US2474619A - Heat-sealable sheet material - Google Patents

Description

June 28, 1949. R. A. FARRELL E-rAl.

HEAT-SEALABLE SHEET MATERIAL Filed Jan` 22, 1944 Patented June 28, 1949 HEAT-SEALABLE SHEET MATERIAL Robert A. Farrell and Charley L. Wagner, Me-

nasha, Wis., asslgnors to Marathon Paper Mills Company, Rothschild. Wis., a corporation of Wisconsin Application January 22, 1944, Serial No. 519,391

10 Claims. l

This invention relates to a heat-scalable sheet material not having any exposed coating material on its outer surfaces. More speciiically, this invention relates to a heat-scalable sheet material having a composition provided internally of the sheet material which is not normally exposed, but which is activated and brought to the surface to provide an adhesive film which forms a seal upon application of heat and pressure to any suitably selected area desired to be sealed.

Further details and advantages oi the invention will be apparent from the following specification and drawings wherein:

Figure 1 is a perspective view of our heatscalable sheet material partly broken away to show the components thereof.

Figure 2 is an enlarged sectional view taken on lines 2--2 of Figure l,

Figure 3 is a plan view of a bag made of our heat-scalable sheet material,

Figure 4 is an enlarged fragmental sectional view taken on lines 4-4 of Figure 3.

Figure 5 is an enlarged fragmental sectional view of the upper portion of Figure 4, and

Figure 6 is an enlarged sectional view taken on lines 6-8 of Figure 3.

Hitherto available heat-sealable sheet mate rials have been provided with a surface coating of suitable compositions which are activated or softened by action of heat when a seal or seam is to be formed. Such sheet materials are dimcult to handle prior to use due to their pressuresensitive properties when they are stacked or rolled up as the outer coating composition has a tendency to cause blocking or sticking together of the contacting sheets or layers. Furthermore, such prior external coatings cause diiiiculty when the sheet materials are handled by wrapping machinery as the coating may adhere to machine parts or scrape oil' and accumulate on moving parts and thus prevent eiilcient operation. There are also many sticky and soft types of heatscalable compositions that could not be possibly used as exposed external coatings that can now be used in heat-scalable sheets made in accordance with our invention as the composition in our sheet is not exposed and will not cause blocking or cause adhesion of any contacting materials.

These disadvantages and dliiiculties have been eii'ectively overcome by our invention as we produce an eiiicient heat-scalable sheet made of superposed plies of sheet materials without having any external coating thereon of any kind. The sheets are united by an intermediate continuous film formed of a suitable composition and of suitable thickness on basis weight (pounds per 480 sheets size 24 x 36 in.) so that upon application of heat and pressure to any selected area thereof an adhesive iilm will be generated on the outer surface of one of the sheets to form an adequate seal or bond. According to one embodiment of our invention, we utilize a sheet material, indicated by numeral 3 in Figures 1 and 2, which is characterized as the fbase sheet. and a relatively porous sheet material I, united by an intermediate smooth. continuous, uniform thermoplastic film 2 formed of a suitable composition. An important characteristic of sheet I is that it is relatively porous and permeable as compared with the base sheet I in regard to the intermediate layer 2 when in softened or molten condition, so that when the combined sheet is subjected to heat and pressure, the lm 2 will migrate, pass er strike through the porous sheet to provide a sealing adhesive lm on the surface of the porous sheet in sufllcient amount to form a strong seal, seam or bond at any area where desired. The porous sheet not only permits the adhesive illm to migrate to the surface of the sheet, but it also serves to reinforce the adhesive film thereby preserving its continuity when the sheet is creased. folded or seamed. The continuity of the intermediate film is thus not broken or impaired by handling, use, or when the sheet is converted into containers and receptacles, or during any packaging operations. thereby tending to retain the initial vapor and moistureproof and other protective properties of the combined sheet. Our sheet material thus can be regarded as comprising a relatively impermeable base sheet l which is coated with a film of thermoplastic adhesive film 2 having applied thereto a normally non-removable relatively porous cover sheet I to avoid exposure of the thermoplastic adhesive and consequent blocking or sticking. the cover sheet having such physical characteristics that when heat and pressure are applied to the combined sheets, the

thermoplastic adhesive will migrate through the cover sheet in sufficient quantity to form an external seal.

Our sheet material may be used to form heatsealable bags, receptacles, containers, cartons, packages, linings for receptacles, tubes and the like of any desired construction. In forming bags, for example, from our sheet material l0, the longitudinal edges 32 of a sheet of suitable dimensions may be folded so as to form an overlapped longitudinal seam having a width B as shown in Figure 3. The sheet is folded so that the dense sheet 3 is on the exterior of the bag and the porous sheet I is presented on the interior surface of the bag as shown in Figure 4. The longitudinal seam is formed by heat sealing the sheet to itself as illustrated in Figure 6 or by use of any suitable external adhesive. The bottom seam 3i is then formed by applying heat and pressure to the bottom edge portion of the bag. The seam is shown in larger scale in Figure 4. Any substance desired to be packaged is then placed within the bag and then the upper seam 30 is formed by applying heat and pressure to the area A. As shown in Figure 5, in forming the top and bottom seams superposed areas of the porous sheets are brought in face-to-face relation and the molten lm 2 at these areas is driven through to the interface between the contacting areas of the sheet I so as to form a very strong and tight seam.

In practical production of our heat-sealable sheet material we apply the homogeneous thermoplastic heat-sealing composition preferably as a smooth continuous flexible coating of suitable uniform thickness on the base sheet by any sultable means and under such controlled conditions as to prevent formation of a surface film on the exposed face of the porous sheet. We may apply our molten adhesive composition between the hase sheet and cover sheet by means of suitable rotating rolls adjusted so as to provide a controlled and predetermined thickness of film between the sheets. The combined sheets may be chilled to controlthe degree of penetration of the adhesive therethrough. The viscosity and physical characteristics of the adhesive composition may also be suitably controlled to prevent migration of the composition through the porous sheet when the sheets are combined with the adhesive. Instead of applying the adhesive as a continuous film we may apply the composition only in certain predetermined areas and of any suitable con tour. The composition, for example, may be applied in the form of bands or stripes at the margins or other portions between the sheets so that the sheets are heat-sealable only in such areas. The adhesive composition may also be applied by means of knurled or specially contoured rollers so as to apply the adhesive in suitably spaced areas or in the form of discrete particles or spots instead of in a continuous film form. In such application a suiilcient quantity of the adhesive is applied so that it will migrate through the porous sheet to form a seal or bond.

Any suitable base sheet material 3 is selected depending upon the particular usage of the final product, such as paper, paper board, regenerated cellulose, glassine, parchment paper, rubber hydrochloride, cellulose acetate, ethyl cellulose. vinyl resins, any suitable synthetic resin foils, metal foils and the like. The sheet material may be treated so as to impart any desired additional characteristics thereto such as greater imperviousness to the adhesive used. wet-strength,

4 greaseproofness and flexibility. In the case of paper, it may be suitably coated and supercalendered for printing purposes.

The sheet l is selected so as to be relatively porous as compared with the base sheet 3, and of such structure as to permit migration of the molten or softened intermediate layer 2 to the surface of the porous sheet, through the material of the sheet itself or through any interstices, pores. channels, openings or perforations present in the sheet i. In other words, the sheet l is selected so as to have suitable physical or structural characteristics so as to permit the molten or softened adhesive layer 2 to migrate or pass outwardly to the exposed surface of the porous sheet. Depending upon the type of porous sheet selected, the molten adhesive will migrate either through the substance of which the sheet may be made or through any lnterstices, pores, channels, slits or openings existing in the sheet. Light weight paper tissue, for example, has a porous structure formed by interlacing of cellulosic fibers which permits the molten or softened adhesive to pass through the sheet readily.

Our invention, however, is not restricted to the use of paper tissue sheets. We may use any suitable type of porous, woven or reticulated sheets, such as woven and knitted fabrics, netting, and the like. We may also use comparatively dense or impervious sheets, such as parchment paper, glassine. regenerated cellulose, and even metal foils, by providing slits, holes, or openings of suitable dimensions and suitably distributed throughout such sheet materials or in selected and predetermined areas so as to permit the molten or softened adhesive layer 2 to pass through such openings. The expression porous sheet" or cover sheet is intended to include any of the previously described sheets which permit the softened or molten adhesive layer 2 to migrate to the surface thereof in sufficient amount to provide an adhesive sealing film on the outer surface of the porous sheet. We prefer to use a porous sheet made of light weight paper tissue relatively lighter in weight than the base sheet, for example, less than 20 lbs. paper sulphite tissue. Such tissue sheet is comparatively porous with respect to the base sheet so as to permit the adhesive layer to migrate differentially in greater amount by weight per unit weight of sheet through the porous sheet rather than the base sheet so as to generate an adhesive nlm on the outer surface of the porous sheet. The porous paper sheet may be treated if desired with urea-formaldehyde resins, or melamine resins, in small amounts, say 1 to 5% by weight, to increase its wet-strength without however affecting its porosity and other original physical characteristics. Both the base sheet and porous paper sheet may be wax-sized or dry-waxed to increase their waterproofness, moldproofness, wrapping machine workability, etc.

In any particular combination of base sheet and porous sheet the intermediate adhesive layer is of such character that upon application of heat and pressure to the combined sheet the intermediate layer upon melting or softening will be driven or migrate differentially through the porous sheet and penetrate to the surface thereof, rather than tend to migrate through the base sheet which resists the migration of the adhesive therethrough as it is relatively more imperious and/or dense than the porous sheet. The adhesive, in other words, will take the path of least metallic soaps such 5 resistance and will penetrate through the porous sheet and only partially, i! at all, through the relatively denser base sheet to generate an adhesive sealing film on the surface of the porous sheet.

The sheet I may be treated so as to permit migration of the adhesive only at certain predetermined areas. This may be accomplished, for example, by lacquering a porous paper sulphlte tissue sheet in certain predetermined areas so that the adhesive will not migrate through the sheet at such treated areas. A dense type of sheet may also be provided with suitable openings, slits, or pinholes at certain predetermined areas through which the adhesive may migrate, but not elsewhere.

We ind it advantageous to form the intermediate adhesive nlm so as to have a basis weight of atleast about 1 t to 2 times or preferably more than the basis weight of the porous sheet when using, for example, a paper base sheet of 17 lb. sulphite and 9 1b. porous sulphite paper sheet. When such thickness of the intermediate film is provided there will be sufficient adhesive composition to bond the sheets together, andalso upon application of heat and pressure, the intermediate composition will penetrate and saturate the porous sheet to such extent as to migrate to the surface and form a suitable bonding lm at the outer surface thereof.

Suitable thermoplastic intermediate adhesive layers which we may use are selected or blended microcrystalline waxes; microcrystalline waxes having one or more added ingredients such as various elastomers, resins, gums, rubber, synthetic rubber, isobutylene and butylene polymers, as aluminum soaps of the higher fatty acids as aluminum stearate, oleate or palmitate in amounts from 1 to 30% by weight; paramn wax containing any of the mentioned ingredients added thereto and in about the same amounts; cellulose derivative compositions; synthetic resins, such as phenolformaldehyde resins, urea-formaldehyde resins, vinyl resins; asphalts: natural gums; proteincontaining compositions such as zein; and casein. 'I'hese compositions are utilized for combining and adhering the base sheet to the porous sheet in any known manner, as previously explained, so as to control selectively the degree of penetration of the composition into the base and relatively porous sheet. When using thermoplastic hot-melt cornpositions having wax as the base ingredient, we may chill the combined sheets at the point of combining so as to control penetration or migration of the composition through both combined sheets. The ingredients of the composition used may be suitably selected and compounded so as to have suitable viscosity so as to be non-penetrating with respect to the sheets to be united during the uniting operation. The conditions under which the sheets are combined, such as speed of uniting, temperature of application of the adhesive, chilling of the combined sheets also can be controlled in any known manner to prevent penetration. In this way we obtain a heat-sealable sheet which has a continuous flexible uniform layer of the intermediate sealing composition without any of the composition being present on the outer exposed surfaces of the sheet. We may retain the original unimpaired physical surface characteristics of the sheet material used so that they can be printed, coated, glued or treatedin any desired manner without disturbing previously com# provides a sealing means only upon application o! heat and pressure to selected areas of the coinbined sheet.

The following are typical specific examples of our sheet material, the numerals preceding each component being the same as in the drawings,

weights being given per ream (480-24 x 36) 3% aluminum stearato, 5% es-teruguI-n-a-nd 3 aluminum stearate, 5%

. 3% aluminum stearate, 5%

. 97% by wt. microcrystalline-wa-ltfei COMPONENT Example 1 p Pounds weight per ream Porous dry-waxed sulphite tissue paper 13.2 Microcrystalline wax M. P. -160 F.-- 19.3 High wet strength bleached kraft paper-- 33.5

Total 66.0

Example 2 Pounds weight per ream Porous sulphite tissue paper 9.0

92% microcrystalline wax M. P. 145 F.,

by wt 22.0 One side clay coated paper 40.0

Total 71.0 1 Example 3 Pounds weight per ream Porous sulphite tissue paper 9.0

ester gum, and 92% microcrystalline wax M. P. 145 F.,

by wt 20.0 Supercalendered sulphite paper 17.0

Total 46.0

Example 4 Pounds weight per ream Porous dry waxed sulphite tissue paper-- 11.0

ester gum, and 92% microcrystalline wax M. P. 145 F.,

by wt 25.0 Regenerated cellulose 20.0

Total Example 5 Pounds weight per ream Porous sulphite tissue paper 9.0 3% aluminum stearate, 5% ester gum, and 92% microcrystalline wax M. P. F., by wt 25.0 Highly plasticized glassine 30.0

Total Example 6 Pounds weight per ream Porous sulphite tissue paper 9.0

145-7 F. and 3% by wt. aluminum stearate 19.0

Highly hydrated greaseproof sulphite paper 17.0

Total 45.0

2. 3% aluminum stearate, 5% ester'gum. and

92% microcrystalline wax M. P. 145 F., by wt. 30.0

3. 0.016 in. machine calendercd paver board 200.0

'rotti 239.0

Our sheet materials are suitable for making heat-scalable containers and for packaging or wrapping any desired articles. Overlapped portions of the container or wrapper can be sealed .by applying heat and pressure thereto as previously explained to form a very strong and tight seal. inasmuch as our intermediate nlm is not exposed, any materials packaged in our sheet material will not come into direct contact with the sealing film. In the previous types of externally coated heat-scalable sheet materials there was a tendency for these coatings to peel and crumble, particularly at low temperatures prevailing for packaging and storing frozen foods. thereby contamlnating the packaged foods. Our inner film is protected against damage, puncture, abrasion, adhesion of foreign substances. dirt. etc. by being covered by the porous sheet. Our sheets will not block or stick together since they have no external coatings to cause adhesion. Both outer sides of some of our laminated sheets may be printed if desired. Usually only the exposed face ofl the base sheet is printed for packaging purposes.

Our combined sheet material has many characteristics which make it highly suitable as a container or wrapper for foodstuils. It is highly moistureproof in both fiat condition as well as after folding or scoring as the adhesive layer is supported by the porous sheet and is highly flexible, water and moistureproof. Our composite sheet is very pliable, flexible and easily folded. It has a little spring-back as compared with ordinary sheets when folds are made during packaging operations, in both manual and automatic packaging operations. When our sheet material is folded it tends to remain ln the folded condition and does not resist bonding when seams are formed. Thus a minimum of heat is required for forming seals at the overlapped portions and the `packaged contents are thus less likely to be deteriorated by the heat applied. Some materials such as yeast, for example, are very sensitive even to slight heat. Our sheet materials provide very effective heat-scalable wrappers for yeast. Such yeast packages have excellent keeping qualities and longer shelf life than prior packages. n account of the flexibility and continuity of our intermediate film our sheet material produces square and well formed packages. No disruption of the intermediate film will occur at the corners of the folds when packages are made as the porous sheet serves to reinforce and protect the intermediate film in those areas where the previous types of exposed coatings are liable to crack and peel during folding and creasing operations, losing their protective qualities.

An advantageous application of our sheet is in the manufacture of heat-sealing labels. In the label printing and die cutting operation the sheet is repeatedly subjected to drastic mechanical pressures. Any exposed coatings produced on l 'such equipment would tend to separate and accumulate on the contacting machine parts and progressively build up accumulations which would interfere with the operation of the equipment. By use of our sheet materials these difilculties are entirely eliminated as no coating is exposed in our sheet. Labels made from our sheet material are readily heat-sealed to any suitable surface by application of heat and pressure.

Numerous modifications and other combinations of laminated sheet materials may be made utilizing the essential features of our invention. For example, instead of using a single base sheet we may utilize a suitable base sheet made of two or more plies of sheet materials selected so as to have any desired characteristics. The base sheet may also be provided with a continuous thermoplastic film on both faces to which a relatively porous sheet is united so that such triple-ply sheet will be heat-scalable on either face.

Our sheet materials are suitable ior forming heat-scalable bags, receptaclesl containers, cartons, tapes, labels, tags, pouches, envelopes, tubes, gaskets, caps, bottle closures and the like; -the term "packaging as set forth in the claims is defined to include materials used in the fabricaiton of any of these articles. In making bags, cartons and receptacles of any kind the base sheet can constitute the exposed surface of the package, while the porous sheet provides the inner surface of the container which contacts the materials packaged therein. After packaging the materials the open ends can be readily sealed by application of heat and pressure. either contacting superposed portions of the porous sheet in face to face contact or by sealing overlapped portions in the same manner.

Numerous changes and modications may be made in the specific embodiments of our invention utilizing the essential and significant features of our invention as fully disclosed herein. It is intended to include such modifications within the scope of the appended claims.

We claim:

1. A heat-sealable packaging material comprising in adhered relation a relatively impermeable base sheet material and a relatively porous tissue sheet material adhered to said base sheet by an intermediate flexible thermoplastic adhesive nlm, said adhesive film being confined to the inner surface of the porous sheet and the outer exposed surface of said porous sheet being substantially unchanged from its original characteristics, said film being present in amount so that upon application of heat and pressure to selected areas of the sheet material said adhesive will migrate differentially through said porous sheet at said areas rather than through said base sheet material to generate an adhesive sealing film on the outer surface of said porous sheet.

2. A heat-scalable packaging material comprising in adhered relation a relatively impermeable base sheet material of celiulosic material having a relatively dense structure and a relatively porous cellulosic tissue sheet material adhered to said base sheet by an intermediate flexible thermoplastlc adhesive i'llm, said adhesive illm being confined to the inner surface of the porous sheet and the outer exposed surface of said porous sheet being substantially unchanged from its original characteristics, said film being present in amount so that upon application of heat and pressure to selected areas of the sheet maandere 9 terial said adhesive will migrate differentially through said porous sheet at said areas rather than through said base sheet material to generate an adhesive sealing film on the outer surface of said porous sheet.

3. A heat-sealable packaging material comprising in adhered relation a relatively impermeable base sheet material of paper having a relatively dense structure and a relatively porous cellulosic tissue sheet material adhered to said ybase sheet by an intermediate flexible thermoplastic adhesive film. said adhesive film being confined to the inner surface of the porous sheet and the outer exposed surface of said porous sheet being substantially unchanged from its original characteristics, said film being present in amount so that upon application of heat and pressure to selected areas of the sheet material said adhesive will migrate differentially through said porous sheet at said areas rather than through said base sheet material to generate an adhesive sealing film on the outer surface of said porous sheet.

4. A heat sealable packaging material comprising in adhered relation a relatively impermeable base sheet material of paper board having relatively dense structure and a relatively porous cellulosic tissue sheet material adhered to said base sheet by an intermediate flexible thermoplastic adhesive film, said adhesive film being confined to the inner surface of the porous sheet and the outer exposed surface of said porous sheet being substantially unchanged from its original characteristics, said film being present in amount so that upon application of heat and pressure to selected areas of the sheet material said adhesive will migrate differentially through said porous sheet at said areas rather than through said base sheet material to generate an adhesive sealing film on the outer surface of said porous sheet.

5. A heat-sealable packaging material comprising in adhered relation a relatively impermeable base sheet material of regenerated cellulose and a relatively porous celiulosic tissue sheet material adhered to said base sheet by an intermediate flexible thermoplastic adhesive film, said adhesive film being confined to the inner surface of the porous sheet and the outer exposed surface of said porous sheet being substantially unchanged from its original characteristics, said film being present in amount so that upon application of heat and pressure to selected areas of the sheet material said adhesive will migrate differentially through said porous sheet at said areas rather than through said base sheet material to generate an adhesive sealing film on the outer surface of said porous sheet.

6. A heat-scalable packaging material comprising in adhered relation a relatively impermeable base sheet material of metal foil and a relatively porous cellulosic tissue sheet material adhered to said base sheet by an intermediate flexible thermoplastic adhesive film. said adhesive film being confined to the inner surface of the porous sheet and the outer exposed surface of said porous sheet being substantially unchanged from its original characteristics, said film being present in amount so that upon application of heat and pressure to selected areas of the sheet material said adhesive will migrate differentially through said porous sheet at said areas rather than through said base sheet material to generate an adhesive sealing film on the outer surface of said porous sheet.

7. A heat-scalable packaging material comprising in adhered relation a` relatively impermeable dense base sheet material and a relatively porous cellulosic tissue sheet material adhered to said base sheet by an intermediate flexible thermoplastic adhesive film, said adhesive film being confined to the inner surface of the porous sheet and the outer exposed surface of said porous sheet being substantially unchanged from its original characteristics, said film being present in amount at least .about 11A times the basis weight of said porous sheet so that upon application of heat and pressure to selected areas of the sheet material said adhesive will migrate differentially through said porous sheet at said areas rather than through said base sheet material to generate an adhesive sealing film on the outer surface of said porous sheet.

8. A heat-sealable label comprising a relatively impermeable base sheet material, a thermoplastic adhesive coating on said base sheet, and a relatively porous normally non-removable fibrous tissue cover sheet adhered to said thermoplastic adhesive coating, said adhesive coating being confined to the inner surface of said porous cover sheet and the outer exposed surface of said porous sheet being substantially unchanged from its original characteristics, said adhesive coating being present in amount of at least about 1% times the basis weight of said tissue cover sheet so that upon application of heat and pressure to the label said adhesive coating will migrate differentially through said cover sheet rather than through said base sheet material and in sumcient amount to generate an adhesive sealing film on the outer surface of said cover sheet to aix the label to a supporting surface.

9. A heat-scalable label comprising a relatively impermeable base sheet material of cellulosic material. a thermoplastic adhesive film on said base sheet and a relatively porous normally non-removable cellulosic fibrous tissue cover sheet adhered to said thermoplastic adhesive film, said adhesive film being confined to the inner surface of said porous cover sheet and the exposed surface of said porous cover sheet being substantially unchanged from its original characteristics, said adhesive nlm being present in amount of at least about lVgAtimes the basis weight of said tissue cover sheet so that upon application of heat and pressure to the label said adhesive film will migrate differentially through said porous cover sheet rather than through said base sheet material to generate an adhesive sealing film on the outer surface of said porous cover sheet to aiiix the label to a supporting surface.

10. A heat-scalable label comprising a, relatively impermeable base sheet material, a. thermoplastic adhesive film on said base sheet and a relatively porous normally non-removable cellulosic fibrous tissue cover sheet adhered to said thermoplastic adhesive film, said adhesive film comprising microcrystalline wax, said adhesive film being confined to the inner surface of said porous sheet and the outer exposed surface of said porous cover sheet being substantially unchanged from its original characteristics, said film being present in amount of at least about 1% times the basis weight of said tissue cover sheet so that upon application of heat and pressure to the label said adhesive film will migrate differentially through said porous cover sheet rather than through said base sheet material to generate an adhesive sealing film on the outer surface of' said 11 porous cover sheet to am! the label to a. supporting surface.

The following references are of record` in the ROBERT A. FABRELL. CHARLEY L. WAGNER.

REFERENCES CITED 111e o! this patent: ,A

Number Number Name Debe Peterson Feb. 27, 1917 Church et al. Oct. 6, 1931 Bennet. Jr. 31111.23, 1934 Prlndle Dec. 11, 1934 Reynolds June 4, 1935 Abram; et al Sept. 15, 1936 Stelkens Sept. 22, 1936 Reid ---f Feb. 23, 1937 Cunnington Dec. 19, 1939 MacDonald Jan. 2, 1940 Grant et Bl Sept. 22, 1942

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