Retort container, and hot melt adhesive therefor

Abstract

A retort container comprises a container body structured and arranged for holding a food product, the container body defining an opening and a sealing surface surrounding the opening, and a lid bonded to the sealing surface of the container body to close the opening, the lid being bonded to the sealing surface with a hot melt adhesive. The adhesive comprises a polyamide resin blended with a second resin that raises the glass transition temperature of the adhesive above the glass transition temperature of the polyamide resin alone, the adhesive bonding the lid to the sealing surface with a temperature-dependent bond strength that is relatively low at room temperature and substantially higher at retort temperatures of 100° C. to 120° C.

Description

BACKGROUND OF THE INVENTION [0001] The invention relates to containers for products, and more particularly relates to retort containers for food. [0002] Retort containers are containers that are hermetically sealed after filling with a food product, and are then heated to a temperature of about 100° C. to 120° C. for a period of time to ensure that all microorganisms in the container have been killed. The chief advantages of retort containers is that they do not require refrigeration prior to opening, and they can be stored for long periods of time in their initially sealed condition. For many years, metal cans were the predominant type of retort container. [0003] More recently, plastic retort containers have been developed. Plastic containers are attractive for various reasons, including microwavability. One of the challenges with plastic retort containers is the closure system. More particularly, the container lid must be hermetically sealed to the container with sufficient streng...

AI Technical Summary

Benefits of technology

[0006] The invention addresses the above needs and achieves other advantages, by providing an all-plastic retort container wherein the lid is adhesively sealed to the container as opposed to being heat-sealed to the container. The adhesive employed

Problems solved by technology

One of the challenges with plastic retort containers is the closure system.

More particularly, the container lid must be hermetically sealed to the container with sufficient strength to withstand the elevated temperature and pressure conditions during retort sterilization; on the other hand, the seal strength must not be so high that the consumer finds it difficult or impossible to remove the lid.

Retort integrity and ease of opening are usually at odds with each other, such that anything that is done to improve retort integrity has a deleterious effect on ease of opening, and vice versa.

The difficulties of accurately controlling the seal strength of heat seals are well known.

If the sealing temperature is too low, the seal strength may be inadequate to prevent failure during retort; if the temperature is too high, the seal strength may be so great that the consumer cannot remove the lid.

It can be difficult to control the sealing temperature with sufficient accuracy to stay within the desired window.

Fast sealing speed is difficult to achieve with all-plastic lids because induction sealing cannot be used, and direct thermal heat sealing is slow because of the poor thermal conductivity of plastic.

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