CA1087529A

CA1087529A - Method of lubrication

Info

Publication number: CA1087529A
Application number: CA299,568A
Authority: CA
Inventors: Heinz Vetter
Original assignee: Roehm GmbH Darmstadt
Current assignee: Roehm GmbH Darmstadt
Priority date: 1977-03-24
Filing date: 1978-03-22
Publication date: 1980-10-14
Also published as: US4179529A; GB1586438A; IT7867677A0; NL7802714A; JPS53119976A; FR2384841A1; DE2712874A1

Abstract

ABSTRACT OF THE DISCLOSURE
A method of lubricating two surfaces, moving relatively to each other, which temporarily come into frictional contact, which comprises applying to at least one of the said surfaces a liquid lubricant thereby reducing frictional resistance between the said two surfaces upon contact, the said lubricant being capable of being hardened by the effect of heat, radiation or a catalyst; and subsequently hardening the said lubricant by the effect of heat, radiation or a catalyst after frictional contact between the said two surfaces has terminated.

Description

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The invention relates to a metT~od of shaping a length of extruded synthetic resim in which friction between the synthetic resin and the shaping means is reduced by the use of a lulbricant which can be su~sequently hardened.
In such shaping methodsJ friction arises between large surface area faces at low shearing speeds and high pressures, furthermore the lubricant is only in use for a short time9 since at the end of the shaping process the faces coated with the lubricant ~;
are separated from one another.
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High-viscosity oils and greases have hitherto been used as lubricants in the shaping of metal sheets or thermoplastic materials. After use, such lubricants generally have to be washed off the surface of the shaped parts7 e.g. by means of organic solvents. The use of organic solvents may present problems since they are expensive 9 often combustible or injurious to health and may require purification by distillation or by burning after use Water-soluble lubricants such as for example lubricating soaps or the high-viscosity aqueous ` `~

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polymer solutions described in German IDffenlegungsschrift 24 S9 306 have the advantage over oils and greases that they can be washed of with water. Although the problems associated with the ~se of organic solvents no longer arise~ the washing process and subsequent drying still involve considerable work and present problems of disposing of the waste water ~ `
It is an object o~ the present invention to provide a method of shaping a length of extruded synthetic resin wherein a lubricant which is employed to reduce frictional resistance between the synthetic resin and the shaping means can be subsequently dried thereby avoiding the need for an expensive washing process.
~ccording to th.e present invention we provide a : 15 method of shaping a length of extruded synthetic resin which comprises applying to the said length of synthetic resin a liquid lubricant which is capable of being hardened by the effect of hea~ radiation or a catalyst, bringing the said length of syntheti`c resin while in the thermoplastic or thermoelastic state into contact with the stationary shaping surface of ..
shaping means and subsequently hardening the said lubricant by the effect of hea~ radiation or a

-3-. i , ~ 3~ 5~9 cata~yst after shaping of the said length of synthetic resin.
The period during which the lubri.cant is employed in a liquid state may vary for example from a few seconds to a few minUteQ, or exceptionlally may extend to ~n hour or more. When its lubricat ng effect is no longer required and the : :

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faces to be lubrica-ted are separated from one another, the lubricant is not removed, as hitherto, in the liquid state, but is con-verted into a solid covering which is either left as it is, on the surface of the re.sin or removed by simple mechanical means. Washing and drying - processes can thus be obviatecl and the difficulties involved in removing the washing liquids no longer arise.
There are a large number of liquids which may be converted into the solid state by the effect of heat, catalysts or suitable radiation. Examples of liquids which are hardeneable by a thermal effect include liquid epoxy resins, alkyd resins or aminoplast resins (provided that they contain little or no non-hardenable solvents) -~
as well as gelling plastisols comprising a liquid softener and polymer particles, especlally PVC, dispersed therein.
Liquid resins containing radically polymerisable groups can be hardened by means of energy-rich radiation, examples of such resins including methacrylate syrups or unsaturated polyester resins in combination with styrene, unsaturated oil alkyds and acrylic or methacrylic acid esters of polyols. Together with thermal free radical-forming agents, these liquids resins can also be hardened solely by thermal action. The above-mentioned liquids have

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, hitherto been used exc].usively as casting resinsJ coating agents and impregnating agents, The desired lubricating efect in the method according to the invention can be produced ~ith vi.rt~ally any h~rdena-ble substance which is liquid at the tetnperature at which it is employed, In order to ensure that the lubricant ~ ~
film provides a sufficiently low frictional resistance, -~ :
it is essential to ensure that a minimum film thickness is maintained during use, This is particularly important :
when the film of lubricant has-to withstand high loads or is subjected to high pressures whereby the lubricating ~gent can be lost by leakage, In such cases .the stability of the lubricating fiIm is assisted by a high viscosity for the lubricant, the viscosi y o the lubricant preferably lying in the range from 1 to 500 ;.
' Pa,s, under the condi~ions of use, .;.
Conversion o the liquid lubricant into the solid form may be e~f.ected by heating to a temperature above thP temperat~re of application or by the effect of , ~ .
s~îtable radiation, If the conversion is effected by heat alone, the conversion temperature is preferably at least 20, advantageously at least 50 or more, above the :~
maximum temperature of application, Thermal con~ersion : ~.
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can be e~ected in any convenlent manner, for example by hot air or more preferably by heat radiation, If high temperatures are encountered during use of the .
` lubricant in ~he liquid state, it is preferred to effect hardening by suitable radiation, for example visible and ultra-violet light, electron-beam radiation, X-ray radiation or nuclear radiation. Because of the low industrial cost and the slight risks involved, ultra~
violet light or visible light are especially preferred . Hardening of the lubrlcant is primarily intended f~ 6~J ~
to make the ~surface coQted with the lubricant fLlm dry and clean for handling and to prevent the liquid `:
lubricant from being transferred to other objects.
To achieve this aim, it is sufficien~ to convert the lubricant into the gelled state In general, however, a .more advanced hardening is preferred up to the rubbery, ductile or even brittle state, A rubbery to ductile ~ ~`
state is of advantage when the hardened film of lubricant does not adhere firmly to the~surface and may be removed as a film leaving the original surface(s) in a .
clean and dry state, It may, however~ be desirable to leave the hardened film o lubricant as it . is on the surface as a protective covering or as a substrate for a further coat, ~. .

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In these cases, hardening to the cluctlle or brittle state is preferred The large number of known hardenable liquids enables lubricants for use ln the method according to the invention to be selected with any clesired visc05ity and any degree of hardenability Selection is, however, ~ ~
restricted in many cases by factors not directly ~ :
connected with the lubricating effect or hardenability ~
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~ Th~s, the lubricant ~h~ not have a corrosive e:Efect -~
on the materials with which it comes in contact Further~
more; in many cases it is necessary or desirabl~
that the lubricant should not be volatile, combustible .
or toxic or should not have an umpleasant odour , .; .
Finally, importance is attached to a low price for the agent, It is, o course, not always possible to meet c : all these requirements simultaneously.
In all cases the lubricant contains a hardenable constituent and a liquid constituentD These : constituents can be identicalD Examples of substances hardenable by heat alone include bisepoxides and lower ~ -polyepoxy compounds as well as aminoplast-and-phenoplast~
;~ precondensates, As long as these substances are Dot ' ~ ~
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themselvPs liquid at the temperature of application, they can be used in the form o solutions in or~anic solvents or so~teners. The proportion of these non-hardenable additives should be maintained at a level such that the lubricant can be hardened to at least a gel-like consistency which cannot separate into a liquid and a solid phase, Particularly preferred hardenable constituents :
for use in the lubricant include mono- or poly-ethylenically unsaturated compounds which are radically polymerisable into a solid body, Radical formation for hardening purposes can be initiated in various ways, `~
e.g, by the addition of polymerisation initiators which are decomposed at a temperature above the temperature of application to form radicals, such:.- as e g, organic :
peroxides, hydroperoxides or azo compounds. Examples of radical forming agents and the temperatures at which they may be used can be found -in the literature, for example, .
in Houben-Weyl, Methods of Organic Chemistry, Vol, lb~/l, ~ .
p 59, or in Brandrup-Immergut, Polymer Handbook (1966) 9 ~:
p, II/1-65, When the lubricant is used at elevated temperatures, e,g, 100 or more, no such radical f~rmers ~37~

are used, as a rule, but polymerisation may be inltiated by one of the above-mentioned types of radiation To facilitate polymerisation by visible or ultra-violet light9 the agents can contain suitable photosensitisers, such as e g benzoin or azo compounds The quantity of radical formers or sensitisers empIoyed ls generally suf- ~ :
~ic~ently great to efect hardening within a few minutes ~:
or seconds. .
Ex~mples of unsaturated, radically pol~mer-isable compounds suitable for use as lubricants in the ~ -method according to the invention include those vinyl : and vinylidene monomers which are conventionally employed :
in the preparation of solid ~.slymers ~t~which ~re not gaseous ~ ~
~ at room temperature Such monomers include methacrylic : ~ :
:~ 15 acid esters with 1 to 8 carbon atoms in the alcohol radical, styrene, vinyl esters of lower carboxylic - :~
acids (with 2 to 6 carbon atoms) or vinylidene chloride, Acrylic acid esters or other monomers which fonm soft ~: homopolymers can be used optionally in - admixture :~
with the above-mentioned monomers, provided that the re-sulting polymer forms a solid, no~-sticky covering, Uardenîng may be accelerated if at least a part of the ~;
radically hardenable compoullds contains two or more ' ', ~':

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~ S ~9 polymerisable double bonds Examples of swch compo~mds include glycol diacrylate or dimethacrylate or the diacrylates or dimethacrylates of higher glycols or condensation products with several hydroxyl groups, ~or example, ~herPaction product of bisphenol A with epichloro-hydrin. These diesters are especially suitable for photopolymerisation with visible or ultra-violet light in the presence o suitable photosensitisers As they are relatively expensive, however, the above-mentioned mono-unsaturated monomers are preferred . The radically polymerisable monomers can be used, if desired, in conjunction with limited quantities of ~ ~:
solvents or softeners These solvents or softeners must be selected so that they are oompatible and form a : -homogeneous phase with both the monomers or monomer mixture used and the polymer obtained therefrom Examples of such additives are aliphatic and aromatic -.
hydrocarbons, oils, chlorohydrooarbons, ketones, esters, : alcohols or water, Examples of softeners are diootyl phthalate, dibutyl phthalate or chloroparaffins, The pol~merisation products obtained ~rom the mixtures of monomers with solvents of softeners are obtained as non-sticky, partly brittle solid materials, "- - 10 - . , .~ . , . - ~ ~ .

generally with polymer contents of 50 to 90~.
The above-men~tioned hardenable compounds, optionally in admixkure with solvents or softener~ are in many cases too thinly li~uid for use as lubricants.
The viscosity of these compositions can however be increased to any value desired by the addition of dissolved macromolecùlar compounds. Such macromol~ecular .
compounds are generally substances which result in a homogeneous mixture with the liquid and/or hardenable constituent. ;~
If the lubricant is removed from the resin `
surface after hardening, polymer additives which may be used with particular advantage are cheap, easily pre- -~
pared polymers. It is especially advantageous to use as lubricants so~called polymer syrups which can be -obtained with any desired viscosity by partial poly~
merisation of a liquid monomer such as methyl methacry-late or styrene.
If the hardened lubricant i5 to be left on the resin surface as a permanent cover~ng or adhesive substrate radiation-hardenable or thermally hardenable covering agents known per se and of suitable viscosity ,. .
are ~;

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~7~29 advantageously used as the lubricant, It may be desirable also to use adhesion~enhancimg additives which may themselves be polymerisable, such as e g acrylic or methacrylic acid or dimethy:Laminoethyl acrylate or methacrylate. .
The lubricant . employed in the ~:
method according to the present invention can be applied in a wide temperature range ~epending on ~.
the composition selected, the lubricant may oomprise a liquid having a suitable viscosit~ even at tem- :
peratures well below 0C Since the film of lubricant ::
is under high pressure in many applications, the boiling ~ ~ :
point(s) ~at normal pressure) of the liquid constituent(s) of the lubricant does not generally limit the use . :~
15 of the lubricant in the method according to the invention, For example, a 2~/o methyl methacrylate syrup can be used at temperatures of 160 or more, ~ even th~ugh methyl methacrylate boils at 100C To : prevent spontaneous evaporation of the volatile 20 fractions before hardening, it is preferred to cool the ~ilm down to below the boiling tem~erature of the : ~ ;
: mixture shortly before separating the contacting f.aces :' ' ' ' ' ~:.
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~ ! ~IL O 87 5 Depending on the requirements of each particular case, the lubricant is generally employed in a film thickness ~`
of from O.Ol to lmm. The pressures applicable are not lim;ted by the nature of the agent.
During the shaping of synthetic resins in the thenmoplastic or thermoelastic stste, e.g. in the deep- -drawing,stretching or moulding of resins in the thermoelastic state or in the extrusion o resins in-the thermoplastic state the synthetic resin comes in to sliding contact with the fixed surfaces of the shaping tools. Even at `
low pressure damage to the surface may occur. At high .~ ~
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pressures, for exampIe, in ~he fonming of hollow ~ ;
strands7 such strong frictional forces can arise that the material moves jerkily or does not move at all in -the absence of a lubricant. In such cases the method according to the invention can be employed.
After separation of the contacting surfaces :~.

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a thread, tape or fabric can if desired, be embedded in the still liquid film of lubricant to facilitate removal o the film after hardening, For the same purpose a layer of paper or a foil can be laid on the film, so that after the film has hardened a protective adhesive coat is present which is optionally left as it is on the surace until further processing, The following Examples illustrate the present .~
invention, ~-Examples 1-6 In the production of a biaxially stretched tube of polymethyl methacrylate an extruded hollow extrudate with a circular cross-section, 40 mm external diameter and 9 mm wall thickness, is gradually expanded to an external diameter o~ 70 mm in the thermoelastic state .
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at 140C and with an internal pressurè of 3 bars, expansion being effected by passing the extrudate at a speed of 40 cm/min through a moulding channel having ~:
an internal diameter of 70 mm, The moulding rhannel ~ :
is heated to:140C in the first portion through which the extrudate passes and to 50 to 70C in the second portion, In the region where the extrudate enters ,. .
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the forming channel, the wall of the c~annel is provided with an annular groove encompassing the extrudate Through this groove, a fllm, approxim~tely 200 ~m thick, of the lubricants mentioned below is applied to the surface of the extrudate, After a residence time of about 1 minute, the stretched extrudate, cooled to.about 500C, emerges from the moulding channel at a speed of 50 cm/min, At the end of the moulding channel, the bulk of the fluid lubricant film is spread into a film of about .~:
15 ~ m thickness by means of an annular rubber rake . ~^
This film is hardened in an ultra-violet irradiation zone, 40 cm in length, by means of 8 ultra-violet lamps (Ultra-Vi~alux, Osram). Finally, the extrudate is passed . :
between a pair of traction rollers which effect longitudinal stretching in the moulding channel.
The following lubricants were used (all parts being parts by weightj:-'~

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~qsz~ -Exampl_ 1 parts of trimethylol-propane triacrylate 35 parts of a commercial unsaturated polyester resin ~ :
3 parts of a photoinitiator (benzoin isopropyl ether) Examp~le; 2 parts of a ~ommercial unsaturated polyester resin (ludopal P6 o~ BASF AG) - 50 parts of a 2-hydroxypropyl acrylate parts of a photoinitiator (benzoin isopropyl ether) Example 3 - -80 parts o~ Bisphenol A diacrylate 20 . parts of trimethylol-propane triacrylate 4 parts of a photoinitiator ~benzil dimethyl ketal) ~-~

Example 4 70 parts of ur.ethane acrylate parts of 1,6-hexanediol diacrylate parts of a photoinitiator (tric~loro-acetophenone) : ~ .

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lO0 p~rts of Bisphenol A -epichlorohydrin-epoxide resin (Epikote) 10 parts of dicyanodiamide, Hardening of the above mixtures takes place at about 150C so that ln these cases a relatively low ~ .
temperature is advantageous in the moulding channel, Example 6 ~ .
40 parts of pvc emulsion, I~-value 70 60 parts of dioctyl ph~halate : :~
The mixture hardens at 180C to a tough elastic coating, ~;, Example _?
~ ' In order to reduce the fri~ctional resistance between two aluminium shee~s, which slide against each other under a pressive of 200 N/cm and a speed of : . .
4 cm/cec, a liquid mix~ure of parts of methyl methacrylate parts of polymethyl methacrylate r - :~
~ 20 2 parts of dibenzoyl peroxide :~.

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' , '' ~ 75;29 which has a viscosity of 2500 mPa,s, at 20Cy is used, The mixture orms a film about 0,1 mm in thickness, The sliding movement is terminated afte}~ 20 seconds by separating the sheets, The sheets which are each covered with a film of the lubricant are heated to a surface temperature of 80 to 100C by means of infra-red radiation, the lubricant films hardening wi.thin a ew minutes. ~;

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of shaping a length of extruded synthetic resin which comprises applying to the said length of synthetic resin a liquid lubricant which is capable of being hardened by the effect of heat, radiation or a catalyst, bringing the said length of synthetic resin while in the thermoplastic or thermoelastic state into contact with the stationary shaping surface of shaping means, and subsequently hardening the said lubricant by the effect of heat, radiation or a catalyst after shaping of the said length of synthetic resin.

2. A method as claimed in claim 1 wherein the said lubricant is capable of being hardened by the effect of heat, the minimum temperature at which the said lubricant may be thus hardened being at least 20°C above the maximum temperature at which it is employed to reduce frictional resistance between the said surfaces.

3. A method as claimed in claim 2 wherein the said minimum temperature is at least 50°C above the maximum temperature at which the said lubricant is employed to reduce frictional resistance between he said surfaces.

4. A method as claimed in claim 1 wherein the said lubricant is capable of being hardened by the effect of radiation in the form of visible or ultra-violet light, electron-beam radiation, X ray radiation or nuclear radiation.

5. A method as claimed in claim 1 wherein the said lubricant comprises at least one ethylenically unsaturated, radically polymerisable monomer.

6. A method as claimed in claim 5 wherein the said lubricant contains a polymerisation initiator which is capable of forming free radicals under the effect of heat or radiation in the form of visible or ultra-violet light.

7. A method as claimed in claim 5 or claim 6 wherein the said ethylenically unsaturated monomer comprises a methacrylic acid ester with 1 to 8 carbon atoms in the alcohol radical, styrene, a vinyl ester of a lower carboxylic acid containing 2 to 6 carbon atoms, or vinylidene chloride.

8. A method as claimed in claim 5 or 6 wherein the said ethyl-enically unsaturated monomer comprises methyl methacrylate.

9. A method as claimed in claim 1 wherein the said lubricant contains a macromolecular compound in solution therein.

10. A method as claimed in claim 9 wherein the said macromolecular compound comprises polymethyl methacrylate.

11. A method as claimed in claim 1, 2 or 3 wherein the said lubri-cant contains a solvent or softener.

12. A method as claimed in claim 1, 2 or 3 wherein the said lubri-cant has a viscosity of 1 Pa. sec to 500 Pa.sec.

13. A method as claimed in claim 1 wherein the said shaping means comprises an apparatus for the deep-drawing stretching or moulding of a length of synthetic resin in the thermoelastic state, the synthetic resin being in the thermoelastic state while in contact with the shaping surface of the said shaping means.

14. A method as claimed in claim 1 wherein the said shaping means comprises an apparatus for the extrusion of a length of synthetic resin being in the thermoplastic state while in contact with the shaping surface of the said shaping means.