FI65795C - SAETT VID TILLVERKNING AV LIMMADE PRODUCT AV CELLULOSA ELLERETT CELLULOSADERIVAT - Google Patents

Description

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Torbjörn Reitberger, Duvholmsgränd 16, 127 4l SkSrholmen,

Sweden-Sweden (SE) (7 * 0 Oy Kolster Ab (5 * 0 Method of making glued products from cellulose or a cellulose derivative - Sät vid tillverkning av 1immade produkter av Cellulosa eller ett cellulosaderivat

It is well known that the so-called ionizing radiation, both mechanically generated and obtained from natural radiation sources, can cause chemical and physical changes in polymeric materials. Thus, some of these show an increased molecular weight and an elevated melting point after irradiation, due to the fact that the new chemical bonds crosslink the substance. Other polymers have little or no effect on products with lower molecular weights, which often simultaneously degrade mechanical properties.

By irradiation in the presence of various additives, it is possible to influence the result, e.g. so that the substance, which mainly decomposes, can also be crosslinked and thus give it improved properties. The presence of air has also been found to play a role in irradiation, as oxygen in many cases accelerates the decomposition of the substance.

2,65795

It is also known that cellulose, cellulose derivatives · and various combinations of natural cellulose, such as wood and vegetable fibers, are among the most radiation-sensitive polymeric materials. If the negligible positive effect is disregarded at very low doses, i.e. ^ 10 krad, the mechanical properties of these substances deteriorate sharply with increasing radiation dose. It is also known that numerous condensation polymers between formaldehyde and urea, melamine or various types of phenol have degraded properties upon irradiation.

The present invention is based on the surprising finding that particle board glued with formaldehyde prea resin has clearly improved mechanical properties after irradiation.

The invention relates to a process for the production of glued products consisting wholly or partly of cellulose or cellulose derivatives, e.g. wood chips, paper or vegetable fibers, using as a glue a condensing resin with an aldehyde, e.g. formaldehyde, and urea, melamine or a phenol type. The invention is characterized in that the product is irradiated with 0.1 to 5 Mrad of ionizing radiation, whereby a certain crosslinking takes place in the substance and at the same time the residual amounts of uncured adhesives are reduced. One Mrad then corresponds to the amount of energy absorbed by a substance of 10 joules / g or 10Ws / g.

In order to improve the properties of the above products, the aim is to increase the aldehyde content in the adhesive.

However, this cannot happen without the excess being removed in some way. The invention then represents a considerable improvement in that the irradiation, in addition to improving the mechanical properties, also contributes to reducing the residual aldehyde in the substance.

The invention can also be applied in combination with various additives which contain functional groups which, according to experience, can increase the degree of crosslinking upon irradiation. Examples of such are hydrocarbons having olefinic, acrylic or other comparable groups. It is also within the scope of the invention that the adhesive itself is modified so that these groups are chemically bonded to one or more of the components contained in the resin.

Example 1

Five groups of four test panels of particle board coated with urea-formaldehyde resin were irradiated with Co 2 radiation at different doses and the surface hardness was determined at different points by ball printing tests.

Dose (Mrad) Surface hardness (working units) 0-sample 2.17 ^ 0.13 0.10 2, «tl ± 0.03 0.33 2.35 ± 0.06 1.0 2.31 - 0.09 4.0 2, 28 - 0.06 1Q 2.12 + 0.12

Example 2

Four groups of four test plates of the same type as above were irradiated with Co 2 radiation at different doses, followed by 60 x 13.9 x 16 mm test rods, which were impact tested with an attachment point spacing of 46.8 mm.

Dose (Mrad) Energy consumed (kpcm) 0-test 10.4 i 0.1 0.10 12.1 * 0.6 0.33 10.6 - 0.5 1.0 11.0 - 0.3 10 9, 7 to 0.5 Irradiations were performed at room temperature and in the presence of oxygen in the air. The dosing rate was about 0.04 degrees / s.

There is nothing to prevent irradiation at elevated temperatures and other dosing rates. In fact, even better effects can be expected as the dosing rate is increased, due to the fact that the degree of binding becomes more striking.

The examples described show that irradiation gives similar changes to the selected material properties. The most significant improvement has already been obtained with a radiation dose of 0.10 Mrad. It is also apparent that the material can be irradiated to multiple Mrads without compromising strength compared to an unirradiated sample. This is very relevant if the purpose of the irradiation is primarily to remove residual formaldehyde.

Irradiation can occur during or immediately during the manufacture of the glued product. Alternatively, however, it is also possible to carry out the irradiation at a later time, e.g. when the product is essentially completely ready for use or perhaps even has already been used. When the glued product is in the form of a semi-finished product, the irradiation delivery - if not already carried out - can take place when the semi-finished product is processed into the final product.

Irradiation can be performed either to affect the surface layer or to provide irradiation directly through the substance. In the former case, a cheaper and simpler accelerator can be advantageously used.

Claims (5)

65795 5 A process for the production of glued products consisting wholly or partly of cellulose or a cellulose derivative, e.g. wood chips, paper or vegetable fibers, using a condensing resin between an aldehyde, preferably formaldehyde, and urea, melamine or a phenol type, characterized in that the product is irradiated 0.1-5 to Mrad with ionizing radiation, whereby a certain crosslinking takes place in the material and at the same time the residual amounts of uncured adhesives are reduced. A method according to claim 1, characterized in that the amount of radiation is adjusted so that the residual amount of aldehyde in the substance is reduced. A method according to claim 2, characterized in that the residual amount of formaldehyde in the substance is reduced. H. A method according to claims 1-3, characterized in that the degree of crosslinking is increased by adding an additive containing olefinic, acrylic or comparable groups. Method according to Claims 1 to 3, characterized in that the degree of crosslinking is increased by modifying the adhesive itself so that olefinic, acrylic or comparable groups are chemically bonded to one or more of the components present.