DE1226451B - Sanding sheet for dry sanding - Google Patents

Description

Sanding sheet for dry sanding For the use of phenolic resin-bonded Abrasive fabrics are used with differently finished backing materials, depending on whether the abrasive cloth is used for dry sanding or for wet sanding shall be.

The following statements relate in particular to sanding sheets, which are used for grinding purposes as dry grinding qualities.

The finishing of the fabrics used as supports for the sanding sheets, z. B. Cotton fabric for dry sanding, is done by impregnation and / or coating these fabrics with hide glue, starch (starch derivatives) or dextrin finishes, the proportionate use of aqueous synthetic resin dispersion for the finishing process of the carrier fabric is also possible.

To prevent too much penetration of the abrasive grain bond then used Avoiding phenolic resin binder in the backing fabric becomes the abrasive grain oriented surface of the carrier fabric with differently structured impregnation or Provided coating compositions, the task of which is to create a good bond between to effect the finished carrier fabric and the abrasive grain binder.

It is also possible to impregnate the pre-finished abrasive cloth with a full bath to be provided with these impregnation or molding compounds. The application of the effective intermediate layer then takes place on both sides.

So far, the following have been used or proposed for this purpose: pure and modified Phenolic resins, especially aqueous phenolic resols; Combinations between phenolic resins and polyamides; Combinations between phenolic resins and plastic dispersions; Combinations of epoxy resins with polyamidoamines; Mixtures of epoxy resins based on bisphenol and diglycid ethers of polyglycols in connection with the usual Hardeners.

When using these known intermediate coatings occur significant disadvantages, namely: When using phenolic resins or phenolic resin-polyamide combinations and combinations of phenolic resins and plastic dispersions are dangerous the embrittlement of the carrier fabric. The adhesive effect achieved in the coarser grain area is insufficient and the tear resistance of the fabric is considerably reduced.

When using combinations of epoxy resins with polyamidoamines the heat resistance is poor. Due to the nature of this coating is the rewettability with aqueous phenolic resin binders, especially if a thin order is to be made is extremely difficult.

Even if only small amounts of polydiol diglycidethers are used in the mixture with epoxy resins based on bisphenol in connection with common hardeners coatings are obtained, which in terms of heat resistance, adhesion promotion, mechanical properties and moisture resistance not in all cases - especially when using grained abrasives in the coarser grain range - fully satisfy.

The present invention relates to sanding sheets for dry sanding, consisting of a finished fabric carrier, an elastic barrier intermediate layer and a phenolic resin make coat for the abrasive grains characterized by the use of a hardening mixture consisting of the combination a) epoxy resin based on bisphenol A, b) an internally plasticized by reaction with castor oil Epoxy resin based on bisphenol A, c) hardeners, as an intermediate layer. For the combination features a) and c) no element protection is claimed. According to the present invention Abrasive sheets are obtained whose abrasive effectiveness is also coarser Grit range compared to those manufactured according to the prior art are superior in several ways. The technical progress achieved is probably due to the fact that the composition of the invention used intermediate layer an excellent adhesion between the Carrier fabric and the phenolic resin binder causes. An impairment tissue strength and flexibility does not occur. on:. Compared to the previously used and proposed interlayer systems include the following particular ones Identify advantages: By using the marked combination as an intermediate layer a significant plasticization of the intermediate layer is achieved, without however, the heat resistance and mechanical strength of the entire coating system are adversely affected and therefore no premature failure of the abrasive fabric occurs in the case of a grinding process that causes high loads.

The following can be used as epoxy resins based on BisphenoLA: liquid and solid epoxy resins with terminal epoxy groups, which are produced by the reaction of bisphenol A can be obtained with epichlorohydrin or dichlorohydrin in an alkaline medium.

The epoxy equivalent weights of these epoxy resins are based on Bisphenol A. between 180 and 500; the viscosities of the liquid resins between 10000 and 60OOOcP at 25 ° C. Solid resins are those with a melting point of up to to 75'C- make D u r r a n suitable. Are also suitable. Mixtures of epoxy resins based on bisphenot A in the form of liquid resins - so-called reactive Thinners with mono-epoxy compounds, such as butyl glycidyl ether, phenol glycidyl ether, Cresyl glycidyl ether, _ styrene oxide.

The viscosities of these mixtures are between 400 and 5000 cP.

Among epoxy resins based on bisphenol A, which by reacting with Castor oil are internally plasticized, resins that are included by reaction of bisphenol A diglycidyl ether with castor oil in a molar ratio of 1: 0.25. up to 1: 0.3 produced, such as Epotuf @ IP. ° The implementation in Presence of Lewis acids, such as tin tetrachloride, boron trifluoride and its < Addition compounds, for example, to acetic acid, ethyl ether, phenol, cresol, Piperidine ,, carried out. The reaction products between epoxy resins and castor oil still contain epoxy groups; so: that ,, they.- are hardened with common hardeners can.-As epoxy resins.- based on bisphenol @ A; are preferably usable: Epotuf @ 37-140, Ep, -kote® 828, urimodified liquid resins with an epoxy equivalent between 170 and 280.

As epoxy resins based on bisphenol A, which are internally plasticized by reacting with castor oil, the following can preferably be used: Reaction products of epoxy liquid resins with an epoxy equivalent between 170 and 280 with castor oil. The reaction products have epoxy equivalents between 450 and 700 and viscosities between 40,000 and 100,000 cl ?. All parts relate to parts by weight; Usable mixing ratios of the resin types mentioned under a) and b) in the main claim are between 10 parts of epoxy resin based on bisphenol A and 90 parts of epoxy resin, based on bisphenol Up to 90 parts of epoxy resin based on bisphenol A and 10 parts of epoxy resin based on bisphenol A, which is plasticized internally by reacting with castor oil.

Preferred mixing ratios are within the limits of 80 parts Epoxy resin based on bisphenol A and 20 parts epoxy resin based of bisphenol A, which is internally plasticized by reacting with castor oil, to e.

95 parts of epoxy resin based on bisphenol Ä and. 5 parts Epoxy resin based on bisphenol A ,. which by reacting with castor oil _ is internally plasticized.

Liquid resins can be used in the form of solvent-free mixtures as well as in the form of. Solutions are applied.

Solid resins, on the other hand, are always processed in the form of a solution. In general, for the use according to the invention as hardeners, all are for hardening from. Suitable substances suitable for epoxy resins, such as. B. aliphatic polyamines, aromatic polyamines, acid anhydrides. Aromatic polyamines are particularly suitable; such as B. metaphenylenediamine, methylenedianiline ,. D aminodiphenyl sulfone. The usage - made possible by these- substances, - by impregnation or .. $ e layered and. subsequent drying - in the usual way to a physically dry, tack-free To get to the intermediate layer, which, from a chemical point of view, has not yet hardened. As a result, there is a subsequent reaction with the, later. applied phenolic resin binder possible, whereby: a particularly good adhesion -between binder and carrier fabric is achieved.

The intermediate layer according to the invention is applied to suitable carrier materials on. Preference is given to certain carrier materials such as suitable ones for dry sanding Cotton and / or viscose tissue.

Examples of the interlayer molding compound claimed according to the invention: . Example l 170 parts of epoxy resin - based on example: nol A (trade name Epotuf @ 37-140, Epikote® 828); 30 parts of bisphenol-A-based epoxy resin, which; internally plastified by reacting with castor oil. is decorated (trade name Epotuf @ Il?), 27.5 parts of metaphenylenediamine will be good. mixed and then. on the Trä germaterial applied.

Example 2 190 parts epoxy resin based on: from. Bisphe "_ nol A (trade name Epotuf @ 37-14I @:. Epikote®- 828), ..:. 1.0 parts epoxy resin based on bisphenol A, which is internally plasticized by reacting with Rieinusöl (trade name Epotuf® IP), 54 parts of 4,4-Dia.minodiphenylmethan, 20 parts solvent (methyl isobutyl ketone xylene 80: 20), viscosity (G ardner): WX, are mixed well and then applied to the carrier material example 3 180 parts of epoxy resin based. of bisphenol A (trade name: Epotufƒ 37-140, Epikote @ 828), 20 parts of epoxy resin based on bisphenol A, which is internally plasticized by reacting with castor oil (trade name of Epotuf @ IP), 67 parts of diaminodiphenylsulfone, 26th parts of solvent (xylene -Methylisobutylketon 80: 20), viscosity (G ardner): WX, are mixed well and then applied to the carrier material.

Examples of the manufacture of phenolic resin-bonded abrasive fabrics using the interlayer molding compounds according to the invention.

A finished abrasive raw fabric in a twill weave serves as the starting fabric with a gross fabric weight of 270 g / m2. The one facing the abrasive grain pad The fabric side is coated with an interlayer molding compound described according to the invention according to Example 1 to 3 in the order of 20 g of solids per square meter coated.

It is also possible; the application of the effective intermediate layer to be achieved by a full bath impregnation of the pre-finished abrasive fabric. When using solvent-containing interlayer molding compounds, at room temperature or dried at a slightly elevated temperature. It then becomes a liquid phenol-formaldehyde condensation product with a viscosity of 8000 to 10000 cP at 20 ° C with a B-time (curing time until transition of the phenolic resin into the so-called B-stage) at 120 ° C of about Applied for 12 minutes at an amount of 120 g / m2. In this still damp phenolic resin binder layer normal corundum with a grain size of 50 is sprinkled.

The pre-hardening of the base binder is now so far above the B point driven out that the abrasive grain is well fixed on the carrier surface, so that it no longer broke out of the basic bond when the size binder was applied can and can no longer change its position.

A liquid phenol-formaldehyde condensation product is used as the top binder with a viscosity of 1000 cP at 20 ° C used in its pure form. Instead of this Sizing agent can also be a mixture of 60 parts of liquid phenol-formaldehyde condensation product and 40 parts of inorganic fillers can be used. This is no longer the subject the invention.

This binder is applied in a quantity using the roller application method applied from 250 to 300 g / m2. The curing will take place within 6 hours a temperature curve that has been empirically determined to be optimal.

Following the hardening process, the during hardening Inevitably dried out grinding tools due to moistening with the help of steam returned to its hygroscopic equilibrium under normal climatic conditions.

This according to Examples 1 to 3 with the interlayer composition according to the invention Abrasive fabrics provided stand out in comparison to those with customary intermediate layers manufactured abrasive cloth by the advantages; those in columns 2 and 3 are mentioned in this description.

The invention is illustrated by the drawings.

F i g. 1 shows the structure of phenolic resin-bound compounds according to the invention Abrasive fabrics with abrasive grain layer 3, with 1 being the abrasive grain carrier made of pre-finished Represents cotton fabric.

The abrasive grain binder6, consisting of the phenolic resin base binder 4 and the phenolic resin neck tie5 is clearly shown. The inventive The intermediate layer bears the number 2. The following can be used as abrasive grain layer 3: corundum, Silicon carbide in various quality classes and in grades, which are common in the: sandpaper and abrasive cloth industry.

F i g. 2 shows the abrasive grain carrier on pre-treated cotton fabric and the intermediate layer 2: with the molding compound according to the invention.

A twill fabric with a gross fabric weight is suitable as the abrasive core carrier of 270 g / m2.

F i g. 3 shows the abrasive grain carrier made of pre-finished cotton fabric and the upper effective intermediate layer 2 and the lower impregnation layer 2 the same material that is inevitably obtained with full bath impregnation will. The lower 'layer 2 has the purpose according to the invention in this. do not fall to meet. This lower layer 2 only contributes to further stiffening and ° increasing the strength of the abrasive backing in an advantageous manner.

F i g. 4 again illustrates an abrasive fabric with the one according to the invention Intermediate layer.

F i g. FIG. 5 shows an abrasive material, which consists of a carrier according to FIG F i g. 3 was made.

To prove the technical progress brought about by the invention is achieved, the following experimental procedure was used: Two of the same type were used Abrasive cloth coated with synthetic resin, pressed together in mirror image, in this one Condition hardened and the peel strength tested according to DIN 53530.

A pure cotton fabric with this finish was used for the experiments was how it was in the abrasive cloth industry for the production of fully synthetic resin-bonded Abrasive cloth is common. It had a basis weight of 325 g / m2 and a density of 32 warp threads per centimeter and 20 weft threads per centimeter.

Prior Art Comparison 1 A strip of fabric with FIG Dimension of 10-20 cm was half with one in the abrasive industry conventional phenol-formaldehyde-based binders. The coating weighed approximately 100 g / m2.

An uncoated, identical abrasive cloth was mirror-inverted (right Side to right), and on the two outer surfaces there was a slight Pressure exerted. This setup was under pressure for 7 hours in a drying cabinet Hardened at increasing temperatures from 40 to 130 ° C. Compare 2 below Use of the intermediate layer according to the invention. Two strips of fabric, likewise with the dimensions 10-20 cm, half of them with 50 g / m2 each were made according to the invention described epoxy resin intermediate layer coated. By lying for several hours These epoxy resin coatings were slightly pre-cured at room temperature. Afterward the coating of a fabric strip on the epoxy resin layer was carried out with a Phenol-formaldehyde-based binders commonly used in the abrasives industry (as in comparison 1). Both fabrics were now placed on top of one another as in comparison 1, lightly pressed together and cured in the same way as in comparison 1.

Testing The samples were stored for 3 days in a standard climate (650 /, relative humidity and 20 ° C), cut straight in the warp direction into double strips 1.5 cm wide, and the non-glued parts of the strip were placed in the upper and lower clamps of a tensile strength tester , Schopper system, clamped.

The forces that were necessary were measured, the two layers of fabric peeling off from each other. Comparison 1 (without epoxy resin intermediate layer) 1.8 kp comparison 2 (with epoxy resin intermediate layer) 2.3 kp summary assessment.

The test result showed that the use of the described according to the invention Epoxy resin interlayer significantly increases the adhesive strength of the cured Binder layer based on phenol-formaldehyde causes on the carrier fabric. There the abrasive grain is embedded in this binder layer, can also with certainty be believed that by using the epoxy resin interlayer of the invention a significant increase in the adhesive strength of the abrasive grain on the backing is achieved can be. A direct test of the adhesive strength of the abrasive grain on the Carrier layers are not possible. The results coincide with experiences that have been obtained in the manufacture of the abrasive sheets according to the invention.

Claims (2)

Claims: 1. Sanding sheet for dry sanding, consisting made of a finished fabric carrier, an elastic barrier intermediate layer and a phenolic resin make coat for the abrasive grains characterized by the use of a hardening mixture consisting of the combination a) epoxy resin based on bisphenol A, b) an internal one by reaction with castor oil plasticized epoxy resin based on bisphenol A, c) hardener, as an intermediate layer. 2. Abrasive sheet according to claim 1, characterized in that the hardener is an aromatic Is polyamine. Publications considered: German Auslegeschriften No. 1153 517, 1111386, 1098195; British Patent No. 738 232.