JPH03230906A - Preparation of lightweight mdf - Google Patents

Abstract

PURPOSE:To fill the interstices of fibers and to especially enhance the paintability of the surface at the cut end by a method wherein wax is added to fibers obtained by beating wood chips and foamable microcapsules are further mixed and emulsified with a thermosetting resin to form an emulsion which is, in turn, applied to the fibers as an adhesive to form the coated fibers into a mat having a predetermined wt. and this mat is pressed under heating to be formed into a plate. CONSTITUTION:Wax is added to beaten fibers in a wt. ratio of 0.5-3.0% and, separately, 10-25wt.% of a for,able capsule-shaped vinylidene chloride resin having a particle size of 20mum or less is mixed with a urea resin adhesive to be sufficiently emulsified therewith and the resulting emulsion is applied to the fibers in an amount of 10-20% by wt. of the fibers. The coated fibers are formed into a mat which is, in turn, pressed at hot plate temp. of 200 deg.C under pressure of 160kg/cm<2> to be formed into a lightweight MDF. This lightweight MDF becomes well in the paintability at the cut end and enhanced in internal release strength and physical properties and, especially, high dimensional stability is obtained as a humidity-resistant and water-resistant material.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing so-called lightweight medium-density fiberboard (herein referred to as "lightweight MDFJ") having a specific gravity in the range of 0.40 to 0.65. The technical feature is that the paintability of the end of the board is particularly improved.

[Conventional technology]

Conventionally, this type of lightweight MDF is made by coating fibers obtained by defibrating wood chips with a thermosetting resin adhesive such as 1 to 2% wax and 10 to 20% urea resin (both of which are based on weight). ratio - the same applies hereafter) Form into a specified cloak shape, 1
The plate was formed by hot pressing at 50 to 230°C.

[Problem to be solved by the invention]

In recent years, from the perspective of protecting wood resources and using them effectively, M.
The popularity of DF is remarkable because its paintability, especially the paintability of the end part, is better as the specific gravity increases.
MDF with a specific gravity of 0.7 or higher has been used. However, the above-mentioned ordinary MDF still has drawbacks such as heavy weight and severe wear of blades during processing, so further weight reduction has been desired, and lightweight MDF has started to be manufactured.

However, the so-called lightweight MD with a specific gravity in the range of 0.40 to 0.65
F has a rough wood edge, so the paint is absorbed quickly.
There was a tendency that the lighter the weight, the lower the suitability for painting.

In addition, lightweight M and DF also have lower physical properties compared to regular MDF, so to improve these properties, the addition rate of adhesive to the material may be increased, or wax, rosin, etc.
Attempts have been made to add water repellents, but the reality is that no significant improvement has been achieved.

[Means to try to solve the problem]

In order to solve the problems seen in the above-mentioned conventional lightweight MDF, the present invention has developed a fiber that is obtained by defibrating wood chips.
．． After adding 5 to 3.0% wax and further mixing 10 to 25% of expandable microcapsules of 20μ or less into the thermosetting resin and emulsifying it thoroughly, use this as an adhesive to the above fiber. 10~20% coated and paper-made to a predetermined weight at 150~230°C, preferably at 160°C.
A method of forming the sheet by hot pressing with a hot press at ~200°C was used.

[For production]

The expandable microcapsules in the above-mentioned manufacturing method of the present invention are foamed into closed cells by heating and pressing during sheet forming, and because they have self-adhesive properties, they fill the voids between fibers, making them especially suitable for painting on the end surface. It has a special effect of improving the

[Example] Hereinafter, the structure of the present invention will be explained in further detail according to 1 to 2 Examples.

Material■ Add 1.0% wax by weight to the defibrated fibers, and add 1.0% wax to the liquid volume of the urea resin adhesive separately.
A mixture of 15% by weight of vinylidene chloride resin in the form of unfoamed capsules of μ was thoroughly emulsified and applied at a coating rate of 13% based on the weight of the above fibers, then formed into a cloak shape and heated on a hot plate. Lightweight MDF with a thickness of 12 mm and a specific gravity of 0.50 is produced by heating and pressing at a temperature of 200°C and a pressure of 160 kg/c.
was plated.

Material ■ As a comparative material for the above Material ■, a lightweight MDF with the same thickness and specific gravity was obtained under exactly the same conditions as Material ■ except that vinylidene chloride resin (microcapsules) was removed from Material ■.

Material■ Add 2% wax by weight to the defibrated fibers, and separately mix 15% styrene resin in the form of unfoamed capsules of 15 μm with respect to the liquid volume of melamine resin adhesive.
The thoroughly emulsified material was applied at a coating rate of 18% based on the weight of the fibers mentioned above, and after being formed into a cloak shape, it was heat-pressed at a hot plate temperature of 180°C and a pressure of 200 Kg/c+ll to give a thickness. A lightweight MDF with a length of 12n and a specific gravity of 0.60 was formed.

Material ■ As a comparative material for the above Material ■, a lightweight MDF with the same thickness and specific gravity was obtained under exactly the same conditions as Material ■ except that the styrene resin microcapsules were removed from Material ■.

The results of measuring the suction speed of the paint at the wood end, internal peel strength, water absorption rate, and thickness expansion rate due to water absorption for each of the above materials ■ to ■ are shown in Table 1, and all of them are the lightweight MI of the present invention) It was confirmed that F (Documents ■ and ■) had significant advantages in coating suitability and other physical properties compared to comparative material ■■.

Table-1 However, the test methods for each item in the table above are as follows.

◎ Paint suction speed at the wood end (seconds): Urethane clear wood MFm 0.5CG was dropped onto the wood end surface, and the time until the entire amount was absorbed was measured.

〔Effect of the invention〕

As is already clear from the above description, the lightweight MDF according to the present invention has the following characteristic effects compared to conventional lightweight MDF products.

(, ]) The suction speed of the paint at the end of the wood is extremely low, and the suitability for painting is that much better.

(b) The internal peel strength of the product is high and the physical properties are improved.

tc+ Water absorption rate and thickness expansion rate due to water absorption are small, and high dimensional stability can be obtained especially as a moisture-resistant and water-resistant material.

that's all

Claims (1)

[Claims] 1. 0.5 to 3 to the fiber obtained by defibrating wood chips
．． After adding 0% wax and further mixing 10 to 25% of expandable microcapsules of 20μ or less into the thermosetting resin and emulsifying it thoroughly, use this as an adhesive and apply 10 to 20% of the foam to the above fiber. (The above percentages are all weight ratios) A method for manufacturing lightweight MDF, characterized by coating the product, forming it into a paper to a predetermined weight, and then hot pressing it into a plate using a hot press.