Connecting Layer for Injection-Moulded Hollow Items
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Solution Overview
Problem
Current industrial processes for producing plastics items with rigid and soft portions, such as sports shoes, face challenges in injecting soft materials into rigid molds due to differences in melting temperatures and hardness, leading to deformation and damage of the soft material, and require additional operations like sewing or gluing for assembly.
Innovation Solution
A process involving a connecting layer with a melting temperature exceeding 150 degrees centigrade and hardness above 80 Shore A, interposed between the soft inserts and the rigid casing, allows for the injection of molten rigid material onto soft inserts without deformation, using either bi-injection or over-injection methods, ensuring a permanent and comfortable connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If soft material is over-injected onto rigid material, then comfort is improved, but the soft material is damaged by dragging and overheating from the rigid material injection
Solution Approach 1:
A connecting layer made of soft material with high melting temperature (exceeding 150°C) and high hardness (above 80 Shore A) is introduced as an intermediary between the soft inserts and rigid casing. This connecting layer protects the soft inserts from dragging and overheating during rigid material injection, while still providing comfort functionality. The connecting layer has thermal and mechanical properties that allow it to withstand the injection process without deforming the soft inserts.
2Strength
If rigid material is injected onto soft material, then structural strength is improved, but the soft material deforms and loses its shape
Solution Approach 1:
The connecting layer serves as a protective intermediary that allows rigid material to be injected onto soft inserts without causing deformation. The connecting layer has sufficient structural integrity to resist the injection pressure and prevent the soft inserts from deforming, while still allowing the soft inserts to maintain their original shape and functionality.
Solution Approach 2:
The connecting layer is designed with specific parameter ranges: melting temperature exceeding 150°C and hardness above 80 Shore A. These parameter changes enable the connecting layer to withstand the high temperature and pressure of rigid material injection while protecting the soft inserts from deformation.
3Adaptability or versatility
If additional operations like sewing or gluing are used to attach soft portions, then assembly flexibility is improved, but production time and complexity increase
Solution Approach 1:
The connecting layer integrates the attachment function into the injection molding process itself. By designing the connecting layer with appropriate adhesion properties to both the soft inserts and rigid casing, the patent eliminates the need for separate sewing or gluing operations. The soft inserts are permanently attached through the connecting layer during the injection process, combining structural attachment with the molding operation.
Solution Approach 2:
The connecting layer provides self-attachment functionality through its material properties. The connecting layer naturally adheres to both the soft inserts and rigid casing through the injection process, eliminating the need for external attachment operations. The material composition and processing conditions enable the connecting layer to bond the components together automatically during molding.
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
Enables the production of hollow items like ski boots with a rigid outer shell and soft internal portions, enhancing user comfort and productivity while avoiding additional operations, using conventional equipment and materials at competitive costs.
Implementation Method 1
a connecting layer with a melting temperature exceeding 150 degrees centigrade and hardness above 80 Shore A, interposed between the soft inserts and the rigid casing
Implementation Method 2
a connecting layer with a melting temperature exceeding 150 degrees centigrade and hardness above 80 Shore A
Implementation Method 3
the plastics material is injected, so that on cooling it substantially retains the form of the cavities into which it was introduced
Data Source
Figure 1~2
Figure 3~5
AI summary
The present invention relates to a process of producing a hollow item by injection-moulding thermoplastic material, said item comprising a rigid external shell (12; 112) and at least one soft internal portion. The process includes the use of a mould comprising a matrix (30), a first semi-mould (37) comprising a first cavity (43) and a second semi-mould (38) comprising a second cavity (45) counter-shaped to the matrix (30) to reproduce a respective semi-shell of said rigid external shell (12; 112). The process comprises the phases of positioning at least one insert (14; 114) made of a soft material, constituting the soft internal portion, on the matrix (30); covering the insert (14; 114) with a connecting layer (15; 115); hermetically sealing the first and second semi-moulds (37; 38) onto the matrix (30) along the edges of the first and second cavity (43, 45); injecting into the space between the first and second cavity (43, 45) and the connecting layer (15; 115) a thermoplastic material destined to form the rigid external shell (12; 112) in order to create a permanent connection of the soft insert (14; 114) to the rigid external shell (12; 112). The connecting layer (15; 115) substantially retains the characteristics of the soft insert (14; 114) unchanged.