Compression-Moulded Preform End Wall Crystallinity Control
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Solution Overview
Problem
Preforms for containers, such as bottles, often exhibit defects like opaque zones and residual tensions in the end wall due to uneven cooling and high crystallinity, leading to potential breakages during stretch-blow moulding and the container's life.
Innovation Solution
A compression-moulded preform with a dome-shaped end wall that is not more crystalline than the side wall, achieved through controlled moulding parameters like temperature, pressure, and filling speed, ensuring even cooling and reduced shear stress, resulting in a preform with reduced defects and residual tensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If injection moulding is used to form preforms, then the preform can be obtained efficiently, but the end wall develops opaque zones and residual tensions due to uneven cooling and high crystallinity
Solution Approach 1:
The patent changes the moulding method from injection moulding to compression moulding, fundamentally altering the processing parameters. This eliminates the injection conduit and associated high-temperature zones, resulting in uniform cooling and crystallinity throughout the preform, particularly in the end wall region, thereby eliminating opaque zones and residual tensions
2Ease of manufacture
If the injection conduit temperature is maintained high to ensure plastic flow, then the plastics can fill the forming chamber easily, but the central region of the end wall cools more slowly creating residual tensions
Solution Approach 1:
The patent removes the injection conduit entirely by using compression moulding instead of injection moulding. This eliminates the temperature gradient issue at the injection point, ensuring uniform cooling and crystallinity throughout the preform, thereby preventing residual tensions and improving structural integrity
3Stability of the object's composition
If the end wall has high crystallinity, then the preform structure is more stable, but opaque zones form and breakages occur during stretch-blow moulding
Solution Approach 1:
The patent achieves uniform local quality throughout the preform by using compression moulding, which eliminates the high-crystallinity zone in the end wall that forms with injection moulding. This uniform structure prevents opaque zones and ensures consistent mechanical properties, thereby preventing breakages during stretch-blow moulding while maintaining overall structural stability
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 solution significantly reduces defects and residual tensions in the preform, enhancing the mechanical resistance and aesthetic quality of the container, thereby minimizing the risk of breakages during and after the stretch-blow moulding process.
Implementation Method 1
the preform is cooled inside the mould arranged in the closed position
Implementation Method 2
the end wall is not more crystalline than the side wall
Data Source
Figure 1~2
Figure 3
Figure 4~6
AI summary
A preform for obtaining a container comprises a hollow body (2) having a side wall (5) extending around a longitudinal axis (Z) and an end wall (4) arranged transversely to said longitudinal axis (Z), a point (A) of said end wall (4) having a value of specific residual melting enthalpy (?Hspec) ; there is at least one point (B, F, L, O) of said side wall (5) having a further value of specific residual melting enthalpy (?Hspec) that is greater than said value. A container comprises a containing body (31) having a first end zone (33) closed by a base wall (32) and a second end zone (34) suitable for engaging closing means; there is at least one point (A') of said base wall (32) having a value of specific residual melting enthalpy (?Hspec) that is significantly less than the specific residual melting enthalpy (?Hspec) of the points (B', F', L') of said containing body (31) distinct from said second end zone (34) .