CA1263905A - Manufacturing method of release paper - Google Patents

Abstract

The present invention relates to a method of manufacturing a release paper characterized in that a mixture of polyolefin and a silicone release agent compatible therewith comprising a reaction product of polymethyl hydrogen siloxane, vinyl group-containing poly-dimethyl siloxane and at least one olefin or polyolefin having one or more double-bonds is extruded onto a substrate of paper, fabric, film etc; the laminate is heat treated to cause the release agent contained in the mixed layer of the laminate to bleed onto the surface of the mixed layer to be thus localized and the localized release agent is fixed by curing. The resultant release agent's compatibility with polyolefin, film forming and stretching properties are improved surprisingly, and since a high concentration of release agent is localized and fixed by curing on the surface of the release agent layer, a small amount of tha release agent sufficies to exhibit a remarkable release effect.

Description

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H~UFACTURING HETHOD 0~ ReLEAS~ PAPER
TECH~ICAL YIELD OF THE INVE~TIO~
The present invention relat~s to a metho~ for manufacturing a release paper by an extruslon laminating process, and more partlcularly to an e~icient and ~conomlcal method for man~facturin~ a releasQ paper by an extrusion laminating proce3s.
T~C~NICAL B~C~ROUND
Prior methods used to manufactu~e sil~cone relsase papers ccn~lsted mainly of coating, the method consisting of forming ~ resln layer, 8 normally a polyethylene laminate, on a substrate such as paper and coat~ng a layQr gf release agent on its surface. ~he release agant used in this metho~ consists of, for instance, polymethyl hydrogen siloxanes and vinyl ~roup-contalnin~
polydimethyl siloxanes. An addition reaction taXe5 place in the pr~sence of platlnum catalysts unaer heating, and the reaction pro~uct sats to form a release film.
Also, as in the present invention, there is known a method of formlng a ralease layer on a substrate b~ an extrusion laminatlng process in a slngle passl but when this method ls used, the resin laminate ltself has release properties. ~s such a release resin, there is used for exampl2, ethylene~~
olefin copolymer elastomer, and it is suitable for acrylîc adh~sives.
When the for~er coating process is adopted, Eirst polyethylene lamination is carried out on the substrate and then the coating of the release a~ent, such as silicone, is carried out in a separat~ step. Thus, the process is a two step process, this being disadvantageous in terms of e~uipment~ time and costs. Furthermore, the release agent applied by coating is ganerally used together with an organic solvent, which can be accompanied by ~rave production problems such a5 fire, explosion and environmental pollutlon.
~ n the other hand, in the latter extrusion laminating process usin~
an ethylene- ~~olefin copolymer elastomer etc. there is concern about heat resistance and resistance to solvents etc. at the time of coating, about dimi~ishing of release potential with re~ard to acrylic adhesives, and furthermore the release potential increases with the lapse of time. ~lthough e~hylene-~ -olefin copolymer elastomer is difficult to extrude whén it is used alone, and h~nce is used, mixed wlth polyethylene, the release effect diminishes with a decrease in the proportion of the elastomer present, whereas an increase in its proportion results in stronger elastomer charactar~tics causing loss in film strength and givin~ rise to workin~ difficultie~ such as blocking.
ThQ present inventors trie~ that method for extrud;ng the r01ea e a~ent hitherto used in the coating proces5 in combination with polyethylene to attempt to eliminate the defects of bvth methods. It ~urned out to lack cowpatibility and to be extremely difficult to extrude due to its poor film formin~ prop~rty and poor stretch. Also curin~ was extremely dif~icult even i~ laminatlon should have been ~easible. Continuin~ thelr in~nsive stu~ies, they discovered that extrusion could be marke~ly improved by a~ing a ~e~tain substance to the compo--nd, and that then curing could be easily accomplished effectively an~ thus resulted the present invention.
DISCLOSURE OF TH8 I~VENTIO~
The present lnvention relates to a method of manufacturing a release paper characterized in that a mixture o~ polyolefin snd a sllicone release agent compatible th0rewith comprislng the r~action product of polymathyl hydrogen slloxane and a vinyl group-contaln~ng poly-dimethyl siloxano w~th at least one olefin or polyolefin having one or more double-bonds i9 extrudad onto a substrate of paper, fabric, film etc., the laminate is then heat treated to cause the release agent contained in the mixed layer of the above-mentioned laminate to bleed onto the surface of the mixed layer to be thus localized and that the localized release agent is fixed by cur~ng.
As a release agent suitable for use in the method of the prasent invention, preferred is a silicone release agent co~patible with polyolefin, being the reaction product of polymethyl hydrogen siloxane, a vinyl group-containing polydimethyl siloxane, and at least one olefin or polyolefin having one or more double-bonds as the third component.
As olefins containing one or more double-bonds there can be used those having 16-24 carbon atoms such as octadecene, while the polyolefins which can be used, for instance, include 1,4-polybutadiene alone or mixed with 1,2-polybutadiene, polyisoprene, polybutene etc. and mixtures tharsof.
An example of the manufacturing method for the release sgent consists in mixing polymethyl hydrogen siloxane (including polymethyl hydro-d~methyl siloxane copolymer), a vinyl group-containing polydimethyl siloxane and the above-mentioned third component, adding di-tertiary butyl peroxide as .:

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cntalyst, proceedln~ wi~h the renction under heatin~ and stoppin~ th~ reaction simultaneously with the recognition of the start of ~ellin~. AlternatiYely, polymethyl hy~ro$en siloxane and the third component may be pr~liminarily cause~ to react under hea~in~ with ~i-tertiary butyl peroxi~e as a catalyst and the reaction product further reactea with ~he vinyl group-contain~ng polydimethyl siloxane or the third component may be simultaneously mix~ and reacted under heatin~ wlth di-tertiary butyl peroxi~e as t~a catalyst and t~e reaction may be stopped simultaneously with the recognitlon of the start of ~ellin~. If t~e reaction is stopped before the start of gelling, the later curin~ is imperfect, w~ile, if gellin~ is allowed to proceed too far, localization o~ bleeding onto the surface of the r~lease ~gQnt becomeg difficult. After stopping the reaction, the rea~tion proauct is ref~ne~ by vacuum treatment to eliminate the unreacted volatile components.
The release agent synthesized by the above-mentioned mathod ls mixed with polyolefin resin a~ a rate of approx. 1 to 10 wei~ht ~, more preferably

2 5 wei~ht ~ based on tho polyolefin resin, and kneaded and p~lleti~ed by a pelletizer to form the resin for the mixed layer ~resin for extru~lon).
Through adjustment of the amount added, it can be made efPective for use as a release a~ent for various adhesives and urethane hard foams etc.
As the polyolefin to be used in the method of the present invention, polyethylene, polypropylene, 4-methyl pentene-l resin, ethylene-vinyl acetate copolymer resin and mixtures thereof can be mentioned. As the polyethylene, linear low density polyethylene with a density of 0.910-0.935 g/cm is particularly suited for its low speed peeling property and, since it can be heat treated ana cured at a high temperature, it is sdvantageous in that it can be heat treated and cured in a short len~th of time. To accelerate localized bleedin~ it is possible to add ethylene-vinyl scetate copolymer resin, polyvinyl ether or the like which acts on polyolefin as a sort of plasticizer.
The release layer resin thus obtained can be extruded onto the substrate by an extrusion laminator and a release layer is formed thereby on the subs~r~te. As the substrate for the p~esent invention, paper, fabric, film, metallic foil and laminatss thereof can be used.
The laminate formed on the substrate is heat-treated. Heat treatment is done by allowing the laminate to stand for approximately 10-60 minutes ~æ~3~t~

after its qurface temperatur~ has reache~ approxlmately 70-120 C. By heat treatment the rele~se a~ent contained in tbe mixed lay~r bl~s towards the surface of the layer ~o be lccalized, and simulate the state in which the release agent is coa~sd on the surface of polyethylane layer as in the conventiDnal process. This is confirmed by measurement of ~he FT-ATX-I~.
The thus localized release agent is perfectly cured and fixed by catalytic ~reatment by the use of, for instance, c~iloroplatinic acid. Curin~
temperature is preferably approximately 100-130 C and curin~ time approxi~ately 1-60 minutes. Hence in a range in which the temperature and time of hea~ tr~atment and curin~ are overlapped, localixation an~ curing msy be carried out simultaneou~ly. The aose of chloroplatsnic acid is preferably ~n a range of 2 x 10 to 3 x 10 m~m . Fixing by curing of th~
release agent is no~ li~ited to the use oE platinum as atalyst but fixing by curing by the use of other catalysts, such as ultraviolet rays, electron beams, gamma rays, etc. is also feasible. The method of applying the catalyst is not limited to surfaca coating.
~ccor~ln~ to the present invention, an adhes~on enhancing layer such of polyethylon~ may be provlded between the release agent and the substrate for improving the adhesive stren~th therebetween.
OPTI~UI~ EUBODIMENT FOR EXECUTING THE INVENTIO~
Uereafter the present invention i5 explained by ~ivin~ examples and control examples, but, needless to say, the present invention is not limited thereby. Parts and percentages given hereafter mean parts by wei~ht and percent by wei~ht unless otherwise specified.
Example 1:
6.6 parts of polymethyl hydrogen siloxane ~P=5-7~, 90.1 parts of vinyl group-containing polydimethyl siloxane (P=150, vinyl group 0.7%), and

3.3 parts of polybutadiene ~MW=1600, 1,4 bondage accountin~ for 99%) were charged into a reactor, 0.286 parts of di-tertiary butyl peroxide was added as catalyst w~en the mixture was heated to 120 C, and reaction was allowed to proceed for 10 hours at 120 C, and the reactor was cooled simultaneously with start of gelling to stop the reaction. The reaction product was treated by refinin~ for S hours st 110 C at a reduced pressure of 5 mmH~ for the elimination of unreacted ~olatile components.
There was added 3~ of the resulting release agent to low-density ~3~

polyethyl~ne ("~-lOPt ~(TM~ of Hitsui Pclychemical, MI:9.5, density: 0.917 gJcm ) and p311ets for the mixed layes were prepared by a pell~tizer at a die temperature of approx. 200 C. The samQ low-~en~;ity polyethylene as was u~ed for the mixeB lay~r was used for the formation o~ the adhesion er.hancing layer.
As a ~ubstrate 73 g~m "Clupa~' (T~) unbleac~d ~raft pap~r was used. Pulyethylene for the adhesiv~ ~nhancing layer was extruded by an ordinary co-a~trusion laminator at 8 die temperaturQ of 310 C with the simultan~ous extrusion of pellets for ~he mixe~ layer at a d~e temperature of 280 C, and a 3-lay~r laminate of substrate-adhe~ion enhancin~ layer-mix~d layer was thus prepared. The thickness of the mixed layer was 20 u~ and that of the adhesion Qnhancing layer was 20 ~. The thus formed e~truslon`s properties are shown in Table 2.
Then the 3-layer laminate was cut ln sheet form and was treated for 10 min. at 120C wlth the rolease layar up.
After heat treatment the surface of tha mlxed layer was coated w~th 1.7 x 10 mg/m chloroplatlnic aci~ (0.001~ IPA solutlon) and cured aga~n for 20 minutes at 120C an~ the role~se papor was obtained.
Of the release paper thus obtained, the release pctential and residual adhesion stren~th was measured as follows:
Adhesive tape:
For the test acrylic adhesive ~raft tape t"Elm (TM) tapa", Soken KaXo) was cut to a size of 25 mm wide and 210 mm long.
~easuring conditions:
The above adbesive tape was stuck to the above-mentioned release paper by pressing, one stroke and back, at a speed of S mmtsecond with a rubber roller of 4.5 kg in wei~ht, and th~ release potential and residual adhesive strength were measured under the following conditions. A~ter stickin~ of the tape, the measurement was taken after sgeing for 20 hours under a pressure of 20 g/cm in an atmosphere of 70 C and 65% RH.
Measuring method:
The force required for low speed S0.3 m/min.) peeling was measured by autograph tension tester ("Strograph-R," (TM) Toyo Seiki~ and that for high speed (3 m/min., 20 m/min~) peelin~ was measured by hi~h speed peeling tester (Tester Sangyo (TM)3 both a peeling angle of lR0 . ~easurement was taken ~æ~3~0~

under the conditions of 23 C and 65~ RUI.
The res~lts of measurement are sbown in Tab3e 1.
Example 2 In Example 1, polybutadiene was replaced by polyisoprene (~W = 29000) and the r~actlon con~ltion was ~hanged to 120 C ~ 14 hours and with the resultln~ release paper, testing was done as aescribed in Example 1. The results are shswn in Table 1.
Example 3 Polymethyl hydrogen siloxane used in ~xample 1 was admixed w~th polybutene ~W = 1450) and di-tertiary butyl peroxi~e was aa~sd as ~atalyst and after 2 hours of prelimlnary reactlon at 120 C 9 ~inyl-~roup containlng polyaimethyl siloxane usad in Exampl~ l was caused to react ~or 4 hollrs at 120 C and the release paper was obtained in otherwi~e the ~ame way, and with it tests were carried out in the same way as describa~ in Example 1. The mixin~ ratio of the indlvidual reaction components W8S the same as ln Example 1 and the coatin~ rate of chloroplatlnic acid was 1.8 x 10 lm~m . The results are shown in Table 1.
Example 4 In Example 3, polybutene was replaced by octadecene and after 2 hours of preliminary reaction at 120C, reaction was conducted for 3 hours at 120C and a release paper was preparea in otherwise the same way and with it tests were made in the ~ame way as described in Exsmple 1. The coatin~ rate of chloroplatinic acid was 1.6 x 10 mg/m . The results are shown in Table 1.
Control example 1 Polybutadiene used in Example 1 alone was mixed at the same ratio (0.099~) with low-density polyethylene, a 3-layer laminate was obtained in the same way and it was heat-treated for 10 minutes at 120 C, and with it tests were made in the same way as described in ~xample 1. The results are shown in Table 1. hptitude for lamination was satisfactory.
Control example 2 In Control example 1, polybutsdie~e was replaced by polyisoprene used in Example 2 and release paper was prepared in otherwise the samé way. The results are shown in Table 1. Aptitude for lamination wss satisfactory.
Control example 3 ~L2~i3~

In Control exampl¢ 1, polybutadi~ne was replaced by polybutene us¢d in ~xa~ple 3 and release paper was prepared in othe~lise the same way. The results are shown in Table 1. Aptltude for lamination was satisfactory.
Control example 4 In Control ex~ple 1, polybutadi~ne was r~plsced by oeta~ecene us~
in Example 4 and release paper WBS prepared in other~lise the same ~ay. Th2 results are shown in Table 1. AptitudQ ~or la~inaticln ~as satisfactory.
Control e~a~ple S
Low-density polyethylene use~ as base resin in e~mple 1 only was extruded onto the same substrs~e for preparation of 1 lamlnate, and with it tests were carried out in the ~ame way as described in Example 1. The results are shown in Table 1. Aptitude for laminatlon was satisfactory.
Control sxample 6 A mixture of 1.7 parts of the mixture of polymethyl hydroger silox~ne and 98.3 parts of vinyl group-containing polydimethyl siloxane was added in an amount of 2.901~ to low-density polyethylene in the same way as descrlbod in Example 1 and pellets for the mixed layer werQ prepare~.
Lamination W8S carried out by extr~dlng polyethylene for the adhesion enhancing layer using a coextrusion laminator at a die temperature of 310 C, and the layer thickness was adjusted to 20 ~. Using pellets for the mixed layer an attempt was made for extruding it at a die temperatur~ of 280 C
with expected layer thickness of 20 ~. The ext~lsion rate was substantially reduced and subject to marked fluctuation, and although extrusion was somehow carried out, the film thickness was subject to marked scattering as was the laminate film width and the resulting laminate was hardly useable in practice. The extrusion performance is shown in Table 2.
Curing was not feasible although an attempt to cure wa.s made under the same conditions as in the present invention, and the sillcone release agent in the release layer migrated into the adhesive tape layer, this resulting in the lowering of the release performance.
As is apparent from the above results, conventional silicone release a~ent intended for coating has no aptitude for lamination, cannot be cured and is not usable as a release agent of the present invention.

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(1) Mea~ured values are all in unit of g/25 mm.
(2) Residual adhesion coefficient = (A/B) x 103 where: A = Adhesive æ~reneth of standard adhesion tape aft~r contact with release pa~per B = Adhesive stren&th of standard adhesion tape before contact with release paper Table 2 Release agant of Conventional release agent present invention (Example 1) (Control example 6) 1. Compatibility Good Poor w. polyethylene 2. E~trusion rate Slightly reducad Considerably decreased, and sub~ect to marked fluctuation 3. Catching of Good ~ad due to screw slippage resin by screw

4. Laminatlng No film deflection Some film deflection.
Good elongation Increased "neck ln" due to decrease of extrusion rate

5. Aptitude for Positive Negative lamination (Overall evaluation) ~ii3~

As is apparent from Table 1, an olefin or a polyolefin having one or more ~oubl2-~bonds as used in the present inven~ion is a minus factor in the rel~ase effect but a5 seen ~rom Table 2, it is apparent that it plays an important rQle with regard to improving laminstion in the process of manufacture of releasc paper by the extrusion method. According to the present invention, Exhibiting a good release effect a:re the two components of the polyorganosiloxane type w~ich assume a three-dimensional crosslinklng structure by fixation by curing.
IMDUSTRIAL POSSIBILITY OF UTILIZ~TIQ~
Ac~ording to the present inven~ion, compatibility ~ith polyolefin3, the ilm forming pr~perty and stretching propertg were i~proved through reaction of an olefin or a polyole~in having one or m~DrQ double bonds as a third component with release components, and its extrusion properties can be astonishinely improved. Also since the relaase agent is localized and fixed at a hieh concentration on the surface of the release layer by heat treatm~nt and curing, a remarkable release effect can be attained despite the small proportion of relea~ agent to polyolefin and as a result a manufacturlng method for release paper, which is che~p and high in product~vity can be provided.
The release paper of the present invention, is widely used as a release paper for adhesive tape, tack paper and stickers etc., as a "process paper" for synthetic leatherette, urethane etc.

Claims (5)

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

1. A method of manufacturing a release paper comprising:
(1) extruding a mixture of a polyolefin resin A and a silicone release agent B compatible therewith onto a substrate to prepare a laminate, said silicone release agent comprising a reaction product obtained by reacting (a) a polymethyl hydrogen silicone, (b) a vinyl group-containing poly-dimethyl siloxane, and (c) at least one compound selected from the group consisting of olefins and polyefins having at least one double bond, said reaction being stopped at the start of gelling;
(2) heat treating the obtained laminate to cause the silicone release agent B contained in the extruded mixture of the polyolefin A and the silicone release agent s to bleed onto the surface of the mixture and thus become localized; and then (3) curing the localized silicone release agent B to fix it.

2. A manufacturing method as recited in claim 1, wherein said polyolefin (c) having at least one double bond is at least one selected from the group consisting of l,4-polybutadine, a mixture of 1,4-polybutadiene and 1,2-polybutadiene polyisoprene and polybutene.

3. A manufacturing method as recited in claim 1, wherein said polyolefin resin A is slected from the group consisting of polyethylene, polypropyene, 4-methylpentene-1 resin, ethylene-vinyl acetate copolymer resin and mixtures thereof.

4. A manufacturing method as recited in claim 1, wherein said release agent B is mixed with the polyolefin resin A at approximately 1-10 weight percents based on the weight of said polyolefin resin (A).

5. A manufacturing method as recited in claim 1, wherein said heat treatment is carried out by leaving said laminate for approximately 10-60 minutes after its surface temperature has reached approximately 70°-120°C.