Methods to protect PU leather surface from nanostructure distortion and mobile phone casing

Abstract

This invention provides a method for protecting the nanostructure of PU leather from distortion during heat lamination. The method includes: slicing fiberglass prepreg rolls and release film rolls; filling the textured surface of the PU leather and the middle layer of the release film with UV resin adhesive using UV transfer printing to obtain a PU leather texture protective sheet; slicing the PU leather texture protective sheet; stacking the release film, PU leather texture protective sheet, and fiberglass prepreg roll from bottom to top; hot-pressing the stacked fiberglass prepreg rolls; placing the hot-pressed product into a shaping mold for cooling and shaping; placing the cooled and shaped product into a cutting machine fixture to cut off the waste area; placing the product into an edge-oiling machine, where an oiling head applies ink to the cut surface of the die for protection; and inspecting the product's appearance. This invention can protect the nanostructure of PU leather from distortion during heat lamination, restoring 100% of the leather texture effect.

Description

Technical Field

[0001] This invention relates to the field of mobile phone casing technology, and in particular to a method for protecting the nanostructure of PU leather surface from distortion during the heat bonding process, and a mobile phone casing thereof. Background Technology

[0002] With the continuous updating and iteration of mobile phone structural components materials, the process of applying PU leather to glass fiber has emerged in the mobile phone industry. The thinness, high strength and rigidity of glass fiber combined with the texture of leather is loved by various mobile phone terminals and consumers.

[0003] The existing technology for bonding fiberglass to PU leather involves: 3D hot-pressing the fiberglass prepreg (glass semi-cured sheet) to the PU leather (coated with hot melt adhesive film), then thermally bonding the product with a 1cm thick silicone pad on the leather texture surface in a hot press. The specific process of this method is as follows: Figure 1 As shown.

[0004] This approach has the following drawbacks:

[0005] 1. PU leather needs to be laminated with a hot melt adhesive film before being bonded to the fiberglass shell using a heat laminating machine, which requires a large number of heat laminating machines.

[0006] Second: During the heat bonding process, the nanostructure of the PU leather surface will deteriorate under the action of temperature / pressure, and the leather texture will be distorted.

[0007] Thirdly, PU leather material softens at temperatures above 40 degrees Celsius, and the bonding temperature is 80-100 degrees Celsius, resulting in a large temperature range. During the bonding process, the pressure is 1T-45T (depending on the structural definition), and the problem of leather texture distortion cannot be solved by adjusting the parameters. Summary of the Invention

[0008] The main objective of this invention is to provide a method and a mobile phone casing for protecting the nanostructure of PU leather from distortion during the heat bonding process, aiming to protect the texture of the PU leather nanostructure from distortion during the heat bonding process and restore 100% of the texture effect.

[0009] To achieve the above objectives, this invention proposes a method for protecting the nanostructure of PU leather from distortion during the thermal bonding process, the method comprising the following steps:

[0010] Step S10, Preparation of glass fiber prepreg / release film: According to the size requirements of the hot-pressed glass fiber shell material, the glass fiber prepreg roll and the release film roll are cut into slices using a die-cutting machine;

[0011] Step S20, Preparation of PU leather texture protective film: PU leather is placed on the glass platform of a UV transfer machine using UV transfer printing. The UV transfer machine's dispensing system adjusts the parameters according to the size of the leather, and UV resin adhesive is linearly dripped onto the edge of the PU leather 2 cm away. PET is then placed on top of the PU leather. The UV adhesive is cured by rolling and LED 395nm band UV lamps. The UV resin adhesive fills the textured surface of the PU leather. The UV resin adhesive does not react with the PU leather to form a molecular bond, thus forming a UV adhesive release layer, resulting in a PU leather texture protective film.

[0012] Step S30, Slicing the PU leather texture protective sheet: The PU leather texture protective sheet is sliced ​​using a die-cutting machine;

[0013] Step S40, Stacking: Stack the release film, PU leather texture protective film and glass fiber semi-cured film from bottom to top;

[0014] Step S50, hot pressing: Place the stacked glass fiber prepreg in a hot pressing mold and hot press to form the shape;

[0015] Step S60, cold pressing: Place the hot-pressed product into an aluminum alloy forming mold to cool and solidify;

[0016] Step S70, punching: Place the cooled and shaped product into the die on the edge trimming machine fixture to cut off the waste area;

[0017] The product is placed into the edge-painting machine, and the oiling head applies ink to the die-cut surface for protection.

[0018] Step S80: Inspect the product appearance.

[0019] A further technical solution of the present invention is that, in step S10, the release film slice is 1 cm larger than the glass fiber prepreg slice to prevent the glass fiber resin from melting and overflowing onto the hot press mold during the hot pressing process. The thickness of a single glass fiber prepreg is 0.1 mm to 0.15 mm. The glass fiber prepreg is stacked according to the actual product design thickness to achieve the product thickness. The thickness of the release film is 0.03 mm to 0.07 mm.

[0020] A further technical solution of the present invention is that step S20 includes:

[0021] Step S201: Place the PU leather on the UV transfer and glass platform;

[0022] Step S202: Using the UV transfer printing machine dispensing system, UV resin system glue is dripped in a line onto one side edge of the PU leather 2cm away.

[0023] Step S203: Place the PET (2cm larger than the leather) centered on the PU leather;

[0024] Step S204: Rotate the UV transfer machine to the rolling position, press down the rubber roller with a pressure of 0.20-0.45 MPa, and press the rubber roller on the PET at a uniform speed to spread the UV resin system glue all over the leather surface.

[0025] Step S205: The glass working platform of the UV transfer machine is moved to the UV curing position, the energy of the upper light source LED lamp is 2000mj / cm2, and the UV resin system adhesive is cured.

[0026] Step S206: Remove the PU leather with PET from the transfer glass platform.

[0027] A further technical solution of the present invention is that, in step S50, the hot pressing parameters are a mold temperature of 130 to 140 degrees Celsius and a hot pressing time of 5 to 12 minutes.

[0028] A further technical solution of the present invention is that, in step S60, the thermoformed product is taken out from the hot press mold and placed in an aluminum alloy mold for cooling and shaping for 4 to 5 minutes.

[0029] A further technical solution of the present invention is that the UV resin system adhesive comprises, by mass percentage: 2%-5% photoinitiator, 10%-18% NVP, 20%-25% HDDA, 39%-45% silicone-modified acrylate with a functionality of 2, and 10%-20% silicone-modified acrylate with a functionality of 9.

[0030] A further technical solution of the present invention is that the preparation steps of the UV resin system adhesive are as follows:

[0031] Production preparation; to make UV resin adhesive, prepare 2-5 grams of photoinitiator, 10-18 grams of NVP, 20-25 grams of HDDA, 39-45 grams of silicone-modified acrylate with a functionality of 2 and 10-20 grams of silicone-modified acrylate with a functionality of 9.

[0032] First batch of ingredients: Add 2-5 grams of photoinitiator, 10-18 grams of NVP, and 20-25 grams of HDDA into the mixing tank;

[0033] First stirring and dispersion; disperse at 100-500 rpm; 5-20 minutes until the photoinitiator is completely dissolved;

[0034] Second batching: Add 39-45 grams of silicone-modified acrylate with a functionality of 2 and 10-18 grams of silicone-modified acrylate with a functionality of 9 into the mixing tank.

[0035] Second stirring and dispersion: Pre-disperse at 200-500 rpm until there are no large lumps in the resin, disperse for 10-20 minutes; after there are no large lumps, increase the speed to 600-1200 rpm and disperse for 30-65 minutes. Stop the machine and scrape the bottom and sides with a spatula. Then start the machine and continue to disperse at 600-1200 rpm for 10-20 minutes until completely uniform.

[0036] Filter packaging: Take samples for testing after the machine is stopped. If the test is qualified, filter and package the filter with two layers of 200-400 mesh filter cloth.

[0037] To achieve the above objectives, the present invention also proposes a mobile phone case, which is made using the method described above to protect the nanostructure of PU leather surface from distortion during the heat bonding process.

[0038] The method for protecting the nanostructure of PU leather during the heat-bonding process and the beneficial effects of this invention on mobile phone casings are as follows:

[0039] 1. The PU leather and fiberglass semi-cured sheet are integrally thermo-pressed, which can 100% protect and restore the texture of the PU leather.

[0040] 2. This invention eliminates the need for fiberglass shell material and PU leather post-application, reducing process costs and hot melt adhesive film material costs.

[0041] 3. This invention shortens the entire product manufacturing and processing cycle. Attached Figure Description

[0042] Figure 1 This is a flowchart illustrating the existing technology of fiberglass-laminated PU leather.

[0043] Figure 2 This is a flowchart illustrating the method of protecting the nanostructure of PU leather surface from distortion during the thermal bonding process according to the present invention.

[0044] Figure 3 This is a schematic diagram of the UV transfer printing process for protecting the surface texture of PU leather.

[0045] Figure 4 This is a schematic diagram of the hot-pressing process for integrating PU leather and fiberglass material;

[0046] Figure 5 This is a schematic diagram of the PET peeling process after integral hot pressing molding.

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0048] It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0049] This invention proposes a method to protect the nanostructure of PU leather from distortion during the heat bonding process. The technical solution adopted in this invention mainly involves filling the textured surface of PU leather and the middle layer of the release film with a high-temperature resistant UV resin system adhesive through UV transfer printing, so as to protect the nanostructure of PU leather from distortion during the heat bonding process and restore 100% of the leather texture effect.

[0050] Specifically, please refer to Figures 2 to 5 A preferred embodiment of the method for protecting the nanostructure of PU leather surface from distortion during the heat bonding process according to the present invention includes the following steps:

[0051] Step S10, Preparation of glass fiber prepreg and release film: According to the size requirements of the hot-pressed glass fiber shell material, the glass fiber prepreg roll and release film roll are sliced ​​using a die-cutting machine.

[0052] In step S10, the release film slice is 1 cm larger than the glass fiber prepreg slice to prevent the glass fiber resin from melting and overflowing onto the hot press mold during the hot pressing process. The thickness of a single glass fiber prepreg is 0.1 mm to 0.15 mm. The glass fiber prepreg is stacked according to the actual product design thickness to achieve the product thickness. The thickness of the release film is 0.03 mm to 0.07 mm.

[0053] Step S20, Preparation of PU leather texture protective film: PU leather is placed on the glass platform of a UV transfer machine using UV transfer printing. The UV transfer machine's dispensing system adjusts parameters according to the size of the leather, and UV resin adhesive is linearly dripped onto the edge of the PU leather 2 cm away. PET is then placed on top of the PU leather. The UV adhesive is cured by rolling and an LED 395nm band UV lamp. The UV resin adhesive fills the textured surface of the PU leather. The UV resin adhesive does not react with the PU leather to form a molecular bond, thus forming a UV adhesive release layer, resulting in a PU leather texture protective film.

[0054] As shown in Table 1, in this embodiment, the UV resin system adhesive comprises, by mass percentage: 2%-5% photoinitiator, 10%-18% NVP, 20%-25% HDDA, 39%-45% silicone-modified acrylate with a functionality of 2, and 10%-20% silicone-modified acrylate with a functionality of 9.

[0055] Table 1

[0056]

[0057] The UV resin system adhesive cannot react with the molecular bonds of PU material and will not stick.

[0058] When using UV transfer printing, UV resin system adhesive is filled into the textured surface of PU leather and the intermediate layer of PET. The UV resin system adhesive does not react with the molecular bonds of PU material and will not stick. The UV resin system adhesive forms a polymerization or cross-linking reaction with PET and sticks together. Therefore, the UV resin adhesive and the PU leather surface form a release layer, which can protect the leather texture and can be peeled off.

[0059] After the PU leather surface is treated, a hot-pressing bonding process is performed to peel off the PET release liner. The PU leather texture attached to the fiberglass shell is well preserved without any distortion.

[0060] This solution ensures that the nano-texture on the surface of PU leather remains unchanged and does not fade under 150 degrees Celsius and 45T pressure.

[0061] Step S20 specifically includes:

[0062] Step S201: Place the PU leather on the UV transfer and glass platform.

[0063] Step S202: Using the UV transfer printing machine dispensing system, UV resin adhesive is dripped in a line onto one side of the PU leather at a distance of 2cm.

[0064] Step S203: Place the PET (2 cm larger than the leather) centered on the PU leather.

[0065] In step S204, the UV transfer machine is rotated to the rolling position, and the rubber roller is pressed down with a pressure of 0.20MP-0.45. The pressing rubber roller is rolled on the PET at a uniform speed to spread the UV resin system glue evenly on the leather surface.

[0066] Step S205: The glass working platform of the UV transfer machine is rotated to the UV curing position, the energy of the upper light source LED lamp is 2000mj / cm2, and the UV resin system adhesive is cured.

[0067] Step S206: Remove the PU leather with PET from the transfer glass platform.

[0068] Step S30, Slicing the PU leather textured protective sheet: The PU leather textured protective sheet is sliced ​​using a die-cutting machine.

[0069] Step S40, Stacking: Stack the release film, PU leather texture protective film and glass fiber semi-cured film from bottom to top.

[0070] Step S50, hot pressing: Place the stacked glass fiber prepreg in a hot pressing mold and hot press to form the shape.

[0071] In step S50, the hot pressing parameters are a mold temperature of 130 to 140 degrees Celsius and a hot pressing time of 5 to 12 minutes.

[0072] Step S60, cold pressing: Place the hot-pressed product into an aluminum alloy forming mold to cool and solidify.

[0073] In step S60, the thermoformed product is removed from the hot press mold and placed in an aluminum alloy mold for cooling and shaping for 4 to 5 minutes.

[0074] Step S70, punching: Place the cooled and shaped product into the edge cutting machine fixture and the die cuts off the waste area; place the product into the edge painting machine and the oiling head applies ink to the die-cut surface for protection.

[0075] Step S80: Inspect the product appearance.

[0076] In this embodiment, the preparation steps of the UV resin system adhesive are as follows:

[0077] Production preparation:

[0078] To make 100 grams of UV resin adhesive, prepare 2 grams of photoinitiator, 16 grams of NVP, 22 grams of HDDA, 45 grams of silicone-modified acrylate with a functionality of 2, and 15 grams of silicone-modified acrylate with a functionality of 9.

[0079] The following points should be noted during production preparation:

[0080] (1) Prepare a clean mixing tank.

[0081] (2) Confirm that the disperser is clean.

[0082] (3) Prepare process cards, materials, tools, etc. in advance.

[0083] (4) Select a mixing tank of appropriate capacity according to the number of process cards.

[0084] (5) Some ingredient tanks should be thoroughly cleaned and checked for any residual solvents or other materials.

[0085] (6) Find out some raw materials and semi-finished products, put them in a row, and confirm with the raw materials used in the process card before feeding them in.

[0086] Ingredient addition:

[0087] First batch of ingredients: Add 2 grams of photoinitiator, 16 grams of NVP, and 22 grams of HDDA into the mixing tank;

[0088] First stirring and dispersion; disperse at 100-500 rpm; 5-20 minutes until the photoinitiator is completely dissolved;

[0089] Second batching: Add 45 grams of silicone-modified acrylate with a functionality of 2 and 15 grams of silicone-modified acrylate with a functionality of 9 into the mixing tank.

[0090] Second stirring and dispersion: Pre-disperse at 200-500 rpm until there are no large lumps in the resin, disperse for 10-20 minutes, and after there are no large lumps, increase the speed to 600-1200 rpm and disperse for 30-65 minutes. Stop the machine and scrape the bottom and sides with a spatula, then start the machine again and continue to disperse at 600-1200 rpm for 10-20 minutes until completely uniform.

[0091] The following points should be noted during the ingredient preparation and feeding process:

[0092] (1) According to the number of process cards, a special person should make the order and a special person should review it. The materials should be added in the order of their sequence. The materials must be added accurately. (The photoinitiator should be dissolved in monomer first and there should be no lumps before adding the next step.) Some raw materials should be prepared according to the first-in-first-out principle.

[0093] (2) Pay attention to accurate weighing of additives; a precision electronic scale is required.

[0094] (3) Each pair of materials should be adjusted in a timely manner and relevant records should be made clearly, such as the batch number and weight.

[0095] (4) The accuracy of the electronic scale needs to be checked every day. Each time you weigh the scale, check whether there are any foreign objects supporting the weighing pan that may affect the accuracy of feeding.

[0096] (5) Avoid direct sunlight to prevent product defects.

[0097] (6) Take precautions, wear gloves, and avoid direct contact with raw materials.

[0098] (7) Pay attention to the safety of using the bucket dumping cart. The upper and lower hooks and safety ropes must be securely fastened.

[0099] (8) Pay attention to the safety of adding materials and prevent materials from splashing out.

[0100] The following points should be noted during the stirring and dispersion process:

[0101] (1) Pay attention to the use of the disperser. When starting the machine, gradually adjust the required speed from 0. When turning off the machine, first adjust the speed to 0 and then turn off the power. The mixing tank must be fixed.

[0102] (2) Control the speed and time according to the product process card.

[0103] (3) Note that the scraping speed should be reduced to ensure that the material in the whole barrel is uniform.

[0104] (4) When stirring, be careful to seal the container to prevent solvent from splashing out.

[0105] Filter packaging:

[0106] Sampling and testing were conducted after the machine was stopped. Once the test results were satisfactory, the sample was filtered through two layers of 200-500 mesh filter cloth. Then it was packaged.

[0107] The following points should be noted during the filtration and packaging process:

[0108] (1) Ensure that the packaging specifications are in accordance with the customer’s requirements.

[0109] (2) Ensure that the packaging barrels are clean. Clean the packaging barrels before packaging and check whether they are clean and whether they need to be washed.

[0110] (3) Pay attention to the specifications and cleanliness of the filter cloth and filter element.

[0111] (4) Ensure the seal is intact to prevent leakage. Press the glue container flat and tighten it, and press the iron drum firmly and lock it to prevent the lid from sticking up on one side.

[0112] (5) Pay attention to the weight of the packaging and mark any small change.

[0113] (6) Check the labels to ensure they are correctly affixed and that the height and orientation are consistent.

[0114] (7) Filter packaging: Select the filter cloth or filter element according to the filter cloth or filter element indicated on the process card. Clean the packaging barrel before packaging and check whether it is clean and whether it needs to be cleaned.

[0115] (8) Seal the packaged products in time to prevent dust and other materials from falling into the container, and affix labels to the covered buckets, with all labels facing the same direction and at the same height.

[0116] The beneficial effects of the method for protecting the nanostructure of PU leather surface from distortion during the heat bonding process, as described in this invention, are:

[0117] 1. The PU leather and fiberglass semi-cured sheet are integrally thermo-pressed, which can 100% protect and restore the texture of the PU leather.

[0118] 2. This invention eliminates the need for fiberglass shell material and PU leather post-application, reducing process costs and hot melt adhesive film material costs.

[0119] 3. This invention shortens the entire product manufacturing and processing cycle.

[0120] To achieve the above objectives, the present invention also proposes a mobile phone case, which is made by the method described above for protecting the PU leather surface nanostructure from distortion during the heat bonding process. The method for protecting the PU leather surface nanostructure from distortion during the heat bonding process has been described in detail above and will not be repeated here.

[0121] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural changes made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for protecting the nanostructure of PU leather from distortion during a heat-bonding process, characterized in that, The method includes the following steps: Step S10, Preparation of glass fiber prepreg and release film: According to the size requirements of the hot-pressed glass fiber shell material, the glass fiber prepreg roll and release film roll are cut into slices using a die-cutting machine; Step S20, Preparation of PU leather texture protective film: PU leather is placed on the glass platform of a UV transfer machine using UV transfer printing. The UV transfer machine's dispensing system adjusts the parameters according to the size of the leather, and UV resin adhesive is linearly dripped onto the edge of the PU leather 2 cm away. PET is then placed on top of the PU leather. The UV adhesive is cured by rolling and LED 395nm band UV lamps. The UV resin adhesive fills the textured surface of the PU leather. The UV resin adhesive does not react with the PU leather to form a molecular bond, thus forming a UV adhesive release layer, resulting in a PU leather texture protective film. Step S30, Slicing the PU leather texture protective sheet: The PU leather texture protective sheet is sliced ​​using a die-cutting machine; Step S40, Stacking: Stack the release film, PU leather texture protective film and glass fiber semi-cured film from bottom to top; Step S50, hot pressing: Place the stacked glass fiber prepreg in a hot pressing mold and hot press to form the shape; Step S60, cold pressing: Place the hot-pressed product into an aluminum alloy forming mold to cool and solidify; Step S70, punching: Place the cooled and shaped product into the die on the edge trimming machine fixture to cut off the waste area; The product is placed into the edge-painting machine, and the oiling head applies ink to the die-cut surface for protection. Step S80: Inspect the product appearance; The UV resin system adhesive comprises, by weight percentage: 2%-5% photoinitiator, 10%-18% NVP, 20%-25% HDDA, 39%-45% silicone-modified acrylate with a functionality of 2, and 10%-20% silicone-modified acrylate with a functionality of 9.

2. The method for protecting the nanostructure of PU leather from distortion during the thermal bonding process according to claim 1, characterized in that, In step S10, the release film slice is 1 cm larger than the glass fiber prepreg slice to prevent the glass fiber resin from melting and overflowing onto the hot press mold during the hot pressing process. The thickness of a single glass fiber prepreg is 0.1 mm to 0.15 mm. The glass fiber prepreg is stacked according to the actual product design thickness to achieve the product thickness. The thickness of the release film is 0.03 mm to 0.07 mm.

3. The method for protecting the nanostructure of PU leather surface from distortion during the heat bonding process according to claim 1, characterized in that, Step S20 includes: Step S201: Place the PU leather on the UV transfer and glass platform; Step S202: Using the UV transfer printing machine dispensing system, UV resin system glue is dripped in a line onto one side edge of the PU leather 2cm away. Step S203: Place the PET piece, which is 2 cm larger than the leather, on the PU leather in the center; Step S204: Rotate the UV transfer machine to the rolling position, press down the rubber roller with a pressure of 0.20-0.45 MPa, and press the rubber roller on the PET at a uniform speed to spread the UV resin system glue all over the leather surface. Step S205: The glass working platform of the UV transfer machine is moved to the UV curing position, the energy of the upper light source LED lamp is 2000mj / cm2, and the UV resin system adhesive is cured. Step S206: Remove the PU leather with PET from the transfer glass platform.

4. The method for protecting the nanostructure of PU leather surface from distortion during the heat bonding process according to claim 1, characterized in that, In step S50, the hot pressing parameters are a mold temperature of 130 to 140 degrees Celsius and a hot pressing time of 5 to 12 minutes.

5. The method for protecting the nanostructure of PU leather surface from distortion during the heat bonding process according to claim 1, characterized in that, In step S60, the thermoformed product is removed from the hot press mold and placed in an aluminum alloy mold for cooling and shaping for 4 to 5 minutes.

6. The method for protecting the nanostructure of PU leather surface from distortion during the heat bonding process according to claim 1, characterized in that, The preparation steps of the UV resin system adhesive are as follows: Production preparation; to make UV resin adhesive, prepare 2-5 grams of photoinitiator, 10-18 grams of NVP, 20-25 grams of HDDA, 39-45 grams of silicone-modified acrylate with a functionality of 2 and 10-20 grams of silicone-modified acrylate with a functionality of 9. First batch of ingredients: Add 2-5 grams of photoinitiator, 10-18 grams of NVP, and 20-25 grams of HDDA into the mixing tank; First stirring and dispersion; disperse at 100-500 rpm; 5-20 minutes until the photoinitiator is completely dissolved; Second batching: Add 39-45 grams of silicone-modified acrylate with a functionality of 2 and 10-18 grams of silicone-modified acrylate with a functionality of 9 into the mixing tank. Second stirring and dispersion: Pre-disperse at 200-500 rpm until the resin is free of large lumps, and disperse for 10-20 minutes; After the large lumps are gone, increase the rotation speed to 600-1200 rpm and disperse for 30-65 minutes. Stop the machine and scrape the bottom and sides with a scraper. Then, turn the machine back on and continue to disperse at 600-1200 rpm for 10-20 minutes until completely uniform. Filtration and Packaging: The machine is stopped for sampling and testing. After passing the test, the filter is filtered with two layers of 200-400 mesh filter cloth and then packaged.

7. A mobile phone casing, characterized in that, The phone casing is made using the method described in any one of claims 1 to 6 to prevent distortion of the nanostructure of the PU leather surface during the heat bonding process.

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