material cannot be maintained in a reduced pressure state due to the outer packaging material scratches or adhesion of the core material to the opening of the outer packaging material, and the yield of the vacuum heat insulating material is reduced. This is because heat insulation is likely to deteriorate due to non-uniformization, but in the present invention, such a problem can be effectively prevented even when a wrinkled core material is used.

  “Sheet” means having a flat plate shape. The sheet-like fiber assembly is preferably processed without using other materials such as a binder. For example, the sheet-like fiber assembly is processed into a sheet by a so-called needle punch method or the like. The chemical bond method using a binder causes a problem in that the heat insulating property is lowered over time due to outgas generation. The needle punching method is a method of repeatedly piercing or pulling up many needles with hooks against a polyester fiber lump in which the directions of fibers are aligned to some extent, that is, a polyester fiber web. It is the method of making it into a sheet form by mutually entanglement.

  “Water” refers to a state like a so-called raw cotton, and means a form in which fibers are irregularly intertwined and integrated. It does not include sheet-like shapes such as a web shape made of so-called raw cotton or a needle punched shape.

  In the present invention, the thickness of the core material composed of such a fiber assembly is not particularly limited as long as the object of the present invention is achieved, and is usually about 1 mm to 100 mm, particularly 5 mm to the vacuum heat insulating material. What is necessary is just about 75 mm. In particular, the sheet-like fiber assembly may be a single-layer sheet, but when it is made of a single-layer polyester fiber sheet and used as a vacuum heat insulating material, it is difficult to manufacture a sheet having a thickness of about 5 mm or more. When it is desired to set a specific thickness, it is preferable to use a laminated sheet-like fiber assembly (core material) in which two or more sheets are laminated.

The density of the core material in the present invention, from the viewpoint of heat insulation and strength, preferably from 100 to 300 / ^{m 3,} more preferably from 150~300kg / ^{m 3.}
The density of the core material is obtained by measuring the density after the inner packaging material containing the core material is accommodated in the outer packaging material and vacuumed. That is, after creating the vacuum heat insulating material, the weight of the inner packaging material, the outer packaging material, the getter material, and the like measured in advance is subtracted from the weight of the vacuum heat insulating material to obtain the weight of the core material. Further, the volume of the getter material or the like measured in advance is subtracted from the volume of the vacuum heat insulating material to obtain the volume of the core material. Note that the inner packaging material and the outer packaging material are very small in thickness, and thus are not considered for volume calculation. The density is calculated from the weight and volume of the obtained vacuum heat insulating material.

  This invention does not prevent that the fiber assembly which comprises a core material contains fibers other than a polyester fiber. The content of the polyester fiber is not particularly limited as long as the object of the present invention is achieved, and is usually 50% by weight or more, preferably 90 to 90% by weight based on the total amount of the core material from the viewpoint of preventing temporal deterioration of heat insulation due to outgas generation. 100% by weight.

  Other fibers that may be contained in the fiber assembly together with the polyester fiber include, for example, polyethylene fiber, polypropylene fiber, acrylic fiber, aramid fiber, nylon fiber, polyvinyl alcohol fiber, fluorine fiber, polyurethane fiber, polynosic fiber, rayon fiber, etc. Synthetic fibers, inorganic fibers such as alumina and potassium titanate, natural fibers such as hemp, silk, cotton and wool.

  The inner packaging material is not particularly limited as long as the core material can be accommodated, and preferably has a form having air permeability. Examples of such a form include a film having a vent hole at least partially, and a woven fabric, a knitted fabric, and a non-woven fabric. The size of the holes in the film and the basis weight of the woven fabric, knitted fabric, and nonwoven fabric are not particularly limited as long as the core material does not scatter from the inner packaging material due to reduced pressure exhaust during the production of the vacuum heat insulating material, and the inner packaging material can be smoothly decompressed and exhausted. . The present invention does not preclude the use of a film form that does not have air permeability as the inner packaging material. By using an internal packaging material that does not have air permeability, the internal packaging material alone can be maintained in a reduced pressure state.

The material of the inner packaging material is not particularly limited as long as the object of the present invention can be achieved, and examples thereof include polyester, polypropylene, and nylon. From the viewpoint of outgas generation, polyester is preferable, and from the viewpoint of recyclability, it is most preferable to use PET as a material for both the core material and the inner packaging material. Further, from the viewpoint of drying the core material during the production of the vacuum heat insulating material, it is preferable to use a material having a melting point of 100 ° C. or higher, particularly about 100 to 300 ° C.
For example, a woven fabric, a knitted fabric and a non-woven fabric made of polyester may be made of the same polyester fiber as described above as a core material.

  As the outer packaging material that contains the inner packaging material containing the core material, any material can be used as long as it has gas barrier properties and can maintain the inside at a reduced pressure, and is preferably heat-sealable. . Preferable specific examples include, for example, a gas barrier film having a four-layer structure of nylon, aluminum vapor-deposited PET (polyethylene terephthalate), aluminum foil, and high-density polyethylene as the innermost layer, from the outermost layer, polyethylene terephthalate resin, intermediate Gas barrier film consisting of aluminum foil as the layer, high density polyethylene resin as the innermost layer, PET resin as the outermost layer, ethylene-vinyl alcohol copolymer resin having an aluminum vapor deposition layer as the intermediate layer, and gas barrier consisting of high density polyethylene resin as the innermost layer A film etc. are mentioned.

  In the vacuum heat insulating material of the present invention, from the viewpoint of further improving heat insulation over time, at least one kind of constituent gas of water vapor or air is adsorbed between the outer packaging material and the inner packaging material or in the inner packaging material. It is preferable to enclose a gas adsorbent (getter material). Preferably, a depression corresponding to the gas adsorbent may be formed in the core material inside the inner packaging material, and the gas adsorbent may be arranged directly in the depression, or the position of the depression from above the inner packaging material. A gas adsorbent may be arranged. The gas adsorbent may be contained in a hard container having vent holes, or may be contained in a soft container having air permeability (for example, a bag made of nonwoven fabric).

Preferred embodiments of the method for producing a vacuum heat insulating material of the present invention will be described below.
First, a core material of a predetermined form is inserted into a bag-shaped breathable inner packaging material. At this time, the gas adsorbent may be inserted into the inner packaging material together with the core material. When the core material is in the form of a sheet, two or more core materials may be stacked and inserted into the inner packaging material. The bag-shaped inner packaging material only needs to have an opening, and examples thereof include a material in which two rectangular inner packaging materials are stacked and joined in three directions. Bonding depends on the material of the enveloping material and may be achieved, for example, by heat sealing or by sewing.

  Next, the opening of the inner packaging material containing the core material is sealed. At this time, it is preferable to seal the above-mentioned predetermined core material thickness with a jig such as a press machine. The surface smoothness of the vacuum heat insulating material is improved by pressing, for example, the workability at the time of attaching to the inner surface of the refrigerator box is improved, and the heat insulating property is further improved. Moreover, it is preferable to apply not only pressure but also heat during pressing. This is because by applying heat and pressure, the surface smoothness of the vacuum heat insulating material is further improved and excellent heat insulating properties can be easily secured. In particular, when a wrinkled fiber assembly is used as the core, it is more preferable to apply heat during pressing. The temperature at the time of pressing is suitably 30 to 100 ° C, particularly 35 to 85 ° C.

  The sealing of the inner packaging material opening may be achieved by heat sealing or may be achieved by sewing.

  After the core material is accommodated in the inner packaging material and the opening is sealed, the obtained inner packaging material is inserted into a bag-shaped outer packaging material that is heat-sealed on three sides. At this time, a gas adsorbent may be inserted together. Two or more inner packaging materials containing the core material may be overlapped and inserted into the outer packaging material.

The outer packaging material in which the inner packaging material is accommodated is transferred into the vacuuming device in an open state, and is evacuated so that the internal pressure becomes a vacuum degree of about 0.1 to 0.01 Torr. Then, the opening part of an outer packaging material is sealed by heat sealing, and a vacuum heat insulating material is obtained.
The vacuum heat insulating material may be pressed at room temperature to adjust the core material thickness and core material density.

  From the viewpoint of further improving the heat insulating properties, it is preferable to dry the core material before sealing the outer packaging material opening. Specifically, the drying may be performed immediately before the inner packaging material containing the core material and the opening sealed is inserted into the outer packaging material, or after being inserted into the outer packaging material and before evacuating under reduced pressure. You may carry out in the state inserted in the outer packaging material. Drying is not particularly limited as long as moisture contained in the core material can be removed, for example, preferably performed under conditions of about 1 hour at 120 ° C., in particular, in order to more effectively remove moisture and the like of the polyester fiber, Vacuum drying at 120 ° C. is preferred. Furthermore, you may use together the drying by far infrared rays. About a vacuum degree, it is preferable to dry at about 0.5-0.01 Torr.

  When using a non-breathable inner packaging material, the core material is inserted into a bag-shaped inner packaging material and placed in a vacuuming device, and the internal pressure is about 0.1 to 0.01 Torr. After exhausting under reduced pressure, the opening of the inner packaging material is sealed by heat sealing. Preferably, the predetermined core material thickness is secured by a jig such as a press while evacuating under reduced pressure. Thereby, the inner packaging material which accommodated the core material in the pressure reduction state inside can be obtained. The bag-shaped inner packaging material in this case only has to have an opening and can be maintained in a reduced pressure state by sealing the opening in a reduced pressure state. A material in which three materials are stacked and heat-sealed on three sides is mentioned. For the core material drying in this case, the core material and the encapsulating material whose opening is not sealed may be subjected to drying before being evacuated under reduced pressure. After obtaining the inner packaging material in which the core material is housed in a reduced pressure state, the inner packaging material is inserted into the outer packaging material in the same manner as in the case of using a breathable inner packaging material, and the outer packaging material opening is sealed under reduced pressure. Good.

<Example 1>
A breathable PET nonwoven fabric (melting point of PET fiber: 260 ° C.) is cut into a square shape (250 mm × 270 mm: including the seal portion), the two nonwoven fabrics are overlapped, and the three sides are bonded together by heat fusion to provide air permeability. A bag-shaped inner packaging material was prepared.
88 g of a wrinkle-shaped core material made of PET fiber (1.5 denier, melting point 260 ° C.) was uniformly inserted into the bag-shaped inner packaging material. While the inner packaging material containing the core material was pressed at a heating temperature of 40 ° C., the opening was sealed by thermal fusion. The core material thickness at the time of pressing was 10 mm. A convex part having a height of 5 mm was formed on the upper die of the press, and a depression for the getter material was formed by the press.
After the core material is accommodated and the opening is sealed, the inner packaging material is dried at 120 ° C. for 60 minutes, and then a gas barrier film outer packaging material (250 mm) made of nylon, aluminum vapor-deposited PET, aluminum foil, and high-density polyethylene. × 270 mm (including the seal portion), and one getter material (SAS Getters: COMBO-3) was inserted on the inner packaging material in the outer packaging material. In this state, it was immediately put into a vacuum evacuation apparatus, and evacuation was performed so that the internal pressure became 0.01 Torr, followed by sealing by heat fusion. The obtained vacuum heat insulating material had a core part size of 200 mm × 200 mm and a thickness of 10 mm. The density of the core material of the obtained vacuum heat insulating material was 220 kg / m ³ .

<Example 2>
88 g of a sheet-like core material made of a web obtained by scouring the cotton-like PET fiber used in Example 1 was inserted into the same bag-like inner packaging material as in Example 1. While the inner packaging material containing the core material was pressed at a heating temperature of 40 ° C., the opening was sealed by thermal fusion. The core material thickness at the time of pressing was 10 mm.
In a state where the core material is accommodated and the opening is sealed, the inner packaging material is inserted into a gas barrier film outer packaging material (250 mm × 270 mm) having a four-layer structure of nylon, aluminum vapor-deposited PET, aluminum foil, and high-density polyethylene. Drying was performed at 120 ° C. for 60 minutes. After drying, one getter material (manufactured by SAES Getters: COMBO-3) was inserted on the inner packaging material in the outer packaging material. In this state, it was immediately put into a vacuum evacuation apparatus, and evacuation was performed so that the internal pressure became 0.01 Torr, and the product was sealed by heat fusion. The obtained vacuum heat insulating material had a core part size of 200 mm × 200 mm and a thickness of 10 mm. The density of the core material of the obtained vacuum heat insulating material was 220 kg / m ³ .

<Example 3>
A PET fiber (melting point 260 ° C.) having a fiber thickness of 1.5 denier and an average fiber diameter of 11 μm was processed into a sheet by the needle punch method. The sheet basis weight was 550 g / m ² . The sheet thickness was 10 mm. The sheet was cut into a size of 200 mm × 200 mm to obtain a core material.
The obtained core material was inserted into the same bag-shaped inner packaging material as in Example 1. The opening of the inner packaging material containing the core material was sealed by heat sealing.
Gas barrier film outer packaging material (250mm x 270mm: including seal part) consisting of four layers of nylon, aluminum vapor-deposited PET, aluminum foil, and high-density polyethylene. In the inserted state, drying was performed at 120 ° C. for 60 minutes. After drying, one getter material (manufactured by SAES Getters: COMBO-3) was inserted on the inner packaging material in the outer packaging material. In this state, it was immediately put into a vacuum evacuation apparatus, and evacuation was performed so that the internal pressure became 0.01 Torr, followed by sealing by heat fusion. The obtained vacuum heat insulating material had a core part size of 200 mm × 200 mm and a thickness of 10 mm. The density of the core material of the obtained vacuum heat insulating material was 220 kg / m ³ .

<Example 4>
A vacuum heat insulating material was obtained in the same manner as in Example 1, except that 176 g of the cotton-like core material was uniformly inserted into the bag-shaped inner packaging material and the core material thickness at the time of pressing was 20 mm. The thickness of the vacuum heat insulating material was about 20 mm, and the core material density was 220 kg / m ³ .

<Example 5>
A vacuum heat insulating material was obtained in the same manner as in Example 2 except that a sheet-like core material 264g formed by stacking three webs was inserted into the bag-like inner material, and the core material thickness at the time of pressing was 30 mm. It was. The thickness of the vacuum heat insulating material was about 30 mm, and the core material density was 220 kg / m ³ .

<Example 6>
A vacuum heat insulating material was obtained in the same manner as in Example 3 except that three sheets for the core material obtained in Example 3 were used as a core material. The thickness of the vacuum heat insulating material was about 30 mm, and the core material density was 220 kg / m ³ .
<Comparative Example 1>
After drying the cotton-like PET fiber core material at 120 ° C. for 60 minutes, a vacuum heat insulating material was obtained in the same manner as in Example 1 except that it was directly inserted into the outer packaging material (250 mm × 270 mm: including the seal portion). It was. The core material density was 220 kg / m ³ .

<Initial insulation>
The initial heat insulation was evaluated by measuring the thermal conductivity at an average temperature of 20 ° C. using “Autoλ HC-074” (manufactured by Eihiro Seiki Co., Ltd.). The measurement was made after 1 day from the vacuuming step.

<Long-term insulation>
Evaluation of long-term heat insulation is carried out by putting the vacuum heat insulating material evaluated for initial heat insulation into a constant temperature bath of 70 ° C. and taking it out after 4 weeks, and using “Autoλ HC-074” (manufactured by Eihiro Seiki Co., Ltd.) This was done by measuring the thermal conductivity at a temperature of 20 ° C.

<Workability>
The workability when inserting the core material or the inner packaging material containing the core material into the outer packaging material was evaluated according to the following criteria.
○: Easy insertion into outer packaging material;
X: The insertion into an outer packaging material is complicated.

<Production efficiency>
In each example or comparative example, the manufacturing procedure of the vacuum heat insulating material was repeated 50 times. Evaluation was made based on the number (x) of the 50 vacuum heat insulating materials obtained that could not maintain the vacuum after 1 day from the production.
○: 0 to 1;
X: Two or more.

Claims (6)

  A vacuum heat insulating material characterized in that an inner packaging material containing a core material containing polyester fiber is accommodated in an outer packaging material in a reduced pressure state.   The vacuum heat insulating material according to claim 1, wherein the fiber thickness of the polyester fiber is 1 to 6 denier.   The vacuum heat insulating material according to claim 1 or 2, wherein the polyester fiber is a polyethylene terephthalate fiber.   The vacuum heat insulating material according to any one of claims 1 to 3, wherein the inner packaging material is an inner packaging material made of polyethylene terephthalate. The vacuum heat insulating material according to any one of claims 1 to 4, wherein the density of the core material is 150 to 300 Kg / m ³ . The vacuum heat insulating material according to any one of claims 1 to 5, wherein the core material comprises only polyester fibers.