DE1504651A1 - Process for the production of dimensionally stable films from cellulose hydrate - Google Patents

Description

BI DU FONT DE NBMOIRS AND COMPANY 10th and Harket Streets » Wilmington» Delaware 19898, V.St.A ₃

Process for the production of foro-resistant polyols from cellulose hydrate

The invention relates to a method for producing dimensionally stable Cellulose hydrate films, whereby the still soft "gel" like cellulose hydrate rolls for gradual reduction the moisture content can be passed through a drying unit with stretching and relaxation.

It has been found that packets wrapped in coated films made of regenerated cellulose, which are exposed to high humidity, form a pattern of furrows or corrugations which run in the machine direction (longitudinal direction) of the films. This corrugation pattern affects the appearance of the packaging so much * that potential buyers question the quality of the films. The term "corrugation" was used for furrow patterns which are calibrated on cellulose glass that is used to enclose a "package"

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was packed at low or normal humidity and is then exposed to high humidity »The corrugation must be distinguished from the wrinkling, a local one Warping de;. · Slide that generally with errors

or unevenness in moisture-proof coatings. A film that has wrinkled _? level is closed _{- I a s} when the moisture equilibrium has been established in all parts of the film o The corrugation lasts ao long _c as the film is exposed to high humidity o The corrugation did a particularly unpleasant problem with those films that were first Foil quality were processed to give the pack an improved appearance.

The corrugation of Zsllglas with high humidity is through simultaneous shrinking of the film in the machine direction and stretching the film in the transverse direction on a

wrapped package hosted, when the moisture > .n the foil is increased.n The size of the corrugation is different ^ and practically all cellulose films ripple a little,

The invention is based on the task of improving the quality of films made from regenerated cellulose .

It was found ^ that in the cast film Tension occurring during drying is the single most important factor that causes fluting. Strong swan

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i | r warping at high humidity! .feei Ver " nen CriesetMiechAnen uit unterohledlichen Trooi-nertyp · «tiöd differentin ^ pajonuagsbildern determined«

ee would be ideal if there is no warping in any direction, but foils that are practically riffolung-free would be obtained if the difference between warping in the horizontal direction and warping in the transverse direction were less than $ 1.5 *. In any case, the warping, either in the Maeohin direction or in the transverse direction alone, must be less than $ _{2 e}

The stated object is achieved according to the invention by that nan to prevent the occurrence of a corrugation of the Foil if it is exposed to high humidity during its later use «

1. a softened, gel-like film made of regenerated cellulose dries to a moisture level of about 100 to 120% «while sau uses a stretching of 2 to 4 % »

2. The film continues to dry to a moisture level of about 25 to 60 % »while letting it relax by about 1.5 to 2.5%» whereupon one

3. Complete drying to a level of about 5 * 0 to 7.5 % while applying a draw of about 0.5 to 1.0 pounds.

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According to a preventive embodiment, the drying in step (2) is carried out to a moisture content of about 25 performed up to $ 35

The use of several ₃ drying processes carried out with stretching and relaxation is known in the production of dimensionally stable cellulose hydrate fluids (US Pat. No. 2,746,167).

However, the method according to the invention by no means differs from the known method only by the degree of Drying and pre-stretching alone «but also in the ■ Task.

The known method is intended to produce an equal measure flat film without marginal distortions, to create at which the permanent shrinkage occurring as a result of the action of moisture on the film is reduced · This Shrinkage is highly undesirable because it is frequent leads to destruction of the film.

Although the known method uses similar measures as the inventive method is not the same by the Registration-appropriate task solved, namely the occurrence of a Corrugation of the film in an atmosphere of high humidity impede. Such a corrugation develops as long as " how the high humidity is present. It diminishes the appearance and thus the sales value of a packaging made with such a film. .

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The well-known procedure was developed around a very specific To solve the problem, however, gives no indication that a modification of the known process conditions also solves a completely different problem than what the known method is based.

In every process step according to the invention, there are two variables, namely moisture and tension, and all variables must be related in the specified manner in order to obtain a usable film impressively evident from example VII of the application, where only one variable was outside the specified range and no more usable film has been obtained. Rather, this exemplary embodiment resulted in a film. with . inadmissible high corrugation in a humid atmosphere.

The expression "# moisture" refers to the "Wasaea", based on the dry weight of the cellulose which is in excess of the dry weight of the cellulose. 50 $> moisture means that in 150 g of wet cellulose, 50 g of water and 100 g of dry cellulose are present.

The term "stretch" means percent stretch the length of the film produced by stretching in the machine is caused ο the expression "application of a stretching" "means stretching the film in the machine direction by a given ^ percent of their original

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De / flustiruck "relaxation" means the opposite of the term "for elongation" and refers to the percentage decrease in length of the film caused by shrinkage in the machine direction. The term "relaxation" refers to reducing the length of the film in the machine direction by a given percentage of its length, taking advantage of the tendency of the moist film to shrink. Special means of stretching and relaxing the film are shown below

The expression "softened gel-like regenerated cellulose" refers to regenerated cellulose in a gel-like state which contains about 3.0 to 3.5 times the weight of dry cellulose in water, _{or the like} . This expression is further clarified below _β

The initial warping of cellulose glass (increase or decrease in length) at the transition from 35% moisture 8i $ ige Moisture int the main characteristic that up now developed to predict corrugation.

When drying a einweichten, gel-like sheet made of regenerated cellulose of about TOO to 120 i »moisture at a draw ratio 2-4 $, then upon further drying under a relaxation of 1.5 to 2.5% to a moisture level of 25 to 60 fo and completion of the drying with a drafting of 0.5 to 1.0 # to a moisture level of 3.0 to 7 * 5 #, - it was found * that the difference between the warping in the transverse

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direction and in the Maechlnearrichtung was not greater than about 1.5 #. Fold the described "method of pollen produced were reefs lung-free if they are high humidity, and indeed some relativer.Feuchtigkeit, exposing * The pollen looked good and had just ·

The optimal increase or decrease on stretching or relaxation, which is achieved by different peripheral speeds of the dryer rolls varies somewhat with the strength and the Weichnachungsgrad of films _o For this Grun ~ de desired, before the difference between the peripheral speeds and the positions having to be able to change the critical polar moisture content _o

f

The method of the invention is generally based on drying

endless webs of any wet-cast cellulose-based film applicable «Due to the economic importance of films made from regenerated cellulose, those made from viscose

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are made, however, such films are the preferred material for erfindun ^ YGT ^a iaäesen treatment, "

The large-scale process for the continuous production of films made of regenerated cellulose from an aqueous solution of the salt of cellulose xanthogenate (viscose) is described in US patents 1,548,864 and 1,601,298 a precipitation bath is pressed to form a coagulated sheet and the freshly coagulated film is immediately regenerated, washed, desulphurised j bleached ₅ softened and dried * ·> die

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Dried FoHe becomes better * hand rub »with the

and Y / eiterverarbeitur.g rolled until the Weichmachungsstufe remains the web of regenerated cellulose in a gel-like state, ₀ ho it is completely saturated with an aqueous solution, since gel-like films from regenerated cellulose about 3.0 to 3.5 times of water, based on the dry weight of the cellulose contained, must be considered when drying a considerable amount of moisture to be removed "at the discharge of this moisture, the film shrinks in all three dimensions, whereby the surface of the obtained film decreases _o to avoid a too strong Flächeneinbuase _s of formation of Irregular "speeds on the surface, wrinkles, creases and the like and the deterioration of transparency _s it is common for the web to dry _s by nan it passes through a number of heated rollers" as such "B _0" in the US patents 2 000 179, 2 141 277, 2 746 166 and 2 746 described iatο The present invention relates to drying ngsstufe of the manufacturing process described above _β

After leaving the softener container, the wet, soft-roughed, gel-like cellulose hydrate film runs between squeezing rollers or scraping devices _s which remove excess soft subsequent bath _? and enters the outermost section of the dryer. It contains about $ 300 to $ 350

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Water, based on the dry weight of the cellulose o In the first stage of the dryer, the film runs over a number of conventional dryer _{rollers 9} which run at a higher peripheral speed than the rollers at the wet end of the Giesamasohineo This keeps the web at a stretch of 2 to 4% ₀ The dryer rollers in the dryer are heated evenly, and warm air is allowed to sweep across the web, so that the web is kept at a practically even drying temperature, and a symmetrical moisture distribution profile in the transverse direction is ensured 100 to 120 #, based on the dry weight of the cellulose "is reduced, the web is guided over a second row of conventional dryer rollers, which are driven at a peripheral speed of about 1.5 to 2.5 $ lower than the preceding rollers, for one _o decrease or relaxation of the tension in the web o In this drying stage, the moisture content of the film is reduced to 25 to 60 % . Thereafter, the film is passed through a further series of conventional dryer rolls which are driven with a large by about 0.5 to 1.0 ^ ereη circumference speed as the rolls in the preceding stage to the film in a stretching of 0.5 to 1 To effect 0% ο In this stage, the moisture content of the film is set to around 3.0 to 7.5 # moisture,

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based on the dry weight of the cellulose, reduced » When the drying process is complete, the polie leaves the dryer and is rolled up »

In the next Table below, the voltage pattern applied in eight different examples are generated warden with the obtained Versiehungen angegebenο Disse, _Ä by nan the finished dried films of regenerated cellulose unterwarfο the Yersiehungsversuch described below In the table, "MR" the warp in min in the machine direction (longitudinal direction) and "QR" the warping in mn in the transverse direction after the samples were subjected to the warping test,

Forgiveness attempt

Film samples made of regenerated cellulose (about 0.0224 mm thick after drying) dried under the conditions specified in Examples 1 to 8 are coated on both sides with a vinylidene chloride copolymer dissolved in a solvent, carefully dried to remove the solvent and then at 24 ⁰ C and 35 ° relative humidity 12 hours kiU.natieierto After the coating, the films are about 0.0254 nm thick = After this air conditioning, strips of the film are 400 mm

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in one direction and 25.4 mm in the other direction, cut from approximately the middle of a full cast width of the coated sheet of regenerated cellulose. The samples are cut out so that some have their long side parallel to the cross direction and some parallel to the machine direction. Each of the film samples is attached to a frame that has approximately the same dimensions as the sample, and the film sample is attached to the upper part of the frame in such a way that its lungs run vertically when the frame is hung in a climatic chamber o At the lower end of each film there is a 20 g weight attached. The frame iet attached to the each film sample at one end, are suspended in a maintained at 2S ⁰ C and 81 1 "relative humidity room" The dimensional change under the conditions of some relative humidity is defined as changing the length in mm after 72 Hours measured * The corresponding values are given in the table below under "MR" and "QR"

The percentage warpage in the machine direction (MR) and the cross direction (QR) is calculated as follows:

in χ tOO β ^ ornamentation in QR

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The different versions Xn £ are calculated as follows:

x 100 - * VeriehungCunterechied

In the tables below, the plus sign (+) in front of MH (mm) and QH (mn) means that the film became longer during the experiment «The minus sign (~) means shrinkage of the film during the experiment if the sign of QR is (now) negative _r QR is always used as a positive value in the above formula for calculating the percentage warp difference ο The calculation is carried out in this way ο because it is desirable that the change in the dimensions of the film (if it occurs at all during the test) is positive in order to avoid any appearance of corrugation ο As already noted above, the percentage warping in both the longitudinal and transverse directions must be less than 2 ^c 'o .

Examples K and 2 illustrate the process of the invention. "

In the case of moisture ~ tension IiR ₅ now QR _f mm distortion play content, fo pattern difference,

Gel up to 100 2.5 fVer- +2.0 ^ 7 * 0 1.25

Elongation

100 to 30 1.5% relaxation

30 to 5 $ 0.7> Ver

stretching

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At- «moisture tension game, salary, # raucter

Gel up to lOOf »

iOC $. to $ 30

30 to 5

₈ mm QR, now there is a difference. _Tir j6

3.2 % Yet- +1.75 +6.0 s-dehydration 1.5 % relaxation.

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Nachstehend.ea the Examples 3 to 8 Open (f for comparison siKd | be explained in which the process geführtp which do not fall under the invention *

In the case of humidity, tension, MR, mm QR _P ram deformation play content ₉ fo pattern difference _r

3 gel
100 until
bio 100
30th ■ $ 2.0
recovery
2 _P Ö $> Ver = -7.1 +8.2 ill 30th until 5 2.0 ■%
a stretching. +7.3 4th gel
ICO until
until 100
5 2.0 <fi ver
sireckung
1.5 Jb JSnU-
excitement * —-— 5 gel
30th until
until 30th
5 1.5 % Ent
tension
2.0 %
Elongation . 1.5

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At- moisture- tension- MR., Mm QR ,, mm warpage content ρ fo pattern difference ,,

Gel up to 100 2.5 5ε Ver +2.75 * 8 »75 1.5

Stretching up to 30 £ 4.6 relaxation up to 5 $ 1.6

Elongation

Gel up to 100 3.9 56 Ver ~ +1.2 * 8.65 1.8.6

Stretching up to 30 1.4 i> relaxation up to 5 $ 0.29

stretch

Gel up to 100 $ 4.9 v _er - +0.5 * 12 _P 75 3. ₉ .06

Elongation

. 100 to 30 4.7 % relaxation up to 5 $ 4.9

Stretching

The underlined values for MR, QR and the g difference (j £) are above the permissible limit values

Further remarks are made below, also after the previous ones The examples described above are given ο

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Example · Comments

The Verziehungsuntereehied is about 1.25 fi film You riffles not _t just did and looks good aue ·

The warpage difference is about 1.05 # The film does not ripple, just let it and looks good

The film has a distortion difference of about 2.3 µs, it has corrugations, is too strong
Edge curvature and poor appearance *

The film has a warp in the transverse direction of more than 2 # and a warp difference of about 1.7 #, but it is too strong Edge curvature on »

The film is flat, but looks bad with water stains and streaks that are too strong.

'Draw difference is approximately 1.5 # «>

The distortion in the transverse direction is greater than 2 Jl (2.18? S) c The film is corrugated, looks bad and has excessive curvature of the edge »

The distortion in the transverse direction is greater than 2 Ji (2.16 #) ♦ The film is corrugated, looks to some extent and has excessive curvature of the edge.

β The distortion in the transverse direction is greater than 2 # (3.18 #) * The film ripples, looks bad and has excessive curvature of the edge ο

The above examples demonstrate the critical limits of the invention. If nan works outside the scope of the invention, films are obtained that consist of one or more Reasons are unacceptable.

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The flatness of a film is a characteristic of endless films and has a significant influence on its running properties on converters and processing systems _o An absolutely flat film without curvature is the goal of all film thermos o Flatness is determined by running a film lengthways over two carefully aligned, horizontal ones parallel support rollers or bars that are 4 _f 57 ^ apart from each other ο The film ends are held in place »and the film is stretched in the longitudinal direction over the untrimmed width of 4» 57 m ο The contour of a transverse section of the film is roughly in the middle of a unsupported stretch is observed and the larger deviations from the straight, horizontal line are measured in mm disadvantageous for a satisfactory operation As with bag animal production machines, wrapping machines, printer presses, etc., the curvature of the film edges is also undesirable, depending on the strength of this effect 5 mm to a tension of 0.635 kg per 2.54 cm of foil width; _; & toeririei $ t <, B # i check after the. protruding teet showed

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the films processed according to the invention have a satisfactory - establishing evenness.

The invention erniöglichi: preparing a fo r the consumer with respect to the corrugation acceptable film _v while good appearance and the desired flatness of the film maintained lead-in?.

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Claims (9)

15 O * 651. a Ε.ϊ. da Pont de Honors and Company claims iy process for the production of dimensionally stable cellulose hydrate films, the still soft, gel-like cellulose hydrate films to gradually reduce the moisture content while stretching and relaxing through a drying unit »characterized in that one is to prevent the occurrence of baffling of the film if it is exposed to high humidity during its subsequent use, 1. a softened, gel-like film made of regenerated CeILulose dries to a moisture level of at about 10G to 120 # while applying a versatility of 2 to 4 ° , 2 ο the oil continues to dry to a moisture level of about 25 to 60 fo , while letting it relax by about 1.5 to 2.5 fo , whereupon one 3 »Ö completed drying to a moisture level of about 5? To 7.5 i>, while a Yerstreckung one of applied about $ 0.5 to $ 1.0 BAD ORIGINAL 90 9 8 U 2/1545 . .,. , ...-.— - ■ .. * ·. -. ·: -WS. y »« V ü · Wi ^l4rt - ⁷ ■■ " 2 «Method according to claim 1, characterized in that drying is carried out in stage 2 to a degree of humidity of about 25" to 35 i * » BATHROOM - 2 - 9 0 9 8 t? < ■ ^ς t 5