KR20230109226A - Laminate comprising foam layer with shock absorption and manufacturing method of thereof - Google Patents

Abstract

The present invention relates to a method for producing a foam sheet having excellent shock absorption and a foam sheet comprising the same, and in detail, preparing a foaming raw material liquid by mixing an acrylic emulsion, a polyurethane resin, a surfactant and a foam stabilizer; preparing a foamed liquid by injecting air into and foaming the foamed raw material liquid; and forming a foam layer by coating the foam liquid on an adhesive layer formed on one side of the release film; thereby producing a foam sheet having excellent shock absorption, physical properties and water repellency with excellent productivity, and including the same. It relates to a foam sheet that does.

Description

Foam sheet containing a foam layer with excellent shock absorption and its manufacturing method

The present invention relates to a foam sheet comprising a foam layer having excellent shock absorption and a manufacturing method thereof.

Precision parts for optical materials such as mobile devices, tablets, and display devices require performance against external shocks and dust, and durability and reliability. Foam is used for the purpose of protecting electronic devices from factors such as impact and dust applied in the external environment. In particular, in the case of smartphones, high integration, high thinning and light weight are required at the same time, and shock absorption, strong adhesiveness and waterproofness are required. However, it is required that the thickness of the thin film not be too thick.

Polyurethane foam or open-celled urethane foam, UV acrylic foam, polyolefin foam, etc. are used for shock absorption of liquid crystal display devices. In the case of a porn material, it has excellent flexibility and adhesion, and is widely used in various electric and electronic products in the form of a sheet. When attaching porn foam to electronic devices, it is attached using a member such as acrylic adhesive. Although porn foam has excellent tensile strength, durability, elasticity and flexibility, it is difficult to sufficiently demonstrate shock absorption performance due to its high compressive elasticity. there is. In the case of acrylic foam, when manufactured to have an open cell structure, it shows a low compressive modulus and a high storage modulus and can exhibit excellent shock absorption. Due to the low durability, breakage and deformation of the film frequently occur during the assembly process or rework, which causes difficulties in the work process, resulting in increased loss of raw materials and reduced productivity.

The cell shape of the foam may have a structure of closed cells or open cells. In the case of closed-cell foam, waterproofness is excellent, but due to its high compressive modulus and low storage modulus, it does not sufficiently absorb shock when an impact such as a fall is applied. prone to problems In the case of open cell foam, since it is vulnerable to waterproofing due to its continuous cell structure, it is difficult to simultaneously satisfy shock absorption, dustproofing and waterproofing performance.

Recently, with the high performance of smartphones, it is becoming very important to secure a competitive advantage through multifunctionalization of members. In this situation, the shock absorbing member is also required to be multifunctional with excellent adhesion, water repellency and waterproofness.

KR 102339322 B1

An object of the present invention is to provide a method for manufacturing a foam sheet for electronic devices including a foam layer having excellent shock absorption and water repellency at the same time.

In addition, another object is to provide a foam sheet manufactured by the above manufacturing method.

According to one aspect of the present invention, 50 to 90 parts by weight of an acrylic emulsion, 10 to 50 parts by weight of an aqueous polyurethane resin, 1 to 5 parts by weight of a surfactant, and 0.1 to 1 part by weight of a foam stabilizer are blended to prepare a foaming raw material liquid. Level 1; a second step of preparing a foamed liquid by injecting air into and foaming the foamed raw material liquid; And a third step of forming a foam layer by coating the foam liquid on an adhesive layer formed on one side of the release film; a method for manufacturing a foam sheet including a may be provided.

In addition, in the first step, a foaming raw material liquid may be prepared by further blending a fluorine-based resin.

Also, in the second step, the bubble cell size may be adjusted to 50 to 150 um.

In addition, the adhesive layer may be formed by coating an adhesive prepared by mixing ethyl acetate and an epoxy curing agent on the release film.

In addition, the manufacturing method may include laminating a PET film layer having a black layer on the foam layer; and forming an adhesive layer on the PET film layer.

According to another aspect of the present invention, a foam sheet manufactured according to the above manufacturing method may be provided.

In addition, in the free fall impact test with a thickness of 80 to 300 um, the foam sheet may have a value obtained by dividing the shock absorption rate (%) according to Equation 1 by the sheet thickness at least 0.1.

[Equation 1]

(In Equation 1, Fi is the impact load when the impact ball is dropped on the reinforcing plate, and Fs is the impact load when the impact ball is dropped after mounting the foam sheet on the reinforcing plate.)

In addition, the foam sheet was left for 2 hours in a state where 60% of the initial thickness was compressed in a high temperature and high humidity environment, the compression was released, and the thickness was measured after one day at 24 ± 1 ° C. to obtain permanent compression according to Equation 2 below. The strain may be 25% or less.

[Equation 2]

(In Equation 2, T1 means the thickness of the first specimen, and T2 means the thickness of the specimen after the test.)

The manufacturing method according to one aspect of the present invention can produce a foam sheet with excellent shock absorption, physical properties and water repellency with excellent productivity.

In addition, it is possible to manufacture a foam sheet having a structure optimized to be applied to a display if necessary, thereby simplifying the overall product process by omitting the laminating process, thereby reducing the loss of raw materials and the defect rate.

The foam sheet produced by the manufacturing method according to another aspect of the present invention includes a foam layer prepared by blending an acrylic resin and a urethane resin to have an open cell structure, and may exhibit excellent shock absorption and water repellency while being soft.

In addition, since high-temperature durability is excellent, deformation can be minimized even in a high-temperature environment in which heat is generated due to the recent high integration of electronic devices, so that performance can be continuously demonstrated.

In addition, since it is thin in thickness and has excellent shock absorption and water repellency, it is suitable for application as a shock absorbing material for high performance slim optical devices including mobile devices, tablets and display devices.

In addition, it can exhibit high shock absorption compared to conventional urethane foam and UV acrylic foam, so that it can exhibit excellent protection performance against dropping shock of electronic devices when mounted on a display. In addition, it can exhibit excellent dustproof and waterproof performance at the same time.

1 is a schematic diagram of a foam sheet according to a first embodiment of the present invention,
2 is a schematic diagram of a foam seat according to a second embodiment of the present invention.

The present invention relates to a method for manufacturing a foam sheet including a foam layer having an open cell structure and a foam sheet manufactured by the method.

Hereinafter, the present invention will be described in more detail.

In describing the present invention, if it is determined that a detailed description of the known technology related to the present invention may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted. In addition, the terms to be described later are terms defined in consideration of functions in the present invention, which may vary according to the intention or custom of a user or operator. Therefore, the definition should be made based on the contents throughout this specification.

Unless otherwise defined, technical and scientific terms used in this specification may be interpreted as meanings commonly understood by those of ordinary skill in the art to which this invention belongs. Also, singular expressions include plural expressions unless the context clearly dictates otherwise. In addition, terms such as 'comprise' or 'having' are intended to designate that the features, numbers, steps, components, or combinations thereof described in the specification exist, but one or more other features, numbers, steps, or components. It should not be construed as excluding the possibility of the presence or addition of elements or combinations thereof. In addition, when a part is said to be 'connected' to another part, this includes not only the case where it is directly connected, but also the case where it is indirectly connected with another element interposed therebetween.

Also, although terms such as first, second, and third are used to describe various elements in various embodiments of the present specification, these elements should not be limited by these terms. These terms are only used to distinguish one component from another. Thus, what is referred to as a first element in one embodiment may be referred to as a second element in another embodiment. Each embodiment described and illustrated herein also includes its complementary embodiments.

The technical idea of the present invention is determined by the claims, and the following examples are only one means for efficiently explaining the technical idea of the present invention to those skilled in the art to which the present invention belongs. In addition, since the accompanying drawings are only examples shown to explain the technical idea of the present invention in more detail, the technical idea of the present invention is not limited to the form of the accompanying drawings.

According to one aspect of the present invention, preparing a foaming raw material solution; preparing a foamed liquid by foaming the foaming raw material liquid; And forming a foam layer with the foaming liquid; a method for producing a foam sheet comprising a may be provided.

First, a step (S1) of preparing a foaming raw material solution may be performed. The foaming raw material solution may be prepared using a polymer.

The polymer is not particularly limited, and for example, at least one selected from the group consisting of rubber-based polymers, acrylic-based polymers, urethane-based polymers, silicone-based polymers, and ethylene-vinyl acetate copolymers may be used. Preferably, acrylic polymers and urethane polymers are preferably included so that the manufactured foam sheet can exhibit sufficient shock absorption performance even when applied to highly integrated electronic parts. When an acrylic polymer is included in the polymer, an excellent impact absorbing performance may be exhibited, and when a urethane-based polymer is included, excellent mechanical properties may be obtained. The urethane-based polymer may be polyurethane.

The acrylic polymer preferably has a Tg value of 50° C. or less in terms of maximizing shock absorption. Preferably, it is good that it is 20 to 40 ℃, but it is not limited thereto. An acrylic emulsion may be used as the acrylic polymer, preferably an ionic acrylic emulsion, more preferably a cationic acrylic emulsion of non-volatile matter, but is not limited thereto. In the polymer, the acrylic polymer may be included in 50 to 90 parts by weight, preferably 50 to 80 parts by weight, but is not limited thereto. If the content of the acrylic polymer is less than 50 parts by weight, it is difficult to exhibit sufficient shock absorbing performance, and if it exceeds 90 parts by weight, a problem of significantly deteriorating the mechanical properties of the foam sheet may occur.

The polyurethane is preferably selected from those having a Tg value of 20° C. or more in order to satisfy mechanical properties such as tensile strength and elongation. Preferably, it is good that it is 20 to 40 ℃, but it is not limited thereto. The polyurethane may be a polyurethane dispersed in an aqueous medium containing 30 to 40% of non-volatile matter, but is not limited thereto. In the polymer, the polyurethane may be included in 10 to 50 parts by weight, preferably 10 to 20 parts by weight, but is not limited thereto. If the content of the polyurethane is less than 10 parts by weight, the tensile strength and elongation are significantly lowered, which may cause a problem in that workability during the process is significantly lowered, and if it exceeds 50 parts by weight, the shock absorption performance of the foam sheet produced is lowered. may occur.

In the polymer, the mixing weight ratio of the acrylic polymer and the polyurethane may be 1:0.1 to 1, preferably 0.2 to 0.4, and more preferably 1:0.33 to 0.38. When the mixing weight ratio of the acrylic polymer and the polyurethane falls within the above-described range, physical properties including shock absorbing performance and durability of the foam sheet prepared using the acrylic polymer may be compatible at a high level.

If necessary, the polymer may further include a hydrophobic resin to enhance water repellency. As the hydrophobic resin, for example, at least one selected from the group consisting of silicone-based, silane-based, siloxane-based, and fluorine-based resins may be used, but is not limited thereto. Preferably, the fluorine acrylate emulsion, which has excellent bonding strength with other polymers due to the acrylate structure in the molecule and can have a low surface energy due to the structure substituted with hydrogen and fluorine in the carbon chain, is more suitable for preparing the foam sheet. It is good to mix. In the polymer, the hydrophobic resin may be included in an amount of 1 to 20 parts by weight, but is not limited thereto. If the content of the hydrophobic resin is less than 1 part by weight, it is difficult to show the effect due to addition, and if it exceeds 20 parts by weight, other physical properties may be deteriorated and manufacturing costs may increase.

If necessary, the foaming raw material liquid may be prepared by mixing the polymer and additives together. The additives may be added to improve physical properties of the foam sheet to be prepared. As the additive, for example, at least one selected from the group consisting of a surfactant, a foam stabilizer, a curing agent, a dispersing agent, a rust inhibitor, a filler, a plasticizer, a reinforcing agent, a flame retardant, and a colorant may be used, but is not limited thereto. When the additive is further mixed with the foaming raw material liquid, the fluidity and cell diameter of the foamed liquid prepared by foaming can be easily controlled, and through this, the physical properties of the foam layer to be formed later can be adjusted. there is. The addition amount of the additive may be adjusted to improve target physical properties within a range in which tensile strength, elongation, shock absorption and compression set are maintained.

In the foam liquid produced through the foaming process to be described later, the size of the bubble cells formed is a factor that greatly affects the physical properties of the foam sheet to be finally manufactured, and is adjusted to have an optimized size in terms of shock absorption performance and process yield among physical properties. It can be. The size of the bubble cell can be controlled by adjusting the type and content of the surfactant and the bubble stabilizer, and it is important to select an appropriate surfactant and bubble stabilizer for the size and stabilization of the bubble cell.

As the surfactant, it is preferable to select one that has excellent compatibility with the polymer, imparts appropriate fluidity during preparation of the foamed liquid, and can control the cell diameter. The surfactant may be added in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the polymer resin, but is not limited thereto.

The foam stabilizer may be added to improve the stability of the micronized foam. As the foam stabilizer, for example, a polysiloxane or paraffin type may be used, and it is preferable to use a polysiloxane foam stabilizer in terms of maintaining microbubbles and suppressing the generation of large bubbles. The foam stabilizer may be added to a content of 0.1 to 1 part by weight based on 100 parts by weight of the polymer resin, but is not limited thereto.

The curing agent may be added to improve reconstitution, heat resistance and strength of the prepared foam sheet. As the curing agent, for example, at least one selected from the group consisting of epoxies, isocyanates, metal salts, and peroxides may be used, but is not limited thereto. In terms of maximizing the durability and shock absorption rate of the manufactured foam sheet, it is preferable to select a polyisocyanate-based curing agent. The curing agent may be added in an amount of 0.1 to 1 part by weight based on 100 parts by weight of the polymer resin, but is not limited thereto.

As the filler, for example, at least one selected from the group consisting of calcium carbonate, clay, zeolite, silica, alumina, aluminum hydroxide, graphite, graphene, carbon nanotube (CNT), and carbon black may be used. The filler may be added in an amount of 0.1 to 50 parts by weight, preferably 5 to 20 parts by weight, based on 100 parts by weight of the polymer resin. When carbon nanotubes are selected as the filler, the viscosity of the foaming liquid becomes excessively high due to the specific surface area of the filler, making it difficult to form a foam and may cause appearance defects due to dispersion problems. It is good.

As the colorant, for example, at least one selected from the group consisting of inorganic pigments, organic pigments, dyes, and carbon black may be used. The colorant may be used in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the polymer resin. When carbon black is selected as the colorant, problems of viscosity and poor dispersion may occur when an excessive amount is added.

A foaming raw material solution may be prepared by mixing and stirring the polymer and the additives.

Next, a step (S2) of preparing a foamed liquid by foaming the prepared foaming raw material liquid may be performed.

Foaming of the foaming stock solution may be performed physically or chemically using a foaming method known in the art. Preferably, it is performed by a physical method. For example, the foaming may be performed by a physical method of injecting air into the raw material liquid using an air injection method and miniaturizing the air with an ultra-precision dispenser.

The size of the cell formed during the preparation of the foamed liquid may be adjusted to 50 to 150 μm, preferably 50 to 120 μm, and more preferably 80 to 120 μm in terms of shock absorption performance and process yield. If the size of the bubble cells is less than 50 μm, the shock absorbing performance of the finally manufactured foam sheet may deteriorate, and if it exceeds 150 μm, it stays between the coater knife and the substrate to be coated during the coating process for forming the foam layer later, and the coating It causes defects such as vertical lines on the surface, and it can be combined with adjacent bubbles to cause spot-shaped defects on the coated surface. The size of the bubble cell may be achieved through control of the high-speed shearing device in addition to the above-described control of the surfactant and the bubble stabilizer.

During the foaming process, the size of the bubble cells formed can be controlled by adjusting the shape of the disks, the number of disks, the disk spacing, and the linear speed of the disks in the high-speed shearing device. Alternatively, it may be controlled by adjusting the flow rate that determines the residence time of the foamed liquid in the high-speed shearing device. If the disc spacing is too narrow or the linear speed of the disc is high, the temperature of the liquid may rise due to the accumulation of frictional heat due to the shear force between the liquid and the liquid and between the liquid and the device, which causes the bubble size to increase and the stability to deteriorate. This phenomenon may occur, and when the disc spacing is too wide or the linear speed of the disc is low, a problem that is not good for miniaturization of air bubbles may occur due to low shear force.

Next, a step (S3) of forming a foam layer with the prepared foam solution may be performed.

A foam layer may be formed by coating the foaming liquid on the adhesive layer formed on the release film and drying it. For the coating, one of commonly known methods may be used, and for example, a slot die, coma, gravure or microgravure coating method may be used, but is not limited thereto. If necessary, the stability of the foam layer formed by using an electron beam (E-BEAM) during curing of the foam layer may be improved.

The foam layer is preferably formed to a thickness of 50 to 200 μm. If the thickness of the formed foam layer is less than 50 μm, it is difficult to exhibit sufficient shock absorption performance when applied to electronic devices, and if it exceeds 200 μm, it may be difficult to apply to microminiature highly integrated electronic devices including mobile devices.

The adhesive layer may be formed by coating and drying an adhesive on one side of the release film. As the pressure-sensitive adhesive, among commonly used pressure-sensitive adhesives, those having a Tg of -20 to -10°C and heat resistance at 70°C may be selected and used. For example, an adhesive prepared by mixing ethyl acetate and an epoxy curing agent may be used, but is not limited thereto. In a preferred embodiment of the present invention, as a pressure-sensitive adhesive for forming the pressure-sensitive adhesive layer, a liquid pressure-sensitive adhesive prepared by mixing 40 to 50 parts by weight of ethyl acetate and 1 to 5 parts by weight of an epoxy curing agent based on 100 parts by weight of the pressure-sensitive adhesive composition was used.

If necessary, a step of further laminating another release film or double-sided tape on the foam layer may be performed. The double-sided tape has an adhesive layer formed on both sides of a support layer made of plastic, and when the double-sided tape is laminated on the foam layer, the foam layer is supported by the support layer and can be made into a sheet having adhesiveness on both sides. .

If necessary, laminating a PET film layer having a black layer on the foam layer; and forming an adhesive layer on the PET film layer. This may be performed to simplify the final electronic product production process by reducing the number of post-processes for applying the foam sheet to electronic components by laminating the PET film having a black layer on the foam sheet. Here, the electronic product may be an optical device including a liquid crystal screen, but is not limited thereto. The PET film on which the black layer is formed may be laminated such that the side on which the black layer is formed faces and adheres to the foam layer. The attachment may be implemented through an adhesive layer, but is not limited thereto.

According to another aspect of the present invention, a foam sheet manufactured by the above manufacturing method may be provided. The foam sheet may include a foam layer; and an adhesive layer formed on at least one side of the foam layer. A preferred embodiment thereof is shown in FIGS. 1 and 2 .

Referring to FIG. 1, the foam sheet 1 includes a release film 10; foam layer 20; and a base film 30. An adhesive layer (not shown) may be formed on at least one side of the release film 10, and the foam layer 20 may be formed on the upper surface thereof, and, if necessary, a base film on the other side of the foam layer ( 30) may be further included. The base film 30 may be included to serve as a liner layer.

When the foam sheet is applied to a display, it may be manufactured in a form in which a PET film layer is included on one side of the foam layer in order to increase manufacturing process efficiency. Specifically, the foam sheet may be provided in a form in which an adhesive layer and an embossed film are laminated to a black-printed PET film on a foam layer of a basic type foam sheet composed of a release film, an adhesive layer, and a foam layer. In this case, after the first adhesive layer and the foam layer are sequentially formed on one side of the release film, the black printed PET film is laminated on the foam layer, and the second adhesive layer and the embossed layer are sequentially laminated again on the PET film layer. A foam sheet may be formed. An example of its shape is shown in FIG. 2 .

Referring to FIG. 2, the foam sheet 1 includes a foam layer 20; base film 30; a printed layer 40; PET film 50; adhesive layer 60; And it may include an embossed film (70). If necessary, a second or third adhesive layer (not shown) may be further included between the layers.

The printed layer 40 may be formed on the layer of the PET film 50, and may be, for example, a black layer. The PET film 50 may be stacked on the foam layer 20 in a direction in which the black layer is attached to the other side of the foam layer 20 . The embossed film 70 may be a release film having an embossed shape. When the foam sheet 1 includes a PET film 50 layer having a black layer, compatibility with electronic devices such as displays is excellent, and thus process efficiency at the time of manufacturing a display can be improved.

The foam sheet may be manufactured in a form including all the layers shown in FIGS. 1 and 2. That is, of course, the release film 10 of FIG. 1 and an adhesive layer (not shown) may be further included on the other side of the foam layer 20 to which the base film 30 is not attached.

Referring to the foam layer, the foam sheet includes a first adhesive layer formed on one side of the foam layer; a PET film layer having one side attached to the other side of the foam layer and having a black layer formed on the one side; and a second adhesive layer formed on the other side of the PET film layer. A release film may be further included on one side of the first adhesive layer not in contact with the foam layer and one side of the second adhesive layer not in contact with the PET film layer. If necessary, the release film may further include an embossed shape.

The foam sheet may have a shock absorption rate (%) of at least 15 according to Equation 1 below in a free fall impact test having a thickness of 80 to 300 μm. Preferably, it may be 15 to 40, but is not limited thereto.

(In Equation 1, Fi is the impact load when the impact ball is dropped on the reinforcing plate, and Fs is the impact load when the impact ball is dropped after mounting the foam sheet on the reinforcing plate.)

In addition, the foam sheet may have a value obtained by dividing the shock absorption rate (%) according to Equation 1 by the sheet thickness in a free fall impact test having a thickness of 80 to 300 μm and at least 0.1. Preferably it may be 0.1 to 1, more preferably, 0.4 to 1.0, but is not limited thereto. The value obtained by dividing the shock absorption rate (%) according to Equation 1 by the sheet thickness will hereinafter be referred to as the shock absorption rate per unit thickness (SA). Here, the sheet thickness may be replaced by the foam layer thickness.

In addition, the foam sheet was left for 2 hours in a state where 60% of the initial thickness was compressed in a high temperature and high humidity environment, the compression was released, and the thickness was measured after one day at 24 ± 1 ° C. to obtain permanent compression according to Equation 2 below. The strain may be 30% or less. Preferably it may be 27% or less, more preferably 25% or less. At this time, the high-temperature and high-humidity environment is a condition of a temperature of 100° C., a pressure of 1.2 atm, and a humidity of 100%.

(In Equation 2, T1 is the thickness of the first specimen, and T2 is the thickness of the specimen after testing. Specifically, T1 is the initial thickness of the specimen before compression, and T2 is the above-mentioned condition in the high temperature and high humidity environment. means the thickness measured after compression and decompression.)

In addition, the initial restoring force at 50% compression is 7.3 gf/mm ² or less, preferably 3 to 7.3 gf/mm ² , but is not limited thereto. In addition, in terms of improving shock absorption performance and durability, the apparent density may be 0.2 to 1.0 g/cm ³ , preferably 0.2 to 0.6 g/cm ³ , but is not limited thereto.

The foam layer included in the foam sheet may have a contact angle between the surface and water of 75 to 130 degrees, preferably 90 to 130 degrees, measured in an environment of 24 ± 1 ° C and 40 to 60% humidity.

A foam sheet according to another aspect of the present invention includes a foam layer having an open cell structure, high shock absorption and low compression set and excellent physical properties. The foam layer has softness and excellent heat durability, so that deformation is reduced even under a high-temperature environment, and it may have excellent water repellency. The foam sheet including the foam layer is compatible with excellent shock absorption rate and physical properties, so it is a shock absorbing sheet for electronic parts requiring high performance and high integration of parts, for example, mobile devices, tablets, and display devices. suitable for application

Hereinafter, more specific and preferred embodiments are presented to help the understanding of the present invention, but these embodiments are only illustrative of the present invention and do not limit the scope of the appended claims, and are within the scope and spirit of the present invention. It is obvious to those skilled in the art that various changes and modifications to the embodiments are possible in, and it is natural that these changes and modifications fall within the scope of the appended claims.

Example

<Formation of adhesive layer>

In order to form an adhesive layer by coating the adhesive, an adhesive liquid to be used as an adhesive was prepared in consideration of coating smoothness and ease of thickness control. An adhesive was prepared by mixing 40 parts by weight of ethyl acetate (Ethylacetate) with respect to 100 parts by weight of the adhesive (38% solid content) and 3 parts by weight of an epoxy curing agent containing 5% of the active ingredient with respect to 100 parts by weight of the adhesive. The prepared adhesive was coated on a 50 μm PET release film coated with silicone using a coating equipment and dried at 120° C. for 3 minutes to prepare a release film coated with an adhesive layer.

<Preparation of foaming liquid and formation of foam layer>

[Production Example 1]

Based on 100 parts by weight of a polymer resin solution composed of 90 parts by weight of acrylic emulsion and 10 parts by weight of aqueous urethane polymer, 3 parts by weight of surfactant, 1 part by weight of carbon black, 10 parts by weight of aluminum hydroxide, 0.5 parts by weight of foam stabilizer and 0.3 part by weight of polyisocyanate curing agent After adding a part by weight, the mixture was dispersed while stirring to prepare a resin mixture solution.

The cell size of the foaming solution was adjusted to be 50 μm. Size controlled by adjusting the type and content of surfactant and bubble stabilizer, or by adjusting the shape of the disk in the high-speed shearing device, the number of disks, the disk spacing, and the flow rate that determines the linear speed of the disk and the residence time of the polymer composition liquid in the high-speed shearing device A foamed liquid having bubble cells could be obtained.

[Production Example 2] to [Production Example 4]

A foamed liquid was prepared in the same manner as in Preparation Example 1, except for preparing a resin mixture in which each component was mixed in the contents of Table 1 below.

Preparation Example 2 Preparation Example 3 Production Example 4 acrylic emulsion 20 50 40 water-based urethane polymer 80 70 50 Surfactants 3 3 3 bubble stabilizer 0.5 0.5 0.5 curing agent 0.3 0.3 0.3

[Production Example 5]

A foamed liquid was prepared in the same manner as in Preparation Example 1, except that 5 parts by weight of the fluoroacrylate emulsion was further added when preparing the resin mixture solution.

The prepared foam solution of each preparation example was coated on the upper surface of the adhesive layer formed on the release film and then dried to form a foam layer. At this time, the drying was carried out by putting it in an oven designed for continuous operation, setting the maximum temperature to 140° C., and then leaving it for 2 to 5 minutes. Through this process, a foam layer was formed with a constant thickness. The thickness of the foam layer formed was 80, 120, 160 and 200 μm for each manufacturing example, respectively, and a laminated sheet was prepared by laminating with a release film of 38 μm on the upper surface of the foam layer.

<Check shock absorbency>

Sheets having different thicknesses of 80 μm, 160 μm, and 240 μm of the foam layer were separately prepared using the foam solution of Preparation Example 1 as samples, and shock absorption performance was evaluated using a free fall impact load meter. The weight of the impact ball was 2.7 g, and the drop height was 200 mm. In addition, a sheet with a thickness of 160㎛ is installed, and the impact load is measured while increasing the drop height of the impact sphere to 150mm, 200mm, and 250mm. The shock absorbency (SA) was obtained and the results are shown in Table 2 below.

Impact ball drop height [mm] 150 200 250 Blank state impact load g 43 50 56 Impact load after seat mounting g 34 40 44 shock absorption rate % 21 20 19.6 SA %/μm 0.131 0.125 0.123

<Confirmation of permanent compression set in high temperature environment>

Sheets having different thicknesses of 80 μm, 160 μm, and 240 μm were separately prepared using the foaming liquid of Preparation Example 1 and used as samples. Before testing, first measure the thickness of the sample, compress it to 60% of the initial thickness of the sample with a compression jig, keep it in a constant temperature chamber at 80 ° C for 72 hours, release the compression, leave it at room temperature for 30 minutes, measure the thickness, and use the above equation The compression set was calculated according to 2. As a result of the test of the three specimens, the compression set was measured as 25.0%, 23.5%, and 24.7%, respectively, and the average value was measured as 24.8%.

<Check surface water repellency>

Surface water repellency was confirmed by measuring the contact angle of water. Each sheet in which a foam layer having a thickness of 160 μm was formed using the foamed liquids of Preparation Example 1 and Preparation Example 5 was used as a sample, and 10 μl of water droplets were dropped on the surface of the foam layer of the sample and formed between the surface and the droplet. The angle of was measured using a static contact angle measuring device (Kruss, Germany). The measurement environment was 24 ° C and 50% humidity, and as a result of measuring three times for each sample and obtaining an average, in the case of Preparation Example 1, it was measured at 92.8 °, 100.2 ° and 93.5 °, and in the case of Preparation Example 5, 118.5 °, 121.2° and 119.2° were measured. The water contact angle of each sample was confirmed to be 90 to 130 °, and the water contact angle of all samples was found to have a value exceeding 90 °, which is the minimum contact angle known to have water repellency. could

<Confirmation of shock absorbency and physical properties of Preparation Examples 2 to 4>

Shock absorption rate, shock absorption rate per unit thickness (SA), tensile strength and elongation were measured using the foam sheets formed using the foamed solutions of Preparation Examples 2 to 4 as samples, and the values are shown in Table 3 below.

The shock absorption rate was measured using the shock absorption performance value measured using the same free fall impact measurement device ('SurTA High Resolution Drop Impact Tester' manufactured by Chemilab) as described above. An impact ball weighing 2.7 g was free-falled to heights of 150 mm, 200 mm, and 250 mm, and the impact load was measured by increasing the impact load. The peak top of the initial impact load was measured and recorded in a state where the sample was not mounted, and the peak top of the initial impact load was measured and recorded after the sample was mounted. The shock absorption rate at a height of 200 mm for each sample was obtained using Equation 1, and at this time, the foam sheet in Equation 1 refers to the sample of this test example. Next, the impact absorption rate (SA) per unit thickness was obtained by dividing the shock absorption rate by the sheet thickness (μm). At this time, the foam sheet means the sample of this test example.

Density (g / cc) was obtained by measuring the thickness by cutting the sheet from which the release film layer was removed into a size of 200 mm × 200 mm with a digital thickness gauge with a minimum graduation of 1 μm, and then measuring the specimen with a precision scale with a minimum graduation of 0.001 g, It was obtained from the measured volume and weight.

Tensile strength and elongation were measured by preparing shock-absorbing sheet specimens according to the KS M ISO 1798 test standard. The width of the frame knife was 10 mm, and it was repeatedly measured three times using UTM and the average value was obtained.

Preparation Example 2 Preparation Example 3 Production Example 4 thickness μm 200 200 200 Shock absorption rate (2.7g, 200mm) % 23 20 19 per unit thickness
Shock absorption rate (SA) %/μm 0.14 0.13 0.12 tensile strength kg/cm ² 6.0 7.3 9.7 elongation % 150 162 181

Referring to the results of the confirmed performance test, it can be confirmed that the foam sheet prepared according to the embodiment of the present invention exhibits excellent physical properties and shock absorption performance. Since the foam sheet manufactured according to the embodiment of the present invention exhibits excellent performance as a thin film, it is suitable for application to slim and highly integrated electronic devices.

10: release film
20: foam layer
30: base film
40: printing layer
50: PET film
60: adhesive layer
70: embo film

Claims (8)

50 to 90 parts by weight of an acrylic emulsion, 10 to 50 parts by weight of an aqueous polyurethane resin, 1 to 5 parts by weight of a surfactant, and 0.1 to 1 part by weight of a foam stabilizer are blended to prepare a foaming raw material solution;
a second step of preparing a foamed liquid by injecting air into and foaming the foamed raw material liquid; and
A method for producing a foam sheet comprising a; third step of coating the foaming liquid on an adhesive layer formed on one side of the release film to form a foam layer.
According to claim 1,
In the first step, a method for producing a foam sheet, further blending a fluorine-based resin.
According to claim 1,
In the second step, the bubble cell size is adjusted to 50 to 150um, a method for producing a foam sheet.
According to claim 1,
The adhesive layer is formed by coating an adhesive prepared by mixing ethyl acetate and an epoxy curing agent on the release film, a method for producing a foam sheet.
According to claim 1,
laminating a PET film layer having a black layer on the foam layer; and
Forming an adhesive layer on the PET film layer; further comprising a foam sheet manufacturing method.
A foam sheet manufactured according to the manufacturing method of any one of claims 1 to 5.
According to claim 6,
In the free fall impact test with a thickness of 80 to 300um, the value obtained by dividing the shock absorption rate (%) according to Equation 1 by the sheet thickness is at least 0.1, foam sheet.
[Equation 1]

(In Equation 1, Fi is the impact load when the impact ball is dropped on the reinforcing plate, and Fs is the impact load when the impact ball is dropped after mounting the foam sheet on the reinforcing plate.)
According to claim 6,
In a high temperature and high humidity environment, 60% of the initial thickness is compressed and left for 2 hours, and after releasing the compression, the thickness is measured after one day at 24 ± 1 ° C. The compression set obtained according to Equation 2 below is 25% or less, foam sheet.
[Equation 2]

(In Equation 2, T1 means the thickness of the first specimen, and T2 means the thickness of the specimen after the test.)

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