GB1581686A

GB1581686A - Process for the manufacture of thermoplastic sheets having a uniformly dull surface

Info

Publication number: GB1581686A
Application number: GB27964/77A
Authority: GB
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1976-07-02
Filing date: 1977-07-04
Publication date: 1980-12-17
Also published as: ATA470877A; NL7707093A; FR2356496A1; JPS535257A; DE2629742A1; SE7707507L; ES460076A1; BE856462A; AT355292B; IT1080775B

Description

(54) PROCESS FOR THE MANUFACTURE OF THERMOSPLASTIC SHEETS HAVING A UNIFORMLY DULL SURFACE (71) We, HOECHST AKTIENGESELLSCHAFT, a body corporate organised according to the laws of the Federal Republic of Germany, of 6230 Frankfurt/Main 80, Postfach 80 03 20, Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:: The present invention relates to a process for the manufacture of thermoplastics sheets having a dull surface, which comprises calendering a plastics material, optionally preplastified, in order to form a sheet, on a calender having at least two rollers in such a manner that a kneading mass is accumulated before each gap between rollers, that the rollers are heated at a temperature within the thermoplastic temperature range of the plastics material, and that the circumferential speeds of the last two rollers are different.

It is known that thermoplastics sheets having a dull (rough) surface on either or both sides may be manufactured in a calendering process wherein the last and/ or penultimate roller has a dull polished or sandblasted surface whereby the sheet takes on the structure of the surface of the roller, so that is shows a uniformly dull surface either on one side only (last roll is sandblasted) or on both sides (the last two rolls are sandblasted). The dull aspect of the surface of the sheet is due to its rough surface structure, so that it can alternatively be referred to as being uniformly rough. Such sheets may be obtained also by pressing the sheet leaving the calender onto a metal plate or between two metal plates, or by passing it over a stamping roll system series-connected to the calender at temperatures of the rolls of 150 to 2200C (see G.Dost, Plast-Verarbeiter 1962, pp. 268-274, especially p. 273, center of left column).

However, these operation modes having the disadvantage of requiring expensive apparatus which generally are not available in a calender plant designed mainly for the manufacture of transparent sheets.

It is also known that, when calendering thermoplastics sheets with accumulation of a kneading mass before the individual gaps between the rollers, each of the subsequent rollers (in the direction along which the sheet travels) is driven at high circumferential speed than the preceding one. The use of different circumferential speeds for adjacent rollers forces the plastified plastic material to follow the desired path through the calender, because the sheet formed in the gap between rollers adheres to that roll which has the higher circumferential speed (see the above paper, p. 271, left and right column, first paragraph).

A friction value (circumferential speed ratio) of a pair of rollers of more than 1 means that, as seen in the direction of operations, the subsequent roller has a higher circumferential speed than the preceding one, and a friction value of less than 1 means that the subsequent roller has a lower circumferential speed than the preceding one. It is known to the expert in calendering that a friction value of 1.2 for the last pair of calender rollers adversely affect the surface of the sheet: when it is withdrawn from the last roller, it possesses an inhomogeneous surface with strains or streaks. For this reason, the expert does not calender using high friction values and sets the friction of the last pair of rollers generally to about 1.1.

Surprisingly, it has now been found that, at friction values of the last two calender rollers in a range of from 1.3 to 20 or of from 0.77 to 0.05 and withdrawing the sheet from the roller having the higher circumferential speed, sheets having a uniformly dull (rough) surface on one side are obtained, which surface is suitable for writing upon. This dull surface is on the side of the sheet remote from the roller from which the sheet is withdrawn i.e. the side contacting the roller having the lower circumferential speed.

The present invention provides a process for the manufacture of thermoplastic sheets having a uniformly dull surface by calendering thermoplastics material on a calender having at least two rollers which are at a temperature within the thermoplastic temperature range of the plastics material in such a manner that a kneading mass is accumulated before each gap between the rollers, and the ratio bf circumferential speed of the last two rollers is in the range of from 1.3 to 20 or of from 0.77 to 0.05, and drawing off the sheet from that roller which has the greater circumferential speed.

It was not to be expected that sheets having a uniformly well dulled surface could be manufactured in this manner, and there is no precise explanation as yet for this phemomenon.

It is conjectured that this surprising effect is due to the sheet (melt) being subjected to a uniform roughening of the surface by being detatched by a sudden tearing action from the surface of the roller which has the lower circumferential speed.

An especially advantageous ratio or the circumferential speed of the last two calender rollers is in the range of from 1.6 to 10 or of from 0.63 to 0.1.

In the case in which the last roller turns at a higher circumferential speed (friction value greater than 1), the sheet is withdrawn therefrom in known manner. When it is the penultimate roller which turns at the higher speed, the sheet must be drawn off from this roller (in analogous manner as in the case of the last roll). Drawing off of a calendered sheet from the last or penultimate roller is usually carried out by means of one or more, preferably 2 or 3, driven rollers (draw-off rollers) which should preferably be positioned as near as possible to that calender roller from which the sheet is off. The sheet is preferably passed over the draw-off rolls in a semi-circular arc of contact.The circumferential speed of the draw-off rollers may be the same as or slightly higher than that of the roller from which the sheet is withdrawn but this is not critical for the process of the invention. The sheet may subsequently be transferred to a wind-up device of known design.

If it is desired that both the surfaces of a sheet be dull (rough), the roller (of the last two rollers) which has the higher circumferential speed may have a roughened surface instead of a smooth (polished) one.

Calendering of the plastics material which is advantageously preplastified in an extruder, a Buss kneader or mixing rolls, and transferred in known manner to the gap between the first two calender rollers, is preferably carried out on calenders having from 2 to 6 rollers mounted in an F, I, L, S or Z arrangement in a manner usual for thermoplastics processing, that is, with accumulation of a kneading mass of excess thermoplastics material before the individual gaps between rollers of the calender (see the above paper p. 269). As is known, the temperature of the individual rollers depends on the plastics material used, but it should be in the thermoplastic temperature range of the particular plastics material used, and will generally lie in the range of from 160 to 2500C.However, in order to minimise the thermal strain necessarily put on the material during the calendering, it is recommended to keep the temperature below 250"C by from 20 to 30"C. However, in order to minimise the thermal strain necessarily put on the material during the calendering, it is recommended to keep the temperature below 250"C by from 20 to 30"C. In the case of plastics derived from vinyl chloride, the temperature of the individual rollers is advantageously in the range of from 170 to 2200C, preferably of from 185 to 2100C. In the case in which the calender comprises from 3 to 5 calender rollers the preferred temperature range is from 180 to 210 C.

The rollers preceding the last pair of rollers may turn at the same speed, that is to say, at a friction value of 1 in which case the path which the sheet follows is determined by the temperature of the various rollers or, preferably, at a friction of about 1.1. The thickness of the sheets manufactured according to the process of the invention ranges generally from 30 to 500 im.

Suitable thermoplastics for the process of the invention are in principle all those materials which may be calendered with accumulation of a kneading mass, for example olefin polymers such as polyethylene or polypropylene; styrene polymers; polymers of acrylonitrile/butadiene/ styrene (ABS), methylmethacrylate/butadiene/styrene (MBS), methylmethacrylate/acrylonitrile/ butadiene/styrene (MABS); polymers of acrylic or methacrylic acid esters such as polybutylacrylate or polymethylmethacrylate. Polymers derived from vinyl chloride, that is, vinyl chloride homo- or copolymers or graft copolymers of vinyl chloride and copolymerizable monomers having at least 50% by weight, relative to the polymer, preferably from 95 to 80% by weight of polymerized vinyl chloride are particularly suitable. Suitable comonomers are for example olefins and diolefins, such as ethylene, propylene, butadiene; vinyl esters of straight-chain or branched carboxylic acids having 2 to 20, preferably from 2 to 4 carbon atoms, such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl stearate; vinyl or vinylidene halides, such as vinyl fluoride, vinylidene fluoride, vinylidene chloride; vinyl ethers; unsaturated acids, such as maleic, fumaric, acrylic and methacrylic acid, and the mono-or di-esters thereof with mono- or dialcohols having from 1 to 10 carbon atoms; acrylonitrile, styrene or cyclohexyl maleimide. Especially advantage ous are those polymers derivable from vinyl chloride which are prepared by polymerization in emulsion at low emulsifier content, in suspension or in bulk and which have a K value according to Finkentscher or from 50 to 80, preferably of from 55 to 70.

Alternatively, mixtures of the cited thermoplastics polymers may be used. Preferred are mixtures of vinyl chloride homo-, co- or graft polymers with so-called resilient resins such as the above ABS, MBS and MABS polymers, or chlorinated polyethylene and, optionally, with so-called processing aids, for example low molecular weight polymethylmethacrylate; the amount of resilient resins and processing aids being preferably from 1 to 15% by weight, relative to the vinyl chloride polymer.

Advantageously, processing additives such as heat and light stabilizers, lubricants, and optionally further special additives such as dyestuffs, pigments, optical brighteners and antistatics are added to the thermoplastic materials. Preferably, polymers having no plastifier are used; however, the process may also be carried out in the presence of usual amounts of plastifiers.

Suitable heat stabilizers include, for example mono- and dialkyl-tin compounds, the alkyl groups having from 1 to 10 carbon atoms and the remaining valencies of the tin being linked via oxygen and/or sulphur atoms to further substitutents; amino-crotonic acid esters; urea and thiourea derivatives; -phenylindole; salts of alkaline earth metals and of zinc or cadmium with aliphatic carboxylic acids or hydroxycarboxylic acids. Organo-tin/sulphur stabilizers such as dimethyl-tin-bis -(2-ethylhexylthioglycolate), di-n-butyl-tin-bis (2-ethylhexylthioglycolate), di-n-octyl-tin-bis -(2-ethylhexylthioglycolate) are preferably employed.The stabilizers may be used in quantities of from 0.2 to 5 % by weight calculated on the total mixture; it is also possible to use them in admixture with one another and with usual co-stabilizers and antioxidants.

Lubricants may also be used, preferably in quantities of from 0.1 to 4% by weight, calculated on the total mixture, such as one or more higher aliphatic carboxylic acids and hydroxycarboxylic acids as well as the esters and amides thereof, such as stearic acid, montanic acid, bis-stearoylethylenediamine or bis-palmitoyl-ethylenediamine, montanic acids esters of ethanediol or 1, 3-butanediol, optionally partially saponified; fatty alcohols having more than 10 carbon atoms as well as the ethers thereof, lower molecular weight polyolefins and hard paraffins.

The thermoplastics materials may contain plasticizers in quantities of from 10 to 40% by weight, calculated on the total mxiture, for example, one or more esters of aromatic or aliphatic di- and tricarboxylic acids, of higher alkyl-sulphonic acids and of phosphoric acid, such as di-2-ethylhexylphthalate, adipate, or sebacate; alkylsulphonic acid esters of phenol or cresol; tricresyl phosphate or epoxidized soya beam oil or caster oil.

The mixtures plastics compositions) made of thermoplastic polymers (in powdered form), processing aids and optionally further additives may be prepared by thorough mixing of the components, for example in one of the high speed mixers usual in plastics processing.

The process of the invention provides a technologically very simple and advantageous method for the manufacture of sheets having a uniformly rough surface on one side or on both sides for it can be provided on a calender now used for the manufacture of transparent hard and soft sheets without additional devices. Furthermore, it is substantially independent of the formulation of the plastics composition to be processed, and therefore extremely versatile.

The process of the invention is also advantageous in that not only the dull (rough) surface of the sheet so obtained is uniformly homogeneous, but also that its structure is maintained nearly entirely and not adversely affected by the further processing of the sheet, for example by deep-drawing or tempering.

The sheets obtained according to the process of the invention may be easily written upon for example by pencil, ink or other writing means, so that they may be used as writing sheets.

They may be employed furthermore as sheets for use in furnishings, ceilings or document folders.

Processes according to the invention will now be described by way of example Example 1: In a high-speed mixer, the following components are mixed: 98.0% by weight of bulk PVC having a K value of 60, 1.5% by weight of di-n-octyl-tin-bis -(2-ethylhexylthioglycolate) 0.5% by weight of wax OP (montanic acid ester of butanediol, partially saponified).

The mixture is preplastified on an extruder at 1600C and calendered on a three-roll calender with accumulation of a kneading mass before each gap; the individual rolls being at a temperature of 200"C. The friction of the last pair of rollers is adjusted to 2.5, the circumferential speed of the first roller is somewhat below that of the central roller. The sheet withdrawn from the last roller has a thickness of 150 m, and the surface of the sheet which is not in contact with the last calender roller is uniformly rough. The mean mean peak-to-valley height Rz according to German Industrial Standard DIN 4768 is 6.0 Zm, the standard deviation 1.5 gm.

Example 2: The following components are mixed in a high-speed mixer: 87.5% by weight of suspension PVC having a K value of 60 1.5% by weight of di-n-octyl-tin-bis -(2-ethylhexylthioglycolate) 0.7% by weight of wax E (montanic acid ester of butanediol) 10.0% by weight of a usual ABS resin for modifying the impact strength.

The mixture is gelled on a mixing roller at 1300C, and the gelled product is forwarded to the first gap of a four-roller S calender, on which it is calendered. In forwarding direction of the sheet, the rollers are at 195, 205, 200 and 1900C. The friction of the last pair of rollers is 1.4 and that of the first two pairs of rollers 1.1. The sheet withdrawn from the last calender roller has a thickness of 200 itm, and that surface of the sheet which is not in contact with this roller is uniformly rough. The peak-to-valley height Rz is 15.2 m at a standard deviation of 3.5,my.

Example 3: A plastics composition of 97.5% by weight of a usual ABS polymer and 2.5% by weight of titanium dioxide in the form of granules is plastified on an extruder at 1800C and then forwarded to the first gap of a three-roller calender the rollers of which are each at 1900C. The friction of the last pair of calender rollers is 1.8. The sheet withdrawn from the last calender roller has a thickness of 250 m and its surface not being in contact with this roller is uniformly dull. The mean peak-to-valley height Rz is 1.05 ,am at a standard deviation of 2 ,um.

Example 4: The mixture of Example 2 is used. Under the conditions of Example 2, it is gelled and calendered; however, the speed ratio of the last pair of rollers is 0.6 and the sheet is withdrawn from the penultimate roll. This sheet, after withdrawal, has a thickness of 200,u m too, and the surface not being in contact with the penultimate roller is uniformly rough.

WHAT WE CLAIM IS: 1. A process for the manufacture of a thermoplastics sheet having a dull surface by calendering thermoplastics material on a calender having at least two rollers at a temperature within the thermoplastic temperature range of the thermoplastics material in such a manner that a kneading mass is accumulated before each gap between adjacent rollers, and that the ratio of the circumferential speeds of the last two rollers is in the range of from 1.3 to 20 or of from 0.77 to 0.05, and drawing the sheet off from that roller of the last two rollers which has the higher speed.

2. The process as claimed in claim 1, wherein the circumferential speed ratio is in the range of from 1.6 to 10 or of from 0.63 to 0.1.

3. A process as claimed in claim 1 or claim 2, wherein the thermoplastics material is pre-plastified before it is calendered.

4. A process as claimed in any one of claims 1 to 3, wherein the calender has from 2 to 6 calender rollers.

5. A process as claimed in claim 4, wherein the calender has from 3 to 5 calender rollers.

6. A process as claimed in claim 4 or claim 5, wherein the calender rollers are arranged in a F, I, L, S or Z configuration.

7. A process as claimed in any one of claims 1 to 6, wherein the last calender roller has a greater circumferential speed than the penultimate calender roller.

8. A process as claimed in any one of claims 1 to 6, wherein the penultimate roller has a greater circumferential speed than the last roller.

9. A process as claimed in any one of claims 1 to 8, wherein the roller (of the last two rollers) which has the greater circumferential speed has a roughened surface.

10. A process as claimed in any one of claims 1 to 9, wherein the temperature of the individual rollers is the same or different and lies in the range of from 1600C to 2500C.

11. A process as claimed in claim 10, wherein said temperature is in the range of from 185"C to 210 C.

12. A process as claimed in any one of claims 1 to 11, wherein the gap between the last two rollers is such that a sheet of a thickness in the range of from 30 to 500,am is produced.

13. A process as claimed in any one of claims 1 to 12, wherein the sheet is drawn off the faster of the last two rollers by 2 or 3 draw-off rollers situated close to the saie faster roller.

14. A process as claimed in any one of claims 1 to 13, wherein the thermoplastics material comprises a polymer derivable from vinyl chloride and containing at least 50% by weight, based on the polymer, of vinyl chloride units.

15. A process as claimed in claim 14, wherein the polymer comprises a graft polymer or a copolymer containing from 80% to 95 % by weight, based on the polymer, of vinyl chloride units.

16. A process as claimed in claim 14, wherein the polymer comprises a vinyl chloride ous are those polymers derivable from vinyl chloride which are prepared by polymerization in emulsion at low emulsifier content, in suspension or in bulk and which have a K value according to Finkentscher or from 50 to 80, preferably of from 55 to 70.

Suitable heat stabilizers include, for example mono- and dialkyl-tin compounds, the alkyl groups having from 1 to 10 carbon atoms and the remaining valencies of the tin being linked via oxygen and/or sulphur atoms to further substitutents; amino-crotonic acid esters; urea and thiourea derivatives; -phenylindole; salts of alkaline earth metals and of zinc or cadmium with aliphatic carboxylic acids or hydroxycarboxylic acids. Organo-tin/sulphur stabilizers such as dimethyl-tin-bis -(2-ethylhexylthioglycolate), di-n-butyl-tin-bis -(2-ethylhexylthioglycolate), di-n-octyl-tin-bis -(2-ethylhexylthioglycolate) are preferably employed.The stabilizers may be used in quantities of from 0.2 to 5%by weight calculated on the total mixture; it is also possible to use them in admixture with one another and with usual co-stabilizers and antioxidants.

The thermoplastics materials may contain plasticizers in quantities of from 10 to 40% by weight calculated on the total mxiture, for example, one or more esters of aromatic or aliphatic di- and tricarboxylic acids, of higher alkyl-sulphonic acids and of phosphoric acid, such as di-2-ethylhexylphthalate, adipate, or sebacate; alkylsulphonic acid esters of phenol or cresol; tricresyl phosphate or epoxidized soya beam oil or caster oil.

The mixtures (plastics compositions) made of thermoplastic polymers (in powdered form), processing aids and optionally further additives may be prepared by thorough mixing of the components, for example in one of the high speed mixers usual in plastics processing.

The mixture is preplastified on an extruder at 1600C and calendered on a three-roll calender with accumulation of a kneading mass before each gap; the individual rolls being at a temperature of 200"C. The friction of the last pair of rollers is adjusted to 2.5, the circumferential speed of the first roller is somewhat below that of the central roller. The sheet withdrawn from the last roller has a thickness of 150 m, and the surface of the sheet which is not in contact with the last calender roller is uniformly rough. The mean mean peak-to-valley height Rz according to German Industrial Standard DIN 4768 is 6.0 clam, the standard deviation 1.5 1lem.

The mixture is gelled on a mixing roller at 1300C, and the gelled product is forwarded to the first gap of a four-roller S calender, on which it is calendered. In forwarding direction of the sheet, the rollers are at 195, 205, 200 and 1900C. The friction of the last pair of rollers is 1.4 and that of the first two pairs of rollers 1.1. The sheet withdrawn from the last calender roller has a thickness of 200,am, and that surface of the sheet which is not in contact with this roller is uniformly rough. The peak-to-valley height Rz is 15.2 m at a standard deviation of 3.5 m.

Example 3: A plastics composition of 97.5% by weight of a usual ABS polymer and 2.5% by weight of titanium dioxide in the form of granules is plastified on an extruder at 1800C and then forwarded to the first gap of a three-roller calender the rollers of which are each at 1900C. The friction of the last pair of calender rollers is 1.8. The sheet withdrawn from the last calender roller has a thickness of 250 calm and its surface not being in contact with this roller is uniformly dull. The mean peak-to-valley height Rz is 1.05 ,um at a standard deviation of 2 ,um.

Example 4: The mixture of Example 2 is used. Under the conditions of Example 2, it is gelled and calendered; however, the speed ratio of the last pair of rollers is 0.6 and the sheet is withdrawn from the penultimate roll. This sheet, after withdrawal, has a thickness of 200,mm too, and the surface not being in contact with the penultimate roller is uniformly rough.

10. A process as claimed in any one of claims 1 to 9, wherein the temperature of the individual rollers is the same or different and lies in the range of from 1600C to 250"C.

12. A process as claimed in any one of claims 1 to 11, wherein the gap between the last two rollers is such that a sheet of a thickness in the range of from 30 to 500,u m is produced.

16. A process as claimed in claim 14. wherein the polymer comprises a vinyl chloride

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. deviation 1.5 1lem. Example 2: The following components are mixed in a high-speed mixer: 87.5% by weight of suspension PVC having a K value of 60 1.5% by weight of di-n-octyl-tin-bis -(2-ethylhexylthioglycolate) 0.7% by weight of wax E (montanic acid ester of butanediol) 10.0% by weight of a usual ABS resin for modifying the impact strength. The mixture is gelled on a mixing roller at 1300C, and the gelled product is forwarded to the first gap of a four-roller S calender, on which it is calendered. In forwarding direction of the sheet, the rollers are at 195, 205, 200 and 1900C. The friction of the last pair of rollers is 1.4 and that of the first two pairs of rollers 1.1. The sheet withdrawn from the last calender roller has a thickness of 200,am, and that surface of the sheet which is not in contact with this roller is uniformly rough. The peak-to-valley height Rz is 15.2 m at a standard deviation of 3.5 m. Example 3: A plastics composition of 97.5% by weight of a usual ABS polymer and 2.5% by weight of titanium dioxide in the form of granules is plastified on an extruder at 1800C and then forwarded to the first gap of a three-roller calender the rollers of which are each at 1900C. The friction of the last pair of calender rollers is 1.8. The sheet withdrawn from the last calender roller has a thickness of 250 calm and its surface not being in contact with this roller is uniformly dull. The mean peak-to-valley height Rz is 1.05 ,um at a standard deviation of 2 ,um. Example 4: The mixture of Example 2 is used. Under the conditions of Example 2, it is gelled and calendered; however, the speed ratio of the last pair of rollers is 0.6 and the sheet is withdrawn from the penultimate roll. This sheet, after withdrawal, has a thickness of 200,mm too, and the surface not being in contact with the penultimate roller is uniformly rough. WHAT WE CLAIM IS:

1. A process for the manufacture of a thermoplastics sheet having a dull surface by calendering thermoplastics material on a calender having at least two rollers at a temperature within the thermoplastic temperature range of the thermoplastics material in such a manner that a kneading mass is accumulated before each gap between adjacent rollers, and that the ratio of the circumferential speeds of the last two rollers is in the range of from 1.3 to 20 or of from 0.77 to 0.05, and drawing the sheet off from that roller of the last two rollers which has the higher speed.

homopolymer.

17. A process as claimed in any one of claims 1 to 13, wherein the polymer comprises a mixture of thermoplastics materials.

18. A process as claimed in claim 17, wherein the polymer comprises a mixture of a vinyl chloride homo-, co-, or graft polymer and a resilient resin.

19. A process as claimed in claim 18, wherein the mixture includes from 1 to 15% of the resilient resin.

20. A process as claimed in any one of claims 1 to 19, wherein the thermoplastics material is any one of those specifically mentioned herein.

21. A process as claimed in any one of claims 14 to 16, 18 and 19, wherein the vinyl chloride polymer has a K value (according to Fickentscher) in the range of from 50 to 80.

22. A process as claimed in claim 21, wherein said K value lies in the range of from 55 to 70.

23. A process as claimed in any one of claims 1 to 22, wherein the thermoplastics material includes 0.2 to 5% of stabilizer based on the weight of the total mixture.

24. A process as claimed in any one of claims 1 to 23, wherein the thermoplastics material includes 0.1 to 4% of lubricant based on the weight of the total mixture.

25. A process as claimed in any one of claims 1 to 24, wherein the thermoplastics material includes from 10 to 40% of plasticizer based on the weight of the total mixture.

26. A process as claimed in any one of claimsl to 25, wherein the thermoplastics material contains no plastifier.

27. A process substantially as hereinbefore described in any one of Examples 1 to 4.

28. A thermoplastics sheet whenever obtained by a process as claimed in any one of claims 1 to 27.

29. A writing surface whenever made from a sheet as claimed in claim 28.

30. Thermoplastics sheet for use in furnishings, ceilings, tiles, or document folders whenever made by a process as claimed in any one of claims 1 to 27.