Instruction manual for powder paints coating of woodwork, products of WFB, chipboard, and medium density fibreboard.

composed by ТЛК Центра Эластомеров

of KSTU Laboratory Head, PhD in

Chemical Sciences V.N. Naumov

1999  

1.     INTRODUCTION

Terms of powder paint (PP) coating application and formation process on wood,WFB, chipboard, and medium density fibreboard vary a lot from those on the metal. These are due to quality diversity of properties of given materials. Formation of flawless PP coating on metals is achieved by such metal properties as conductivity, high density and heat capacity.

Wood is dielectric and has significantly less density and heat capacity. Moreover the latter contains significant amount of water, gas voids, sublimating products, resins etc., which actively evolve while heating. The above mentioned reasons make it difficult to form quality coating on wood and its conversion products which leads to restriction in PP using. In order to equalize the difference in properties of above-mentioned materials by, for instance, heat capacity enhancing, voids content elimination and evolving products fixing, woodworks placed in autoclaves at higher temperature or in reactors at lower pressure are subjected to phenol-formaldehyde resins treatment. The following drying at 100-150^oC allows to form compact, void-free material, which is suitable for PP application. However, this method can not be considered acceptable to the full extent due to high unit costs.

As a result of several years work we managed to obtain fair results in wood coating with material containing wood conversion product (ДСМ), which are presented in this document.

2.     REQUIREMENTS TO WOODEN MATERIALS SUBJECTED TO COATING

ДСМ products should meet the following requirements:

1. High density and heat capacity;

2. Void-free or small void rate;

3. Optimal required moisture content;

4. Resin substances deficiency.

First quality (high density and heat capacity of the material) allows to good flow of paint, reduces sharkskin defects, which may vary in color of spot and bands background, which can be characterized as two-tone coating presence.

Second condition is being void-free which leads to uniform void-free coating formation.

Materials with excessive void rate should be thoroughly covered with primer and in this case PP masking these defects should be used (hammer paints, mat paints, paint with moiré, orange peel effect etc.).

Materials should be used in furniture industry which were ripened during certain time (more than 1 year) in dry stock-room. This is necessary to obtain certain humidity (7-10% of residual humidity) of wooden workpieces, which should keep their shape and sizes while service (product shouldn’t shrink).

The third condition, i.e. optimal moisture content should not exceed 5-7%, should be kept as while the PP coating formation on wood the latter is subjected to heat treatment.

The fourth characteristic determines the possibility of PP coating formation on wood. Resinous species should be subjected to preliminary drying to obtain optimal moisture content and full expulsion of resins evolving while heating.

The above-mentioned requirements are mostly suitable for the following species – oak, beech, nutwood and birch. Resinous species such as whitewood, pine wood and fir should be preliminary treated using vacuum drying and resin substances extraction.

Materials, containing wood conversion products, i.e. MDF, chip board and fibreboard, can be used as a base for applying PP coating providing standard treatment such as padding, polishing and applying of conducting layer.

3.     POWDER PAINT SELECTION

Type of PP should be selected considering the specificity of PP coating application on wood and fibreboard. Main requirement is low temperature of PP curing. Optimal temperature of coating formation should not exceed 120-160^oС.

For products maintained indoors all types of PP are suitable, as for the products maintained outdoors special polyester PP should be used. In order to highlight wood surface structure glossy and matt paints should be used, to hide surface defects and wood structure mixed paints or paints which form own pattern (moiré, sharkskin, orange peel, , hammer effect) should be selected.

4.     SURFACE PRETREATMENT

Wood and ДСМ surface pretreatment consist of following stages:

1.     Grinding;

2.     Filling and padding;

3.     Drying;

4.     Polishing.

Material surface is grinded with grinding tool or manually with flint-paper prior to coating. Preliminary grinding is not needed for chip board and MDF surface. Grinding is followed by filling and padding with water-reducible primer based on PVA glue.

To fill in deep checks and holes primer is mixed with cement of grade 400, grinded glass or marshallite to get viscous state. On large surfaces firstly water-reduced primer is applied with brush, sponge or flock-spray gun (type СО, КР).

Primer dries at room temperature during 15-20 minutes. Hereafter surface is polished with fine flint-paper. In order to remove volatile products out of wood it is recommended to dry it at room temperature during 30 minutes and afterwards in heat chamber at temperature 15-20^oC higher than coating formation temperature. Padded product heat treatment time is 20-30 minutes.

5.                 APPLYING POWDER PAINT ON WOODEN MATERIALS

«Elektro» conducting composition is applied on the primer layer prior to PP applying on wood and ДСМ. On large surfaces «Elektro» is applied with flock-spray gun, on smaller surfaces with rags which doesn’t leave fringes. Rag is moisted with «Elektro», allowed for 3-4 minutes on air to remove solvent, and detail is rubbed to obtain full wetting of surface. Part is dried on air to get rid off «wet» surface during 3-4 minutes, carefully grounded and powder paint is applied. Grounding should be carried out on reverse side of front surface in order to get rid of unpainted spots around grounding point. After PP application part is placed into drying chamber and coating forms at temperature of 120-160^oС with infra-red radiators or air flow inside chamber.

6.     COATING PROCESS SAFETY PRECAUTIONS

 Safety precautions and fire safety terms should strongly be kept while using PP.

1. All works using PP, solvents for defatting, “Elektro” composition should be carried out in rooms equipped with supply-and-exhaust ventilation and fire-safety devices. Supply-and-exhaust ventilation should provide content of substances in working zone which doesn’t exceed maximum allowed concentration according to GOST 1.005-76 state standard requirements.

Hazardous gases, dust, solvent fumes content in air of workshops and fire safety of substances in terms of microclimate should regularly be controlled. Terms and time of atmosphere analyses are settled by administration of the company.

Those who work with PP and defatting solvents should be provided with workwear and individual protection facilities according to requirements of GOST 12.4.011-75, GOST 12.4.015-76, GOST 12.4.017-76 and GOST 12.4.019-75 state standards. Labcoats, costumes and footwear treated with antistatic substance should be used. Hands protective equipment are rubber gloves, shielding ointments, creams of types HIOT-4, HIOT-6, IER, paste «Biologicheskie perchatki» etc. Glasses and masks should be used for eyes protection. For face and respiratory organs safety respirators of types RPP-57, ShB-1 should be used according to GOST 12.4.028-76 state standard.

3. All the works involving solvents or compositions containing organic solvents should be carried out according to fire safety rules and industry sanitary terms provided in GOST 12.3.055-75 state standard.

Fire safety which consists of fire prevention system and fire safety system should be provided in workshops according to GOST 12.1.004-76 state standard.

Fire prevention system includes exception of combustible medium formation, аs well as temperature maintenance and keeping airdust mixture volume below maximum level. Fire safety requirements are: limitation of amount of combustible substances and their disposal, combustible medium isolation, use of fire fighting means, fire alarm devices and fire alerting system.

4. Sand, asbestine cloth (GOST 6102-78 state standard), fire foam producing machines of type ОP-5 (GOST 16003-70 state standard), carbon dioxide fire extinguishers of types ОU-2, ОU-5 (GOST 7276-77 and GOST 9230-77 state standards), thin dispersed water (GOST 1430-80 state standard) are used for firefighting

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