DE2746833A1 - Carrier for flexible abrasive papers - coated with heat-activated adhesive for the abrasive grains - Google Patents

Abstract

Carrier for flexible abrasive papers is coated on one side with a thermoplastic adhesive, which is non-tacky at ambient temps. but softens on heating to a temp. lower than that causing damage to the carrier, and allows the grit particles to embed themselves by gravity alone, and become firmly bonded on cooling. The carrier is pref. a paper sheet impregnated with synthetic resin. For water-resistant abrasives, it is pref. a highly-porous packing paper impregnated with 15-40 wt. % synthetic elastomer, e.g. NBR, with base wt. 70-200g/m2 and Gurley porosity 10s/100cc. air. For dry abrasives, it is pref. a very fine packing paper with base wt. 65-200g/m2 and Gurley porosity >10s/100cc. air, contg. up to 15 wt. % synthetic elastomer. No separate barrier coating between carrier and adhesive is required, and atmos. pollution due to use of solvent-based adhesives is avoided.

Description

Backing material for flexible sanding sheets

The invention relates to abrasive sheet material in general and on a carrier material for this purpose in particular.

Coated abrasive sheet material including that known in the trade waterproof sandpaper and another type known as dry sheet paper used for fine grinding of metal and wood for many years. The ones for crafting The backing used by waterproof sandpaper is usually a very porous, pliable paper made with about 15 "to 40" of a synthetic resin or elastomer is soaked to have toughness and durability, especially when it is wet, to obtain. Current production techniques require this to be very porous Paper is coated with a barrier of synthetic Xarz to the surface to compact before the adhesive or coating is applied that the abrasive grains or the sanding grit binds to the base.

The backing used for dry sandpaper is stiffer and non-porous and with these products the bonding adhesive coating is usually immediate put on paper without first providing a barrier to oppression.

The glue used to bind the grit on waterproof sandpaper contains epoxy resins, epoxy esters, phenolic resins and lik7d resins in corresponding Solutions. Binding adhesives for dry sandpaper, on the other hand, are common animalistic Water-based glues and synthetic resins.

In the usual production of both types of paper, the binding adhesive is used dissolved in a solvent and sprinkled on a support and the mixture is then applied to the continuous backing web by pressure coating. The abrasive grit then deposit on the moving web before the Solvent or the carrier is driven off and while the adhesive is still liquid is. The grit particles are usually aligned by electrostatic means, in order to obtain maximum grinding or cutting properties. After knocking down no external pressure is applied to the particles if this is the orientation of the Particles could influence what, while the particles sink in when they are inserted both are undesirable. After the solution or the carrier has been driven off, the Adhesive and grit-bearing sheet is passed through an oven that separates the material heated for a few minutes and a few hours to those commonly used as glue, cure thermosetting resins.

Dry sandpaper glue can be used to drive off the liquid carrier be used.

After the grit is firmly bound, a grain-sized coating is applied over it brought the layer of abrasive particles to complete the manufacturing step. The grain size coating is usually its hard, thermoplastic resin or an animal glue that anchors the particles more firmly so that they can become Stay aligned to maintain maximum cutting ability.

The production of sandpaper is therefore a slow and long one ongoing process. Because the coating with the glue, the particle precipitation, the drying and hardening must be carried out in a continuous process many variables, such as the viscosity of the solution, the weight of the coating, the weight of the grit precipitate and the web tension can be controlled at the same time.

If not properly regulated, problems such as puckering often arise and breaking of the moving web or insufficient bond strength. even if the inlay with a barrier layer before the application of the binding the grit Once adhesive has been coated, sticking often occurs between the barrier coating and the adhesive layer, unless the two layers are carefully chosen and have been tested. It is quite impossible to have an abrasive with a single one Barrier coating manufacture that for all of the many types and variations is compatible with adhesives used by the sandpaper manufacturers. Thus, the barrier coatings are individually tailored to the respective To meet the requirements of the many manufacturing options.

The current regulations concern air pollution which has Situation further complicated. Many abrasives manufacturers that have so far based on solution-based resins for making wet or dry sandpaper are now forced to use water-based systems to remove air pollution to avoid.

This change makes extensive testing of new adhesive systems and the Development of new barrier coatings necessary.

The backing material for flexible abrasives such as waterproof sandpaper and also dry fine abrasive papers, are according to the invention with an adhesive for Attach the Grit coated, the glue in its normal Condition is not sticky and does not flow easily at ambient temperatures, however becomes thick at higher temperatures. The adhesive is characterized by that it becomes sufficiently soft at a temperature at which the paper base is not damaged and in their softened state the knocked down grit particles lets sink into the softened adhesive by its own weight.

The coated carrier material according to the invention can be used for storage and transport conveniently wrapped in rolls.

When making sandpaper according to the invention and using it a coated base or carrier, the material is above the softening point of the glue is heated to a point where the viscosity is down to a state is reduced when abrasive grit particles are deposited on the backing and the electrostatic align the particles by their own weight in the penetrate the softened coating and bond there with the carrier. It will no pressure other than the gravity of the particles is and is not used he wishes.

Depending on the processing speed, it may be necessary to the heat on the substrate at a temperature above the softening point of the adhesive for about 30 minutes after deposition and electrostatic alignment to hold in order to obtain a corresponding penetration of the grit particles. After this Precipitation and embedding when cooling the carrier or removing the heat source hardens the adhesive is in its original state and the abrasive particles are thus firmly integrated there.

A final step in the manufacture of the fine grinding plate is the application a conventional grain size resin layer over the abrasive particles, as with conventional Sandpaper happens.

The base on which the adhesive is applied is a flexible, thin material, preferably a resin or a latex impregnated paper, does not soften or coat the temperatures used in softening the adhesive - is damaged. The tightness of the adhesive applied to the carrier is adjusted so that that the abrasive particles of the desired size are only partially embedded in the adhesive but don't sink into it.

The procedure for adjusting abrasive products that coat the of the carrier material according to the invention can be used with the current Procedure can be easily applied. For example, the coating device in the usual methods by a device for heating the moving Replaced the web of the coated carrier material. An infrared heating device, Rows of electrical elements, gas burners or cylinders made of heated metal to be used. A second heating device is preferably also used for heating the web for a few seconds after the grit has been deposited in the softened coating intended. This speeds up the embedding process and requires less heat to keep the thick fluid of the liver during and after the application of the grit.

Such a carrier with previously applied heat-activated adhesive results in an economical and efficient approach Able to go through which the abrasive manufacturers eliminate many of the problems listed or very much can keep them small. There is no need for the sandpaper manufacturers to to apply a special adhesive before depositing the grit and thus the production is significantly simplified.

A simple device for heating the precoated substrate can replace the more complicated primer coater. Problems like that Noise and wrinkling of the moving web are thereby kept very small. Air pollution that accompanies the use of solution-based adhesives will be also eliminated, as well as the ongoing problem with low bond strength between the adhesive coating and the barrier coating. Because according to the invention these two coatings by a single heat-activated, by the carrier paper supplier previously applied adhesive coating is replaced.

The cost of the raw material when manufacturing the carrier material according to of the invention are slightly higher than those of the usual carrier material because the preferred water-based heat-activatable adhesives of the invention are more expensive than the currently used barrier coatings and weights of the coatings in most cases larger than that of the barrier coatings on running products are. The other advantages mentioned, including the use of single stratification and not a double coater make the invention for sandpaper manufacturers attractive.

Two types of paper or backing are preferred for the support. The first, commonly used for waterproof sandpaper, is a highly porous one Wrapping paper with 15 to 4% nitrile rubber or an acrylic elastomer. Pigments can also be added.

The preferred weight basis for the paper is between 70 and 200 Grams per square meter and the preferred Gurley porosity below 10 seconds per 100 cc air for a single sheet. The second type of paper that is commonly used Dry fine sandpaper is used with a finer wrapping paper, though desired, a filler and dyes or pigments and between 0 to 15 ° h nitrile rubber or acrylic elastomer. The base weight the latter Paper is between 65 and 200 grams per square meter and the Gurley porosity of the single sheet is over 10 seconds per 100 cc of air.

Functional additives that can be used with this type of paper contain sizing agents and starch.

It goes without saying that the base paper used for regrinding has it the so far hardened or thermoplastic impregnation agent that is used for this Uses has sufficient wet strength.

For the adhesive coating, many are water-based heat sensitive Adhesive systems have been tested and many of them have been shown to be suitable. Many others have not proven themselves and are specifically excluded.

Examples of adhesives that are not suitable are: 1) polyvinyl chloride latexes, mixed with various calibration polymers, such as acrylic elastomers or common ones Plasticizers. These do not soften sufficiently under 2200C, so that abrasive particles can sink by gravity alone and thus a require too high a temperature to be applicable.

2) SBR, ABS, polyvinyl acetate and most acrylic latexes are available not suitable for the same reason.

3) wax, polyethylene, and ethylene, organic acidic copolymer with low molecular weight or latexes stick weakly to the paper and / or the Silicon carbide grit commonly used in preferred sandpaper, and are unsuitable for these reasons.

Several ethylene-vinyl acetate copolymer latexes have proven to be among the adhesives used and ionomer resin dispersions such as ELVAX D (trademark) from DuPont and described identified as suitable in DuPont Technical Bulletin A 86 826. This glue can also be mixed with nitrile rubber or acrylic latexes for coatings that have better flexibility and better adhesive strength on the paper backing especially if it has been impregnated with the same latexes. That Mixing these ethylene-vinyl acetate copolymer latexes or ionomer latexes with polyterpene emulsions results in such mixtures with very low desired softening temperatures, While these blends are useful, the bond strength on paper is not as well as with mixtures with acrylic or nitrile rubber latexes. Xuch are ethylene, Acrylic acid copolymer dispersions of relatively high molecular weight, e.g. B. PCX 300, an alkali dispersible ethylene copolymer from Union-Carbide (described in their Technical Bulletin F 42958-A), if it is with acrylic Nitrile rubber or polyterpene latexes, as well as mixtures of a Novalach resin, e.g. Durez (trademark) from Hooker Chemical with ACRYSOL (trademark) .SS-32, a Röhm & Haas polymeric acrylic resin in aqueous dispersion.

Other useful polymers include polyvinyl butyral, ethylene-ethyl-acrylate copolymers and linear aliphatic polyamides and polyesters. Many other types of polymers or mixtures with the specified similar properties are of course also possible possible. the necessary characteristic is that the chosen adhesive is at ambient temperature and at such a low temperature that the cellulose pads do not go so far soften, abrasive particles embed themselves in it only by gravity does not become sticky. The following examples show different versions according to the invention: Example I The paper backing in this example is a very porous wrapping paper impregnated with 33% by weight nitrile rubber and about 80 grams weighs per square meter. The impregnated paper is coated with a mixture of 33 polymeric sacraliles Latex and 67N dry weight of the mentioned ionomer resin dispersion coated the is known under the trademark ELVAX D-1265. The total percentage of solids the coating mix is 47 ». The applied layer is at a dry layer weight of 22 grams per square meter using a "Meyer" wire wrap bar measured what is well known in the trade. The layer is then dried and a sample sheet 216 x 280 mm with the coated side down against one uncoated Sheet together at ambient temperature in one hydraulic press brought together. The pressure is up to 0.84 kg / cm2. It it has been shown that the leaves were not tied together after 16 hours and can be separated with a very low level of glue after removal from the press can.

A sample sheet of coated paper is then coated with the Page placed on a hot plate until the surface temperature of the paper between 150 and 220 ° C. Then silicon carbide 200 is lined up against one edge of the Cast sheet. The sheet is then quickly lifted at this edge, around the silicone crab to distribute on the sample. As is well known, this method of applying grit is used used for the continuous application used in the manufacture of sandpaper to simulate. After shaking off the excess grit, a uniform remains Precipitation of silicon carbide of 70 grams per square meter bound to the sample. Although the particles could be removed by scratching with a sharp tool, They are tied tight enough to allow the process with a coating of a size can be continued without losing a substantial part of the silicon carbide goes.

The formal coating that is a thermoplastic phenolic resin solution is applied to the sample over the bilicon carbide, again using a MEyer wire winding rod for applying a dry format coating of approx 33 grams per square meter. The sample is then placed in an oven for six hours held where the phenolic resin hardens. Then it will be cut into pieces of 12 x 15 for testing cm cut. A sample is in for an hour Water held, to test them wet and the other is tested dry. Adhesive and peel strength are done by rolling the corners of the samples between your thumb and forefinger ten times tested. This resulted in no delamination or loss of silicon carbide from a sample. A steel rod with a diameter of 6 mm is ground off with the wet sample until the surface of the sample became smooth as a result of the steel loading and corrosion is.

The steel precipitate is washed off the sample with water and this does not result in a substantial loss of silicon carbide particles. The grinding the steel rod and the washing of the sample is repeated ten times until a 60 cm Part of the rod is free from corrosion. There is no essential here yet Peeling of glue or loss of silicon carbide from the specimen.

Example II In this example the pad for the wearer is a Wrapping paper with an inorganic filler and 10% by weight of a polymer-acrylic Impregnated elastomer.

The paper is coated with a mixture of DUREZ 12686 -Novalak resin, a Phenolic resin from Hooker Chemical, coated and in water with methyl ethyl ketone and the aforementioned ACRrSoL-WS-32 acrylic latex emulsified. The ratio of Phenolic resin to acrylic polymer in the mixture is 1: 0.9 and the total percentage the solids of the mixture is 35. Coating is done with a Mayer rod and results in a dry coating weighing 15 grams per square meter. Three hundred and twenty yards of silicon carbide heated to 2500 C are placed on the paper applied. The layer side is on a hot plate using one Temperature between 150 and 2000C. The silicon carbide is evenly through rapid lifting of an edge distributed on the carrier as in the previous example. The sample is then placed in a 16500 oven for 30 seconds. After this Removal of the excess is the weight of the deposited silicon carbide 33 Grams per square meter. The sample is then assembled with a mixture thereof as for the adhesive coating format coated. Roof drying the format coating the sample is kept in an oven at 1650C for five minutes to remove the layers to harden.

The silicon carbide has shown itself to be very strongly bound to the carrier and there is no substantial loss of particles when the sample is used for grinding used by metal or wood.

While in these examples the abrasive grit is preheated before application to speed embedding, further testing shows no need preheating to obtain satisfactory results.

In the latter case, however, the coating is done with applied grit preferably kept at higher temperatures for a slightly longer time to achieve a satisfactory Ensure embedding and binding of the particles.

While latex-impregnated paper is the preferred underlay for the Abrasive backing material according to the invention can of course also be other flexible ones Documents are used.

The requirements of the document itself are not mandatory.

Paper made primarily from chemical pulp fibers is preferred because it is easily available and inexpensive. Highly porous Wrapping paper with a nitrile rubber or an acrylic elastomer similar to the current one used waterproof sandpaper backing has shown the best results in laboratory tests. More refined, much less porous paper like the dry fine sandpaper that is currently used also gives sufficient results when used in the manufacture of Dry fine abrasive papers. Other ellulose fibers, e.g.

B. cotton or rayon, can be used alone or with the addition of wood pulp fibers as well as synthetic or glass fibers can be used. When using wood pulp or other cellulosic fibers in the backing, the chosen adhesive must be at temperatures become sufficiently soft below 2200C, because at this temperature the fibers in this Paper begins to char quickly. Adhesive coatings that require higher temperatures Need to bind the grit can be combined with higher heat-resistant Straps are used. In general, the base should be so flexible that it can be wrapped in rolls for storage and transportation. The underlay should have sufficient thermal stability to support the adhesive layer, while the rolls are being unwound and the material is above the softening point the glue is heated. The document should also be relatively closed Have surface so that the abrasive grit particles only through the softened adhesive layer and not penetrate the substrate itself.

The heat-activated adhesive can be used in different weights Except for different sized grit particles. Generally will it is preferred that the adhesive have the following characteristics: 1. For application on the pad can be in the form of a solution in an appropriate solvent as a Emulsion or latex in water or melted plastic be.

2. The adhesive layer should in its applied state after Driving off the solvent or carrier or after cooling and solidifying the molten coating will not be tacky, so that the substrate will be in Rolls can be wound and stored without sticking together so that the rolls can be unwound again without damaging the material. bie should too do not remain sticky in the normal range of ambient temperatures, which at the Treatment can occur, i.e. at least above about 35 ° C.

3. Heated to a temperature at which the glue softens, which but is so low that the carrier material is not softened or weakened, If the adhesive layer is supposed to be a viscous liquid, the precipitated particles can only be embedded by its own weight. A print from the outside for embedding and avoid binding the particles to the carrier. In some cases the coated Carrier held above the softening point for about 30 seconds or a Ensure adequate wetting and embedding of the particles through the softened adhesive.

4. The softened adhesive should harden in its original state while the abrasive particles remain bonded to the backing at least so that a conventional format coating without removing a significant amount of the embedded Grit particles can be applied from the carrier.

5. The adhesive layer should be a tough, flexible polar material, that sticks well to the carrier and the silt particles and does not peel off the carrier, when the finished abrasive is bent and deformed in use. The one before properties mentioned are consistent with this requirement.

6. An optional feature of the adhesive coating is that it continues polymerized or cross-linked with prolonged aging or at higher temperatures, while maintaining the essential characteristics stated.

While particular example is made by a periodic process It has been found that pads according to the invention are easily used at now Devices are suitable for uninterrupted production of sandpaper, which are now commonly used by the leading manufacturers. All of this must can be done to adapt this paper to the existing abrasive manufacturing plants, to provide the current adhesive layer sections with a heating section and after after applying the grit to provide additional heating to ensure a full To enable embedding, followed by normal or accelerated cooling.

Claims (15)

Claims I1 ,, 'Embossing material for use in manufacturing flexible sanding sheets with a flexible path of a backing, marked thanks to a one-sided thermoplastic adhesive coating that turns into a Ambient temperatures is not in a sticky solid state and at Heating to a temperature that is not sufficient to thermally weaken the substrate reaches a viscous, liquid state and still precipitates grit particles on the softened layer and electrostatically aligning these particles can sink into the softened layer solely through their force of gravity and themselves embed in it and firmly bound when the heat is removed and re-solidified stay. 2. Material according to claim 1, characterized in that the base is a paper web impregnated with a synthetic resin. 3. Material according to claim 1, characterized in that the base A highly porous wrapping paper that is made with a synthetic elastomer in the crowd between 15 and 40 °> (weight 0.0) is impregnated and has a basis weight of about 70 to 200 grams per square meter and that has a Gurley porosity of has less than 10 seconds per 100 cc of air. 4. Material according to claim 1, characterized in that the base a very fine wrapping paper with a basis weight between 65 and 200 grams per Square meters and a Gurley porosity of more than 10 seconds per 100 cc of air is. 5. Material according to claim 4, characterized in that the paper contains up to 15 wk of synthetic elastomer. 6. Material according to claim 1, characterized in that the base a sheet of paper is mainly made of cellulose fibers and the border to which the The temperature can rise to soften the adhesive without weakening the substrate, 2200C. 7. Material according to the preceding claims, characterized in that that the layer is a mixture of a polymeric acrylic latex and an innomer Hars dispersion is. 8. Material according to claim 7, characterized in that the acrylic Latex 33 by weight so and the ionomer resin 67 Ges. » the mix has. 9. Material according to claim 8, characterized in that the base is a porous packing paper that is impregnated with about 33 total * nitrile rubber, a basis weight of 80 grams per square meter and a Gurley porosity of less than 10 seconds per 100 cc of air. 10. Material according to claims 1 to 6, characterized in that that the layer is a mixture of phenolic resin and a polymeric acrylic latex. 11. Material according to claim 10, characterized in that the ratio from phenolic resin to acrylic latex is 1: 0.9. 12. Flexible sanding sheet with a backing material according to the preceding Claims, characterized in that the layer is embedded in its surface which is a layer of uniformly distributed grit particles that is one on top of it contains applied grain size coating. 13. A method of manufacturing an abrasive sheet according to claim 12 characterized by heating the carrier material according to claim 1 above the softening point of the deposited adhesive and the electrostatic alignment of the abrasive grit particles on the support while maintaining the heat until the particles Sink into the softened layer due to their own weight, whereupon the adhesive cools down and can sit down. 14. The method according to claim 12, characterized in that the adhesive above its softening point for about 30 seconds after precipitation and straightening the particle is heated. 15. The method according to claims 13 and 14, characterized in that that a conventional hars coat or grit size is applied over the abrasive particles will.