JPS5841179B2 - Watukusukotoshita Polyethylene Sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of applying a wax coating to one or both sides of a polyethylene-based film that reduces the dimensional stability problems of conventional wax coated films.

More specifically, the present invention provides a method for obtaining a waxed polyethylene film having a degree of dimensional stability hitherto unobtainable.

Polyethylene film carrying a surface coating of petroleum wax composition has excellent protective properties in many packaging applications, and has special value as an inner sheet for packaging various grains, crackers, etc. There is.

Unfortunately, the waxed polyethylene sheet materials produced to date suffer from abnormal and troublesome production or elongation in both directions when the waxed polyethylene sheet material is rolled up after the waxing operation is completed and stored in warehouse conditions during the summer months. characteristics arose.

The elongation spread of the web is often sufficient to separate the web from the core of the stock roll, and such deformation of the roll stock has made the web unsatisfactory for use in automated food packaging machines.

The growth or elongation of waxed films was often as high as 0.5 to 1.0 inches per foot of web length and width, or about 4% to 8%.

The elongation that occurs during storage of waxed polyethylene films is fairly slow at room temperature (70-75 T'), but the elongation Q rate increases rapidly as the storage temperature increases.

It has heretofore been impossible to store waxed films during the summer months, when temperatures in typical storage areas may reach the 100-130°C range.

This is because the films exhibit dimensional instability even when subjected to moderately elevated storage temperatures.

It has been found that waxed films that exhibit dimensional changes of more than 2-3% during storage are unsatisfactory for use in high speed packaging machines commonly used for a variety of packaging applications.

It is therefore a commercial necessity that the elongation of the sheet be maintained within the above-mentioned limits even when stored in warehouses where summer temperatures can reach 100-130'F, and preferably the dimensional change is Under such conditions it is preferable not to exceed 1.5%.

It is an object of the present invention to make it possible to produce waxed, polyethylene-based webs that are dimensionally stable during use for storage and packaging applications.

Another object is to provide waxed polyethylene webs with low moisture vapor permeability for the satisfactory packaging of grains, crackers, and similar food products susceptible to deterioration by atmospheric moisture at moderately elevated temperatures. The object of the present invention is to produce polyethylene webs that can be stored without substantial dimensional changes even in the 1990s and can be used for food packaging in high-speed packaging machines.

Further objects will become apparent from a careful reading of the following description and claims with reference to the accompanying drawings.

The growth or elongation of waxed polyethylene-based films, even when stored in rolls at temperatures up to 120-130'T'', is now reduced or reduced to a negligible extent by the uniform waxing method. I understand.

In this method, the polyethylene web is subjected to tensile stress during and immediately after the application of molten wax and is tensioned to a controlled amount ranging from 5 to 20% of its original length.

The actual application of molten wax is immediately continued to impart the desired degree of tension to the sheet, the wax-coated sheet is cooled while the sheet is held under tension to solidify the wax, and the coated web is cooled. Roll and store for later use in packaging operations.

According to the method of the invention, the wax sheet exhibits a dimensional stability within ±2% even after long periods of storage and exhibits highly desirable protective properties as a packaging film.

The polyethylene film as a substrate, preferably coated with petroleum wax, is first coated with a more even coating on the film so that the surface of the film is easily wetted by the molten wax and then the molten wax forms a smooth overall coating of uniform thickness. The surface of the film is subjected to an oxidative type surface treatment in order to spread it out.

Several known polyolefin surface treatments are used.

This includes corona discharge, flame treatment, or oxidizing chemical treatments, all of which are carried out in known manner and do not form part of this invention.

The protective properties of waxed films are based in large part on the uniform distribution of the wax composition coating on the surface of the polymeric film, which is generally enhanced by surface treatment of the base film.

For example, a 1.5 mil (1 mil - 0,001 inch) thick high density polyethylene film has a moisture transfer rate in the range of 5 to 10 grams per square meter in 24 hours.

If this film is corona discharge treated and 135″F
1 ream (30 g) of paraffin wax with a melting point of
Moisture Transfer Rate (MVTR) is 0.5 to 1.0 gr/M2 when only 4 lbs.
Reduced to 724 hours.

On the other hand, a similar film coated with wax without prior corona discharge treatment has an MVTR of 2 to 4 gr.
/M2/24 hours.

All data presented herein are therefore based on films that have undergone an oxidative surface treatment prior to the waxing operation.

In a preferred embodiment of the invention, the tensioning and waxing operations are carried out by means of equipment such as that suggested in the accompanying drawings.

In the figure, a polyethylene web 10 is unwound from a stock roll 11 and guided through an idler roll 12 and through a nip formed between a backup roll 16 and an applicator roll 17.

The applicator roll 17 has its lower part filled with molten wax 20 which is heated to a desired wax coating temperature in a wax pan 21.
It is rotatably supported so that it can be immersed in the bath.

The applicator roll preferably has an etched, carved, or textured surface that overflows into the nip between rolls 16 and 17 through which the web passes. Sufficient molten wax is pumped from the pan 21 to maintain a level of molten wax in contact with the web 10.

If desired, rolls 16 and 11 can be used to extend the web 16 and 11 so that both sides of the web receive a coating of the wax composition.
may be placed in the wax bath.

After passing through the nip, the coated side (or both sides) of the web passes over a heated metering rod or roll 22.

The metering rod may be a conventional wire wrapped rod or other equivalent device which removes excess wax from the web surface and smooths the wax film to provide a uniform coating thickness on the web surface. obtain.

If both sides of the web are coated, then both sides are of course subject to metering operations.

After passing through the idler roll 23, the coated web then passes through the tempering drum 25, which is maintained at a temperature slightly lower than the melting point of the wax, and then passes through the cooling drum 2.
It reaches the surface of 7,28.

These cooling drums complete the coagulation and solidification of the wax coating, and after passing over idler rolls 30, the final wax-coated sheet is wound into a roll shape onto take-up rolls 32.

The web is exposed to harsh areas (crit) during wax application work.
The applicator roll 1 is used to apply a controlled amount of tension to the polymer web during the transfer of the
7 and the backup roll 16 are operated by a first variable speed drive (
(not shown), tempering drum 25, cooling drum 27
, 28 and take-up roll 32 are provided with a second variable speed drive.

To this end, the tempering drum, cooling drum and take-up roll are rotated as desired at variably higher speeds than the applicator roll and back-up roll.

This provides a preselected degree of tension to the waxed film at critical points between the waxing nip and the conditioning and cooling drums.

These particular working conditions have been shown to cause the film to reach temperatures above the melting point of the wax in the wax pan, and the film is heated to temperatures above the wax melting point (usually less than 130°C).
It is important for the dimensional stability of the final wax-coated film to impart the desired degree of tension to the film while heating to a temperature range between 'F) and the maximum temperature close to the softening point of the polyethylene. .

The softening temperature of polyethylene depends on its molecular weight and density.

Low density polyethylene generally softens around 220-230'F, while high density polyethylene softens at temperatures below 260'F or slightly above.

Therefore, the temperatures of the wax bath, applicator roll, backup roll, and metering roll are controlled to initially raise the temperature of the film to the desired temperature range and then maintain the temperature within that temperature range throughout the waxing and tensioning operation. It is important to do so.

Generally, the heated molten wax provides sufficient heat to achieve the desired results described above, but the film may be heated, for example, by utilizing one or more idler rolls 12 as rolls to preheat the film. It will be appreciated that it is partially preheated before being selected.

PREFERRED EMBODIMENTS OF THE INVENTION To illustrate the effect of tensioning a high density polyethylene film to various degrees during wax application in the above-described apparatus, we used Chemplex 6108 high density polyethylene resin (K. 1, which is made by blow molding (available from Plex).
A 5 mil polyethylene film was waxed with 4.8 pounds of paraffin wax with a melting point below 135-140 held at 210''F.

The film was fed to the coating roll nip at 50 feet per minute.

The chill roll and take-up roll were operated at speeds sufficient to provide varying degrees of tension on the waxed surface as shown in the table below, and the wax-coated polyethylene film was then stored under 120°C for 8 days and heated to 1B respectively. , 4B, tested the dimensional stability of the film after 8 days of storage.

The results are shown in Table ■. The data in Table I is 10% during wax coating at a speed of 50 feet per minute with a wax temperature below 210°C.
High-density polyethylene strained to a range between It is clearly shown that a waxed polymer film can be obtained within the range of properties (maximum dimensional change of 2% or less).

It is also clear that the waxed films without tension (control) did not exhibit the desired degree of dimensional stability.

As previously mentioned, a thin coating of wax on a polyethylene film greatly reduces the rate of water vapor transmission through the film and therefore waxed polymer films have great application in the packaging of articles susceptible to the adverse effects of moisture. It is.

The amount of wax coating required will vary somewhat depending on the specific protection requirements of the particular packaging situation and also on the type and thickness of the underlying polyethylene film as well as on the wax composition used.

It will be appreciated that a variety of wax compositions based essentially on petroleum waxes may be used.

Either paraffin wax or fine petroleum wax may be used.

Either or both may also be used in combination with other known wax composition components such as polyolefins, ethylene-vinyl acetate copolymers, natural and synthetic resins, and the like.

Standard wax composition acids suitable for this invention range from 1% to 50%
Mixtures of paraffin wax with a small amount of fine quality wax and paraffin wax, including ethylene vinyl acetate copolymers, and/or polyethylene, polyisobutylene, rosin, natural and synthetic rubbers, hydrogenated rosin esters, etc.

Generally, from 1 pound to about 10 pounds of wax composition per rem (3000 square feet) of polyethylene when coating one or both sides of the web is adequate to provide the desired degree of protection for the packaging film. It is.

If the amount of coating is too large, it will be an economic loss, and if it is too small, it will generally not be effective.

The preferred coating weight range is 3 to 6 pounds per ream of pace web.

The table below shows the water vapor transmission rate of unwax coated high density polyethylene film (1.5 mil thick) made from Kemplex 6108 polyethylene resin and the 135-1
4.4% per ream of paraffin having a melting point below 40%.
MVTR of a similar film waxed by 8 lbs. and stretched to 12% during the waxing operation according to the method of the invention described above.
(moisture transfer rate).

MVTR was determined by all samples by TAPPI's T-464-m-45 method.

The waxed films were conditioned at 120°C for 8 hours before MVTR testing.

MVTR values are expressed in grams per square meter per 24 hours.

The data in the table above shows that the wax-coated polyethylene film has a substantially reduced MVTR and that the wax-coated film/L/M according to the method of this invention has a substantially lower MVTR than the unwax-coated polyethylene. This is written down.

As noted in Table 2, the taut wax-coated film has satisfactory dimensional stability, while the wax-coated non-taut film has poor stability.

The phenomenon of growth or elongation after wax coating is common to both high density and low density polyethylene films and has also been shown to be somewhat less with polypropylene films.

The table below shows that unstrained polyolefin films from various raw materials are coated with 4.0 to 4.5 pounds per ream of 170'F paraffin wax (melting point: 135 to
It shows the elongation when coated at 140'F) and stored for 3 days at temperatures below 100 to 120 degrees.

In the front, HDPE is high-density polyethylene, LDP
E indicates low density polyethylene, and PP indicates polypropylene.

Sample A is a high density polyethylene film designated as philjo 606W.

Sample B is a density polyethylene film designated as Filgeo 670W.

Sample 1 is a polypropylene film designated as Philgeo 410. Samples A, B, and 2 are obtained from the Phillips Geoanna Division of Geoanna Western Mills, Inc., Wood, Illinois.

Sample C is a high density polyethylene film obtained from Allied Chemical Co., Plastic Film Division, Chicago, IL.

The sample was a blown high density polyethylene film prepared from a pelletized resin called Kemplex 6108, obtained from Kemplex Corporation of Rolling Mead, Illinois.

Samples E and F are high density cast polyethylene films prepared from pelletized resin designated by numbers 7140.7150, respectively, and were obtained from the Electrochemistry Division of E and I DuPont Denemose End Co., Chicago, IL. can get.

Sample G is a cast high density polyethylene film formulated from a pelleted resin designated Amoco 650-B4.

Amoco 650-B4 is obtained from Amoco Chemical Co., Chicago, IL.

Sample H is a cast low density polyethylene film prepared from pelletized low density polyethylene designated USl,N,A,222 obtained from U,S Industrial Chemical Co., Oakbrook, IL.

The data in the table above indicates that untensioned socked polyethylene film made as a blow-molded film from a tubular extruder or as a cast-formed film from a slot die extruder was stored at suitably elevated temperatures. The results clearly indicate that the company will receive substantial growth.

Both low-density polyethylene films and high-density polyethylene films exhibit this property significantly, with polypropylene films simply showing the least elongation after the waxing process.

The sample data above shows that storage temperature has a significant effect on both the rate of elongation or growth and spread of the waxed film.

It is stored at 120'F for 16 hours and stored at 100'F.
This is because the result is greater growth than storage for 0 hours.

Furthermore, this test shows that at storage temperatures below 120°F, the waxed film elongates to 5% in about 1 hour, at 110'F it takes about 10 hours to elongate 5%, and at temperatures below 100°F the same elongation does not occur. It was shown that it could be obtained in about 30 hours.

The growth rate is very slow at normal room temperature of 73,
There was only a 5% film elongation due to storage over time.

When stored under warehouse conditions (90y to 130y) in the summer, the elongation rate of the waxed film is the fastest (60% of the final growth amount) for the newly wax-coated film.
~80% occurs in the first 10-20 hours.

Growth tests were conducted at 100, 110, and 120 temperatures for 500 hours.

The final numbers for percent elongation of the waxed films at the end of the test period were 8%, 8.5%, and 9.6%, respectively.

The degree to which a given polyethylene film must be taut during the waxing operation to obtain maximum dimensional stability during storage and use of the socked film depends on the type of film, the degree of crystallization, the waxing operation and It varies depending on many factors, including the temperature reached by the film during tensioning, the length of time the waxed film is exposed to molten wax before it is cooled sufficiently to solidify the wax, etc.

For example, if the polyethylene is subjected to a waxing and tensioning operation, the film will be at least 130'
When a temperature of It is known to exhibit stability.

Generally, it is not desirable to tension the film by about 20% in the longitudinal direction.

This is because "necking-in" or reduction in width of the film tends to occur under these conditions and is undesirable.

Preferably, when the film is heated to a temperature above 130°C, the degree of tension that must be exerted on the film during meniha wax application to obtain satisfactory dimensional stability rarely exceeds 15% and is simply as described below. It is 6-8%.

Varying the temperature of heating the film between 130'F and below about 210F has a relatively small effect on the amount of tension required for dimensional stability of the waxed film.

However, the time that the film is exposed to molten wax during waxing and tensioning operations has a profound effect on the degree of tension that must be exerted on the polyethylene film to obtain optimum results.

For example, if a polyethylene web is molten wax and is coated with a film of molten wax that is held in liquid form for a sufficient period of time before cooling the wax-coated sheet to solidify the wax, the wax-coated web must be 5 to 9% stressed.

During this time, the wax is melted to obtain optimum dimensional stability so that the wax-coated sheet will undergo less than 2% dimensional change even during long-term storage under summer warehousing conditions.

In contrast, if polyethylene were to be wax coated at commercially acceptable speeds in a high speed waxing apparatus such as that shown in the accompanying drawings, the polyolefin web would be filled with molten wax, the excess wax would be metered out, and the excess wax would be metered out. The time for tensioning the waxed film and finally cooling the molten wax to a solid will be only a fraction of a second.

These conditions have shown that the polyolefin web must be stretched 10-18% during the waxing operation to obtain dimensional stability of the product within a given range.

The effect of the linear speed of the wax applicator (inversely proportional to the contact time of the polyolefin web to the molten wax) is set forth in Table 1 below.

This table provides data on the dimensional stability of waxed polyethylene webs subjected to varying degrees of tension during waxing operations.

In each case, the wax was molten paraffin below 135-140, the bath was maintained below 220, and the polyethylene web was a 1.5 mil thick dense film.

Further, the waxed sheet was stored at 120°C for 10 days before dimensional changes were observed.

Dimensional changes are measured in the direction of machine movement.

From the data in the table above, it can be seen that the polyethylene web becomes more taut in order to obtain dimensional stability of the waxed sheet if the waxing machine Q speed increases or conversely if the contact time of the polyethylene to the molten wax decreases.

As previously mentioned, the minimum degree of tension in the polyethylene during the waxing operation to obtain a satisfactory dimensionally stable sheet is between 5 and 8.
% range.

Because this minimum tension can only be used when the wax coating is held in the molten state for more than 30 seconds or so, production of waxed polyethylene sheet material on a commercial basis under these conditions is extremely economical. You will be at a disadvantage.

Practically speaking, therefore, this operation is preferably carried out in a wax applicator that coats the polyethylene web at several hundred feet per minute.

This reduces the contact time between the web and the molten wax to a fraction of the time.
Since the contact time is effectively reduced to seconds, it is necessary to increase the degree of tension in the polyethylene web to compensate for the short contact time.

Reduce the wax application speed to about 500 feet per minute and apply 10-18% to the polyethylene web during the wax application process8.
It has been found that when stretched under a certain degree of tension, the resulting waxed sheet exhibits dimensionally stability within the desired range of less than 2% under summer storage conditions.

These results range from about 0.0005 inches to about 0.005
It has been found to be applicable to polyethylene sheets with thicknesses in the inch range.

Films approximately 0.001 to 0.0025 inches thick are desired for high volume packaging operations performed on high speed automatic packaging equipment.

crystalline petroleum wax with a melting point of 135-140'F
Optimum working conditions for applying ax) to 1.5 mil high density polyethylene film are as follows:
Maintaining the temperature at 0 T, wax is fed to the web at 400 to 450 feet per minute, excess wax is removed with a conventional wire-wound rod so as to leave 4.5 pounds of wax on the web, and During the wax application process, as mentioned above, 12
Tighten the web by about ~15%.

The sheets thus produced have excellent dimensional stability and very low vapor permeability.

The sheet thus produced has excellent uses as a grain encapsulating material.

It is clear that the invention described in detail above is capable of various modifications without departing from its spirit.

Therefore, the invention is limited only by the scope of the claims.

The embodiment will be described below.

(1) In the claimed method, the steps of contacting, measuring, tensioning, and cooling are carried out at a speed of between 200 and 500 feet per minute and between 10 and 18 of the film length with said tensioning. The method implemented in the expansion between %.

(2) The method of (1) above, wherein the weight of the wax composition after the measuring step in the method of (1) above is 93 to 6 pounds per ream.

(3) In the above method (2), the thickness of the polyethylene film is o, ooi to 0.0025 inch.
)the method of.

(4) The method of (3) above, wherein the polyethylene film has a surface treated to be sensitive to fluid coating.

(5) applying a molten petroleum wax composition to at least one side of a polyethylene web having a thickness of from 0.0005 to 0.005 inches, maintaining the wax coating in a molten state and depositing the coated polyethylene web on at least one side of the coated polyethylene web; holding the polyethylene web at a temperature between about 130 °C and the softening temperature of the polyethylene while mechanically tensioning it in the machine direction by an amount of 20% to 20%; A method for obtaining a dimensionally stable wax coated polyethylene web suitable for use in high speed packaging operations comprising the steps of cooling the coated and taut web.

(6) The method of (5) above, wherein the wax composition is applied to a surface-treated polyethylene web moving at about 200 to 500 feet per minute, and the coated polyethylene web has a content of 12% to 15%. The method of (5) above, in which the tension is applied by the amount of .

[Brief explanation of the drawing]

The drawings show one embodiment for carrying out the present invention. Explanation of symbols, 10: polyethylene web, 17; application roll, 20; molten wax, 22: weighing lot, 27
, 28; cooling drum.

Claims (1)

Claims: 1. (a) A temperature sufficiently above 130"F such that a polyethylene film having a thickness of 0.0005 to 0.005 inches reaches a temperature between below 130"F and the softening point of the film. (b) measuring excess wax from the film so that on at least one side of the film, 1 to 10 pounds of wax composition is present in 3000 square feet of the film; (C) tilting the film in the machine direction by 5 to 20% of the original length of the film while in contact with the molten wax composition; (d) applying the wax and cooling the stretched film so that the wax composition coating hardens. Method.