CA2037713C

CA2037713C - Rolls having synthetic coatings, and process for manufacturing same

Info

Publication number: CA2037713C
Application number: CA002037713A
Authority: CA
Inventors: Johann Weinert; Gerhard Dau
Original assignee: Felix Boettcher GmbH and Co KG
Current assignee: Felix Boettcher GmbH and Co KG
Priority date: 1990-03-07
Filing date: 1991-03-07
Publication date: 2000-07-18
Anticipated expiration: 2011-03-07
Also published as: EP0445753B1; EP0445753A3; FI103126B; ES2076387T3; FI911151A0; DE4007141C1; EP0445753A2; KR0154337B1; NO910885L; JPH05240237A; DE59106338D1; FI911151A; NO301485B1; CA2037713A1; NO910885D0; ATE127074T1; KR910016883A; JP2655015B2; FI103126B1

Abstract

Rolls with synthetic coating have a coating of poly-2-oxazolidinones being optionally present as a mixture with isocyanurates. Preferably, said synthetic coatings are modified by flexibilizers and inorganic fillers. Manufacture is carried out by addition of multifunctional epoxides to multifunctional isocyanates, in the presence of catalysts, and optionally with the addition of flexibilizers and fillers.

Description

ROLLS HAVING SYNTHETIC COATINGS, AND PROCESS FOR MANUFACTURING SAME
Rolls having synthetic coatings are employed for many different user, and are manufactured according to many different processes. Typical synthetic coatings consist of rubber, polyamides, polyurethanes, polyesters, polyester amides, epoxide resins, silicone resins, phenol resins, polyacetate~ resins, polyamide resins, melamine resins and the like. Depending on use and requirements, said coatings are modified in known manner by inorganic fillers, flexibilizers, impact modifiers, and other additives with respect to hardness, abrasion resistance, impact resistance, temperature resistance, as well as resistance to solvents and chemicals. Generally, manufacture is carried out by casting, extruding or winding the synthetic coating onto the roll shell being optionally provided with an adhesive layer. With thermoplastics, final curing is effected by cooling, and with other syr.thetic:s, by subsequent cross-linking.
One disadvantage of most synthetic coatings being used hitherto, .is their relatively low temperature resistance. For example, although coatings made of silicone and fluorine rubber, respectively, do have high temperature resistance, they do not have the hardness required for certain uses. The trend towards faster production and hence higher rotational speed increasingly requires better resistance to high temperatures, as well as rapidly changing temperatures and short-termed local overheating.

Thus, it is an object of the invention, to develop rolls having such synthetic coatings which are resistant to high tempenature;~, and which, in addition, are able to be adjusted variably with respect to hardness, abrasion resistance, impact resistance, resistance to solvents and chemicals and otherwise required physical properties.
It has :zow been found that this problem can be solved by using coatings made of poly-2-oxazolidinones.
Here, said poly-2--oxazolidinones may be admixed with certain amounts of isocyanurates. Furthermore, they may be modified by admixing or incorporating other components.
Poly-2-ox:azoli<~inones are formed, for example, in the catalyzed reaction of diepoxides with diisocyanates at temperatures a~>ove 120 C. Since under these conditions isocyanates also self-react to form isocyanurates, the thus produced synthetic coatings generally contain more or less large quantities of isocyanurates. However, it is possible by varying the conditions of the process, selecting catalysts, and by other modifying additives to suppress or enhance formation of isocyanurates, thereby modifying the properties of the final synthetic coating.
Moreover, of c:our~~e not only diepoxides and diisocyanates may be used, but. also other multifunctional epoxides and/or isocyar.ates.
Linking epox:ides to isocyanates with formation of oxazolidinone structures is known per se, but hitherto said linking is hardly utilized technically on a large scale. See, Bec:ker/Braun, Kunststoff Handbuch 10, "Duroplaste", page 111. Known hitherto above all are oligomeric polye~>o:~ides containing oxazolidinone, and which are made of bisepoxides and diisocyanates according to EP-A-0 296 450.-These oligomers have been admixed in particular wii~h other liquid or solid epoxide resins or reactive diluents, and have been cured by means of usual curing agents such as polyamines, acid anhydrides or polyisocyanates. 'fhf~ thus obtained products show enhanced tensile strength, breaking elongation, impact resistance, ball indentation hardness, and deflection temperature.
However, unti7_ now they have not been used to self-react with only relatively small quantities of a catalyst and then cured. Here, this can be attributed to the formation of very hard and brittle products, and hence ultimately unusable products. It has now been found that it is possible, howeverr to cure such oligomeric pre-polymers having isocya:zurate moieties by means of catalysts and relatively small quantities of flexibilizers to obtain products being excellently suitable for use as hard synthetic coatings for rolls. Furthermore, it has been confirmed that it is easily possible to react said diepoxides and diisocyanates being used in the manufacture, with a catalyst and a flexibilizer to obtain products, which, depending on reaction conditions, contain a substantially smaller amount of isocyanurate moieties.
Furthermore, it has been found that by varying said multifunctional epo:~ides used, on the one hand, and said multifunctional isocyanates, on the other, the properties of the synthetic may be varied considerably, and thus may be adjusted to any required property of a synthetic coating for rolls. Likewise, it is possible to vary and modify such synthet_Lcs by means of inorganic fillers.
However, all such synthetic coatings according to the invention when compared to synthetics used hitherto show substant:iall.y higher temperature resistance and resistance to temperature fluctuations, and nevertheless are sufficiently flexible.
This should be attributed to the fact that both the oxazolidinone strucaure and the isocyanurate structure are very insensitive to temperature stress. Since pure poly-2-oxazoli.dinones, as well as their mixtures with isocyanurates, are very brittle, particularly when manufactured from diepoxides based on bisphenol A, and diisocyanates based on diphenylmethane, this group of synthetics has received little attention. Thus, it was not to be foreseen that these synthetics could be further developed to ~=xcellent synthetic coatings for rolls with only slight modification, in particular by using flexibilizers.
According to the invention, however, bisepoxides generally can be used, not only those based on bisphenol A, but also ot=her commercial bisepoxides having been used as epoxide components in synthetics. A summary of such epoxides is j=ound in Becker/Braun, Kunststoff Handbuch 10, "Duroplaste", pp. 115-118. In addition, components having three or more epoxide moieties, may likewise be used.
Similarly, all industrially available diisocyanates may in principle be considered as diisocyanate components. Furthermore, substances having three or more isocyanate moieties, are likewise possible.
Most di_=ferent product groups are possible as catalysts for the addition of epoxides to isocyanates.
Suitable are, for instance, tertiary bases such as pyridine, tribenzylamine, N-methyldibenzylamine, but also Lewis acids such a:~ zinc chloride, iron chloride, boron trifluoride; alkali and alkaline earth alcoholates such as calcium and magnesium ethylate; and aluminum isopropylate. Other catalysts are lithium chloride, tetramethylam~r~onium iodide, and phosphonium salts.
Substances which are candidates for flexibilizers include those in which the functional groups are joined together within th.e molecule at a wide distance via principally aliphatic structural elements. Typical flexibilizers are p~zlypropylene glycol diglycidyl ethers, oligoesters, oligoether esters having terminal carboxy groups, amine groups or hydroxy groups being able to react, at least <~t elevated temperatures, with epoxide groups or isocyanate groups left, leading to flexibilizing cross-linking. Thus, also flexibilized epoxides, polybutad:iene, polyisoprene, and polybutadienes having terminal epoxide or hydroxy groups, have good flexibilizing properties.

In princ:~ple, all known inorganic fillers that are used already now as fillers for synthetics, and, in particular, for synthetic coatings of rolls, may be used as inorganic fillers in the invention. For instance, aluminum oxide, ;silicon dioxide, silicon carbide, and granite powder, are well suited where hard, wear-resistant coatings having good grip are desired.
The manufacture of said synthetic coatings on the rolls is like;aise carried out in known per se and usual manner. For this purpose, the roll shell is usually degreased and sandblasted. It is often convenient to apply an adh~=sine layer as a primer, for instance a phenol resin. Fux_thermore, it is convenient with hard rolls to apply <~ polyurethane layer, onto which the synthetic coating of poly-2-oxazolidinone according to the invention is coated as a stress relaxating factor between the shell and the synthetic coating. This can be carried out ai. temperatures of up to 100 C. Final curing is then carried out at temperatures above 120 C.
Preferably, said c:u:ring is carried out at temperatures of between 130 ,end 180 C. In order to obtain synthetic coatings free of bubbles, it is advisable to degas and homogenize the lie~u:id components in a vacuum. If a higher proportion of isocyanurate structures is desired, the diisocyanate component, for instance, may be heated in advance with catalysts such as alkali and alkaline earth alcoholates to a temperature at which the isocyanurate structure is formed. Another possibility for raising the proportion of said isocyanate structure is the use of oligomeric pre-polymers, as described, for instance, in EP-A-0 296 450.
The objects of the present invention is therefore not the production of rolls having a synthetic coating in general, or the process for their manufacture, but the use of poly-2-oxaz:olidinones, optionally admixed with isocyanurates as well as flexibilizers, fillers, and other additives, as material for roll covers. Another object of the in~Tention is the use of oligomeric pre-polymers containing oxazolidinone moieties, and being made of diepo:~ides and diisocyanates, in the manufacture of roll covers..
Several embodiments of rolls according to the invention, and the process for manufacturing them, are described in t:he f=ollowing examples. Properties, however, can conveniently be varied in a wide range, depending on purpose of application and use.

20 parts by weight of diepoxide based on bisphenol A
(Lekutherm X 18) are mixed with 80 parts by weight of a diisocyanate (mixture of 4,4- and 4,2-diisocyanatodi-phenylmethane (MDI),, Baymidur VP 50021, and mixed with 5 parts by weight of :N-methyldibenzylamine (as a catalyst), and 10-30 parts b~~ weight of polybutadiene (R 20 LM with terminal hydroxy groups ) . To the mixture is added 160 to 220 parts by weight silicon carbide. The mixture, degassed at 80 C and homogenized, is cast onto a roll -shell pre-coated with an adhesive layer and a polyurethane .Layer. being about 1 mm thick, and cured at 130 C. The thus c>btained synthetic coating shows all required physical. properties, and, in addition, is resistant to nigh temperatures.

In an analogous manner, as described in example 1, 100 parts by weight of a pre-polymer having been prepared from 20 parts by weight of the same diepoxide and the same diisocy<~natE~ are used, the pre-polymer still containing about 20% free isocyanate groups, and, additionally, isocyanurate groups to a considerable extent (BlendL.r I-VF? KU 3-4516, from Bayer AG) .

In an analogous manner, as described in example 2, 100 parts by weight: of the same pre-polymer (Blendur KU
3-4516) are mixed with 15 parts by weight of diepoxide based on bisphenol A (Epikote 828), 15 parts by weight of hexamethylene di:isocyanate having isocyanate groups (Desmodur N 3300), and 10 parts by weight of N-methyl-dibenzylamine as <~ catalyst. Further admixed are 160 to 200 parts b_~ w.=fight silicon carbide. The mixture, degassed at 80 C and homogenized, is cast onto a roll shell pre-coated with an adhesive layer and a polyurethane =~ayer being about 1 mm thick, and cured at 130 C. The thus obtained synthetic coating shows all _ g -required physical properties, and, in addition, is resistant to high temperatures.

In an analogous manner, as described in example 3, 100 parts by weight of the pre-polymer (Blendur KU 3-4516) are mixed with 12 parts by weight of butane-1,4-diol-diglycidyl ether (Araldit DY 026 SP), 9 parts by weight of hexamethylene diisocyanate (Desmodur N 3200), parts by weight of N-methyl-dibenzylamine, and 160 to 220 parts by weight: silicon carbide, and processed to a roll cover. The thus obtained synthetic coating shows all required phy:~ical_ properties, and, in addition, is resistant to nigh temperatures.

In an analogous manner, as described in example 1, 100 parts by weight of butane-1,4-diol-diglycidyl ether (Araldit DY 02.6 Sf), are mixed with 80 parts by weight of hexamethylene diisocyanate (Desmodur N 3200), 18 parts by weight of N-methyl-dibenzylamine, and up to 220 parts by weight fillers, and processed to a roll cover. This coating is relatively soft, and has a relatively low hardness (about 50 Shore A). Thus, it is possible to blend this formulation with harder formulations to adjust the desired hardnes:~.

Claims

1. A roll having a synthetic coating consisting of a poly-2-oxazolidinone in admixture with an isocyanurate and an inorganic filler, and modified with a flexibilizer.

2. A roll according to claim 1, wherein said flexibilizer is selected from propylene glycol diglycidyl ethers; oligoesters; oligoesters having terminal groups selected from carboxy groups, amine groups and hydroxy groups; flexibilized epoxides, polybutadiene, polyisoprene and poly butadienes having terminal epoxide or hydroxy groups.

3. A process for manufacturing a roll having a synthetic coating, comprising:
applying onto a roll shell a mixture of a multifunctional epoxide, a multifunctional isocyanate, a catalyst, a flexibilizer and an inorganic filler, and curing said mixture by heating to a temperature above 120°C.

4. A process according to claim 3, wherein prior to applying said mixture to said roll shell, a layer of adhesive is applied to said roll shell.

5. A process according to claim 3 or 4, wherein the multifunctional epoxide is predominantly or entirely in the form of a oligomeric pre-polymer of diepoxides and the multifunctional isocyanate is predominantly or entirely in the form of oligomeric prepolymers of diisocyanates.

6. Use of poly-2-oxazolidinones admixed with isocyanurates as well as flexibilizers, fillers and other additives, as a material for roll covers.

7. Use according to claim 6, wherein oligomeric prepolymers containing oxazolidinone moieties, and being made of diepoxides and diisocyanates are used.