Curved-Surface Laminate Structure for Wrinkle-Suppressed Bonding
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Solution Overview
Problem
Existing methods for bonding laminates with heat seal layers to curved surfaces, such as windshields, often result in wrinkles and inadequate followability due to the lack of stiffness and require time-consuming mold removal processes.
Innovation Solution
A laminate structure with a hard coat layer, resin base material, and heat seal layer, characterized by a flexural stiffness coefficient of 5×10^6 GPa·μm^3 or more and an average thermal contraction rate of 0.3% or more, allowing for mold-free bonding to curved surfaces with reduced wrinkle formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a laminate with heat seal layer is bonded to a curved surface using a mold, then the bonding coverage and followability are improved, but the process complexity and time consumption increase due to mold removal
Solution Approach 1:
The patent removes the mold from the bonding process entirely. By formulating the heat seal layer with specific properties (glass transition temperature 60-100°C, storage modulus 100-500 MPa at bonding temperature), the laminate can be directly bonded to curved surfaces without requiring a mold for support or shaping, thereby eliminating the mold removal step while maintaining good followability.
Solution Approach 2:
The patent changes the thermal and mechanical parameters of the heat seal layer to enable mold-free bonding. By controlling the glass transition temperature (60-100°C) and storage modulus (100-500 MPa at bonding temperature), the material becomes sufficiently compliant at bonding temperature to conform to curved surfaces without mold support, yet maintains enough stiffness at service temperature to provide structural integrity.
2Manufacturing precision
If the laminate stiffness is increased to reduce wrinkles, then the manufacturing precision is improved, but the followability to curved surfaces deteriorates
Solution Approach 1:
The patent makes the stiffness of the heat seal layer dynamic through temperature control. At bonding temperature (above glass transition temperature of 60-100°C), the storage modulus is reduced to 100-500 MPa, allowing the laminate to conform to curved surfaces easily. After bonding, upon cooling below the glass transition temperature, the storage modulus increases significantly, providing sufficient stiffness to suppress wrinkles and maintain manufacturing precision.
Solution Approach 2:
The patent utilizes the glass transition phase transition of the heat seal layer polymer. By heating above the glass transition temperature (60-100°C), the polymer transitions from a glassy rigid state to a rubbery compliant state, enabling easy conforming to curved surfaces. After bonding, cooling below the glass transition temperature returns the polymer to the rigid state, providing wrinkle suppression and structural stability.
3Manufacturing precision
If a mold is used for bonding the laminate to curved surfaces, then the bonding uniformity is improved, but the productivity decreases due to time-consuming mold removal
Solution Approach 1:
The patent extracts the mold from the bonding process by using a mold-free bonding approach. The heat seal layer's controlled mechanical properties (storage modulus 100-500 MPa at bonding temperature) and thermal properties (glass transition temperature 60-100°C) enable direct bonding to curved surfaces while maintaining bonding uniformity, eliminating the time-consuming mold removal step and improving productivity.
4Ease of operation
If the heat seal layer is made more compliant to improve followability, then the ease of operation is improved, but the wrinkle suppression capability worsens
Solution Approach 1:
The patent employs dynamic stiffness control through temperature variation. The heat seal layer is designed with glass transition temperature of 60-100°C, so that during bonding (heated above Tg), the storage modulus drops to 100-500 MPa providing high compliance for excellent followability. After bonding and cooling below Tg, the storage modulus increases significantly, providing sufficient stiffness for wrinkle suppression, thus resolving the contradiction between compliance and stiffness.
Solution Approach 2:
The patent exploits the glass transition phase transition to dynamically adjust the heat seal layer's mechanical properties. Above the glass transition temperature (60-100°C), the polymer is in a rubbery compliant phase with low storage modulus (100-500 MPa), enabling easy conforming to curved surfaces. Below the glass transition temperature, the polymer transitions to a glassy rigid phase with high storage modulus, providing wrinkle suppression capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The laminate effectively adheres to curved surfaces without molds, ensuring uniform and small wrinkles, improving followability and reducing the need for time-consuming mold removal operations.
Implementation Method 1
an average thermal contraction rate at 140° C. is 0.3% or more
Implementation Method 2
a method of bonding a sheet-like material such as the reflection film to the adherend having such a curved surface, a method conceptually shown in FIG. 6 by thermal compression bonding using a heat seal layer
Data Source
AI summary
An object of the present invention is to provide a laminate which can be bonded to an adherend having a curved surface with favorable curved surface followability while suppressing occurrence of wrinkles after bonding, a bonded body and an image display system using the laminate, and a method for manufacturing a bonded body. The laminate of the present invention includes a hard coat layer disposed on the outermost side, a resin base material, and a heat seal layer in this order, and has a flexural stiffness coefficient S represented by an expression “Flexural stiffness coefficient S=Average tensile modulus of laminate (GPa)×(Thickness of laminate (μm))3” of 5×106 GPa·μm3 or more, and an average thermal contraction rate at 140° C. of 0.3% or more.