Requirements and production process for raw materials used in impregnated paper-faced plywood and blockboard

Author: Peng Limin

Unit: Research Institute of Wood Industry, Chinese Academy of Forestry

Source: China Wood-Based Panels, Issue 5, 2018

Introduction

The paper introduces the raw material requirements, production process and hot pressing technology for the preparation of impregnated paper veneer plywood and blockboard in my country at the current stage, and analyzes the causes of product defects.

Impregnated paper-faced plywood and blockboard (commonly known in the market as eco-board) are a new type of decorative board material developed based on impregnated paper-faced wood-based panels. Around 2005, domestic companies, through innovation and improvement based on the raw materials and processing technology of impregnated paper-faced wood-based panels, developed a new type of board material using plywood and blockboard as the base material and impregnated paper as the facing material. This product, with its high dimensional stability, excellent decorative properties, and environmental friendliness, is gaining increasing popularity among consumers and driving the maturity and growth of the impregnated paper-faced plywood and blockboard industry. While the eco-board market is currently developing well and boasting a rich product range, its development time is relatively short compared to traditional wood-based panels, and product quality varies widely.

The Wood Industry Research Institute of the Chinese Academy of Forestry, in collaboration with relevant domestic testing agencies and representative manufacturers of impregnated paper-faced plywood and blockboard, has developed GB/T 34722-2017, "Impermanent Film-faced Plywood and Blockboard," which will come into effect on May 1, 2018. During the standardization process, the author, through extensive factory and market research, discovered varying degrees of quality defects in some eco-friendly boards. This document summarizes these issues and proposes specific requirements for substrates and production processes, hoping to provide guidance to eco-friendly board manufacturers and consumers, thereby ensuring that the requirements of national standards and consumer demand are met and promoting the healthy and sustainable development of this product.

1 Requirements for raw materials for impregnated paper-faced plywood and blockboard

The composition of impregnated film paper veneer plywood and blockboard mainly includes multi-layer plywood or blockboard substrate, thin board (veneer, technical wood) and impregnated film paper.

1.1 Requirements for substrate

Plywood and blockboard substrates should comply with the requirements of GB/T 9846-2015 "Ordinary Plywood" and GB/T 5849-2006 "Blockboard" respectively. The following aspects should be noted:

1) The thickness of the substrate should be uniform and the board surface should be smooth and clean, otherwise sanding treatment should be performed;

2) The appearance quality of both sides of the base material should meet the requirements of GB/T 9846-2015 first-class products, and the bonding strength should meet the requirements of Class II plywood;

3) The moisture content of the substrate is an important indicator. If the moisture content of the substrate is too low, the surface bonding strength of the impregnated paper veneer plywood and blockboard will be reduced and defects such as surface drying will occur. If the moisture content of the substrate is too high, defects such as bubbling, delamination, and wet spots will easily occur during hot pressing. Therefore, the moisture content should be controlled between 6% and 16%;

4) The surface of the base material should be a whole single board as much as possible. If the board is used, the joints must be tight, otherwise the joint defects will be reflected on the surface of the impregnated adhesive paper veneer plywood and blockboard.

1.2 Requirements for thin plates

Thin sheets are placed between the base material and the impregnated paper, concealing defects to a certain extent. These typically include veneer and reconstructed decorative veneer (commonly known as technical wood). Thin sheet requirements: 1) uniform thickness; 2) essentially flawless surface and consistent color; 3) seamless sheet; 4) moisture content of 6% to 16%.

1.3 Requirements for impregnated film paper

Generally speaking, most manufacturers take into account the commercialization and use of impregnated film paper and adopt the secondary impregnation method, that is, the decorative paper is first impregnated with urea-formaldehyde resin, dried, and then the surface is sprayed with melamine resin glue.

The physical and chemical properties of impregnated paper, such as volatile content, pre-curing degree, and formaldehyde emission, directly impact the quality of eco-friendly boards. Low volatile content can easily lead to dried-out patterns; insufficient impregnation can easily create surface porosity and poor abrasion resistance; high volatile content can easily lead to uneven surface gloss; and poor adhesive flow and sealing properties can lead to poor surface resistance to contamination and water vapor.

2 Production process of impregnated paper-faced plywood and blockboard

2.1 Direct-attach veneer production process

2.2 Production process of veneer by lamination method