Paper honeycomb products must have a certain moisture-proof function, but how to define the moisture-proof grade of paper honeycomb products, how to produce qualified moisture-proof products, and how to determine the moisture resistance and water resistance of the substrate, etc. Improve the quality of products, enhance product competitiveness and promote the development of the industry's major issues.
First, why the paper honeycomb products moisture-proof
The so-called moisture-proof is the ability of the bonding structure to adapt to environmental factors. It is precisely the product's ability to withstand moisture, moisture, and temperature. Paper is the base material of honeycomb products, and its main components are cellulose and hemicellulose. According to the structure of cellulose, using Fedors' method and Lee's formula, the surface tension of cellulose is calculated as rc=72.4 dyne/cm, which is almost equal to the surface tension of water, so cellulose is easily wetted by water. The surface of the paper is also porous, and water vapor easily penetrates into the interior of the paper and reaches the bonding surface between the adhesive and the fiber, gradually causing the bonding interface to break down and forming a weak interface layer.
The porosity, wettability, and permeability of the paper substrate show a weak interface in a wet environment, resulting in a reduction in the rigidity of the honeycomb structure and a decrease in strength, and this decrease is exacerbated by increasing humidity. When cellulose absorbs moisture and expands in its own volume, its expansion ratio is longitudinal: transverse: thickness 2:1:50, resulting in loss of structural strength. There is no power in leaving the dried honeycomb cardboard or rain-dried honeycomb products, and of course there is no use value.
Tests have shown that moisture damage to bond strength is more severe than water, especially in coastal areas where salt water and salt fog are more destructive, because the molecules of water in moisture are smaller and penetrate into the interior of the paper.
The decline in structural strength is also proportional to the ambient temperature, high temperature, high and bad, so that the product's resistance to the environment is greatly enhanced.
Second, paper cellular moisture technology
The first is the scientific use of moisture-proof paper as a substrate. Most of our country: several paper honeycomb products use cardboard, corrugated paper, wood pulp noodle paper. National standards GB5034 and GBl3024-91 only provide provisions for moisture delivery of 7-11% and 6-14%, and there are no regulations in the standards on moisture protection. Some domestic companies, such as the Beijing Fulcrum Company and Suzhou Shengbao Company, have established the fixed-point paper suppliers by setting the standards for the paper board's water absorption rate for paper honeycombs.
In the GBl3024-91 box board technical standard, for Class A paper: (export boxboard paper) there is a provision for water absorption not more than 35/50 (g/m2). Grades B and C water absorption only specify positive: 40/-60/, but no requirement for negative.
Judging from the current standards for corrugated base paper and linerboard in China, strictly speaking, it is not ideal as a base material for paper honeycomb paper.
Japan's corrugated board industry standard JISZ1574 specifies three indexes: hydrophobic, water-repellent, and water-resistant. Water barrier indicators are 24h, 48h impermeable two. Anti-water refers to water-impermeable contact with water for a long time. The water resistance index is further subdivided into several grades such as R8, R9, and RlO in JISZl573. Water-resistant paper is made by adding synthetic resins (urea, melamines, epoxies).
The scientific and technical personnel of the paper industry in China have devoted themselves to the study of various water-repellent agents or water-repellent agents (water-proof and moisture-proof), which can be used for secondary processing of paper, ie, water-repellent treatment, such as adding paraffin, fatty acid derivatives, synthetic resin, and chromium. Salt complexes, etc., technology is mature, the effect is obvious.
Paper honeycomb products, especially those used in the field of force, such as building materials, pallets, packing boxes, cushioning materials, etc., have been accepted and valued by many manufacturers in recent years for their moisture-proof performance. However, there are still some paper and honeycomb manufacturing enterprises that use whole recycled paper and pure straw pulp fiber paper to make honeycomb paper products. This is the main reason why a large number of manufacturers of honeycomb products have fallen into difficulties in previous years.
Paper is the basis for the production of cellular products. To make products stand on the market, moisture protection should be an important condition that cannot be ignored. As for the classification of different product moisture levels and water, moisture-proof test methods, the industry has yet to further study and discussion.
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