CS197514B1 - Method of producing urea-formaldehyde resinous adhesives with improved cold binding power for chipboards production - Google Patents

Abstract

Prodn. of urea-formaldehyde resin adhesives comprises first precondensing urea and HCHO in a molar ratio of 1:1.8-2.2 at 100-140 degrees C and elevated pressure in the presence of 0.5-5 wt.% (based on urea) of an acid (esp. HCOOH) for 10-100 min. to form a precondensate with a predetermined viscosity. The precondensate is neutralised or made weakly basic and condensn. is continued at 40-80 degrees C while adding urea until the final urea-HCHO molar ratio is 1:1.3-1.8. Water is opt. removed to obtain the required solids content. The adhesives are esp. useful for the mfr. of wood chipboard. They have good cold bonding properties, allowing continuous board prodn. by cold pressing to form a self-supporting rough board, which can then be passed for hot pressing without a support.

Description

The invention relates to urea-formaldehyde - resin adhesives tackifier cold for the manufacture of particle board by condensing urea and formaldehyde in te du ^{y p} diisopropylamine, at ⁰ ° ^d 1 ° ^C *

Urea-formaldehyde resin adhesives have. extensively. use as a binder in the particle board industry. In conventional manufacturing processes, the chips are coated with a resin solution, shaped into a carpet, and cold pre-pressed. This is carried out on the support substrate, for example on a support plate. The preformed - raw particle boards - are then conveyed for hot pressing and compressed. Only after pressing, the plates are separated from the finished chipboard. Before the backing sheets can be reused, they must be cooled before preforming new preforms. This constant - rapid change in temperature - leads to high wear of the backing plates and requires, in addition, a considerable amount of energy, a large part of which is lost without use. To avoid these - considerable - losses, new technologies have been developed, the so-called belt-type method, the belt-type method with the insertion of tablets and the tabletless method. These methods require adhesives which, in addition to the hitherto required properties, still have high cold tack.

In these new processes, the raw particle board preform after cold forming and molding is separated! from the backing pad by rolling- or shifting and most of it

197 514

197,514 cases are hot stamped. This process requires high strength of the particle board preform to avoid fracture or deformation equal to production losses.

With the commercial urea-formaldehyde adhesives, the stated high strengths of the particle board preforms, which are needed in particle board production machines operating without a support, are not achieved. Increasing the pressing pressure during cold pre-pressing as well as increasing the proportion of glue to an economically viable rate also do not lead to satisfactory results. Attempts have therefore been made to achieve better strengths by adding to conventional particle board adhesives.

It is known to improve the tackiness of cold urea-formaldehyde resin adhesives, melamine-formaldehyde condensers and phenol-formaldehyde condensers by adding sulphite lye, i.e., calcium lignin sulphonate solution, which falls off in the production of sulphite cellulose in a dry matter content of up to 10% concentration of 45 to 70%. The sulphite liquor can be used in liquid or powder form (DT-OS 2 354 928). The drawback is that this requires additional operation to develop the additive, additional energy and equipment needs.

It is further known to incorporate additives into commercial wood glues prior to processing for workpieces or glued workpieces. These additives are solutions of polybasic and / or lead finely unsaturated carboxylic acids in a water-soluble mono- or polyamine. The pH * of these solutions is 6.5-11 (DT-OS 2,351,981). The disadvantage here is that in addition to the need for additional energy and equipment for the additional incorporation of additives, the properties of the adhesive are adversely affected. For this reason, it is recommended in the cited file DT-OS to incorporate ingredients immediately before processing the adhesive.

The object of the present invention is to provide a urea-formaldehyde resin adhesive having a high cold tack that imparts to the cold pressed particle board preforms such a high strength that they can be transported to the particle board press without fracture and deformation during processing without a support.

This object is achieved according to the invention by condensing continuously or discontinuously urea and formaldehyde in a molar ratio of 1: 1, 8 to 1: 2.2 at a pressure of 0.1 to 0.4 MPa and at temperatures of 100 to 140 ° C. in the presence of 0.5 to 5% by weight, of organic or inorganic acids such as formic, acetic, hydrochloric, sulfuric, phosphoric acid, based on the amount of urea used, basified and condensed further at pH 7 to 9 in 10 to 100 minutes addition of urea up to a final molar ratio of urea to formaldehyde of 1: 1.3 to 1: 1.8 at temperatures of 40 to 80 ° C and a pressure of 5.3 to 79.8 k₽a, or thickened simultaneously.

The concentration of acids used may be in the range of 2 to 15%.

Surprisingly, by the condensation at temperatures above 100 ° C with the addition of acid, urea-formaldehyde resin adhesives are obtained, with which

197 514 to produce preformed chipboards of sufficient strength for said chipboard manufacturing apparatus.

A particular advantage is that the use of a new chipboard adhesive in said chipboard production plant can reduce the proportion of adhesive based on the chip weight, depending on the technological conditions (wood type, chip moisture, etc.) by up to 5%. A further significant advantage is that the use of the particle board adhesive according to the invention no longer results in production and material losses due to mechanical breakdowns of the production line due to mechanical failures. When using conventional chipboard adhesives, the raw material loses the chipboard preforms at the stoppers so much moisture that they can under no circumstances be transported to the hot press, but must be discarded. By using the particle board adhesive according to the invention, on the other hand, the strength of the particle board preforms is maintained and the chipboard production line can be restarted without delay.

In addition to increased cold tack, these resins have good reactivity, storage stability and water compatibility.

The cold strength of the preformed carpet is determined by forming glue-coated chips into a 750 x 300 mm carpet and then compressing cold. The pressed carpet is laid on two supports at a distance of 650 mm from each other and measures the time between laying and breaking the carpet. The measured time is proportional to the cold tack.

Cold tack:

time elapsed from ^l to Omen ^s preform in seconds

Conventional Resin 72 Resin of the Invention, Example 1 394 Resin of the Invention, Example 2 '515

He did

A urea in formaldehyde solution containing 700 parts by weight of a solution of 700 parts by weight of a 37% neutralized formaldehyde solution and 259 parts by weight of urea at a rate of 100 parts by weight per hour is metered into a reaction vessel equipped with level control and a stirrer. At the same time, 0 is continuously fed into the vessel^,25 wt^andho dHu 10% k^yse^ifny mraven^whose.^při rea^točn^and tapiok¹²⁸ ° C has rea^kčnímixture under these conditions^to you know^toozitu 48_mp_and<^andm^Eřeno při^{20 May} ° c. Run^em one hour^ny with^E odvá 100 parts by weight of this capacitor were charged to a second reaction vessel into which 16.2 parts by weight / hour of a 55% urea solution and 0.35 parts by weight / hour of a 10% sodium hydroxide solution were added. In this second reaction vessel equipped with a circulation device, condensation is effected from the reduced pressure and the product. concentrating to 67% dry matter at^tepl^otě 40^and80 ° C. Continuum^andlně o^din^andděné mo^Covinoformalde^hydové pr^ysk^yřAdhesive adhesive oⁱⁿand^withko^of970 rnP^and.^with/ 20 °^C m^and ve^lkou cold tack^, je s^meltedE^exi s^kladov^andn^and

197 514 and particularly suitable for the production of particle board without backing sheets.

Example 1 a d 2

600 parts by weight of neutralized 37% formaldehyde solution are charged into a heatable and cooled reaction vessel equipped with a stirrer and thermometer. 207 parts by weight of urea are dissolved therein. The thus obtained ^{urea-extensible} about ^to warm to ³⁰ m ^{and weighing} nu ^t p ^{s 70} ° C _t ^p of ^the PHDA with ^1.3 pbw of 1-molar ^alkyl petroleum jelly c ^hl orovo b ^s and ^{thanks to} ondenzuje ^BC and 112 ° C. up to ^d at a temperature of ⁵⁰ m ^P / ²⁰ ° C. ^P op ^Rida hmotnostnteh n ^{of 3.5 parts of 2,} 5-mo ^la RN ^¹H droxidu of ^HY sodium ^h the cooled to 80 0 C, added with 72 parts by weight of urea. Condenses at this temperature. 'After concentration at 50 ° ^C and ^0.4 M ACCOUNTS ^P and the ZIS ^{ka urine} ov er ^{i d y} noformal dov ^Star Lb ^PIDL oo vis ^{OZ ITE 1020} m and ^P / ²⁰ ° C and ^68% dry matter.

Claims (1)

SUBJECT OF THE INVENTION The process of urea-formaldehyde resin glue with tackifying cold for the manufacture of particle board by condensation of urea and formadehydu at ^t e ^p lo ^tray h above ¹⁰⁰ ° ^C, the tutors Иш, ^Z e ^to ondenzuje continua ^and adheres or diskontýnuálně urea and formaldehyde in a molar ratio of 1 : 1.8 to 1: 2.2 under a pressure of 0.1 to ^{0.4 MPa at t} ep 9 ^l o c ^{h th 100} to ¹⁴⁰ ° C. řítomnosti ^{p 0,} 5-5% by weight. Or ^gan i ^{c yc} h or inorganic acids, such as formic, acetic, hydrochloric, sulfuric, phosphoric, based on the amount of urea, for 10 'to 100 minutes, made basic and condensed further at pH 7-9 with the addition of urea to the final mo ^eh limb of urea ^to Omer ^p u ^f orma ^ld e ^hy du 1: ^1.3 and ^1: 1.8 at te ^p l ^o Tachi 40 to 80 - ° C and a pressure of 5.3 to 79, 8 kPa, or thickened if necessary.