US3235443A - Process for forming transparentized paper containing cotton linter fibers and paper thereof - Google Patents

Description

United States hatent C PRGCESS FQR FORMING TRANSPARENTHZED PAPER QONTAINKNG CQTTON ENTER FIBERS AND PAPER THEREUF Edwin 'Gardner Greennran and Paul Thomas Kitze, Nowell, Wis assignors to Kimberly-(Hark Corporation, Neenah, Wis, a corporation of Delaware N Drawing. Filed July 15, 1963, Ser. No. 295,233

9 Claims. .(Cl. 162-135) This invention relates to an improved transparentized paper and production methods therefor. More particularly, it relates to the production of improved translucent tracing or diazo intermediate papers containing cotton linters as an economical replacement for the more expensive all rag fibers employed in conventional rag tracing papers.

Transparentized tracing papers for engineering drafting and diazo intermediate use, traditionally have been made from well-beaten all rag'fibers, internally sized with rosin, top sized with glue in a loftirig operation, and subsequently made translucent by impregnation with an oil or resin in organic solvent, or by treatment with a hot melt resin.

Preparation of conventional all rag fiber base papers for transparentized paper is inherently difficult. Fiber formation in the sheet must be clear and uniform. Sizing and density must be rigidly controlled to permit subsequent solvent impregnation and yet hold out diazo solution or ink and provide a good erasing surface.

An object ofthe present invention is to provide a lower cost transparentized or translucent sheet containing cotton linters as the principal fibers in the furnish.

A further object is to provide a process for transparentizing a cotton linter base sheet without the need for supplementary internal or surface sizing.

Another object is to provide a process for transparentizing paper which utilizes an aqueous emulsion system and a single saturation srep'ro' obtain transparency, hardness, and good sizing properties.

Conventional tracing papers are made from high quality, strong rag fibers normally obtained by pulping high grade cotton rags such as white table cuttings from shirt or similar garment factories. The resulting fibers are relatively easy to hydrate and fibrillate and in the process of preparing base sheets are well beaten or highly refined to produce well-formed hard sheets of high strength subsequently treated to obtain translucency therein. A high degree of refining is necessary both to obtain good, clear formation and to develop suflicient fiber-to-fiber bonding to provide the necessary high strength. Without initial high strength the resulting product is unsatisfactory since the solvent-based resins or oils used in the conventional transparentizing step tend to weaken the sheet to some extent.

Tracing or diazo intermediate papers are designed primarily to serve as masters in some type of photochemical copying process, such as blueprint or diazo processes, therefore, these papers should desirably have the ability to transmit ultra-violet light readily. This is one of the main reasons for transparentizing the paper. Since extraneous coloring matter in these papers absorbs ultraviolet light strongly, 'it is important to eliminate such materials from the paper if possible. Many of the bleached rag cuttings used for conventional rag fiber 3,235,443 Patented Fee. 15, 1966 "ice pulps now contain fluorescent dyes, so-called optical bleaches, whose absorption band nearly always coincides with those of the sensitizing chemicals used in photochemical reactions. Thus, the presence of such dyes cuts down detrimentally on the speed of the reproduction process. At the present time, it is becoming increasingly difficult to obtain rag cuttings free of such dyes. Since the tracing papers of this invention avoid using these traditional rag fibers in the furnish, the possibility of having such undesirable dyes present is eliminated.

Because bleached cotton linters are much less expensive than the bleached rag fibers used in conventional tracing papers, attempts have been made in the past to substitute these more economical linters for the traditional more expensive rag fibers. However, such attempts have been largely unsuccessful. Linters have difierent characteristics than regular textile length cotton fibers used in rag papers. Linters do not hydrate easily, and even when they are beaten severely in an attempt to obtain good binding properties and tight formation, a sheet formed from cotton linters is not of sufficient hardness and strength for transparentizing by conventional solventbased materials. Because they do not hydrate easily and develop good binding properties, substitution of cotton linters for rag fibers in conventional tracing papers and the like has been satisfactory, heretofore, only up to the extent of about 10% to 15% of the total fiber content in the furnish.

By the process of this invention it is now possible to use up to 100% linters, or other short, high alphacellulose content fibers, and obtain satisfactory tracing papers comparable in physical and optical properties to the higher priced all rag fiber papers. While considerable savings are possible in the original cost of the fibers themselves, it was found that additional savings could be obtained with a cotton linter sheet because the higher freeness of such fibers usually permits better drainage, easier handling on the paper machine, and potentially higher paper machine speeds. The initially short cotton linter fibers also permit good formation. The base sheets thus formed do not have high strength, even when well-beaten, but since the transparentizer employed in this invention acts as a binder for the fibers in the finished sheet, initial high sheet strength is not necessary. A minor amount of longer and stronger fibers may be added to build up other strength properties, such as tear, without departing from the inventive concept taught herein.

The transparentizers employed in this invention are aqueous emulsions of clear, film-forming polymers, instead of the conventional transparentizers employed for all rag papers, the latter including oil, resins in organic solution, or hot melt resins. It was found that clear filmforming polymers not only transparentize the cotton linter ba-se paper, but also act as binders for the fibers and perform the necessary sizing function as well. Conventional rag base papers do not saturate well with aqueous emulsions because such papers are normally too hard and close in formation and resist penetration by aqueous media.

While it was found that a large number of aqueous emulsions of film-forming resins, including many wellknown synthetic latices, were capable of transparentizing the waterleaf cotton linter base paper, those comprising acrylic material as a major ingredient are preferred because of their light color and superior heat and light aging properties. Although waterleaf cotton linter papers treated with aqueous emulsions of many of the acrylate polymers now commercially available were transparentized and sized to a satisfactory degree, many of the papers so treated had a relatively soft hand, which is suitable for some uses but lacked the snap or rattle generally characteristic of, and desirable in, hard-beaten all rag papers. For example, when aqueous emulsions of soft, thermoplastic acrylate resins are employed as the saturant, the paper is satisfactorily transparentized but is relatively limp. Soft thermoplastic resins of this type are wellknown and include alkyl acrylate polymers and copolymers and copolymers of alkyl acrylates and styrene. While such paper is suitable for use as a reproduction paper, it is not generally considered satisfactory for tracing paper use because of its lack of hardness and stiffness. Aqueous emulsions containing harder acrylic resin mix tures and especially resins of the thermosetting type do produce papers which have the desired hardness and stiffness commonly associated with conventional tracing paper. Accordingly, hard acrylic resins of the thermosetting type comprise the preferred embodiment when tracing papers are desired.

Compositions of this latter type are described in detail in US. Patent 3,033,811, which issued May 8, 1962. As described therein, these compositions are prepared by mixing (1) an aqueous dispersion comprising a copolymer of (a) at least one monomer selected from the group consisting of styrene, vinyltoluene, acrylonitrile, and acrylic and methacrylic acid alkyl esters in which the alkyl group contains from 1 to 8 carbon atoms and (b) a monomer selected from the group consisting of acrylamide or methacrylamide, and the formaldehyde reaction products of said amides including methylol and methoxymethyl derivatives, with (2) a water-soluble thermosetting aminoplast, and (3) a volatile tertiary amine. Preferably, but not necessarily, the mixture may also include (4) an additive which is a dispersant in the form of an amine or ammonium salt of a polymeric carboxylic acid.

As noted in the patent, the aqueous dispersion thus prepared is preferably, but not necessarily, deionized if Watersoluble ionizable compounds are present.

Suitable water-soluble thermosetting aminoplasts include the methylol derivates of urea, cyclic ethylene urea, cyclic propylene urea, thiourea, cyclic ethylene thiourea, melamine, alkyl melamines, aryl melamines, guanamine, alkyl guanamines, aryl guanamines, and mixtures thereof.

A preferred class of Water-soluble aminoplasts are the condensates of formaldehyde and the reaction products of urea and malamine with a lower alkanol, such as methanol. These condensates are heat-convertible to insoluble cross-linked polymers. The condensates of methoxymethylureas and formaldehyde are particularly suitable.

Typical volatile tertiary amines are the trialkylamines containing 3 to 12 carbon atoms, triethanolamine, and N- methylmorpholine. Triethanolamine and triethylamine are particularly suitable.

For the dispersant, the ammonium and lower amine salts of polyacrylic and polymethacrylic acids and similar salts of the polymeric acid obtained by copolymerizing methyl vinyl ether with maleic anhydride are suitable. A particularly preferred mixture employs the ammonium half amide salt or the diammonium salt of a diisobutylene-maleic anhydride copolymer having a number average molecular weight of from 2000 to about 4000.

A coalescent such as isophorone, Z-ethyl-hexanol, or tributyl phosphate may also be added to aid fusion of the resln.

As noted previously, cotton linters do not hydrate or fibrillate easily, hence even when well-beaten, do not produce the strong paper normally considered necessary for transparentizing. However, paper made from well-beaten linters does have a clear uniform formation, which is essential in producing satisfactory transparentized or translucent paper. Hitherto it had not been possible to obtain a transparentized sheet with the hardness, water resistance and ink acceptance required for tracing papers from a bibulous Waterleaf base sheet such as paper made primarily from cotton linters provides. It has been found unexpectedly that when a relatively weak cotton linter base sheet is impregnated with an aqueous resin emulsion of the type described herein, the resin intrudes between the fibers, filling the voids therebetween to produce an optically continuous sheet, and additionally forming fiberresin-fiber bonds, which when cured, provide the desired strength. At the same time, the cured resin imparts a sizing effect to the finished sheet to make it water resistant, resistant to diazo solvents, and acceptable to ink, while providing a hard, dense sheet resistant to pencil embossing. Thus, the simplicity of the single saturation with an aqueous emulsion system employed in this invention to obtain simultaneous sizing, hardness, and transparency, as opposed to conventional multiple-step sizing and oil or solvent impregnation, results in a highly desirable ease and economy of operation.

To provide a clear uniform formation, the cotton linters, before being formed into a web, should be well beaten to a Canadian standard freeness value of from about to 300. The preferred range of freeness is about to 250.

A wet strength resin such as melamine or urea formaldehyde may also be added to give the web additional strength for subsequent saturation with the aqueous emulsion of the transparentizing resin.

In the saturating step the transparentizing resin should be added in a manner to deposit in the web between 15 and 30 parts of resin solids per 100 parts of fiber. Between 20 and 25 parts of resin solids per 100 parts of fiber appear to give the best results.

In one example of the process of this invention, bleached cotton linters were well beaten to a Canadian standard freeness of about 200, then formed into a waterleaf sheeet having a basis weight of about 12# per 17 x 22-500 sheet ream. The furnish contained about 1%, based on dry fiber weight, of a melamine formaldehyde resin to impart a small degree of wet strength to the sheet. The wet strength was provided to make the sheet easier. to handle during saturation.

The waterleaf paper was then saturated, by conventional means, with an aqueous emulsion containing about 25% solids, of a thermosetting acrylic resin composition.

In this case the saturant composition comprised about 100 parts of a 48% solids deionized emulsion of a methyl methacrylate-ethyl acrylate-methacrylamide copolymer in the ratio of about 52.5:42.5:5.0 respectively, mixed with about 15 parts of an 80% solids aqueous solution of an aminoplast consisting of a methylated melamine-formaldehyde resin, and with about 1 part of triethylamine. Five parts of a coalescent, in this case isophorone, were also used. A dispersant, the ammonium salt of a maleic anhydride-diisobutylene copolymer with a number average molecular weight of 3000, was also added in the amount of about 5.5 parts of a 22% solids aqueous solution.

The saturant was retained by the base sheet in the amount of about 23 parts by weight per hundred parts of the fiber. After saturation, the sheet was dried on rotat-- ing cylinders maintained at about 230 F. The heat.

below. The conventional tracing paper was purchased,

8,2 from an office supply store and consisted of 100% rag fibers apparently transparentized with a phthalic polyester resin from solvent solution. The tracing paper also contained a rosin and alum internal sizing and had an animal glue top size.

It will be noted that the lower cost cotton linter sheet is the equivalent of, or better than, the more expensive conventional rag paper in almost every respect except machine direction fold. However, in this latter property it is still within an acceptable range. The cotton linter sheet shows a marked decrease in fiuoresence, which accounts for its better performance in print speed. It is also noted that the cotton linter sheet ages better and actually increases in fold properties with age. This is probably attributable to additional curing of the resin.

While only one specific embodiment of the inventive concept has been set forth herein, it is understood that the invention is not to be construed as limited thereby, and that any suitable changes, modifications, and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A transparentized paper comprising a Web of cotton linter fibers, which fibers have been beaten to a Canadian Standard Freeness of about 100 to 300, impregnated with a clear polymeric film-forming acrylic resin of the aqueous emulsion type; said resin being present in the amount of 15 to 30 parts resin solids per 100 parts of fiber; said resin being selected from the group consisting of soft thermoplastic acrylic resins and hard thermosetting acrylic resins; said soft thermoplastic resins being selected from the group consisting of alkyl acrylate polymers and copolymers of alkyl acrylates and styrene, and said hard thermosetting acrylic resins comprising a mixture of (1) a copolymer of (a) at least one monomer selected from the group consisting of styrene, vinyltoluene, acrylonitrile, and acrylic and methacrylic acid alkyl esters in which the alkyl group contains from 1 to 8 carbon atoms and (b) a monomer selected from the group consisting of acrylamide or methacrylamide, and the formaldehyde reaction products of said amides including methylol and methoxymethyl derivatives, with (2) a water-soluble, thermosetting aminoplast and (3) a volatile tertiary amine; said resin binding said fiber together in a substantially fiberresin-fiber relationship while substantially filling the voids between said fibers to provide an optically continuous sheet.

2. The transparentized paper of claim 1 in which the 5 resin is a soft thermosplastic acrylic resin selected from the group consisting of alkyl acrylate polymers and copolymers of alkyl acrylates and styrene.

3. The transparentized paper of claim 1 in which the resin is a hard thermosetting acrylic resin comprising a mixture of (1) a copolymer of (a) at least one monomer selected from the group consisting of styrene, vinyltoluene, acrylonitrile, and acrylic and methacrylic acid alkyl esters in which the alkyl group contains from 1 to 8 carbon atoms and (b) a monomer selected from the group consisting of acrylamide or methacrylarnide, and the formaldehyde reaction products of said amides including methylol and methoxymethyl derivatives, with (2) a water-soluble, thermosetting aminoplast and (3) a volatile tertiary amine.

4. The transparentized paper of claim 2 in which the resin is substantially cured.

5. The transparentized paper of claim 3 in which the resin is substantially cured.

6. A process for manufacturing transparentized paper which comprises beating an aqueous suspension of cotton linter fibers to a Canadian Standard Freeness of about to 300; forming from said suspension a waterleaf web comprised of said Well-beaten cotton 1inters; drying said formed Web; saturating said web with an aqueous emulsion of a polymeric film-forming acrylic resin in an amount of from 15 to 30 parts resin per 100 parts fiber; said resin being selected from the group consisting of soft thermoplastic acrylic resins and hard thermosetting acrylic resins; said soft thermoplastic resins being selected from the group consisting of alkyl acrylate polymers and copolymers of alkyl acrylates and styrene, and said hard thermosetting resins comprising a mixture of 1) a copolymer of (a) at least one monomer selected from the group consisting of styrene, vinyltoluene, acrylonitrile, and acrylic and methacrylic acid alkyl esters in which the alkyl group contains from 1 to 8 carbon atoms and (b) a monomer selected from the group consisting of acrylamide or methac-rylamide, and the formaldehyde reaction products of said amides including methylol and methoxymethyl derivatives, with (2) a Water-soluble, thermosetting aminoplast and (3) a volatile tertiary amine; and heating said saturated web sufficiently to dry said Web and cure said resin.

7. The process of claim 6 in which the dried and cured Web is subsequently calendered.

8. The process of claim 6 in which the resin-containing aqueous emulsion is deionized.

9. The process of claim 6 in which about one percent of a melamine formaldehyde resin is added to the aqueous suspension of cotton linter fibers before forming the web therefrom.

References Cited by the Examiner UNITED STATES PATENTS 2,629,295 2/ 1953 Ruchter et a1 9685 2,999,038 9/1961 Drennen et al 162-168 3,033,811 5/1962 Brown et al 260-294 3,105,826 10/1963 Iaggard 117155 OTHER REFERENCES Casey, Pulp and Paper, 2nd Edition, Vol. 1, 1960, Interscience Publishers, Inc., N.Y., page 395.

DONALL H. SYLVESTER, Primary Examiner,

MORRIS O. WOLK, Examiner.

Claims (2)

1. A TRANSPARENTIZED PAPER COMPRISING A WEB OF COTTON LINTER FIBERS, WHICH FIBERS HAVE BEEN BEATEN TO A CANADIAN STANDARD FREENESS OF ABOUT 100 TO 300, IMPREGNATED WITH A CLEAR POLYMERIC FILM-FORMING ACRYLIC RESIN OF THE AQUEOUS EMULSION TYPE; SAID RESIN BEING PRESENT IN THE AMOUNT OF 15 TO 30 PARTS RESIN SOLIDS PER 100 PARTS OF FIBER; SAID RESIN BEING SELECTED FROM THE GROUP CONSISTING OF SOFT THERMOPLASTIC ACRYLIC RESINS AND HARD THERMOSETTING ACRYLIC RESINS; SAID SOFT THERMOPLASTIC RESISN BEING SELECTED FROM THE GROUP CONSISTING OF ALKYL ACRYLATE POLYMERS AND COPOLYMERS OF ALKYL ACRYLATES AND STYRENE, AND SAID HARD THERMOSETTING ACRYLIC RESINS COMPRISING A MIXTURE OF (1) A COPOLYMER OF (A) AT LEAST ONE MONOMER SELECTED FROM THE GROUP CONSISTING OF STYRENE, VINYLTOLUENE, ACRYLONITRILE, AND ACRYLIC AND METHACRYLIC ACID ALKYL ESTERS IN WHICH THE ALKYL GROUP CONTAINS FROM 1 TO 8 CARBON ATOMS AND (B) A MONOMER SELECTED FROMTHE GROUP CONSISTING OF ACRYLAMIDE OR METHYACRYLAMIDE, AND THE FORMALDEHYDE REACTION PRODUCTION OF SAID AMIDES INCLUDING METHYLOL AND METHOXYMETHYL DERIVATIVES, WITH (2) A WATER-SOLUBLE, THERMOSETTING AMINOPLAST AND (3) A VOLATILE TERTIARY AMINE; SAID RESIN BINDING SAID FIBER TOGETHER IN A SUBSTANTIALLY FIBERRESIN-FIBER RELATIONSHIP WHILE SUBSTANTIALLY FILLING THE VOIDS BETWEEN SAID FIBERS TO PROVIDE AN OPTICALLY CONTINUOUS SHEET.

6. A PROCESS FOR MANUFACTURING TRANSPARENTIZED PAPER WHICH COMPRISES BEATING AN AQUEOUS SUSPENSION OF COTTON LINTER FIBERS TO A CANADIAN STANDARD FREENESS OF ABOUT 100 TO 300; FORMING FROM SAID SUSPENSION A WATERLEAF WEB COMPRISED OF SAID WELL-BEATEN COTON LINTERS; DRYING SAID FORMED WEB; SATURATING SAID WEB WITH AN AQUEOUS EMULSION OF A POLYMRIC FILM-FORMING ACRYLIC RESIN IN AN AMOUNT OF FROM 15 TO 30 PARTS RESIN PER 100 PARTS FIBER; SAID RESIN BEING SELECTED FROMTHE GROUP CONSISTING OF SOFT THERMOPLASTIC ACRYLIC RESINS AND HARD THERMOSETTING ACRYLIC RESINS; SAID SOFT THERMOPLASTIC RESINS BEING SELECTED FROM THE GROUP CONSISTING OF ALKYL ACRYLATE POLYMERS AND COPOLYMERS OF ALKYL ACRYLATES AND STYRENE, AND SAID HARD THERMOSETTING RESINS COMPRISING A MIXTURE OF (1) A COPOLYMER OF (A) LEAST ONE MONOMER SELECTED FROM THE GROUP CONSISTING OF STYRENE, VINYLTOLUENE, ACRYLONITRILE, AND ACRYLIC AND METHACRYLIC ACID ALKYL ESTERS IN WHICH THE ALKYL GROUP CONTAINS FROM 1 TO 8 CARBON ATOMS AND (B) A MONOMER SELECTED FROMTHE GROUP CONSISTING OF ACRYLAMIDE OR METHACRYLAMIDE, AND THE FORMALDEHYDE REACTION PRODUCTS OF SAID AMIDES INCLUDING METHYLOL AND METHOXYMETHYL DERIVATIVES, WITH (2) A WATER-SOLUBLE, THERMOSETTING AMINOPLAST AND (3) A VOLATILE TERTIARY AMINE; AND HEATING SAID SATURATED WEB SUFFICIENTLY TO DRY SAID WEB ANC CURE SAID RESIN.