GB1018241A - Improvements in or relating to method of making corrugated fibre board and products obtained thereby - Google Patents

Abstract

Adhesives which may be used in the production of multiple wall corrugated fibre board (see Division D2) and which are required to set at different temperatures are based upon sodium silicate or upon starch. A 38 DEG Be sodium silicate solution having a silica to soda ratio in the range of 3.2 to 3.33 is suitable as a high temperature adhesive; the addition of 12% clay reduces the setting temperature, while a still lower temperature adhesive is obtained by using 70% silicate, 6% starch, 18% clay and 6% borax. A starch mix of 20% solids and having a caustic content of about 2.7% may be used as a high temperature adhesive. The caustic content may be raised to about 3.3% to reduce the setting temperature while still further reduction may be effected by the addition of about 20% of a polyvinyl acetate emulsion.ALSO:A process for making multiple-ply corrugated fibre board comprises a first step of producing three single face boards each consisting of a liner sheet of relatively thin but very dense, highly calendered paper to which corrugated medium weighing at least 30 lbs/1,000 square feet is adhesively secured at the tips of the corrugations; and a second step of adhesively uniting the several single face boards together with an additional liner sheet to form the composite board. The adhesive applied in the first step, is compounded to set at a relatively high temperature and is partly set and dried at this stage by means of a heated roll. This first adhesive is either a sodium silicate solution or a starch. (see Division C4). In the second step, adhesive of lower-temperature-setting characteristics is applied to the exposed crests of the corrugated medium, and the separate layers, together with the additional liner sheet, while being pressed together under the action of a belt to maintain flatness and to prevent relative slippage are passed over a heated plate which serves to set the adhesive. The second adhesive is either a silicate formula or a starch modified to contain 20% of a polyvinyl acetate emulsion. Owing to the temperature characteristics chosen for the first adhesive the reheating involved in the second step does not result in embrittlement. As the adhesive of the uppermost layer is the least easily heated in the second step it may be compounded to set at the lowest temperature. As shown, the two upper layers of corrugated medium are of greater height and pitch than the lowermost layer. While all the liners are of equally dense paper e.g. Kraft paper the outer liners are preferably thicker and the corrugated medium is of heavier type than is conventionally used in corrugated board of this type and weighs at least 30 lbs/1,000 square feet, to increase the strength of the board. After the heating process, which is arranged not completely to dry the adhesive, the board is cooled, and may be scored transversely to the corrugations by a pair of mating rotatable die wheels as and where required for subsequent folding operations e.g, for making cartons. The board may be stacked for a curing period to allow the moisture content of the board to reach equilibrium with the surrounding atmosphere.