Polyurethane skin film for shoe upper using screen printing and manufacturing method thereof

Abstract

The present invention relates to a PU skin film for bonding to the surface of a shoe upper using a heat press, comprising: a thermoplastic polyurethane (TPU) hot melt film (10) with a thickness of 0.02 to 0.3 mm containing hydrophobic nanosilica with a primary particle size of 1 to 100 nm in a range of 0.1 to 5 phr (Parts per Hundred Resin); and a polyurethane (PU) binder layer (20) with an average thickness of 0.005 to 1 mm applied on the upper surface of the thermoplastic polyurethane (TPU) hot melt film (10) by a screen printing method. The present invention relates to a PU skin film for a shoe upper using screen printing and a method for manufacturing the same, wherein a polyurethane (PU) ink layer (30) with an average thickness of 0.005 to 2 mm, applied by screen printing, is integrally laminated on the upper portion of the polyurethane (PU) binder layer (20), and the polyurethane (PU) binder layer (20) and the polyurethane (PU) ink layer (30) located on the upper portion of the thermoplastic polyurethane (TPU) hot melt film (10) form a pattern by screen printing with an average thickness of 0.01 to 3 mm.

Description

Technology Field

[0001] The present invention relates to a PU skin film for a shoe upper using screen printing and a method for manufacturing the same. More specifically, the invention relates to a PU skin film for a shoe upper using screen printing and a method for manufacturing the same, wherein when a skin film having a hot melt film formed thereon is bonded to the surface of a shoe upper in a no-sewing manner using a heat press, a PU skin film manufactured by screen printing is used without using a separate release paper, thereby being environmentally friendly and reducing product production costs, as well as enabling the precise formation of a high-quality three-dimensional pattern. Background Technology

[0002] Recently, the no-sewing method, which involves producing fabrics using adhesives or hot-melt films without sewing, has become widely applied in the production of fabrics used in the fields of household goods such as shoes, clothing, and bags. In particular, a process of attaching skin film materials to the surface via the no-sewing method is frequently carried out to decorate products made from fabrics such as natural or synthetic fibers, synthetic resins, and natural or synthetic leather.

[0003] This bonding process has the advantage of reducing processing time and manpower compared to the sewing process by applying a liquid adhesive to the substrate and bonding the fabrics together after the solvent or moisture has evaporated through drying. Additionally, to maximize cost savings, a process of bonding the fabrics using a heat press with a thermoplastic hot melt film can be implemented instead of using a liquid adhesive.

[0004] For example, when manufacturing a product by laminating a skin film made of polyvinyl chloride or polyurethane resin with a fabric, a technology is widely used in which a skin film is manufactured by printing a film having a specific color or the surface of the film using a comma coater method, a screen method, or a transfer method, and then a hot melt film is formed on the bottom and bonded to the fabric by a high-frequency welding method.

[0005] When the skin film manufactured as described above is bonded to the surface of a fabric, it is placed on the upper surface of the fabric and a heat press is performed. As a result, the hot melt film constituting the bottom surface of the adhesive sheet melts due to heat and pressure and adheres to the fabric, while the skin film coated on top of the hot melt film does not melt and functions as a material capable of decorating the product.

[0006] Most skin film materials that are bonded using the above-mentioned non-sewing method are adhesive sheets having a structure of two or more layers, which are based on a thermoplastic hot-melt film made of one or more resin compositions selected from thermoplastic polyurethane (TPU) and ethylene vinyl acetate (EVA), and then coated or co-extruded with a colored polyurethane skin film (PU Skin Film) on top of it.

[0007] In addition, when forming an embossing on a skin film formed on the upper part of the adhesive sheet, a coating layer is formed on the surface of a release paper processed with various patterns of embossing, and then the dried coating layer is laminated with another fabric or film and aged for a certain period of time, and then the release paper is peeled off to obtain a skin film with the embossing pattern of the release paper transferred thereon. The skin film manufactured in this way is widely applied for surface decoration of various products such as shoe uppers, bags, clothing, and furniture.

[0008] However, the conventional method of forming embossing patterns on skin films using embossed release liners has many limitations. First, since release liners must be discarded after approximately 3 to 8 uses, they generate a large amount of non-recyclable industrial waste, placing a significant burden on the environment. Second, because most users purchase and use off-the-shelf release liners, there are limitations in implementing unique and complex designs desired by the user. Third, when a coating layer is formed on an embossed release liner, it is not only difficult to form thick and three-dimensional embossing patterns, but there is also a risk of product quality degradation due to the occurrence of air bubbles during the coating and drying processes.

[0009] Looking at the prior art for forming a pattern on a skin film as described above, Korean Patent No. 10-0473221 comprises: a first step of coating a transfer sheet using an adhesive and a pretreatment agent; a second step of offset printing a predetermined pattern on the coated transfer sheet; a third step of bonding the printed transfer sheet using an adhesive; a fourth step of pressing the transfer sheet on the surface of a fabric using a heat press at 80 to 120°C with a pressure of 30 to 60 kgf / ㎠ for 5 to 20 seconds, and then separating the transfer sheet from the fabric; a fifth step of coating the separated fabric surface using a coating agent; and a sixth step of using a high-frequency device to cause a predetermined pattern formed on the surface of the fabric to protrude. This proposes a method of forming a pattern on the surface of a fabric made of synthetic leather by offset printing a predetermined pattern on a coated transfer sheet and then using a high-frequency device.

[0010] In addition, Public Patent No. 10-2021-0062970 describes a method for manufacturing artificial leather having a breathable portion capable of imparting breathability, comprising the steps of: preparing a release liner (S1); screening at least a portion of the release liner using a screen member (S2); applying a resin solution onto the release layer of the release liner and the screen member and drying to form a resin skin layer (S3); forming an adhesive layer on the resin skin layer (S4); removing the screen member used in the screen step (S2) (S5); laminating a fabric onto the adhesive layer (S6); and removing the release liner from the resin skin layer to obtain artificial leather (S7); wherein the artificial leather has a breathable portion formed using a screen member before applying the resin skin layer to the release liner.

[0011] Meanwhile, the inventor has developed a multilayer adhesive sheet having a color transfer prevention function through Patent No. 10-2805046, wherein when a heat press operation is performed to attach a color skin film formed with a hot melt film on a fabric (adhesive), a color transfer prevention film made of a styrene acrylonitrile copolymer (SAN) single resin is formed on the upper surface of a hot melt film having a suitable thickness, thereby preventing the overflow phenomenon of the hot melt film and preventing the dye of the fabric from transferring upward and contaminating the polyurethane color skin film, and having excellent washfastness and flexibility, as well as effectively blocking the phenomenon where the dye of the fabric transfers to the skin film and the color changes even during long-term use. Prior art literature

[0012] Korean Registered Patent Publication No. 10-0473221 (Publication Date: March 14, 2005) Korean Published Patent Publication No. 10-2021-0062970 (Publication Date: June 1, 2021) Korean Registered Patent Publication No. 10-2805046 (Publication Date: May 13, 2025) The problem to be solved

[0013] The objective of the present invention is to provide a PU skin film for a shoe upper using screen printing and a method for manufacturing the same, which is environmentally friendly and reduces product production costs by not generating release paper waste and harmful substances such as DMF (dimethylformamide) by producing a PU skin film using a screen printing method without using a separate release paper to form a pattern on the skin film for a shoe upper, and also allows for the precise formation of high-quality three-dimensional patterns.

[0014] Another objective of the present invention is to provide a PU skin film for a shoe upper and a method for manufacturing the same, which can improve product quality by reducing the molding time and increasing product productivity and saving energy by using a TPU hot melt film containing hydrophobic nanosilica when a PU skin film with a pattern formed by screen printing is integrally bonded to a shoe upper by a heat press, and thereby minimizing deformation of the fine pattern formed by screen printing on the upper surface of the PU skin film due to heat and pressure. means of solving the problem

[0015] A PU skin film for a shoe upper using screen printing according to the present invention is a PU skin film for bonding to the surface of a shoe upper using a heat press, comprising: a thermoplastic polyurethane (TPU) hot melt film (10) with a thickness of 0.02 to 0.3 mm containing hydrophobic nanosilica with a primary particle size of 1 to 100 nm in a range of 0.1 to 5 phr (Parts per Hundred Resin); and a polyurethane (PU) binder layer (20) with an average thickness of 0.005 to 1 mm applied by a screen printing method on the upper surface of the thermoplastic polyurethane (TPU) hot melt film (10). A polyurethane (PU) ink layer (30) with an average thickness of 0.005 to 2 mm, applied by screen printing, is integrally laminated on top of the polyurethane (PU) binder layer (20); and the polyurethane (PU) binder layer (20) and the polyurethane (PU) ink layer (30) located on top of the thermoplastic polyurethane (TPU) hot melt film (10) are characterized by forming a pattern by screen printing with an average thickness of 0.01 to 3 mm.

[0016] According to a preferred embodiment of the present invention, the hydrophobic nanosilica contained in the thermoplastic polyurethane (TPU) hot melt film (10) comprises one or more hydrophobic functional groups selected from alkyl groups, dimethyl groups, trimethyl groups, dimethylsiloxane groups, and methacrylate groups on the particle surface of the nanosilica, and is characterized by existing in the state of nanosilica aggregates having an aggregate size of an average of 100 to 1200 nm within the TPU hot melt film. .

[0017] The above polyurethane (PU) ink layer (30) is characterized by forming a flat-type or embossing-type pattern consisting of various shapes and colors by applying a printing number within 1 to 100 times using a screen printing plate that has the same or different designs or colors. .

[0018] The method for manufacturing a PU skin film for a shoe upper using the above screen printing comprises: a step (S100) of preparing a thermoplastic polyurethane (TPU) hot melt film (10) with a thickness of 0.02 to 0.3 mm containing hydrophobic nanosilica with a primary particle size of 1 to 100 nm in a range of 0.1 to 5 phr (Parts per Hundred Resin); and a step (S200) of forming a polyurethane (PU) binder layer (20) by installing a screen printing plate on the upper surface of the thermoplastic polyurethane hot melt (TPU) film, applying a polyurethane binder with an average thickness of 0.005 to 1 mm, and drying it. The method sequentially includes a step (S300) of forming a polyurethane (PU) ink layer (30) by installing a screen printing plate on the upper surface of the polyurethane (PU) binder layer (20), applying polyurethane (PU) ink with an average thickness of 0.005 to 2 mm, and drying; wherein the polyurethane (PU) binder layer (20) and the polyurethane (PU) ink layer (30) located on the upper surface of the thermoplastic polyurethane (TPU) hot melt film (10) form a pattern by screen printing with an average thickness of 0.01 to 3 mm. .

[0019] The above polyurethane (PU) ink layer (30) formation step (S300) is characterized by forming a flat-type or embossing-type pattern consisting of various shapes and colors by applying a printing number within 1 to 100 times using a screen printing plate that has the same or different designs or colors. .

[0020] In addition, the method for manufacturing a shoe upper bonded with the above-described PU skin film is characterized by cutting a PU skin film for a shoe upper obtained by screen printing using the above-described manufacturing method into a desired shape, arranging the cut PU skin film on the surface of the shoe upper, and then processing it within 15 to 25 seconds using a heat press at a temperature of 120 to 140℃ and a pressure of 40 to 50 kgf / ㎠ to form it integrally with the shoe upper. . Effects of the invention

[0021] The PU skin film for shoe uppers using screen printing according to the present invention is environmentally friendly and reduces product production costs by producing the PU skin film by screen printing without using a separate release paper to form a pattern on the skin film, thereby not generating release paper waste or harmful substances such as DMF (dimethylformamide), and also has the effect of precisely forming high-quality three-dimensional patterns.

[0022] The method for manufacturing a shoe upper with a PU skin film bonded according to the present invention has the advantage of significantly improving product quality by reducing the molding time using a TPU hot melt film containing hydrophobic nanosilica when a PU skin film with a pattern formed by screen printing is bonded integrally with the shoe upper by a heat press, thereby increasing product productivity and saving energy. As a result, the intricate pattern formed by screen printing on the upper surface of the PU skin film is minimized from deformation due to heat and pressure. Brief explanation of the drawing

[0023] FIG. 1 is an exemplary cross-sectional view of a PU skin film according to the present invention. FIG. 2 is a process flowchart showing a method for manufacturing a PU skin film according to the present invention. FIGS. 3a and 3b are actual photographs of an example of a shoe upper with a PU skin film bonded thereto according to the present invention. Specific details for implementing the invention

[0024] Hereinafter, a PU skin film for a shoe upper using screen printing according to the present invention and a method for manufacturing the same will be described with reference to the drawings. This is intended to be an example sufficient to enable a person skilled in the art to easily practice the invention, and does not imply that the technical concept and scope of the present invention are limited thereby.

[0025] As illustrated in FIG. 1, the PU skin film for a shoe upper using screen printing according to the present invention is a PU skin film for bonding to the surface of a shoe upper using a heat press, comprising: a thermoplastic polyurethane (TPU) hot melt film (10) with a thickness of 0.02 to 0.3 mm containing hydrophobic nanosilica with a primary particle size of 1 to 100 nm in a range of 0.1 to 5 phr (Parts per Hundred Resin); and a polyurethane (PU) binder layer (20) with an average thickness of 0.005 to 1 mm applied by a screen printing method on the upper surface of the thermoplastic polyurethane (TPU) hot melt film (10). The technical gist is that a polyurethane (PU) ink layer (30) with an average thickness of 0.005 to 2 mm, applied by screen printing, is integrally laminated on top of the polyurethane (PU) binder layer (20), and the polyurethane (PU) binder layer (20) and the polyurethane (PU) ink layer (30) located on top of the thermoplastic polyurethane (TPU) hot melt film (10) form a pattern by screen printing with an average thickness of 0.01 to 3 mm.

[0026] The term 'PU skin film' used in the present invention refers to polyurethane skin materials (PU skin materials) that are attached to form a surface to reinforce or decorate fabrics made of materials such as fibers, synthetic resins, natural and artificial leather used for shoe uppers, and the 'PU ink layer' can be applied with a printing frequency of 1 to 100 times using a single or multiple screen printing plates to form a pattern consisting of various shapes and colors on the surface of the PU skin film at a desired thickness (3 mm or less).

[0027] The PU skin film of the present invention is formed by stacking a PU binder layer (20) and a PU ink layer (30) on top of a TPU hot melt film (10) using a screen printing method. This is technically distinct from methods of coating in the form of a film or bonding by co-extrusion, and there is a significant difference in the three-dimensional effect of the surface. The thickness of the PU binder layer (20) and the PU ink layer (30) applied by this screen printing is based on the cured 'dried film'.

[0028] The base film among the above PU skin films is formed as a thermoplastic polyurethane (TPU) hot melt film (10) with a thickness of 0.02 to 0.3 mm containing hydrophobic nanosilica with a primary particle size of 1 to 100 nm in the range of 0.1 to 5 phr (Parts per Hundred Resin), which is suitable for securing stable adhesion between the fabric and the skin film. If the thickness of the above hot melt film (10) exceeds 0.3 mm (300 μm), the fabric product becomes heavy overall and feels hard to the touch, and there is a disadvantage that it does not meet the development trend of becoming increasingly lightweight.

[0029] This phenomenon occurs because when a press is performed while the hot melt film is inserted between a substrate and a fabric with different tissue densities, the amount of hot melt film is concentrated on the side with lower tissue density or the side with larger fabric weaving holes due to heat and pressure. Therefore, it is most desirable to appropriately adjust the thickness of the hot melt film (10) based on a standard of 120 to 150 μm (0.12 to 0.15 mm), taking into account the porosity according to the type of fabric, synthetic resin, natural and artificial leather fabric, etc., considering adhesion and flexibility of the product.

[0030] For example, when compared to the case where a general TPU hot melt film that does not contain hydrophobic nanosilica is applied with a thickness of about 200 μm instead of the thermoplastic polyurethane (TPU) hot melt film (10) described above, the hot melt film (10) containing hydrophobic nanosilica in the range of 0.1 to 5 phr as in the present invention is formed with a thickness of about 120 to 150 μm, it has superior adhesion and product lightness, as well as a reduction in thickness of about 25 to 40%, which reduces the step difference at the boundary with the bonded fabric, thereby improving the surface flatness of the product.

[0031] For reference, hot-melt film is a solid material at room temperature, but when heat is applied, it melts into a fluid state and acquires adhesion to the substrate. When the molten hot-melt film is cooled, it returns to a solid form and regains its cohesiveness. The adhesive strength of this hot-melt film is influenced by the effect of the liquid adhesive penetrating into surface clearances or holes to increase adhesion. To utilize this effect effectively, sufficient flowability is required when the hot-melt film is melted, so it is used after being melted at a relatively high temperature to have an appropriate viscosity.

[0032] The hot melt film (10) made of a thermoplastic polyurethane (TPU) resin as in the present invention has good extrusion workability and good productivity, and is environmentally friendly as it does not use solvents, and is a material with excellent compatibility with the same type of PU binder layer (20) and PU ink layer (30) and has a good touch, and is confirmed to be the most suitable for securing good adhesion with various fabrics with low affinity.

[0033] Generally, polyurethane resin is a resin produced based on urethane bonds formed by the reaction of isocyanate groups (-NCO) and hydroxyl groups (-OH) within a polymer. Its raw materials include polyols, isocyanates, chain extenders, etc., and it is typically manufactured by solution polymerization with the addition of various solvents. Accordingly, the characteristics of polyurethane resin include excellent film strength and adhesive strength, which enables the production of thin coating films; the coating film has abundant elasticity, resulting in a soft texture; it also has excellent cold resistance; and since it is processed without using plasticizers, there are fewer workability issues caused by plasticizers.

[0034] The above polyols are used in various types depending on their molecular structure, molecular weight, functional group, and OH-value, and they have a direct effect on the physical properties of polyurethane. For example, compared to polyurethane using polyester polyols, polyurethanes using polyester polyols have higher tensile strength, hardness, and elongation, as well as excellent flame retardancy and excellent chemical resistance, making them resistant to oxidation. In addition, while they have excellent adhesion to the substrate, a disadvantage is that they have a hydrolytic nature unlike polyether polyols, resulting in poor water resistance. However, using polyester polyols with a number average molecular weight of 400 to 8,000 is suitable for exhibiting strong adhesion and good fluidity, and if the value falls outside this range, the viscosity, feel, and the adhesion of the resin itself decrease.

[0035] Meanwhile, in order to improve the adhesion and moldability of the hot melt film, the present invention prepares a thermoplastic polyurethane resin composition for a hot melt film in which nanosilica (hydrophobic nanosilica) containing hydrophobic organic functional groups on the particle surface is blended. It was confirmed that the hydrophobic nanosilica is contained in a range of 0.1 to 5 phr (Parts per Hundred Resin) based on the total weight of the thermoplastic polyurethane resin composition, and the film thickness can be manufactured up to about 0.02 mm to 0.3 mm.

[0036] Methods for incorporating the above-mentioned hydrophobic nanosilica include mixing the nanosilica with the raw materials during the polymerization of the TPU resin and then polymerizing to produce a thermoplastic polyurethane resin for hot melt films, or preparing a masterbatch using hydrophobic nanosilica and then mixing it with the TPU resin to produce a thermoplastic polyurethane resin for hot melt films.

[0037] In the present invention, when hydrophobic nanosilica with a particle size of 1 to 100 nm was incorporated and applied to manufacture a hot melt film, it was confirmed that adhesiveness was improved even when only a small amount of 0.1 phr (Parts per Hundred Resin) or more was added. However, when the content of the nanosilica exceeded 5.0 phr, side effects were confirmed, such as the surface of the thermoplastic hot melt film becoming opaque and the adhesive strength decreasing, as well as a blooming phenomenon occurring on the surface of the hot melt film over time.

[0038] As described above, when manufacturing a hot melt film, the present invention incorporates nanosilica containing hydrophobic organic functional groups (lipophilic) on its surface to improve dispersibility and reinforce water resistance, thereby increasing tensile strength. This allows for the production of a thinner hot melt film with uniform adhesive strength and superior durability compared to conventional products, while simultaneously reducing material costs, saving energy, and enabling multi-press molding, which increases productivity.

[0039] The above 'Nano Silica (NS)' refers to silica (SiO2) particles with a primary particle size of 100 nanometers (nm) or less, and 'Nano Silica containing hydrophobic functional groups organically treated on the surface of the particles (hydrophobic nano Silica)' means that hydrophobic organic functional groups are introduced to part or all of the surface of the nano Silica particles. Conventional nano Silica particles have a hydrophilic surface, but the nano Silica of the present invention has a hydrophobic surface through the introduction of hydrophobic organic functional groups (lipophilic) via separate surface treatment (or surface modification), so the surface becomes hydrophobic, resulting in excellent dispersibility and reinforced water resistance of the thermoplastic hot melt film itself, thereby increasing tensile strength.

[0040] And 'nanosilica aggregate,' which refers to a collection of multiple nanosilica primary particles, indicates a state in which more than 70% of the nanosilica primary particles are strongly bound together by physical and chemical interactions. Within the TPU hot melt film, these nanosilica aggregates are in a state where it is difficult to further separate them into smaller entities (nanosilica particles).

[0041] The thermoplastic polyurethane (TPU) hot melt film (10) used in the present invention is formed by incorporating nanosilica containing hydrophobic organic functional groups on the particle surface, thereby enabling the hot melt film to be uniformly distributed on the surface of the fabric and not melt into one side of the fabric due to heat and pressure when the hot melt film is inserted between fabrics and bonded by a no-sewing press operation, whether the fabric's thread density is high or low, or the size of the weaving hole is large or small, thereby improving the adhesive strength.

[0042] The meaning of "uniformly distributed on the surface of the fabric" above refers to a uniform state in which, during the press operation, the hot melt film does not melt and flow into the side of the fabric with a high yarn density or the side of the fabric weaving hole with a large size, but is distributed approximately 1 / 3 to the fabric above the hot melt film, 1 / 3 to the fabric below the hot melt film, and 1 / 3 between the fabrics (adhesive interface).

[0043] As described above, the TPU hot melt film (10) of the present invention is uniformly distributed on the surface of the fabric due to the action of hydrophobic nanosilica, thereby improving adhesion strength and having no problems with adhesive strength and excellent durability. Even if formed with a thickness about 25 to 40% thinner than that of a conventional TPU hot melt film that does not contain hydrophobic nanosilica, it is possible to secure adhesive strength equal to or greater than that of a conventional hot melt film.

[0044] Hydrophobic organic functional groups that can be introduced to the surface of the above nanosilica particles may be alkyl groups, dimethyl groups, trimethyl groups, dimethylsiloxane groups, methacrylate groups, etc. For example, the nanosilica particles used in the thermoplastic polyurethane resin composition for hot melt films of the present invention are nanosilica obtained by controlling the temperature and pressure in a fumed silica manufacturing process, and then treated with an organosilane compound to include dimethyl groups on the surface of the nanosilica particles.

[0045] The nanosilica particles with the above-mentioned hydrophobic organic functional groups have an OH group density of 1.0 OH / nm. 3 It is preferable that it be less than or equal to 0. The OH group density can be verified by known methods, such as reacting nanosilica particles with introduced hydrophobic functional groups with lithium aluminum hydride and measuring the molar absorbance (ε) of the OH group stretching vibration band in the free silanol group at 3750 cm using IR spectroscopy.

[0046] The hydrophobic nanosilica contained in the thermoplastic polyurethane (TPU) hot melt film (10) comprises one or more hydrophobic functional groups selected from alkyl groups, dimethyl groups, trimethyl groups, dimethylsiloxane groups, and methacrylate groups on the surface of the nanosilica particles, and exists in the state of nanosilica aggregates having an average aggregate size of 100 to 1200 nm within the TPU hot melt film, and the aggregates preferably have an average aggregate size of 100 to 1200 nm, and more preferably have an aggregate size of 200 to 500 nm.

[0047] When the size of the above hydrophobic nanosilica aggregates is an average of 100 nm or more, the dispersion of nanosilica is well achieved, but when it exceeds 1200 nm, the thickening effect decreases, and defects such as surface defects and gelation occur frequently during the molding process using a T-die extruder. The size of the above nanosilica aggregates refers to the length in the direction of the major axis of the nanosilica aggregates and can be measured using a transmission electron microscope, etc.

[0048] Generally, thermoplastic polyurethane resins are obtained by polymerizing raw materials such as polyols and isocyanates with chain extenders such as low molecular weight glycols. Examples of polyols used here include polyester glycol, polyether glycol, and polycaprolactone; examples of isocyanates include aromatic isocyanates and aliphatic isocyanates; and examples of low molecular weight glycols include 1,4-butanediol. In addition, ethylene vinyl acetate (EVA), polyamide, and polyester resins can be used as materials for hot melt films, but the present invention has concluded that using thermoplastic polyurethane resin is more effective for the mixing, dispersibility, and adhesion performance with hydrophobic nanosilica {refer to Patents No. 10-2057036 and No. 10-2440469}.

[0049] Furthermore, the above TPU hot melt film (10) may further enhance the three-dimensional effect of the PU skin film for shoe uppers according to the present invention by applying a multilayer structure TPU hot melt film (10) having an additional TPU film with a thickness of 0.05 to 1 mm (50 to 1,000 μm) interposed on its upper side.

[0050] Next, a polyurethane (PU) binder layer (20) with an average thickness of 0.005 to 1 mm is formed on the upper surface of the thermoplastic polyurethane (TPU) hot melt film (10) by screen printing, and the PU binder layer (20) strengthens the adhesion and durability of the TPU hot melt film (10) and the PU ink layer (30).

[0051] For the reasons mentioned above, the PU binder layer (20) has a solid content of 40 to 60 wt% and a viscosity of 300,000 to 800,000 cps / 25℃, and due to its excellent adhesion to the TPU hot melt film (10), it performs the role of maintaining the thickness of the PU ink layer (30) applied on top of it by screen printing.

[0052] Finally, a polyurethane (PU) ink layer (30) with an average thickness of 0.005 to 2 mm, applied by screen printing, is integrally laminated on top of the polyurethane (PU) binder layer (20), and as a result, the polyurethane (PU) binder layer (20) and the polyurethane (PU) ink layer (30) located on top of the thermoplastic polyurethane (TPU) hot melt film (10) form a pattern by screen printing with an average thickness of 0.01 to 3 mm.

[0053] The above PU ink layer (30) is preferably formed with a solid content of 20 to 40 wt% and a viscosity of 3,000 to 50,000 cps / 25℃ depending on the color of the ink, in terms of physicochemical properties, mechanical strength and durability.

[0054] As a result, the PU skin film for a shoe upper using screen printing according to the present invention can form a flat-type or embossing-type pattern consisting of various shapes and colors by applying the polyurethane (PU) ink layer (30) to a screen printing plate with the same or different designs or colors within 1 to 100 printing cycles, and thus it is possible to realize various patterns such as more three-dimensional gradation, reflective, flocking, gloss, matt, fluorescence, etc. {See FIG. 3a, FIG. 3b}.

[0055] As illustrated in FIG. 2, a method for manufacturing a PU skin film for a shoe upper using screen printing according to the present invention comprises: a step (S100) of preparing a thermoplastic polyurethane (TPU) hot melt film (10) with a thickness of 0.02 to 0.3 mm containing hydrophobic nanosilica with a primary particle size of 1 to 100 nm in a range of 0.1 to 5 phr (Parts per Hundred Resin); and a step (S200) of forming a polyurethane (PU) binder layer (20) by installing a screen printing plate on the thermoplastic polyurethane hot melt (TPU) film, applying a polyurethane binder with an average thickness of 0.005 to 1 mm, and drying it. The method sequentially includes a step (S300) of forming a polyurethane (PU) ink layer (30) by installing a screen printing plate on the upper part of the polyurethane (PU) binder layer (20) and applying and drying a polyurethane (PU) ink with an average thickness of 0.005 to 2 mm, wherein the polyurethane (PU) binder layer (20) and the polyurethane (PU) ink layer (30) located on the upper part of the thermoplastic polyurethane (TPU) hot melt film (10) form a pattern by screen printing with an average thickness of 0.01 to 3 mm.

[0056] The above polyurethane (PU) ink layer (30) formation step (S300) forms a flat-type or embossing-type pattern consisting of various shapes and colors by using a screen printing plate with the same or different designs or colors and applying the printing number within 1 to 100 times.

[0057] Since the screen printing method for forming a pattern on a skin film for a shoe upper allows the printing plate to be reused semi-permanently for typically more than 2,000 times, it is environmentally friendly and increases product productivity, as well as enabling the precise formation of high-quality three-dimensional patterns, because it does not generate release paper waste or harmful substances such as DMF (dimethylformamide), compared to the release paper method, which requires the release paper to be discarded after performing the process of transferring the pattern and separating it from the substrate about 3 to 8 times using a synthetic resin-coated release paper with a separate embossed pattern.

[0058] It goes without saying that the PU skin film manufactured as described above can be recycled into materials such as dry coating materials by crushing the scrap generated after cutting, due to the characteristics of the same type of polyurethane material.

[0059] As described above, the screen printing method for directly forming the PU ink layer (skin layer) in the present invention is called the 'R-Max method' to mean that it maximizes the pattern without using release paper. As a result, the cost of purchasing expensive release paper is reduced, and not only are non-recyclable release paper waste and harmful substances such as DMF (dimethylformamide) not generated, but the process is simplified and productivity is improved. Furthermore, it enables the realization of embossing patterns consisting of various shapes and colors on the surface of shoe uppers, etc., compared to conventional methods.

[0060] In addition, the method for manufacturing a shoe upper with a PU skin film bonded thereto, as described above, involves cutting the PU skin film for the shoe upper using the screen printing method into a desired shape, arranging the cut PU skin film on the surface of the shoe upper, and then processing it within 15 to 25 seconds using a heat press at a temperature of 120 to 140°C and a pressure of 40 to 50 kgf / ㎠ to form it integrally with the shoe upper.

[0061] This is attributed to the action of a TPU hot melt film (10) containing hydrophobic nanosilica in the range of 0.1 to 5 phr, which is bonded to the upper part of the shoe upper among PU skin films. In the case of applying a TPU hot melt film that does not contain hydrophobic nanosilica, it must be processed for more than 30 seconds by a heat press under the same conditions (temperature 120 to 140°C, pressure 40 to 50 kgf / ㎠) to be molded integrally with the shoe upper. Based on this, the present invention has confirmed that by using a TPU hot melt film (10) containing hydrophobic nanosilica as described above, the time required for the molding process is shortened, thereby increasing product productivity and reducing high energy costs. Consequently, the pattern formed on the upper part of the PU skin film is minimized by heat and pressure, thereby significantly improving the quality of the product.

[0062] [Experimental Example]

[0063] To demonstrate the effectiveness of the PU skin film manufactured as described above, a PU skin film was cut into a specific shape by applying a PU binder layer and a PU ink layer to a TPU hot melt film using a screen printing method with a thickness of 70 μm. Then, the film was arranged on the surface of an engineered mesh or sandwich mesh fabric used for shoe uppers, and then processed with a heat press at a temperature of 130°C and a pressure of 45 kgf / cm² to be integrally molded with the shoe upper. As for the TPU hot melt films, a conventional TPU hot melt film (NASA-T) and a TPU hot melt film (NASA-TT) blended with hydrophobic nanosilica were used, respectively.

[0064] As described above, the average value of the test results of measuring the thickness reduction rate and appearance condition several times before and after molding by a heat press for a shoe upper bonded with a PU skin film is shown in [Table 1] below.

[0065] TPU hot melt film Plastic surgery time SP thickness (PU binder layer + PU ink layer) Thickness reduction rate Type (thickness) Hydrophobic NS Before plastic surgery After plastic surgery Thickness deviation ① NASA-T(0.2t) 0 phr 30 seconds 140㎛ 100㎛ 40㎛ 28.6% ② NASA-T(0.12t) 0 phr 30 seconds 140㎛ 108㎛ 32㎛ 22.9% ③ NASA-TT(0.12t) 0.5 phr 20 seconds 140㎛ 135㎛ 5㎛ 3.6% ④ NASA-TT(0.12t) 2.0 phr 15 seconds 140㎛ 137㎛ 3㎛ 2.1%

[0066] From the test results of [Table 1] above, the present invention, etc. When a PU skin film with a pattern formed by screen printing is bonded integrally with a shoe upper using a heat press, the molding time using a TPU hot melt film (③, ④) containing a certain amount of hydrophobic nanosilica is reduced by approximately 30 to 50% compared to a general TPU hot melt film (①, ②), thereby increasing product productivity and saving energy. At the same time, it was confirmed that the reduction rate of the thickness of the PU binder layer and PU ink layer formed by screen printing is significantly reduced, and the appearance is also very good. Based on these facts, the pattern formed on the upper surface of the PU skin film can be significantly improved in product quality by minimizing deformation caused by the heat and pressure of the heat press.

[0067] Accordingly, the PU skin film for shoe uppers using screen printing according to the present invention can be substituted, modified, and changed in various forms within the scope of the technical concept of the present invention, and can be applied to various uses such as sports goods, household goods, and industrial goods, as well as leather and plastic products, as well as fabric fields required for various shoes, clothing, bags, home interiors, and automotive interior materials that require uniform adhesion and durability. Explanation of the symbols

[0068] 10: Hydrophobic NS-containing TPU hot melt film 20: Screen printing PU binder layer 30: Screen printing PU ink layer

Claims

Claim 1 A PU skin film for bonding to the surface of a shoe upper using a heat press comprises: a thermoplastic polyurethane (TPU) hot melt film (10) with a thickness of 0.02 to 0.3 mm containing hydrophobic nanosilica with a primary particle size of 1 to 100 nm in a range of 0.1 to 5 phr (Parts per Hundred Resin); a polyurethane (PU) binder layer (20) with an average thickness of 0.005 to 1 mm applied by screen printing on the upper surface of the thermoplastic polyurethane (PU) hot melt film (10); and a polyurethane (PU) ink layer (30) with an average thickness of 0.005 to 2 mm applied by screen printing on the upper surface of the polyurethane (PU) binder layer (20); wherein the polyurethane (PU) A PU skin film for a shoe upper using screen printing, characterized in that the ink layer (30) forms a flat-type or embossing-type pattern consisting of various shapes of designs and colors by applying a screen printing plate with the same or different designs or colors within 1 to 100 printing cycles, and the polyurethane (PU) binder layer (20) and polyurethane (PU) ink layer (30) located on the upper part of the thermoplastic polyurethane (TPU) hot melt film (10) form a pattern by screen printing with an average thickness of 0.01 to 3 mm. Claim 2 A PU skin film for a shoe upper using screen printing according to claim 1, wherein the hydrophobic nanosilica contained in the thermoplastic polyurethane (TPU) hot melt film (10) comprises one or more hydrophobic functional groups selected from alkyl groups, dimethyl groups, trimethyl groups, dimethylsiloxane groups, and methacrylate groups on the particle surface of the nanosilica, and exists in the state of nanosilica aggregates having an average aggregate size of 100 to 1200 nm within the TPU hot melt film. Claim 3 delete Claim 4 A step (S100) of preparing a thermoplastic polyurethane (TPU) hot melt film (10) with a thickness of 0.02 to 0.3 mm containing hydrophobic nanosilica with a primary particle size of 1 to 100 nm in a range of 0.1 to 5 phr (Parts per Hundred Resin); a step (S200) of forming a polyurethane (PU) binder layer (20) by installing a screen printing plate on the upper surface of the thermoplastic polyurethane hot melt (TPU) film, applying a polyurethane binder with an average thickness of 0.005 to 1 mm, and drying it; and a step (S200) of forming a polyurethane (PU) ink layer (30) by installing a screen printing plate on the upper surface of the polyurethane (PU) binder layer (20), applying a polyurethane (PU) ink with an average thickness of 0.005 to 2 mm, and drying it. A method for manufacturing a PU skin film for a shoe upper using screen printing, wherein the polyurethane (PU) ink layer (30) formation step (S300) is formed by applying a printing number of 1 to 100 times using a screen printing plate having the same or different designs or colors to form a flat-type or embossing-type pattern consisting of various shapes and colors, and the polyurethane (PU) binder layer (20) and polyurethane (PU) ink layer (30) located on the upper part of the thermoplastic polyurethane (TPU) hot melt film (10) form a pattern by screen printing with an average thickness of 0.01 to 3 mm. Claim 5 delete Claim 6 A method for manufacturing a shoe upper with a PU skin film bonded thereto, characterized by cutting a PU skin film for a shoe upper using screen printing obtained by the manufacturing method of claim 4 into a desired shape, arranging the cut PU skin film on the surface of the shoe upper, and then processing it within 15 to 25 seconds using a heat press at a temperature of 120 to 140℃ and a pressure of 40 to 50 kgf / ㎠ to form it integrally with the shoe upper.

Images