SE445054B - PAPER SUBSTRATE IMPREGNATED WITH HEATING PHENOL HEARTS - Google Patents

Description

resistance of the filter medium. gtiiiscåna. 7901882-6 2 The corrugated sheet is then transported through an oven so that the resin-impregnated material is cured to a fusible intermediate or a B-stage, after which it is rewound on a roll. The transfer to the B ~ stage may follow immediately or be time-shifted relative to in the saturation step.

The buns of partially hardened, corrugated impregnated paper thus reach the filter manufacturer, where production is completed. The latter completion originally comprises suitable folding of the paper and then heat curing of the same finally thermoset stage in order to achieve the desired degree of chemical, oil and moisture. In curing resoles of the type indicated above in the manufacture of paper filters, a abundant amount of blue smoke. This smoke is released into the atmosphere, and due to its harmful nature, it creates environmental pollution problems. The multi-restrictions that currently applies in some states means that emissions may only be made_of such effluents that pass the test with 80% light transmission. In addition to striving to meet these requirements, it is desirable to reduce smoke generation. In addition, the losses of valuable phenol are thereby reduced. In addition, discharged effluents with a high content of phenol derivatives eventually form deposits on the exhaust fan, which impairs its effect. Furthermore, such deposits tend to drip back into the oven and thus contaminate the paper which is subjected to curing. The problem of smoke formation has been largely eliminated by significantly increasing the amount of formaldehyde used in the preparation of the resole. This solution initially leads to the formation of phenol-formaldehyde polymers with higher average bridging density, which are less likely to be emitted in the form of smoke under the conditions necessary to convert the phenolic condensate to thermoset. The disadvantage of this solution, however, is that the cured phenolic resin becomes too brittle to be used in filter paper applications. The object of the present invention is therefore to provide a phenolic resole which cures to a thermoset state without any appreciable degree of smoke formation, while the cured product formed retains sufficient flexibility to be used in the production of LW 10 Le u * 40 3 g79o1ss2-6 paper filter.

Thus, according to the present invention, modified phenol-formaldehyde resoles are obtained, which primarily comprise a mixture of polymeric condensates with crosslinking density resulting from condensation of one mole of a phenol with from 1.25-1.75 moles of formaldehyde to a suitable end point. The indicated modification is effected by carrying out the condensation purification in the presence of a diol in the form of a glycol or polyalkylene glycol derived from either ethylene or propylene oxide. During the formation of the resole, a part of the diol is structurally bound into the resin chain, which results in units which help to improve the flexibility properties of the thermoset products of said resole, while the unreacted diol remains as an external plasticizer.

The preparation of a resole according to the present invention generally follows the reaction conditions which normally apply in the preparation of conventional condensates of this type, namely the use of a base catalyst and carrying out the condensation reaction under a slightly elevated reaction temperature. Accordingly, the reaction is preferably carried out under reflux at atmospheric pressure depending on the particular form of formaldehyde used.

In this context it may be mentioned that aqueous formaldehyde containing about 57-55% formaldehyde is the preferred form of this reactant. The methyl hemiacetal form of formaldehyde ("Methyl Formcel") containing about 54% formaldehyde also represents a suitable. All of these solutions give a reflux temperature of the order of 98-110 ° C. Nothing particularly critical when carrying out the reaction. Lower temperatures can also be used, which includes the use of vacuum for reflux purposes.

The phenol, which includes phenol alone or in combination with a substituted phenol, is reacted on a base of one mole thereof with from 1.25 to 1.75 moles of the formaldehyde.

Preferably 1.4-1.6 moles of formaldehyde are used per mole of the phenol. The optimum ratio of formaldehyde to phenol in view of the use aspects of the invention, as set forth above, is about 1.5: 1. The present invention differs most substantially from the prior art method of making resoles therein. 4 in that a diol is present during the initial phase of this pre-curing process. Useful diols are the glycols and polyalkylene glycols derived from either ethylene or propylene oxide. Preferred glycols include diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol and mixtures of these glycols. However, the higher polyethylene glycols having a molecular weight of from 200 to 1000 are The glycol is present in an amount of 10-40% by weight shaved on the bay of the phenol present in the condensation mixture. on the order of 20-25% by weight based on the phenol.

As in the preparation of conventional resoles, a basic catalyst was used. Representative examples of useful catalysts are the hydroxides of the alkali metals. Sodium hydroxide is preferred for this purpose. The amount of the base catalyst specified is in the range from about 0.5 to 1.5% by weight based on the weight of the phenol. When using the preferred combination ratio of reactants indicated above in conjunction with the preferred operating conditions, the optimum amount of sodium hydroxide is of the order of 1%.

The condensation reaction is carried out until the resole exhibits the ability to cure to a thermoset state in 5-40 sec. according to Stroke's hardening test. also suitable.

Even more preferably, the diol is used in an amount of the mixture on the surface of a curing plate, which is maintained at 15,000, so that it covers an area of approximately 2.5 cm x 7.5 cm. The film then hardens to a hard, indigestible stage; and the time in seconds for this is noted. When an end point of the indicated order of magnitude is reached, the reaction mixture is cooled to a temperature in the range of about 40-6000, after which it is vacuum dehydrated. the water or moisture content does not exceed about 5% by weight.

The moisture determination method according to Karl Fischer (ASTM method E203) is the procedure commonly used for this purpose. When the required degree of dehydration has been reached. add a polar solvent to the dehydrated product to provide a solution which usually contains 50-65% solids. The lower alcohols represent the preferred ones. ..._..., .....- .. 10 15 20 25 ÉO 35 HO 5 in 79o1ss2-e solvents, although ketones and the like can be used.

Further details betr. the preparation of the phenolic resins according to the invention is given in the following examples, which also indicate the best embodiment for carrying out the present invention. All parts and percentages refer to parts by weight resp. weight percent, unless otherwise stated.

Example 1 5 'In a suitable resin reactor vessel equipped with standard accessories, 100 parts of phenol, 20 parts of diethylene glycol, 92.5 parts of 50% formaldehyde solution in water and 2 parts of 50% caustic solution were charged. With stirring, the batch was slowly heated to 110 ° C and kept at this temperature under strong reflux conditions for about 2 hours. The curing time in the curing test according to Stroke was 28 sec. at this point. The reaction mixture was rapidly cooled to 54-60 ° C, and full vacuum was applied to the reaction vessel. Dehydration was started and continued for 45 minutes, by which time the temperature had risen to 7700. The reactor vessel was freed from vacuum, and complete cooling was applied simultaneously, and 75 parts of methyl alcohol were slowly added.

Upon further cooling to 49 ° C, additional methyl alcohol was added to give a product having a solids content of 58% and exhibiting a Brookfield viscosity at 2500 of 200 oP and a curing stroke of ao sec.

The above phenolic resin was evaluated as a filter paper impregnating agent, noting the tendency to smoke during a simulated curing operation on a factory scale, as well as noting the relevant physical properties imparted to the filter paper both before and after curing of the treated paper. The latter properties were determined according to standardized test methods. For comparison, a commercial phenolic resin for filter paper ("Arotap II76-Me-66" ~ Ashland Chemical Co.) was included, which will be given below as ex. on the prior art.

When performing these tests, sheets with the dimensions 20.3 x 27.9 cm were impregnated with standard filter paper with resp. resin solutions for producing a 20% resin uptake as a solid. Treatment of the impregnated paper in order to transfer resin components to stage B was accomplished by first performing air drying for 15 minutes. and then heating in a preheated air oven at -177 ° C for 10 minutes. 57901882-e 5 5 6 for 5 min., Which resulted in the proportion of volatile material being reduced to 6-77. Final curing was obtained by heating the paper treated as described above in the Smoke Test was performed by visually noting the density of the smoke rising from a 5.8 cm long tube connected to the oven during curing. The results were graded on an arbitrary scale between 0 and 10. The grade 10 indicates dense, mainly opaque smoke. Grading 3 indicates that the smoke corresponds approximately to the density prescribed by the current EPA regulations. The results of all experiments are given in Table I below.

TABLE I _. Phenol impregnation resins ¶g§§_ Qppfinning Known technology Basepag%% solids content of the resin 20.0 19.5 - Smoke value (original) 2-3 5 10 - Smoke value (1 week) 1 10 - Properties in uncured state:.

Bursting strength acc. Mullen 21 26 15 Tensile strength (MD) 15 18 14 Tensile strength (CD) 7 9 7 Dry stiffness (M) 1867 2134 1512 Dry toughness (CD) 800 1067 711 Properties in hardened condition: 0 Explosive strength acc. Mullen 56,5 38 - Tensile strength (M) 36 55 - Tensile strength (CD) 19 19 - Dry stiffness fi (lvnn) 4445 4356. - Dry stiffness (CD) 2045 2045 -

Claims (6)

7 0 7901882-6 Patent claims 1. A paper substrate impregnated with thermosetting phenolic resin, characterized in that the phenolic resin is prepared by reacting aqueous formaldehyde or the methyl hemiacetal form thereof with a phenol in a molar ratio of from about 1.25: 1.0 to 1.75: 1.0, in the presence of a diol in an amount of 10-40% by weight, based on said phenol, and about 0.5-1.5% by weight, based on said phenol, of an alkali metal hydroxide until that the resulting condensate exhibits a curing time of 5-40 seconds in the Stroke curing test, and by subsequently dehydrating the reaction mixture to such an extent that the water content is less than about 5% by weight. Paper substrate according to Claim 1, characterized in that the formaldehyde is reacted with phenol 1 in a molar ratio of from 1,4: 1, 0 to 1,6: 1, 0. Paper substrate according to claim 1 or 2, characterized in that the diol is diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol or mixtures thereof. Paper substrate according to any one of the preceding claims, characterized in that the molar ratio of formaldehyde to phenol is about 1.5: 1. g Paper substrate according to claim 3 or 4, characterized in that the glycol is present in an amount of 20-25% by weight, based on the phenol. 0 Paper substrate according to claim 5, characterized in that the glycol is diethylene glycol.