CA1076991A - Process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A process for making a silane-grafted thermoplastic copolymer by treating a thin solid thermoplastic shaped poly-meric article which contains a radiation sensitizer and a silane with electromagnetic radiation of wavelength in the range from 180 to 800 nanometres.

Description

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- 2 -This invention relates tv the graft copolymerisation of thermoplastics with silane.
In the past polyolefines have been grafted with ole-finically unsaturated silanes to give a graft copolyr.ler capable of being extruded and shaped using normal plastics processing apparatus but which by suitable treatment may be subsequently crosslinked to give a rigid polymer oE high softening point.
The polyolefines have hitherto been grafted by re-action of molten polyolefine or polyolefine in solution withthe ol0finically unsaturated silane in the presence of peroxides. This known process has the grave disadvantage that the polyolefine must be molten or in solution in suit-able solvent such as xylene during the reaction and hence the resultant grafted copolymer must be subsequently converted to granules at extra cost or be used immediately in a forming operation. We have now found a process whereby granules or o~her shaped articles of polyolefines may be grafted with silane in the solid phase ko give a graft copolymer.
Accordingly we provide a process of manufacturing a silane-grafted thermoplastic copolymer which process com-prises treating in the solid form a thermoplastic shaped polymeric article having a thickness up to 5 millimetres and containing a radiation sensitizer as hereinafter defined and a mono-olefinically unsaturated silane said silane con-I~ .

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`-` 10'7~991 taining at least two hydrolyzable organic radicals with an amount of electromagnetic radiation of wavelength in the range of 180 to 800 nanometres (nm) sufficient to form the said graft copolymer.
In a preferred embodiment of this invention the said thermoplastic shaped article is in particulate form.
In a further preferred embodiment of this invention the said article is in a sheet-like form.
The nature of the polymer from which the thermoplastic shaped article is derived is not narrowly critical. Satis-factory results have been obtained with both high and low density polyethylene, and polypropylene. Polybutene-l, poly(4-methylpentene-l), chlorinated polyethylene~ and chloro-sulphonated polyethylene may be used. Blends of different polyolefines may also be used.
The article may also be prepared from copolymers.
Typical examples of such copolymers include those derived from ethylene and monomers such as vinyl acetate~ ethyl acrylate, ethyl methacrylate, or acrylic acid partially or completely neutralized.
The process of our invention may also be used for other polymers such as for example nylon, polyethylene tere-phthalate and polyvinyl chloride.
The silane is selected from the group having the general formula . ." : ' ~. - ' ":
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R SiY
n (4-n) wherein each R which may be the same or different is selected from the group comprising monovalent olefinically-unsaturated hydrocarbyl, alkoxyalkyl~ acyloxyalkyl, and acyloxyalkoxyalkyl, each Y which may be the same or di.fferent is hydrolyzable organic radical, and n is 1 or 2.
. Examples of R are vinyl, allyl, butenyl, cyclohexenyl, cyclopentadienyl, cyclohexadienyl, (CH2=C~CH3)COOtCH2)3-, CH2=C(CH3)COOCH2CH2CH20(CH2)3- and : OH
~H2=C(CH3)COOCH2CH20CH2CHCH20(CH2)3-, the vinyl radical being preferred. The Y substituents are selected from alkoxy or alkoxyalkoxy radicals having less than 6 carbon atoms for ex-ample the methoxy, ethoxy and butoxy radicals, acyloxy radicals having less than 6 carbon atoms for example the formyloxy, acetoxy and propionoxy radicals, and oximo radicals having less . lS than 14 carbon atoms for example -ON=C(CH3)2, -ON=C(CH3)C2H5 and -ON=C(C6H5)2.
Preferably the silane will have the formula RSiY3 and contain three hydrolyzable organic radicals, the most preferred silanes being vinyltriethoxysilane and vinyltrimethoxysilane.

Silanes having only two hydrolyzable groups for example vinyl-~-`'' ' .
methyldiethoxysilane and vinylphenyldimethoxysilane, are however also operative.

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_ 5 _ , The amount of the silane used is not narrowly critical.
Obviously the higher the amounts of silane the greater will be the amount of grafting. However, amounts of silane in the range from 0.1 to ?Q% w/w of the thermoplastic article~
preferably from 0.5 to 5% w/w give commercially effective graft copolymers.
The proportion of silane employed will depend in part upon the reaction conditions and in part on the degree of modi*ication required.
By radiation sensitizer is meant a compound capable of absorbing the electromagnetic radiation and promoting the reaction of the silane with the said thermoplastic article.
Suitable radiation sensitizers for electromagnetic radiation of any given wavelength are known to those skilled in the art.
Thus for example it is well known to those skilled in the art that ketones such as for example acetone are suitable sensi-- tizers for electromagnetic radiation of waveLength in the region from 200 to 300 nm, and that certain natural products such as for example riboflavin are suitable radiation sensitizers . 20 for sunlight. Aromatic ketones such as benzophenone and aceto-phenone are active for radiation with wavelength from 200 to 360 nm.
Sensitizers normally used by those skilled in the art - include azo-bis-isobutyronitrile~ peroxides such as di-cumyl peroxide, di-tert-butyl peroxide, benzil, and benzoin and .

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benzoin derivatives such as benzoin methyl ether, allyl benzoin methyl ether, benzoin isopropyl ether and methyl benzoin methyl ether. Benzil, benzoin and benzoin derivatives are actlve sensitizers for radiation of wavelength from 300 to 400 nm.
A suitable sensitizer for any particular wavelength of electromagnetic radiation may be found by simple experi-mentation.
The sensitizer may be added to the thermoplastic article by any suitable method known to those skilled in the art for the incorporation of additives into thermoplastic articles.
Suitable methods include melt mixing or compounding. Altern~-tively in certain cases the sensitizer has a sufficiently high vapour pressure for the sensitizer to permeate into a solid thermoplastic article merely by keeping the solid thermoplastic article in the presence of the vapour of the sensitizer.
The sensitizer may also be incorporated into the thermo-plastic article by soaking the article in a liquid sensitizer or in a solution of the sensitizer in a solvent. Preferably the solvent is able to swell the thermoplastic article and thus facilitate the penetration of the sensitizer.
The anlOUnt of the sensitizer and the d~ration and intensity of exposure to the electromagnetic radiation are preferably such that crosslinking of the polymer of the said ` 25 article is minimized during the process of the invention. When :
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benzophenone an~ acetophenone are used as sensitizers in the graft polymcrization of thermoplastic articles derived from polyolefines~ amounts of the said sensitizers in the range from 0.01 to 10% w/w of the polyolefine preferably 0.05 to 1% w/w of the polyolefine and using low powered (15 to 30 watts) lamps with radiation in the range from 200 to 400 nm, particularly 254 nm, for from 5 minutes to 10 hours give good yields of graft copolymer. With higher powered (2000 to 3000 watts) lamps the irradiati~n time is reduced and irradiation times from 15 to 60 seconds give excellent yields.
~ lthough the thermoplastic may be irradiated prior to addition of the silane we prefer that the thermoplastic is irradiated in the presence of both sensitizer and silane.
The process of the invention may be used at all temperatures up to the melting point of the polymeric component of the said thermoplastic article. Preferably the temperature is between 0C and a temperature about 20C below that of the softening point of the said thermoplastic article.
The thermoplastic articles may optionally be subjected to successive treatments with radiation by the process of this invention to produce high levels of grafting.
The resultant graft copolymers of this invention are not crosslinked and can be moulded and caused to flow in a manner acceptable for processing with conventional moulding .5 and extrusion equipment. When the graft copolymer is exposed -,,' . ' : ~ ' ' :
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._ to water, most usually in the presence of a condensation catalyst such as dibutyltin dilaurate, then the graft co~
polymer may be converted to a crosslinked form. Suitable methods of inducing crosslinking and of working silane poly-olefine graft copolymers are known to those skilled in theart.
The polymeric materials from which the thermoplastic shaped articles of this invention are derived include not only polymeric materials in their natural state but also include polymeric compositions comprising one or more con- , ventional additives such as for example stabilizers, fillers, lubricants~ slip additives, antioxidants, antistats and the like. Since the process o f this invention is conveniently performed at temperatures below the temperatures normally used in conventional plastics compounding processes, it is parti- -cularly suited for plastics compositions containing materials whicll are prone to degrade in conventional processes. Other additives which could prevent transmission of the electro-magnetic radiation may be incorporated into the grafted product made by the process of the invention before any crosslinking step is performed. Such additional additives include dyes, pigments, mineral fillers, non-conductive carbon black and conductive carbon black.

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_ 9 _ The invention will now be illustrated by, but by no means limited to~ the following examples. All per-centages are on a weight basis.
Example 1 Low density polyethylene was melt mixed with a solu-tion of benzophenone in vinyltriethoxysilane and extruded to give cylindrical granules of diamcter 4 mm and 2-3 mm thick.
The granules were then irradiat~d under a 15 watt germicidal lamp emitting a major proportion of light at 254 nm.
The proportion of reagents and results are shown in Table 1.
; TABLE 1 . . _ _ _ .
Rxperi- % ~ ation Gel content (~) ment benzo- silane time ,_ No phenone ~hrJ After After , _ irrad3ation crosslinking 1 0.025 2 1 0 2 2 0.1 2 1 1 29

3 0.1 2 2 2 42 0.1 3 1 0 39 0.25 2 1 8 _ 30 The gel content is the insoluble content after 16 hours ex-tracting with boiling xylene.
The gel content after irradiation is a measure of the ;~.~ . .
amount of crosslinking occurring during irradiation.

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Thc gel content after crosslinking the graft copolymer with water in the presence of dibutyltin dilaurate is a measure of the grafting efficiency.
Example 2 Mixtures of melt mixed low density polyet.hylene prepared by the method of Example 1 were pressed into a film.
The film was irradiated as in Example 1. The results are shown in Table 2.

. ~ _ _ Film Irradi- Gel content (%) Experi- % % thick- ation _ ment benzo- silane ness time irradi- cArOters_ ation linkin~
l 0.025 2 500 1 0 2 2 0.1 2 125 1 5 39 3 0.1 2 500 1 2 42

4 0.1 .2 500 2 5 48 0.1 3 500 1 1 so 6 0.25 2 500 l6 44 ExamPles .s to 36 inclusive For these examples a Philips TUV 30 watt lamp was used except where indicated.
Examples ~I to 8 inclusive These examples illustrate the effect of variation in ..
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irradiation time on the gel content after grafting and after crosslinking. The polyethylene was a commercial sample designated XJG143 and having a density of 0.922, and a melt flow index of 2.5, and in granular form of 5 mm thickness.
Benzophenone (0.1% based on the polyethylene to be grafted) was dissolved in vinyltriethoxysilane (2% based on polyethylene) and compounded into the polyethylene granules.
The granules were then exposed to radiation from the lamp for various times and the gel content after grafting and after crosslinking measured as described in Example 1. The lamp surface was placed in contact with the granules to provide the maximum intensity of radiation. The temperature rise in the granules with this procedure was low, and no cooling was re-quired. The results are shown in Table 3. The granules were irradiated from both sides and the two figures in the ~irradiation time" column refer to these two treatments.

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,. . . . j .1, , _ I d at on Gel content (%) Example time (minutes) After After . grafting crosslinking 3 2.5/2.5 o 18 -622.5/22.5 3 61 .

8 60/60 __ 15 65 Examples 9 to 11 inclusive : These examples illustrate the effect of variation in the distance between the source of irradiation and the polymer

5 on the gel content after grafting and after crosslinking.
The conditions of Example S were used~ except that the distance between the surface of the lamp and the surface of the granules was varied between 2.5 cm and 10 cm. The re-duction in gel content after crosslinking as the distance from .~ 10 the lamp increased is shown by the results in Table 4.

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:-1076~1 _ .... ........ _ _ Gel content (%) Distance from Example , ~ .
lamp ~cmJ After After grafting crosslinking , _ _ _ . ~ .
9 2.5 1 33 11 I~l 2 ~6 ExamPles 12 and 13 These examples illustrate the effect of variation in silane content on the gel content before and after cross-linking.
For Example 12 and 13 conditions of Example 5 and 6 respectively were used~ except that the concentration of vinyltriethoxy-silane was 3% (based on polyethylene).
The results are shown in Table 5.
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. , . _ Gel content (%) : Example .. _... ....
: After After grafting crosslinking . 12 - _ ' .

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t E~ ~ 5 These examples show the effect of variation in ¦ -sensitizer concentration of the gel content after grafting and aftcr crosslinking.
For Examples 14 to 17 inclusive the conditions of Example 7 were used except that the lamp of that example was replaced by a Philips TL 20 watt lamp and the concentration of benzophenone (based on pol~ethylene) was varied as shown. The results are shown in Table 6.

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Gel content (%) Example Benzophenone (%) .
After After grafting crosslinking _ _ 14 0.1 48 0.15 1 60 16 0.2 2 61 ~ 17 0.3 6 _ 7 ,:
Examples 18 to 20 inclusive These examples show the effect of addition of anti-oxidants. The conditions of Example 6 were used~ except that 0.05% (based on polyethylene) of antioxidant was added.
~Flectol" H is 2~2~4-trimethyl-1-hydroquinoline ~"Flectol~ is a registered trade mark). ~Santanox~l R is 4,4t-thiobis(6-tert-butyl-m-cresol) (IlSantanox'l is a registered trade mark).

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t~Topanol~ OC is 2j6-ditert-butyl-p-cresol and ~Nonox" WSP
is 2,2t-methylene-bis-/~-(1-methylcyclohex~l)-p~cresol)7.
(I~Topanol'l and ~Nonox~ are registered trade marks of Imperial Chemical Industries Limited).
The results are sho~n in Table 7.

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Example Antioxidant After After ~
grafting crosslinking , -- r -- _ _ , _ .
18 ~'Flectol" H 7 37 19 "Santanox~ R 6 5o IlTopanol~ OC 3 6l ExamPles 21 to 25 inclusive These examples illustrate the effect of variation in type of polymer. The conditions of Example 5 were used except that the XJG143 granules of that example were replaced by granules of equal weights of/the following polymers derived from ethylene.

Dasignation , Density Melt flow . . , .
1503~ 0.915 60 XRM21 0.921 20 WJG117- 0.918 1.8 EVA 28-os _ 5 Wl~760 _ 1.2 , ' ` ' ` ~ ' 10~ 9~i , EVA 28-05 is copolymer derived from ethylene and vinyl acetate acetate and wherein the vinyl/units constitute about 28% of the copolymer. The results are shown in Table 8.

. . . _ Gel content (%) Example Polymer _ After After grafting crosslinking __ _ _ r 21 1503I, 14~ 53 Examples 26 to 36 inclusive These examples illustrate the effect of variation in the quantity and nature of the sensitizer on the gel content after grafting and after crosslinking. For Examples 26 to 35 inclusive the conditions of Example 5 were used except that the benzophenone of that example was replaced by the sensitizers shown in Table 9. For Example 36 the conditions of Example

6 were used except that halP of the benæophenone of that example was replaced by an equal weight of acetophenone. The results are shown in Table 9.

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Sensitizer (% based Gel content Example on polymer) ~
After After .. grafting crosslinki.ng ., , . . . _ . ~ __ .: 26 0.1% acetophenone 0 55-2y 0.2% t 2 66 . 28 ~3% tt 13 72 :~. 29 0.1% benzaldehyde 0 41 . .
. 3 0.3% '' 2 61 .. 31 -3% p-tolualdehyde 2 55 .
32 0.2% dicumyl peroxide 0 45 33 0.1% 2-methylanthraquinone 5 25 34 0.1% anthrone 4 18 0.1% benzil 14 36 (-$% benzophenone 2 60 . . (0.05% acetophenone .' . ~ . ................. , Exam~les 37 to_ ~ inclusive In these Examples a 4Ormulation was prepared by - dissolving the sensitizer and anyadditional agents in the - 5 silane and compounding - . into the polethylene granules , at 60 C. The grafting was carried out by exposure of the .
granules to the radiation from a Philips HPM 15 2000 watt lamp which is a high-pressure mercury-vapour lamp emitting .. multiple bands of radiation in the region of 2~0 to 365 nm.
The temperature at the surface of the lamp was above the ,. ........... . . .

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melting point of the granules and the granules were there-for placed 120 5 cm from the surface of the lamp to allow air cooling of thc granules.
The granules used were commercial polyethylene designated S XJG 143 except where indicated. ET 3042, ET 901, and XNM 158 are designations of commercial polyethylene. ET 3042 has a density of 0.922 and a melt flow index of 7. ET 901 has a density of 0.926 and a melt flow index of 2.5. XNM 158 has a density of 0.926 and a melt flow index of 1.8.
HM 61 is the designation of a commercial grade of polypropylene. The silanes of thesè examples are as follows:
Silane A = vinyltriethoxysilane Silane B = t~-methacryloxypropyltrimethoxysilane Silane C = vinyltrimethoxysilane In the irradiation-time column of Table 10 a single figure for the time of irradiation indicates that a single exposure was made from one side of the layer of granules.
Two figures indicate that two exposures were given. Where the figures are separated by a stroke the exposures were given on opposite sides of the layer of granules. The "+" signifies that the granules were tumble mixed after the flrst exposure~
and the second exposure was then applied without moving the lamp.
After irradiation the grafted polymer was crosslinkèd by boiling with an emulsion of 0.1~ dibutyltin dilaurate in

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water for 17 hours. The gel content after graf~ing and after crosslinking was measured as desc~ibed in Example 1.
The results obtained are shown in Table 10.
TA~LE 10 _ -- .
. Gel content (%) Irradiation Example Formulabiontime After After (seconds) graft- cross-ing linking . . ~. _ , _ .: 372% silane A 30 ' o 52.8 0.1% benzophenone 0.1% dimethylaminoethanol 38 2% silane A 30/30 o.6 74.5 o .4% benzophenone 39 2% silane A 30/30 4.8 78.4 o.5% benzophenone 2% silane A 30+30 1.2 71.8 0.4% benzophenone 41 2% silane A 30/30 0.2. 74.3 0.7% acetophenone .
. 42 2% silane A 30/30 o.3 52.6 : . . o.5% dicumyl peroxide 43 2% silane B 30/30 1.2 72.9 ~ o.35% benzophenone : 44 2% silane C 30/30 o.3 77. o . o .35% benzophenone ;~ 45 2% silane C 30/30 O.5 68.7 o.35% benzophenone o . o5% dibutyltin dilaurate 46 1. 5% silane C 30/301. 2 72.9 o.35% benzophenone . 47 2% silane A 30~30 o 51.4 . 0.3% benzaldehyde 48 2% silane A 30+30o. l 58. o .3% tolualdehyde ~ _ _ ''` ' .~ .

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TABLE 10 Continued _ , , ,__ ,. l Gel content (%) Irradiation _. .
Example Formulation time Af~er After .
(seconds) graft- cross-ing linking . .-_ _ __ . . _ =_ 49 2% silane A 30~30 0.1 62.9 0.5% tolualdehyde 5o2% silane A 30+30 4 . o 55 . 7 0.1% 2-methylanthraquinone 5~2% silane A 30 1. 5 56. 8 . 0.1% benzophenone WJG 117 granules 522% silane A 30/30 0.8 65 . 8 0.4% benzophenone XRM21 granules 532% silane A 30/30 o.6 68.7 0.4% benzophenone ET3042 granules 542% silane A 30/30 l. 6 69 . 8 0.35% benzophenone ET901 granules . 552% silane A 30/30 0. 8 61. 2 0.35% benzophenone XNM158 granules 562% silane A 30/30 1. 4 70. 6 0.35% benzophenone : EVA28-05 granules . 572% silane C 1 30/30 0 55.8 0.35% benzophenone . polypropylene granules _ .

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Granules of low density polyethylene (XJG 143) were com-pounded with a solution of benzophenone (0.35% based on j polyethylene) in vinyltriethoxysilane (2% b-sed on poly-; ' , ,:

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1(~'7~991 _ 21 -ethylene). The granules were pressed at 140C to give plaque,s of 1.3 mm thickness.
The p]aques were grafted by irradiating them with a Phillips HPM-15 lamp for 30 seconds from each side and then the graft polymer crosslinked by boiling with an aqueous emulsion of 0.1% d;butyltin dilaurate. The gel content measured as described in Example 1 was o.6% after grafting and 73.6 after crosslinking.
ExamPle 59 Example 58 was repeated except that the vinyltrieth oxysilane was replaced by vinyltrimethoxysilane. The gel conte,nt was o.6% after grafting and 75 . 4% after crosslinking.

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Claims (15)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process of manufacturing a silane-grafted thermoplastic copolymer which process comprises treating in the solid from a thermoplastic shaped polymeric article having a thickness up to 5 millimetres and containing a radiation sensitizer as hereinbefore defined and a mono-olefinically unsaturated silane said silane containing at least two hydro-lyzable organic radicals with an amount of electromagnetic radiation of wavelength in the range of 180 to 800 nanometres sufficient to form the said copolymer.

2. A process according to Claim 1 wherein the wavelength of the said electromagnetic radiation is in the range from 200 to 400 nanometres.

3. A process according to Claim 1 wherein the said article comprises a polymer derived from an alpha-olefine.

4. A process according to Claim 3 wherein the said alpha-olefine is ethylene.

5. A process according to Claim 3 wherein the said alpha-olefin is propylene.

6. A process according to Claim 1, 2 or 3 inclusive wherein the said silane is selected from the group consisting of vinyltrimethoxysilane, vinyltriethoxysilane, and gamma-methacryl oxypropyltrimethoxy-silane.

7. A process according to Claim 1 inclusive wherein the amount of the said silane is in the range from 0.1 to 20%
w/w of the said article.

8. A process according to Claim 7 wherein the amount of the said silane is in the range from 0.5 to 5% w/w of the said article.

9. A process according to Claim 1, 2 or 3 inclusive wherein the said radiation sensitizer is selected from the group consisting of acetophenone and benzophenone,

10. A process according to Claim 1 inclusive wherein the amount of the said radiation sensitizer is in the range from 0.01 to 10% w/w of the said article.

11. A process according to Claim 10 wherein the amount of the said radiation sensitizer is in the range from 0.05 to 1% w/w of the said article.

12. A process according to Claim 1 inclusive wherein the said article additionally contains a cross-linking catalyst.

13. A process according to Claim 12 wherein the said crosslinking catalyst is dibutyltin dilaurate.

14. A process according to Claim 1, 2 or 3 inclusive wherein the said article is in a particulate form.

15. A process according to Claim 1, 2 or 3 inclusive wherein the said article is in a sheet-like form.