Injection molding parts with fastener elements

Details Injection molding parts with fastener elements Injection molding parts with fastener elements

1998-05-13

2001-02-13

Heitbrink, Tim (Department: 1722)

Plastic and nonmetallic article shaping or treating: processes

Mechanical shaping or molding to form or reform shaped article

Shaping against forming surface

C264S328100, C425S139000, C425S438000, C425S444000, C425S545000, C425S556000

Reexamination Certificate

active

06187247

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to the ejection from injection molds of products having arrays of molded fastener elements.
The process for producing an injection molded product typically includes filling a mold cavity with molten polymer, cooling to solidify the molten polymer, opening the mold cavity, and ejecting the molded product. Products having an array of many, small integrally molded fastener elements, such as hook elements for hook and loop fastening, can be difficult to eject, for example, due to their small dimensions, low strengths or their tendency to be retained by features of the mold cavity. This is particularly the case when it is sought to design the hooks with complex or minute features to obtain improved hook performance.
SUMMARY OF THE INVENTION
An injection mold is provided that includes an ejection system capable of ejecting a molded product that includes an array of integrally formed fastener elements that extend from a base. In some cases, the ejection system includes a series of ejector pins which extend through the surface of the mold to eject the product in a progressive manner. In other cases, the ejection system includes moveable mold parts which pull fastener elements out of mold cavities, which may reduce or eliminate the use of pins.
In a general aspect, an injection mold for producing a product having an array of fastener elements integrally molded with and extending from a first side of a base and a method for ejecting the product from the mold are featured. The mold has a first mold surface penetrated by an array of fastener cavities. The mold includes a series of ejector pins distributed along the extent of the array of fastener cavities and adapted to extend through the first mold surface to eject the product. An ejector pin actuator is constructed and arranged to move the pins in a predetermined progressive sequence to push the molded product away from the first mold surface in the manner to pull the fastener elements from the cavities progressively across the array of cavities.
Embodiments of this principle may include one or more of the following features. At least many of the fastener cavities include undercut portions. The fastener cavities are hook-shaped. The undercut portions of the fastener cavities extend in a common direction. The pre-determined progressive sequence proceeds in the direction in which the undercut portions extend. The injection mold has an array including first and second types of fastener cavities, the fastener cavities of the first type all extending in a first direction and the fastener cavities of the second type all extending in a second direction. The injection mold defines a mold cavity for the base of deformable shape whereby the predetermined progressive sequence of the pins progressively deforms the base of product during the progressive action of the sets of ejector pins. The mold cavity for the base defines a sheet-form base that can progressively bend during the progressive action of the sets of ejector pins. The ejector pins are arranged across the array in a series of rows, with ejector pins of individual rows constructed and arranged to extend through the mold surface simultaneously, and ejector pins of consecutive rows extending through the surface in a progressive sequence.
In some embodiments, the first mold surface is curved. The ejector pins have a curved push surface arranged to follow the shape of the first mold surface. At least one of the ejector pins is adapted to extend at an oblique angle through the first mold surface.
In some configurations, the ejector pin actuator is a stepped ejector plate. The ejector pin actuator is a rotational cam assembly. The ejector pin actuator is a series of individual actuators.
In some cases, the injection mold further includes a second mold surface opposing the first mold surface with the first and second mold surfaces defining therebetween a base cavity for molding the base. The second mold surface has a second array of fastener cavities extending therefrom for forming a second array of fastener elements integrally molded with and extending from a second side of the base. The second mold surface is constructed to retract from the first mold surface to pull the array of fastener cavities extending from the second mold surface away from the fastener elements extending from the second side of the base, while the product is retained in the first mold surface. An ejector is arranged to push against perimeter portions about the second array of fastener elements to hold the molded product while the second mold surface retracts.
Among other advantages, the molded product, particularly products having uni-directional fastener elements, can be ejected from the injection mold without significantly deforming fastener elements as they are removed from the mold cavities. As a result, the fastener elements on molded product are not significantly distorted from their molded shape. In general, distortion of fastener elements during de-molding can sacrifice the ability of the fastener elements to engage loops in use, thus limiting the effectiveness of the molded product. By rolling the fastener elements out of their mold cavities, a relatively small amount of force may be used to eject the product. Molded products having thin bases and or products made of relatively soft plastics can be ejected without damaging the base due to forces applied by ejector pins. The invention may also the ejection of products at higher temperatures and thus reduce cycle time.
In another general aspect, an injection mold for producing a molded product having an array of loop-engageable fastener elements integrally molded with and extending from a first broad side of a base and at least one retaining element integrally molded with and extending from the base opposite the first broad side and a method for ejecting the product from the mold are provided. The mold includes a first mold section defining a first mold surface with multiple fastener element-shaped cavities extending therefrom for forming the array of fastener elements. The mold includes at least a second mold section adapted to be aligned with the first mold section and defining a second mold surface having at least one retaining element-shaped cavity extending therefrom for forming the retaining element. The first mold section is constructed to retract relatively from the second mold section to pull the fastener element-shaped cavities away from the fastener elements while the molded product is retained in the second mold section by the retaining element.
Embodiments of this principle may include one or more of the following features. The second mold surface includes an array of retaining element-shaped cavities shaped to form loop-engageable fastener elements. The at least second mold section defines a mounting stud integral with the base. The injection mold includes an ejector arranged to push against a perimeter portion about the array of fasteners on a first broad side of the base as the first mold section retracts. The second mold section is constructed to open the retaining element-shaped cavity to release the product.
Among other advantages, the injection mold featured in this aspect can enable the molding of products with a high fastener element density (number of fastener elements per area of base). Fastener element density is sacrificed on products that include areas of the base from which no fastener elements extend that are contacted by ejector pins. Because the injection mold does not use ejector pins to eject the molded product, fastener element density is not limited by the presence of such areas. Additionally, damage to the base of the product by ejector pins is eliminated.
In another general aspect, an injection mold for forming a product having an array of loop-engageable fastener elements integrally molded with and extending from one side of a base and a method for ejecting the product from the mold are provided. The base includes a perimeter area about the array having no fastener elements

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