CH616717A5 - Dense paper and process for its manufacture - Google Patents

Abstract

The paper is impregnated with a rigid polymer and a filler. In order to give it good penetration resistance to oils and solvents, the impregnating matter is in a proportion of 8.5 to 50 % by weight, relative to the total weight of the paper, and consists of a mixture of 35 to 90 % of a polymer which has a glass transition temperature of 15 to 60 DEG C and 10 to 65 % of a compatible inert filler. An aqueous dispersion of the impregnating mixture is employed for the impregnation, the excess of which is removed by wringing, after which the sheet is heated to melt the polymer in the sheet. This dense paper is suitable for the manufacture of book covers and as a substrate for separable coatings.

Description

The present invention relates to dense paper and its production method.

Papers having different densities have already been produced for various applications. Low density papers are soft and porous and have high absorption properties unless they have been treated for reduction. Medium density papers are those used for writing, printing and packaging as well as for forming bags and liners. Examples of very dense papers are crystal paper, parchment paper, parchment paper for vegetables, vulcanized fiber paper and super-calendered paper.

U.S. Patent No. 3,839,144 describes an example of dense writing paper. Although this paper is dense and has excellent oil absorption resistance properties, i.e. it can be erased, among other properties, it has certain restrictions. For example, its manufacture is not cheap because it is prepared from a material formed by a very refined dough, up to a predetermined Schopper-Riegler drip index, with the addition of certain quantities of unrefined dough , or by combining alpha or cotton pulp with ordinary pulp, and by advanced refining of combined pulp, before application of the material on the canvas of the papermaking machine. It is found that the water drips relatively slowly from these very refined materials so that the production of a desired dense paper is very difficult at high machine speeds. Consequently, the production of this paper is more expensive than that of other papers. In addition, the maximum thickness of such paper has a limit, and the need for further refining of the pulp also increases the cost of making paper.

Dense papers have certain advantageous properties, in particular high tensile and burst strengths (Mullen test), great folding endurance, good bond between fibers and good resistance to disintegration, good resistance to penetration. oil and solvents, and good abrasion resistance as well as good rigidity. On the other hand, dense papers have low tear strengths, are fragile, have poor dimensional stability as well as poor aging qualities and high manufacturing prices. For example, parchment papers for vegetables and papers formed by the vulcanized fiber process, although dense, have relatively low tear strengths, as do dense papers formed by super-calendering of density sheets average.

In the stationery industry, use has been made of the impregnation of relatively low density papers with polymer resins. However, these papers usually have, before impregnation, densities which vary between 0.38 and 0.45 g / cm3 and can even drop to 0.32 g / cm3. After impregnation, the papers are still relatively porous, although the amount of impregnating resin may exceed 50% of the weight of the paper, based on dry solids. Given its porosity and low density, such a paper is not suitable for the formation of a striking paper allowing erasing and does not have properties of resistance to solvents.

The polymer resins used in the form of coatings and impregnating materials in low density papers are relatively soft and elastic, unlike hard and inelastic polymer resins. The glass transition temperature Tg is a measure of the rigidity or tenacity of a polymer resin film. This temperature corresponds to the value at which a sudden increase in the coefficient of expansion and the specific heat of the polymer takes place. For example, the glass transition temperature of relatively soft and elastic polymer resins is lower

1 "

15

2? ”

2s

1 (1

35

40

45

50

55

60

65

3

616,717

below about 0 ° C. Rigid or tough and inelastic polymers, on the other hand, have glass transition temperatures which range from approximately 15 to 60 ° C.

Papers of 0.5 g / cm3 and above have already been impregnated with rigid polymers and have been found to have certain desirable characteristics. For example, they have better tensile and burst strengths, better resistance to abrasion and disintegration, better resistance to penetration by greases and solvents and better bending endurance. On the other hand, these papers have certain undesirable characteristics which are not suitable for their use in the form of punching papers or when the papers have to be dense. These undesirable characteristics are low tensile strength, poor writing qualities and high brittleness. Since the sheets of dense paper do not accept as much impregnation material as the sheets of porous paper, it is generally believed that the increase in the physical properties of a paper as a result of the impregnation can only be obtained when the sheet is porous and when the resin content of the finished paper exceeds about 50% of its weight.

Tests have shown that the density of a sheet of paper before impregnation and the amount of resin that impregnates the sheet have an effect on reducing the tear resistance that accompanies the impregnation of a paper with a polymer. -rigid. For example, sheets of base paper having various initial densities are impregnated using an aqueous dispersion of a rigid homopolymer of polyvinyl acetate PVAC sold under the trademark "VINAC 880" from Air Products and Chemical Co. , Allentown, Pa, United States of America. The dispersion contains 40% by weight of "VINAC 880". The impregnation is carried out by soaking the sheets in the aqueous dispersion and then passing the sheets between clamping rollers which expel the excess of impregnation material. The sheets are dried for 4 min in a sheet dryer 1 "Williams" paper at 105 ° C, 2 min per side. After balancing for several days, the strength and thickness of each sheet are measured, as well as the tear resistance before and after impregnation. The following results are obtained:

Sample

Density

initial

(g / cm3)

PVAC in leaf,%

Density after impregnation (g / cm3)

Change in tear resistance,%

AT

0.35

48.5

0.58

gain

20%

B

0.52

41.5

0.82

loss

33%

VS

0.56

38.6

0.77

loss

43%

D

0.60

42.1

0.88

loss

37%

E

0.63

30.1

0.85

loss

25%

The foregoing description indicates that when impregnating dense papers with rigid polymers, the tear resistance decreases significantly. This characteristic is unfortunate because other properties of the paper such as tensile strength and burst strength, abrasion resistance and resistance to disintegration have their maximum value when the paper is dense.

U.S. Patent No. 3,634,298 describes (f) (1 a coating composition for paper. This contains a rigid polymeric material (having a glass transition temperature Tg between 29 and 43 ° C) mixed with a clay slip The composition is applied in the form of a coating on a sheet of paper so that it h5 is well glazed.

The invention relates to dense paper having the advantageous physical properties of dense paper without having its drawbacks. This paper, which is defined in claim 1, can be produced cost effectively with relatively high speeds of paper making machines.

It is resistant to oil and solvents, and preferably also to tearing, abrasion and folding.

It is useful for forming book covers or for supporting separable coverings among other applications.

The invention also relates to the process for preparing this dense paper, defined in claim 8.

It is found that the desired properties are obtained when a paper sheet is impregnated, preferably having a dry density in the non-calendered state of approximately 0.45 to 0.70 g / cm 3, with an aqueous dispersion containing essentially a poly-; rigid mother and an inert, compatible load, mixed in predetermined proportions. The impregnation material is dispersed over the entire thickness of the sheet and it forms 8.5 to 50% and in particular approximately 15 to 40% of the final weight of the paper. The filler forms 10 to 65% of the weight of the impregnation material, advantageously 20 to 65% of this weight. The polymer has a stiffness or a hardness in the form of a film, determined by the glass transition temperature, of between 15 and 60 ° C., preferably between 22 and 44 ° C. Advantageous polymers are polyvinyl acetate, polyacrylate and polyvinyl chloride. nylon, in the form of homopolymer and copolymer as well as in the form of mixtures. Advantageous inert fillers are for example clay, calcium carbonate, mica, talc and their mixtures.

The paper according to the invention, preferably having a density) in the finished and non-calendered state of 0.69 to 0.90 g / cm 3 has certain properties which are unforeseen in the case of dense and impregnated papers. For example, the paper according to the invention, once impregnated with a dilute rigid polymer, has a folding endurance which is much greater than that of an impregnated paper; by a rigid polymer only. The impregnation of dense base paper with a rigid polymer normally reduces significantly the tear resistance. However, a base paper preferably impregnated according to the invention surprisingly retains a significant part of its tear resistance and simultaneously has excellent oil penetration resistance properties. The use of an impregnation material containing large quantities. tants of a filler makes it possible to reduce the cost of manufacturing paper by reducing the total quantity of polymer necessary to obtain the desired properties, since the high-cost polymer is replaced by inexpensive fillers. However, although paper is inexpensive to manufacture, it has the advantageous properties of dense paper, the manufacture of which is more expensive.

i

It is desirable that the sheet of paper be impregnated when it undergoes the papermaking operation, for example in a Fourdrinier machine in which a cellulosic paper-forming material is applied to a moving canvas and forms a sheet before its separation of the canvas and its drying. The impregnation step must be carried out after the sheet has been formed and after it has been brought into the coherent state, after at least partial drying, and the sheet can be impregnated after the paper has been dried and completely laminated, for example at ! during a later stage of manufacture. The sheet of paper is advantageously impregnated at the level of the sizing press of the conventional paper-making machine. It is desirable that the density of the sheet is adjusted in a conventional manner so that, before impregnation, its dry density in the non-calendered state is between 0.45 and 0.70 g / cm3 and preferably between 0.54 and 0.69 g / cm3. The sheet advances in an aqueous dispersion which preferably contains 12.5 to 60% and in particular 12.5 to 40% by weight of impregnation material, and

616,717

4

the sheet, after impregnation, is heated so that the material of the papermaking operation. Specialists know associates with the sheet by fusion. that two types of glue presses are widely used in the

During the manufacture of a paper according to the invention, the stationery, and these two types give satisfaction for the imprint

Rigid polymers capable of giving satisfaction are in particular paper during the process of the invention. Polyvinyl acetate copolymer latexes such as 5 can thus be used horizontal and vertical size presses.

“Resyn” 1,105 and 1,255 manufactured by National Starch and In a horizontal press, two opposite rollers rotate

Chemical Corporation, New York, N.Y. and “Vinac” 880 which is on distant axes horizontally and the sheet is advancing verti-

a homopolymer manufactured by Air Products and Chemicals, steadily descending between the rollers which exert a

Co., Allentown, Pa. Suitable polyacrylates are the presses on the opposite sides of the sheet. The imprint material

"Rhoplex" AC 201 and TR 407, manufactured by Rohm and Haas generation, forms a pool between each side of the leaf and the

Company, Philadelphia, Pa. A polyvinyl chloride roller which cooperates with it. In another vertical press suitable is the "Geon" 351 manufactured by B.F. Goodrich Chemi- part, the rollers rotate on vertically distant axes and cal Company, Akron, Ohio. Each of the polymers indicated is the sheet advancing horizontally between the rollers. The commercially available quality roller and it is sold for lower rotates in a channel, takes up the impregnating material.

stationery applications. It should be noted that the polymer can be applied and applied to the underside of the sheet, the material also being a copolymer or can contain certain amounts of impregnation flowing on the top side of the sheet,

other polymers or mixtures of polymers; however, for example by pumping from a reservoir. In both as the glass transition temperature of the device types, pressures from 88 to 438 N / linear cm are jolymer is within the range indicated, must be obtained applied to the sheet which advances between the rollers and these satisfactory results. 20 last cooperate and drive out the impregnation material in the

The inert filler mixed with the rigid polymer for the sheet by removing the excess on the opposite faces.

The formation of the aqueous dispersion is advantageously fine. Whatever the stage of the operation at which is carried out divided and commercially available, of a type sold impregnation, it is important that the mixture of the resin and for stationery. The particular advantageous dimensions of the filler is dispersed throughout the thickness of the sheet so fillers are between 2 and 5 Examples of fillers 25 the invention fully presents these advantages. One obtains minerals which give satisfaction are kaolin clays, not these when the mixture is simply applied under calcium carbonate, mica and talc. forms a coating on the surface of the sheet, for example

The amount of impregnation material contained in the aid of an immersion roller assembly and finished paper device must be within a predetermined range. scraping described in U.S. Patent No.

Thus, the impregnation material should form 8.5 to 50% by weight. 10 3 634 298 and intended for the application of a coating on approximately one of the total finished weight of the paper, in the form of sheets. In such an assembly, the lower periphery of a dry solid third. When the quantity of impregnation material rotates in a channel containing a composition, and the generation is less than the lowest limit, the paper formed upper periphery cooperates with the lower face of the present poor qualities of erasure. On the other hand, being leaf that advances. Thus, the roller picks up the coating under the restrictions imposed on the density of the base paper, channels it and applies it to the underside of the sheet. The thick-

the impregnation of the paper, beyond the upper limit, is its coating is adjusted by passing the sheet over a difficult. The impregnation material is preferably made of a scraper blade which is located downstream of the roller and which does not leave in a weight range of between 15 and 40% approximately. The that a determined quantity of coating on the lower density side of the finished paper and not calendered after impregnation must of the sheet.

preferably be between about 0.69 and 0.90 g / cm3. 40 _

Obtaining the desired physical properties for paper,. Certain conditions must be advantageously respected.

according to the invention requires the dilution of the rigid polymer, in * ees au? ° urs f faction so that the mixture is well within the prescribed limits, by at least one of the mineral fillers d.sperse in the sheet. For example, before impregnation, the t 1.. _ • 1 n - one hundred <- at dry and uncalendered sheet density is advantageously mentioned above. The charge should form about 10 to 65% and from. . n a c <.n m, 1 ^ - 1 ,,

preferably 20 to 65% of the weight of the solids of the material 45 between 0.45 and 0.70 g / cm3. We can adjust the density j ,. , .. T. j.,, .. _ ..... c - according to various techniques well known to specialists. The impregnation. The rest of the weight of this material is formed by ,, ,,, ^ ^

. . . 0. ., ... ,, .. _. j adjusting the density before impregnation is important because,

the rigid resin, so that it forms 35 to 90 and. ,. x '. ,,,. ,,. '„

preferably 35 to 80% of the weight of the material. It is noted that, the third, a dry state in 1 state in Flanders is less than when the percentage discharged decreases below 0.45 g / cm 3, the resulting paper may be too porous. On the other lower limit from the advantageous range, the resistance to 5o Par * 'density in dry and 1 non-calendered state exceeds paper tear decreases a lot. On the other hand, when the °' l ° S / (f; la fe " lf Pf u cannot absorb a quantity

percentage charge exceeds the upper limit of the range "alk's vo ^ l impregnatl ° n P ° Ur qUC ^ papiCT P ° SSde advantageous, resistance to solvents and penetration"

paper oil tends to decrease. Another important step in papermaking according to

The paper according to the invention is prepared by a machine 55 the invention is the adjustment of the quantity of conventional solid matter, for example of the Fourdrinier type. In this machine, present in the aqueous dispersion through which the material passes is deposited on a metal wire which advances and, sheet. For example, the solids content, including after forming a sheet, this is removed from the canvas and the combined weight of the rigid polymer and the filler, should be on a series of heated rollers or cylinders of drying, preferably between 12.5 and 60% approximately of the total weight

Usually the leaf, at least partially dried and r> o of the dispersion. When this content is below the limit before further treatment, undergoes sizing at a lower level, the sheets included in the indicated range of sizing press which is located downstream of the drying rollers. densities (0.45 to 0.70 g / cm3) may not collect as much

During the production of the paper according to the invention, there is sufficient quantity of impregnation material to have the advantages that the impregnation is carried out when the sheet is desired advantages. On the other hand, when the percentage exceeds become consistent after at least partial drying and when it reaches the upper limit, the dispersion tends to be viscous and is practically devoid of its size. Preferably, the resin-filler mixture tends to coat the surface of the sheet sheets is impregnated at the sizing press; however, the density of which is close to 0.70 g / cm 3 instead of ensuring that the impregnation can be carried out later during the impregnation.

5

616,717

The sheet of paper undergoes heating after impregnation so that the material is fixed in the paper by fusion. In a conventional papermaking operation, the sheet is heated to a temperature of about 100 ° C so that it is dried and the rigid polymers whose glass transition temperature is 15 to 60 ° C have been shown to be those , which crack in the leaf at these temperatures.

The process described has certain advantages during the production of paper. For example, the use of a material based on a rigid polymer, very diluted with fillers, tends to suppress any adhesiveness of the impregnation material so that cleaning of the drying drums is facilitated.

The importance of the aforementioned parameters for the manufacture of the paper according to the invention is apparent from the examples which follow. Examples 1 and 2 indicate the most advantageous dilution of the rigid polymeric material by an inorganic filler. Example 3 shows the importance of the rigidity of the polymer. Example 4 relates to the charges which give satisfactory results. Example 5 concerns the adjustment of the density of the paper before impregnation. Example 6 relates to the quantity of impregnation material which is advantageously used for the preparation of the desired properties. Example 7 concerns the nature of the rigid polymer. Example 8 relates to the abrasion resistance properties of a paper according to the invention and Example 9 corresponds to the properties of a paper impregnated with a composition according to the invention, compared with those of a paper coated with the same composition.

Example 1

As base paper, for the determination of the limits of possible dilution of the resin by an inert filler, sheets of unglued paper formed from a mixture of 50% bleached kraft pulp of hardwood and 50% Nordic bleached kraft wood pulp. The paper strength is 84.4 g / m2, and the thickness of a sheet of paper is 140 microns. As the density of the paper can advantageously be indicated in the form of its weight per micron of thickness, it is noted that this density is approximately 0.60 g / cm 3. The impregnation material is prepared by dispersing a fine powder of calcium carbonate with a particle size of the order of 2 microns in water, and by stirring. A finely divided rigid polyvinyl acetate emulsion is mixed with the aqueous dispersion so that the total solid content of the resin and the filler is 40% of the weight of the dispersion. The calcium carbonate used is sold under the designation "Camel White" by Harry T. Campbell Sons Co., Towson, Maryland. The polyvinyl acetate emulsion used

is sold under the brand name “Vinac” 880 by Air Products and Chemical Company, Allentwon, Pa.

The sheets of paper are dipped in the dispersion and, after removal, passed through rubber rollers which remove excess. The leaves are then dried for 4 min at 105 ° C., 2 min per side, in a dryer for "Williams" paper sheets. The leaves are allowed to equilibrate (ripen) for several days before the tests. The tests of resistance to tearing, of bursting Mullen and of folding are carried out according to the TAPPI standards, indicated in table I. The properties of resistance to oil penetration are determined by typing a character on the paper. , with a portable typewriter of the trade, and observation of difficulty or ease of removal of the character by rubbing with an eraser i5 with pencil. Since conventional typewriter ribbon inks contain large amounts of non-drying oil, there is a direct correlation between the fading properties of a paper and its oil penetration resistance properties. The "excellent" result indicates that the entire character-2 (; tère is erased in a few strokes. The "good" result indicates that the character can be observed after a few strokes but that it does not appear with the naked eye when another character is struck over the erased character. A "suitable" result indicates that the erasure is acceptable. A "bad" result indicates an unsuitable erasure.

The solvent resistance properties of the sheets are determined by placing a drop of colored toluene (purple) on the surface of each sheet, and maintaining contact with a predetermined surface for 30 s. The drop of toluene is then wiped with a paper towel and the surface is rubbed with another paper towel saturated with uncolored toluene. The dye remaining on the surface is thus removed so that the penetration of the paper can be determined by observing the presence of the remaining purple dye. A "good" result indicates penetration at several points, but with a light spot, covering less than about 50% of the test area. A "suitable" result indicates a relatively weak spot over most of the test area. A "bad" result indicates that the entire surface is very stained. The "null" result indicates that the stain has completely penetrated to the other side of the leaf.

Table I gives the results of the tests. The XD reference indicates that the test is carried out in the direction of the paper which corresponds to the transverse direction of the machine. The units of measurement and the references of the standards used for the various examples are indicated in Table I.

Table I

Filler and physical properties CaCO3 / polyvinyl acetate

Sample Resistance to Resistance2 Test Tightness to 4 Resistance to 5

CaC03 / TVAC tear in folding

Mullen3

oil solvents

(XD)

(XD)

A6

0/100

80

3171

5.46

excellent excellent

B

10/90

91

3610

5.25

excellent excellent

VS

20/80

112

-

5.25

excellent excellent

D

30/70

105

6013

5.25

excellent excellent

E

40/60

117

5585

5.18

good excellent

F

60/40

95

4435

4.97

good good

G6

70/30

96

3429

4.48

suitable suitable

H *

-

147

111

-

none zero

616,717

4.5 6

paper before processing TAPPI Standard Test no.

T414ts-64, in grams (g)

TAPPI Standard Test no.

T423os-50, in folds until rupture (f) TAPPI Standard Test no.

T — 403, in 105 Pa as indicated previously comparative only

In the above table, it is noted that a sheet of paper has, before treatment (sample H) a tear strength of 147 g. A similar sheet impregnated with a 100% solution of polyvinyl acetate (sample A) has a tear strength of 80 g. However, it should be noted that, when the impregnation material has been diluted with calcium carbonate, at a rate of 10 to 70% as indicated for the

Table II

Filler and physical properties Clay / polyvinyl acetate Sample Clay / PVAC ratio

A * B C D

0/100 20/80 30/70 40/60

Tear resistance (g) (XD)

80 117 114 117

Resistance to bending (f) (XD)

3171

4179

samples B to G, the tear strengths of the sheets decrease but not as much as when the impregnation material contains only polyvinyl acetate. The properties of resistance to solvents and to oil penetration are conserved; despite dilution of the impregnation material with calcium carbonate, up to 70% by weight. In addition, it is noted that the folding endurance of the impregnation material containing diluted resin is greater than that which is measured when the material contains only polyvinyl acetate.

Example 2

The tests of Example 1 are repeated, but kaolin clay is used as mineral filler in place of the calcium carbonate. This clay is sold under the brand name "Hydraprint" of the J.M. Huber Corporation, Huber, Georgia, United States of America. The results of the tests are shown in Table II.

Oil tightness excellent excellent excellent good

Solvent resistance excellent excellent excellent excellent

* comparison only

The above tests show that kaolin clay and calcium carbonate are fillers which have practically the same effect on the properties of a base paper, when they are mixed with a rigid polymer and impregnated in the base paper. based.

Example 3

The base paper of Example 1 is impregnated with a series of polymer-filler mixtures which differ only in the glass transition temperature Tg of the polymer in order to demonstrate the importance of impregnating a sheet of paper with a polymer having a determined rigidity. As indicated above, this temperature Tg is a measure of the rigidity or the toughness of a polymer film. In the example, the polymer is diluted with calcium carbonate at the rate of 60% of polymer for 40% of calcium carbonate.

The results are shown in Table III.

Table III

Elasticity of the polymer, measured by the glass transition temperature, and physical properties - polyvinyl acetate and poly-acrylate

40% CaCO d / 60% polymer

Polymers of the Material of im- Density fi- Tg (° C) trade pregnation,% naie *

(g / cm3)

Tear resistance (g) (XD)

Bursting strength (f) Mullen (XD)

Resistance to bending (f) (XD)

Oil tightness

Resistance to polyacrylate solvents "Rhoplex" B-85 ** 26.3 "Rhoplex" AC201 32.7 "Rhoplex" TR407 28.3 "Rhoplex" B 15 26.3 "Rhoplex" E49 ** 29.1

0.69

101 +

101

1.61

27

none zero

0.83

29

94

5.11

1761

excellent good

0.77

22

89

5.53

4093

excellent good

0.81

0

97

3.99

3589

bad bad

0.84

<0

113

4.27

1752

none bad

Polyvinyl acetates

"Resyn" 1105

27.7

0.80

44

86

5.04

1927

good good

"Vinac" 880

38.2

0.79

31

117

5.18

5585

good excellent

"Resyn" 1255

29.1

0.77

16

109

4.69

1371

suitable suitable

"Resyn" 5000 **

31.7

0.79

2.0

114

4.90

2744

bad suitable

"Resyn" 2873 **

24.6

0.81

-36

122

3.15

189

none bad

* uncalendered

** comparison only

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The above results indicate that the sheet impregnated with polyvinyl acetate having a temperature Tg of 16 ° C has suitable properties of resistance to oil penetration and suitable resistance to solvents. On the other hand, a sheet impregnated with a polyacrylate having a temperature Tg greater than 101 ° C. when it is treated at the temperatures of the usual papermaking process, has neither resistance to oil penetration, nor resistance to solvents.

Thus, a satisfactory polymer must have a rigidity, that is to say a temperature Tg, of between 15 and 60 ° C. (Table m VIII relates to a polyvinyl chloride whose temperature Tg is equal to 60 ° C.) when the results must be satisfactory. The most advantageous temperature range Tg is between 22 and 44 ° C so that the polymer is associated by fusion with the temperatures conventionally used for processing in the stationery industry.

Example 4

The nature of the inert filler used as a resin diluent has a great importance on the properties of the paper: o impregnated. This characteristic appears in this example in which the base paper of Example 1 is used which is impregnated with polyvinyl acetate which has been mixed with a series of different mineral fillers. Each mixture contains 40% filler and 60% polyvinyl acetate, considered as dry solid matter. Calcium carbonate and clay are those that we have already used, talc is sold under the brand "Mistron Vapor" of the United Sierra Division, Cypress Mines, Trenton, New Jersey, mica is sold under the brand " Dave-nite Mica "P-12 from the Hayden Mica, Co., Wilimngton, Massachusetts, and diatomaceous earth is sold under the brand name" Cellite "of Johns-Manville Corporation, New York, New York. Each of these fillers is of commercial quality, normally used for stationery, the dimensions being between 2 and 5 microns. The results are shown in Table IV.

It is believed that the unsatisfactory results obtained with diatomaceous earth may be due to its extremely high specific surface, which makes it incompatible with the rigid polymer. Fillers incorporated for the purpose of the invention are here called "compatible fillers", that is to say fillers permitting the impregnation of the base paper satisfactorily with the rigid polymer and therefore which give a satisfactory resistance to the penetration of oil and solvents.

Table IV Miscellaneous charges

60% polyvinyl acetate / 40% filler

Load used

Material Density of impregnation- after im-tion,% pregnation (g / cm3)

Tear resistance (g) (XD)

Bending resistance (g) (XD)

Bursting strength (Mullen) 105Pa

Oil tightness

Solvent resistance none

31.7

0.88

80

3171

5.46

excellent excellent

CaC03

117

5585

5.18

good excellent clay

117

4179 *

good excellent talc

34.3

0.79

101

3334

5.88

good suitable

"Davenite"

mica P-12

32.4

0.77

99

2825

5.67

good excellent

"Cellite" earth at

diatoms ***

32.4

0.74

100

2234

5.88

bad bad

* clay 30%

** uncalendered *** comparative only

The above table indicates that calcium carbonate, clay, talc and mica constitute satisfactory fillers while diatomaceous earth is not satisfactory because the paper obtained has poor oil penetration resistance properties. and solvents.

Example 5

This example concerns the effect of using sheets of paper having different densities before impregnation. An aqueous dispersion of polyvinyl acetate and calcium carbonate is prepared as described in Example 1. The polymer-filler mixture forms 40% of the weight of the dispersion, and the polymer / filler weight ratio is equal to 60/40 . A series of sheets of unglued paper of different densities is dipped into the dispersion and the excess impregnation material is removed by passing the sheets between rubber rolls and blotting the surface with paper towels so that the excess impregnation material is removed from the surface of the sheets. These then undergo drying for 4 min at 105 ° C., maturation for several days and the tests are carried out as indicated above. For comparison, a dispersion of container is prepared as polyvinyl acetate in an amount of 40% by weight of solid matter and a second set of base paper is impregnated in a similar manner. In a further comparison, a normal paper is also impregnated.

The results of the tests are shown in Table V.

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8

Table V Without impregnation Paper Strength (g / m2)

Material Density (g / cm3) * of impregnation - CaC03

generation

%

leaves impregnated with CaCO 40% PVAC 60%

PVAC / Resistance to de- (g / cm3) * tear (XD), g

Normal sheets

100% PVAC impregnated sheets

Waterproof- Resist- Resist- ity to this with oil ply ** ge (XD), g tear (f) (XD), g

Résistan- Résis- Résis-

this folding tance tance

at the tear-off rure (f) (XD), g

Oil tightness

^ ***

50.0

0.35

45.8

0.62

52

NOT

594

32

10

38

821

NOT

g ***

52.0

0.44

48.5

0.72

65

M

2774

74

11

67

M

vs

56.4

0.47

47.7

0.79

94

E

3200

-

-

_

B

D

69.6

0.54

33.5

0.70

66

VS

3221

78

-

60

2207

VS

E

62.2

0.58

29.3

0.71

50

E

2687

118

-

46

2291

E

F

84.4

0.60

38.2

0.77

117

B

5585

147

-

80

3171

E

G

56.4

0.63

36.2

0.79

50

E

3221

64

153

46

2207

E

H

56.4

0.66

26.9

0.79

56

E

1351

61

93

53

958

E

I

54.7

0.70

25.5

0.90

52

B

704

50

199

56

350

B

d ***

62.9

0.83

9.1

0.91

30

E

3621

25

2247

34

-

E

* not calendered ** N = zero; M = bad; E = excellent; C = suitable - *** ble; B = good comparison only

The above table indicates that the minimum density of an un-calendered sheet before impregnation must be greater than 0.44 g / cm3, as indicated for sample B. The maximum impregnation density, without calendering, must not exceed 0.70 g / cm3, as indicated for sample I. It should be noted that, although sample B contains 48.5% of impregnation material, it is not satisfactory for the resistance to penetration of oil. Although the sample J has excellent oil penetration resistance properties, it acquires 9.1% of impregnation material but has a very low tear resistance. It is further noted that each of the papers which give satisfaction has a final density in the non-calendered state.

which exceeds 0.69 g / cm3 and which is less than about 0.90 g / cm3.

25

Example 6

This example relates to the quantity of polymer-filler impregnation material desirable for the formation of a satisfactory paper, the base paper being produced from a milled kraft pulp bleached from Nordic wood and containing approximately 5% of titanium dioxide. . Although the paper is not glued, a slight gluing is due to the presence of residual pitch; however, it is believed that this amount is sufficient to prevent penetration of the impregnation material into the interior of the sheet. The paper strength is 56.4 g / m2. The samples are prepared as indicated in Example 5, but the solids content of the impregnation material varies between 10 and 40%.

Table VI shows the results of the test.

Table VI

Resin content and physical properties PVAC6) 0% / CaCO 3 40%

Sample

Content

Density

Resistance

Resistance

Sealing

Material content

charge %

after im folding

at the dice

solu solids oil

pregnation

(f)

tear (g)

impregnation

(g / cm3) *

%

A1

0

0.66

65

58

nothing

B3

6.0

0.66

1141

53

fair

10

VS

11.1

0.68

1874

51

good

15

D

15.6

0.70

3069

56

excellent

20

E

24.0

0.80

2915

51

total

30

F

20.6

0.79

1731

56

total

40

G2

30.2

0.83

831

53

total

1 - base paper 2-PVAC 100% only 3 - comparison only * - not calendered

The results in the table above indicate a significant improvement in the properties of resistance to oil penetration and of bending endurance when the polymer-filler impregnation material forms approximately 8.5% of the weight of the sheet (compare sample B), the properties being very advantageous when the impregnation material forms 15 to 25% of the weight of the sheet as indicated for samples D and E, this amount being able to reach 48% as indicated in (, o Example I.

Example 7

The sheets of paper of Example 1 are impregnated with a polymer-filler dispersion having a solids content (15% of 40% by weight, the weight ratio of the polymer to the filler being 60/40, at using different types of rigid polymers which can be used satisfactorily for the production of the paper according to the invention.

9

616,717

caclium nate, and the polymers are the "Rhoplex" AC-201 polyvinyl chloride emulsion manufactured by the B.F.

which is a polyacrylate emulsion manufactured by Rohm & Goodrich Chemical Co., Akron, Ohio.

Haas Co., Philadelphia, Pa and "Geon" 351 which is a Table VII gives the results of the tests.

Table VII

Evaluation of various types of polymers Diluted impregnation material, having a polymer /

CaCO j 60/40, and undiluted material Polymer Material Rigidity Density Content

impregnation (Tg) material after impregnation

impregnation- impregnation,% (g / cm3) *

Résistan- Résistan- Résistan- Etanche- Résistance ce à la ce au ce à l'ité à aux sol-

tear folding flat oil ** flaps ** (XD) (g) (XD) (f) Mullen 105 Pa

"Rhoplex" 1 poly- 29 ° C 32.7, 0.83 94 1761 5.1 E B

Ac201 / acrylate

CaC03

"Rhoplex" 2

Ac / 201

single polyacrylate

20 ° C

42.0

0.90

83

1226

5.6

"Geon" 1 351 / CaC03

polyvinyl chloride

60 ° C

42.0

0.87

96

672

4.48

B

"Geon" 2,351 polyvinyl chloride alone

60 ° C

43.2

0.83

89

297

3.5

M

M

1

2 *

**

- polymer dilute impregnation material / CaC03 60/40

- undiluted impregnation material;

comparative only

- not calendered

- E = excellent; B = good;

M = bad; C = suitable

The above table shows that an impregnation material containing a rigid polyacrylate diluted with calcium carbonate has practically the same effect on a base paper as an impregnation material containing rigid polyvinyl acetate and carbonate of calcium, with the exception of the folding values, (comparison of Tables I and VII). It is noted that similar results are obtained, but with lower folding values, when the impregnation material contains a mixture of polyvinyl chloride diluted with calcium carbonate, but the resistance to solvents and the penetration properties of impregnated paper oil are better with diluted material than with undiluted material. Thus, it is clear that advantageous results are obtained by the use of certain types of polymers such as polyvinyl acetate, polyacrylate and polyvinyl chloride.

Example 8

The paper according to the invention has good resistance to bruising although the mixture used for the impregnation is diluted by a filler present in a large percentage, and although it is possible that the impregnation material forms well less than half the weight of the paper. When determining the abrasion resistance of the paper according to the invention, it is impregnated

50

the base paper sheets of Example 1 with various rigid polymers and various polymer-filler mixtures according to the process described in Example 1. The polyvinyl acetate is of the “Vinac” 880 type, the polyacrylate is of the “ Rhoplex ”407, and polyvinyl chloride is of the“ Geon ”type 351. The leaves undergo the Tabor abrasion test described in standard TAPPI T 476 ts-63. An H-18 abrasive wheel is used during the test, and the number of cycles of rotation of the wheel is counted until a hole is formed in the sheet. Table VIII gives the results obtained.

Table VIII

Tabor abrasion comparison test Roughness wheel H-18

55

Impregnation material

Cycles

Content

until

matter

impregnation wear of polyvinyl acetate alone *

600

31.7

polyvinyl acetate / 30% CaC03

530

32.2

polyvinyl acetate / 30% clay

800

32.0

polyacrylate alone *

1500

39.5

polyacrylate / 40% CaC03

1700

28.3

polyvinyl chloride alone *

354

43.2

polyvinyl chloride / 40% CaCO3

400

42.0

untreated base paper

20-50

0

* comparison only

The results of the table show that the resistance to water absorption of a sheet of paper impregnated with a mixture of acetate

10

616,717

rigid polyvinyl and a mineral filler such as calcium carbonate, is only slightly lower (530 cycles) than that of a paper impregnated with polyvinyl acetate alone (600 cycles). A sheet impregnated with polyvinyl acetate diluted with clay, in the proportions indicated, has an abrasion resistance which is even higher than that of a sheet impregnated with polyvinyl acetate alone. A sheet impregnated with polyacrylate diluted with calcium carbonate also has better abrasion resistance than a sheet impregnated with polyacrylate alone. The abrasion resistance of a sheet impregnated with a mixture of polyvinyl chloride diluted by a filler has an abrasion resistance slightly higher (400 cycles) than that of a similar sheet impregnated with polyvinyl chloride alone.

Example 9

The above dispersion should be impregnated in the paper according to the invention, since simple application in the form of a coating is not suitable. This is demonstrated by impregnating and coating sheets of base paper having a strength of 88.1 g / m2 and a thickness of 140 microns with a polymer-filler composition. For example, a sheet of base paper is impregnated with the composition of Example 1 and 5 another sheet of the same paper is coated with the composition as described in Example 1 of the aforementioned United States patent. America No. 3,634,298, but the synthetic polymer of Example 1 of the aforementioned patent is replaced by polyvinyl acetate "Vinac" 880 which has a temperature Tg of 31 ° C, Ki for the formation of the aqueous dispersion clay-polymer. The dispersion contains 55% by weight of the clay-polymer mixture, at a rate of 83% of clay for 17% of polymer. The resulting dispersion is applied to one side of the base paper in the form of a coating, using a Meyer bar as described in Example 1 of the aforementioned patent. The coated paper is then dried for 1 min at 149 ° C.

Next, on the coated and impregnated papers, the properties of tear resistance and bursting and of endurance in folding are determined, and Table IX gives the results obtained.

Table IX Sample

Pigment

"Vinac"

%

Thickness Density g / cm3

Tear resistance (XD)

Bursting resistance Mullen, 102 Pa

Humidity

relative

10-20%

Humidity

relative

90%

Resistance to disintegration, g / cm base paper *

140

0.63

115

2.30

502

1633

80

30.3 138 paper

impregnated base

0.92 89 5.35

1284 7018 320

24.7 160 0.73 136 3.36 356 1065 80 paper

coated base *

* comparison only

The table above indicates that the impregnation reduces the tear resistance by approximately 13% while the coating increases it by approximately 12%. Impregnation more than doubles the burst strength while the coating increases it by only about 50%. During the bend test, the impregnation does much more than double the bending endurance (even for low relative humidity from 10 to 20%) while the coating actually reduces this endurance by about 30% . The resistance to disintegration of paper is the same as that of base paper, but that of impregnated paper exceeds 320 g /

cm, the paper then tearing without falling apart. Consequently, the foregoing results indicate that the polymer-filler mixture should be impregnated into the sheet of paper and not simply applied to the surface as a coating.

The invention therefore relates to a dense paper which has the advantageous properties of dense papers, the undesirable properties of the latter however being improved so that the paper according to the invention is useful in numerous applications. In addition, the dense papers according to the invention can be made cost-effectively with relatively high speeds of papermaking machines.

Claims (14)

616,717 1. Dense paper having good resistance to the penetration of oils and solvents, characterized in that it comprises a sheet of cellulose fibers as well as an impregnation material dispersed in the sheet, the latter comprising, with respect to on the total weight of the finished paper, 8.5 to 50% by weight of impregnation material which, relative to its total weight, consists of 35 to 90% by weight of a rigid polymerized material having a glass transition temperature included between 15 and 60 ° C, and in 10 to 65% by weight of compatible inert filler. 2. Paper according to claim 1, characterized in that the glass transition temperature of the polymerized material is between 22 and 44 ° C. 2 3. Paper according to one of the preceding claims, having, in the finished state, before calendering, a density equal to or greater than 0.69 g / cm3 and less than 0.90 g / cm3. 4. Paper according to one of the preceding claims, comprising, relative to its total weight in the finished state, 15 to 40% by weight of impregnation material. 5. Paper according to one of the preceding claims, comprising, relative to the weight of the impregnation material, 20 to 65% by weight of inorganic filler. 6. Paper according to one of the preceding claims in which the polymerized material is chosen from copolymers and homopolymers of vinyl acetate, an acrylate, vinyl chloride, and mixtures of these substances. 7. Paper according to one of the preceding claims, in which the inorganic filler comprises kaolin, calcium carbonate, mica, talc, or mixtures of these substances. 8. A method of manufacturing dense paper according to claim 1, characterized by the successive steps of advancing a strip of paper, of impregnating the sheet of paper during its advancement by applying thereto an overdose of aqueous dispersion which contains a mixture comprising , relative to the total weight of the mixture, 35 to 90% by weight of a rigid polymerized material and 10 to 65% by weight of an inert filler, the rigid ploymerized material having a glass transition temperature of 15 to 60 ° C. , to pass the sheet of paper between opposite pressure rollers, so as to ensure the penetration of the dispersion into the paper sheet as well as to eliminate the excess dispersion and to heat the sheet after it has passed between the rollers opposite and after removal of the excess dispersion, so as to melt the mixture dispersed in the sheet in the proportion of 8.5 to 50% of the total weight of the sheet when dry. 9. Method according to claim 8, characterized in that the sheet of unimpregnated paper, before calendering and in the dry state, has a density between its opposite surfaces of between 0.45 and 0.70 g / cm3. 10. Method according to claim 8 or 9, characterized in that the polymerized material is chosen from homopolymers and copolymers of polyvinyl acetate, an acrylate, vinyl chloride, as well as mixtures of these substances. 11. Method according to one of claims 8 to 10, characterized in that the inert filler is chosen from kaolin, calcium carbonate, mica, talc and mixtures of these substances. 12. Method according to one of claims 8 to 11, characterized in that an aqueous dispersion is used comprising, relative to its total weight, 12.5 to 60% by weight of said mixture. 13. Method according to one of claims 8 to 12, characterized in that a sheet of paper is used which, in the non-impregnated state of said mixture, has a density of 0.54 to 0.69 g / cm3. 14. Method according to one of claims 8 to 13, characterized in that a sheet of paper is used which, before its impregnation, is practically free of any sizing.