Talking about the Control of Formaldehyde Content in Plywood

Talking about the Control of Formaldehyde Content in Plywood

China Quality News Network

Formaldehyde is a highly toxic chemical that ranks second in the priority list of toxic chemicals in China. Formaldehyde has been identified by the World Health Organization as a carcinogenic and teratogenic substance. It is a recognized source of allergies and one of the potential strong mutagens. At present, many countries and regions in the world, such as the European Union, the United States, and Japan, have limited formaldehyde emission, and China’s national mandatory standards, “Limited Release of Formaldehyde in Interior Decoration Materials, Wood-based Panels and Products” (GB18580-2001), apply to formaldehyde. The amount of release is also limited. The standard provides for formaldehyde emission from plywood (artificial panel): E1 level ≤ 1.5 mg/L, E2 level ≤ 5.0 mg/L. E1 grade standards can be used directly for interior decoration. Only conforms to the E2 standard and must be finished before use. Therefore, how to control the formaldehyde content of plywood is an urgent need to discuss and solve the problem.
To control the formaldehyde content of plywood, it is first necessary to clarify the cause of excessive formaldehyde content in the plywood. In order to analyze the causes of excessive formaldehyde in plywood, it is necessary to clarify the source of formaldehyde.
There are four main sources of formaldehyde in plywood: one is the free formaldehyde in the adhesive, and the other is a part of the unstable structure of the adhesive in the hot-pressing process, such as ether bonds, methylol groups, and methylene groups. During the use of plywood, the cured structure decomposes to release formaldehyde. Fourth, some woods also contain natural aldehyde and ketone chemicals. Therefore, there are four reasons for excessive formaldehyde content in plywood, namely: improper formulation of adhesives, excessive amount of glue, unreasonable production process, and neglect of wood species selection.
Therefore, the control of formaldehyde content of plywood should start from the three aspects of raw materials, production and finished product testing.
First, raw material control. Plywood commonly used plastic urea-formaldehyde resin (UF), phenolic resin (WBP), melamine modified urea-formaldehyde (Mel). Urine aldehyde rubber is processed from formaldehyde and urea as the main material. Free formaldehyde content is usually between 1% and 2%. To control formaldehyde, suppliers must use a low molar ratio of formaldehyde to urea to effectively control the release of free formaldehyde. The amount is less than 0.2%; phenolic glue is processed with formaldehyde and phenol or resorcinol as the main material, due to the role of phenol and resorcinol in the benzene ring, can reduce the release of free formaldehyde; melamine modified urea-formaldehyde adhesive to Formaldehyde and urea as the main material, melamine as a modifier can effectively absorb free formaldehyde, free formaldehyde can achieve the required requirements in the glue.
Therefore, it is extremely important to strengthen the control of free formaldehyde in plywood production glue. If the manufacturer uses self-made glue, it must strictly follow the formula and process flow. The glue should be sent to the authoritative department for testing to ensure that the free formaldehyde content is controlled. If the glue is purchased, the purchased glue must be approved by an authoritative department. Whether self-made or purchased glue, the free formaldehyde content must reach the E2 level before use.
In addition, a few woods such as poplar wood contain aldehydes and ketones, and formaldehyde may be released during processing. Therefore, the factory should also pay attention to the choice of wood species when selecting raw materials.
Second, the control of the process. According to the different glue characteristics, the corresponding process flow is formulated, including the gluing process (adding amount and action time of various catalysts in different glues and different temperatures) and the hot pressing process (hot pressing temperature, hot pressing time). Shortening the hot-pressing time and reducing the hot-pressing temperature will reduce the formaldehyde emission. Regular training is required for plastics and hot-press process personnel, and the staff involved in these two processes are required to strictly implement the technological process to ensure that the unstable structure during the hot-pressing process is decomposed to release formaldehyde at the minimum. The factory inspection personnel should strictly inspect according to regulations. , Found that the defective glue should stop production immediately, found that unreasonable process should be corrected immediately.
When controlling the process, it is also important to note that the factory cannot omit the health process. Sometimes the delivery time of the factory is urgency, artificially eliminating this process, and in fact, the slow release of free formaldehyde takes some time.
Third, finished product testing control. The factory shall establish a physical and chemical laboratory, and carry out formaldehyde testing for each batch of products according to the relevant standards (sampling in the workshop). If the result is unqualified, the production department shall be notified immediately to stop the production, identify the cause, re-treat the unqualified product, re-treat and test again, and only the qualified product can be stored in the warehouse.
In addition, it is necessary to strengthen logo management, and indoor and outdoor panels should be clearly identified.
In summary, the key to producing low-formaldehyde emission plywood is to use a one-time glue with low free formaldehyde content, and adopt scientific process and strictly control the time and temperature of hot-pressing. At the same time, we must strengthen the detection and control of finished products. And pay attention to the choice of wood species. If you can do the above points, you can effectively control the amount of formaldehyde released from plywood.

浅谈胶合板甲醛含量的控制

中国质量新闻网

甲醛是一种有较高毒性的化学物质,在我国有毒化学品优先控制名单上高居第二位。甲醛已经被世界卫生组织确定为致癌和致畸形物质,是公认的变态反应源,也是潜在的强致突变物之一。目前,世界上许多国家和地区如欧盟、美国、日本等对甲醛释放量均有限定,我国国家强制性标准《室内装饰材料、人造板及其制品中甲醛释放限量》(GB18580-2001)对甲醛释放量也作出了限定。该标准对胶合板(人造板)甲醛释放量的规定为:E1级≤1.5mg/L,E2级≤5.0mg/L。达到E1级标准的可直接用于室内装饰。仅符合E2级标准的必须经饰面后方可使用。因此,如何控制胶合板甲醛含量,是目前迫切需要探讨和解决的课题。
要控制胶合板甲醛含量,首先要弄清造成胶合板甲醛含量超标的原因。而要分析导致胶合板甲醛含量超标的原因,则要先弄清其甲醛的来源途径。
胶合板中甲醛主要来源途径有四:一是胶黏剂中的游离甲醛,二是热压过程中胶黏剂的一部分不稳定结构如醚键、羟甲基团、亚甲基发生分解,三是胶合板在使用过程中,固化后的结构发生分解而释放甲醛,四是有些木材本身也含天然醛、酮类化学物质。因此,造成胶合板甲醛含量超标的原因有四个,即:胶黏剂配方不当、涂胶量过高、生产工艺不合理和忽视了材种选择。
因此,控制胶合板甲醛含量应从原料、生产和成品检测三个方面入手。
第一,原料控制。胶合板常用胶为尿醛树脂胶(UF)、酚醛树脂胶(WBP)、三聚氰胺改性脲醛胶(Mel)。尿醛胶由甲醛和尿素为主材料加工而制得,游离甲醛含量通常在1%至2%,为控制甲醛,供应商必须采用甲醛与尿素低摩尔比生产工艺,才能有效控制游离甲醛的释放量在0.2%以下;酚醛胶以甲醛和苯酚或间苯二酚为主要材料加工制作,由于苯酚和间苯二酚中苯环的作用,可使游离甲醛释放量降低;三聚氰胺改性脲醛胶以甲醛和尿素为主材料,三聚氰胺作为改性剂能有效吸收游离甲醛,可使胶水中游离甲醛达到规定要求。
因此,加强对胶合板生产用胶水的游离甲醛控制显得极为重要。生产者如果使用自制胶水,则必须严格按照配方和工艺流程生产,胶水要送权威部门进行检测以确保游离甲醛含量得到控制;如是采购胶水,则所购胶水必须批批经权威部门检测。不论是自制或是采购的胶水,其游离甲醛含量均要达到E2级标准方可使用。
另外,杨木等少数木材含有醛和酮类,在加工过程中也有可能释放甲醛。因此工厂在选择原料木材时也要注意材种的选择。
第二,加工过程的控制。针对不同的胶水特性制定相应的工艺流程,包括和胶工艺(各种催化剂在不同胶水中、不同温度下的添加量和作用时间),热压工艺(热压温度、热压时间)。缩短热压时间,降低热压温度,甲醛释放量则相应减少。对和胶、热压工序人员进行定期培训,要求从事这两道工序的工作人员严格执行工艺流程,确保热压过程中不稳定结构最低限度发生分解而释放甲醛,工厂检验人员应按规定严格督察,发现不合格的胶水应立即停止生产,发现不合理的工艺流程应立即纠正。
在控制加工过程时,还需要注意的是工厂不能省略养生工序。有时工厂交货期急,会人为省去这道工序,而实际上,游离甲醛缓慢释放,是需要一定时间的。
第三,成品检测控制。工厂应建立理化室,按相关标准对每一批产品进行甲醛检测(在车间抽样)。如结果不合格,应立即通知生产部门停止生产,查明原因,对不合格产品重新处理,重新处理后再检测,只有检测合格的成品才能进库。
此外,还需加强标识管理,室内室外用板应标识清楚。
综上所述,生产低甲醛释放量胶合板的关键是采用低游离甲醛含量的一次性胶水,并且采用科学的工艺流程和严格控制热压的时间和温度,同时,还要加强成品的检测控制,以及注意材种的选择。如能做到以上几点,就能有效控制胶合板的甲醛释放量。

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